Bettley, R.M., Fortey, R.A. and Siveter, D.J. 2001. High resolution correlation of AngloWelsh Middle to Upper Ordovician sequences and its relevance to international chronostratigraphy. Journal of the Geological Society, London, 158, 937952.
Cooper, R.A., Sadler, P.M., Munnecke, A. and Crampton, J.S. 2014. Graptoloid evolutionary rates track Ordovician—Silurian global climate change. Geological Magazine, 151, 349364.
Cooper, R.A. and Sadler, P.M. 2012. The Silurian Period. In: Gradstein, F.M., Ogg, J.G. and Smith, A.G. (eds), A Geologic Time Scale 2012. Elsevier Press. 489523.
Fan Junxuan, Chen Qing, Melchin, M.J., Sheets, H.D., Chen Zhongyang, Zhang Linna and Hou Xudong. 2013. Quantitative stratigraphy of the Wufeng and Lungmachi black shales and graptolite evolution during and after the Late Ordovician mass extinction. Palaeogeography, Palaeoclimatology, Palaeoecology, 389, 96114.
Kleffner, M.A. 1989. A conodontbased Silurian chronostratigraphy. Geological Society of America Bulletin, 101, 904912.
Mann, K.O. and Lane, R.H. 1995. Graphic correlation: a powerful stratigraphic technique comes of age. SEPM Special Publication, 53, 313.
Macleod, N. and Sadler, P.M. 1995. Estimating the line of correlation. SEPM Special Publication, 53, 5164.
Murphy, M.A. and Salvador, A. 1998. International stratigraphic guide—an abridged version. Episodes, 22, 255271.
Sadler, P.M. 2012. Integrating carbon isotope excursions into automated stratigraphic correlation: an example from the Silurian of Baltica. Bulletin of Geosciences, 87, 681694
Sadler, P.M., Cooper, R.A. and Melchin, M.J. 2011. Sequencing the graptoloid clade: building a global diversity curve from local rangecharts, regional composites and global timelines. Proceedings of the Yorkshire Geology Society, 58, 329343.
Sadler, P.M., Kemple, W.G. and Kooser, M.A. 2003. CONOP 9 programs for solving the stratigraphic correlation and seriation problems as constrained optimization. In: Harries, P. (ed.), High Resolution Stratigraphic Approaches in Paleontology. Plenum Press, Topics in Geobiology, 21, 461465 and CD.
Sheets, H.D., Mitchell, C.E., Izard, Z.T., Willis, J.M., Melchin, M.J. and Holmden, C. 2012. Horizon Annealing: a collectionbased approach to automated sequencing of the fossil record. Lethaia, 45, 532547.
Smith, A.G., Barry, T., Bown, P., Cope, J., Gale, A., Gibbard, P., Gregory, J., Hounslow, M., Kemp, D., Knox, R., Marshall, J., Oates, M., Rawson, P., Powell, J. and Waters, C. 2014. GSSPs, global stratigraphy and correlation. Geological Society London, Special Publications, 404, doi:10.1144\/SP404.8.
Sweet, W.C. 1984. Graphic correlation of upper Middle and Upper Ordovician rocks, North American Midcontinent Province, U.S.A. In: Bruton, D.L. (ed.), Aspects of the Ordovician System. Palaeontological Contributions from the University of Oslo, 295, 2335.
Environmental distribution and diversity of Ordovician Porifera in the Builth Inlier, Wales
Lucy A. MUIR1 and Joseph P. BOTTING1,2
1Flat 4 White Heather, Western Promenade, Llandrindod Wells, Powys, LD1 5HR, UK
2Nanjing Institute of Geology and Palaeontology, 39 East Beijing Road, Nanjing 210008, China.
Sponges were major components of Cambrian ecosystems. In the Chengjiang Biota, sponges make up approximately 12% of the generic diversity (Dornbos and Chen, 2008), in the Phyllopod Bed of the Burgess Shale they are second only to arthropods in species diversity and abundance of individuals (Caron and Jackson, 2008), and they are similarly important in many of the other Cambrian Burgess Shaletype faunas. During the Cambrian, individual sponge taxa were widely distributed, with many genera and even species shared across widelyseparated paleocontinents. However, the fossil record of Ordovician and Silurian sponges is not well known, and there is little understanding of their distribution patterns or true diversity (Muir et al., 2013). In particular, modern sponge faunas are extremely patchy, so regional diversity is much greater than local diversity; this appears not to have been true for the Cambrian faunas. Until now, it has not been possible to assess the patchiness of the Ordovician sponge communities, because data have not been available for multiple sponge faunas within a small region.
A significant part of the Great Ordovician Biodiversification Event (GOBE) was the rise of the Paleozoic Evolutionary Fauna (Sepkoski, 1981), of which filter and suspensionfeeding organisms such as brachiopods, echinoderms and bryozoans were major components. Sponges show a slightly more complex pattern, with a late Cambrian assemblage that is intermediate between the Cambrian and Paleozoic faunas (Carrera and Botting, 2008). Global Ordovician biodiversity increases were accommodated particularly by increasing alpha and beta diversities (Sepkoski, 1988), i.e. the withincommunity diversity rose, but intercommunity differences also increased. This understanding is based largely on shelly fossils, whereas most sponges require a degree of exceptional preservation; their Ordovician record is therefore extremely sparse, and patterns of sponge diversity are understood only at an extremely crude level. Relatively few Ordovician faunas have been documented worldwide (Muir et al., 2013), and descriptions of single faunas significantly change the global diversity curve (Botting and Muir, 2008), implying that our knowledge of them is extremely incomplete.
This paper discusses the Ordovician sponge faunas of the Builth Inlier of midWales, UK. The inlier preserves sponge communities from a short time interval and small spatial area but a variety of water depths. This allows an assessment of variations in sponge abundance and diversity over a small area, and the environmental preferences of different sponge groups.
Geological setting
The fiftysquarekilometre Builth Inlier, Powys, UK, contains rocks of middleDarriwilian to basal Sandbian age (Didymograptus artus to Nemagraptus gracilis biozones). The sequence represents the formation, erosion and burial of a volcanic island complex. Full details of the Builth Inlier stratigraphic sequence are given in Botting and Muir (2008).
The Builth Inlier contains rocks deposited at a variety of depths, from nearshore to probably around 200 m. The localities representing the deepestwater facies, in the Hustedograptus teretiusculus Biozone, contain cyclopygids and agnostids (Owens, 2002), with water depths likely to have been between 150 and 200 m (McCormick and Fortey, 1998).
Due to widespread rapid burial and high sedimentation rates, many of the Builth Inlier faunas are in situ, or underwent only limited transport. As the rock sequence preserves faunas representing a variety of water depths, it is possible to assess how those faunas varied along a depth transect. Variation in the faunas cannot be explained through different latitudes or continental blocks, which are confounding factors in studies conducted at larger scales. The rock sequence was deposited over four graptolite biozones, so the faunas will have varied with time because of immigration, evolution and extinction. However, the total duration of the sequence is only around 5 million years and these effects, while perhaps being significant at the species level, probably did not affect the largerscale taxonomic and paleobiological patterns.
The Builth Inlier contains both standard shelly assemblages and localised exceptional preservation (Botting and Muir, 2008, 2012; Botting et al., 2011). The trilobite, brachiopod and graptolite faunas are similar to those found elsewhere in the Welsh Basin (e.g. C.P. Hughes, 1969, 1971, 1979; R.A. Hughes, 1989; Lockley and Williams, 1981; Sutton et al., 1999; Owens, 2002), so it must be assumed that the exceptional elements are also not aberrant. Thus, study of the sponge distribution may allow prediction of the types of sponges that ought to have existed in other areas. The same approach has already been applied to echinoderms (Botting et al., 2013), confirming and revealing patterns of environmental distributions that are more widely applicable.
Fig. 1. Log showing the temporal distribution of spongebearing sites within the Builth Inlier, and diversity of different groups. Coarser sediments normally represent shallower environments. The thickwalled hexactinellidlike sponges include various stemgroup lineages, and constitute a morphologically distinctive ecological grouping rather than a natural group.
Results and Discussion
This summary is based on extensive collection made over many years, with taxonomic studies currently in progress.The already known total sponge diversity of the Builth Inlier is over 100 species, of which 29 have been formally described and a few others illustrated or mentioned. The majority of Builth Inlier sponges are hexactinebearing, but the taxonomy of these is complex (Botting and Muir, 2013); they are included here as ‘reticulosans’ (thinwalled taxa), and ‘thickwalled hexactinellidlike taxa’ (which may include stemgroup hexactinellids and stemgroup siliceans). Other faunas include at least some demosponges and protomonaxonids. Although isolated heteractinid (hexaradiate) spicules are not uncommon in deeperwater localities, only one articulated heteractinid has been found (in shallow water). The distribution and relative diversity of the different groups is shown in Figure 1.
Sponges in the coarse inshore sediments are generally large, abundant and diverse (Botting, 2005). There are equally diverse and abundant faunas of more delicate reticulosans and protomonaxonids in the fine, deepwater deposits (e.g. Botting, 2004). The lowest diversity habitat was in shallow, slightly offshore sandstones, where only a few species of thickwalled hexactinebearing sponges have been found. This is a similar pattern to that of the cooccurring echinoderm faunas (Botting et al., 2013), where different groups dominated in shallow and deep water, and the smaller species occupied deeper environments. Protomonaxonids occurred most abundantly at intermediate depths, where they could dominate assemblages in offshore siltstones.
Cambrian deepwater faunas were dominated by reticulosans, with shallowerwater assemblages dominated by protomonaxonids and, locally, some demosponges (Carrera and Botting, 2008). This pattern is generally followed in the Builth Inlier, with protomonaxonids occupying a shallowerwater offshore environment than the majority of reticulosans. The inshore communities, in contrast, were dominated by derived groups that were mostly absent from Cambrian communities. These derived groups, as with the echinoderms (Botting et al., 2013), include lineages that typify the Palaeozoic and Modern evolutionary faunas (e.g. brachiospongioids and agglutinating demosponges).
The most striking feature of the distribution of sponges within the Builth Inlier is how few species, and even genera, are shared between sites. This is consistent with modern sponge distribution, which is very patchy (Gutt and Koltun, 1995). Modern sponges can be dependent on not only particular sediment conditions, but also precise seawater chemistry, temperature and turbulence conditions; their reproductive behaviour also tends to encourage clustering of species and smallscale patchiness.
In contrast,assemblages of the betterknown groups in the Builth Inlier, such as brachiopods, trilobites and graptolites, are usually very similar between sites. Most species have some environmental constraints, but are found at several sites within a broad zone. It is unusual to find a species of trilobite, brachiopod or graptoloid that is not already known from the inlier, but any sponge collected from a new site is likely to not only be new to the area, but also to be undescribed.
Conclusions
Builth Inlier sponge diversity was extraordinarily high. Different sponge groups primarily occupied different environmental zones, but each depth zone supported a diverse community. The extent of this diversity has not been recognised because exceptional conditions are normally needed to allow preservation of articulated sponges, and these conditions are encountered only occasionally. The Builth Inlier preserves faunas from a wide range of sites, and show that not only was alpha diversity extremely high in many communities, but beta diversity was also much higher than for other cooccurring fossil groups. The total, regional diversity was therefore much greater than is normally appreciated.
If the Builth Inlier is typical, as suggested by the “standard” components of the faunas, then sponges were a major component of many communities in siliciclastic settings in the Middle and Late Ordovician. If this pattern applies in other areas, then a large component of Ordovician biodiversity has been overlooked.
References
Botting, J.P. 2004. An exceptional Caradoc sponge fauna from the Llanfawr Quarries, central Wales, and phylogenetic implications. Journal of Systematic Palaeontology, 2, 3163.
Botting, J.P. 2005. Exceptionallypreserved Middle Ordovician sponges from the Llandegley Rocks Lagersttte, Wales. Palaeontology, 48, 577617.
Botting, J.P. and Muir, L.A. 2008. Unravelling causal components of the Ordovician Radiation: the Builth Inlier (central Wales) as a case study. Lethaia, 41, 111125.
Botting, J.P. and Muir, L.A. 2012. Fauna and ecology of the Holothurian Bed, Llandrindod, Wales, UK (Llandeilian, Middle Ordovician). Palaeontologia Electronica, 15(1), 9A, 128, http:\/\/palaeoelectronica.org\/content\/2012issue1articles\/191welshholothurianbed.
Botting, J.P. and Muir, L.A. 2013. Spicule structure and affinities of the Late Ordovician hexactinellidlike sponge Cyathophycus loydelli (Llanfawr Mudstones Lagersttte, Wales). Lethaia, 46, 454469.
Botting, J.P., Muir, L.A., Sutton, M. and Barnie, T. 2011. Welsh gold: a new exceptionally preserved pyritized Ordovician biota. Geology, 39, 879882.
Botting, J.P., Muir, L.A. and Lefebvre, B. 2013. Echinoderm diversity and environmental distribution in the Ordovician of the Builth Inlier, Wales. Palaios, 28, 293304.
Caron, J.B. and Jackson, D.A. 2008. Palaeoecology of the Greater Phyllopod Bed community, Burgess Shale. Palaeogeography, Palaeoclimatology, Palaeoecology, 258, 222256.
Carrera, M.G. and Botting, J.P. 2008. Evolutionary history of Cambrian spiculate sponges: implications for the Cambrian evolutionary fauna. Palaios, 23, 124138.
Dornbos, S.Q. and Chen Junyuan. 2008. Community palaeoecology of the early Cambrian Maotianshan Shale biota: ecological dominance of priapulid worms. Palaeogeography, Palaeoclimatology, Palaeoecology, 258, 200212.
Gutt, J. and Koltun, V.M. 1995. Sponges of the Lazarev and Weddell Sea, Antarctica: explanations for their patchy occurrence. Antarctic Science, 7, 227234.
Hughes, C.P. 1969. Ordovician trilobite faunas from central Wales, Part I. Bulletin of the British Museum of Natural History (Geology), 18, 39103.
Hughes, C.P. 1971. Ordovician trilobite faunas from central Wales, Part II. Bulletin of the British Museum of Natural History (Geology), 20, 115182.
Hughes, C.P. 1979. Ordovician trilobite faunas from central Wales, Part III. Bulletin of the British Museum of Natural History (Geology), 32, 109181.
Hughes, R.A. 1989. Llandeilo and Caradoc graptolites of the Builth and Shelve inliers. Monograph of the Palaeontographical Society, 141, 189.
Lockley, M.G. and Williams, A. 1981. Lower Ordovician Brachiopoda from mid and southwest Wales. Bulletin of the British Museum (Natural History) Geology, 34, 178.
McCormick, T. and Fortey, R.A. 1998. Independent testing of a paleobiological hypothesis: the optical design of two Ordovician pelagic trilobites reveals their relative paleobathymetry. Paleobiology, 24, 235253.
Muir, L.A., Botting, J.P., Carrera, M. and Beresi, M. 2013. Cambrian, Ordovician and Silurian nonstromatoporoid Porifera. In: Harper, D.A.T. and Servais, T. (eds), Early Palaeozoic Palaeobiogeography and Palaeogeography. Geological Society of London, Memoir, 38, 8195.
Owens, R.M. 2002. Cyclopygid trilobites from the Ordovician BuilthLlandrindod Inlier, central Wales. Palaeontology, 45, 469485.
Sepkoski, J.J. Jr. 1981. A factor analytic description of the Phanerozoic marine fossil record. Paleobiology, 7, 3653.
Sepkoski, J.J. Jr. 1988. Alpha, beta or gamma: where does all the diversity go? Paleobiology, 14, 221234.
Sutton, M.D., Basset, M.G. and Cherns, L. 1999. Lingulate Brachiopods from the lower Ordovician of the AngloWelsh Basin. Monograph of the Palaeontographical Society, 610, 1114.
Ontogenetic development of the genus Akadocrinus (Eocrinoidea, Echinodermata) from the Barrandian area, Czech Republic
Martina NOHEJLOVA＇ and Oldrˇich FATKA
Institute of Geology and Palaeontology, Faculty of Science, Charles University, Albertov 6, Prague 2, 128 43, Czech Republic
Fig. 1. Akadocrinus jani Prokop, 1962. Latex cast of internal surface of thecal plates; whitened with NH4Cl. Scale bar = 1 mm.
Eocrinoid echinoderms are abundant at several horizons of the Cambrian sequence in the Barrandian area (Czech Republic). Material used in this study belongs to diverse ontogenetic stages of the genus Akadocrinus Prokop, 1962. All specimens were collected from the Drumian Jince Formation in the PíbramJince Basin and are currently deposited in the National Museum in Prague.
This work represents the first study of ontogenetic development ofthe class Eocrinoidea made on the material from Czech Republic. Comparable eocrinoid material has been studied from the Balang and Kaili formations of South China, where ontogeny of three gogiid eocrinoid species was investigated by Parsley (2012).
The body of Akadocrinus can be divided into three major parts: brachioles, theca and stem. Detailed morphological study on the ontogenetic changes has been conducted, including the measurements of diverse parameters. Length of brachioles, dimension of theca and outline of thecal plates and length of stem were evaluated for Akadocrinus jani Prokop, 1962. With the aid of measurements, it is possible to differentiate three ontogenetic stages based mainly on thecal height: (1) juvenile stage, (2) mature stage, and (3) gerontic stage. Each of these stages shows specific morphological characteristic. Some trends were observed during the ontogenetic development of Akadocrinus jani. Juvenile specimens have less brachioles which are composed of generally smaller brachiolar plates when compared with mature specimens. The average size of thecal plates is increasing during the ontogeny. Two types of theca can be distinguished. It is also possible to determine several generations of thecal plates. Mature specimen usually contains three generation of thecal plates.
Recently collected large specimens with exceptionally wellpreservation make it possible to understand skeletal changes associated with the ontogeny for this group of echinoderms. The internal surface of thecal plates of Akadocrinus is described for the first time (Fig. 1).
Acknowledgements
This research is supported by GA UK (Grant Agency of Charles University) no.776213: Ontogeny of class Eocrinoidea.
References
Parsley, R.L. 2012. Ontogeny, functional morphology, and comparative morphology of Lower (Stage 4) and Basal Middle (Stage 5) Cambrian Gogiids, Guizhou Province, China. Journal of Paleontology, 86, 569583.
Prokop, R.J. 1962. Akadocrinus nov.gen. a new crinoid from the Cambrian of the Jince area. Sbornik Ustredniho Ustavu geologickeho,Paleontology, 27, 3139.
Morphological and microstructural features of Early Cambrian Archiasterella (Chancelloriida) of the Siberian Platform
Natalya V. NOVOZHILOVA
Trofimuk Institute of Petroleum Geology and Geophysics SB RAS 630090, Russia, Novosibirsk, 3 Akademika Koptyuga Prosp
Chancelloriids is one of the very problematic and enigmatic groups of Cambrian fauna, with saccular body covered with sclerites of various morphological types. Chancelloriids are often found as isolated sclerites, which are assigned to different species. But the foundations of articulated scleritomes are rare and known from the Cambrian of China (Chen et al., 1996; Bengtson and Hou, 2001), Canada and the United States (Walcott, 1920; Sdzuy, 1969; Rigby, 1978; Rendell et al., 2005), Iran (Mostler and Mosleh Yazdi, 1976). There are different views on the taxonomy of
Fig. 1. SEM photomicrographs of Archiasterella sp. Lower Cambrian, Tommotian Stage, Siberian Platform. A, B—general view of sclerites; C, D—fragment of external ornamentation around basal foramens.
the group, some see them as sponges (Walcott, 1920; Sduy, 1969; Goryansky, 197; Butterfield and Nicholas, 1996; Mehl, 1996), others as a group of uncertain systematic position, accepting their scleritom nature (Bengtson and Missarzevsky, 1981; Qian and Bengtson, 1989; Bengtson et al., 1990; Rendell et al., 2005; etc.). Recently most researchers consider the chancelloriids in the class Coeloscleritophora Bengtson and Missarzevsky, 1981 (Esakova and Zhegallo, 1996; Demidenko, 2000; etc.), leaving aside the question of higher taxonomic ranks of this group. It is considered that chancelloriids were epibenthic dwellers (Bengtson et al., 1990; Parkhaev and Demidenko, 2010; etc.). Some express the opinion of the relationship of this group with octocorals, which produce a dermal layer of imbricated, platelike sklerites (Randell et al., 2005).
Isolated phosphate sclerites Archiasterella sp. (Fig.1A, B) were find from the Lower Cambrian of the Siberian Platform (Pestrosvet Formation of the “Dvortsy” section; Tyuser Formation of the section in the western limb of the Chekurovka anticline). All chancelloriids sclerites picked up from the insoluble residue after treatment of rock samples by 3％—5% acetic acid. The most interesting were the billaterally symmetrical robust sclerites (4+0) with three subhorizontal lateral rays, which lie in the plane of the basal facet and located opposite the subvertical ray. And one median recurved ray. Each ray has two foramens (basal pores) and the one that is closer to the center of the sclerite is smaller than the other. Diameter of sclerites is 1.1 mm, and the length of rays are about 300—340 μm. The angle between the median ray and the basal plane is about 85°—90°. The lateral rays lie within the basal plane or inclined at a small angle of 2°—5°.The biggest foramens characterized by roundedtriangular form with height 42—50μm and width 62—80μm. The smallest foramens have ovaltriangular shape with a height of 38—42μm and length 50—55μm. Microstructure of the outer wall is represented by thin longitudinal sections, from center to outer edge of the sclerite. Around the foramens there are “porous” layers (Fig. 1C, D).
The described Archiasterella sp. is most similar to A. tetractina Duan, 1983 and A. hirundo Bengtson, 1990. And differs from all other species of the genus, which have four rays, by the presence of two foramens in each of the rays. In addition, the rays are nearly perpendicular to each other.
On the basis of the findings can be assumed that the presence of two foramens was due to the more reliable attaching sclerites to the main saccular body. On the other hand, thus the old sclerites could be replaced by new ones. Perhaps that is why we find in the fossil record a huge amount of individual sclerites сhanсelloriids.
Acknowledgements
This study was supported by the Program of the Presidium of the Russian Academy of Sciences “Problems of Life Origin and Development of Biosphere”, and by the Russian Foundation for Basic Researches, project no. 130500334.
References
Bengtson, S. and Missarzhevsky, V.V. 1981. Coeloscleritophora—a major group of enigmatic Cambrian metazoans. U.S. Geological Survey OpenFile Report, 81743, 1921.
Bengtson, S., Conway Morris, S., Cooper, B.J., Jell, P.A. and Runnegar, B.N. 1990. Early Cambrian fossils from South Australia. Memoirs of the Association of Australasian Palaeontologists, 9, 1364.
Bengtson, S. and Hou Xianguang. 2001. The integument of Cambrian chancelloriids. Acta Palaeontologica Polonica, 46(1), 122.
Butterfield, N.J. and Nicholas, C.G. 1996. Burgess Shaletype preservation of both nonmineralizing and ‘shelly’ Cambrian organisms from Mackenzie Mountains, northwestern Canada. Journal of Paleontology, 70, 893899.
Chen Junyuan, Zhou Guiqin, Zhu Maoyan and Yeh, K.Y. 1996. The Chengjiang Biota: A Unique Window of the Cambrian Explosion. Taichung, National Museum of Natural Science (in Chinese).
Demidenko, Yu.E. 2000. New Chancelloriid Sclerites from the Lower Cambrian of South Australia. Paleontological Zhurnal, 4, 2024 (Paleontological Journal, 34(4), 377383).
Esakova, N.V. and Zhegallo, E.A. 1996. Biostratigrafiya i fauna nizhnego kembriya Mongolii. Trudy Sovmestnoj rossijskomongolskoj paleontologicheskoj ehkspeditsii Moscow, 46, 1214.
Goryansky, V.V. 1973. One the necessity of excluding the genus Chancelloria Walcott from the phylum Porifera. Trudy Institut Geologii i Geofiziki SO AN SSSR, 49, 3944 (in Russian).
Mehl, D. 1996. Organization and microstructure of the chancelloriid skeleton: implications for the biomineralization of the Chancelloriidae. Bulletin de Iinstitut océanographique, Monaco, Numéro special, 14, 377385.
Mostler, H. and Mosleh Yadzi, A. 1976. Neue Poriferen ausoberkambrischen Gesteinen der Milaformation im Elburzgebirge (Iran). Geol. Palaontol. Mitt. Inssbruck, 5(1), 136.
Parkhaev, P.Yu. and Demidenko, Yu.E. 2010. Zooproblematica and Mollusca from the Lower Cambrian Meishucun section (Yunnan, China) and taxonomy and systematics of the Cambrian small shelly fossils of China. Paleontological Journal, 44(8), 8831161.
Qian Yi and Bengtson, S. 1989. Palaeontology and biostratigraphy of the Early Cambrian Meishucunian Stage in Yunnan Province, South China. Fossils and Strata, 24, 1156.
Rigby, J.K. 1978. Porifera of the Middle Cambrian Wheeler Shale, from the Wheeler Amphitheater, House Range, in western Utah. Journal of Paleontology, 52(6), 13251345.
Randell, R.D., Lieberman, B.S., Hasiotis, S.T. and Pope, M.C. 2005. New chancelloriids from the Early Cambrian Sekwi Formation with a comment on chancelloriid affinities. Journal of Paleontology, 79, 987996.
Sdzuy, K. 1969. Unterund mittelkambrische Porifera (Chancellorrida und Hexactineliida). Palaontol. Ztschr., 43,115147.
Walcott, C.D. 1920. Cambrian geology and paleontology IV: 6Middle Cambrian Spongiae. Smithsonian Miscellaneous Collections, 67(6), 261364.
On the stratigraphy of Aldanella attleborensis—potential indexspecies for defining the base of Cambrian Stage 2
Pavel Yu. PARKHAEV
Borissiak Paleontological Institute of the Russian Academy of Sciences
The longterm discussion about the suitability of fossil species as a primary markers for substantiation of stage boundaries has been recently reopened for the lower stages of the Cambrian system (e.g. Landing et al., 2013). The main argument for replacement of the biostratigraphic tool by the chemostratigraphic one is supposed diachroneity of FAD of a particular fossil species, which is originally caused by the dispersal pattern and biofacies peculiarities, and later tangled by different preservation, various collection methods, and imperfect taxonomy. The chemostratigraphic method has its own demerits, e.g. (1) each particular peak of a curve or group of peaks are faceless (one can find similar excursion patterns in different parts of the timescale), (2) there is no guarantee that in various basins the change in isotope ratios was simultaneous and uniform, (3) local diagenetic process can distort isotope record, (4) many sections are not suitable for chemostratigraphic analysis at all, and etc. As we can see from a vast paleontological literatures, the specimens with the same generic or species names actually look more similar than the isotope curves of the same intervals but from different areas (e.g. Parkhaev and Demidenko, 2010, figs. 5, 6; Landing et al., 2013, fig. 5). Possibly, the global and well recognizable shifts in Cisotope compound do exist (e.g. BACE, ZHUCE, and SPICE in the Late Precambrian—Cambrian, see Zhu et al., 2006), but they are too scare to provide detailed stratigraphy with the stages and zones substantiated on it. We can accept the chemostratigraphic method only as a secondary tool, for clarification of some local stratigraphic question within a paleobasin or between neighboring areas, when the fossils can not ensure reliable data for correlation and\/or subdivision. On the other hand, several decades of successful usage of various biostratigraphic zonation scales in the geological practice through all of the Phanerozoic systems is the most convincing reason to ignore the mainly theoretical diachroneity of species appearance in the geological record. Sometimes diachroneity does occur, but it can be detected biostratigraphicaly, by means of analyzing a number of fossil species ranges. This fact emphasizes the importance of entire fossil assemblages for elaboration of scales of different ranks. However, the formal rules of GSSP substantiation compel us to choose a single species to mark the particular boundary.
Stage scale of the lower part of the Cambrian system is still under construction, and the GSSPs and stage names are still wanted for Stage 2, Stage 3, Stage 4 and Stage 5 (ISC v2014\/02, http:\/\/www.stratigraphy.org\/index.php\/icscharttimescale). The Stage 2 approximately corresponds to the Tommotian stage of the Siberian Stage Standard (SSS) (see Rozanov et al., 2008 for the working model of the Cambrian stage subdivision).
Two mollusk species were recently proposed to determine the base of Cambrian Stage 2, i.e.Aldanella attleborensis (Parkhaev et al., 2011, 2012; Parkhaev and Karlova, 2011) and Watsonella crosbyi (Li et al., 2011). A. attleborensis is welldistributed geographically, with records from the Siberian Platform, South China, Avalonia, and Baltia. W. crosbyi has wider geographic range, besides Siberian Platform, South China, and Avalonia, it also occurs in Mongolia, South France and South Australia, but lacks in Baltica. It should be noted, that W. crosbyi is a rather longliving taxon, ranging from the beginning of the Tommotian up to the middle of the Botomian (Gravestock et al., 2001) in the terms of the SSS. So that, the usage of W. crosbyi as the index fossil is not very accurate, providing the resolution of two and a half stages.
Fig. 1. Aldanella attleborensis (Shaler and Foerste, 1888), internal mold, specimen PIN, no. 5083\/565; Tommotian Stage, Nochoroicyathus sunnaginicus Zone, Siberian Platform, Uchur—Maya Region, upper reaches of Selinde River, MarKyuel section, 2.5—1.3 m above the base of the Pestrotsvet Formation.
A. attleborensis (Fig. 1) is a comparatively shortliving species, occurring only in the lower part of the Tommotian Stage. The most numerous and welldocumented records of the species come from the Siberian Platform, where it occurs in almost all facies regions and different lithological types. The species occurs in more than 50 Siberian outcrops; 19 reference and key sections with occurrences of A. attleborensis are given by Parkhaev and Karlova, 2011 on their textfigure 5. According to the published data, the species is very common in the basal part of redor mottlecolored clayish limestones of the Tommotian Stage (Pestrotsvet Formation in AldanLena and UchurMaya regions, Medvezhya Formation in West Anabar region, Emyaksin Formation in East Anabar region, etc.), i.e. in the strata overlying the light colored limestones or dolomitic limestones of the Upper Vendian (NemakitDaldynian). Possibly, the abundance of A. attleborensis in colored clayish limestone can be explained by the favorable facial conditions. However, the FADs of A. attleborensis take place below, i.e. in the uppermost part of the light colored limestones or dolomitic limestones, where the species is more or less uncommon. These particular discoveries may correspond to the evolutionary appearance and immediate dispersal of the species over the regions. So that, the A. attleborensis FADs in the Siberian Platform are the following: uppermost Yudoma Formation in UchurMaya region and Aldan River, uppermost Tolba Formation on Lena river, uppermost NemakitDaldynian Formation in West Anabar region, upper part of the Kesyusse Formation in Olenek Uplift, uppermost Sukharikha Formation in Igarka Region, and uppermost Polba Formation in Norilsk area (Fig. 2).
On the Siberian Platform A. attleborensis is a member of the SSF assemblage of Nochoroicyathus sunnaginicus Zone. In several regions the FAD of A. attleborensis coincides directly with the FAD of the first arcaeocyaths of that zone (Fig. 2). So that, the isochronous nature of A. attleborensis first appearance is controlled, besides the number of SSF taxa, by reliable data from archaeocyaths. In addition to the platform sections, A. attleborensis occurs in the Lower Tommotian of the Eastern Kolyma Uplift and folded zones of the Taimyr Peninsula.
Fig. 2. The FADs of Aldanella attleborensis and archaeocyaths in the key regions of the Siberian Platform.
Fig. 3. Stratigraphic distribution of Aldanella attleborensis and some important SSF species in Siberia, North America, China and Europe.
In North America A. attleborensis occurs (Fig. 3) in the thick Watsonella crosbyi Zone of the middle part of the Chapel Island Formation (upper part of the Member 3 and Member 4, Burin Peninsula, Newfoundland, Canada), the Bonavista Formation (Avalon Peninsula, Newfoundland, Canada) and the Weymouth Formation (Massachusetts, USA) (Landing, 1988; Landing et al., 1989). These terrigenous strata of temperate latitudes are not very rich in fossils as compared with carbonate shallow water ‘tropical’ deposits of Siberian or Chinese lower part of the Cambrian. Possibly poor paleontological characteristic is the reason for rather controversial conclusions on the duration of that zone and its correlation, e.g. with the SSS (Landing et al., 2013). Another reason for some misleading conclusions is different approach to taxonomy of Aldanella species. The taxonomic revision of the genus Aldanalla was published recently (Parkhaev and Karlova, 2011). It was shown, that the genus includes 6 valid species, 8 species were considered as junior synonyms. However, if all 6 valid species are accepted as a single highly variable taxon (e.g. Landing, 1988; Landing et al., 2013), its stratigraphic range can be unreasonably exaggerated. For instance, the subTommotian records of A. attleborensis, mentioned by Landing et al., 2013, actually correspond to A. crassa, which FAD occurs in the Purella antiqua Zone of the NemakitDaldynian Stage.
In Europe A. attleborensis occurs in the upper part of the Lontova Horizon, Kestla Member, Estonia (Isakar and Peel, 2007, as A. kunda). Here in Baltia the range of A. attleborensis is very narrow, and corresponds only to a fragment of the entire stratigraphic range of the species, somewhere within the lower part of the Tommotian Stage.
In China A. attleborensis was found in Yunnan (Dahai Member of the Zhujiaqing Formation) and Hubei (Yanjiahe Formation and Huangshandong Member of the Dengying Formation) provinces, and in Xinjiang Autonomous Region (Yurtusi Formation), where it was reported under the name of A. yanjiaheensis. The discoveries in the Zhonguicun Member of the Zhujiaqing Formation are also possible (Steiner et al., 2007, fig. 12). Accompanying SSF suggests that the strata are roughly the Tommotian equivalent (Parkhaev and Demidenko, 2010).
Thus, the most complete and reliable data on the stratigraphy of A. attleborensis come from the territory of the Siberian Platform. Representative fossil assemblages below the FAD of A. attleborensis and above its LAD bracket the stratigraphic range within the lower part of the Tommotian Stage. Hence the species can be used as a good index fossil for that interval of the lower Cambrian deposits, whereas the FAD of A. attleborensis can be used as a biostratigraphic marker for the base of Stage 2.
Acknowledgements
Study was supported by RFBR grants nos. 130500632 and 130400322.
References
Gravestock, D.I., Alexander, E.M., Demidenko, Yu.E., Esakova, N.V., Holmer, L.E., Jago, J.B., Lin, T., Melnikova, L.M., Parkhaev, P.Yu. and Rozanov, A.Yu. 2001. The Cambrian Biostratigraphy of the Stansbury Basin, South Australia. Moscow, MAIK Nauka Interperiodica. 344 pp.
Isakar, M. and Peel, J.S. 2007. Lower Cambrian Helcionelloid Molluscs from Estonia. GFF, 129, 255262.
Landing, E. 1988. Lower Cambrian of Eastern Massachusetts: Stratigraphy and Small Shelly Fossils. Journal of Paleontology, 62(5), 661695.
Landing, E., Geyer, G., Brasier, M.D. and Bowring, S.A. 2013. Cambrian Evolutionary Radiation: Context, correlation, and chronostratigraphy—overcoming deficiencies of the first appearance datum (FAD) concept. EarthScience Reviews, 123, 133172.
Landing, E., Myrow, P., Benus, A.P. and Narbonne, G.M. 1989. The Placentian Series: appearance of the oldest skeletalized faunas in southeastern Newfoundland. Journal of Paleontology, 63(6), 739769.
Li Guoxiang, Zhao Xin, Gubanov, A., Zhu Maoyan and Na Lin. 2011. Early Cambrian mollusc Watsonella crosbyi: a potential GSSP index fossil for the Base of the Cambrian Stage 2. Acta Geologica Sinica, 85(2), 309319.
Parkhaev, P.Yu. and Karlova, G.A. 2011. Taxonomic revision and evolution of Cambrian mollusks of the genus Aldanella Vostokova, 1962 (Gastropoda, Archaeobranchia). Paleontological Journal, 45(10), 11451205.
Parkhaev, P.Yu., Karlova, G.A. and Rozanov, A.Yu. 2011. Taxonomy, stratigraphy and biogeography of Aldanella attleborensis—a possible candidate for defining the base of Cambrian Stage 2. Bulletin of Museum Northern Arizona, 67, 298300.
Parkhaev, P.Yu., Karlova, G.A. and Rozanov, A.Yu. 2012. Stratigraphic distribution of two potential species for the GSSP of Cambrian Stage 2—Aldanella attleborensis and Watsonella crosbyi. Journal of Guizhou University, 29(suppl.), 179180.
Rozanov, A.Yu., Parkhaev, P.Yu, Shabanov, Yu.Ya., Pegel, T.V., Raevskaya, E.G., Zhuravlev, A.Yu., Gmez Vintaned, J.A. and Ergaliev, G.Kh. 2008. The 13th International Conference of the Cambrian Stage Subdivision Working Group. Episodes, 31(4), 440441.
Steiner, M., Li Guoxiang, Qian Yi, Zhu maoyan and Erdtmanna, B.D. 2007. Neoproterozoic to Early Cambrian Small Shelly Fossil Assemblages and a Revised Biostratigraphic Correlation of the Yangtze Platform (China). Palaeogeography, Palaeoclimatology, Palaeoecology, 254, 6799.
Zhu Maoyan, Babcock, L.E. and Peng Shanchi. 2006. Advances in Cambrian stratigraphy and paleontology: integrating correlation techniques, paleobiology, taphonomy and paleoenvironmental reconstruction. Palaeoworld, 15, 217222.
Biostratigraphic study on the Balang Formation (Series 2, Cambrian) of Guizhou, China
PENG Jin, ZHAO Yuanlong, SUN Haijing, YAN Qiaojie, WEN Rongqin, SHEN Zhen and LIU Shuai
College of Resources and Engineering Environment,Guizhou University, Guiyang 550025, China
The Balang Formation is a Cambrian lithostratigraphic unit named by Yang Jingzhi and Qian Yiyuan in 1959 with the type locality near Balang Village, Duyun City, eastern Guizhou Province (Qian, 1961). Owing to a fault occurring at the section, the exposed sequence at the type locality is incomplete. Subsequent investigation showed that a more complete section was found at Zhangjiapo Village in Jiangko County (Yin, 1987). Therefore the type section of this formation was suggested to be changed to the section at Zhangjiapo. The lower part of the Balang Formation is dominated by greyishgreen and greenishyellow shale intercalated with a few thinbedded siltstones, while the upper part is mainly composed of light grey calcareous shale, silty mudstone and shale intercalated with thinbedded argillaceous limestone. The Balang Formation is mainly distributed in eastern Guizhou and western Hunan, located at the transitional belt between Yangtze and Jiangnan belts. Its thickness ranges from 87 m to 660 m in Yuping area, e.g. 597.1 m thick at Jianggu section, Zhenyuan County; from 187 to 361 m in southern Duyun, while from 229 to 467 m in northern Jiangkou. In general, changes of thickness show two directions: gradually thinner to the northeast and southwest, and also thinner to its western boundary. Sediments are mainly terrigenous detrital with a little carbonates. In eastern Guizhou its overlying Tsinghsutung Formation is dominated by greyishgreen thinbedded limestone, while in Nangao of Danzhai, due to the change of lithofacies, the overlying Wuxun Formation is composed of greyishgreen silty calcareous shale. The underlying grey to dark grey mudstone of the Bianmachong Formation changes to greyishyellow shale southward. It is known that the Balang Formation was a famous stratigraphic unit with abundant oryctocephalid trilobite such as Arthricocephalus, Balangia and Changaspis (abbreviated as A, B, C elements). The biostratigraphic formwork of the Balang Formation was originally established as the Arthricocephalus Zone and the ArthrococephalitiesChangaspisBalangia Assemblage Zone (Zhou et al., 1980) that was revised as the Arthricocephalus Zone and the Arthrococephalities—Changaspis Zone afterwards. Subsequently, it was revised as the ArthricocephalusChangaspis Assemblage Zone (Yin, 1987). In recent 20 years, there are a lot of discussions on the taxonomy of corynexochid trilobites and the trilobite species ranges with the Balang Formation, which result in a continuous change of the biostratigraphic framework of the formation. Arthricocephalus and A. (Arthrococephalities) are thought to be highly diversified on the species level, including A. chauveaui, A. jiangkouensis, A. granulus, A. taijiangensis, Ar. jishouensis, Ar. xingzhaiheensis. According to the heterochronic evolution of species of Arthricocephalus Bergeron, 1889, Yuan et al. (2001) revised the biostratigraphic subdivision of the Balang Formation and proposed some new biozones, ascendingly the A. jiangkouensis Zone, A. granulus Zone, A. chauveaui Zone, and the Ar. taijiangensisAr. jishouensis Assemblage Zone. Subsequently, the biozones were also revised by Yuan et al. (2002) as the Arthricocephalus jiangkouensis Zone in the lower part, the Arthricocephalus granulus Zone in the middle and the Arthricocephalus chauveaui Zone in the upper. In 2006, the biostratigraphic subdivision of the Balang Formation was changed to the Arthricocephalus jiangkouensisArthricocephalus granulus Assemblage Zone and the Arthricocephalus chauveaui Zone. The upper zone is characterized with abundant Redlichia (Pteroredlichia) chinensis. A diverse fossil assemblage named as the Balang Fauna was found at 43 m near the top part of the Balang Formation at northwest Kaili City (Peng et al., 2005). A. chauveaui and A. taijiangensis were also discovered in this fauna. Investigation on the Balang Fauna effectively promotes the study of the Balang Formation in eastern Guizhou. Recent field work shows the presence of the fauna in the middle to upper part of the formation and 7 localities discussed in this paper (Peng et al., 2012). New collections we made recently provide more reliable data for use to further revise those corynexochid trilobites and their biostratigraphical division. Firstly, the species diversities of Arthricocephalus and Changaspis are not as high as previously thought. And a new biostratigraphic formwork is proposed for the Balang Formation, and the Arthricocephalus chauveauiChangaspis micropyge Assemblage Zone was established (Peng, 2009). Recently, Changaspis micropyge was revised as a junior synonym of Changaspis elongata (Qin et al., 2010). The Balang Formation yields the Arthricocephalus chauveauiChangaspis elongata Assemblage Zone. In addition, another situation occurs, i.e. one specimen or some similar specimens were identified as different species in three different monographs (Lu et al., 1974; Yin and Lee, 1978; Zhang et al., 1980), which results in widely cited misleading information. Secondly, corynexochid trilobites may not be found in every fossil zone on the species level. Our work indicates that A. chauveaui firstly appears near the base of the four sections of the Balang Formation, including the Geyi section of Taijiang, the Jiaobang section of Jianhe, the Jianggu section of Zhenyuan, and the Huanglian section of Songtao, three of which only expose the upper strata but also yield fossils of this species. And the A. chauveaui biozone usually contains Ar. xinzhaiheensis, Ar. jishouensis, B. balangensis, C. elongata, D. duyuanensis, D. laevigatus. A. jiangguensis, identified through only a few thoracic segments, differs from A. chauveaui. It was discovered at the Jiaobang section, and its precise stratigraphic position is unclear.
Recently, a diverse fossil assemblage was discovered from the middle to upper part of the overlying Tsinghsutung Formation near Balang village, Jianhe County (Sun et al., 2014), C. micropyge (elongata) also occurs in the fossil assemblage and could be abundant (Yang et al., 2010), which indicates that it could range into the upper part of the Tsinghsutung Formation. Starting from the first zone of the formation, the Redlichia (Pteroredlichia) murakamii—Hoffetella—Eoptychoparia Assemblage Zone, this species has a very long range and loses its biostratigraphic significance. It might be suitable that the biostratigraphy of the Balang Formation could be revised as a single zone, i.e. the A. chauveaui Zone. Only when the corynexochid trilobites are systematically revised and the stratigraphical range of all species from the Balang Formation is clear, the biostratigraphic formwork of the formation could be effectively established.
It is known that A. chauveaui, Ar. jishouensis, and C. elongata also occur in the lower Cambrian Henson Gletscher Formation of Greenland (Blaker and Peel, 1997), which provides significant information for global correlation. New data from the Balang Formation make it possible to revise the taxonomy of corynexochid trilobites and provide significant information for global correlation of the Stage 4 of Cambrian.
References
Blaker, M.R. and Peel, J.S. 1997. Lower Cambrian trilobites from North Greenland. Meddelelser om Grnland Geoscience, 35, 1145.
Lu Yanhao, Zhang Wentang, Qian Yiyuan, Zhu Zaoling, Lin Huanlin, Zhou Zhiyi, Zhang Shengui and Wu Hongji. 1974. Cambrian trilobites. In: Nanjing Institute of Geology and Palaeontology, Academia Sinica (ed.), A handbook of stratigraphy and palaeontology in Southwest China. Beijing, Science Press. 82107(in Chinese).
Peng Jin, Zhao Yuanlong, Wu Yishan, Yuan Jinliang and Tai Tongshu. 2005. The Balang Fauna―A new early Cambrian fauna from Kaili City, Guizhou Province. Chinese Science Bulletin, 50(11), 11591162.
Peng Jin. 2009. The Qiandongian (Cambrian) Balang Fauna from Eastern Guizhou, South China. Ph.D. thesis, Nanjing, Nanjing University. 137 pp.
Peng Jin, Zhao Yuanlong and Sun Haijing. 2012. Discovery and significance of Naraoia from the Qiandongian (lower Cambrian) Balang Formation, eastern Guizhou, South China. Bulletin of Geosciences, 87(1), 143150.
Qian Yiyuan. 1961. Cambrian trilobites from Shandu and Duyun counties, Guizhou Province, South China. Acta Palaeontologica Sinica, 9(2), 91129.
Qin Qin, Peng Jin, Fu Xiaoping and Da Yang, 2010. Restudy of Changaspis (Lee, 1961) from the Qiandongian (lower Cambrian) Balang Formation near eastern Guizhou, South China. Acta Palaeontologica Sinica, 49(2), 220230 (in Chinese with English summary).
Sun Haijing, Zhao Yuanlong, Peng Jin and Yang Yuning. 2014. New Wiwaxia material from the Tsinghsutung Formation (Cambrian Series 2) of eastern Guizhou, China. Geological Magazine, 151(2), 339348.
Yang Xinglian, Zhao Yuanlong, Peng Jin, Yang Yuning and Yang Kaidi. 2010. Discovery of Oryctocephalid trilobites from the Tsinghsutung Formation (Duyunian Stage, Qiandongian Series, Cambrian), Jianhe County, Guizhou Province. Geological Journal of China Universities, 16(3), 309316 (in Chinese with English abstract).
Yin Gongzhen and Lee Shanji. 1978. Arthropods. In: Handbook of Palaeontology of Southwest China. Beijing, Geological Publishing House. 383385.
Yin Gongzhen. 1987. Cambrian. In: Bureau of Guizhou Geology and Mineral Resources (ed.), Regional Geology of Guizhou Province. Beijing, Geological Publishing House. 4996 (in Chinese with English summary).
Yuan Jinliang, Zhao Yuanlong and Yang Xinglian. 2006. Speciation of the genus Arthricocephalus Bergeron, 1899 (Trilobita) from the late Early Cambrian and its stratigraphic significance. Progress in Natural Science, 16(6), 614623.
Yuan Jinliang, Zhao Yuanlong, Li Yue and Huang Youzhuang. 2002. Trilobite fauna of the Kaili Formation(uppermost Lower Cambrianlower Middle Cambrian) from southeastern Guizhou, South China. Shanghai, Shanhai Science and Technology Press. 422 pp (in Chinese with English summary).
Yuan Jinliang, Zhao Yuanlong and Li Yue. 2001. Biostratigraphy of oryctocephalid trilobites. Acta Palaeontologica Sinica, 40 (Supplement), 143156.
Zhang Wentang, Lu Yanhao, Zhu Zaoling, Qian Yiyuan, Lin Huanlin, Zhou Zhiyi, Zhang Shengui and Yuan Jinliang. 1980. Cambrian Trilobite Faunas of Southeastern China. Beijing, Science Press. 497 pp (in Chinese with English summary).
Zhou Zhiyi, Yuan Jinliang, Zhang Zhenhua, Wu Xiaoru and Yin Gongzhen. 1980. The classification and correlation of Cambrian strata in Guizhou, China. Journal of Stratigraphy, 4(4), 273281 (in Chinese with English abstract).
Biostratigraphy and biogeographic affinities of middle to late
Cambrian linguliformean brachiopods from Australasia
Ian G. PERCIVAL1 and Peter D. KRUSE2
1Geological Survey of New South Wales, NSW Trade & Industry, W.B. Clarke Geoscience Centre, 947953 Londonderry Road, Londonderry NSW 2753, Australia
2South Australian Museum, Adelaide; PO Box 825, Normanville SA 5204, Australia
Cambrian brachiopods have been described from three major types of tectonostratigraphic setting in Australia. They are most widely distributed in intracratonic basins of northern and central Australia, including the Georgina Basin of western Queensland (Henderson, 1974; Rowell and Henderson, 1978; Henderson and MacKinnon, 1981; Popov et al., 1994; Laurie, 1997; Henderson and Dann, 2010) and the Northern Territory (Laurie, 1987; Kruse, 1991, 1998; Percival and Kruse, 2014). These faunas range through the Stage 4 to Paibian interval. Other Stage 4 to early Stage 5 Cambrian brachiopod faunas are known from the Amadeus (Laurie, 1986), Daly (Kruse, 1990), Ord (Kruse et al., 2004) and eastern Wiso basins (Kruse, 1998) of the Northern Territory (Fig. 1).
The second major suite of basins with brachiopod faunas of Cambrian age are contained within the Delamerian Orogen which represented the eastern margin of Gondwana at the time. In far western New South Wales, the area known as the Gnalta Shelf yields Stage 4 to early Stage 5 faunas described by Roberts and Jell (1990) and Brock and Percival (2006), together with an isolated Paibianage occurrence (Percival in Powell et al., 1982). Recent studies of brachiopods from the Arrowie and Stansbury Basins of the Delamerian Orogen of South Australia, largely of Cambrian Series 2 age, include those by Brock and Cooper (1993), Ushatinskaya and Holmer (2001), Holmer et al. (2006), Paterson et al. (2007), Holmer et al. (2011) and Topper et al. (2013).
Thirdly (and much less common) are Cambrian faunas possibly inhabiting the flanks of oceanic islands in the Panthalassic Ocean east of the cratonic margin. Linguliformean brachiopods have been described from the Series 3 (Drumian to Guzhangian) Murrawong Creek Formation in the New England Orogen of northern New South Wales (Engelbretsen, 1996), and from slightly younger (late Guzhangian to Paibian) limestones at Dolodrook River in eastern Victoria (Engelbretsen, 2004, 2006). A poorly preserved fauna of middle to late Cambrian age, including fragmentary brachiopods, has been reported from parautochthonous and allochthonous limestones on the south coast of NSW (Bischoff and Prendergast, 1987). Cambrian brachiopods from Tasmania are relatively poorly known (Jago, 1977, 1989).
During the Cambrian, part of presentday New Zealand (now incorporated into the Takaka Terrane at the northern extremity of the South Island) was situated south and east of the Gondwana margin. Brachiopod faunas of late Series 3 age (Guzhangian: Boomerangian) from the Tasman Formation of this region were described by Henderson and MacKinnon (1981) and MacKinnon (1983), and Furongian brachiopods from the Maruia area were recently documented by Percival et al. (2014).
This review analyses the stratigraphic distribution and biogeographic affinities of Cambrian lingulate brachiopods spanning the Stage 4 to Jiangshanian interval in Australia and New Zealand, concentrating on recently published information (Percival and Kruse, 2014; Percival et al., 2014) which adds considerably to previously known faunas of Australasia. Sparse faunas containing Cambrian brachiopods are also known from Antarctica but in general their stratigraphic position is poorly resolved and so they will not be considered further here.
Intracratonic basins of northern and central Australia
Two depositional sequences are recognised in Cambrian rocks of central and northern Australian intracratonic basins (Fig. 1). Depositional Sequence 1 is characterised by the Thorntonia Limestone of the Georgina Basin and correlatives with brachiopod faunas of Ordian age (Stage 4 to early Stage 5), dominated by lingulates (linguloids, acrotheloids and acrotretoids) with a minor paterinate component. The disconformably overlying Arthur Creek Formation of the Georgina Basin (and its correlatives) spans uppermost Sequence 1 and all of Depositional Sequence 2 (latest Ordian to at least Boomerangian age in terms of the Australian Cambrian stage scale, or Stage 5 to early Guzhangian). Stratigraphic distribution of brachiopods in these two sequences is depicted in Figure 2. Particularly striking is the absence of species crossing the boundary between the two depositional sequences, so that their characteristic assemblages are completely distinct. Cambrian faunas from the eastern Georgina Basin in Queensland are mostly younger, overlapping in part with those of Depositional Sequence 2 and spanning several intervals from Floran (early Drumian) to Mindyallan (late Guzhangian), with a separate Idamean (= Paibian) assemblage less well known.
Fig. 1. Map of Australia and New Zealand showing location of major basins with Cambrian deposition, and other important outcrops of Cambrian strata discussed in text. Adapted from Kruse et al. (2009). NZ = New Zealand. Australian states and territories: NSW = New South Wales, NT = Northern Territory, QLD = Queensland, SA = South Australia, TAS = Tasmania, VIC = Victoria, WA = Western Australia.
Gnalta Shelf (Delamerian Orogen)
Within the Delamerian Orogen, only those brachiopod faunas of the Gnalta Shelf in New South Wales are considered within the timeframe encapsulated by Figure 2. These are predominantly confined to the Ordian and are therefore equivalent in age to those of Depositional Sequence 1. The youngest of four successive brachiopod assemblages recognised by Jago et al. (2006) from the Arrowie and Stansbury Basins of the Delamerian Orogen in South Australia also correlates with Depositional Sequence 1.
Fig. 2. Stratigraphic distribution of genera and species of Cambrian linguliformean brachiopods in Australia and New Zealand relative to international and regional chronostratigraphic scales (at left).
Fig. 2. Continued.
Areas off shore to the Gondwana margin
Brachiopods from the Murrawong Creek Formation (northeastern New South Wales), the Dolodrook limestone of Victoria and the Tasman Formation of the Takaka Terrane in New Zealand display numerous similarities at species level. The Murrawong Creek assemblage is the oldest, overlapping in part towards the top of its range with the Tasman Formation. The Dolodrook limestone is distinctly younger but still shares five out of nine of its named species with the Murrawong Creek Formation.
Compared with the brachiopod fauna of the lower Sluice Box Formation (Paibian to Jiangshanian) of the Maruia area of the Takaka Terrane in New Zealand (Fig. 1), there is a very noticeable difference in species content, with no taxa in common even with the most geographically proximal Tasman Formation fauna, or with the Dolodrook limestones which partially overlap in age the Maruia assemblage (Fig. 2).
Biogeographic affinities of linguliformean brachiopods
Fig. 3. Cluster analysis (Dice coefficient 0.9412) for middle and late Cambrian linguliformean brachiopods of Australia and New Zealand, also including comparative data from Maliy Karatau, Kazakhstan (Holmer et al., 2001) and Huaqiao Formation of South China (Engelbretsen and Peng, 2004). Data analysis conducted using PAST (Hammer et al., 2001). Area and stratigraphic horizon codes explained in text. Colours: blue = Depositional Sequence 1; green = Depositional Sequence 2 and correlatives (Series 2: light = Australasia (note that Dolodr includes late MindyallanIdamean = late GuzhangianPaibian), dark = Kazakhstan and South China); yellow = Furongian (light = Australasia, dark = Kazakhstan).
Biogeographic affinities of Australasian Ordian to Iverian brachiopods were analysed using the statistical program PAST (Hammer et al., 2001). To further relate these faunas of eastern Gondwana and adjacent oceanic regions to contemporaneous assemblages that were known to share some species and genera, faunas from the Maliy Karatau Range of Kazakhstan (Holmer et al., 2001) and the Huaqiao Formation of South China (Engelbretsen and Peng, 2007) were also included in the analysis (Fig. 3). For greater precision, the Maliy Karatau Range faunas were divided into five temporal intervals: (1) late Templetonian to Floran equivalents (ultimus to atavus trilobite zones), designated MKTeFl in Figure 3; (2) Undillan equivalent (punctuosus to nathorsti zones) [MKUnd]; (3) Boomerangian and Mindyallan equivalents (armata to stolidotus zones) [MKBoMi]; (4) Idamean equivalent (reticulatus to acutus zones) [MKIda]; and (5) Iverian equivalent [MKIver].
The analysis shows that Depositional Sequence 1 faunas (southern Georgina Basin [GEORG1] and other centralnorthern Australian intracratonic basins [NTBas1]) group closely—the Gnalta Shelf assemblage [GNALTA] less so—at the righthand side of Figure 3.
As previously noted, no similarity is evident between Depositional Sequence 1 and 2 faunas (compare GEORG1 and GEORG2). There is a noticeable overprint of age control, so that contemporaneous faunas (and those approximately equivalent) are more closely aligned. This result highlights the biostratigraphic potential of brachiopods in the Cambrian. Thus, among younger Cambrian faunas, the South China assemblage [HuaSC] shares some affinities with that from Murrawong Creek [MurrCk], which is also reasonably close to faunas from the Dolodrook limestone of Victoria [Dolodr], Tasman Formation of New Zealand [TasmNZ], and the Floran to Mindyallan interval of the eastern Georgina Basin [EGFlMi] at the lefthand side of Figure 3.
Secondarily, this latter grouping shows affinity with contemporaneous assemblages of Kazakhstan [MKTeFl, MKUnd, MKBoMi]. Holmer et al. (2001) previously identified biogeographic affinities among late middle Cambrian faunas of Kazakhstan terranes (e.g. Maliy Karatau Range) and FloranMindyallan linguliformean brachiopods of the Murrawong Creek Formation (Engelbretsen, 1996).
Linguliformean brachiopods of Paibian to Jiangshanian age from the lower Sluice Box Formation of the Maruia area, New Zealand [MaruNZ] display closest biogeographic affiliation with coeval assemblages of the eastern Georgina Basin [EGIda]. However, with the exception of the endemic genus Maruia, all other identified New Zealand genera are otherwise largely restricted in distribution to Kazakh terranes, specifically the Maliy Karatau Range (Holmer et al., 2001), and contemporaneous strata in the northeastern part of Central Kazakhstan (Popov and Holmer, 1994). Two species described from the Furongian at Maruia, and another in open nomenclature, are provisionally referred to genera (Mirilingula, Experilingula and Akmolina) otherwise known only from Kazakhstan. The unnamed new species of Quadrisonia in the Maruia fauna is morphologically closest to Q. suspensa from Kazakhstan (and conversely is dissimilar to species from the Great Basin of western USA). The constituent Notiobolus has previously been described from Kazakhstan (Holmer et al., 2001) and West Antarctica (Popov and Solovev, 1981). The latter occurrence is intriguing, as Antarctica may have been relatively close to the Takaka Terrane in the Early Palaeozoic as part of eastern Gondwana.
References
Bischoff, G.C.O.and Prendergast, E.I. 1987. Newly discovered Middle and Late Cambrian fossils from the Wagonga Beds of New South Wales, Australia. Neues Jahrbuch für Geologie und Palontologie, Abhandlungen, 175, 3964.
Brock, G.A.and Cooper, B.J. 1993. Shelly fossils from the Early Cambrian (Toyonian) Wirrealpa, Aroona Creek, and Ramsay Limestones of South Australia. Journal of Paleontology, 67, 758787.
Brock, G.A.and Percival, I.G. 2006. Cambrian stratigraphy and faunas at Mount Arrowsmith, northwestern New South Wales. Memoirs of the Association of Australasian Palaeontologists, 32, 75101.
Engelbretsen, M.J. 1996. Middle Cambrian lingulate brachiopods from the Murrawong Creek Formation, northeastern New South Wales. Historical Biology, 11, 6999.
Engelbretsen, M.J. 2004. Cambrian paterinid brachiopods from the Dolodrook River limestones, eastern Victoria. Memoirs of the Association of Australasian Palaeontologists, 30, 145152.
Engelbretsen, M.J. 2006. Early Late Cambrian lingulate brachiopods from the Dolodrook River limestones, eastern Victoria. Memoirs of the Association of Australasian Palaeontologists, 32, 225246.
Engelbretsen, M.J. and Peng Shanchi. 2007. Middle Cambrian (Wulingian) linguliformean brachiopods from the Paibi section, Huaqiao Formation, Hunan Province, South China. Memoirs of the Association of Australasian Palaeontologists, 34, 311329.
Hammer, ., Harper, D.A.T.and Ryan, P.D. 2001. PAST: Paleontological Statistics Software Package for Education and Data Analysis. Palaeontologia Electronica, 4(1), 9 pp.Henderson, R.A. 1974. Shell adaptation in acrothelid brachiopods to settlement on a soft substrate. Lethaia, 7, 5761.
Henderson, R.A.and Dann, A.L. 2010. Substrate control of benthos in a Middle Cambrian nearshore, epeiric palaeoenvironmental setting. Palaeogeography, Palaeoclimatology, Palaeoecology, 292, 474487.
Henderson, R.A.and MacKinnon, D.I. 1981. New Cambrian inarticulate Brachiopoda from Australasia and the age of the Tasman Formation. Alcheringa, 5, 289309.
Holmer, L., Popov, L.E., Koneva, S.P. and Bassett, M.G. 2001. CambrianEarly Ordovician brachiopods from Malyi Karatau, the western Balkhash region, and northern Tien Shan, Central Asia. Special Papers in Palaeontology, 65, 1180.
Holmer, L.E., Skovsted, C.B. and Brock, G.A. 2006. First record of canaliform shell structure from the Lower Cambrian paterinate brachiopod Askepasma from South Australia. Memoirs of the Association of Australasian Palaeontologists, 32, 15.
Holmer, L.E., Skovsted, C.B., Brock, G.A. and Popov, L.E. 2011. An early Cambrian chileate brachiopod from South Australia and its phylogenetic significance. Memoirs of the Association of Australasian Palaeontologists, 41, 289294.
Jago, J.B. 1977. A late Middle Cambrian fauna from the Que River beds, western Tasmania. Papers and Proceedings of the Royal Society of Tasmania, 111, 4151.
Jago, J.B. 1989. Late Cambrian brachiopods from the Denison Range, southwestern Tasmania. Papers and Proceedings of the Royal Society of Tasmania, 123, 3742.
Jago, J.B., Zang Wenlong, Sun Xiaowen, Brock, G.A., Paterson, J.R. and Skovsted, C.R. 2006. A review of the Cambrian biostratigraphy of South Australia. Palaeoworld, 15, 406423.
Kruse, P.D. 1990. Cambrian palaeontology of the Daly Basin. Northern Territory Geological Survey Report, 7, iii+58 pp.
Kruse, P.D. 1991. Cambrian fauna of the Top Springs Limestone, Georgina Basin. The Beagle, Records of the Northern Territory Museum of Arts and Sciences, 8, 169188.
Kruse, P.D. 1998. Cambrian palaeontology of the eastern Wiso and western Georgina Basins. Northern Territory Geological Survey Report, 9, iv+68 pp.
Kruse, P.D.,Jago, J.B. and Laurie, J.R. 2009. Recent developments in Australian Cambrian biostratigraphy. Journal of Stratigraphy, 33, 3547.
Kruse, P.D., Laurie, J.R.and Webby, B.D. 2004. Cambrian geology and palaeontology of the Ord Basin. Memoirs of the Association of Australasian Palaeontologists, 30, 158.
Laurie, J.R. 1986.Phosphatic fauna of the Early Cambrian Todd River Dolomite, Amadeus Basin, central Australia. Alcheringa, 10, 431454.
Laurie, J.R. 1987. The musculature and vascular system of two species of Cambrian Paterinida (Brachiopoda). BMR Journal of Australian Geology and Geophysics, 10, 261265.
Laurie, J.R. 1997. Silicified Late Cambrian brachiopods from the Georgina Basin, western Queensland. Alcheringa, 21, 179190.
MacKinnon, D.I. 1983. A late Middle Cambrianorthidekutorginide brachiopod fauna from northwest Nelson, New Zealand. New Zealand Journal of Geology & Geophysics, 26, 97102.
Paterson, J.R., Skovsted, C.B., Brock, G.A. and Jago, J.B. 2007. An early Cambrian faunule from the Koolywurtie Limestone Member (Parara Limestone), Yorke Peninsula, South Australia and its biostratigraphic significance. Memoirs of the Association of Australasian Palaeontologists, 34, 131146.
Percival, I.G.and Kruse, P.D. 2014. Middle Cambrian brachiopods from the southern Georgina Basin of central Australia. Memoirs of the Association of Australasian Palaeontologists, 45, 349402.
Percival, I.G., Zhen, Y.Y.,Simes, J.E. and Cooper, R.A. 2014. Furongian (Late Cambrian) brachiopods and associated conodonts from the Takaka Terrane in the Springs Junction—Maruia area, South Island, New Zealand. Memoirs of the Association of Australasian Palaeontologists, 45, 5570.
Popov, L.E., BergMadsen, V.and Holmer, L.E. 1994. Review of the Cambrian acrotretide brachiopod Neotreta. Alcheringa, 18, 345358.
Popov, L.and Holmer, L.E. 1994. CambroOrdovician lingulate brachiopods from Scandinavia, Kazakhstan, and South Ural Mountains. Fossils & Strata, 35, 1156.
Popov, L.E.and Solovev, I.A. 1981. Srednekembriyskie bezzamkovye brakhiopody, khantsellorii, konikonkhii i trilobity zapadnoy Antarktidy (khrebty Sheklton i Ardzhentina) [Middle Cambrian inarticulate brachiopods, chancelloriids, coniconchiids and trilobites from West Antarctica (Shackleton and Argentina ranges)]. Antarktika, 20, 6472.
Powell,C.McA., Neef, G., Crane, D., Jell, P.A. and Percival, I.G. 1982. Significance of Late Cambrian (Idamean) fossils in the Cupala Creek Formation, northwestern New South Wales. Proceedings of the Linnean Society of New South Wales, 106, 127150.
Roberts, J.and Jell, P.A. 1990. Early Middle Cambrian (Ordian) brachiopods of the Coonigan Formation, western New South Wales. Alcheringa, 14, 257309.
Rowell, A.J. and Henderson, R.A. 1978. New genera of acrotretids from the Cambrian of Australia and the United States. University of Kansas Paleontological Contributions, 93, 112.
Topper, T.P.,Holmer, L.E., Skovsted, C.B., Brock, G.A., Balthasar, U., Larsson, C.M., Petterson Stolk, S. and Harper, D.A.T. 2013. The oldest brachiopods from the lower Cambrian of South Australia. Acta Palaeontologica Polonica, 58, 93109.
Ushatinskaya, G.T. and Holmer, L.E., 2001. Brachiopods.120132. In: Alexander, E.M., Jago, J.B., Rozanov, A.Yu. and Zhuravlev, A.Yu. (eds), The Cambrian biostratigraphy of the Stansbury Basin, South Australia. Palaeontological Institute, Russian Academy of Sciences, Transactions, 282.
Recognizing triggers for extensive liquefaction structures in two Early Paleozoic shallowmarine sandstones, NW Estonia: Earthquake shock vs. cyclic storm loading
Kairi PO~LDSAAR and Leho AINSAAR
Department of Geology, University of Tartu,Ravila 14a, 50411 Tartu, Estonia
Liquefaction and\/or fluidization (and clay thixotropy) of unconsolidated watersaturated sediments are by far the most common sediment deformation mechanisms during deposition or shortly after the burial has started (Allen, 1982). The so called softsediment deformation structures (SSDS) that are preserved in the sedimentary record serve as useful glues for interpreting the sedimentary history or the geodynamic evolution of a sedimentary basin. However, many distinctly different geological processes are capable of triggering such deformations and the resulting structures are often very similar in their morphologies. For example, in shallowmarine sandstone environments sediment liquefaction can be induced by storm wave loading, tidal bores, slope failure deposits, breaking waves or occasionally even by tsunamis and stresses caused by passing earthquake waves. Hence, there are many variables related to the identification of SSDS triggers.
Here we compare two distinct SSDS horizons from shallowmarine environments—the midOrdovician (Darriwilian) Pakri Formation and Cambrian Series 2 (Dominopolian) Tiskre Formation. Both are deposited within the Baltoscandian Paleobasin geographically closely distributed in NW Estonia. Both contain extensive (up to several meters in height) SSDS structures distributed over relatively large geographical areas. Relying on threestep approach (faciestriggercriteria assessment) suggested by Owen et al. (2011) to identify the deformation triggers, we were able to conclude vastly different triggering agents for each case.
For the Ordovician Pakri Formation, 5 distinct outcrops in NW Estonian coastal cliff and 17 drillcore sections were analysed for SSDS. Results of this study have recently been published (Pldsaar and Ainsaar, in press). Here we report our preliminary observations and results for the Cambrian Tiskre Formation. For this study, numerous outcrop sections within approximately 30 km long section of the NorthEstonian coastal cliff were analysed.
Geological setting
The studied sedimentary successions—the Ordovician Pakri Formation and the Cambrian Tiskre Formation—are both deposited within a large intracratonic basin that existed within Baltica paleocontinent from the Neoproterozoic Ediacaran to the Early Devonian time. Sediments of the paleobasin represent the filling of a slowly subsiding epeiric sea. The Baltoscandian Paleobasin formed on the southern flank of the Fennoscandian Shield and eventually covered much of present Sweden, NE Poland, the Baltic States and NW Russia. Preliminary sedimentation in the Baltoscandian basin started with the accumulation of the EdiacaranCambrian siliciclastics onto the extremely peneplanised Precambrian metamorphic rocks. Gradually, the coldwater siliciclasticsdominated platform was replaced with temperateclimate carbonate ramp during the Middle Ordovician and with tropical carbonate shelf by the Late Ordovician (Dronov and Rozhnov, 2007). The corresponding sediments are well preserved in most localities and unaffected from beep burial diagenesis. The craton of Baltica became tectonically inactive soon after the Ediacaranearly Cambrian Timanide Orogeny and Baltoscandian Paleobasin remained tectonically quiescent for the first half of the Paleozoic (Nielsen and Schovsbo, 2011).
Results
Sedimentary environments. The Ordovician Pakri Formation is a 1 to 4.3 metres thick bed of sandy limestone or limey quartzose sandstone distributed in NW Estonia. The Cambrian Tiskre Formation is characterized by finegrained sandstone distributed all over the northern Estonia with thickness up to 20 metres. Both sediments were deposited in shallowmarine settings (Orviku, 1960; Pirrus, 1978). However, the sedimentary characteristics reveal different environmental conditions prevailing during the deposition of each unit. In the Pakri Formation abundant nearshore shelly fauna along with highrate bioturbation is found. Convenient beltlike arrangement of the sedimentary bed along the theoretical palaeoshoreline and abundance of skeletal or peloidal (glauconite, iron or phosphatic) grains indicate shallow subtidal depositional environment. No tempestite or other indications of storm or waveinfluences (i.e. hummocky crossstratification or ripple marks) occur in this formation. The Tiskre Formation, on the other hand, contains numerous sedimentary features indicative of regular highenergy sedimentary processes especially in the lower part (612 m) of this sedimentary succession. Among other current or waveinduced structures (ripple and drag marks, reactivation surfaces etc), pervasive occurrence of herringbone crossstratification, typical tidal depositional pattern of the rhythmite, and presence of hummocky crossstratification throughout the lower part of the Tiskre Formation enabled us to infer that the studied unit represents a classical opensea storminfluenced tidalite with gradually decreasing influence of storms upward in the section as the basin gradually subsided.
Types and distribution of SSDS. SSDS in the Pakri Formation are distributed within an area of up to 9000 km2 in NW Estonia and SE Sweden (Pldsaar and Ainsaar, in press). Deformations encompass the entire up to 4 m thick Pakri Formation and were mostly probably generated during a single deformation event or eventseries (among other, there are no overprinting of older deformations and interconnected or single waterescape channels and dykes are often crosscutting the entire deformation horizon and open to the sedimentary surface). The deformation horizon is bounded by undeformed layers from top and below (except for Osmussaar Island, NW Estonia where deformations are severe and encompass brittle destruction of older strata) and is well correlative throughout the entire area of the Pakri Formation. Combinations of specific types of SSDS can be distinguished in 3 deformation zones, with radially decreasing extent of deformation from a single epicentral region (on Osmussaar Island). In the most severely damaged epicentre, large sedimentary dykes and brecciation of the complete succession occurs (stage G, Fig. 1). And 30 km away only singlestanding large dykes cutting through the Pakri Formation along with partial homogenisation of the bed, occur (stage F, Fig. 1). In the most distal zone 100 to 250 km away from the epicentre, smaller but most numerous liquefaction deformations (various load structures) occur (Stages AE, Fig. 1; Pldsaar and Ainsaar, in press).
Fig. 1. Schematic succession of the development stages of the SSDS within the Pakri Formation (modified after Pldsaar and Ainsaar, in press). AE represent liquefaction driven load features that occur further from Osmussaar Island; FG represent liquefaction features with increasing intensities of deformative force up to brittle disruption and brecciation of sediments. H is an example of a small waterescape channel in the distal deformation zone; I is a planar view of a mediatesize sedimentary dyke opening to the surface of the Pakri Formation.
SSDS in the Tiskre Formation have been recorded within at least 30 km long coastal cliff section in NW Estonia. Individual beds with SSDS within the Tiskre Formation occur at several different levels, and due to the lenticular bedding of the rhythmites, can be traced laterally max. 50 m, before they fade out along with the thinning layers. However, deformations are clearly more profound in the storminfluenced lower part of the formation. Only faintly preserved SSDS (especially pillow structures) are found within the horizontally laminated and relatively thickbedded sandstones of the upper part. Morphologies, presence and types of SSDS in the Tiskre Formation are location specific, hence good categorization is complicated and further analysis is necessary here. Our preliminary classification includes (1) cmscale SSDS (load casts, asymmetrical flame structures, destructed laminae etc.) characteristic to thin tidal laminae and crossbedded units, (2) mediate (up to 30 cm in height) structures (load casts, flame structures, flattened pillows) on the interfaces between lightcoloured, crossbedded silt and darkcoloured clayey silt units accompanied often by hummocky crossstratification, (3) large (30 cm or more) deformation structures (pillows, irregular flame structures, contorted bedding, irregular slumplike folds etc.) associated with thick tidal bundles observed only in a specific geographical region (Suurupi Peninsula). Numerous other SSDS were documented throughout the outcrops at Tiskre cliff (i.e. homogenized zones, dishandpillar structures, water\/sediment movement channels (Neptunian dykes), breccias etc.)
Conclusions
Considering the facies associations, the applicable triggering mechanisms and the available additional criteria in each individual case we were able to deduct seismictrigger (earthquake shaking) for the SSDS in the Pakri Fm (Pldsaar and Ainsaar, in press) and complex interaction of two triggers, cyclic stormwave loading and stress applied by the recurrent tidal bores, in the Tiskre Formation case.
References
Allen, J.R.L. 1982. Sedimentary Structures, Vol. II.Developments in Sedimentology, Vol. 30B. Amsterdam, Elsevier. 663 pp.
Dronov, A. and Rozhnov, S. 2007. Climatic changes in the Baltoscandian basin during the Ordovician: sedimentological and paleontological aspects. Acta Palaeontologica Sinica, 46, 108113.
Nielsen, A.T. and Schovsbo, N.H. 2011. The Lower Cambrian of Scandinavia: depositional environment, sequence stratigraphy and palaeogeography. Earth Science Reviews, 107, 207310.
Orviku, K. 1960. O litostratigrafii volhovskogo i kundaskogo gorizontov v Estonii [Litostratography of the Volkhov and Kunda stages in Estonia]. Eesti NSV Teaduste Akadeemia Uurimused, 5, 4587 (in Russian).
Owen, G.,Moretti, M. and Alfaro, P. 2011. Recognising triggers for softsediment deformation: current understanding and future directions. Sedimentary Geology, 235, 133140.
Pirrus, E. 1978. The use of oriented structures for a reconstruction of Cambrian paleogeography in Estonia. Proceedings of the Estonian Academy of Sciences, Geology, 27, 3541 (in Russian).
Pldsaar, K. and Ainsaar, L. in press. Extensive softsediment deformation structures in the early Darriwilian (Middle Ordovician) shallow marine siliciclastic sediments formed on the Baltoscandian carbonate ramp, northwestern Estonia. Marine Geology.
The preHirnantian Late Ordovician shallow water brachiopod biogeography of Tarim, Qaidam, North and South China： A preliminary report
RONG Jiayu, ZHAN Renbin and HUANG Bing
State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, 39 East Beijing Road, Nanjing 210008, China
Faunal analysis of marine benthos like brachiopods is of great significance for the investigation of global paleobiogeography. The Ordovician biogeography of brachiopods was first studied by Williams (1972) and Jaanusson (1973), and later by others (e.g. Sheehan and Coorough, 1990). They recognized a variety of provinces basically based on the faunal information from North America and Europe, but rarely from Asia, particularly China and Kazakhstan where the preHirnantian Late Ordovician (Sandbian and Katian) brachiopods were poorly known. Recently, many investigations on the shallow water brachiopods of Kazakhstan and China have been documented by Nikitin and Popov (1996), Nikitin et al. (1996, 2003, 2006), Popov et al. (1997, 1999, 2000, 2002), and Popov and Cocks (2006, 2014) for Kazakhstan, and by Rong et al. (1994), Zhan and Rong (1995), Rong and Zhan (1996), Xu (1996), Zhan and Cocks (1998), Zhan and Jin (2005) and Zhan et al. (2008) for South and North China. These studies indicate that there is a close relationship between Kazakhstan and North and South China which possessed a variety of brachiopods with a high level of endemism and may have behaved as key cradles for the origin and early evolution of some major groups of brachiopods during the Late Ordovician. Although further systematic investigation is necessary when more and better material available, we present a preliminary report on the preHirnantian Late Ordovician shallow water brachiopod biogeography of various blocks of China on our preliminary revisions on the published collections, along with our own new material (Fig.1). It is noted that the deep water Foliomena fauna in China (Rong et al., 1999; Zhan and Jin, 2005) is excluded from our discussion.
Fig.1. Occurrences of selected genera and species of the PreHirnantian Late Ordovician shallow water brachiopod faunas from North and South China (with East Qinling), Qaidam, Tarim and Hainan Island, Kazakhstanian terranes (ChuIli, Chingiz, and others) and adjacent regions (such as Tien Shan), and Australia. Note that these genera are mostly endemic to the regions or have their first appearance in these regions and later on dispersed to elsewhere. S： Sandbian, K： Katian and H： Hirnantian.
1) East Qinling. Fairly diverse brachiopods are known from the Shiyanhe Formation (middleupper Katian) of Xichuan, western Henan (Zeng et al., 1993; Xu, 1996) which is considered as the northern margin of the South China paleoplate in Lower Paleozoic. It has a certain similarity to that of Kazakhstan, emphasized by the cooccurrence of Altaethyrella, Sowerbyella, Bokotorthis and Rongatrypa (Popov et al., 2014). The latter is very abundant in the argillaceous limestone.
2) Southern Hainan. The brachiopods from the possibly lower Katian of Yaxian were preserved in finegrained clastic rocks, including Sowerbyella, Altaethyrella, Qilianotryma?, Dulankarella and others (Xu and Su, 1977; this paper). It has a closer affinity to Katian brachiopods of Qaidam (Xu in Jin et al., 1979) and Kazakhstan (Popov et al., 2000; Nikitin et al., 2006).
3) North China. Brachiopods briefly described from the Jingxian and Beiguoshan formations (Sandbian and lowermiddle Katian; mainly carbonate buildup) in Liquan and Longxian, Shaanxi (Fu, 1982) have many common constituents with those of Kazakhstan, such as Altaethyrella of rhynchomnellides, Eospirigerina, Pectenospira and Schachriomonia of early atrypoids, Plectosyntrophia of camerelloids, Didymelasma and Schizostrophina of paralellasmatids, and common Parastrophina (Popov et al., 2002; this paper).
4) Qaidam. Shallow shelf, mediumdiverse assemblages of brachiopods from the middle Katian of Qilian, Qinghai and from SandbianKatian of Tianzhu and Yumen, Gansu contains Altaethyrella, Bokotorthis, Eospirigerina, Parastrophina, Pectenospira, Plectosyntrophia, Protozyga (similar to Kellerella), Qilianotryma, Sowerbyella, Sulcatospira and many others (Xu in Jin et al., 1979; Fu, 1982; this paper). It indicates a closer faunal relationship with those of the Kazakhstanian terranes and North China than elsewhere, partly due to the cooccurrence of Bokotorthis, Pectenospira, Plectosyntrophia, Qilianotryma and Sulcatospira.
5) Tarim. Brachiopods from the carbonate mud mound of the Lianglitag Formation (middle Katian), Bachu, western Tarim include Camerella, Didymelasma, Dinorthis, Grammoplecia, Parastrophina, Pectenospira, Placotriplesia, Plectosyntrophia and some new forms, showing a close affinity with those of Qaidam, North China and ChuIli, Kazakhstan. At Mengdaleke, north of Wushi, northwestern Tarim, a middle Katian brachiopod association was recently discovered including Altaethyrella, Christiania, Dolerorthis, Eospirigerina, Hesperorthis, Leptellina, and Schachriomonia. The predominance of Schachriomonia is particularly notable, indicating a close relationship with the other regions compared during the Katian.
It is true that there occur a number of endemic genera confined to the regions studied and of taxonomic differences among contemporaneous faunas since they possessed a geographical isolation of the faunas and different tectonosedimentary backgrounds. Meanwhile, there occur a great number of cosmopolitan genera that are not the focus of this paper. We will particularly concentrate on those mutual taxa known in those Chinese blocks and the Kazkahstanian terranes (see Table 1). Most of them are either entirely endemic to the regions or having their first appearance in these regions and later on spread across a wider geographical range.
Our preliminary investigation provides the following points confirming a close relationship of the Sandbian and Katian faunas between Kazakhstan, Tarim, Qaidam, North and South China. 1) There are many genera (e.g. Bokotorthis, Diambonioidea, Pectenospira, Plectosyntrophia, Qilianotryma, Rongatrypa, Schachriomonia, Schizostrophina and Sulcatospira) that are known only from various blocks of China and the Kazakhstanian terranes. Among them, the atrypides are predominant and camerelloids are common. 2) Dulankarella, Mabella, Metambonites and Synambonites of plectambonitoids, Altaethyrella of rhynchonellides, and Palaeotrimerella of trimerellides are recorded from the regions compared, SayanoAltai (only Altaethyrella) and Australia (all the rest). 3) The following species, Bokotorthis plicadua, Christiania egregia, Didymelasma transversa, Dinorthis kassini, Pectenospira tetraplicata, Schizostrophia margarita and Psilocamerella planisulcata are known only from ChuIli and\/or Chingiz, Tarim, Qaidam and\/or North China.
The strong endemism of the Late Ordovician brachiopods in centraleast Asia can further be approved by the following evidences. 1) The early trimerellides of South China show a strong endemism with some connections with those of Kazakhstan (such as Palaeotrimerella). The earliest known Trimerella occurs only from South China and not from other regions. 2) The early atrypides of North China, Qaidam, Tarim and Kazakhstan may have originated and diversified in shallow water regimes in Sandbian to earlymiddle Katian. The earliest known ribbed atrypide Pectenospira and Eospirigerina occurred in ChuIli and North China during Sandbian and then migrated to Qaidam and Tarim around middle Katian. The primitive atrypides known in Darriwilian and Sandbian of North America are substantially different from those in China and Kazakhstan (Popov et al., 1999; Copper, 2002). 3) The early athyridides in North China are represented by Aphaeathyris which possesses a spiralia with many whorls in the shallow water regimes in middle Katian (Fu, 1982). It might be true that earlier athyridides may have been collected in this region, if there is any. The earliest known athyridide is Kellerella from the Sandbian of Kazakhstan (Nikitin et al., 1996). Protozyga tianzuensis from the Sandbian of Qilian, Qaidam (Fu, 1982) is externally similar to Kelerella. Thus, Kazakhstan and possibly Qaidam may represent regions where this major group originated and first diversified. 4) The earliest known spiriferide is recorded from the upper Katian of South China (Rong et al., 1994, 1995, 2013; Zhan and Cocks, 1998; Zhan et al., 2012) and northeastern central Kazakhstan (Nikitin et al., 2006). Thus, China and Kazakhstan may have played a key role in the brachiopod origination and early evolution of some major groups, particularly the spirebearing brachiopods and trimerellides during the Late Ordovician. Significantly, these major groups disappeared or became extremely rare in Hirnantian (Rong and Harper, 1988; Rong et al., 2006), but survived the end Ordovician mass extinction and radiated in late Llandovery of Silurian (Harper and Rong, 1995; Rong and Harper, 1999).
The relationship of Late Ordovician brachiopod faunas between South China and Australia has been documented by Percival et al. (2011). Here we would like to add two points. 1) There occur a number of common genera between South China and Australia, such as Durranella, Mabella, Metambonites, Rongnambonites and Synambonites of plectambonitoids and Belubula (=Zhuzhaiia), Palaeotrimerella and Paradinobolus of trimerellides. However, the composition of mutual genera between these two blocks is significantly different and their number is fewer than that between Kazakhstan and South China. 2) There are no mutual taxa between parts of China (e.g. North China, Qaidam and Tarim) and Australia. It may suggest that the former three blocks may have probably situated closer to the Kazakhstan terranes than to Australia in Late Ordovician.
The faunal affinity may have been controlled by various factors, such as incompleteness of fossil record, collecting bias, and different sizes of collections. Meanwhile, again importantly, faunal differences may be explained by the position and distance of paleogeographical entities, mobile capability of brachiopod larvae, differentiations of environment conditions (e.g. carbonate mudmound and silicious clastic facies), tectonic backgrounds and sedimentary facies where the brachiopods living and being preserved. Many of the continental blocks, terranes, microplates and island arcs in centraleast Asia, in particular South China, Tarim and possibly Qaidam, moved northwards to the then low latitudes straddling equatorial zones in Late Ordovician. Benthic faunas adapted well in shallow water regimes experienced high rates of turnovers with a high degree of provincialism. They could have been exchanged by oceanic currents along the equator in both westward and eastward directions. A relatively long distance and thus a high isolation, together with a different ability of larvae swimming of different brachiopod taxa, may have been substantial for dispersion and faunal exchanges.
The preHirnantian Late Ordovician brachiopods of North China, South China (with East Qinling), Tarim, Qaidam, and possibly Hainan Island had much higher faunal similarity first with the Kazakhstanian terranes and then South China with Australia, than with those of Laurentia, Siberia and its associated island arcs (such as Greater and Lesser Khingan, Northeast China and SayanyAltai), Avalonia, Baltica, southern European terranes and others. The former regions which may correspond to the east part of the LowLatitude Province of Harper et al. (2013) might represent a substantial biogeographical entity separated and differentiated from the others during the preHirnantian Late Ordovician. Such inference is generally in accordance with Candela (2006), Nikitin et al. (2006), Percival et al. (2011), Cocks and Torsvik (2013), and Popov et al. (2014) for the brachiopods, Zhou and Zhen (2008) for the trilobites, and Lin et al. (1988) for the corals Agetolites Fauna.
Paleogeographic positions of various blocks of China are controversial because they are not well constrained both longitudinally and latitudinally during the Early Paleozoic (e.g. Scotese and McKerrow, 1990; Li and Powell, 2001; Fortey and Cocks, 2002; Isozaki et al., 2011; Wilhem et al., 2012; Boucot et al., 2013; Cocks and Torsvik, 2013; Metcalfe, 2013). Our work demonstrates that there were Australia, South and North China, Qaidam, Tarim and Kazakhstanian terranes with their adjacent microplates and island arcs distributed from east to west along the equatorial zone during the Late Ordovician. Australia was situated on eastern margin of the Gondwana landmass; South China may have been closest to Australia; the Kazakh terranes were in the westernmost, while Tarim, Qaidam and North China in between, i.e. west of South China and east of Kazakhstan.