Marine carbonate facies in response to climate and nutrient level: The upper carboniferous and permian of central spitsbergen (Svalbard)

Summary Carbonate-dominated successions of the Gipsdalen and Tempelfjorden Groups from Svalbard record a significant shift from Photozoan to Heterozoan particle associations in neritic settings during the late Palaeozoic. During the Bashkirian, benthic particle associations which included photoautotrophs such as phylloid algae (Chloroforam Association) characterised shallow subtidal environments. Most depositional settings which endured siliciclastic terrestrial input exhibited poorly diversified associations dominated by brachiopods, bryozoans and siliceous sponges (Bryonoderm Association). During the Moscovian to Asselian, highly diversified associations typified by various calcareous green algae,Palaeoaplysina, Tubiphytes, fusulinids, smaller and encrusting foraminifers (Chloroforam Association) prevailed in carbonate sediments from supratidal to shallow subtidal environments. During the Sakmarian and Early Artinskian, oolitic carbonate sands (Chloroforam Association) typified intertidal flats, whereas shallow subtidal environments were occupied by moderately diversified associations with fusulinids, smaller foraminifers, echinoderms and bryozoans (Bryonoderm-extended Association) and poorly diversified associations with echinoderms, brachiopods and bryozoans (Bryonoderm Association). During the Late Artinskian to Kazanian, poorly diversified associations characterised by brachiopods, echinoderms and bryozoans (Bryonoderm Association), and sponge-dominated associations (Hyalosponge Association) reigned within siliceous carbonates of intertidal and shallow subtidal environments. This trend is interpreted as a result of climatic cooling and fluctuations of prevailing levels of trophic resources within shallow-water settings during the studied time period. While raised nutrient levels were restricted to near-shore settings during the Bashkirian, steady mesotrophic conditions arose from the Sakmarian onward and increased to late Permian times.     

Marine faunal assemblages in the Silurian-Devonian Keyser Limestone of the central Appalachians

Sedimentological analysis of the Keyser Limestone (Upper Silurian - Lower Devonian of the central Appalachians) indicates that its sediments were deposited in a range of marginal and shallow marine environments. Major depositional environments include: tidal flat, lagoon, barrier bar and island, and open marine shelf. Each major environment is represented by a lithofacies which is lithologically and faunally distinct. Tidal flat lithofacies are characterized by eurytopic organisms, including ostracodes, gastropods, stromatoporoids and blue-green algae. Lagoon lithofacies are dominated by bryozoans, brachiopods, ostracodes and stromatoporoids. Barrier lithofacies are characterized by rooted crinoids, encrusting bryozoans and robust brachiopods. Open shelf lithofacies contain a diverse fauna of cystoids, crinoids, bryozoans and brachiopods.
The distributions of faunal assemblages in the Keyser show no simple relationship to either water depth or distance from shore. They are, in general, related to the distributions of depositional environments.
Recurring associations of brachiopod genera were not found in the Keyser. With few exceptions, any genus may be found in any subtidal environment. Abundance of brachiopods is related to the abundance of local hard substrates (usually bryozoans).     

Depositional facies and cyclic patterns in a subtidal-dominated ramp during the Early-Middle Ordovician in the western Tarim Basin (NW China)

Due to a long-term transgression since the Early Cambrian, an extensive shallow-water carbonate platform was developed in the entire Tarim Basin (NW China). During the deposition of the Yingshan Formation (Early-Middle Ordovician), a carbonate ramp system was formed in the intrashelf basin in the Bachu-Keping area of the western basin. Four well-exposed outcrop sections were selected to investigate their depositional facies, cycles, and sequences, as well as the depositional evolution. Detailed facies analyses permit the recognition of three depositional facies associations, including peritidal, semi-restricted subtidal, and open-marine subtidal facies, and eleven types of lithofacies. These are vertically arranged into meter-scale, shallowing-upward peritidal, semi-restricted subtidal, and open-marine subtidal cycles, in the span of Milankovitch frequency bands, suggesting a dominant control of Earth’s orbital forcing on the cyclic sedimentation on the platform. On the basis of vertical facies (or lithofacies) and cycle stacking patterns, as well as accommodation changes illustrated graphically by Fischer plots at all studied sections, six third-order depositional sequences are recognized and consist of lower transgressive and upper regressive parts. In shallow depositional settings, the transgressive packages are dominated by thicker-than-average, shallow subtidal cycles, whereas the regressive parts are mainly represented by thinner-than-average, relatively shallow subtidal to peritidal cycles. In relatively deep environments, however, the transgressive and regressive successions display the opposite trends of cycle stacking patterns, i.e., thinner-than-average subtidal cycles of transgressive packages. Sequence boundaries are mainly characterized by laterally traceable, transitional zones without apparent subaerial exposure features. Good correlation of the long-term changes in accommodation space inferred from vertical facies and cycle stacking patterns with sea-level fluctuations elsewhere around the world suggests an overriding eustatic control on cycle origination, platform building-up and evolution during the Early-Middle Ordovician, although with localized influences of syndepositional faulting and depositional settings.     

Early Ordovician bathyurid province lithofacies, biofacies, and correlations -their relationship to a proto-Atlantic Ocean

The Early Ordovician bathyurid faunal province includes North America, Greenland, Spitsbergen, Scotland, and western Ireland and Norway. Dominant provincial lithofacies and biofacies include a Dolomite Suite with molluscan-stromatolite fossil content rimmed by Limestone Belts with dominantly trilobite-brachiopod faunas on a platform. Shale Belt rocks bearing graptolites, deposited on the platform slopes, rim the Limestone Belts. Volcanic rock-rich terrain partly borders the Shale Belts. Correlation between the lithofacies indicates that change from an expansion to contraction phase of a proto-Atlantic coincided with uplift of the carbonate platform and with tectonic activity in the Atlantic volcanic rock rich terrain. Brachiopods replaced trilobites as dominant faunal elements in more shallow platform waters at the same time. High trilobite diversity remained in deeper waters near platform margins. The changes took place in Earliest Mohawk-ian (Latest Arenig-Earliest Llanvirn).     

Episodic development of Cambrian eocrinoid-sponge meadows in the Iberian Chains (NE Spain)

Summary The Lower-Middle Cambrian transition in the Iberian Chains (NE Spain) records a transgressive deposition from peritidal to open-shelf environments. This overall trangressive trend took place across an interval of syndepositional tectonic processes. which have been illustrated during late Bilbilian to Leonian times. The scarcity of building organisms in this areas seems to be directly related to a rhythmic influence of fine terrigenous decantation, which inhibited and interrupted the carbonate production. Only in the more proximal and quiet environments, the episodic establishment of stromatolitic boundstones is evidence. Eocrinoid-sponge meadows were developed in shallow subtidal environments, and were completed by the presence of trilobites, inarticulate brachiopods, hyoliths and Chancelloriid sclerites. The biggest accumulation rates associated to these complex meadow communities seem to be reflected by differential synsedimentary faulting processes.     

Foliomena Fauna (Brachiopoda) from the Upper Ordovician of Sardinia

The late Ordovician brachiopod assemblage from Sardinia is one of the youngest members of the deep-water Foliomena fauna and is characterized by the following core taxa: Christiania , Cyclospira , Dedzetina and Foliomena . The fauna also contains Epitomyonia , Leangella , Glyptorthis and Skenidioides , which are more typical of shallower-water environments during the late Ordovician but occupied deeper-water niches during the Silurian following the termination of the Foliomena fauna. The suprafamilial placement of the family Chrustenoporidae is discussed and the new species Dedzetina serpaglii and Leangella ( Leangella ) fecunda are established. In common with many mid-Ashgill Foliomena faunas the Sardinian assemblage shows significant differences from other faunal developments of this type, reflecting its geographical position and shallower water conditions than those of the classic early Ashgill Foliomena faunas. The brachiopods occur with abundant trilobites belonging to a variant of the cyclopygid fauna. The faunas developed on part of a complex of microcontinents derived from peri-Gondwana during the Ordovician.     

内蒙古达茂旗巴特敖包地区包尔汉图剖面牙形刺生物地层

内蒙古达茂旗(达尔罕茂明安联合旗)巴特敖包地区志留纪、泥盆纪碳酸岩相地层发育,本区珊瑚、腕足类、层孔虫等底栖大化石的研究工作已有一定基础。但志留纪、泥盆纪地层在时代确定和对比上还存在很多问题,必须用主导化石门类牙形刺加以解决。研究表明：包尔汉图剖面的顶部属泥盆系无疑,应归入阿鲁共组,而不是西别河组;巴特敖包地区的海侵,始于罗德洛统卢德福德阶(Ludfordian)早期。本剖面没有发现文洛克世和罗德洛世早期的海相沉积。本文描写了一个志留纪牙形刺新种：Ozarkodina uncrispa sp．nov．。     

Biostratinomy and palaeoecology of the cassian formation (Triassic) of the Southern Alps

The sediments forming the Cassian Formation (Middle—Upper Triassic) of the Central Dolomites represent the following environments: back-reef areas, shallow marginal basins, slope, and central basin. In each of these major environments faunal assemblages were found whose composition, mode of preservation and occurrence proved to be characteristics. In the back-reef areas, algal/foraminifera- and calcareous sponge/coral-patch reefs with a highly diverse fauna of frame-builders and reef-dwellers, in some localities excellently preserved, form the most conspicuous feature. In the shallow marginal basins autochthonous algal meadow/soft-bottom associations dominated by gastropods and deposit-feeding bivalves prevail. Slope deposits do not contain any autochthonous associations but either remains of pelagic faunas or transported faunal elements of shallow-water origin in the form of Cipit boulders (subaerially cemented parts from the outer edge of the carbonate platforms), worn Pachycardia rugosa-dominated, or echinoderm debris-dominated assemblages. Sediments of the central basin lack benthic faunas but contains pelagic assemblages of low diversity dominated by Daonella, Posidonia, and some ammonites.     

Oldest known Dicoelosia and Epitomyonia,deep water brachiopods from the Beiguoshan Formation (Middle Katian,Upper Ordovician), Shaanxi,north China

Abstract: A diverse brachiopod fauna from a relatively deep water carbonate facies of the Upper Ordovician Beiguoshan Formation (uppermost Caradoc – lower Ashgill, middle Katian) is characterized by small shells and contains the oldest known Dicoelosia and Epitomyonia, two diagnostic taxa of deep water brachiopod palaeocommunities during the Late Ordovician and Silurian. Three new species are recognized: Dicoelosia cordiformis sp. nov., Dicoelosia perbrevis sp. nov. and Epitomyonia fui sp. nov. These pioneer forms of the family Dicoelosiidae show a relatively high degree of morphological plasticity. The shells of Dicoelosia from the Beiguoshan Formation range from the typical slender‐lobed form with a concavoconvex profile to the strongly equibiconvex, fat‐lobed morphotype that was not known previously until the late Silurian. The Beiguoshan dicoelosiids point to an important attribute of the deep water brachiopods: small generalists with high morphological plasticity, which make them ideal candidates as progenitors for the evolution of shallow water brachiopod faunas in shelf and platform depositional environments.     

Late Cambrian hard substrate communities from Montana/Wyoming: the oldest known hardground encrusters

Hardground surfaces from the Late Cambrian Snowy Range Formation in Montana/Wyoming are the oldest known non-reefal hard substrates exhibiting encrusting fossils. These surfaces range in age from Early Franconian to early Trempealeauan. Hardgrounds were developed on slightly hummocky to planar, truncated surfaces of glauconite-rich, carbonate, flat pebble conglomerates, which were deposited during episodes of storm scouring in shallow subtidal environments of the Montana/Wyoming shelf. Snowy Range hardgrounds are encrusted by a low diversity assemblage of fossils dominated by simple discoidal holdfasts of pelmatozoans, probably crinoids, and including small conical spongiomorph algae? and probable stromatolites. Macroborings (e.g. Trypanites) are notably absent from all hardground surfaces, although sharp-walled, vertical, cylindrical holes (borings?) occur in micrite clasts imbedded in certain flat pebble conglomerates. No evidence of faunal succession or microecologic partitioning of irregular surfaces was observed on these Cambrian hardgrounds.     

Influence of the Late Ordovician glaciation on basin configuration of the Yangtze Platform in China

The Late Ordovician paleogeographic changes in the Yangtze Platform indicate a widespread regression and consequent subaerial exposure probably caused by the 'locking up' of substantial amounts of marine waters during the Late Ordovician glaciation. The subsequent rapid paleogeographic changes on the Yangtze Platform during the earliest Silurian suggest a rapid melting of the ice. The relatively cool waters in the partially closed Yangtze basin during the latest Ordovician were replaced by open and warm waters during the earliest Silurian. Sedimentation rates and composition of faunal assemblages underwent marked changes during latest Ordovician and Early Silurian. Glaciation, Ordovician, Silurian, Paleogeography, sedimentary rate, faunal change.     

How far did feedback between biodiversity and early diagenesis affect the nature of Early Palaeozoic sea floors?

Latest Precambrian to Early Palaeozoic biosphere evolution triggered changes in early diagenesis and carbonate precipitation which fed back to biodiversity through colonization of hard substrates. Progressive increase in the depth and intensity of bioturbation and bio‐irrigation lowered the zone of early carbonate cementation in the uppermost sediment column. This firstly led to a decline in the abundance of the flat‐pebble conglomerates which had been a common feature of Cambrian and Early Ordovician successions, replaced by the peak and subsequent decline in the Palaeozoic abundance of submarine hardgrounds. The availability of very widespread lithified sea floors in shallow subtidal settings during the Ordovician promoted a rapid expansion in sclerobiont diversity and contributed to the Great Ordovician Biodiversification Event.     

The relation of Late Ordovician glaciation to the Ordovician-Silurian changeover in North American brachiopod faunas

Sheehan, P. M.: The relation of Late Ordovician glaciation to the Ordovician-Silurian changeover in North American brachiopod faunas.
The Ordovician-Silurian changeover of brachiopod faunas in North American epicontinental seas involved the abrupt extinction of endemic Late Ordovician stocks and subsequent repopulation of North American seas by Old World taxa. The Late Ordovician Gondwanaland glaciation may have lowered sea levels sufficiently to place severe stress on the widespread shallow marine faunas in North America, resulting in their eventual extinction. The Late Ordovician depositional history in North America is not well enough known to establish the presence of a latest Ordovician regression, but the earliest Silurian was an interval of off-lap in North America. Therefore, the glacial lowering of sea level is considered to be the most likely cause of the faunal changeover.     

Spatio‐temporal transitions in Paleozoic Bivalvia: A field comparison of upper Ordovician and upper Paleozoic bivalve‐dominated fossil assemblages

Because of the uncertain relationship between relative abundance and taxonomic richness, abundance data are potentially critical components in any analysis of faunal dominance within fossil assemblages. However, such data are often not available in the literature. In this paper, relative abundance data collected during field work at 25 Upper Ordovician and 22 Upper Pennsylvanian to mid‐Permian localities are used to evaluate Paleozoic transitions in the environmental distributions of bivalve molluscs. On the basis of multivariate analyses of these data, it is shown that even early in their history, during the Ordovician, bivalves were generally not restricted in abundance to just marginal environments. They apparently thrived in terrigenous—dominated regions, both nearshore and offshore, but were less abundant in carbonate settings. However, by the late Paleozoic, bivalve abundances had increased in some carbonate environments, in part because of the growing abundances of free‐burrowing suspension‐feeders, which had been substantially less abundant even in terrigenous environments earlier in the Paleozoic. The results of this study corroborate those of a companion analysis, using literature‐derived data, of paleoenvironmental diversity transitions exhibited by Paleozoic Bivalvia.     

Euryhalinity of Palaeozoic articulate brachiopods

OMonotypic and very low diversity virgianid shell beds from the Upper Ordovician to Lower Silurian dolomites of North Greenland were formed in marginal marine quiet-water hypersaline environments. In the light of this evidence the salinity tolerances of other Palaeozoic articulate brachiopods is evaluated. There are only a small number of species apparently invading hypersaline or brackish environments, but it is significant considering that previously all articulate brachiopods were thought to be fully marine. Two types of occurrence are noted, those species specifically related to marginally marine environments, disappearing with the introduction of fully marine faunas, and the majority of species which extend their normal marine range into marginal conditions. No brachiopod species appears to have invaded very hypersaline or truly brackish conditions. No single group of articulate brachiopods specifically specialised in colonising marginal marine environments, apart from possibly the virgianid pentamerids. Palaeozoic, Upper Ordovician, Lower Silurian, Brachiopoda. Pentamerida, Virgianidae, Greenland, palaeoecology. hypersaline environments, brackish environments .     

Reef reconstruction after extinction events of the latest ordovician in the Yangtze platform,South China

Summary Early Silurian reef reconstruction on the Yangtze Platform, in the northern part of the South China Block, is preceded by a combination of regional and global processes. During most of Ashgill time (Late Ordovician), the area was dominated by Wufeng Formation deep water graptolitic black shales. Reefs largely disappeard in the middle of the Ashgill Stage, from the northwestern margin of Cathaysian Land (southeastern South China Block), in advance of the Late Ordovician glaciation and mass extinction, due to regional sea-level changes and regional uplift, unrelated to the mass extinction itselt. Late Ordovician microbial mudmound occurrence is also found in the western margin of the Yangtze Platform, its age corresponding to theDicellograptus complexus graptolite biozone of pre-extinction time. On the Yangtze Platform, a thin, non-reef-bearing carbonate, the Kuanyinchiao Formation (=Nancheng Formation in some sites), thickness generally no more than 1m, occurs near several landmasses as a result of Hirnantian regression. Reappearance of the earliest Silurian carbonates consisting of rare skeletal lenses in the upper part of Lungmachi Formation, are correlated to theacensus graptolite biozone, early Rhuddanian of Shiqian, northeastern Guizhou, near Qianzhong Land. Carbonate sediments gradually developed into beds rich in brachiopods and crinoids in the lower part of Xiangshuyuan Formation, middle Rhuddanian. In the middle part of Xiangshuyan Formation, biostromes, containing abundant and high diversity benthic faunas such as corals, crinoids and brachiopods, show beginnings of reconstruction of reef facies. Substantial reef recovery occurred in the upper part of Xiangshuyuan Formation, lower Aeronian, as small patch reefs and biostromes. During the late Aeronian, carbonate sediments, especially reefs and reef-related facies, expanded on the upper Yangtze Platform, and radiation of reefs occurred in Ningqiang Formation, upper Telychian. The long period of reef recovery, taking several million years, remains difficult to explain, because redistribution of any refugia faunas would be expected to take place soon after the extinction. Reefs and reef-related facies subsequently declined after Telychian time due to regional uplift of the major portion of the Yangtze Platform. Carbonate facies are therefore uncommon in South China during the rest of Silurian time.     

Ostracodes from the Early Cenomanian of Jordan.A preliminary report

Ostracode faunas have been identified for the firsttime in Early marine Cenomanian sediments of the Ajlun Group (Jordan) outcropping East of the Jordan Rift Valley. The faunal assemblages contain 14 genera and 17 species. Sediments indicate the internal part of a carbonate platform. The Ostracodes are closely related to those of neighbouring regions; accordingly, in the Tethyan context, Jordan belongs to the North Africa — Middle East bioprovince.     

DISTRIBUTION AND DIVERSITY OF PENNSYLVANIAN MARINE FAUNAS RELATIVE TO WATER DEPTH AND DISTANCE FROM SHORE

Variability of marine faunas in Middle Pennsylvanian rocks in central Colorado, as generally of modern marine faunas, increases with increasing depth and distance from shore in shallow water. Less than 3 genera of brachiopods lived nearshore, whereas 10 were present in water computed to have been 22 meters deep, about 5 kilometers offshore. Foraminifers increase from 1 or 2 irregularly formed types nearshore, to 6–8 types in offshore areas, and foraminiferal density increases sharply 3^l/2 kilometers offshore at a depth of about 15 meters. Several genera of brachiopods, 3 types of foraminifers, and phylloid algae show a distribution closely related to depth of water and distance from shore. On the basis of significant changes in genera of brachiopods, types of foraminifers, general faunal diversity, and foraminiferal density, three distinct biotopes can be recognized. These biotopes were occupied by the euphemitid, dictyoclostid- Composita , and fusulinid fossil communities.     

Phanerozoic changes in the high-rank suprageneric diversity structure of brachiopods: Linear and non-linear effects

Phanerozoic evolution of brachiopods produced many linear (established by a comparison of successive geologic time units) and non-linear (established by a comparison of non-successive geologic time units) effects, which can be examined quantitatively by using the similarity coefficients (Czekanowski's Quantified Coefficient and Gower Index) and correlation tools. The high-rank suprageneric diversity structure accounts for a number of superfamilies in each of 26 orders for every epoch of geological time. The intensity of turnovers in this structure was generally low during the entire Phanerozoic. It was slightly stronger during the Early Paleozoic, but close to zero during the Cenozoic, when the high-rank suprageneric diversity structure of brachiopods stabilized finally. Significant turnovers took place at the Middle Cambrian–Early Ordovician, the Late Ordovician–Early Silurian, the Late Silurian–Early Devonian, the Middle Devonian–Mississippian, and the Permian–Triassic transitions. Influences of mass extinctions, both major like those End Ordovician or Permian/Triassic and minor like Early Jurassic or Jurassic/Cretaceous, on the high-rank suprageneric diversity structure of brachiopods is registered. The strongest was the consequences of the Permian/Triassic catastrophe, which perhaps even reset the brachiopod evolution. No evident direct relationships are established between intensity of turnovers and eustatic fluctuations. However, the changes in the diversity structure recorded with the Gower Index provide evidence that eustatic lowstands were more favorable for intensification in these changes.     

The life habits of the Ordovician illaenine trilobite Bumastoides

The Ordovician illaenine Bumastoides exhibits a distinctive effaced and strongly convex morphology. Orientation of the visual field, the extreme convexity of the cephalon and the nature of the thoracic articulation support an interpretation of Bumastoides as an infaunal trilobite that was poorly suited to epifaunal crawling. The genus may have been sedentary; spending most of its post-larval life cycle within a burrow. Suspension feeding would be a viable existence for a sedentary trilobite such as Bumastoides. Maintenance of a burrow is essential for respiration and would require a firm, cohesive substrate. The infaunal niche had become occupied by trilobites by at least the Late Cambrian and continued to be exploited through the Ordovician, Silurian and. possibly, into the Devonian. Convergence has led to the appearance of the effaced, strongly convex morphotype in a number of unrelated families, including the Illaenidae, Asaphidac, Aulacopleuridae, Plethopeltidae and Scutelluidae. A high numerical abundance of illaenid trilobites, such as Illaenus and Bumastoides , is characteristic of the illaenid–chcirurid association, which persisted from the early Ordovician until at least the Late Silurian. This association has been recorded from shelf-edge and on-shelf carbonate buildups and shallow subtidal level bottom environments. It appears to be confined to firm substrates.