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1.
《Gondwana Research》2014,25(3):983-990
The bivalved bradoriid arthropod Kunmingella douvillei (Mansuy, 1912) is the most common species in the Lower Cambrian Chengjiang Lagerstätte. Its soft anatomy has been reported based on well-preserved specimens. However, as with other Cambrian arthropods, its reproductive behavior is poorly documented. Rare specimens of K. douvillei preserved with eggs have been reported. Our new collections confirm that the eggs were directly attached to the last three pairs of biramous appendages and verify the head–trunk boundary suggested by previous work. The brooding behavior of K. douvillei was most probably related to its small body size, as in living crustaceans. The K. douvillei female could carry 50–80 eggs ranging from 150–180 μm in diameter, possibly indicating a K-reproductive strategy; its ontogenetic and reproductive mode might have been an adaptation in response to increasing predatory pressure across the Ediacaran–Cambrian boundary. All of the three main directions of development in the life history of living marine invertebrates, namely planktotrophic larvae, lecithotrophic larvae, and brood care, most likely evolved by Stage 3 of the Cambrian.  相似文献   

2.
A wide variety of scalidophoran worms have been found in the Cambrian Fortunian in recent years, suggesting that scalidophorans diversified during this age. Here, we report new scalidophoran material obtained from the 2nd member of the Kuanchuanpu Formation(Fortunian Stage) in Zhangjiagou Lagerst?tte, Xixiang County, Shaanxi Province, South China. Three indeterminate forms of scalidophoran worms are described in detail. The morphology of these worms differs from that of any coeval worms and may ...  相似文献   

3.
The Cambrian explosion, c. 530–515 Ma heralded the arrival of a diverse assembly of multicellular life including the first hard-shelled organisms. Fossils found in Cambrian strata represent the ancestors of most modern animal phyla. In contrast to the apparent explosiveness seen in the Cambrian fossil record, studies of molecular biology hint that the diversification observed in Cambrian strata was rooted in ancestry extending back into the Ediacaran (635–542 Ma). Fossil evidence for this mostly cryptic phase of evolution is derived from the soft-bodied fossils of the Ediacaran biota found throughout the world and bilaterian embryos found in the Doushantuo lagerstätte in South China. The first appearance of Ediacara fauna is thought to have followed the last of the ~ 750–635 Ma Neoproterozoic glacial episodes by 20–30 million years. In this paper, we present evidence for the oldest discovery of the ‘Ediacara’ discoidal fossils Nimbia occlusa and Aspidella terranovica (?) that predate the early Cryogenian glaciations by more than fifty million years. There is considerable disagreement over the significance of discoidal Ediacaran fossils, but our findings may support earlier suggestions that metazoan life has roots extending deeper into the Proterozoic Eon. We also confirm the presence of a Late Cryogenian (e.g. “Marinoan”) glaciation on the Lesser Karatau microcontinent including dropstones and striated clasts within the glacial strata.  相似文献   

4.
《China Geology》2020,3(4):558-566
It has been an intense debate on the exact boundary between Ediacaran and Cambrian in the southwest Yangtze Block. The calibration of this critical boundary has a remarkable influence on the further investigation of the break-up of the Rodinia Supercontinent, the early life evolution, and the mechanism of the phosphorite deposit. Ediacaran and Cambrian strata and fossils are widely distributed in Anning, Yunnan Province in China. In recent years, the Xiaowaitoushan Member from the Lower Yuhucun Formation has been studied. Through this interval with continuous collections, the first appearance datums (FADs) of the protoconodont (Fomitchella cf. inchoate Yang et He, Protohertzina cf. anabarica Missarzhevsky) and globular embryos fossil (Olivooides sp.) earlier than these in the Lower Cambrian strata of the Meishucun Formation were discovered. This discovery indicates that the Xiaowaitoushan Member has included more FADs than the previously discovered single FAD of Anabarites primitivus Qian et Jiang, and the Ediacaran–Cambrian boundary in southwest China should be replaced below the Point “A” of the Meishucun Formation in Yunnan Province. The Point “B” of the Meishucun Formation is younger than the suggested age 541 Ma of the Ediacaran–Cambrian boundary and can no longer reference the Global Boundary Stratotype Section and Point (GSSP) correlation in southwest China. It can be suggested based on the previous stratigraphy and palaeontology studies from northern Sichuan and southern Shaanxi and the FAD of the globular embryos fossils that the Ediacaran−Cambrian boundary in the southwest Yangtze Block should be placed at the base of the Xiaowaitoushan Member; other phosphorite strata refer to Xiaowaitoushan Member. The discovery of the FADs of the shelly fossils in the Xiaowaitoushan Member provides new evidence for the global correlation of the Ediacaran –Cambrian boundary in the southwest Yangtze Block. The conodont discoloration index (CAI) of the specimens in Anning is between 2 and 3, which indicates that the organic matter in Xiaowaitoushan Member is matured and has high potential to form a shale gas reservoir.  相似文献   

5.
Ribbed mussels (Geukensia demissa) help form the basis of highly productive salt marshes along the Atlantic coast of North America, in southern New England, and further south. Little is known about their ecology and reproductive biology at more northern latitudes (Maritime Canada; >43o N). As a step in determining the sustainability of ribbed mussel populations near the northern limit of their range (Northumberland Strait, Gulf of St. Lawrence, Canada), gametogenesis and spawning were monitored over 3 years (May–August 2012, June–November 2014, and April–October 2015) at four sites spanning ~100 km of coastline. These sites are typically ice-covered from mid-December to March or April. The onset of gametogenesis was later, the reproductive stages on any given date were more varied, and the reproductive season was shorter than for southern populations of ribbed mussels. Oocyte density and size did not vary among sites, indicating similar site-level processes, but did vary among years. Oocyte density and size varied greatly among mussels at a given site, and within a single gonad. This highlights the importance of individual variability, perhaps related to mussel location within a marsh, and the effects of nutrients and temperature on gonads. Accounting for the individual-level variability, reproductive output was estimated at ~105 oocytes per ripe female mussel, which is within the fecundity estimates for other marine bivalve broadcast spawners.  相似文献   

6.
The circum-Gondwana subduction initiated by the early Cambrian has been suggested to reflect the establishment of the modern plate tectonics. The metamorphic rocks with low thermobaric (T/P) ratios indicative of cold subduction in the present tectonic regime have not been well investigated. To better understand the circum-Gondwana subduction and to test its possible link with the emergence of the modern plate tectonics, this study focused on blueschist-facies metamorphic rocks in the Altyn Tagh of the southeastern Tarim craton. Mineral assemblage and chemistry, phase equilibrium modelling, and quartz-in-garnet Raman elastic geobarometry reveal that the zoisite blueschist and glaucophane (Gln)-bearing quartz schist in northern Altyn Tagh were metamorphosed to lawsonite to epidote blueschist-facies at 520–545 °C and 16–19 kbar. It reflects high-pressure (HP)/low temperature (LT) metamorphism with low T/P ratios of <300 °C/GPa and thermal gradients of <10 °C/km. These blueschist-facies metamorphic rocks underwent rapid decompression starting at P-T conditions of <495 °C and <9.6 kbar during exhumation. Ar-Ar geochronology records paragonite Ar-Ar plateau ages of 520–506 Ma for the zoisite blueschist samples and phengite Ar-Ar plateau ages of 522–516 Ma for the Gln-bearing quartz schist samples, suggesting that the peak HP/LT metamorphism occurred prior to ca. 522 Ma. Based on new results and available data from the major Gondwana blocks, cold subduction was suggested to profoundly operate along circum-Gondwana in the early Cambrian after the amalgamation of Gondwana. The extensive circum-Gondwana subduction represents the earliest global cold subduction in Earth’s history associated with the establishment of the modern plate tectonics, as directly recorded by the studied early Cambrian blueschist-facies metamorphic rocks and a dramatic drop in the mean T/P of metamorphism since the early Paleozoic.  相似文献   

7.
The Middle Cambrian succession of the Parahio Valley in general and Debsakhad section in particular is dominated by trilobites. Genus Opsidiscus, along with other trilobite forms dominates the lower Middle Cambrian succession. In the present study two new species of Opsidiscus, Opsidiscus wadiai and Opsidiscus srikantiai are reported from the lower Middle Cambrian succession of Debsakhad section. The species were differentiated on their morphological features and their multivariate analysis. The multivariate analysis applied here is used as a supplement method to qualitative analysis in order to differentiate between the cranidial characters of Opsidiscus. The qualitative study of each species studied individually shows more or less close affiliation as is observed by different quantitative methods. The presence of Opsidiscus has a great stratigraphic significance in this region, as they first appear from informal Stage 5 of Series 3 and goes up to the Drumian Stage of Series 3 of the Cambrian System in the Debsakhad section, which helps to correlate this section with other well known sections of the Middle Cambrian.  相似文献   

8.
The biostratigraphy of the Cambrian of Kashmir based on trilobite assemblage zones and trace fossils has been attempted. Faunal gaps occur in lower part of Lower Cambrian, upper Lower Cambrian, lower Middle Cambrian and upper part of Upper Cambrian. In the Lower Cambrian Cruziana—Rusophycus and Redlichia Zones, in the Middle Cambrian Solenopleura—Tonkinella, Tonkinella—Anomocare, Anomocare—Bailiella and Bolaspidella Zones, and in the Upper Cambrian Chuangia and Dikelocephalites Zones are recognized. The position of intrasystem boundaries is also discussed. While the various taxa have lithological preferences and are not necessarily found in a continuous sequence, an attempt has been made to interpret the ranges of different genera. The affinities of the fauna with that of other Cambrian basins of the world are discussed. It is concluded that the bulk of the fauna is of a cosmopolitan nature.  相似文献   

9.
《Gondwana Research》2014,25(3):999-1007
Abundant data have been acquired on the lower Cambrian small shelly fossils (SSFs) of the Yangtze platform during the last three decades, demonstrating that these fossils are an important piece of evidence for the Cambrian radiation and are useful biostratigraphic tools for correlating the lower Cambrian. Here we report SSF associations from the Yanjiahe Formation in the Three Gorges area, South China. The Yanjiahe Formation is well exposed near the Yanjiahe village, and its 40-m-thick sequence can be subdivided on the basis of lithology into five stratigraphic intervals (beds). Small shelly fossils occur mainly in Beds 2 and 5, but abundant SSFs were discovered in thin sections of siliceous–phosphatic nodules from Bed 3 for the first time. No skeletal fossils were discovered in the basal siliceous rock interval (Bed 1), but the negative δ13Ccarb excursion and the occurrence of the acritarch Micrhystridium regulare indicate that it belongs to the basal Cambrian. The SSF associations are somewhat similar to those of East Yunnan, and can be differentiated into three biozones (in ascending order): the Anabarites trisulcatus–Protohertzina anabarica assemblage zone (Bed 2), the Purella antiqua assemblage zone (Bed 3), and the Aldanella yanjiaheensis assemblage zone (Bed 5). The occurrence of A. yanjiaheensis in Bed 5 probably indicates that Bed 5 belongs to Cambrian Stage 2, but the Stage 2/Stage 1 boundary is uncertain since Bed 4 lacks fossils. SSF biostratigraphy indicates that the Yanjiahe Formation is pretrilobitic Meishucunian in age (equivalent to the Nemakit–Daldynian to Tommotian of Siberia, Terreneuvian). Five SSF genera occur in Bed 2, more than six genera in Bed 3, and twenty-three genera in Bed 5. The stepwise increase in generic diversity through the Yanjiahe Formation is comparable with the global diversity increase through the Nemakit–Daldynian to early Tommotian interval.  相似文献   

10.
Definition of early Cambrian chronostratigraphic boundaries is problematic with many subdivisions still awaiting ratification. Integrated multi-proxy data from well-resolved regional-scale schemes are ultimately the key to resolving broader issues of global correlation within the Cambrian. In Australia, early Cambrian biostratigraphy has been based predominantly on trilobites. Phosphatic shelly fauna have great potential as biostratigraphic tools, especially in pre-trilobitic strata because they are widespread and readily preserved, but they have remained underutilised. Here we demonstrate their value in a new biostratigraphic scheme for the early Cambrian of South Australia using a diverse shelly fauna including tommotiids, brachiopods, molluscs and bradoriids.Biostratigraphic data are derived from ten measured stratigraphic sections across the Arrowie Basin, targeting Hawker Group carbonates including the Wilkawillina, Wirrapowie and Ajax limestones and the Mernmerna Formation. The stratigraphic ranges of shelly fossils are predictable and repeatable across the Arrowie Basin, allowing three discrete shelly biozones to be identified, spanning Terreneuvian, Stage 2 to Series 2, Stages 3–4. The Kulparina rostrata Zone (new) and part of the overlying Micrina etheridgei Zone (new) are pre-trilobitic (predominantly Terreneuvian). The Cambrian Series 2, Stage 3 Dailyatia odyssei Zone (new) features a very diverse shelly fauna and will be described in detail in a separate publication. These zones provide robust means to correlate Terreneuvian–Series 2 successions in neighbouring coeval basins in Australia, particularly the Stansbury Basin. Wider correlation is possible throughout East Gondwana, and especially with South China.  相似文献   

11.
The oldest bradoriid fauna from Australia, occurring in the lower Cambrian Ajax and Wirrapowie limestones of the Flinders Ranges, South Australia consists of eleven taxa, including one new genus and species, Quadricona madonnae gen. et sp. nov. and two new species, Liangshanella circumbolina sp. nov. and Zepaera jagoi sp. nov. In the Ajax Limestone, Liangshanella circumbolina sp. nov. occurs c. 20 m below the FAD of the zonal trilobite Abadiella huoi. This pre-trilobitic occurrence represents the oldest bivalved arthropod hitherto known from East Gondwana and suggests a lower Cambrian (Series 2, Stage 3) age for the assemblage. The recognition of distinct bradoriid assemblages associated with the Abadiella huoi (Atdabanian), Pararaia tatei, P. bunyerooensis and P. janeae (all Botoman) trilobite biozones in South Australia indicates great potential for future regional biostratigraphic correlation. Quantitative biogeographic analysis including new taxonomic data from the lower Cambrian of South Australia, highlights the strong endemism displayed by early Cambrian bradoriid communities and strengthens the close faunal affinities with South China and Antarctica.  相似文献   

12.
Additional latest Middle Cambrian polymerid trilobites are recorded from the Teta Member (Karsha Formation) along the Tangze-Yogma-Kuru section, Kurgiakh Valley, southeastern Zanskar, Northwest Himalaya. It includes record of a new genus Pianspis Saito & Sakakuru, 1936 of family Lisianiidae and others associated fauna comprises of Neoanomocarella asiatica (Lisianiidae), Parablackwelderia sp., (Damesellidae) and two undetermined pygidium and one unidentified cranidia. All these specimens are collected from the level representing the Lejopyge acantha Zone of Guzhangian Stage (Cambrian Series 3) of the Middle Cambrian. The fauna is mainly correlated with the South China, North Korea, Kazakhastan, Uzbekistan, Siberia and Australia.  相似文献   

13.
《Gondwana Research》2016,29(4):1543-1565
Early Cambrian small skeletal fossils (SSFs) are studied and revised from the Zhenba–Fangxian Block of the transitional zone between the Yangtze Block and the South Qinling Terrane. The study reveals a diverse fauna with 47 species of various biological affinities, including the new species Gapparodus gapparites sp. nov. The SSFs are assigned to the newly defined Cambroclavus fangxianensis–Rhombocorniculum cancellatum Assemblage Zone. Based on the investigated SSF fauna from Zhenba County, Southeast Shaanxi of China and published data, a palaeobiogeographic study is carried out for the Cambrian Stage 3 (equivalent to the Atdabanian–Botoman of Siberia). A hierarchical Pearson similarity cluster analysis of 295 species from 32 regions of the world indicates a distinct palaeobiogeographic pattern with seven faunal provinces. The result is mostly consistent with existing palaeogeographic reconstructions for the early Cambrian. However, it is also shown that the SSF assemblages of the Zhenba–Fangxian Block have low similarity with those of the Yangtze Block. Instead, they share high similarity with those from Armorica, Tarim and the Karatau–Naryn terranes (South Kazakhstan/North Kyrgyzstan). The Yangtze Block has a unique SSF assemblage dissimilar to most of other regions. The Terreneuvian–Cambrian Stage 3 sedimentary sequence of the Zhenba–Fangxian Block is more consistent with that of the South Qinling Terrane. Besides, sedimentary Ediacaran manganese ore deposits and Cambrian barite/witherite deposits have unique distribution pattern on the Zhenba–Fangxian Block. Derived from the profound dissimilarities in faunal composition, sedimentary sequence and distribution of sedimentary ore deposits, we hypothesize that during the Neoproterozoic–Cambrian transition, the Zhenba–Fangxian Block might have been an independent terrane and more distant from the Yangtze Block. The palaeobiogeographic analysis of SSFs also indicates a closer alliance between Avalonia and Siberia. It corroborates the palaeogeographic reconstruction of North China at the margin of Gondwana, in the vicinity of Australia, Antarctica, and Armorica.  相似文献   

14.
This study investigated the geochemical features of the lower Paleozoic strata of Yaerdang Mountain outcrop along with the core samples from well TD2∈ in the eastern Tarim Basin,NW China.The total organic carbon abundance,hydrocarbon-generating precursor biospecies,and stable isotope ratios of organics and carbonate(δ~(13)C_(ker),δ~(13)C_(carb) and δ~(18)O_(carb)) were comprehensively studied for their possible correlative constraints during sedimentary evolution.The results revealed that the δ~(13)C_(ker)(VPDB) of Cambrian kerogens along the outcrop section varied from-34.6‰ to-28.4‰,indicating an increasing tendency from the lower Cambrian to the upper Cambrian.This was on the whole accompanied by the variation in the δ~(13)C_(carb) and δ~(18)O_(carb) along the profile,which might be associated with the changes in the sea level and also in the compositional variation of benthic and planktonic biomass.The large variation in the stable carbon isotope ratios up to 6‰ along the outcrop section reflected the heterogeneity of the Cambrian source rocks from the eastern Tarim Basin.Hence,the ~(13)C-enriched crude oils from well TD2∈might have been derived from a localized stratum of Cambrian source rocks.The results from this study showed the possibility of multiple source kitchens in the Cambrian-lower Ordovician portion of Tarim Basin.  相似文献   

15.
24-n-Propylcholestane (24-npc), a C30 sterane compound derived from sterol precursors which are the major sterol constituents of modern pelagophyte microalgae, occurs in certain Neoproterozoic rocks and oils and throughout the Phanerozoic rock record. This broad distribution leads 24-npc to be widely considered a reliable indicator of open to partially restricted marine depositional conditions for source rocks and oils. Here we report two significant hiatuses in the occurrences of 24-npc in the Lower Paleozoic marine rock record: the first in the Middle–Late Cambrian and the second in the Late Ordovician–early Silurian transition for a range of lithofacies (carbonates and siliciclastic rocks), organic carbon contents (both organic-lean and organic-rich), and paleoceanographic environments (shelf and deeper water marine settings) and observed offshore of two paleocontinents, Laurentia and Baltica. The Ordovician–Silurian gap is at least 9 million years, and possibly up to 20 million years, in duration. Robust older occurrences of 24-npc steranes in some Neoproterozoic rocks and oils suggest that oceanographic conditions in our intervals of Lower Paleozoic time were unfavorable for the proliferation of pelagophyte algae as phytoplankton. Caution should therefore be applied when interpreting a lacustrine versus marine depositional environmental setting for source rocks and oils in these intervals of Early Paleozoic time using lipid biomarker assemblages.  相似文献   

16.
The Ediacaran–Cambrian transition signals a drastic change in both diversity and ecosystem construction. The Ediacara biota (consisting of various metazoan stem lineages in addition to extinct eukaryotic clades) disappears, and is replaced by more familiar Cambrian and Paleozoic metazoan groups. Although metazoans are present in the Ediacaran, their ecological contribution is dwarfed by Ediacaran-type clades of uncertain phylogenetic affinities, while Ediacaran-type morphologies are virtually non-existent in younger assemblages. Three alternative hypotheses have been advanced to explain this dramatic change at, or near, the Ediacaran–Cambrian boundary: 1) mass extinction of most Ediacaran forms; 2) biotic replacement, with early Cambrian organisms eliminating Ediacaran forms; and 3) a Cheshire Cat model, with Ediacaran forms gradually disappearing from the fossil record (but not necessarily going extinct) as a result of the elimination of unique preservational settings, primarily microbial matgrounds, that dominated the Ediacaran. To evaluate these proposed explanations for the biotic changes observed at the Ediacaran–Cambrian transition, environmental drivers leading to global mass extinction are compared to biological factors such as predation and ecosystem engineering. We explore temporal and biogeographic distributions of Ediacaran taxa combined with evaluations of functional guild ranges throughout the Ediacaran. The paucity of temporally-resolved localities with diverse Ediacaran assemblages, combined with difficulties associated with differences in taphonomic regimes before, during, and after the transition hinders this evaluation. Nonetheless, the demonstration of geographic and niche range changes offers a novel means of assessing the downfall of Ediacara-type taxa at the hands of emerging metazoans, which we hypothesize to be most likely due to the indirect ecological impact metazoans had upon the Ediacarans. Ultimately, the combination of studies on ecosystem construction, biostratigraphy, and biogeography showcases the magnitude of the transition at the Ediacaran–Cambrian boundary.  相似文献   

17.
《Gondwana Research》2014,25(1):420-437
A new assemblage of early Cambrian bivalved arthropods (Bradoriida) is described from the Arrowie Syncline in the northern Flinders Ranges, South Australia. The well preserved, largely endemic fauna comprises a total of six taxa (including five new species): Jiucunella phaseloa sp. nov., Jixinlingella daimonikoa sp. nov., Mongolitubulus anthelios sp. nov., Neokunmingella moroensis sp. nov., Phasoia cf. spicata (Öpik, 1968), and Sinskolutella cuspidata sp. nov. This assemblage is derived from a carbonate sedimentary package representing a high energy, shallow water archaeocyath-Renalcis biohermal facies of Terreneuvian, Stage 2 age which transitions up-section to a more restricted, low energy, intra-shelf lagoonal environment that correlates with a Cambrian Series 2, Stage 3 age. The new taxon J. phaseloa sp. nov., has a first appearance datum (FAD) in shallow water biohermal facies of the Hideaway Well Member of the Wilkawillina Limestone at a level 47 m below the FAD of Pelagiella subangulata which is taken to approximate the base of Series 2, Stage 3 in South Australia. Along with Liangshanella circumbolina, this makes J. phaseloa sp. nov. amongst the oldest bivalved arthropods in South Australia and potentially greater Gondwana. The presence of 25 bradoriid taxa from the early Cambrian of South Australia suggests East Gondwana represents a major centre of origin for the Bradoriida.  相似文献   

18.
《Gondwana Research》2014,25(3):966-974
Substrates have perpetually played a crucial role in shaping the morphology of animal bodies, particularly the sedentary apparatus of benthic suspension feeders. In-situ preservation of sedentary forms from Cambrian Lagerstätten, especially the Lower Cambrian Chengjiang Lagerstätte, Yunnan Province, southwestern China, provides a unique opportunity for studying ancient interactions between the benthos and their substrates. The sedentary apparatuses of anthozoa-like animals Xianguangia sinica Chen & Erdtmann, 1991, Archotuba conoidalis Hou et al., 1999 and Archisaccophyllia kunmingensis Hou et al., 2005 from the Chengjiang Lagerstätte are investigated in their sedimentary context. X. sinica bears a cylindrical, rigid column and a basal, rounded, cuticularized attachment disc that partially attached into the soft muddy substrate; A. kunmingensis has a prominent, flexible pedal-shaped disc that attached directly to the substrate by expanding its disc surface area; whereas A. conoidalis has a unique, posterior-tapering tube and probably might have secreted mucus to firmly attach to the ‘sclerotized’ substrates. These three sedentary taxa employed different adaptive strategies, i.e., the ‘iceberg’, the ‘snowshoe’ and one newly defined but later widespread in Phanerozoic period, the ‘anchoring-nail’, to cope with the soft substrates. Furthermore, the anchoring-nail mode, sclerite-sticking behavior represented by Archotuba is a Phanerozoic innovative strategy in response to the appearance of pelagic larvae and small shelly fossils, especially to the first widespread biomineralization event at the beginning of the Cambrian, whereas the other two modes have already developed for about 90 Ma from the Ediacaran.  相似文献   

19.
Stromatolite, as the representative of recorder in the early life history of the Earth, has been traced back from 3.5 billion years to 3.7 billion years ago. Stromatolites do provide indirect evidence for the existence of early life on the Earth, especially the composition of modern carbonate stromatolites, which further proves that stromatolites are calcified structures of cyanobacterial mats. Among the modern carbonate stromatolites, the following examples have been studied for a long time: Coarse stromatolites on the platform of Bahamas, fine stromatolites in the ultra-salinity environment of Australia and ultra-salinity lagoon of southeastern Brazil. Based on the predecessors' research results, by tracing the growth mechanism of modern carbonate stromatolites and the complex microbial activities and deposition processes, the formation of stromatolites in the middle of the Zhangxia Formation of Cambrian in the Huolianzhai section of Benxi is obviously different from that of modern carbonate stromatolites, which indicates that the sedimentary model of modern stromatolites cannot be fully applied in the ancient stromatolites. Therefore, the comparison between modern carbonate stromatolites and ancient stromatolites provides a rich way to further understand the construction of Cambrian stromatolites and microbial carbonate factory.  相似文献   

20.
Historical published works on the fossil fauna of the Llanberis Slates Formation in Gwynedd, North Wales, concentrated on the endemic trilobite Pseudatops viola (Woodward, 1888), and placed the formation towards the top of Stage 3 (Series 2) of the Cambrian chronostratigraphy.The impression given was that the fauna is not particularly diverse and fossils are rare. However, recent collecting has produced a comprehensive fauna of sponges, hyolithids and diverse arthropods including over 250 trilobite specimens from two localities of the uppermost Green Slate horizon. Among them are examples of the endemic trilobite Pseudatops viola, sufficiently well preserved to enable a reappraisal of its status. The most abundant trilobite is a form of Strenuella (cf. strenua), but the collection includes previously unrecorded eodiscoid trilobites and specimens representing unrecorded and potentially new taxa. These additions result in the most comprehensive lower Cambrian trilobite assemblage yet described from Wales, and place it in the lower part of Stage 4, Series 2 in standard global terms.  相似文献   

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