Cambrian microfossils from the Tethyan Himalaya (original) (raw)
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Cambrian–Ordovician unconformity in the Tethyan Himalaya
2007
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Small bilaterian fossils from 40 to 55 million years before the cambrian
Science (New York, N.Y.), 2004
Ten phosphatized specimens of a small (<180 micrometers) animal displaying clear bilaterian features have been recovered from the Doushantuo Formation, China, dating from 40 to 55 million years before the Cambrian. Seen in sections, this animal (Vernanimalcula guizhouena gen. et sp. nov.) had paired coeloms extending the length of the gut; paired external pits that could be sense organs; bilateral, anterior-posterior organization; a ventrally directed anterior mouth with thick walled pharynx; and a triploblastic structure. The structural complexity is that of an adult rather than a larval form. These fossils provide the first evidence confirming the phylogenetic inference that Bilateria arose well before the Cambrian.
The Cambrian in the Lesser Himalaya
Himalayan Geology, 2022
We present lithostratigraphic correlations, paleocurrent analysis, general pattern of sedimentation, regional setup, tectonics, and the basin configuration of the Ediacaran-early Cambrian in the Lesser Himalayan zone (LHZ). The Ediacaran-early Cambrian sequences from the west to the east are preserved as Hazira Formation in Hazara, and as the the Tal Group in the Nigalidhar, Korgai, Mussoorie, Garhwal, and Nainital synclines. The age of these sediments based on acritarchs, small shelly fauna, brachiopod and trilobite ranges from latest Ediacaran to earliest Cambrian Series 2, Stage 4 (~512 Ma). Besides these, the Chilar (Himachal and Uttarakhand), Kerabari (Nepal) and Miri (Arunachal) of the latest Ediacaran age formed another basin south of the Hazira-Tal basin. The Tal basin extended in the west covering the Hazara region, turned south towards Bikaner-Salt Range and chased its own tail to form the Tethyan basin in the north. The overall thickness of the Tal sediments is maximum in the Nigalidhar Syncline, and the least in the Nainital Syncline; the Nigalidhar region formed the deepest part and the Nainital-the shallowest part of the basin. the There was a shallowing of the basin after the deposition of Krol E dolostone, leading to deposition of clastics of the Earthy Siltstone Member (Shaliyan Formation, Tal group), as a result in shallower parts, the Earthy Siltstone Member was not deposited. The Chert Member marks flooding in subtidal/shallow anaerobic conditions; thereafter, the basin gradually further shallowed. The palaeocurrent directions in general are towards NE. The late Cambrian/early Ordovician Kurgiakh orogeny caused the obliteration and deformation of the Cambrian basin.
Before the Cambrian Small Bilaterian Fossils from 40 to 55 Million Years
2008
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This paper reviews the global biogeography and affinities of the Bradoriida, a group of Cambrian–early Ordovician arthropods. Bradoriida appear in the fossil record during the early Cambrian, just prior to the earliest trilobite faunas. Seven families may form a natural (monophyletic) group of Bradoriida sensu stricto, comprising Cambriidae, Kunmingellidae, Comptalutidae, Bradoriidae, Hipponicharionidae, Beyrichonidae and Svealutidae. Amongst the Bradoriida sensu lato, some forms that lie outside these families have carapace designs that suggest an ostracod affinity, particularly Altajanella and Vojbokalina. Bradoriida formed a major element of the 'Cambrian evolutionary fauna' and are components of the Chengjiang, Burgess Shale, and Buen Formation Lagerstätten. Bradoriida achieved global distribution from the Atdabanian (early Cambrian). Their diversity peaked during the early and middle Cambrian, with highest diversity at the species and genus level amongst the palaeo-tropical faunas of the South China (17 genera) and east Gondwana palaeocontinental regions (23 genera). By contrast Laurentian faunas were of much lower diversity (10 genera for the whole Cambrian). Bradoriid diversity declined rapidly from the latest middle Cambrian, a trend that may be related to the major extinction of trilobites at the base of the late Cambrian. The youngest Bradoriida comprise a few, rare Ordovician forms. Bradoriids appear to have occupied well-oxygenated marine shelf facies. The biogeographical patterns of early and middle Cambrian Bradoriida suggest climatic control on their distribution (temperate and tropical faunas), together with palaeogeographical constraints that also reflect trilobite provinciality. Kunmingellids and comptalutids were restricted to palaeo-tropical/subtropical sites, but migrated between South China, Siberia and eastern Gondwana palaeocontinents. They are absent from the mid-and high latitude faunas of the western Gondwana, Avalonia and Baltica palaeocontinental areas that were dominated by hipponicharionids, beyrichonids and Bradoriidae. The Laurentia palaeocontinent was isolated from the main zones of bradoriid diversity, but its faunas include a number of early and middle Cambrian Bradoriidae (Indota, Bradoria, Walcottella), and the region was colonised by cosmopolitan cambriids during the early Cambrian and by supposed pelagic svealutids (Liangshanella and Anabarochilina) during the middle Cambrian. The genera Walcottella, Dielymella and Bullaluta were endemic to Laurentia. One species of Anabarochilina that possibly dwelt near the sea-surface achieved an equatorial to high southern latitude (70° S) distribution during the late middle Cambrian (Lejopyge laevigata Biozone), perhaps reflecting a reduced latitudinal temperature gradient for near surface ocean waters.