Palaeobiogeographic distribution patterns and processes of neochonetes and fusichonetes (brachiopoda) in the late palaeozoic and earliest mesozoic

The global palaeobiogeographic distributions of two resembling genera, Neochonetes and Fusichonetes (Brachiopoda), from the Carboniferous to Griesbachian are analysed. This analysis provides insight into the biotic response of two related genera to changing palaeoclimate, regional tectonics, and environmental crises. Neochonetes originated in the equatorial area in the Mississippian, and it mostly retained this position during the peak of the glaciation in the Carboniferous–Permian ice age (namely in the Pennsylvanian). Neochonetes then dispersed globally during the Cisuralian when the climate became warmer and the ice sheet started to retreat. In the Guadalupian and Lopingian, following the closure of the Ural seaway at the end of the Cisuralian and the regression at the end-Guadalupian, Neochonetes almost disappeared in the western part of Gondwana. Subsequently during the Lopingian the genus retracted to the middle- and low-latitude Palaeo-Tethys and Tethys. In comparison, Fusichonetes originated in the equatorial area in the late Guadalupian and was still present in that area in the Lopingian. Both genera occurred only in South China in the Griesbachian. It is inferred that this could be related, not only to the deteriorated palaeoenvironmental conditions (e.g., anoxia, global warming) leading up to the extinction of most of the Neochonetes and Fusichonetes species in other areas, but also to the better physiological adaptation of the smaller shells of Neochonetes and Fusichonetes species in South China.

Palaeobiogeographic significance of Jurassic and Cretaceous Western Australian ostracod faunas

The palaeobiogeographic distribution of Western Australian ostracods during the Jurassic and Cretaceous illustrates how Gondwana broke apart to form the South Atlantic and Indian Oceans, and how the new ostracod genera from here migrated into the Atlantic Ocean, Mediterranean Sea, Western Pacific Ocean and the Western Indian Ocean.

Discovery of the Early Ordovician strata in Xianza County, Tibet and its significance

There is no any sediments contain fossils which formed earlier than Middle Ordovician in northern Tibet yet. It is very important whether have developed the Cambrian to Early Ordovician sedimentary strata. During geological mapping of Xainza County in 2000, Tetragraptus approximatus, the typical one of graptolite belts which cosmepolitically distributed in the Arenigian of Early Ordovician, was collected from the so-call Pre-Sinian Nianqingtanggula Group. So there is developped the Early Ordovician sediments and we have established Zakang Formation and Taduo Formation which perfected the Plaeozoic sequences in northern Tibet. According to these, we can realize tectonic control, palaeogeographrc pattern as well as palaeobiogeographic distribution of the Qinghai-Tibet Plateau in the early Paleozoic and also provided the materials to the cosmepolitical biostratigraphic contrast.

Rovearinids (stemless crinoids) in the Albian carbonates of the offshore Santos Basin, southeastern Brazil: stratigraphic, palaeobiogeographic and palaeoceanographic significance

Microfacies analysis of marine carbonates cored by Petrobras well 1-SPS-6 in the offshore Santos Basin (southeastern Brazil) has revealed a remarkable fossil assemblage of calpionellids (colomiellids), favusellids, hedbergellids, globigerinelloidids, buliminids, radiolarians, inoceramid prisms, roveacrinids, and saccocomids(?) preserved in lower Albian calcimudstones-wackestones of the lower part of the Guaruja Formation. This assemblage represents an allochtonous accumulation in a deep neritic to shallow bathyal hypoxic environment. Besides 'saccocomid-like' sections, the only determinable sections of roveacrinids are thecal plates of Poecilocrinus dispandus elongatus Peck, 1943. This species was previously only known from the Weno Formation of Texas. The Brazilian material extends its records farther south from at least the lower Albian, which then represents the earliest occurrence of this peculiar family in the South Atlantic region. Taking into account their Albian global distribution and the location of their oldest representative (Hauterivian near Alicante, Spain), the Roveacrinidae dispersed westward throughout all of Cretaceous Tethys. The Tethyan origin of Roveacrinidae is further evidence that, during late Aptian-Albian times, the northern South Atlantic (north of the Walvis-SBo Paulo Ridge) was supplied by a Tethyan water mass. (C) 2001 Elsevier B.V. Ltd. All rights reserved.