Late Ordovician brachiopods from the Tarim Basin in Northwest China

Please join us for a special presentation on Friday Sept 28 at 3:30 pm in rm 155 Geology – our newest faculty member Dr. Colin Sproat will be presenting the following:

Late Ordovician brachiopods from the Tarim Basin in Northwest China

My postdoctoral studies at the Nanjing Institute of Geology and Palaeontology in Nanjing, China, were focused on a Late Ordovician brachiopod fauna found on the northeastern edge of the Taklamakan Desert in Xinjiang, Northwest China. These shells were collected from a remote locality on the boundary of the Tarim Basin in an area that forms the edge of the Upper Ordovician Kuruktag carbonate platform. This platform was part of the Tarim paleoplate, a small plate that encompasses much of northwestern China today between the North China plate and the Kazakh terranes and was located near the paleoequator during the Late Ordovician.

The diversity of the brachiopod fauna is relatively low (~15 genera). The vast majority of the shells belong to the early atrypide Schachriomonia pentagonia (2108) followed by the rhynchonellide Altaethyrella tarimensis (287). The plectambonitide Sowerbyella and orthide Weberorthis are less common, and other genera are generally represented by less than 10 shells each.

Although brachiopod shells are abundant at this locality, the desert environment has had a negative effect on preservation. Weathering of the outcrop by persistent abrasive desert winds has resulted in poor preservation of most specimens. Complete shells are uncommon, and well-preserved shells are rare. Important diagnostic characteristics such as surface ornamentation and shell structures are commonly damaged or missing altogether. Even in relatively well-preserved shells, the interior is often obscured by calcite crystals that have infilled the mantle cavity.

Despite the relatively poor preservation of the fauna, there are several significant aspects to its study. Due to the poor paleomagnetic coverage on Tarim, fossils are useful tools in locating the plate paleogeographically relative to nearby North and South China and the Kazakh terranes during the Late Ordovician. The high abundance of S. pentagonia and the preservation of a range of different shell sizes in the collection provides a unique opportunity to investigate the ontogeny of early atrypides from the Late Ordovician. Most importantly, the detailed systematic description of the fauna is contributing to our understanding of the global paleobiogeography of Late Ordovician brachiopods, revealing trends obscured by misclassification of earlier material from China and Central Asia.

Following the presentation, at 4:30 pm, you are also invited to an informal social gathering to welcome Colin to our Department. We will meet upstairs at Alexanders Restaurant.