Upper Ordovician Bryozoans of the Pin Formation (Spiti Valley, Northern India)

Abstract

Twenty-nine species of bryozoans from the Upper Ordovician-Lower Silurian Pin Formation (Spiti, India) have been identified. Eight of these are new: Trematopora minima, Ulrichostylus bhargavai, Ptilodictya exiliformis, Phaenopora ordinarius, Oanduellina himalayaica, Pesnastylus? vesiculosum, Ralfina? originalis and Pinocladia triangulata. The fossil record and facies analyses of the area investigated indicate shallow-water conditions within the subtropicaltropical realm. The distribution pattern of fossils among the Ordovician ⁄ Silurian succession on the Northern Gondwana shelf and the influence of the Late Ordovician cooling phases on marine organisms are distinctive owing to a dramatic reduction in diversity globally. As far as the bryozoan taxa of Spiti are concerned, only one (Helopora fragilis) of the 29 species was recorded above the Ordovician ⁄ Silurian boundary. Observed bryozoan communities are very similar to faunas of Laurentia, the Baltic, Siberia and southern China of early-late Ordovician age.

The upper Katian (Ordovician) bryozoans from the Eastern Iberian Chain (NE Spain)

“…Trematopora tuberculosa Hall, 1852, Trematopora sardoa (Vinassa de Regny, 1942, and Trematopora gracile Ernst & Key, 2007 from the upper Katian of Montagne Noire (France), Sardinia and the Carnic Alps (Italy) [see Conti (1990) and Ernst & Key (2007)] as well as Trematopora minima Suttner & Ernst, 2007 from the upper Katian of India, are other species of the genus previously described from the Mediterranean Province (Jiménez-Sánchez & Villas in press). Trematopora acanthostylita sp.…”

“…Tripolitania Formation (upper Katian) in Djeffara, Libya (Buttler et al 2007). Pin Formation, Upper Katian, in India (Suttner & Ernst 2007). The siltstone/sandstone member of the Uggwa Formation (upper Katian) in Valbertad, Carnic Alps, Italy, and the carbonate and clastic sequence from Montagne Noire, France (Ernst & Key 2007).…”

Latitudinal distribution of bryozoan-rich sediments in the Ordovician

“…Data for this analysis was gathered in the same way as described by Taylor & Allison (1998), except that online literature searches were undertaken in addition to trawling through printed sources such as the large collection of bryozoan reprints in the Department of Palaeontology at the Natural History Museum, London (NHM). Very few papers actually quantify the abundance of bryozoans in Ordovician deposits.…”

“…Bryozoans played a prominent role in the Great Ordovician Biodiversification Event, rapidly attaining a family-level diversity that was to persist throughout much of the Palaeozoic (Taylor & Ernst 2004). Taylor & Allison (1998) drew attention to the striking contrast between the latitudinal distributions of Palaeozoic and post-Palaeozoic bryozoan-rich deposits (see also Allison et al 1999). Nearly all post-Palaeozoic deposits in which bryozoans comprise a significant proportion (ca > 20%) of the sediment were deposited in mid-to high-latitudes, outside the tropics (defined as 23.5°north or south of the equator).…”

“…We add new occurrences to the database of bryozoan palaeolatitudes utilized by Taylor & Allison (1998) and consider reasons why bryozoans had a proportionally higher biomass in the Ordovician tropics than they do in the modern tropics.…”