Late Ordovician to earliest Silurian graptolite and brachiopod biozonation from the Yangtze region, South China, with a global correlation

Abstract

Late Ordovician to earliest Silurian is an important geological period marked by large geological and biological events. However, the strata and fossils of this interval are not complete in many parts of the world. Based on studies of 43 sites in South China, in particular the continuous sections on the Yangtze platform, we recognize a complete succession including seven graptolite zones and two shelly faunas. In ascending order, the graptolite zones are the Dicellograptus complanatus, Dicellograptus complexus, Paraorthograptus pacificus (including Lower Subzone, Tangyagraptus typicus Subzone and Diceratograptus mirus Subzone), Normalograptus extraordinarius–Normalograptus ojsuensis, Normalograptus persculptus, Akidograptus ascensus and Parakidograptus acuminatus zones. The shelly faunas are the Foliomena–Nankinolithus and Hirnantia faunas, which may be correlated with D. complanatus Zone and N. extraordinarius–N. ojsuensis to part of N. persculptus zones respectively. The biozonation through this interval from the Yangtze region can be correlated with that of other parts of the world such as Dob's Linn in Scotland, Spain and Portugal, Thuringia–Saxonia–Bavaria, Bohemia, Poland, Kazakhstan, Kolyma, Malaya Peninsula, Yukon, Canadian Arctic Islands, Nevada, Argentina, Niger and Victoria, Australia. The Hirnantian Substage, which has been proposed by us recently, includes the N. extraordinarius–N. ojsuensis Zone, Hirnantia fauna and N. persculptus Zone. The base of the Hirnantian Substage is marked by the First Appearance Data (FADs) of N. extraordinarius and N. ojsuensis, which have been determined to be synchronous on a global scale.

Uppermost Ordovician (upper Katian-Hirnantian) graptolites of north-central Nevada, U.S.A.

“…uniformis, and Po. pacificus) also recur as very rare specimens in the persculptus Zone above the Hirnantia-bearing Kuanyinchiao Beds in the Yangtze Platform region of China along with three other very rare diplograptine species not found among the Lazarus taxa here (Anticostia lata, Paraorthograptus "brevispinus" and Rectograptus abbreviatus; Chen et al 2000Chen et al , 2005a, but most have never been recorded from late Hirnantian strata previously. Most of these taxa are represented in this interval at Vinini Creek by one or two specimens, mostly not well preserved, that were overlooked in previous collections of this interval.…”

“…-The extraordinarily diverse graptolite assemblage reported by Chen et al (2000) from the Dicellograptus complexus Biozone of the Wufeng Formation correlates with the less diverse graptolite fauna of the Dicellograptus ornatus Biozone recognized in the lower part of the Vinini Creek trench. Dicellograptus complexus Davies is absent in the measured part of the Vinini Creek section, although was previously reported by and .…”

“…A distinct subzone, tentatively correlative with China (Chen et al 2000) and northwestern Canada (Chen & Lenz 1984), can be recognized in the uppermost 3.2 m of the pacificus Biozone at the Vinini Creek section. The base is taken at the lowest occurrence of Diceratograptus mirus.…”

“…Mu et al 1993;Chen et al 2000Chen et al , 2005a, Yukon Territory and Arctic islands of Canada (Chen & Lenz 1984, Melchin 1987, north-eastern Siberia (Koren' et al 1983), southern Kazakhstan (Apollonov et al 1980(Apollonov et al , 1988 and British Isles (Toghill 1970;Williams 1982Williams , 1983. These are discussed below, together with mid-latitude successions of peri-Gondwanan Europe which are less suitable for correlation but important to further studies on graptolite faunal dynamics before, through and after the end Ordovician glaciation.…”

“…In addition, the graptolite successions can be integrated with conodont and chitinozoan biostratigraphy and with carbon isotope stratigraphy (see . Furthermore, graptolites of correlative sections in the Yangtze Platform of China already have been described and illustrated and recently revised (Mu et al 1993;Chen et al 2000Chen et al , 2005a, and work is well underway on the graptolites from an important section in the Yukon (Loxton pers. comm.…”