Temporal Distribution of Diagnostic Biofabrics in the Lower and Middle Ordovician in North China:Clues to the Geobiology of the Great Ordovician Biodiversification Event

The temporal distribution of the diagnostic biofabrics in the Lower and Middle Ordovician in North China distinctly illustrates that the sedimentary systems on the paleoplate have been changed markedly as consequences of the Great Ordovician Biodiversification Event （GOBE）. The pre-GOBE sedimentary systems deposited in Tremadoc display widespread microbialite and flat-pebble conglomerates, and a less extent of bioturbation. Through the transitional period of early Floian, the sedimentary systems in the rest of the Early and Mid- Ordovician change to GOBE type and are characterized by intensive bioturbation and vanishing flat-pebble conglomerates and subtidal microbial sediments. The irreversible changes in sedimentary systems in North China are linked to the GOBE, which conduced the increase in infaunal tiering, the expansion of infaunal ecospace, and the appearance of new burrowers related to the development of the Paleozoic Evolutionary Fauna during the Ordovician biodiversification. Thus, changes in sedimentary systems during the pivotal period of the GOBE were consequences of a steep diversification of benthic faunas rather than the GOBE＇s environmental background.

Biodiversification of Late Ordovician Hirnantia Fauna on the Upper Yangtze Platform,South China

The Hirnantia Fauna is a globally-represented,cool water brachiopod fauna that originated and flourished in shallow marine environments at intermediate to low latitudes after the first episode of the end-Ordovician mass extinction.It was well-developed,widely distributed,long in stratigraphical range,and complex in palaeoecological differentiation on the Upper Yangtze Platform of the South China paleoplate,where it has been extensively studied.Qualitative and quantitative analyses show that the FAD of the Hirnantia Fauna in South China becomes stratigraphically higher from nearshore to offshore localities on the Yangtze Platform,while the range of the fauna becomes shorter whereas the taxonomic diversity increases.Over its stratigraphical range the diversity of the Hirnantia Fauna at nearshore localities consistently decreases,but trends in the opposite direction at offshore,deeper water localities.The fauna was represented by different communities,subcommunities or associations with changing environmental factors(such as water depth and substrate) at different localities or horizons.

Reconstruction of the Yangtze Ramp during Floian to Darriwilian(Ordovician)in South China:Its Morphology,Controlling Factors and Significances

A robust stratigraphic framework and a coherent depositional ramp model for the Zitai,Dawan,Meitan and Ningkuo formations of Floian–Darriwilian age(Early–Middle Ordovician)in the Yangtze(Daoba,Xiangshuidong,Daling,Gudongkou and Honghuayuan sections)and Jiangnan regions(Nanba section)was created based on lithofacies and major element analysis.Three siliciclastic(LF1–3)and six carbonate(LF4–9)lithofacies are recognized representing sediments that were deposited in mixed siliciclastic and carbonate ramp environment.The intensity of mixed sedimentation and terrigenous input were evaluated using the elemental proxies Intensity of Mixed sedimentation(IM)and Aluminum Accumulation Rate(Al AR),as well as their mean values during certain time intervals.Mixed sediments are most well-developed along the marginal Yangtze region,strongly impacted by recurrent influx of westerly derived terrigenous materials in response to global eustatic changes and regional tectonic movements,shaping the gently southeast-dipping morphology.Regular terrigenous influx resulted in periods of enhanced primary productivity on the Yangtze Ramp as evidenced by matching biodiversity peaks in planktonic organisms,i.e.,chitinozoans and acritarchs.Brachiopods and other shelly fauna were also able to proliferate as new niches developed along the gently dipping ramp floor with substrate changes.The biodiversification patterns suggest that terrigenous influx controlled in part by regional tectonics played a more important role than previously thought in the development of Great Ordovician Biodiversification Event in South China.

Replacements of Major Cephalopod Faunas in Late Cambrian and Ordovician in South China

1 Introduction As one of the major groups in the Great Ordovician Biodiversification Event(GOBE),cephalopods may have played a critical role in the marine ecosystem in late Cambrian and Ordovician.Among the few predators in the Ordovician,cephalopods are typified by their big sizes and the development of swimming ability.