INTEGRATED SEQUENCE-STRATIGRAPHY, BIO-STRATIGRAPHY AND CHEMOSTRATIGRAPHY OF THE TERMINAL PROTEROZOIC TO LOWERMOST CAMBRIAN BLACK ROCK SERIES FROM CENTRAL SOUTH CHINA

Integrated litho-, bio-, and chemostratigraphic study front the strati graphic interval of the Nantuo postglacial to Lowermost Cambrian in th e central South China suggests that five sequences of third grade coul d be recognized in the central Yangtze platform (CYP) and its Jiangnan marginal slope (JMS) or basin (JMB) and Xiang-Qian back-arc basin (XQ BB). Each sequence turnover is always related to the occurrence of ''b lack rock series'' (cherts, shales, dolomites and limestones) accompan ied by an oxidizing TST following a shallowing upward HST of the last sequence. These ''black rock series'' are thought to be formed in a re latively low-energy but current-influenced subtidal environment, regar dless of their difference in paleogeographic locations, and characteri zed by high original organic matter contents, probably derived from pr imary rather highly diversified megaalgae, vendobiota, soft-bodied met abiota and prokaryotic bacteria during the Neoproterozoic III, and lat er from multiphyletic small shelly fossils and planktonic trilobites d uring the lowest Cambrian. The differentiation of organic matter conte nts for different black rock types of the same horizon is related to p aleo-weathering activities and to the hydrothermal activities in assoc iation with the impregnation of high sulfide-related rare and precious metal elements caused by subsequent tectono-thermal events. For the m ost cherts of the Upper Sinian Liuchapo Formation or coeval beds the s ilicification is interpreted to have resulted from prediagenetic hydro thermal replacement of primary black muds. The apparent ''anoxia'' exp ressed by these ''black rock series'' does not mean the absence of oxy gen in the original oceanic environment during that time or in the sha llow water column, but rather virtually the depletion of oxygen occurs at the sediment/water interface die to sedimentary, organic surplus s tockpiling and disruption as well as disintegration of organic matter during burial and also during early phases of diagenesis. The occurren ce of four main biotic assemblages i.e. the Miaohe biota, Vendotaenia with Ediacara-type soft-bodied metazoans, multiphyletic small shelly f ossils and trilobites in the terminal Precambrian to earliest Cambrian ''black rock series'' is related to shallow-water originally oxidizin g transgressive environments in the CYP and JMB. The main reason for t he usual absence of most of these organic-walled non-skeletal biota in the ''black rock series'' of same age in the XQBB would probably have been influenced by volcanically derived hydrothermal activities leadi ng to a rising seafloor water temperature during that time, and coinci dentally to a relative deep ''anoxia'' environment as well. Two obviou s changes in the distribution of REE, EBP and Sa/Ar are observed betwe en sequence 3 and 4 and between sequence 4 and 5 in XQBB. These two se quence boundaries would separately be equivalent to those between the Precambrian and Cambrian and between the Yanjiahe and Shujingtuo Forma tions in the Yangtze Platform.