Ediacaran-Ordovician landscape of eastern South China: Constraints from sedimentary indices and detrital zircon U-Pb-Hf isotopes from the southeastern margin of the Yangtze Block

Abstract

Abstract The paleogeographic landscape is an important clue to clarify the controversy on the paleoposition of South China within the supercontinental cycles. We therefore conducted a study of directional structures (34 datasets) and detrital zircons (707 analyses of five samples) from the southeastern margin of the Yangtze Block (SMYB). The principal results are as follows. (1) The sedimentary transport directions indicated by cross-beddings and ripple marks are 295°-354°; the orientation of the relatively deep-water facies indicated by the lateral boundaries of different lithofacies is 332°; and the slump directions of sedimentary layers are 324°-359° and 280°-N-31° (or 100°-S-211°), based on the syndepositional faults and most of the syndepositional folds, respectively. (2) Detrital zircons have U-Pb ages of 3340-487 Ma, and the U-Pb spectrum of each sample has the same age-peak interval of 900-680 Ma. For the late Cryogenian-Ediacaran samples and Cambrian-Ordovician samples, the major age peaks, eHf(t) and Hf-TDM2 are characterized by ~740 Ma, negative values and clustering at 2.6-1.9 Ga, and by ~810 Ma, positive values and clustering at 1.5-0.9 Ga, respectively. These new data indicate that, during the Ediacaran to middle Ordovician, the landscape of eastern South China, from north to south, consisted of the following five paleogeographic domains: (i) the Yangtze Sea covering the Yangtze Platform; (ii) the Zhe-Gan-Wan Sea covering the SMYB basin with opposite dips on the north and south sides, and the northeast margin basin of the Cathaysia Block; (iii) the Zhe-Min Land located in the northeastern Cathaysia Block and derived from the Cryogenian land; (iv) the Gan-Min-Zhe Sea covering the northwest and south of the eastern Cathaysia Block; and (v) an unknown land, that was located to the south of the eastern Cathaysia Block and underwent the Grenvillian and Pan-African orogenies. According to the landscape configuration, South China may have been a peripheral component of East Gondwana, and the Cathaysia Block may have been adjacent to India, West Australia, and/or East Antarctica.