Stratigraphic architecture of the Cryogenian successions of South China
Thursday, 18 December 2014
Stratigraphy and sedimentology of the Cryogenian glacial successions provide primary data for elucidating climatic change of this critical interval. The Cryogenian strata of South China were deposited in a rift basin, and exhibit dramatic facies change from the basin center to margin, which complicates stratigtraphic correlations. Here we present new sedimentological, geochemical and stratigraphic data based on the detailed analyses of more than ten well exposed sections along a basinward transect from north-south. In the basin center, Cryogenian strata are about 4000 m thick and characterized by two glaciogenic diamictite units separated by a diamictite-free siliciclastic interval. Initiation of the Chang’an glaciation (Sturtian equivalent) is conformable and gradational with dropstones appearing in siltstone at the basal part of the Chang’an Formation followed by a shoaling-up sequence that is interpreted to represent a glacio-eustatic sea-level fall. In the basin center, >600 m of graded beds of siliciclastic rocks and debrites of the Fulu Formation overlie the Chang’an Formation. The Fulu Formation is succeeded by a thin (<10 m) fine-grained siliciclasitic unit with black shale and manganese carbonate at the base, which is assigned to the Datangpo Formation, and massive glacigenic diamitictite of the Marinoan-age Nantuo Formation. On the basin margin, the Datangpo Formation is up to 300 m thick and is underlain by a glaciogentic diamictite (Tiesi’ao/Dongshanfeng/Gucheng Formations). Taking factors of glacial dynamics and active tectonism into account, we develop a facies model to interpret the sedimentology and stratigraphic architecture of these successions. Combined with new geochronological data, our data will provide tests for Cryogenian climatic models.