Generation Time and Accumulation of Lower Paleozoic Petroleum in Sichuan and Tarim Basins Determined by Re–Os Isotopic Dating

With the targets of petroleum exploration transferred to deep and ancient strata, abundant oil gas resources have been found in Lower Paleozoic older strata central western China. Due complex evolutionary processes including multiple episodes hydrocarbon accumulation ubiquitously accompanied by secondary alterations, significant uncertainties remain concerning generation time these revealed sources. In this paper, relative pure Re Os elements existing asphaltene fractions Cambrian solid bitumen collected from Guangyuan area, Sichuan Basin, SW China Middle–Lower Ordovician heavy oils Aiding area Tahe oilfield Tarim NW were successfully obtained sample pretreatments, Re–Os isotopic analysis was subsequently carried out for dating these. The composition indicates a between 572 Ma 559 Ma, corresponding late Sinian period Neoproterozoic era. By means isochron aging, initial 187Os/188Os ratios, carbon compositions, is supposed originate source rocks Doushantuo Formation migrated into reservoirs Dengying Formation. This previously reserved transformed its present state destruction caused tectonic uplift. results Basin suggest that it formed 450 436 Late Ordovician–Early Silurian system, generated likely migrate karst form early reservoirs. uplift, degraded reformed heavy-oil today.