Indosinian Supergene Karsts in the Qaidam Basin, NW China: Evidence from Paleo-tectonics, Paleoclimates and Paleo-fluids

In the Qaidam basin, Northwest China, karstic fissures and caves are developed in many places of the Lower Carboniferous Chengqianggou Fm. and Huaitoutala Fm. and the Upper Carboniferous Keluke Fm., in which are found typical karstic marks. Several suites of transgressive carbonate rocks formed during the Late Paleozoic epoch are preserved as reservoir properties in the Qaidam basin, with paleokarst-related cave-fractured diagenetic structures, which provided the basis for cave-fractured development. Carbonate and clastic samples covering or infilling caves and fractures in Carboniferous strata were collected in the eastern Qaidam basin to focus on petrological and geochemical analyses of karst and infilling materials. Based on this study of the Caledonian diagenetic sequence, and bitumen-infilled inclusion temperature and burial history, there existed a continuous atmospheric freshwater leaching process, which played a critical role in the construction of the Carboniferous supergene paleokarsts. Investigation and survey of the tectonic setting, plate paleolatitude and river development intensity also proves that there was abundant rainfall during the Indosinian period, after which the strata undergo a shallow burial process. Because Indosinian period is earlier than the key timing of hydrocarbon-generation of the Carboniferous source rocks, this kind of karst reservoir has potential significance for oil-gas resources in this area.