Early paleozoic tropical paleokarst geomorphology predating terrestrial plant growth in the tahe oilfield, Northwest China

Abstract

A deeply buried tropical paleokarst landscape that predates terrestrial plant growth was discovered in West District 10 of the Tahe Oilfield, located on the northern margin of the Tarim Basin in the Xinjiang Uygur Autonomous Region of northwestern China. The paleokarst unconformity surface at depths deeper than ~6000 m had been subjected to subaerial karstification under humid tropical climatic conditions during the first hiatus period in the Early Paleozoic. A high-quality, full-azimuthal 3D seismic survey was conducted in this study area (area of 10 × 10 km2) in order to visualize the buried paleokarst landscape with high-resolution seismic data. With this data and previous geological, geochemical, and paleomagnetic data, we reconstructed the large-scale paleokarst landform assemblage, compared it to a modern humid tropical/subtropical karst, and investigated the different controlling factors for the formation of the paleokarst and the modern karst. Results show that (1) the original landform assemblages of the tropical paleokarst landscape are distinct from those of the modern humid tropical/subtropical karst geomorphology; (2) the paleokarst denudation surface that formed in the Early Paleozoic was relatively smooth with shallow depressions, and the relative relief was less than that of the modern tropical/subtropical cockpit karst area; (3) during the time of epigenetic paleo-karstification, lithological, hydrogeological, and climate conditions were optimal for the formation of cockpit karst. The tropical paleokarst landscape demonstrates that extensive terrestrial plant growth plays an important role in creating large-scale karst landform assemblages of peak clusters and depressions (cockpit karst).