Abstract: Interplay of Mesozoic Tectonics and Climate in Central Asia: Implications for Mesozoic-Sourced Oil Fields of Northern China and Mongolia

M. S. Hendrix, S. A. Graham, J. Y. Amory, L. Lamb, A. M. Keller, R. Barsbold, D. Badamgarav

Mesozoic tectonic and paleoclimatic interactions in central Asia resulted in favorable petroleum source-rock deposition in Late Triassic through Middle Jurassic (northwest China, western, southern, and eastern Mongolia) and Late Jurassic through Early Cretaceous time (eastern Mongolia, northeastern China). Triassic through Middle Jurassic source-rock deposits are likely the result of monsoon-driven high-rainfall levels across much of central Asia and the creation of meandering fluvial and lacustrine deltaic systems. Poorly circulating, commonly anoxic lakes were widespread and were supplied with an abundance of higher land plant-derived organic matter as indicated by plant debris, including in situ remains, and biomarker data. At least one Lower Jurassic anoxic lacustrine deposit with algal-derived biomarker characteristics and Type I kerogen was discovered in the Noyon Syncline of extreme southern Mongolia, however. Model predictions of Early Cretaceous atmospheric circulation patterns for much of central Asia suggest northerly trade winds similar to modern circulation patterns. Northwestern China and western Mongolia were the sites of well-circulating regionally extensive Early Cretaceous lakes which did not preserve sufficient organic matter for source-rock viability. Eastern Mongolia and northeastern China basins (including the Nilga, Tamstag, Hailar, Erlian, Gobi, and Songliao basins) were the site of regional, poorly circulating lakes which preserve considerable quantities of organic matter and source the petroleums of those basins. Biomarker suites from bitumen extracts and oils are dominated by algal-derived compounds (e.g., abundant steranes) and are very waxy. Kerogens are Type I. Upper Jurassic/Lower Cretaceous anoxic lacustrine deposits are the combined result of regional rifting, rapid subsidence and increased accommodation space, the Early Cretaceous global warming trend, and the region's proximity to Pacific maritime moisture.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994