Subsurface evidence for late Mesozoic extension in western Mongolia: tectonic and petroleum systems implications

Abstract

New seismic reflection profiles from the Tugrug basin in the Gobi‐Altai region of western Mongolia demonstrate the existence of preserved Mesozoic extensional basins by imaging listric normal faults, extensional growth strata, and partially inverted grabens. A core hole from this region recovered ca. 1600 continuous meters of Upper Jurassic – Lower Cretaceous (Kimmeridgian–Berriasian) strata overlying Late Triassic volcanic basement. The cored succession is dominated by lacustrine and marginal lacustrine deposits ranging from stratified lacustrine, to subaqueous fan and delta, to subaerial alluvial‐fluvial environments. Multiple unconformities are encountered, and these represent distinct phases in basin evolution including syn‐extensional deposition and basin inversion. Prospective petroleum source and reservoir intervals occur, and both fluid inclusions and oil staining in the core provide evidence of hydrocarbon migration. Ties to correlative outcrop sections underscore that, in general, this basin appears to share a similar tectono‐stratigraphic evolution with petroliferous rift basins in eastern Mongolia and China. Nevertheless, some interesting contrasts to these other basins are noted, including distinct sandstone provenance, less overburden, and younger (Neogene) inversion structures. The Tugrug basin occupies an important but perplexing paleogeographic position between late Mesozoic contractile and extensional provinces. Its formation may record a rapid temporal shift from orogenic crustal thickening to extensional collapse in the Late Jurassic, and/or an accommodation zone with a Mesozoic strike‐slip component.

Folded Basinal Compartments of the Southern Mongolian Borderland: A Structural Archive of the Final Consolidation of the Central Asian Orogenic Belt

“…The regional, long wavelength, open folds of the Sherigyn Gashoon Basin contrast with the tighter folds to the south of Permian-Triassic and Jurassic age. They are more similar to Late Cenozoic folds documented in the Valley of Lakes region directly north (Figure 1; [15,50]). …”

“…In the central and southern Gobi Altai and eastern Mongolia, this event is characterized by metamorphic core complex formation, rift basin development, and up to 1700 m of fluvial, lacustrine and aeolian sedimentation [33,34,[47][48][49][50]. Organic shales deposited in Cretaceous lakes within individual rifts and linked graben systems comprise important oil source rocks in southern and eastern Mongolia and adjacent regions of China [51,52].…”

Relict Topography Within the Hangay Mountains in Central Mongolia: Quantifying Long‐Term Exhumation and Relief Change in an Old Landscape

“…Strike‐slip system development and gravitational collapse of the upper crust gave way to the continental‐scale extensional setting in East Asia accommodating India‐Asia collision (Yin, ). Seismic analysis in the Tugrug Basin (Valley of Lakes region) also supports a rapid change from orogenic thickening to collapse in the Late Jurassic (Johnson et al, ). Thermochronologic data from the Kyrgyz Tian Shan and Siberian Altai‐Sayan confirm regional cooling during the initial stages of the Mongol‐Okhotsk orogeny and contemporaneous Lhasa collision at about 150 Ma, with orogenic collapse occurring afterward around 100 Ma (Glorie & De Grave, ).…”

Jurassic tectonostratigraphic evolution of the Junggar basin, NW China: A record of Mesozoic intraplate deformation in Central Asia

“…Upper Jurassic bimodal volcanic rocks with an age range of 162–151 Ma were developed in half‐grabens in Transbaikalia (Figure ), suggesting an extensional setting related to subduction of the Mongol‐Okhotsk Ocean or intraplate rifting [ Donskaya et al ., ]. The Block V area, central Mongolia, was in an extensional setting during the Late Jurassic [ Johnson et al ., ] (Figure ).…”

“…Uplift of the Altai Shan produced coarse clastic sedimentation in western Mongolia [ Sjostrom et al ., ]. A prominent unconformity formed between the Upper Jurassic Sharilyn Formation and Lower Cretaceous Tsagantsav Formation in the Block V, Tugrug basin, and the East Gobi Basin, Mongolia [ Jerzykiewicz and Russell , ; Graham et al ., ; Johnson et al ., ]. Compressional deformation occurred in the Turfan Basin and northern Tarim Basin, forming angular unconformities between Jurassic strata and overlying Lower Cretaceous strata [ Greene et al ., ; Deng et al ., ; Wang et al ., ].…”