Characteristics and implications of Albian volcanism in a magma-rich rift basin: Seismic volcano stratigraphic and geomorphological evidence from the Upper Suhongtu Member in the Chagan Sag, China-Mongolia border region

Abstract

Buried volcanic successions imaged by 3D seismic data reveal facies components of Albian volcanism in the Chagan Sag of the Yingen-Ejinaqi Basin. The volcanic rocks of the Upper Suhongtu Member are composed mainly of vesicular and tight massive basalts and andesites. Three types of volcanoes, including monogenetic volcanoes, flood basalts, and shield volcanoes were recognized through detailed seismic facies analysis. A seismic geomorphological study showed that volcanism declined from Unit 1 to Unit 2, with the decline being strongly associated with the transition from the rift climax to the later syn-rift phase. In Unit 1, a center-type eruption arose at the onset, and was subsequently overwhelmed by multistage basaltic lavas supplied by fissure vents of the Maoxi, Tulage, and Barun faults in response to increased thermal fluid activity. Several cone- and crater-shaped monogenetic volcanoes formed by the center-type eruption that developed in Unit 2. In addition, a large shield volcano supplied by fissure vents and a major volcanic conduit developed in the northwestern part. The Albian volcanism of the Yingen-Ejinaqi Basin and the whole volcanic province contributed to a much hotter and more arid paleoclimate, and their records can be recognized from palynological and elemental geochemical evidence in the Chagan Sag and its surrounding area. Volcanism not only produced widely distributed strongly heterogeneous volcanic reservoirs but also accelerated the thermal maturation of source rocks, contributing to near-source hydrocarbon accumulation in Lower Cretaceous magmatic-rich rift basins of the East Asian region.