Abstract

The Minle and Chaoshui Basins of northern China are pull-apart basins that originated during Jurassic to Early Cretaceous strike-slip and extensional deformation in the western North China block (Alashan), and the region to its southwest, known as the Hexi Corridor. The basins are separated by the Longshou Shan, which has been a positive topographic feature since Jurassic time.

Lower Cretaceous successions in the Minle and Chaoshui Basins display similar rift-related, fining-upward motifs. These comprise alluvial conglomerates and sandstones that pass upward into lacustrine mudrocks, followed by a final fine-grained alluvial phase with extensive paleosol development. The upper part of each succession includes a second lacustrine interval, which is related either to a short-lived humid climatic period, or downstream damming of the exit for the fluvial systems of both basins. North-south–trending normal faults and rare synsedimentary rotation and slump structures affect the basin fills.

The Minle and Chaoshui Basins are only two of a series of Late Jurassic–Early Cretaceous strike-slip–related basins in this region that nucleated on three basement blocks, Tarim, Qilian Shan, and Alashan. All of the basins are characterized by a nonmarine, alluvial-lacustrine fill, controlled by a combination of strike-slip and normal faults. From an analysis of the distribution, orientation, and motion sense of subsurface and exposed faults we conclude that three types of strike-slip–related basins are present: pull-apart basins (Minle, Huahai-Jinta, Chaoshui), transtensional basins (Southwest Badanjilin, northern Wuwei), and a third type that developed between divergent strike-slip faults of opposing motion senses. We term this type “extrusion fault-wedge basins” (Jiuquan, Bayanhaote, western Wuwei).

The cause of Late Jurassic to Early Cretaceous strike-slip and extension in this region is interpreted to be the Lhasa block–Asia collision. Compression arising from this event is speculated to have caused eastward extrusion of the crust of the Hexi Corridor and Alashan. Deformation was accommodated by a 25° counterclockwise rotation of the Alashan with respect to the remainder of the North China block; thrusting occurred in the intervening Helan Shan. The extension in the Hexi Corridor occurred at the same time as vast foreland basins formed to the west (Tarim) and east (Ordos), and while extension affected much of eastern Mongolia and northeastern China.

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