Sequence framework of two different kinds of margins and their response to tectonic activity during the Middle-Late Triassic, Ordos Basin

Abstract

Two kinds of margin respectively occur in the Ordos Basin during the Middle-Late Triassic (Yanchang Age), one is foreland margin developed under the background of flexural subsidence by thrusting intensively in the southwest margin, and the other is intracratonic basin margin by stable subsidence in northern and central parts of the basin. The Middle-Late Triassic YanchangFormation can be divided into four regional third-order sequences, which are separated by gentle angular unconformity or regional erosion surface, made up of lowstand system tract (LST), expanding system tract (EST) and highstand system tract (HST) from lower to upper within a sequence. But there are distinct differences of the sequence framework between the southwest margin and northern and central parts of the basin. The southwest margin develops heavy conglomerate layer and unconformity as a result of orogeny by thrusting, and the intracratonic basin margin by stable subsidence in the northern and central parts grows aggradational sandstone, conglomerate in fluvio-delta system and parallel unconformity. The depositional framework of southwest margin reflects the tectonic evolution from flexural subsidence by thrusting to rebounded uplift. The formation of sequence boundary is related to the resilient uplift and erosion. The sequence stratigraphic framework and depositional system tract configuration in the foreland basin are controlled by structural activity of the fold and thrust belt, and the sequence succession reflects episodic thrusting of the Middle-Late Triassic toward the foreland basin. The sequence evolution in northern and central parts reflects the depositional succession of fluvio-delta system under intracratonic background, composed of coarse-grained sediment in braided channel deposit at the lower, meandering channel deposit in the middle and fine-grained sediment in the flood plain at the upper, dominated by lake level fluctuation. During the deposit of the LST in the intracraton basin, accommodation space is limited, and results in abundant fluvial sediment migration laterally, erosion and transport, forming laterally sandstone composite and aggradational deposit on the alluvial plain, which constitutes specific erosion unconformity boundary. sequence architecture, tectonic response, basement structure, the Middle-Late Triassic (Yanchang Age), Ordos BasinAfter multi-phase rifting [1,2] , the North China Plate and South China Plate in the east of China collided in the Early Triassic Indosinian Stage [3][4][5][6] , which is continentcontinent collision related to Thetys and paleo-Pacific

Determining the Age of Terrace Formation Using Luminescence Dating—A Case of the Yellow River Terraces in the Baode Area, China

“…The Ordos Plateau, with an area of 320,000 km 2 located in the western part of the North China block, is a relatively stable rigid block ( Figure 1a) [27,28]. It is bounded by a series of marginal faults and orogenic belts [29][30][31][32][33][34]. The basement of the plateau is composed of Archean and Proterozoic metamorphic rocks that are overlain by Cambrian and Ordovician marine carbonates with the lack of Silurian and Devonian strata.…”

Reservoir Potential of Deep‐water Lacustrine Delta‐front Sandstones in the Upper Triassic Yanchang Formation, Western Ordos Basin, China

“…The intracratonic Ordos Basin in north-central China Yang et al, 2007;Wang and Al-Aasm, 2002) is composed of a number of first-order structural units: the Yimeng and Weibei uplifts, the Jinxi foldbelt, the Yishan slope, the Tianhuan syncline, and an unnamed western fold-and-thrust belt (Yang et al, 2005) (Fig. 1).…”

Mesozoic structural evolution of the Hangjinqi area in the northern Ordos Basin, North China

“…North of the NCC, the Suolon Orogenic Belt marks the Permian collision between the NCC and the Mongolian arc, which may have experienced continued convergence well into the Triassic, as evidenced by shortening in the northern Ordos Basin (Darby et al, 2001;Davis and Darby, 2010). On the southern margin of the NCC, the EeW Qinling-Dabie Orogenic Belt marks a Permian-Late Triassic collision between the NCC and the Yangtze Plate that drove shortening (Ames et al, 1996;Zhang et al, 1989;Meng and Zhang, 1999;Ratschbacher et al, 2000) and foreland basin subsidence in the southern part of the Ordos Basin as well as on the NCC (Yang et al, 2007. In addition, approximately 800 km southwest of the Ordos Basin, the Jinsha Orogenic Belt marks the latest Triassic collision of the Qiantang Plate, which was preceded by Late Paleozoic through Triassic northward subduction beneath the Kunlun Shan and Qaidam Basin (Ritts and Biffi, 2001;Ritts et al, 2004).…”