Cenozoic basin-filling evolution of the SW Tarim Basin and its implications for the uplift of western Kunlun: Insights from (seismo)stratigraphy

Highlights

• Onset of Cenozoic SW Tarim foreland basin since the Keziluoyi period.

• Foredeep of the foreland basin migrating northward by >~56 km.

• Upper crustal Tarim/W. Kunlun boundary is a northward movable feature.

• >~56 km lower Tarim Plate has underthrusted southwards beneath W. Kunlun.

Abstract

The western Kunlun Mountains and the adjacent southwestern Tarim Basin define the northwestern boundary of the intensely deformed Cenozoic Tibetan Plateau, and thus should bear important information on the growth processes of the NW Tibetan Plateau. In this study, the integration of a stratigraphic investigation of the Cenozoic Keliyang succession section and a seismostratigraphic analysis on the seismic reflection profile reveal the sedimentary evolution and basin-filling processes of the southwestern Tarim Basin. Our results suggest a significant depositional shift from marine facies during the depositional periods of the Aertashi to Bashibulake Formations to continental facies during the depositional periods of the Keziluoyi to Xiyu Formations. This shift, which corresponds to southward depositional thickening, has been attributed to the uplift of South Kunlun and the onset of foreland basin subsidence along the southwestern Tarim Basin. Strata from the Keziluoyi to Xiyu Formations form an upward-coarsening sequence that is interrupted by a subordinate upward-thinning sequence in the Anjuan Formation. These results, in combination with the northward migration of the depocenter by at least ~56 km since the depositional period of the Artux Formation and previous studies on basinward deformation propagation, demonstrate that the tectonic loading of the western Kunlun has propagated northward to North Kunlun, which suggest expansion of the NW Tibetan Plateau since this period. We posit that the upper-crustal boundary between western Kunlun along the NW Tibetan Plateau and the Tarim Basin is a northward movable feature. This would support the hypothesis that the substantial lower Tarim Plate (>~56 km if calculated from the magnitude of the northward depocenter migration) has underthrusted southward beneath western Kunlun.

Introduction

The India-Eurasia collision since the early Cenozoic (Rowley, 1996; Ding et al., 2005, Ding et al., 2016; Najman et al., 2010, Najman et al., 2016; DeCelles et al., 2014; Hu et al., 2012, Hu et al., 2015a, Hu et al., 2015b, Hu et al., 2016) has created the Tibetan Plateau (Dewey and Burke, 1973; Molnar and Tapponnier, 1975; England and Houseman, 1986; Yin and Harrison, 2000), which defines a wide intracontinental deformation zone that extends as far as thousands of kilometers north from the convergent front (e.g., Molnar and Tapponnier, 1975; Yin, 2010)(Fig. 1A). This wide intracontinental deformation zone has been termed the Circum-Tibetan Plateau Basin and Orogen System (CTPBOS; Jia, 2005, Jia, 2009; Jia et al., 2008; Chen et al., 2020, An et al., 2020). Understanding the Cenozoic evolution of the CTPBOS will enhance the knowledge on whether the northern plateau margin has remained steady or propagated northward to more distal regions (e.g., Yin and Harrison, 2000; Clark et al., 2010; Zuza et al., 2016; Tapponnier et al., 2001; Wang et al., 2014a, Wang et al., 2014b; Wang et al., 2017) and will have even broader implications for deciphering the characteristics of the plateau crust, which is either a rigid/rigid-plastic body (e.g., Peltzer et al., 1989; Avouac and Tapponnier, 1993; Peltzer and Saucier, 1996) or a continuum with a Newtonian or power-law rheology (e.g., England and McKenzie, 1982; England and Houseman, 1986; Zhang et al., 2007; Wright et al., 2004).

The western Kunlun Mountains (simplified as western Kunlun in the following text), which delimit the NW margin of the Tibetan Plateau and separate the plateau from the stable Tarim Basin to the north (Fig. 1A and B), supply a key region that constrains the plateau growth processes. During the last two decades, a wealth of studies have accumulated data on the lithospheric structures via geophysical investigations (e.g., Matte et al., 1996; Gao et al., 2000; Kao et al., 2001; Li et al., 2001, Li et al., 2002; Jiang et al., 2004, Jiang et al., 2013; Wittlinger et al., 2004), on deformation processes of the thrust belts via structural analyses (Cowgill, 2001; Li and Wang, 2002; Cowgill et al., 2003; Qu et al., 2005; He et al., 2005; Cui et al., 2008; Huang et al., 2011; Wei et al., 2013; Jiang and Li, 2014; Wang et al., 2014a, Wang et al., 2014b; Suppe et al., 2015; Li et al., 2016a, Li et al., 2016b; Cheng et al., 2017; Guilbaud et al., 2017; Laborde et al., 2019), on sedimentary processes via stratigraphic analyses (Zheng et al., 2000, Zheng et al., 2003, Zheng et al., 2006, Zheng et al., 2010, Zheng et al., 2015a; Yin et al., 2002; Jin et al., 2003; Sun and Liu, 2006; Sun and Jiang, 2013; Sun et al., 2009, Sun et al., 2015, Sun et al., 2016; Wei et al., 2013), and on exhumation processes via thermochronologic investigations (Sobel and Dumitru, 1997; Wang et al., 2003; Cao et al., 2013, Cao et al., 2014, Cao et al., 2015; Cheng et al., 2017; Li et al., 2019). Despite progress, the uplift history of western Kunlun remains controversial, with proposed Cenozoic uplift events varying from the Eocene to the Pliocene in previous studies (e.g., Sobel and Dumitru, 1997; Zheng et al., 2000; Yin et al., 2002; Bosboom et al., 2011, Bosboom et al., 2014a, Bosboom et al., 2014b, Bosboom et al., 2014c; Sun and Jiang, 2013; Cao et al., 2013, Cao et al., 2015; Wei et al., 2013; Jiang et al., 2013; Jiang and Li, 2014; Zheng et al., 2015a; Sun et al., 2015, Sun et al., 2016; Blayney et al., 2016, Blayney et al., 2019; Cheng et al., 2017; Zhang et al., 2018; Li et al., 2019). Whether these documented uplift events represent the gradual approach of the orogenic front or episodic uplift of western Kunlun remains to be determined (Wei et al., 2013; Cao et al., 2013, Cao et al., 2015; Blayney et al., 2016, Blayney et al., 2019). The former model predicts a gradual shift from low- to high-energy deposition and northward migration of foreland basin depocenters, which would support a northwardly movable plateau margin. In contrast, the latter model predicts episodes of high-energy deposition and a spatially steady but temporally fluctuating depocenter; these phenomena are consistent with a steady plateau margin.

Uplift of western Kunlun triggered substantial subsidence in the southwestern Tarim Basin where thick Cenozoic deposits have accumulated. These Cenozoic strata supply a continuous record for deciphering the evolution of western Kunlun. In this study, we investigate the sedimentology of the Keliyang Cenozoic succession to elucidate the sedimentary processes of the southwestern Tarim Basin, which is complemented by an analysis of a seismic reflection cross-section from the mountain front to the interior of the Tarim Basin to examine the basin subsidence processes (Fig. 1B). This integrated study sheds new light on the Cenozoic evolution of western Kunlun, and the results have regional implications for the growth processes of the NW Tibetan Plateau.