Search

The Sikouzi Section is located towards the northern limits of the East Asian summer monsoon, providing the opportunity of placing the stratigraphic record into the context of the East Asian summer monsoon history. We present here the results of the details of the sedimentology of the Neogene succession of the section and use these to provide insights into the evolving history of the East Asian summer monsoon. The record is marked by a strongly expressed early Miocene lacustrine phase. A well-defined evaporate bed defines the top of the lacustrine succession, marking the onset of more arid conditions during the middle Miocene. The overlying succession is dominated by a series of alluvial packages, extending into the late Pleistocene with varying stratigraphic architectures and including a subordinate lacustrine component. Given the regional setting, the onset of drier conditions during the middle Miocene must relate to a downturn of summer monsoon activity. We focus on the question: what 'forced' this palaeoclimate event? Earlier biostratigraphic work places the explanation of this change into the context of the global-scale middle Miocene climate reorganisation. Here we explore this question in the context of regional-scale climate dynamics and propose that the onset of drier conditions over the study area was a response to atmospheric subsidence driven by circulation changes related to the growth of the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

[Display omitted] • Onset time of the basin was the late Miocene to early Pliocene (∼5.8–4.6 Ma). • Multiple depocenters existed in the basin and intergraded to one in the Quaternary. • Eastward migration of the depocenter records the collision between the Pamir and South Tian Shan. The Pamir salient is the preeminent example of an intracontinental collision and defines the western end of the Himalayan-Tibetan orogen. Previous work has paid much attention to reveal the internal evolution of the Plateau. However, the structural growth and expansion of the Northern Pamir still have several unknowns. To address this process of the indentation, we describe the architecture of the Wupoer Piggyback Basin (WPB), the westernmost tip of the Tarim Basin, in between the northeastern Main Pamir Thrust (MPT), and the Pamir Frontal Thrust (PFT). The geometry of the WPB growth strata and its relationship with the compressive structures were explored through six seismic sections, five cutting the WPB along dip and one along strike. According to the sense prevailing in the literature, we define the onset of a piggyback basin with the first evidence of tectonic deformation within the basin fill. Interpreted from the seismic sections and field work, an unconformity between the Atushi Fm. and the underlying strata marks the base of the WPB, dated the onset of the basin at the latest Miocene to early Pliocene (∼5.8–4.5 Ma). The growth strata were separated into 6 units above the unconformity (G1-G6). The relative isopach maps reveal the existence of three main depocenters, evolving to a single one in the Quaternary. The structural interpretation documents the PFT is significantly segmented by transfer faults and lateral ramps. The eastward migration of the depocenter since the Quaternary points to the oblique collision between the Pamir and the South Tian Shan and gradual encroachment of deformation towards the east. [ABSTRACT FROM AUTHOR]