Flexural subsidence by 29 Ma on the NE edge of Tibet from the magnetostratigraphy of Linxia Basin, China

This study provides a detailed magnetostratigraphic record of subsidence in the Linxia Basin, documenting a 27 Myr long sedimentary record from the northeastern edge of the Tibetan Plateau. Deposition in the Linxia Basin began at 29 Ma and continued nearly uninterruptedly until 1.7 Ma. Increasing rates of subsidence between 29 and 6 Ma in the Linxia Basin suggest deposition in the foredeep portion of a flexural basin and constrain the timing of shortening in the northeastern margin of the plateau to Late Oligocene–Late Miocene time. By Late Miocene–Early Pliocene time, a decrease in subsidence rates in the Linxia Basin associated with thrust faulting and a 10° clockwise rotation in the basin indicates that the deformation front of the Tibetan plateau had propagated into the currently deforming region northeast of the plateau.     

Tectonic uplift and sedimentary evolution of the Jiuxi Basin in the northern margin of the Tibetan Plateau since 13 Ma BP

Sediments shed from the northern margin of the Tibetan Plateau, the Qilian Mountains, are widely deposited in the foreland basin, the Jiuxi Basin, archiving plenty of information about the mountain surface uplift and erosion history. The Laojunmiao section, 1960 m thick, representing the upper sequence of the Cenozoic basin sediments, is paleomagnetically dated to about 13-0 Ma BP. Detailed sedimentary study of this sequence has revealed five sedimentary facies associations which determine four stages of sedimentary environment evolution. They are: (I) the half-deep lake system before 12.18 Ma BP, (II) the shallow lake system between 12.18 and 8.26 Ma BP, (III) the fan delta dominated sedimentary system in dry climate between 8.26 and 6.57 Ma BP, and (IV) alluvial fan system since 6.57 Ma BP. The associated mountain erosion and uplift are suggested to have experienced three phases, that is, tectonic stable (13-8.26 Ma BP), gradual uplift (8.26-<4.96 Ma BP), and rapid intermittent uplift (>3.66-0 Ma BP). The uplift at ∼3.66 Ma BP is of great importance in tectonics and geomorphology. Since then, tectonic uplift and mountain building have been accelerated and become strong intermittent. At least three significant tectonic events took place with ages at <1.80-1.23, 0.93-0.84 and 0.14 Ma BP, respectively. Thus, the uplift of the northern Tibetan Plateau is a complex process of multiple phases, unequal speed and irregular movements.

     

临夏盆地新生代沉积物粒度记录与亚洲内陆干旱化

临夏盆地毛沟剖面高分辨率粒度记录研究表明,29-7.4Ma间,临夏盆地的古气候一直保持相对稳定,而其中短暂的沉积相的改变是盆地对该期间青藏高原构造隆升事件的响应;从7.4Ma开始,流域外的风尘物质开始逐步被带人盆地,并经过了6.4Ma和5.3Ma的两次加速过程,揭示了我国西北内陆干旱气候可能从7.4Ma左右开始,且在6.4Ma和5.3Ma左右经过两次加强.通过与青藏高原构造隆升事件记录和全球气候记录对比。揭示高原在9-7Ma开始的逐步隆升和期后的阶段性加速隆升以及同期开始的全球变冷,尤其北极冰盖的形成和扩张可能是亚洲内陆干旱化的重要驱动机制.     

Detrital zircon provenance evidence for an early Permian longitudinal river flowing into the Midland Basin of west Texas

ABSTRACT

Collision of Gondwana and Laurentia in the late Palaeozoic created new topography, drainages, and foreland basin systems that controlled sediment dispersal patterns on southern Laurentia. We utilize sedimentological and detrital zircon data from early Permian (Cisuralian/Leonardian) submarine-fan deposits in the Midland Basin of west Texas to reconstruct sediment dispersal pathways and palaeogeography. New sedimentological data and wire-line log correlation suggest a portion of the early Permian deposits have a southern entry point. A total of 3259 detrital zircon U-Pb and 357 εHf data from 12 samples show prominent groups of zircon grains derived from the Appalachian (500–270 Ma) and Grenville (1250–950 Ma) provinces in eastern Laurentia and the peri-Gondwana terranes (800–500 Ma) incorporated in the Alleghanian-Ouachita-Marathon orogen. Other common zircon groups of Mesoproterozoic-Archaean age are also present in the samples. The detrital zircon data suggest throughout the early Permian, Appalachia and Gondwana detritus was delivered by a longitudinal river system that flowed along the Appalachian-Ouachita-Marathon foreland into the Midland Basin. Tributary channels draining the uplifted Ouachita-Marathon hinterland brought Gondwana detritus into the longitudinal river with headwaters in the Appalachians or farther northeast. This drainage extended downstream westward and delivered sediments into the Permian Basin near the west terminus of the Laurentia-Gondwana suture. Estimated rates of deposition and proportions of zircons from more local (Grenville) versus more distal (Pan-African) sources indicate that river strength decreased throughout early Permian time. Primary sediment delivery pathway was augmented by minor input from the Ancestral Rocky Mountains and wind deflation of fluvial sediments north and east of the basin. Slope failure associated with early Permian deposition in the southeastern margin of the Midland Basin triggered gravity flows leading to submarine fan deposition.