Magnetostratigraphic and rock magnetic study of the Neogene upper Yaha section, Kuche Depression (Tarim Basin): Implications to formation of the Xiyu conglomerate formation, NW China

Abstract

Magnetostratigraphic study of 251 horizons through the younger Yaha succession in the Kuche Depression of the Tarim Basin, NW China, lying beneath a massive regionally extensive (Xiyu) conglomerate formation identifies nine reversed and eight normal polarity chrons correlating with the Geomagnetic Polarity Time Scale to show that deposition spanned the interval ∼5.3 to ∼1.7 Ma. Sedimentation rates fell episodically from ∼49 to ∼24 cm/kyr as neotectonic deformation in the southern Tian Shan thrust belt became focused on two major anticlines with the northern (Qiulitage) anticline being initiated at ∼5.5 Ma and developing a northern hinged limb that embraces the basal part of the studied section. Rock magnetic parameters show multiple signatures of lithologic change, deformation, burial diagenesis, and climate with the latter identifying an early Pliocene warm/humid interval followed by cooling and desertification after ∼2.6 Ma. Diachronous commencement of Xiyu conglomerate deposition ranged from mid‐Miocene in the north of the southern flank of the Tian Shan to Pleistocene in the south advancing as a clastic wedge derived from the uplifted range front to the north. This southward progradation was not climatically controlled although climatic effects may have modulated deposition during the Pleistocene. Uplift in the Tian Shan at ∼16–15 Ma correlates with rapid increase in sedimentation rate and episodic increases occurred subsequently until the initiation of the Qiulitage anticline. Reduced rates since ∼5.0 Ma contrast with increases more commonly recorded in foreland basins and have been controlled by accelerated growth of this regional structure counterbalancing uplift of the mountain front to the north.