Geological and chronostratigraphic overview of the Upper Triassic and Jurassic successions of the Junggar Basin, NW China

Abstract

Abstract The vast, widely exposed terrestrial (lacustrine to fluvial) Upper Triassic–Jurassic (except Tithonian) successions of the Junggar Basin not only record most of the stratigraphic boundaries of the Upper Triassic and Jurassic, including the Triassic–Jurassic boundary and the Hettangian–Sinemurian, Sinemurian–Pliensbachian, Pliensbachian–Toarcian, Lower–Middle Jurassic, Middle–Upper Jurassic and Oxfordian–Kimmeridgian boundaries, but also record a range of geological, organic, palaeogeographic and palaeoclimatic events known to have happened globally in the Late Triassic and Jurassic. The Triassic–Jurassic boundary is placed in the stratigraphic interval of the first occurrence of Retitriletes austroclavatidites and Callialasporites dampieri and the last occurrence of Lunatisporites rhaeticus . The end-Triassic mass extinction is characterized by the disappearance of most of the sporomorph and macro-plant taxa. The end-Triassic mass extinction occurred before the first occurrence of the sporomorph Cerebropollenites thiergartii , and ended after its appearance when life began to revive. The Junggar Basin was situated at a high latitude during the Late Triassic–Early Jurassic Pliensbachian ‘hothouse’ and ‘greenhouse’ periods. The Late Triassic–Mid Jurassic Bajocian was humid and warm, and rich in coal swamps, except the Toarcian, which yields little coal because it was relatively warmer and drier. It became arid from the early Late Jurassic Oxfordian.