Stratigraphy of the Triassic–Jurassic Boundary Successions of the Southern Margin of the Junggar Basin, Northwestern China

Abstract

The Triassic–Jurassic (Tr–J) boundary marks a major extinction event, which (∼200 Ma) resulted in global extinctions of fauna and flora both in the marine and terrestrial realms. There prevail great challenges in determining the exact location of the terrestrial Tr–J boundary, because of endemism of taxa and the scarcity of fossils in terrestrial settings leading to difficulties in linking marine and terrestrial sedimentary successions. Investigation based on palynology and bivalves has been carried out over a 1113 m thick section, which is subdivided into 132 beds, along the Haojiagou valley on the southern margin of the Junggar Basin of the northern Xinjiang, northwestern China. The terrestrial Lower Jurassic is conformably resting on the Upper Triassic strata. The Upper Triassic covers the Huangshanjie Formation overlaid by the Haojiagou Formation, while the Lower Jurassic comprises the Badaowan Formation followed by the Sangonghe Formation. Fifty six pollen and spore taxa and one algal taxon were identified from the sediments. Based on the key‐species and abundance of spores and pollen, three zones were erected: the Late Triassic (Rhaetian) Aratrisporites‐Alisporites Assemblage, the Early Jurassic (Hettangian) Perinopollenites–Pinuspollenites Assemblage, and the Sinemurian Perinopollenites–Cycadopites Assemblage. The Tr–J boundary is placed between bed 44 and 45 coincident with the boundary between the Haojiagou and Badaowan formations. Beds with Ferganoconcha (?), Unio–Ferganoconcha and Waagenoperna–Yananoconcha bivalve assemblages are recognized. The Ferganoconcha (?) bed is limited to the upper Haojiagou Formation, Unio–Ferganoconcha and Waagenoperna–Yananoconcha assemblages are present in the middle and upper members of the Badaowan Formation. The sedimentary succession is interpreted as terrestrial with two mainly lake deposit intervals within Haojiagou and Badaowan formations, yielding fresh water algae and bivalves. However, the presence of brackish water algae Tasmanites and the marine‐littoral facies bivalve Waagenoperna from the Badaowan Formation indicate that the Junggar Basin was influenced by sea water caused by transgressions from the northern Tethys, during the Sinemurian.

Reconstructing the Late Palaeozoic – Mesozoic topographic evolution of the Chinese Tian Shan: available data and remaining uncertainties

“…Sha et al, 2011). Indeed, from the Middle Triassic to the Middle Jurassic, a widespread coalbearing sediment sequence developed throughout the Tian Shan and surrounding basins, most probably in a warm humid climate (Hendrix et al, 1992;Pfretzschner et al, 2005;Li et al, 2004;Tükten et al, 2004;Ashraf et al, 2010;Pan et al, 2013. During the same period, the relative topography between the range and the northern margin of the Tarim decreased while the Junggar Basin widened towards the south Fang et al, 2005;Li and Peng, 2010;Yang et al, 2012).…”

“…), a brackish-water fauna and flora (Waagenoperma bivalve assemblages and Tasmanites sp. alga) developed in some restricted areas along the southern margin of the Junggar Basin (Sha et al, 2011). Pan et al (2013) suggested that small short-lived transtensional basins formed through reactivation of the North Tian Shan Fault.…”

“…The Permian magmas were then emplaced in a post-collisional setting and several authors suggested that slab break-off and lithospheric delamination may explain their mantle signature (Han et al, 1999(Han et al, , 2009Chen and Jahn, 2004;Zhao et al, 2008;Shu et al, 2010). By Late Carboniferous -Early Permian, the Junggar Basin, disconnected from the Palaeo-Tethys ocean (Sha et al, 2011), initiated as a half-graben structure in a post-collisional extensional setting (Qiu et al, 2005(Qiu et al, , 2008Yang et al, 2012).…”

Latest Triassic climate humidification and kaolinite formation (Western Carpathians, Tatric Unit of the Tatra Mts)

“…The strati graphic pat terns of car bon iso tope in or ganic matter may be com pared with ichnological and palynological data (Kuerschner et al, 2007;Ruckwied et al, 2008;Ruckwied and Götz, 2009;Michalik et al, 2010, Götz et al, 2011Sha et al, 2011) and with the geo chem is try of ter res trial shale. Car bon isotope anal y sis is a gen er ally ac cepted in di ca tor of chages in the global car bon cy cle es pe cially in ma rine se quences (e.g., McRoberts, 1994;Pálfy et al, 2001;Ward et al, 2004Ward et al, , 2007.…”

The Triassic to Early Jurassic palynological record of the Tarim Basin, China

“…Core and interval: Lunnan-1, 4782-4771 m. Wang 1986, 1990;Sha et al 2011Sha et al , 2015 and the Ordos Basin (Qu 1980;Liu et al 1981). However, Zebrasporites spp.…”