Tuesday, May 31, 2016

Evidence of Extreme Aridification Across the Jurassic/Cretaceous Boundary From North China

Jurassic–Cretaceous terrestrial transition red beds in northern North China and their implication on regional paleogeography, paleoecology, and tectonic evolution


xu et al


Craton are associated with a number of major geological issues that remain controversial, such as paleogeography, biotic transition, and tectonic evolution. Based on previous studies and new progress related to stratigraphy, sedimentology, provenance, biotas, and tectonics, this paper performs a comprehensive review of the red beds in the northern North China Craton represented by the Tuchengzi/Houcheng/Daqingshan Formation (ca. 154–137 Ma) and offers some new perspectives. Based on the 15 measured sections, five facies units including alluvial fan, fluvial, delta, lacustrine, and eolian facies have been recognized and described in detail. Provenance analysis indicates that the red beds were derived from local sources. Deposits in the basins in the eastern Yinshan–Yanshan orogenic belt were derived mainly from volcanic rocks of the Middle–Late Jurassic Tiaojishan Formation and the Mesoproterozoic–Early Paleozoic carbonate, siliceous, and clastic rocks present around the basin, especially in the north. In contrast, sediments in the basins in the western Yinshan–Yanshan orogenic belt were provided predominantly by the Neoarchean–Paleoproterozoic metamorphic rocks exposed mainly in the north of the basin. Paleocurrent features in different regions show characteristics of a localized convergent paleo-drainage system, suggesting that a series of relatively independent small- to mid-scale basins developed in the northern North China Craton. The east–west-trending Yinshan–Yanshan orogenic belt, formed in the late Middle Jurassic, uplifted successively and constituted a paleogeographic highland in northern North China during the Jurassic–Cretaceous transition time. The presence of eolian deposits in the early Early Cretaceous indicates degradation of the severe arid and hot environment, which may have been an essential factor in the dying out of the Yanliao Biota. Combined with regional Late Jurassic–Early Cretaceous A-type granites, mafic dykes, and metamorphic core complexes and rift basins, this suggests that the Jurassic–Cretaceous transition red beds were formed in an extensional tectonic setting controlled by the post-orogenic collapse of the Mongol–Okhotsk orogenic belt.

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