Discovery of the Lower Cretaceous aeolian sandstones in the Wulong Formation in Yichang, Hubei Province, and its provenance

Abstract

Objective Eolian sandstones were widely developed in the middle latitudes of China during the Cretaceous era, which indicated the existence of subtropical desert belts. Studies on the age, distribution, provenance, and paleowind directions of Cretaceous aeolian sandstones would be helpful for the reconstruction of paleogeography and paleoclimate in East Asia during different periods of the Cretaceous era. Methods Here, we report the origin and provenance of a >40 m-thick sandstone layer within the Lower Cretaceous Wulong Formation (K1w) in Yichang, Hubei Province by systematically investigating its sedimentary facies in the field, particle size distribution, quartz grain surface textures, and detrital zircon U-Pb chronology. Results The results show that ① The Cretaceous sandstones were developed distal to an alluvial fan system that formed on the western margin of the Jianghan Basin. The thickness of the sandstones outcropped over 40 meters, with large scale high angle cross-bedding, and its grain size is extremely uniform. These sedimentary characteristics are in accordance with modern aeolian sandstones. ②Scanning election microscope images show that the quartz grains are generally well rounded, with disk-shaped and crescent-shaped impact scars and microfeatures caused by dissolution and precipitation on their surface, and these features are consistent with aeolian sands. ③ Four major age peaks were shown at~2.46 Ga, ~1.85 Ga, ~780 Ma and~170 Ma in the detrital zircon spectrum of the sandstones in the Wulong Formation. These peaks are consistent with the zircon ages of the Qinling-Dabie Orogen Belt and the sedimentary cover of the Huangling Dome, indicating that the sandstones may be mainly derived from the erosion of the Nanhua-Jurassic strata after the uplift of the Huangling Dome, as well as erosions from the Qinling-Dabie Orogen. ④ The youngest zircon grain in the sandstone was (119.9±2.8) Ma, indicating that the age of the Wulong Formation was not earlier than the late Early Cretaceous and was consistent with the conclusion from geological survey which considered the Lower Cretaceous Wulong Formation. Conclusion These results show that the sandstones were desert deposits that developed at the margin of diluvial fan of arid basin under the late Early Cretaceous arid climate, indicating that the Yichang area of Hubei Province was within the zonal deserts since the Early Cretaceous period under the influence of the subtropical high.

Keywords

• cretaceous area
• eolian sandstones
• detrital zircon
• provenance
• planetary wind system
• yichang, hubei province