Sedimentary Characteristics and Development Model of the Red Layer and Gypsum-Salt Layer in the Paleogene Kumugeliemu Formation, Kuqa Depression, Northwestern China

In recent years, extensive exploration efforts have revealed significant advancements in the geological formations of the Kuqa Depression. Particularly, the Paleogene Kumugeliemu Formation has exhibited the development of expansive red layer and gypsum-salt layer deposits. The combination of red layer sandstone, red layer mudstone, and gypsum-salt layers holds immense potential as a reservoir and cap association, thereby offering promising prospects for oil and gas exploration. However, the understanding of the sedimentary system and model governing this formation remains limited, impeding progress in the field of oil and gas exploration. To address this gap, this study delved into a detailed examination of the stratigraphy, depositional system, and model of the Kumugeliemu Formation, through the application of core samples, logging data, and seismic analysis. The primary objective was to establish a comprehensive theoretical foundation for future oil and gas exploration endeavors targeting the Kumugeliemu Formation. The findings unveiled a distinct division of the Kumugeliemu Formation into two 3rd order sequences, each characterized by a lowstand systems tract, a transgressive systems tract, and a highstand systems tract. Moreover, all the systems tracts was further subdivided into 14 parasequence sets. During the depositional period of the Kumugeliemu Formation, the ‘alluvial fan, delta, salt lake’ deposition system developed from the periphery to the central region of the Kuqa Depression. The alluvial fan mainly exhibited braided channel sedimentary microfacies, while the delta region indicated plain distributary channel, submerged distributary channel, and interdistributary sedimentary microfacies. The salt lake area was characterized by shore-shallow lacustrine mud, beach-bar, salt mud flat, and salt flat sedimentary microfacies. Throughout the deposition of the Kumugeliemu Formation, the climate of the Kuqa Depression oscillated between arid and humid conditions. During arid periods, the depression experienced diminished water body extent, heightened salinity levels, and extensive distribution of salt flats and salt mud flats within the basin, with the alluvial fan and delta deposits primarily confined to the basin margins. Conversely, during the humid period, the depression experienced an expansion in water body extent, leading to a decrease in salinity levels. The distribution of salt flat and salt mud flat deposits within the basin diminished, while alluvial fan and delta deposits advance extensively across the basin. The establishment and spatial arrangement of the sedimentary system within the Kumugeliemu Formation were governed by a complex interplay of certain factors, such as the semi-closed paleotectonic pattern, the paleoclimatic conditions of both dry and wet alternation, and the salt source supply brought by the transgression of the Paleo-Tethys Ocean. The findings of this study offered not only a valuable reference framework for the prospective exploration of hydrocarbon resources within the Kumugeliemu Formation of the Kuqa Depression, but also potential insights into the evolution of similar depressions in other basins.