Depositional evolution and provenance analysis of the early to middle Jurassic Tiaohu-Malang depressions, Santanghu Basin, Xinjiang

Key words: 
• Santanghu Basin /
• Tiaohu Depression /
• Malang Depression /
• braided river delta /
• provenance analysis /
• heavy mineral /
• zircon U-Pb dating

Abstract: The Santanghu Basin is an important oil and gas exploration area in northern Xinjiang, and a good understanding of sedimentary facies, sandbody distribution and associated provenance system within the basin play an important role in guiding the oil and gas exploration and development of the study area. This study uses core and well logging data to systematically study the distribution characteristics and depositional evolutions for the lower to middle Jurassic Tiaohu-Malang depressions in the Santanghu Basin. Additionally, heavy minerals and detrital U-Pb dating were combined to analyze the provenance for key intervals. During the lower to middle Jurassic, the Tiaohu-Malang depressions was mainly in a braided-river deltaic depositional environment. The Badaowan Formation was characterized by widespread distribution of braided-river delta fronts due to the large lacustrine basin. The sedimentary system was more developed in the northern part of Tiaohu Depression and extends far to the south, while the southern system has a limited distribution. The sedimentary system in the northern and southern parts of the Malang Depression extends a short distance into the depression. The Sangonghe Formation was dominated by isolated distributary channel deposits on the braided delta front with decreased lacustrine basin. As the lacustrine basin of the Tiaohu Depression migrated southward during the early Xishanyao time, a large area of lower delta plain developed in the north, and delta front developed in the central and southern parts. In the Malang Depression, the braided river delta fronts in the north are contiguously distributed, while the sand bodies in the south are relatively isolated. The analysis of heavy minerals and zircon U-Pb ages suggest that main sediments in the northeastern Tiaohu Depression were originated from the western Erdelunjin Mountains through a long transport distance during the lower Jurassic period. In the northern Malang Depression, the source-sink system had two possible sediment transport paths in the middle Jurassic time. Sediments were transported from the eastern part of the Erdelunjin Mountains and deposited near the Shayisubei and the Chahaquan area, and they were subsequently transported and deposited to the northern part of the Malang Depression as the area were uplifted. Another possible explanation is that sediments flowed from the eastern Erdelunjin Mountains into the northern part of the Malang Depression along the low paleotopographic areas with some sediments contributed from the Shayisubei Mountains.