Search

This paper addresses the Phanerozoic tectonic evolution of the western Tarim Basin based on an integrated stratigraphic, structural and tectonic analysis. P-wave velocity data show that the basin has a stable and rigid basement. The western Tarim Basin experienced a complex tectonic evolutionary history, and this evolution can be divided into six stages: Neoproterozoic to Early Ordovician, Middle Ordovician to Middle Devonian, Late Devonian to Permian, Triassic, Jurassic to Cretaceous and Paleogene to Quaternary. The western Tarim Basin was a rift basin in the Neoproterozoic to Early Ordovician. From the Middle Ordovician to Middle Devonian, the basin consisted of a flexural depression in the south and a depression that changed from a rift depression to a flexural depression in the north during each period, i.e., the Middle–Late Ordovician and the Silurian to Middle Devonian. During the Late Devonian to Permian, the basin was a depression basin early and then changed into a flexural basin late in each period, i.e., the Late Devonian to Carboniferous and the Permian. In the Triassic, the basin was a foreland basin, and from the Jurassic to Cretaceous, it was a downwarped basin. After the Paleogene, the basin became a rejuvenated foreland basin. Based on two cross sections, we conclude that the extension and shortening in the profile reflect the tectonic evolution of the Tarim Basin. The Tarim Basin has become a composite and superimposed sedimentary basin because of its long-term and complicated tectonic evolutionary history, highly rigid and stable basement and large size. [ABSTRACT FROM AUTHOR]

The Holocene hydrological regime on the Heixiazi Island is critical for understanding the evolution of the East Asian summer monsoon (EASM) for the island's climate-sensitive location on the northern fringe of the EASM domain. In this paper, a marsh depression on the central island was selected to reconstruct the locally hydrological variation and to discuss its indications for the Holocene EASM evolution. This work is based on multi-proxy (magnetic susceptibility, grain size, loss-on-ignition, and carbonate content) analyses of 22 modern sedimentary samples with a water-level gradient of 0–66 cm and 100 cored sedimentary samples covering last ~ 9.0 ka BP. The proxies' hydrological significance was previously interpreted by the 22 modern samples using linear regression equations to construct their relationships to water-level changes. Among these proxies, the magnetic susceptibility, carbonate content, as well as the Md and sand fraction of grain size exhibit high-level relationships against the water-level changes with R2 > 0.6. Thus, these four proxies' linear-regression equations were selected and used on the 100 cored samples, and the Holocene water-level changes in the studied depression were quantitatively reconstructed. It shows that two relatively high water-level stages with strengthened EASM occurred during 8.0–4.5 ka BP and 3.0–1.4 ka BP, which were alternated by three low water-level stages with declined EASM during ~ 9.0–8.0 ka BP, 4.5–3.0 ka BP, and 1.4–0 ka BP, respectively. Among these fluctuations, the highest water-level stage with most strengthened EASM which is defined as the Holocene Monsoon Maximum occurred during 6.4–4.5 ka BP. Such a new evolution pattern of the EASM can be further supported by a large variety of records from monsoon-margin regions. We suggest the Holocene EASM evolution was generally associated with the thermal conditions in both the inner Eurasia landmass and the West Pacific Ocean, with an exception of the weak EASM before 8.0 ka BP due to the enhanced Siberia High with the dominance of the Eurasia ice sheet in the early Holocene. [ABSTRACT FROM AUTHOR]

Thermal evolution of source rocks and dynamic sealing evolution of cap rocks are both subjected to tectonic evolution. The marine sequences in South China have experienced superposed structural deformation from multiple tectonic events. To investigate the effectiveness of preservation conditions, it is of great importance to understand the controls of key tectonic events on the dynamic evolution of cap rocks. This paper discusses the controls of Late Jurassic-Early Cretaceous (J-K) tectonic event on source and cap rocks in marine sequences in South China based on the relationships between J-K tectonic event and the burial history types of the marine sequences, the hydrocarbon generation processes of marine source rocks, the sealing evolution of cap rocks, the preservation of hydrocarbon accumulations, and the destruction of paleo-oil pools. The study has the following findings. In the continuously subsiding and deeply buried areas during the J-K period, marine source rocks had been generating hydrocarbons for over a long period of time and hydrocarbon generation ended relatively late. At the same time, the sealing capacity of the overburden cap rocks had been constantly strengthened so that hydrocarbons could be preserved. In the areas which suffered compressional deformation, folding and thrusting, uplifting and denudation in J-K, the burial history was characterized by an early uplifting and the hydrocarbon generation by marine source rocks ended (or suspended) during the J-K period. The sealing capacity of the cap rocks was weakened or even vanished. Thus the conditions for preserving the hydrocarbon accumulations were destroyed. The continuously subsiding and deeply buried areas during the J-K period are the strategic precincts of the petroleum exploration in marine sequences in South China. [ABSTRACT FROM AUTHOR]

The Chengjiang Formation is the earliest continental clastic deposit after the Jinning Orogeny in central Yunnan Province, and therefore its accurate depositional age is significant for understanding the formation and evolution of the Neoproterozoic rift basins in southern China. However, hampered by accuracy of the dating technique, the existing age data for the Chengjiang Formation are not very reliable. A large number of magmatic zircons were obtained from the tuff interbed in the lower part of the Chengjiang Formation in Jinyang area and the bottom part of the Chengjiang Formation in Dongchuan area, central Yunnan Province, and high-precision SHRIMP U-Pb dating was carried out on these zircons. The results show that the weighted mean Pb/U ages are 797.8±8.2 and 803.1±8.7 Ma respectively. In combination with related geological evidence, it has been demonstrated that the bottom boundary age of the Chengjiang Formation should be 800±5 Ma, whereas the top boundary age could be ca 725 Ma. By synthetically analyzing the latest age data for the relevant strata, it has been confirmed that the Chengjiang Formation should be correlated with the Suxiong Formation and the Kaijianqiao Formation in western Sichuan Province, the Liantuo Formation in the middle and lower Yangtze, the Hongchicun Formation and the Shangshu Formation in northern Zhejiang Province, the Puling Formation in southern Anhui Province, the Luokedong Formation and the Majianqiao Formation in northwestern Jiangxi Province, the Wuqiangxi Formation in northwestern Hunan Province, the Fanzhao Formation and the Qingshuijiang Formation in southeastern Guizhou Province, and the Sanmenjie Formation and the Gongdong Formation in northern Guangxi Province. Sedimentary cycle analysis shows that the sedimentary filling sequence of the Neoproterozoic rift basins in southern China can be divided into four cycles. Among them, Cycle II began at ca. 800 Ma, accompanied by intensive tectonic-thermal events. The zircon U-Pb ages from the bottom of the Chengjiang Formation reported in this paper indicate that the Neoproterozoic Kangdian rift subbasin probably started to develop at ca. 800 Ma and therefore missed Cycle I of the Neoproterozoic sedimentary filling sequence in southern China. [ABSTRACT FROM AUTHOR]