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Current Issue   2022 Vol.  11 No.  3 Published: 2022-07-20 Palaeoclimatology Lithofacies palaeogeography and sedimentology Tectonopalaeogeography and palaeotectonics Biopalaeogeography Lithofacies palaeogeography and sedimentology 315 Research status of lacustrine mudrock deposition constrained from astronomical forcing Qi Zhong, Jian-Guo Zhang, Dong Tang, Jian-hui Jiang, Jing-Jing Shen, Mu-Xin Cai, Pin-Xie Li The sources, transportation and depositional processes of lacustrine mudrock are still poorly understood. Existing studies have demonstrated the controlling effect of astronomical forcing on lacustrine mudrock deposition, but its depositional mechanism and evolution are still not systematically investigated. Most research related to astronomical forcing exclusively highlights the sedimentation of carbonate rocks in deep-water lacustrine setting, with insufficient attention paid to the thick organic-rich, deep-lake mudrock. With the increasing interest in exploration and development of shale oil and gas accumulations, it is urgent to deeply understand depositional rules of lacustrine mudrock. This study reviews sediment sources, depositional mechanism and evolution process of mudrock through expounding the correlations between the periodic changes of astronomical forces, the parameters of Earth orbital and mudrock compositions. By investigating the existing literature and using some actual data of Jiyang Depression, Bohai Bay Basin in East China, this study expounds on the influence of astronomical cycles on the deposition of lacustrine mudrock. Moreover, efforts are made to analyze the effects of various orbital parameters (e.g., precession, obliquity, and eccentricity with the periods ranging from tens of thousands years to million years) on the deposition of mudrock from small-scale (decimeters to meters) to large-scale (10s to 100s meters). Further, it is feasible to apply the high-precision isochronous stratigraphic correlation into clarifying the distribution of favorable shale oil and gas reservoirs. To conclude, this study enunciates the sedimentation of mudrock from a new perspective (astronomical forcing) and provides a direction for the research on sedimentation of fine-grained sedimentary rocks. 2022 Vol. 11 (3): 315-331 [Abstract] ( 161 ) [HTML 1KB] PDF (8718 KB)   ( 26 ) 332 Origin of soft-sediment deformation structures in Nihewan Basin De-Chen Su, Ai-Ping Sun, Zhao-Li Li, Song-Yong Chen, Zhen-Jie Wu The Nihewan Basin is a rift basin at the junction of northern Shanxi Province and northwestern Hebei Province in north China. The basin is known for its rich paleontological fossils and ancient human remains. There are also abundant soft-sediment deformation structures (SSDS) in the thick lacustrine sediments. Previously, most SSDS have been interpreted as ice-edge features or ignored entirely. Recently, the authors have carried out several field surveys in the Nihewan Basin and found that many SSDS are sandwiched between normal lacustrine strata at multiple sections. In the excavation pit at the 10th Locality of Maliang Site (ML10), 10 horizontal SSDS layers and two vertically developed geological features have been identified. Based on genesis analysis and related criteria, these features are divided into two categories: cryoturbation-triggered SSDS and earthquake-triggered SSDS. Among them, a special type of ancient ice-wedge pseudomorph (SSDS-8) of the ML10 is recognized in the basin for the first time. The other 9 horizontal SSDS are mainly caused by earthquake-triggered liquefaction and slumping. They can be further divided into 14 seismic event layers. These findings indicate that the tectonic activity in the Nihewan Basin is very strong and frequent, and there were cold periods in the geological history of the basin. At the same time, the SSDS with distinct morphological characteristics and stable horizontal distribution in the basin can be used as an important indicator of stratigraphic correlation. 2022 Vol. 11 (3): 332-359 [Abstract] ( 146 ) [HTML 1KB] PDF (62336 KB)   ( 23 ) 360 Diagenetic mineralogy and its effect on the reservoir properties of the sandstones of the Permian S120 block (Sulige gas field), Ordos Basin, NW China Qi Wan, Aiping Fan, Renchao Yang, Nils Lenhardt The characteristics of diagenetic minerals and their effects on reservoir quality of the tight sandstones of the Permian in Sulige gas field of the Ordos Basin were studied through observations on thin sections, scanning electron microscopy, energy dispersive spectroscopy analysis and electron microprobe analysis. Diagenetic minerals in the Permian sandstones consist of illite, kaolinite, chlorite, siliceous and calcite cements. Large amounts of intercrystalline pores between kaolinite and illite provide channels for acidic fluids flow and thereby were conducive to the formation of clastic solution pores, intergranular solution pores and composite pores. Authigenic chlorite occurs in the form of three morphotypes as grain-coating, pore-lining and pore-filling. Grain-coating and pore-lining chlorite with different crystal shapes occur as coatings on the framework grains. Pore-filling chlorite precipitated as discrete flaky plates in pore spaces. Quartz microcrystals developed but quartz overgrowth did not develop because of the occurrence of pore-lining chlorite. This, in turn, led to the preservation of primary pores by occupying potential nucleation sites for quartz overgrowth and thereby preventing quartz microcrystals from merging into quartz overgrowth. This process is regarded as the most important for influencing the quality of the lithophysical properties. Calcite cement was mainly precipitated during a late diagenetic stage and has a negative effect on the reservoir quality. This study provides important insights into analyzing the relationship between diagenetic minerals and reservoir quality and the results are directly applicable to the exploration and development of tight sandstone reservoirs all over the world. 2022 Vol. 11 (3): 360-386 [Abstract] ( 86 ) [HTML 1KB] PDF (35403 KB)   ( 21 ) Palaeoclimatology 387 Clay mineral formation and transformation in non-marine environments and implications for Early Cretaceous palaeoclimatic evolution: The Weald Basin, Southeast England Oladapo O. Akinlotan, Ogechukwu A. Moghalu, Stuart J. Hatter, Sunday Okunuwadje, Lorna Anquilano, Uche Onwukwe, Safiyeh Haghani, Okwudiri A. Anyiam, Byami A. Jolly Analyses of clay minerals within the Early Cretaceous Weald Basin, Southeast England reveal kaolinite, illite and chlorite as the main detrital clay minerals while glauconite and smectite are subordinates. A kaolinite-rich assemblage which characterized the sand-dominated Ashdown and Tunbridge Wells Sand formations and an illite-dominated assemblage associated mostly with the Wadhurst Clay and Weald Clay formations are recognized. Kaolinite was enriched in the Ashdown and Tunbridge Wells Sand formations during warm and humid climate with high precipitation that encouraged chemical weathering and leaching, while cold and dry conditions favoured the concentration of illite in the Wadhurst Clay and Weald Clay formations. Rainfall patterns associated with warm climate were drastically reduced during the drier climatic conditions. Most clay minerals are detrital in origin, with chlorite being more prominent than previously recognized. Contrary to previous studies and assumptions, this study revealed that authigenic clay minerals are present in the Hastings Beds, with vermiform and mica-replacive kaolinite being the most common, consistent with humid depositional environments. Isolated authigenic illite is also present, along with a chloritized grain, providing evidence for mesodiagenesis. The absence of dickite and occurrence of kaolinite, suggest that authigenic illite formed in relatively shallow burial conditions, indicating a maximum burial depth of 2500 m-3000 m, about 1000 m deeper than previous estimates of 1500 m-2000 m. Authigenic clay minerals are absent in the Weald Clay Formation possibly because of hindered flow of meteoric water and limited growth space for authigenic minerals. This study is significant in: 1) reinforcing multiple methods to facilitate a robust and balanced knowledge of formation and transformation of clay minerals; 2) investigating detrital and authigenic clay mineral assemblages when assessing the palaeoenvironments of sedimentary basins. 2022 Vol. 11 (3): 387-409 [Abstract] ( 88 ) [HTML 1KB] PDF (24638 KB)   ( 22 ) 410 Hydroclimate changes related to thermal state of the tropical Pacific in the northern coast of the South China Sea since ~8000 cal yr B.P. Yue-Qin Wu, Xiao-Qiang Yang, Jian Yin, Franz T. Fürsich, Ting-Wei Zhang, Chun-Lian Liu Under the complex influences including the monsoonal climates and tropical hydrological cycle, the features and forcing mechanisms of precipitation changes in the tropical monsoon regions remain controversial. The northern coast of the South China Sea (NCSCS), connecting the South China Sea (SCS) and the Pearl River Estuary (PRE), is a critical area providing reliable tropical precipitation records and probing the possible forcing mechanism of tropical precipitation, benefitted from its high deposition rate and hydroclimatic sensitivity. Here, δ18O variations of planktonic (δ18OG. ruber) and benthic foraminifera (δ18OC. lobatulus) were investigated respectively to reconstruct a high-resolution low-latitude precipitation record from the core 17NH-NC3 in the NCSCS. The results show a distinct δ18O difference between δ18OG. ruber and δ18OC. lobatulus, not only with respect to values, but also with respect to trends in some time intervals. The clear difference between the planktonic and benthic foraminifera (Δδ18Ob-p) illustrates the significant vertical salinity stratification. And the temporal trend of Δδ18Ob-p indicates the degree of salinity stratification variated since the mid-Holocene. We assume that the degree of stratification in the NCSCS was mainly controlled by tropical precipitation changes. Thus, the trend of Δδ18Ob-p values could indicate the temporal change of the tropical precipitation. The precipitation record of our research area is closely related to the tropical atmosphere-ocean dynamics stimulated by sea surface temperature (SST) changes of the tropical Pacific zone, analogous to the El Niño-Southern Oscillation (ENSO) events. During the mid-Holocene (from 8260 to 5180 cal yr B.P.), the sustainable higher Δδ18Ob-p values (> 1.23‰) suggested a large amount of precipitation, pointing to a sustained state of La Niña-like, which is associated with lasted higher difference between Western SST and Eastern SST (W-E SST gradient) in the equatorial Pacific. Since 5180 cal yr B.P., the decreasing Δδ18Ob-p indicates less low-latitude precipitation, which can be ascribed to an El Niño-like mean state arising from decreased W-E SST gradient. Our study provides a new continuous high-resolution archive of low-latitude precipitation in the tropical monsoon region since 8260 cal yr B.P. And this record highlights that the thermal state of the tropical Pacific most likely adjusted the low-latitude precipitation since the mid-Holocene. 2022 Vol. 11 (3): 410-426 [Abstract] ( 105 ) [HTML 1KB] PDF (19994 KB)   ( 21 ) Tectonopalaeogeography and palaeotectonics 427 Petrography and tectonic provenance of the Permian Tunas Formation: Implications on the paleotectonic setting during the Claromecó Foreland Basin evolution, southwestern Gondwana margin, Argentina María Belén Febbo, Renata N. Tomezzoli, Nora N. Cesaretti, Giselle Choque, Natalia B. Fortunatti, Guadalupe Arzadún The Claromecó Basin is located at the south-western sector of the Buenos Aires province, Argentina. This basin is considered a foreland basin closely related to the evolution of the southwestern Gondwana margin. This contribution focuses on the provenance analysis of the Tunas Formation (Permian, Pillahuincó Group), which represents the last filling stage for the Claromecó Foreland Basin. Petrographic and tectonic provenance analyses were performed in sandstones recovered from subsurface (PANG 0001 and PANG 0003 exploration wells) and outcrops located close to the basin center (Gonzales Chaves locality). In the subsurface, the analyzed succession is composed of medium- to fine-grained sandstones interbedded with tuffs, mudrocks, carbonaceous mudrocks and coal beds. In outcrops, the succession is dominated by medium- to fine-grained sandstones interbedded with siltstones. Modal composition patterns are distributed into the recycled orogen and transitionally recycled to mixed fields. Petrographic analyses, in addition to provenance and sedimentological studies, confirm that sedimentary material was derived from a mixed source, which largely comes from the Sierras Australes fold and thrust belt, located towards the W-SW, where the sedimentary succession is interbedded with volcanic material. The Tunas Formation shows clear differences in its modal composition, paleocurrent direction and paleoenvironmental conditions with respect to the underlying units of the Pillahuincó Group (Sauce Grande, Piedra Azul and Bonete formations). Source areas changed from cratonic to mixed fold belt/arc-derived material, suggesting variations in the Claromecó Basin configuration during the Late Paleozoic. Changes in the paleotectonic scenario during the deposition of the Tunas Formation have been interpreted as a consequence of a compressive post-collisional deformation event, the product of adjustment, accommodation and translation of terrains towards the equator during the Permian-Triassic to form Pangea. 2022 Vol. 11 (3): 427-447 [Abstract] ( 82 ) [HTML 1KB] PDF (17445 KB)   ( 20 ) Biopalaeogeography 448 Intensive peatland wildfires during the Aptian-Albian oceanic anoxic event 1b: Evidence from borehole SK-2 in the Songliao Basin, NE China Zhi-Hui Zhang, Da-Wei Lü, Tian-Tian Wang, Dong-Zhao An, Hai-Yan Liu, Dong-Dong Wang, Cheng-Shan Wang The Cretaceous has been considered a “high-fire” world accompanied by widespread by-products of combustion in the rock record. The mid-Cretaceous oceanic anoxic event 1b (OAE1b) is marked by one of the major perturbations in the global carbon cycle characterized by deposition of organic-rich sediments in both marine and terrestrial settings. However, our understanding is still limited on changes in wildfire activity during OAE1b period. Here, we carried out a comprehensive analysis, including organic carbon isotope (δ13Corg), total organic carbon (TOC), coal petrology, trace elements, and pyrolytic polycyclic aromatic hydrocarbons (pyroPAHs), of coal seams of the middle Aptian to early Albian Shahezi Formation from borehole SK-2 in Songliao Basin, Northeast China. Two negative δ13Corg excursions in the Shahezi Formation can be corresponded with the 113/Jacob and Kilian sub-events of OAE1b. Moreover, the intensive peatland wildfires have been identified during the sub-event periods of OAE1b based on the co-occurrence of high abundance of charcoal and pyroPAHs at that time. In addition, Sr/Ba, Sr/Cu and Sr/Rb ratios demonstrate that enhanced peatland wildfires were controlled by dryer climate conditions owing to episodic northward migration of arid zones in East Asia related with rising global temperature during the sub-events of OAE1b. The climate-driven extensive wildfire activity in the mid-latitude terrestrial ecosystems can be a contributing factor for OAE1b through the increased flux of nutrients fuelling primary producers in the lake and marine environments and leading to more speculative anoxia to allow the deposition of organic-rich sediments. Our results provide essential understanding of the importance of wildfires in driving mechanism of OAEs in Earth's history. 2022 Vol. 11 (3): 448-467 [Abstract] ( 92 ) [HTML 1KB] PDF (32233 KB)   ( 25 )

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