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	JOPC 2021 Vol.23 Number 6
	2021, Vol.23 Num.6
	Online: 2021-12-01

	SUMMARY LITHOFACIES PALAEOGEOGRAPHY AND SEDIMENTOLOGY GEOCHEMISTRY AND SEDIMENTARY ENVIRONMENTS BIOPALAEOGEOGRAPHY AND PALAEOECOLOGY PALAEOGEOGRAPHY AND MINERAL RESOURCES

SUMMARY

	1067	Shi Zhi-Qiang, Wang Mei-Ling, Chen Bin

		Distribution,characteristics and significances of burnt rocks in northern China
		Burnt rocks are widely distributed in many sedimentary basins located in the northern China that are bounded by Kunlun mountain-Qinling-Dabie mountain. However,few studies have focused on the origin,age and geological significance of these kinds of metamorphic rocks. Based on our field investigation,four distribution modes of the burnt rocks are found: (1)large area distribution,(2)linear distribution along the mountain range alignment,(3)distribution along the river incised-valley and(4)covered by the Quaternary loess. These burnt rocks were mainly caused by the self-ignition of Jurassic and Carboniferous-Permian coals. Various burnt rocks developed in the burnt rock area on different levels. The vitrified structure,whitened structure,lava structure,residual structure,pore structure,columnar jointing structure,breccia structure,fissure structure and filling minerals are often found in these burnt rocks. The burnt rocks are mainly red,mixed with brown,black and steel-gray colors. The typical high temperature minerals as cristobalite,tridymite,cordierite,sekaninaite and mullite are common in these burnt rocks. The active tectonic movements and arid climate in northwestern China triggered the formation of burnt rocks since the Miocene. The relationship between the palaeotectonic,palaeoclimate,palaeo-wildfire and the coal self-ignition,however,has been seldomly studied. Such information implied from the formation of burnt rocks should be paid more attention in the future work.
		2021 Vol. 23 (6): 1067-1081 [Abstract] ( 420 ) [HTML 1KB] [PDF 12697KB] ( 513 )

	1082	Zhou Wei

		Research progress on architectural patterns and formation mechanisms of deep-water unidirectionally migrating channels
		Deep-water channels are a common topography developed on continental slopes-submarine plains. Unidirectionally migrating channels(UMCs)are a special type of deep-water channels,which are mainly caused by the interaction of the down-slope turbidity currents with along-slope bottom currents(i.e. contour currents). There are currently two distinct patterns in the migration-architecture characteristics of UMCs. The first is the downstream migration pattern,where the channel migrates unidirectionally in the direction of the contour current,and is characterized by an asymmetric‘U’or‘V’ shaped channel profile,a straight to low-sinuosity plan form,and a predominance of intra-channel erosion-infill construction lacking of bilateral outer levees. The second is the upstream migration pattern,where the channel migrates unidirectionally in the direction of the source of the contour current,which is characterized by an asymmetrical‘gull-wing shaped’ channel profile,a low-to high-sinuosity plan form,and is dominated by the channel-levee construction with a single, more developed outer levee. These two distinct migration-architecture characteristics suggest that the formation mechanisms and the paleoceanographic significance of deep-water UMCs of interacting origin are still highly controversial. Interaction simulation experiments of modern gravity flows and bottom currents(e.g.,flume-tank experiments and numerical simulations),geological outcrop analyses,and in-situ near-seafloor flow monitoring may be the most powerful tools of resolving these controversies.
		2021 Vol. 23 (6): 1082-1093 [Abstract] ( 347 ) [HTML 1KB] [PDF 8904KB] ( 262 )

LITHOFACIES PALAEOGEOGRAPHY AND SEDIMENTOLOGY

	1094	Huang Cheng, Shen Yu-Wei, Wen Xin

		Sedimentary characteristics and its palaeoenvironmental significance of the Upper Devonian storm deposits at Qingfengxia section in Guangyuan City,Sichuan Province
		It is well known that environmental changes during the Devonian Givetian-Frasnian(G-F) transition initiated the beginning of the Late Devonian extinction. However,it is still controversial as to the understanding of environmental changes in this period. For that,this study conducted detailed sedimentological study on six sets of tempestites in the Devonian Guanwushan Formation at the Qingfengxia section in Guangyuan City,Sichuan Province,China. Some typical storm depositional indicators,including erosional structures,coarse lag deposits,graded bedding,and hummocky cross-stratification were identified. Three proximal storm sedimentary sequences have been established based on the combined characteristics of storm sedimentary structures in the Guanwushan Formation. Storm sequence Ⅰ consists of calcirudites with erosional surface at the bottom and homogeneous mudstones at the top. Storm sequence Ⅱ is characterized by calcirudites with erosional surface at the bottom and calcarenites with graded bedding at the top. Storm sequence Ⅲ is composed of calcirudites with erosional surface at the bottom,coquinas with graded bedding in the middle interval,hummocky cross-stratificated wackestones in the upper part,and mudstones with wavy and horizontal beddings at the top. The tempestites were formed in the early Frasnian age according to the biochronological analysis of conodont assemblages. Based on the analysis of origin of modern storms,the widely distributed tempestites in early Frasnian age at the low-latitude areas might have resulted from climate warming and rapid transgression. Discovery of tempestites in the study area is of great significance in understanding of the Late Devonian sedimentary environment, palaeogeography,and palaeoclimate in the upper Yangtze region.
		2021 Vol. 23 (6): 1094-1109 [Abstract] ( 467 ) [HTML 1KB] [PDF 12135KB] ( 312 )

	1110	Quan Zi-Ting, Tan Xiu-Cheng, Zhang Ben-Jian, Tang Hao, Luo Bing, Yang Xun, Zhang Ya, Xiao Di, Tang Yan-Ling

		Discovery of microbial mounds of the Lower Permian Qixia Formation in northwestern Sichuan Basin and its geological significance
		Through analysis of outcrops and drilling profile data in the field and laboratory,microbial mounds were found in the Lower Permian Qixia Formation in the northwestern Sichuan Basin. The microbial mound is mainly composed of thrombolites,stromatolites,and microbial bindstones. These microbial carbonates are characterized by development of typical clots,stromatolitic,fenestral,and microbial bonding fabrics. Microbial mounds of the Qixia Formation are typical mound-shaped with flat bottom and convex-up top,and various in size. They range from tens of centimeters to several meters in height and from several meters to tens of meters in width. The mounds are characterized by shallowing-upward sequences,which are generally composed of mound base,core and cap,and also may form a mound-bank complex with carbonate shoals. Analysis of regional paleogeographic background and the characteristics of microbial mounds suggests that the Qixia period in northwestern Sichuan was deposited in a semi-restricted platform,with shallow-water and the relatively low-energy conditions. The high-frequency sea-level change,lateral migration,and superposition of microbial mounds lead to the restricted environment on carbonate platform with ramp background,which results in penecontemporaneous dolomitization in earlier sediments. Microbial mound-bank complexes provide basis for development of the dolomite reservoirs in the Qixia Formation. The slope-break belt of platform margin,gentle slope break belt,and local highland inside carbonate platform are favorable zones for the development of the dolomite reservoirs in the Qixia Formation. This understanding plays an important guiding role in finding banded dolomite reservoirs with unstable scale horizons,and will greatly expand the exploration field of dolomite reservoirs in the Qixia Formation.
		2021 Vol. 23 (6): 1110-1124 [Abstract] ( 441 ) [HTML 1KB] [PDF 26358KB] ( 345 )

	1125	Yang Meng-Ying, Tan Xiu-Cheng, Yang Ming-Yi, Xu Yu-Qing, Yan Wei, Su Wen-Jie, Zhong Shou-Kang, Xiong Ying, Guo Mu-Shi

		Basin-scale distribution and dominant controlling factors of microbialites of the Ma₅⁵ sub-member of Ordovician Majiagou Formation in Ordos Basin
		Based on the analysis of core,thin section and logging data,basin-scale microbial carbonate with stable distribution developed in the lower part of the Ma⁵₅ sub-member of the Ordovician Majiagou Formation in Ordos Basin. The rock types include argillaceous limestone,limestone,stromatolite,thrombolite,bound sand-clastic limestone,karst breccias. It contains various shaped stromatolite and thrombolite,such as laminar,wavy and columnar stromatolite,laminar,nodular and arborescent thrombolite. Vertically,four typical sedimentary sequences closely related to microbialites are identified,indicating relative sea-level fluctuations. The division and comparative analysis of the small layers with high-frequency cycles suggest that the microbialites are stably distributed laterally,and have basin-scale distribution. Based on the logging template established by core-log calibration,the lithology of 404 wells in the whole basin were interpreted.The result shows that cumulative thickness of microbialites range from 3 to 7m,and the thickness shows a decreasing trend from west to east.Furthermore,the continuous distribution area of microbialites can exceed 2.5×10⁵km²in area,demonstrating that the basin-scale microbialites developed in a relatively shorter time.Analysis of sedimentary sequence in the early depositional stage of Ma⁵₅ sub-member indicates that the relative sea level first slowly rises and then falls in a single cycle,while it shows an oscillating and slowly rising trend in a multi-cycle combination.Further research suggests that the relatively stable paleo-tectonic environment coupled with the filling of early evaporite provides relatively flat paleo-geomorphic conditions.Under the background of continuous slow transgression in the depositional stage of Ma⁵₅ sub-member,the bottom shape condition of environmental homogeneity is the fundamental reason for the development of large-scale microbial carbonate in shallow water.This paper reports the development and distribution of basin-scale microbialites in the depositional stage of Ma⁵₅ sub-member,which not only enriches the research of microbialites in the Majiagou Formation,but also helps improve the understanding of development mechanism of large-scale microbialites in carbonate platforms.
		2021 Vol. 23 (6): 1125-1139 [Abstract] ( 434 ) [HTML 1KB] [PDF 19154KB] ( 397 )

	1140	Wu Dong-Xu, Yu Jian, Zhou Jin-Gao, Wu Xing-Ning, Yu Zhou, Ding Zhen-Chun, Wang Shao-Yi, Li Wei-Ling, Cai Jun

		Sedimentary characteristics and reservoir controlling effect of the Member 4 of Ordovician Majiagou Formation in Ordos Basin
		The Member 4 of Majiagou Formation(i.e. Ma₄Member)of Ordovician in the Ordos Basin is the key target for risk exploration of natural gas in Lower Paleozoic. Based on the observation of core and thin section,the stratigraphic correlation,sedimentary structure description,well logging interpretation of rock structure and composition,and the combined well-seismic method for palaeogeomorphologic restoration,the palaeogeomorphology,sedimentary features and reservoir distribution of the Member 4 of Majiagou Formation in the Ordos Basin were analyzed in detail. Results show that: (1)Controlled by the palaeogeomorphologic pattern of uplift and depression in the depositional period,a lot of mound and bank microfacies developed in the Ma₄ Member and the penecontemporaneous dissolution and dolomitization were prone to occur,making it become the favorable sedimentary facies belt for reservoir development. (2)The reservoir of Ma₄ Member is mainly composed of(algal)arenaceous dolostone and silt-fine grain dolostone,and the reservoir space is mainly characterized as intergranular pores,intercrystal pores and dissolution pores. (3)The reservoirs are mainly distributed in Ma₄¹ and Ma₄² submembers,which are located at the low uplift belt in the platform and the platform margin belt. (4)The development of the reservoir is controlled by three factors.The mound-bank body developed in the palaeo-uplift is the material basis. The penecontemporaneous dissolution controlled by the high frequency sequence is the key to the formation of the reservoir,and dolomitization is an important factor for the preservation of the reservoir in the later period. The palaeogeomorphology of alternating uplift and depression in the carbonate platform during the Ma₄ depositional period controlled the distribution of mound-bank facies and dolomite reservoirs,which provided a strong support for gas exploration in the Lower Paleozoic,and also provides a new idea for the study of the sedimentary reservoir in the carbonate platform.
		2021 Vol. 23 (6): 1140-1157 [Abstract] ( 455 ) [HTML 1KB] [PDF 14829KB] ( 320 )

	1158	Chen Yu-Hang, Yao Gen-Shun, Shao Da-Li, Lu Yin-Tao, Lü Fu-Liang, Cao Quan-Bin, Tang Peng-Cheng, Li Shi-Fang

		Sedimentary characteristics and its controlling factors of continental slope canyons in Tanzania Coastal Basin
		The East African continental margin deep-water basins have great oil and gas potentials. However,only few studies were carried on the sedimentary features of slope canyon and prohibit the prediction of favorable reservoir. We use 3D seismic data to investigate the sedimentary characteristics of slope canyon in the offshore of the Tanzania Coastal Basin. The result are as follows. (1)Large submarine canyons are developed in the study area. The upper slope is steep,where the canyon is dominated by erosional process,with limited deposition at the limb of fold and thrust belt. The gentle lower slope area is outside the fold and thrust belt,where the sheet-like sandy deposits and sand-mud mixed debris-flow deposits accumulated. Meanwhile,the mound-shaped muddy drift is developed on the northern canyon bank and extends northward. Slumps occur at the edge of slope margin,forming the mass transport deposits. (2)The sedimentary feature of the canyon is controlled by multiple factors,including terrigenous sediment supply,fold and thrust belt,North Atlantic Deep Water,and slope margin fault. Influenced by the activity of the offshore branch of East African Rift System,the study area is characterized by a narrow continental shelf and steep slope. Consequently,the terrigenous material can easily pass through the continental shelf and enter the continental canyon. The canyons connected with the river have sufficient sediment supply and are in large scale,while the canyons disconnected with the river have limited terrigenous sediment supply and are in small scale with no obvious sediment found in the canyon. Fold and thrust belt controls the sedimentary distribution in the canyon by changing the seafloor topography,with erosions occurred on the core and depositions occurred on the wings of the fold. Outside the fold and thrust belt,the North Atlantic Deep Water interacts with the gravity flow at the end of the canyon,transporting fine particles to the northern canyon bank and forming drifts. The fault activity at slope margin cut the canyons and triggers the sediment collapses. No channels and lobes formed on the continental slope,and the terrigenous material are transported to the deeper basin through the canyons.
		2021 Vol. 23 (6): 1158-1173 [Abstract] ( 358 ) [HTML 1KB] [PDF 18543KB] ( 239 )

GEOCHEMISTRY AND SEDIMENTARY ENVIRONMENTS

	1174	He Jia-Wei, Xie Yuan, Hou Ming-Cai, Liu Jian-Qing, He Li, Lu Yun-Fei

		Geochemical characteristics and geological significance of the Silurian Longmaxi Formation shale in Yanjin area,southwestern Sichuan Basin
		In order to find out the element geochemical characteristics of Silurian Longmaxi Formation shale in Yanjin area,southwestern Sichuan Basin,as well as the material source and structural background of shale formation,the petromineralogy and geochemistry of 19 shale samples from Niuzhai section of Yanjin area were tested and analyzed. Combined with the previous research results and adjacent areas,the rare earth elements were mainly applied to discuss the sedimentary environment, the accumulation rate,material source and tectonic setting of the Longmaxi Formation shale in the study area. The results show that the mineral composition of the Longmaxi Formation in Niuzhai section of Yanjin is mainly quartz,carbonate minerals and clay minerals. The mineral triangle diagram shows that the Longmaxi Formation shale is mainly a combination of clay shale and mixed shale. The normalized partition pattern of rare earth elements is characterized by Ce deficit and weak Eu enrichment. The δCe values,Ni/Co and V/Cr values of the samples indicate that the paleo-water depth increases suddenly in the early stage and becomes shallow gradually in the later stage. Oxygen content gradually changes from anoxic reduction state in the early stage to weak oxidation state in the later stage. La_N/Yb_N values show that the shale deposition rate increases firstly and then decreases under the influence of sea level and terrigenous debris input. Provenance analysis shows that the source rocks area are mainly felsic igneous rocks and intermediate-acid geological bodies of granitoids. The La-Th-Sc diagram and tectonic setting characteristics show that the main tectonic setting of the source rocks is passive continental margin. Combined with previous studies and tectonic setting,it is inferred that the main source of the Longmaxi Formation shale is formed in the Passive continental margin of hypoxia,and the provenance is mainly from the Kang-Dian ancient land to the west of the study area,followed by the Central Guizhou uplift.
		2021 Vol. 23 (6): 1174-1191 [Abstract] ( 448 ) [HTML 1KB] [PDF 5577KB] ( 243 )

	1192	Fu Han-Jing, Jian Xing, Liang Hang-Hai

		Research progress of sediment indicators and methods for evaluation of silicate chemical weathering intensity
		Chemical weathering is a key process in source-to-sink depositional systems,which is controlled by climate,tectonics,topography,vegetation and lithology. Quantifying the intensity of silicate chemical weathering is beneficial to carry out global case study comparison. This paper aims to summarize the sediment chemical weathering indicators,including petrological and mineralogical,element geochemical and non-traditional stable isotope proxies,and point out the potential problems in application. Among these proxies,the composition of sandy sediment framework grains,mineral composition of silty sediments and textural characteristics of mineral surface can clearly indicate chemical weathering intensity,which have been overlooked in most studies and deserve more attention. Clay mineral assemblages and element geochemical indicators,such as CIA,Rb/Sr and α^AlE,are most widely used for quantitative analysis of chemical weathering intensity. However,these proxies are easily affected by the sediment source and hydrodynamic sorting. The newly developed indexes of Li,B,K,Mg and Si isotopes show high potentials to evaluate chemical weathering intensity and need further study on their fractionation mechanism. It's important to note that all indicators can be affected by other geological processes from source to sink,e.g., source,hydrodynamic sorting,diagenesis,sediment recycling,pedogenesis,leaching and biological utilization. It is highly suggested to comprehensively use multiple indexes for evaluating silicate chemical weathering intensity,which can effectively improve the accuracy of the analytic results.
		2021 Vol. 23 (6): 1192-1209 [Abstract] ( 374 ) [HTML 1KB] [PDF 1522KB] ( 277 )

BIOPALAEOGEOGRAPHY AND PALAEOECOLOGY

	1210	Li Tong, Dong Lin, Yuan Zhi-Wei, Ling Kun, Ning Meng, Qin Shu-Jian, Yang Run-Yu, Liu Wei, Nie Ting, Li Chen-Qing, Sun Yuan-Lin

		*Taphonomic features and population dynamics of the Upper Devonian Famennian Dzieduszyckia* fauna in South China**
		Dzieduszyckia is a rhynchonellide brachiopods genus,featured by its bisulcate,strongly costate shell. It is widely accepted that Dzieduszyckia developed in cold-seep environments. This study aims to investigate the primary living environments of Dzieduszyckia in South China and their population features. Comparison of depositional features between coquinas from platform and intra-platform basin indicates that Dzieduszyckia in South China primarily occupied the platform niches,which is different from that in North American and Morocco. It suggests that Dzieduszyckia had a larger ecological plasticity than the modern organisms present in the cold-seep environment. More than one thousand specimens of Dzieduszyckia from three localities were collected in this study. These three populations have an extremely high abundance with high proportions of growth asymmetry,which resulted from squeezing of individuals during growth,suggesting a dense crowed life habit for the brachiopods. The Dzieduszyckia populations barely coexisted with other benthic animals,showing an extremely low diversity in the entire area. Length-frequency distribution and survivorship curve reveal that each of the Dzieduszyckia populations has a low juvenile mortality. The identical shell length in the same natural coquina also supports that the majority of individuals grew up and died naturally. All evidence suggests that Dzieduszyckia takes tight-growth pattern as the survival strategy,living in a unique environment that was not suitable for other benthic organisms.
		2021 Vol. 23 (6): 1210-1224 [Abstract] ( 341 ) [HTML 1KB] [PDF 10929KB] ( 175 )

PALAEOGEOGRAPHY AND MINERAL RESOURCES

	1225	Lai Jin, Bao Meng, Liu Shi-Chen, Li Dong, Wang Song, Yang Ke-Fu, Chen Xu, Wang Gui-Wen, Ding Xiu-Jian

		Prediction of high quality deep and ultra-deep dolostones reservoirs in Tarim Basin by well logs
		The Cambrian dolostone is one of the most important exploration targets of deep and ultra-deep strata in Tarim Basin. However,it has characteristics of ancient geological age,deep burial,and complex tectonic and diagenetic evolution. Therefore,it is of great significance to understand the genetic mechanism,and establish a matched well logs evaluation method for various kinds of dolostone. Based on the comprehensive observation of core,thin section,conventional and imaging logs,two types of dolostone i.e. ,“karst transformation type”and “sedimentary facies dominated”are recognized in the Tarim Basin. The karst transformation dolostone reservoir are controlled by karst facies belt and can be divided into four zones in the vertical direction,namely the surface karst zone,vertical vadose zone,horizontal hyporheic zone and deep slow flow zone. The reservoir quality of depositional facies controlled dolostone is evidently controlled by high energy depositional facies such as the grain bank. The recognition patterns of karst dissolution belt and sedimentary microfacies by conventional and imaging logs data and marked by core sample are established and applied in the comprehensive interpretation of dolostone reservoir in the single well and prediction of favorable development area. The high angle fractures and horizontal dissolution vugs in the vertical vadose zone,horizontal hyporheic zone are favorable for the formation of high quality karst transformation type dolostone with fracture-cave system. The high energy depositional facies(shoal and reef facies,and tidal flat)are favorable for the formation of primary pores and secondary pores in the sedimentary facies dominated dolostone,and therefore become the high quality reservoirs. The results will provide theoretical guidance and technical support for the prediction of the spatial distribution of favorable deep and ultra-deep dolostone reservoir.
		2021 Vol. 23 (6): 1225-1242 [Abstract] ( 547 ) [HTML 1KB] [PDF 21482KB] ( 216 )

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