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Current Issue   2013 Vol.  2 No.  3 Published: 2013-07-09 Biopalaeogeography and palaeoecology Lithofacies palaeogeography and sedimentology Tectonopalaeogeography and palaeotectonics Lithofacies palaeogeography and sedimentology 225 Palaeogeographical zonation of gypsum facies: Middle Miocene Badenian of Central Paratethys (Carpathian Foredeep in Europe) Tadeusz Marek Peryt Studies on Middle Miocene Badenian gypsum in various parts of Central Paratethys, the oldest widespread primary marine gypsum, in western Ukraine, southern Poland and Moravia (Czech Republic) indicate that there are three principal gypsum facies: crystalline gypsum, stromatolitic gypsum and clastic gypsum. The latter typically occurs between crystalline and stromatolitic gypsum and between stromatolitic gypsum and the land. In addition, it is common in channels within gypsum microbialites, and is the main facies during the deposition of the upper part of Badenian gypsum when important bathymetric differences existed within the marginal part of the Carpathian Foredeep Basin, the largest foredeep basin in Europe. Within crystalline gypsum facies, it is observed the overall size of the crystals increases and that the layering declines towards the permanent, stabilized brine body, and thus the giant gypsum intergrowths-non-layered coarse-crystalline selenite is the end-member of gypsum facies continuum. Typically it passes into layered selenites although owing to fluctuations of pycnocline level, some transitional gypsum subfacies may be missing both in the vertical section as well as in particular outcrops. The following important controls on the development of gypsum facies have been identified: pycnocline level fluctuations, brine level fluctuations including brine sheets and floods, rare marine transgressions, pedogenesis leading to “alabastrine” gypsum development, and rate of inflow of continental water. 2013 Vol. 2 (3): 225-237 [Abstract] ( 2865 ) [HTML 1KB] PDF (6358 KB)   ( 480 ) 238 Lithofacies and sedimentary characteristics of the Silurian Longmaxi Shale in the southeastern Sichuan Basin, China Jiang Zaixing, Guo Ling, Liang Chao The Silurian Longmaxi Shale (SLS) is the target for shale gas exploration and exploitation in the southeastern Sichuan Basin. Based on detailed description of cores and outcrops, analysis of Gamma Ray (GR) logs, thin sections and mineralogical data, the SLS can be subdivided into six lithofacies: (1) clayey shale, (2) siliceous calcareous shale, (3) siliceous dolomitic shale, (4) silty-clayey interlaminated shale, (5) muddy siltstone, and (6) graptolite shale. Three facies associations are recognized in the study area, i.e., inner shelf, outer shelf, and bathyal plain (including turbidite) facies. Outer shelf and bathyal plain facies dominate the lower interval of the SLS, while inner shelf facies dominates the upper part of the SLS. The thickness of the black shale in the northern part of the study area is the greatest, where siliceous calcareous shale, siliceous dolomitic shale, and graptolite shale are predominant. These three kinds of shale are rich in total organic carbon (TOC) content and brittle minerals, which is favourable for the accumulation of shale gas and its future exploitation. 2013 Vol. 2 (3): 238-251 [Abstract] ( 3329 ) [HTML 1KB] PDF (6194 KB)   ( 460 ) 252 Lithofacies palaeogeography and biostratigraphy of the lowermost horizons of the Middle Triassic Hallstatt Limestones (Argolis Peninsula, Greece) Fotini A. Pomoni, Vassilis Tselepidis Condensed ammonoid beds of the Hallstatt facies (Anisian-Ladinian) are widespread around the Ancient Theatre of Epidaurus, in the locality Theokafta of the Argolis Peninsula (eastern Peloponnesus). The Hallstatt Formation in Argolis appears, generally, in the form of lensoid bodies of variable sizes, inclination and direction and is always found overlying a formation consisting of keratophyric tuffs. In fact, the contact of the keratophyric tuffs with the overlying limestones, specifically evidenced by an in situ brecciated zone, is stratigraphic and constitutes the base of the Hallstatt Limestones. The contact of the Hallstatt Limestones with the overlying radiolarites is stratigraphic as well. 2013 Vol. 2 (3): 252-274 [Abstract] ( 3799 ) [HTML 1KB] PDF (16770 KB)   ( 737 ) Biopalaeogeography and palaeoecology 275 Environment controls on Mesoproterozoic thrombolite morphogenesis: A case study from the North China Platform Tang Dongjie, Shi Xiaoying, Jiang Ganqing, Pei Yunpeng, Zhang Wenhao Thrombolites are widespread in the Mesoproterozoic Wumishan Formation in the North China Platform. This study shows that they mainly concentrated in subtidal carbonate facies with relatively low hydrodynamic conditions, rather than in intertidal zone as suggested previously. From the deep lower to the shallow upper subtidal facies, the thrombolites show evident changes in morphology from dominantly domal to tabular forms, likely suggestive of environmental controls on their morphogenesis and distribution. As the most important component in thrombolites, mesoclots typically consist of organic-rich micritic nuclei and organic-poor fibrous aragonite rims. Mesoclots may vary considerably in their morphology, but a type of specifically shaped mesoclots tends to concentrate predominantly in a particular group of thrombolites. The proportion of the fibrous aragonite rims in mesoclots decrease as the depositional environments become shallower, likely suggesting that the environmental changes also have controls on the internal fabrics of thrombolites. Putative filamentous bacterial colonies are well preserved in some aragonite fans in the matrix between mesoclots, invoking rapid precipitation and aragonite-supersaturated conditions in the ambient waters. It seems that a suboxic to anoxic environment, highly alkaline seawater and relatively low hydrodynamic conditions were among the important factors that facilitated the development and preservation of thrombolites in the Mesoproterozoic epeiric sea on the North China Platform. 2013 Vol. 2 (3): 275-296 [Abstract] ( 2364 ) [HTML 1KB] PDF (19134 KB)   ( 412 ) 297 Artemisia pollen-indicated steppe distribution in southern China during the Last Glacial Maximum Liu Hongyan, Liu Kan, Wei Fangling The Last Glacial Maximum (LGM) was the coldest period during the previous 20,000 years. There have been different points of views on steppe distribution during the LGM period in southern China, partly due to the different interpretations of Artemisia occurrences. To make a reliable interpretation of the pollen fossil Artemisia, the modern distribution of Artemisia species and the relationship of pollen with climate and vegetation over a large spatial scale in China was thoroughly analyzed. Information about Artemisia species and pollen distributions used in this paper were collected from published works completed by other researchers as well as ourselves. The southern limit of steppe vegetation during the LGM period was interpreted from the published contour map of Artemisia pollen percentages during the LGM. Artemisia species in China are mostly distributed either in the horizontally distributed steppe regions or in the vertically distributed desert-steppe in the desert region, which indicates a cold and dry climate. The steppe is a distribution center of Artemisia pollen. Fractions of Artemisia in surface pollen assemblages are lower in both the desert and the temperate forest. Neither high Artemisia species cover nor high percentages of Artemisia pollen were found in the coast areas of China. Twenty-five percent of Artemisia pollen in sediments might indicate a local occurrence of steppe vegetation. Percentages of Artemisia pollen in the subtropical and tropical forest are less than 10%. A close relationship between Artemisia pollen and temperate steppe in China is demonstrated. The southern edge of the steppe vegetation during the LGM might be along the middle reach of the Yangtze River. Our results support the hypothesis that the isolated high fraction of Artemisia pollen along the northern edge of the South China Sea was transported from a large source area. 2013 Vol. 2 (3): 297-305 [Abstract] ( 2293 ) [HTML 1KB] PDF (1706 KB)   ( 353 ) Tectonopalaeogeography and palaeotectonics 306 Palinspastic reconstruction and geological evolution of Jurassic basins in Mongolia and neighboring China Wu Genyao The important event in Jurassic tectonics in Mongolia was the subduction and closure of the Mongolia-Okhotsk ocean; correspondingly, basin evolution can be divided into two main stages, related to the orogeny and collapse of the orogenic belt, respectively. The developing of Early-Middle Jurassic basins to the north of the ocean resulted from back-arc extension. The fossil sutures, from the China-SE Asia sub-continent to the south of the ocean, were rejuvenated by subduction-related orogeny; in addition, the Yanshanian intra-continental movement occurred. Three Early-Middle Jurassic molasse basins were developed by movement in Inner Mongolia, all of which stretched westwards (or northwards) into Mongolia; therefore, the molasse basins in eastern and southern Mongolia had the same geometric and kinematic features as the basins in the Inner Mongolia. Owing to the collapse of the Mongolia-Okhotsk orogenic belt, a group of rift basins developed during the Late Jurassic. In eastern Mongolia, the NE orientated extensional basins were controlled by the neogenic NE-structure. The contemporary basins in southern Mongolia and the neighboring areas in China were constrained by remobilization (inherited activation) of the latitudinal or ENE-directional basement structures. Three stages can be recognized in the evolution of the Early-Middle Jurassic basins after reversal; the basins also experienced four episodes of reformation. 2013 Vol. 2 (3): 306-317 [Abstract] ( 2590 ) [HTML 1KB] PDF (2240 KB)   ( 375 )

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