Lithofacies palaeogeography of the Late Permian Wujiaping Age in the Middle and Upper Yangtze Region,China

The lithofacies palaeogeography of the Late Permian Wujiaping Age in Middle and Upper Yangtze Region was studied based on petrography and the ＂single factor analysis and multifactor comprehensive mapping＂ method. The Upper Permian Wujiaping Stage in the Middle and Upper Yangtze Region is mainly composed of carbonate rocks and clastic rocks, with lesser amounts of siliceous rocks, pyroclastic rocks, volcanic rocks and coal. The rocks can be divided into three types, including clastic rock, clastic rock-limestone and limestone-siliceous rock, and four fundamental ecological types and four fossil assemblages are recognized in the Wujiaping Stage. Based on a petrological and palaeoecological study, six single factors were selected, namely, thickness （m）, content （%） of marine rocks, content （%） of shallow water carbonate rocks, content （%） of biograins with limemud, content （%） of thinbedded siliceous rocks and content （%） of deep water sedimentary rocks. Six single factors maps of the Wujiaping Stage and one lithofacies palaeogeography map of the Wujiaping Age were composed. Palaeogeographic units from west to east include an eroded area, an alluvial plain, a clastic rock platform, a carbonate rock platform where biocrowds developed, a slope and a basin. In addition, a clastic rock platform exists in the southeast of the study area. Hydro- carbon source rock and reservoir conditions were preliminarily analyzed based on lithofacies palaeogeography. Sedimentary environments have obvious controls over the development of the resource rocks. With regard to the abundance of organic matter, the hydrocarbon potential of the coastal swamp environment is the best, followed by the basin environment and the carbonate rock platform. The gas reservoir types of the Wujiaping Stage can be classified as conventional and unconventional gas reservoirs, like coal bed gas and shale gas; all of them have well exploration prospects.

Reply to Shanmugam,G.“Review of research in internal-wave and internal-tide deposits of China:Discussion”

We are glad to know that our paper ＂Review of research in internal-wave and internal-tide deposits of China＂ （Gao et al., 2013） published in Journal of Palaeogeography has attracted close attention of international peers, and we noted that Shanmugam has provided a critical assessment of our paper. He claimed that ＂interpretations of ten ancient exam- ples in China and one in the central Appalachians （USA） as deep-water deposits of internal waves and internal tides are unsustainable＂, among many other comments and criticisms, and he concluded that ＂any interpretation of ancient strata as deposits of internal waves and internal tides is premature＂. This article is aimed at responding to his major criticisms. We believe that constructive discussions will benefit the development of the study in internal-wave and internal-tide deposits. Unfortunately, Shanmugam seems not to follow this line of scientific criticism, but is trying to reject all research results in this subject based on his illogical and inconsistent reasoning, and distortion of others＇ points of view. In this article, with facts and evidences, we will refuse the main wrong assertions of Shanmugam＇s, for example, ＂the use of bidirectional cross-bedding as evidence for deposition by baroclinic currents in outcrop studies is sedimentologically erroneous ＂ and ＂any interpretation of ancient strata as deposits of internal waves and internal tides is premature＂. We will also use typical characteristics of the ancient examples to demonstrate that they are certainly not turbidites, or contourites, or tsunami-related deposits, but internal-wave and internal-tide deposits as the most plausible to defend the rationality of our interpretation in our previous papers.

Quantitative lithofacies palaeogeography

Quantitative lithofacies palaeogeography is an important discipline of palaeogeography.It is developed on the foundation of traditional lithofacies palaeogeography and palaeogeography,the core of which is the quantitative lithofacies palaeogeographic map.Quantity means that in the palaeogeographic map,the division and identification of each palaeogeographic unit are supported by quantitative data and quantitative fundamental maps.Our lithofacies palaeogeographic maps are quantitative or mainly quantitative.A great number of quantitative lithofacies palaeogeographic maps have been published,and articles and monographs of quantitative lithofacies palaeogeography have been published successively,thus the quantitative lithofacies palaeogeography was formed and established.It is an important development in lithofacies palaeogeography.In composing quantitative lithofacies palaeogeographic maps,the key measure is the single factor analysis and multifactor comprehensive mapping method—methodology of quantitative lithofacies palaeogeography.In this paper,the authors utilize two case studies,one from the Early Ordovician of South China and the other from the Early Ordovician of Ordos,North China,to explain how to use this methodology to compose the quantitative lithofacies palaeogeographic maps,and to discuss the palaeogeographic units in these maps.Finally,three characteristics,i.e.,quantification,multiple orders and multiple types,of quantitative lithofacies palaeogeographic maps are conclusively discussed.