Sequence-stratigraphic frameworks and their palaeogeographic patterns for the Permian Lopingian of the Dianqiangui Basin and its adjacent areas of Southwestern China

Abstract

The Permian Lopingian in the Dianqiangui Basin and its adjacent areas is marked by the coal measures of the Wuchiapingian and the carbonate strata of the Changhsingian stages. For the Lopingian of the Dianqiangui Basin and its adjacent areas, the diversity of sedimentary facies and the obviousness of facies change provide an advantaged condition on a study of sequence stratigraphy. Approximately, the Wuchiapingian stage constitutes a third-order sequence and the Changhsingian stage forms another. For the Wuchiapingian stage in the study area, coal-measures were developed on the attached platform and, in addition, a special coal-measure that is composed of both limestone beds and coal beds was also developed in the central part of some isolated platforms. Grain-bank grainstones and packstones were formed on the margin of the attached platform as well as in the windward part of isolated platforms. For the Changhsingian stage in the study area, open-platform limestones were formed on the attached platform, while sponge-reef limestones were developed both on the margin of the attached platform and on the isolated platforms. The Lopingian Series is a set of basin-facies muddy shales with interbeds of silicalites in the inter-platform basin, which appears a set of the large-thick coarse clastic strata of molasses covering direct the deep-water strata from the Devonian to the Permian Yangsingian in the Qinzhou-Fangcheng region in the southern part of the study area. All of these features indicate the complexity of temporal-spatial facies-changes. Sequence-stratigraphic frameworks could be established, which would illustrate two types of facies-changing surfaces and diachronisms in the stratigraphic records, based on the combination of both biostratigraphic and chronostratigraphic materials and the regularity reflected by temporal evolutionary succession of sediments as well as spatial distributional patterns of sedimentary facies. Ultimately, features of sedimentary succession and palaeogeographical evolution of the Permian Lopingian in the study area are revealed clearly in a series of the panel diagrams of sequence-stratigraphic frameworks and the outline maps showing the sedimentary-facies and palaeogeography. The Permian Lopingian formed by two third-order sequences differs from the stratigraphy of the same era characterized by the constant regression along Euramerica. Most specially, if the end-Guadalupian mass-extinction event is genetically related to a regressive event represented by the unconformity of the first episode of the Dongwu movement in the study area, the mass-extinction event at the turn from the Permian to the Triassic is genetically related to a rapid transgressive event reflected by the drowning unconformity in the study area. These phenomena might reveal a complex relationship between mass-extinction events and transgressive-regressive events.

Formation and Forward Propagation of the Indosinian Foreland Fold‐Thrust Belt and Nanpanjiang Foreland Basin in SW China

“…The Triassic sediments in this region are characterized by transitions from a Lower Triassic starved basin with pelagic carbonate and shale and local shallow marine carbonate platform deposits, to Middle and Upper Triassic deep marine siliciclastic turbidites deposited during rapid subsidence, followed by continental clastic deposition (Lehrmann et al, 2005(Lehrmann et al, , 2015. These strata were subsequently deformed into a WNW-striking fold-thrust belt followed by the superposition of NNE-striking folds (Huang et al, 2013;Mei et al, 2003Mei et al, , 2007Mei et al, , 2001Minzoni, 2007;Wang et al, 2013;Yan et al, 2006). Previous studies, focusing on the formation, depositional history, sedimentary provenance and tectonic evolution (e.g., Duan et al, 2018;Faure et al, 2016bFaure et al, , 2016aHu et al, 2017;Liu et al, 2018;Qiu et al, 2017), have revealed several deformation episodes (e.g., Early Paleozoic Kwangsian, Triassic Indosinian, and Jurassic to Cretaceous Yanshanian events) and magmatic events in the Nanpanjiang region (Faure et al, 2014;Li et al, 2016Li et al, , 2014Qiu et al, 2016;Shu et al, 2009;Wang et al, 2018;Wang, Fan, Zhao, et al, 2007;Wu et al, 2019;Yang et al, 2018).…”

Extreme enrichment of rare earth elements in hard clay rocks and its potential as a resource

“…Along with the following intensive investigations and studies, this sedimentary sequence had been divided into two parts. The upper part is mainly continental coal-bearing sandy shale (Chen et al, 2003;Mei et al, 2007), whereas the lower part consists of coal-bearing clastic rocks covered by ancient weathered crusts on the surface with different thicknesses that unconformably covered the Emeishan Basalts (Huang, 1997;Wang et al, 2006). On the geological sections, weathered basaltic and tuffaceous rocks were found, and also some typical mineralization of iron and copper was observed, which was considered as being related to strong weathering after the eruption of the Emeishan Basalts (Geological Team 108, Guizhou Bureau of Geology and Mineral Resources, 1973;Yang et al, 2008;Yang et al, 2011).…”

Giant Induan oolite: A case study from the Lower Triassic Daye Formation in the western Hubei Province, South China

“…Siliciclastic facies, 1e2 Z Feixianguan Formation, carbonate facies; 3e5 Z Daye Formation, shelf facies; 6 Z Luolou and Qingyan formations. The south is part of the Dianqiangui or Nanpanjiang Basin (Mei and Tucker, 2007;. marked by a set of limestones with some oolitic grainstones in its upper part.…”

“…(1) The basal boundary of DS 1 equates to a clear drowningunconformity, exhibited by basin siliceous rocks of the Permian Dalong Formation that lie directly over high-stand carbonates of the Upper Permian Changxing Formation (Schlager, 1989(Schlager, , 1999Chen, 1995;Hallam and Wignall, 1999;Mei and Tucker, 2007;; this larger-scale rapid transgression that occurred at the turn of the Permian to the Triassic, formed an upward-shallowing succession of sedimentary facies from basin to shallow ramp making up DS 1 ; (2) An abrupt transfer boundary of sedimentary facies from shallow to deep ramp in the middle part of the Daye Formation forms the basal boundary of DS 2 , which is marked by a transitional type of sequence-stratigraphic boundary as defined by Vail et al (1977), and an exposure-punctuated surface formed in the lower part of the Jialingjiang Formation, which is similar to the type-II sequence-stratigraphic boundary defined by Vail et al (1977), between which an upward-shallowing succession of sedimentary facies from deep ramp to top oolitic-bank constitutes DS 2 . Consequently, a set of oolitic-bank limestones with a thickness of about 50 m makes up the early high-stand system tract (EHST), and a set of dolomites with some dolomitic limestones and few oolites belonging to the lower Jialingjiang Formation makes up a forced-regressive wedge system tract (or late high-stand system tract (LHST); Hunt and Tucker, 1992) of the thirdorder sequence DS 2 .…”

“…1), most of ooids have a grain size of more than 2 mm and represent a particular giant oolite occurrence in the Phanerozoic. These oolitic limestones formed during a special geological period, i.e., the Induan, and in a special sedimentary setting, i.e., on a ramp carbonate platform after a major transgression and severe biological mass extinction at the turn of the Permian to Triassic in South China (Chen, 1995;Hallam and Wignall, 1999;Mei and Tucker, 2007;. Thus, similar to the giant oolites of the Neoproterozoic (Summer and Grotzinger, 1993;Grotzinger and James, 2000), several features, which include the special forming geological time period, the special sedimentary setting, and the unusual appearance of giant oolites throughout the Phanerozoic in general, endow the Triassic giant oolites in the study area with an important sedimentological significance.…”