Characteristics of subaerial karstification and late reconstruction in the Dengying Formation, Sichuan basin, southwestern China

Abstract

Tectonic uplift at the end of Sinian resulted in the denudation of the Dengying (灯影) Formation on a different scale and the development of a great number of secondary dissolution vugs beneath the unconformity between Sinian and Cambrian. Geological and geochemical characteristics such as the development of caves, sinkholes, karst tubes and weathering crust, abrupt depletion and negative deflection of δ 13 C and δ 18 O in country rock and vug filling toward unconformity surface suggest that subaerial karstification is responsible for the development of secondary karst vugs within 150 m or so beneath the unconformity surface. This kind of secondary dissolution vug was partially or completely filled by different stage dolomite, calcite, quartz and bitumen during the later deep burial and uplift. Facts such as the obvious difference in δ 13 C and δ 18 O of the filling in the subaerial karst vug from the country rock and the value of δ 13 C and δ 18 O of the filling increasing or decreasing with that of the country rocks, suggest that the hydrothermal fluid charged in vugs is allogenic fluid. Subaerial karstification vug acted as a conduit for allogenic corrosive fluid which can create new secondary vugs and enlarge previous karst vugs. corrosive fluid introduction and petroleum thermal cracking, caused contraction or enlargement of the subaerial karstification vugs and the development of new secondary vugs during the deep burial and uplift. The ultimate vug of deep burial dolomitite is determined not only by fluid charge, dissolution, mineral precipitant, and petroleum thermal cracking during the deep burial and tectonic uplift, but also by Characteristics of Subaerial Karstification and Late Reconstruction in the Dengying Formation, Sichuan Basin 291 the amount of initial secondary dissolution vugs created by subaerial karstification.

Sedimentology and chemostratigraphy of the terminal Ediacaran Dengying Formation at the Gaojiashan section, South China

“…Sedimentological observations suggest that the karstification events of shallow carbonate platforms may be widespread in the late Ediacaran Period. Notably, similar karstification textures of carbonate breccia, aragonite crystal fans and botryoidal aragonites have also been found from other correlative sections, including the other Dengying sections in South China (Zhang, 1980;Cao & Xue, 1983;Siegmund & Erdtmann, 1994;Xiang et al 2001;Wang et al 2010Wang et al , 2012Shi et al 2011;Liu et al 2012;Mo et al 2013;Zhang et al 2014b;Lin et al 2015;Mou et al 2015;Lian et al 2016Lian et al , 2017, the Qigebulake Formation in the Tarim basin in Northwestern China (Qian et al 2017), the Buah Formation in Oman (Gorin et al 1982;Cozzi & Al-Siyabi, 2004;K. D. Bergmann, unpub.…”

“…In geological records, botryoidal aragonites of both marine origin (Ginsburg & James, 1976;Mazzullo & Cys, 1979;Aissaoui, 1985;Jiang et al 2006a) and non-marine origin (Mazzullo, 1980;Aissaoui, 1985) have been reported. Proposed interpretations for the Dengying aragonites include primary syn-depositional seafloor precipitates (Zhang, 1980;Cao, 2002;Zhang et al 2014b;Lin et al 2015;Peng et al 2017), authigenic carbonates formed in meteoric waters (Wang et al 2010;Shi et al 2011), authigenic carbonates formed in marine environments (Si et al 2014;Hao et al 2015;Mou et al 2015;Tan et al 2015) and late authigenic carbonates formed during burial diagenesis (Wang et al 2000).…”