Tectonic paleogeography of Late Sinian and its significances for petroleum exploration in the middle-upper Yangtze region, South China

WANG Zecheng,JIANG Hua,CHEN Zhiyong,LIU Jingjiang,MA Kui,LI Wenzheng,XIE Wuren,JIANG Qingchun,ZHAI Xiufen,SHI Shuyuan,LI Qi

Table 1 Types and main characteristics of sedimentary facies of the Sinian Dengying Formation in the middle-upper Yangtze region.

Facies Subfacies Microfacies Facies Representative well/ profile, horizon Restricted evaporation platform Marl mounds, microbial mound beach, grain beach, dolomitic flat; seas between mounds and beaches; restricted platform, evaporative lagoon and tidal flat Spheroidal thrombolite framework dolomite, microcrystalline thrombolite dolomite, foam sponge layer dolomite, stromatolite, layered dolomite; gravel, dolarenite, oncolite dolomite, silicon strip dolomite, muddy dolomite; micritic dolomite, silty dolomite; nodular, layered anhydrite, gypsum- containing (nodules, clumps, crystals, pseudocrystals) micrite and muddy dolomites, sand-bearing muddy dolomite, etc. With small uplifts, no anti-wave structure; small thickness of granular dolomite in uplift wing; and gypsum-bearing micritic dolomite, gypsum and halite Dengying Formation in Well Moxi 8, Moxi 10 and Moxi 11; Deng 1 Member in Well Wei 117 and Well Ning 2; Deng 4 Member in Well Gaishi 18, Zeng 1, Hui 1; Deng 2 Member of Huichang Yinchangpo Section in Northeast Yunnan Intra- platform rift Depression upper slope, lower slope; shallow trough basin and deep trough basin Bypass gravel dolomite on the upper slope of the sag; nodular dolomite, dolomite with argillaceous laminae or strips on the lower slope of the sag; thin layers of argillaceous dolomite and dolomitic mudstone in the under-filled shallow trough basin; shale in under-filled deep trough basin Mud-bearing micrictic dolomite, nodular muddy micritic dolomite, mud laminae, dolomite with muddy strip in band shape Deng 1 of Well Chang 3; Deng 2 of Well Heshen 1 and Gaoshi 17 Margin of platform sag Microbial mound, small microbial reef, grain beach, tidal flat Thrombolite dolomite, spherical oncolite dolomite, dolomite in foam sponge layer, stromatolite, stratified, snowflake-like dolomite, interbedded with thin layers of microbial reefal dolomite, gravel, dolarenite, etc. Rich in microbial fossils, large microbial mounds and beaches distributed in strips, and small microbial reefs Deng 2 and Deng4 members in Well Zi 4, Gaoke 1, and Gaoshi 1 etc. Platform margin Large-scale microbe reef, microbe mound, grain beach, and tidal flats Microbial reefal dolomite, thrombolite framework dolomite, foam sponge layer dolomite, stromatolite, stratified dolomite, snowflake-like dolomite, oolite, oncolite, gravel, dolarenite etc. Large microbial reef shoals, mounds and grain shoals with the highest microbial abundance distributed in an ring Deng 2 Member on Xianfeng section, Deng 4 Member on Gaojiashan section, Deng1 Member on Zunyi Songlin section Slope- basin Platform front upper and lower slopes; shallow and deep water underfilled wide basin Upper slope: Bypass gravel dolomite constitutes gravel piles around the edge of the craton; Lower slope: bypass gravel-bearing carbonate, nodular or argillaceous lamina, argillaceous carbonate, slump carbonate rock, turbidite carbonate rock. Shallow water under-fill- ed basin: thin plate-shaped and banded muddy micritic carbonate rock and mud shale; deep water under-compensated basin: dark mud shale and dark carbon-silicon mud shale Bypass gravel dolomite, nodular and thin platy muddy micritic dolomite interbedded with shale, gravity flow limestone, sandy dolomite, dark mudstone, carbon silicon mudstone Dengying Formation in Lijiagou section in southern Shaanxi, Deng 2 in Xiushan Rongxi section, Deng 3 in Zigui Sanguiping section, West Hubei, Dengying Formation in Jianhe Wuhe section, Guizhou province