Biogenic Leopard Patch Structures From The Zhushadong Formation(cambrian Series 2),Dengfeng Area,Western Henan

The Zhushadong Formation(Cambrian Series 2), well exposed in Dengfeng area, western Henan, China, is characterized by stromatolite dolomitite, calcarenite, leopard patch dolomitite, leopard patch limestone and earthy yellow mudstone. Abundant distinctive leopard patch structures occur in the leopard patch structures from Zhushadong Formation in Dengfeng area, western Henan. The leopard patches in the leopard patch structures, gray to dark gray in colour, display tubal, piebald and grid distribution and mainly consist of subidiomorphic and idiomorphic dolomite. The matrix in the leopard patch structures, grey-white to light gray in colour, mainly consists of microcrystalline calcite and has the clear boundaries with leopard patches.The leopard patches can be divided into three types: banded,piebald and grid structures based on their morphological and development characteristics. The three types of the leopard patch structures can respectively belong to dolomictic patchy limestone, calcareous patchy dolostone and patchy dolostone.The study shows that the leopard patch strucutures were produced by the diagenetic dolomite replacement which preferentially began within the complex burrow systems built by Thalassinoides trace-makers. The leopard patches from the Zhushadong Formation evolved from the banded structures via piebald into grid structures from the bottom to up, reflecting the gradually reducing water energy, more stable environment, more complex burrow systems, increasing bioturbation intensity and enhancing diagenetic dolomitization.