165 / 2022-02-27 20:56:05

北京西山下苇甸寒武系昌平组白云岩的成因与分布特征

Dolomitization model; Recrystallization; Sequence stratigraphy; Paleogeography; Stable isotope

Tidal flat and lagoon carbonates of the Lower Cambrian Changping Formation in the West Mountain of Beijing are mainly composed of dolomites, limestones and dolomitic limestones which represents a complete carbonate cycle in sequence stratigraphic framework. Based on petrographic textures, two types of dolomites were identified: micritic dolomite(D1) and fine-crystalline dolomite(D2). Integration of petrographic, stable oxygen and carbon isotope, and fluid inclusions data with the paleogeography and paleoclimate revealed two major diagenetic stages: Dolomitizing hypersaline fluids during the early Cambrian resulted in formation of the dolomite at the bottom of Changping Formation in supratidal and sabkha settings. During the late period of the Changping Formation, the peritidal carbonates were dolomitized by refluxing evaporatively concentrated brines from the overlying Mantou Formation strata. In this paper we discussed the original sedimentary environment of dolomite and the dolomitization in the sequence stratigraphic frameworks by using petrology, geochemistry and sequence stratigraphy. There is already some evidence suggesting that the different kind of dolomites in the study area have a corresponding relationship with the sequence stratigraphic framework. The factors influencing sequence stratigraphic framework could have a profound impact on the original depositional environment and component of deposited material resulting in the differences in the micromorphology of the dolomites. Sabkha dolomite formed by evaporation pumping is developed near the maximum flooding surface and seepage reflux dolomite is usually accompanied with the evaporation pumping dolomite, which forming a vertical cycle in sequence stratigraphic framework: from top to bottom are, in order, sabkha dolomite, seepage-reflux saccharoidal dolostone, mottled micrite dolomitic limestones and limestone.

This study identifies two types of dolomites within Changping Formation carbonates of West Mountain in Beijing and provides conclusive evidence suggesting that the relationship between the distribution of dolomite and sequence stratigraphy.