Characteristics and Genesis Mechanisms of Deep Ordovician Dolomites in the Fuman Area, Tarim Basin

Abstract

The deep Ordovician Yingshan Formation dolomites in the Fuman area of the Tarim Basin possess enormous potential for hydrocarbon exploration and development, yet their development characteristics and formation mechanisms remain uncertain. Focusing on the deep Ordovician Yingshan Formation dolomites in the Fuman area, this study integrates observations from single-well cores, thin sections, scanning electron microscopy, and in situ carbonate geochronology to analyze dolomite characteristics and formation mechanisms. The results show that: (1) the rocks display clear mottled textures, with two typical dissolution styles, namely fabric-selective and non-fabric-selective dissolution; (2) the dolomites record at least two diagenetic episodes: an early shallow-burial dolomitization/recrystallization event constrained by Ordovician carbonate paragenesis and U–Pb systematics and a later burial-related dolomitization event at ca. 394–335 Ma; and (3) two genetic dolomite types are recognized: fine- to medium-crystalline dolomite formed by burial recrystallization of penecontemporaneous dolomite and medium- to coarse-crystalline dolomite formed by burial dolomitization of limestone. Dolomitization during different periods provided the foundation for the development of deep reservoirs and constitutes an important guarantee for deep hydrocarbon accumulation.