The present study investigates the processes responsible for Middle Eocene dolomite occurrences in Kachchh Basin in the western Indian Continental Shelf. Three types of dolomites are identified. They exhibit euhedral to subhedral crystal boundaries and a core of calcite or amorphous organic matter. Non-stoichiometric dolomite is the major component, while calcite, pyrite, glauconite, palygorskite, chlorite and quartz are minor constituents. The presence of algal micritization, oxidized organic matter, framboidal pyrites and filamentous- to net-like microbial covering around dolomites suggests an organogenic origin. The studied dolomite sustained marine–phreatic, meteoric–phreatic and meteoric–vadose diagenesis. The marine–phreatic diagenesis is evidenced by algal micritization, pyritization, matrix-replacive early dolomitization and marine cementation; the meteoric–phreatic diagenesis by neomorphism or crystal coarsening, shell dissolution and pore-filling sparitic cement and the meteoric–vadose diagenesis by secondary porosity and permeability, partial filling of meteoric–vadose cements and ferruginization, reflecting regression of seawater. The δ¹⁸O (− 1 to 1.7‰ VPDB) values of the studied dolomites infer modified seawater as the diagenetic fluid for dolomitization. The δ¹⁸O-based diagenetic temperature varies between 18° and 32 °C. The diagenetic temperature, inhomogeneous texture and point to tangential contacts of allochems reflect a shallow burial origin. The extremely negative δ¹³C values (− 26 to − 39‰ VPDB) reflect mixing of normal marine carbon with a carbon reservoir strongly depleted in ¹³C, most likely oxidation of methane or biodegradation of crude oil. Methane would have been supplied through upward seepage of thermogenic methane from underlying hydrocarbon reservoir(s).

本研究调查了印度大陆架西部 Kachchh 盆地中始新世白云岩产状的过程。确定了三种类型的白云岩。它们表现出自面体到半面体晶界和方解石或无定形有机物质的核心。非化学计量白云石是主要成分，方解石、黄铁矿、海绿石、坡缕石、绿泥石和石英是次要成分。藻类微晶化、氧化有机物、球状黄铁矿和覆盖在白云岩周围的丝状至网状微生物的存在表明有机起源。所研究的白云岩持续了海洋-潜水、大气-潜水和大气-包气成岩作用。海洋-潜水成岩作用由藻泥化、黄铁矿化、基质置换早期白云石化和海相胶结；大气-潜水成岩作用由新生或晶体粗化、壳层溶解和孔隙充填散粒胶结作用，大气-包气成岩作用由次生孔隙度和渗透率、大气-包气胶结物部分充填和铁锈化作用，反映海水退缩。δ^{所研究的白云岩的18} O (− 1 to 1.7‰ VPDB) 值推断改性海水是白云石化的成岩流体。基于 δ ¹⁸ O 的成岩温度在 18° 和 32°C 之间变化。成岩温度、不均匀的质地和异生物质的切向接触点反映了埋藏较浅的起源。极负的 δ ¹³ C 值（- 26 到 - 39‰ VPDB）反映了正常海洋碳与¹³ C 强烈耗尽的碳储层的混合，很可能是甲烷氧化或原油生物降解。甲烷将通过从下面的碳氢化合物储层向上渗出的热成因甲烷来提供。