Abstract:

Carbonate diagenesis is one of the most active fields in sedimentology. The related research results directly influence peoples understanding about the formation mechanisms of carbonate oil/gas reservoirs and stratabounded deposits. In recent years, carbonate diagenesis has gotten prominent achievements in many fields, including the following aspects. (1) Man has succeeded in precipitating the dolomite with superstructure reflection under the conditions of bacterial sulfate reduction environment of sea water (lagoon) at normal temperature. (2) Hydrothermal dolomitization as the main model becomes the focus of the study. People come to an understanding that hydrothermal dolomite reservoirs, sedimentary exhalative (SEDEX) PbZn deposits and Mississippi valley type (MVT) of PbZn deposits have similar formation mechanisms. They are all controlled by the tectonics (extensional or/and strikeslip (wrench) faults) and fluid flow. (3) More attention is being focused on the deepburial closedsystem dolomitization. Some dolomitization of practical significance to the oil/gas reservoir and to the stratabounded deposits mainly occurred in closed system, which is different from the open system in the contribution to the change of reservoir space and the corresponding geochemical index. (4) Mixingzone model for dolomitization is being questioned. The typical Dorag model in Wisconsin of USA is restudied. Based on the studies using the fluid inclusions method, cathodoluminescence analysis, thin section identification, and stable isotope testing, and combined with organic maturity data, we concluded that the waterrock interaction relating to dolomitization is caused by the concentrated brine relating to increasing temperature. The dolomitization resulted from hydrothermal diagenesis. (5) The meteoric diagenesis mechanism is being challenged. The recent research shows that largescale sea level lowstands may not have chemically active meteoric lenses. The marine environment can produce mature limestone. The sea water can be under saturated with respect to carbonate by the result of bacterial sulfate reduction, which challenges a number of current diagenetic paradigms. (6) Strontium isotope is widely applied to the study of marine carbonate. Different from the oxygen and carbon isotope which has fractionation affected by temperature, pressure and microbial action, strontium isotope of mineral can directly reflect the isotopic composition of fluid. Meanwhile, the marine strontium isotope in geology history has particular long time trends, which make the tracing of marine carbonate strontium isotope composition be widely used in the postsedimentary fluid. (7) Influence of sulfate reduction on carbonate diagenesis has been paid more attention, which include the decrease of kinetic inhibitor for dolomitization or dolomite precipitation, the dissolution and alteration of carbonate reservoirs by H2S and CO2 that are the products of TSR, and the increase of the content of strontium in diagenetic pore water to form celestite deposits.

Key words: Key words: carbonate diagenesis; origin of dolomite; diagenetic environment; strontium isotopic tracer; sulfate reduction