Stratigraphic Sequence And Sedimentary Characteristics Of Marine Carbonate

After absorbing and summarizing the results of previous studies, we held a meticulousresearch of stratigraphic sequence and sedimentary features on the18carboniferous sectionswhich scattered in Qaidam area. We subdivided the main sedimentary facies, summarized theevolutionary pattern, analyzed the carboniferous sedimentation rules of this area andconfirmed features of section distribution of the area.According to the theories of sedimentology and sequence stratigraphy and the previousstudies, we analyzed the outcrop sections in the Qaidam Basin one by one. We came up tworesults as below：(1)The carboniferous system of the research area mainly is ashoreline-neritic sea carbonatite platform sedimentary environment. We subdivided them into10kinds of sedimentary facies. Since the littoral and neritic marine is potential environmentwhere source rock may develop, we had a detailed analysis on the shoreline environmentalpattern and its evolution laws. There are two shoreline environmental patterns in the researcharea. They are tidal flat-lagoon-restricted platform pattern and delta-restricted platformpattern. When there are abundant land-based fragments in shoreline area, it will be relativelysuitable for the development of tidal flat, lagoon and obstruct sand bank. While the land-basedfragments are undersupply, obstruct sand bank will be replaced by carbonatite deposition,except tidal flat and lagoon. Moreover, while the delta in shoreline area developes, platformcarbonate limestone is the main feature of prodelta parfacies clay shale in this pattern.(2)Through stratigraphic division and detailed comparison on the section, we summarized thedepositional evolution rules of the carboniferous system in the area. With the influence offilling a gap, the C1a which deposited as continental facies will not integrated with thedevonian system or other older stratums. As the continuously extending of the scope of sea transgression, the C1a transfers to shoreline-neritic sea carbonatite platform sedimentary.During the deposition to the C2k，tidal flat-lagoon-obstruct sand bank(carbonate platforms)sedimentary system will be more developed and will have larger deposition thickness andstable transverse distribution.Combining the studies on sequence stratigraphy framework and sedimentary facies, wefound that the carboniferous system in Qaidam Basin Area is mainly a shoreline-neritic seacarbonatite platform sedimentary environment.