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Objective Limestone-marlstone alterations （LMAs） are important archives of climatic， hydrological， and geological events. However， as a typical endmember of the LMAs， knowledge regarding the genesis of the LMAs with eyelid-eyeball structure from First member of the Maokou Formation in the Sichuan Basin is not widely accepted. This not only seriously affects environmental research of the LMAs with eyelid-eyeball structure， but also affects the efficiency of its exploration. Dolomitization is developed in the LMAs with eyelid-eyeball structure （mainly in the eyelids） of First member of the Maokou Formation of well DB1 during the penecontemporaneous and early diagenetic phase can be used to constrain the depositional environments of carbonate rocks. Methods Petrological and geochemical analyses have been conducted in detail， the process and the fluid properties of dolomitization has been discussed to constrain the process of LMAs with eyelid-eyeball structure. Results Three types of dolomitization developed in First member of the Maokou Formation， which are muddy dolomitic （EDM-I）； limy dolomitic （EDM-II）； and dolomitic marlstone （EDL）. EDM-I has the highest degree of dolomitization， distinct bands of cathodoluminescence， a flat rare earth partitioning pattern， higher δ13C and δ18O values， but lower Y/Ho values relative to seawater； it was dolomitized by penecontemporaneous seawater mixed with a small amount of meteoric freshwater during the penecontemporaneous phase. EDM-II has a middle degree of dolomitization， a left leaning rare earth partitioning pattern， and values of δ13C， δ18O， 87Sr/86Sr， and Y/Ho similar to seawater； it was dolomitized by seawater with high Mg/Ca， which was induced by frequent sea-level rise and fall changes during the syn-sedimentary and penecontemporaneous phase. EDL has the lowest degree of dolomitization， a left leaning rare earth partitioning pattern， higher δ13C and δ18O values relative to EDM-II， and seawater-like Y/Ho values. EDL was dolomitized by the sealed seawater of the syn-sedimentary phase that has been alterated with the wall rocks in the early diagenetic stage. Conclusions The dolomitization of the LMAs with eyelid-eyeball structure by weakly evaporating seawater and seawater mixed with freshwater during the penecontemporaneous and early diagenetic phase requires that the LMAs deposited in a shallower water. The high mud content， high strontium isotope and rare earth element values， low carbon and oxygen isotope values，and Y/Ho values of the eyelid-like marlstone relative to the eyeball-like limestone indicate that the depth of water for the eyelid-like marlstone is shallower than that of the eyeball-like limestone during deposition. Therefore， the LMAs in First member of the Maokou Formation were produced under cyclic oscillation in the depositional environment， and their genesis may have been mainly influenced by sedimentary process.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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