Full
GAO Qiuling,born in 1986,associate professor,is engaged in researches on reservoir sedimentology and petrogeochemistry. E-mail: g3q7l91@163.com.
Outline
The lacustrine carbonates of the Lower Cretaceous Barra Velha(BVE)Formation are important pre-salt oil and gas reservoirs in the deep-water Santos Basin in eastern Brazil,and their unique rock fabric characteristics have become the focus of academic attention. Over the past decade,numerous studies have been published on the fabric and genesis of these carbonates,yet controversies persist. Existing researches indicate that the in-situ carbonates of the BVE Formation mainly consist of calcite shrubs,calcite spherulites,and magnesium-rich clay minerals. There are opposing views on the genesis of the sedimentary fabric,whether it is microbial or chemical in origin,and correspondingly different classification schemes for the rocks. The deposition models also vary,including microbial deposition,chemical deposition,and travertine deposition. Since no obvious biological structures/substances have been identified so far,and the shrubs and spherulites exhibit fibrous crystal structures,an increasing number of studies support the view that chemical precipitation is the dominant process. However,it remains difficult to determine whether microbial and/or hydrothermal activity was involved. The comprehensive investigation of paleontological,autogenetic clay minerals and C-O-Sr isotopes shows that the sedimentary environment of BVE carbonates is a lake with high salt,high alkali and high evaporation,but the water temperature,water depth,material sources such as Mg-Si-Ca,carbonate formation stage or sedimentary and diagenetic superposition process and effect are still unclear. Based on the review of the relevant research progress,it is suggested that future studies should start from environmental medium parameters,material sources,and the origin of the main components,and carry out matched high-precision micro-fabric and in-situ major and trace elements,isotope analyses,as well as supporting experiments and numerical simulation,combined with modern investigation,macroscopic rock distribution,and dynamic system information on basin paleostructure and paleoclimate evolution,to unravel the enigma of the genesis of these carbonates together.
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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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