Objective The Second member of the Middle Permian Lucaogou Formation is the main exploration target for lacustrine carbonate shale oil in the Santanghu Basin, Xinjiang province, China. Clarifying its paleoenvironment and organic matter enrichment mechanism provides scientific evidence in support of shale oil exploration and development in the study area. Methods Tests for total organic carbon content, major and trace elements and carbon-oxygen isotopic composition of primary carbonate rocks were conducted on shale samples collected from the well Luye 1 in the Second member of the Lucaogou Formation in the in the Malang Sag, Santanghu Basin. These deciphered the paleoenvironment and associated organic matter enrichment mechanism of the shale sequence, hence helping to gain a better understanding of the effects of paleoproductivity, paleoclimate, paleosalinity and paleoredox conditions on the organic matter enrichment and the key elements. Results Shale oil sweet spots are present in the middle and upper parts of this shale sequence. The tests indicated a closed lacustrine setting. The lowest part of the middle sweet spot was deposited in an arid, saline and reduced deep-water environment with low paleoproductivity, whereas its upper section has high paleoproductivity and was deposited in a semi-arid, brackish and weakly reducing deep-water environment. The upper sweet spot was deposited in an arid, saline and weakly reduced semi-deep water setting with medium paleoproductivity. Conclusions The organic matter enrichment mechanisms vary between the different shale sections. The influencing elements were the redox conditions and paleoproductivity in the lowest part of the middle sweet spot, paleoclimatic conditions and paleoproductivity for the upper part of the middle sweet spot, and paleoproductivity in the upper sweet spot. This study will assist in shale oil exploration and development in the Second member of the Lucaogou Formation in the Santanghu Basin.
| 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 |