Full
YANG Mengying,born in 1997,a doctoral candidate,is engaged in research on carbonate deposits and reservoirs. E-mail: ymying22@163.com.
Outline
Recently,mixed sedimentation involving clastic,carbonate,and evaporite components has been identified at the base of the Majiagou Formation in the Ordos Basin,offering significant insights into the tectonic-palaeogeographic framework during its early depositional phase. This study systematically examines macroscopic and microscopic petrological features,along with representative depositional sequences,to reconstruct the depositional environment. Integrated geochemical analyses were conducted to investigate the genetic mechanisms,geological significance,and elemental behavior associated with this mixed sedimentary system. Key findings include: (1)The mixed sedimentary assemblage comprises three primary lithological components—clastic rocks,carbonate rocks,and anhydrite.(2)Sedimentary structures indicative of tidal flat environments,including scour surfaces,normal grading,transitional bedding,and brecciated anhydrite,were observed and used to define four subfacies: tidal-dominated channels(F1),muddy/arenaceous dolomitic flat(F2),gypsum-bearing dolomitic flat(F3),and supratidal sabkha(F4).(3)Geochemical data reveal distinct elemental partitioning during sedimentation,with vertical variations reflecting fluctuating terrestrial input driven by sea-level changes. Laterally,rare earth elements exhibit greater mobility compared to terrigenous elements,suggesting longer transport distances. The results indicate that the mixed sedimentation originated from reworking of sandstones derived from the exposed Changcheng System within the central Wushen Banner-Jingbian palaeouplift,triggered by marine transgression during the early stage of Majiagou deposition. This unit thus serves as critical evidence for the existence and persistence of the Wushen Banner-Jingbian palaeouplift during the O1m1 to O1m2 intervals,which played a critical role in facilitating regional uplift and ensuring sustained supply of terrigenous clastics throughout this period.
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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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