Full
GUO Mengmeng,born in 2002,is a master degree candidate. She is mainly engaged in sedimentology. E-mail: 2171516975@qq.com.
Outline
Based on field outcrops,microscopic observation and grain size analysis,this study investigates the sedimentary types,characteristics and evolution of the gravity flows in the Ordovician Yingtaogou Formation at the western margin of the Ordos Basin,and establishes a corresponding sedimentary model. The results show that: (1)Four deep-water sedimentary types are developed in the study area,namely debris flow deposits,high-density turbidity current deposits,low-density turbidity current deposits and deep-water autochthonous deposits. Debris flow deposits are mainly composed of calcirudite and develop massive bedding;high-density turbidity current deposits show inverse-to-normal grading sequence and develop Bouma-like sequence;low-density turbidity current deposits develop groove cast,flute mark and incomplete Bouma sequence;deep-water autochthonous deposits develop horizontal bedding.(2)Four types of gravity flow sedimentary microfacies are mainly developed in the study area,namely main channel deposits,channelized lobe deposits,sheet lobe deposits and distal lobe deposits. Main channel deposits are mainly debris flow deposits;channelized lobe deposits are composed of high-density turbidity current deposits superimposed on each other;sheet lobe deposits have high-density turbidity current deposits at the bottom and low-density turbidity current deposits at the top;distal lobe deposits mainly develop low-density turbidity current deposits.(3)The Yingtaogou Formation is divided into five evolutionary stages,from bottom to top: high sea level stage,low sea level stage,high sea level stage,low sea level stage and high sea level stage. In the high sea level stage,low-density turbidity currents and deep-water suspension deposits are mainly developed,while in the low sea level stage,debris flows,high-density turbidity currents and low-density turbidity currents are mainly developed.(4)The average porosity of sheet lobe deposits in the study area is about 6.61%,and the average permeability is about 6.02×10-3 μm2,which is better than that of channelized lobe deposits and distal lobe deposits,and has good reservoir performance. The deep-water autochthonous deposits and sheet lobe deposits of the Yingtaogou Formation are superimposed,forming an ideal combination of source reservoir and covering rock with them. Therefore,the Ordovician gravity flow deposits at the western margin of the Ordos Basin are potential targets for the next oil and gas exploration.
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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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