Petrographical and geophysical investigation of the Ecca Group between Fort Beaufort and Grahamstown, in the Eastern Cape Province, South Africa

被引:2
|
作者
Baiyegunhi, Christopher [1 ,2 ]
Nxantsiya, Zusakhe [2 ,3 ]
Pharoe, Kinshasa [2 ,3 ]
Baiyegunhi, Temitope L. [2 ]
Mepaiyeda, Seyi [2 ]
机构
[1] Univ Limpopo, Dept Geol & Min, Private Bag X1106, ZA-0727 Sovenga, South Africa
[2] Univ Ft Hare, Fac Sci & Agr, Dept Geol, Private Bag X1314, ZA-5700 Alice, Eastern Cape Pr, South Africa
[3] Council Geosci, 280 Pretoria St, ZA-0184 Pretoria, South Africa
来源
OPEN GEOSCIENCES | 2019年 / 11卷 / 01期
关键词
Density; dolerites; Ecca Group; gravity; magnetic; porosity; KAROO BASIN; SEDIMENTARY ENVIRONMENTS; BALFOUR FORMATION; STRATIGRAPHY; PROFILE;
D O I
10.1515/geo-2019-0025
中图分类号
P [天文学、地球科学];
学科分类号
07 ;
摘要
The outcrop of the Ecca Group in the Eastern Cape Province was investigated in order to reveal petrographic and geophysical characteristics of the formations that make up the group which are vital information when considering fracking of the Karoo for shale gas. The petrographic study reveals that the rocks of the Ecca Group are both argillaceous and arenaceous rock with quartz, feldspar, micas and lithics as the framework minerals. The sandstones are graywackes, immature and poorly sorted, thus giving an indication that the source area is near. The observed heavy minerals as well as the lithic grains signify that the minerals are of granitic, volcanic and metamorphic origin. The porosity result shows that of all the formations that make up the Ecca Group, the Whitehill Formation is the most porous with an average porosity of about 2.1% and also least dense with an average dry density of about 2.5 g/cm(3). The least porous unit is the Ripon Formation with porosity of about 0.8% but has the highest dry density of approximately 2.8 g/cm(3). The magnetic map shows some ring-like structures which coincide with dolerites that were mapped in the field. As revealed by the depth slices result, dolerite intrusions are pervasive in the northern part of the study area, extending to a depth of about 6000 m below the ground surface. The appearance of dolerite intrusions at the targeted depth (3000 - 5000 m) for gas exploration could pose a serious threat to fracking of the Karoo for shale gas.
引用
收藏
页码:313 / 326
页数:14
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