Rock composition and origin of late Cretaceous shales in the Duwi Formation, Upper Egypt
Rock composition and origin of late Cretaceous shales in the Duwi Formation, Upper Egypt
复制标题
上埃及杜维组晚白垩世页岩的岩石成分和成因
DOI：
10.2465/jmps.98.76
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发表时间：
2003
影响因子：
0.7
通讯作者：
M. Helmy
中科院分区：
文献类型：
--
作者：
H. Baioumy;Abd El;S. Boulis;M. Hassan;M. Helmy
杜威组北出露于Qena，南出露于IDFU，由多个磷岩夹层组成，夹层有页岩、泥灰岩、硅质岩和石灰岩。对页岩夹层进行了野外、岩石学、矿物学和地球化学研究，以检验其岩石成分和成因。页岩主要是化石，主要由泥质物质、石英、长石、磷酸盐球体和骨骼碎片组成。分离出的砂组分轻组分由石英、斜长石和微斜长石组成。重矿物包括不透明矿物、锆石、电气石、绿帘石、石榴石、金红石和磷酸盐。块状岩石的X射线衍射分析表明，石英、方沸石、石膏、硬石膏、微斜长石、钠长石、岩盐、针铁矿和褐铁矿为非粘土矿物。粘土矿物有蒙脱石、高岭石和伊利石。研究表明，这些页岩的成分继承自研究区南部和东南部的镁铁质火成岩和石英质沉积岩的风化作用，并通过河流体系输送到浅海环境。蒙皂石的丰度表明这些页岩是在海侵时期和干旱至半干旱的气候条件下沉积的。
Duwi Formation that crops out between Qena to the north and Idfu to the south is composed of a number of phosphorite beds intercalated with shales, marls, cherts, and limestones. The shale intercalations were subjected to field and petrographic, mineralogical and geochemical investigations in order to examine their rock composition and origin. Shales are mainly fossiliferous and composed essentially of argillaceous materials, quartz, feldspar, phosphatic pelloids and skeletal fragments. The light fraction of the separated sand fraction is composed of quartz, plagioclase and microcline. The heavy fraction consists of opaque minerals, zircon, tourmaline, epidote, garnet, rutile and phosphates. X-ray diffraction analyses of bulk rocks identified quartz, francolite, gypsum, anhydrite, microcline, albite, halite, goethite and limonite as non-clay minerals. The clay minerals are smectite, kaolinite, and illite. The study have revealed that the constituents of these shales were inherited from the weathering of mafic igneous rocks as well as quartzose sedimentary rocks situated to the south and southeast of the study area, transported via a fluvial system into shallow marine environment. The abundance of smectite suggests the deposition of those shales in a period of transgression and arid to semi-arid climatic conditions.