干旱区生态环境知识资源中心(Arid): Origin of chert within the Turonian carbonates of Abu Roash Formation, Abu Roash area, Egypt: Field, petrographic, and geochemical perspectives

Arid

DOI	10.1002/gj.3566
	Origin of chert within the Turonian carbonates of Abu Roash Formation, Abu Roash area, Egypt: Field, petrographic, and geochemical perspectives
	Hussein, Ahmed W.1; Abd El-Rahman, Yasser M. H.2
通讯作者	Hussein, Ahmed W.
来源期刊	GEOLOGICAL JOURNAL
ISSN	0072-1050
EISSN	1099-1034
出版年	2020
卷号	55 期号:4 页码:2805-2833
英文摘要	This paper tries to elucidate the origin of the siliceous rocks (cherts) within the Turonian flint-bearing chalky limestone member of Abu Roash Formation, Abu Roash area, north Western Desert, Egypt. Understanding the formation mechanism of the studied chert was gained through field and petrographic investigations, supplemented by geochemical analyses of both cherts and host Turonian carbonates. The field observations reveal that the chert is found in two forms: banded and nodular. The microscopic investigation determined that the cherts exhibit two types of silica: replacive silica (cryptocrystalline and microcrystalline quartz) and silica cement (length-fast chalcedony and megaquartz). The chert texture corroborates that the examined authigenic silica was formed diagenetically by the replacement and void-filling of the host carbonate rocks. The silica was most likely derived from the biogenic opal-A of the siliceous radiolarian tests. The silica-phase transformation started with the dissolution of the biogenic opal-A and precipitation of opal-CT. Subsequently, opal-CT was recrystallized into crypto- and microquartz at low pH and high temperature. The length-fast chalcedony and megaquartz occur later as infill to the cavities and pore spaces. The formation of chert is interpreted to be a result of mixing marine-meteoric waters. The effect of the freshwater diagenesis on carbonates is manifested by the dissolution of the allochems, precipitation of granular, drusy, and blocky calcite (meteoric cements), aggrading neomorphism of matrix, and calcitization of the skeletal particles. Geochemical analyses of the host carbonates indicate nearly flat REE patterns and absence of a negative Ce anomaly. This confirms the deviation from the typical seawater and supports the effect of phreatic meteoric water in the chert formation. The paragenetic relationships reveal that the chertification process was performed after dolomitization and before the carbonate meteoric cementation.
英文关键词	Abu Roash chert Egypt geochemistry petrography Turonian
类型	Article
语种	英语
国家	Egypt
收录类别	SCI-E
WOS记录号	WOS:000475825700001
WOS关键词	RARE-EARTH-ELEMENTS ; EARLY DIAGENETIC CHERT ; AMURI LIMESTONE GROUP ; SOUTH CHINA ; SILICA DIAGENESIS ; LOWER EOCENE ; DEPOSITIONAL-ENVIRONMENTS ; SEQUENCE STRATIGRAPHY ; YANGTZE PLATFORM ; FACIES ANALYSIS
WOS类目	Geosciences, Multidisciplinary
WOS研究方向	Geology
资源类型	期刊论文
条目标识符	http://119.78.100.177/qdio/handle/2XILL650/215963
作者单位	1.Fayoum Univ, Fac Sci, Geol Dept, Al Fayyum 63514, Egypt; 2.Cairo Univ, Fac Sci, Geol Dept, Giza, Egypt
推荐引用方式 GB/T 7714	Hussein, Ahmed W.,Abd El-Rahman, Yasser M. H.. Origin of chert within the Turonian carbonates of Abu Roash Formation, Abu Roash area, Egypt: Field, petrographic, and geochemical perspectives[J],2020,55(4):2805-2833.
APA	Hussein, Ahmed W.,&Abd El-Rahman, Yasser M. H..(2020).Origin of chert within the Turonian carbonates of Abu Roash Formation, Abu Roash area, Egypt: Field, petrographic, and geochemical perspectives.GEOLOGICAL JOURNAL,55(4),2805-2833.
MLA	Hussein, Ahmed W.,et al."Origin of chert within the Turonian carbonates of Abu Roash Formation, Abu Roash area, Egypt: Field, petrographic, and geochemical perspectives".GEOLOGICAL JOURNAL 55.4(2020):2805-2833.