TY - JOUR
T1 - Clay mineral diagenesis in Cretaceous clastic reservoirs from West African passive margins (the South Gabon Basin) and its impact on regional geology and basin evolution history
AU - Zanoni, Giovanni
AU - Šegvić, Branimir
AU - Moscariello, Andrea
N1 - Funding Information:
Financial support for this research was provided by Addax Petroleum Corp. (Geneva office) ( 168/141715 ) which is gratefully acknowledged. We extend our appreciation to the company for giving us the access to their core material and to some of the unpublished research on the Gabon area, as well as for granting us a permit to publish this study. We are particularly indebted to L. Tranchet for his support and kind availability. F. Gischig is thanked for an outstanding quality of thin and polished sections needed for QEMSCAN® and SEM-EDS investigations, whereas R. Cerny is acknowledged for providing excellent working conditions during extensive XRD measurements. A great appreciation is addressed to A. Ristić for his assistance with English and to R. Ferreiro Mählmann for a fruitful discussion during the Swiss Geoscience Meeting-2015 held in Basel on the preliminary results of this project. Finally, constructive reviews by W. D. Huff and O. Bozkaya as well as the editorial handling and suggestions by E. Galán contributed greatly to the quality of the final version of this manuscript.
Publisher Copyright:
© 2016 Elsevier B.V.
PY - 2016/12/1
Y1 - 2016/12/1
N2 - The Gabon coastal region located along the western African margin hosts several sedimentary basins that developed prior, during and after the opening of the South Atlantic Ocean. A range of diagenetic processes controlled the distribution of clay paragenesis shown to be of high importance for the understanding of the basin's burial history and geotectonic development. Materials acquired for this study stem from the siliciclastic fluvio-lacustrine-deltaic, petroleum bearing, Early Cretaceous Dentale and Gamba formations cored by two respective wells at depths of ~ 1500 m. Sampled materials were analysed by X-ray diffraction, automated electron microscopy, and inductively coupled plasma mass spectrometry in order to reconstruct eogenetic and mesogenetic variations directing the formation of clay assemblages in the basin. The clay contents in both cores consist of authigenic mixed-layer minerals like illite-smectite, chlorite-smectite and berthierine-chlorite, and some minor detrital illite/mica and chlorite. I-Sm and C-Sm phase chemistry implied that the original dioctahedral (montmorillonite to beidellite) and trioctahedral (saponite) smectite precursors formed out of acid volcanic feedstock during eogenesis. Different magmatic fractionation degrees, from rhyodacite to trachyandesite, reflected in the uniform REE curves of volcanic glass conform to an active geotectonic development of the Cretaceous margins of Africa. Mesogenesis led to the decrease of smectite and formation of mixed-layered phases; I-Sm composition showed maximal burial depths of sediments to be ~ 1000 m and ~ 500 m deeper than today for Gamba and Dentale sediments, respectively. Besides, temperature, a major role in the formation of mixed-layer minerals had the porosity of sediments and geochemistry of smectitic precursors. Thus, Fe-Mg smectite showed higher thermal stability and lower rates of transformations in non-expanding clays during burial compared to Al-rich smectite. Different burial histories of sediments from the two cores can be attributed to rift-related normal faulting and subsequent differential denudation.
AB - The Gabon coastal region located along the western African margin hosts several sedimentary basins that developed prior, during and after the opening of the South Atlantic Ocean. A range of diagenetic processes controlled the distribution of clay paragenesis shown to be of high importance for the understanding of the basin's burial history and geotectonic development. Materials acquired for this study stem from the siliciclastic fluvio-lacustrine-deltaic, petroleum bearing, Early Cretaceous Dentale and Gamba formations cored by two respective wells at depths of ~ 1500 m. Sampled materials were analysed by X-ray diffraction, automated electron microscopy, and inductively coupled plasma mass spectrometry in order to reconstruct eogenetic and mesogenetic variations directing the formation of clay assemblages in the basin. The clay contents in both cores consist of authigenic mixed-layer minerals like illite-smectite, chlorite-smectite and berthierine-chlorite, and some minor detrital illite/mica and chlorite. I-Sm and C-Sm phase chemistry implied that the original dioctahedral (montmorillonite to beidellite) and trioctahedral (saponite) smectite precursors formed out of acid volcanic feedstock during eogenesis. Different magmatic fractionation degrees, from rhyodacite to trachyandesite, reflected in the uniform REE curves of volcanic glass conform to an active geotectonic development of the Cretaceous margins of Africa. Mesogenesis led to the decrease of smectite and formation of mixed-layered phases; I-Sm composition showed maximal burial depths of sediments to be ~ 1000 m and ~ 500 m deeper than today for Gamba and Dentale sediments, respectively. Besides, temperature, a major role in the formation of mixed-layer minerals had the porosity of sediments and geochemistry of smectitic precursors. Thus, Fe-Mg smectite showed higher thermal stability and lower rates of transformations in non-expanding clays during burial compared to Al-rich smectite. Different burial histories of sediments from the two cores can be attributed to rift-related normal faulting and subsequent differential denudation.
KW - Berthierine-chlorite
KW - Diagenesis
KW - Gabon Basin
KW - Mixed-layer clay minerals
KW - Passive margins
KW - Sandstone
KW - South Atlantic
UR - http://www.scopus.com/inward/record.url?scp=84992045487&partnerID=8YFLogxK
U2 - 10.1016/j.clay.2016.09.032
DO - 10.1016/j.clay.2016.09.032
M3 - Article
AN - SCOPUS:84992045487
VL - 134
SP - 186
EP - 209
JO - Applied Clay Science
JF - Applied Clay Science
SN - 0169-1317
ER -