Naslov
Clay mineral diagenesis in Cretaceous Dentale and Gamba clastic reservoirs from the South Gabon Basin (West African passive margin) – new insights on the regional geology and basin evolution history

Autori
Zanoni, G ; Šegvić, Branimir ; Moscariello, A

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Skup
14th Swiss Geoscience Meeting

Mjesto i datum
Ženeva, Švicarska, 18.11.2016. - 19.11.2016

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
diagenesis ; Gabon ; West Africa ; Dentale ; Gamba

Sažetak
The Gabon coastal region located along the equatorial West African continental margin, hosts several sedimentary basins with well- developed and prolific petroleum systems whose two key elements (source and reservoir) developed prior, during and after the opening of the South Atlantic Ocean in Cretaceous time. In this study, we focus on the Early Cretaceous Dentale and Gamba Formations in the onshore part of the South-Gabon sub-basin formed during the syn-rift and transition to post-rift time respectively. The two formations are both consisting of siliciclastic rocks thought to be accumulated in fluvial and lacustrine environments. The exceptional access to core material from two wells from these two reservoirs allowed us to provide unprecedented information on their mineralogy, geochemistry and thus origin and post-depositional diagenetic processes that controlled the distribution of clay parageneses. The latter is considered to be of high importance for the understanding of the basin's burial history and geotectonic development. Sampled material was analysed by X-ray diffraction, automated electron microscopy, and inductively coupled plasma mass spectrometry in order to reconstruct early and burial diagenetic variations directing the formation of clay assemblages in the basin.The clay content in both cores consists of authigenic mixed-layer minerals like illite-smectite (I-S), chlorite- smectite (C-S) and berthierine-chlorite (B-C) and some minor detrital illite/mica and chlorite. Illite-smectite and C-S phase chemistry are interpreted as the product of progressive evolution from the dioctahedral (I- S) and trioctahedral (C-S) smectitic precursors formed out of acid volcanic feedstock during early diagenesis. Different magmatic fractionation degrees, from rhyodacite to trachyandesite, reflected in the uniform REE curves of the volcanic glass conform to an active geotectonic development of the Cretaceous margins of Africa. If this is confirmed, this will be the first account of active volcanism recorded during Barremian- Aptian times in the eastern coast of South Atlantic. Finally, the study on clay minerals allowed us to provide accurate description and quantification of pore filling minerals, a new controlling factor for log calibration, all of which having a direct impact on porosity calculation. Overall the findings provide new insights and ideas at regional and reservoir scale that may assist the future exploration and development of hydrocarbons in these two 'mature' reservoirs formations.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

POVEZANOST RADA