Origin of “septarian barite concretions” of the upper Cretaceous – Paleocene formations from the Biban area (north Algeria) Nabila GACI (09 October - h 5 pm - Aula Pognante DST)
Septarian barite concretions have historically attracted scientists and mineralogists due to their concentric structure and the presence of septarian cracks. The aim of this study is to present detailed results from barite concretions occurring in Upper Cretaceous-Paleocene marl layers within the Southern Tellian Atlas (Northern Algeria). It focuses on: (1) petrographic and mineralogical analyses of these barite concretions, (2) geochemical studies (major, trace, and rare earth elements) to decipher the source of barite and diagenetic conditions, and (3) discussing the first sulfur isotopic (d34S) data on these concretions. Petrographic and mineralogical analyses of the studied concretions suggest three discernible growth modes of barite crystals: (i) formation of small, turbid, lamellar crystals intertwining to create rosette-like structures within concretion cores; (ii) radial-fibrous crystals in concretion cortexes; and (iii) infilling of septarian cracks. REE geochemistry and the d34S values of the studied barite concretions (ranging from 16‰ to 24.4‰)supports a seawater origin of diagenetic fluids. We propose that the investigated concretions grew in organic-rich, fine-grained sediments at shallow depths below the sea floor, during sedimentation halts. Barium was supplied to porewaters as a result of microbial degradation of organic matter within the methanogenic zone, and precipitated as barite upon migrating upwards and reaching the boundary with the overlying sulfidic zone.
The Speaker
Nabila GACI - Department of Geologic Sciences, FSBSA-Mouloud Mammeri University- UMMTO, Tizi Ouzou, Algeria. Metallogeny and Magmatism Laboratory of Algeria, FSTGAT- USTHB, BP 32 El Alia, Bab Ezzouar, Algeria.
Onsite: h. 17:00 Aula Pognante DST
Contacts: geoseminar.dst@unito.it
-
Allegato
(6.3 MB)