The carbonates of the Permian Lakes of North Massif central, France

Abstract

During the Permian, large fluvio-lacustrine basins occurred within the West European Hercynian chain. The deposits were mainly detrital (conglomerates, sandstones and pelites). The two studied sites, Couy borehole and Aumance basin contain several dolomitic beds alternating with pelites containing Ostracods. The carbonate layers constitute various dolomitized facies with dolosparite, laminated and bituminous dolomites, oolites, oncolites and stromatolites, and pedological nodules. Microfacies are varied. The dolomite crystals can be either isolated rhombs scattered in pelites or rhombs and xenomorphic crystals cementing sandstones; in dolomicrites, dolomicrosparites and dolosparites, crystals are xenomorphous and very irregular in size.All the layers are interpreted as the result of the dolomitization of an initial calcitic mud. Some columnar stromatolites had their thin primary fabric well preserved by siliceous early replacement, while dolomitization poorly preserved laminations. The fluvio-lacustrine sediments associated with carbonates are red, mottled and grey. The carbonates were deposited in small lacustrine basins and in the flood plain pelites. Climate conditions were not desertic, but dry tropical with alternating wet and dry seasons allowing for a periodic hydromorphy responsible for oxido-reduction of iron, and carbonate nodulization.

Sedimentary evolution of the Pennsylvanian–Permian Mulargia–Escalaplano molassic basin (Sardinia, Italy): the most complete record in the Southern Variscan Realm

“…Rosen, 1994;Briere, 2000;Deroin, 2008;Lopez et al 2008;Konrád et al 2010) with fluctuating saline content. This interpretation is in good accord with the local Permian climate (Freytet et al 1992;Cassinis et al 2000;Boucot et al 2013), assumed to be tropical dry with a marked wet season. This matches the tropical location of Sardinia in early Permian time (Vai & Izart, 2000) and the morphotectonic setting of the chain (Costamagna, 2019(Costamagna, , 2021a.…”

The carbonates of the post-Variscan basins of Sardinia: the evolution from Carboniferous–Permian humid-persistent to Permian arid-ephemeral lakes in a morphotectonic framework

“…The Aumance basin of the Northern Massif Central (France; Courel et al 1989;Freytet et al 1992) shows a different evolution and different features (such as the distribution of the carbonates) in respect to the Sardinian basins. It is characterized first by Stephanian siliciclastic deposits pertaining to the limnic facies, which rest unconformably on top of the Variscan basement.…”

“…Dolomitization processes may also follow. According to Freytet et al (1992), the dominating climate was tropical dry with a marked wet season.…”

Reconsidering Carboniferous–Permian continental paleoenvironments in eastern equatorial Pangea: facies and sequence stratigraphy investigations in the Autun Basin (France)

“…Therefore, their presence implies a low water column (euphotic zone) with reduced sediment supply (no turbidity), allowing for chemical or biologically-induced carbonate precipitation when the concentration in carbonate and calcium ions is sufficient. Some carbonate microbial deposits have already been described in French CP basins, and assigned to shallow aquatic environments, either marginal lacustrine or fluvial, based on sedimentological evidence (features reflecting shallow environments, like mudcracks or root marks, oncoids or oolites) and biological evidence (photosynthetic metabolisms, e.g., Freytet al 1992Freytet al , 1999Freytet al , 2000Gand et al 1993;Stapf and Gand 1994).…”