Palaeoenvironmental changes at Col des Tribes (Montagne Noire, France), a reference section for the Famennian of north Gondwana-related areas

Abstract

We present detailed biostratigraphy based on conodonts and palaeoenvironmental trends deduced from microfacies and conodont abundance through the Famennian (Late Devonian) at Col des Tribes (Montagne Noire, France). The succession is characterized by micritic limestones deposited in settings oscillating between mid to outer ramp. Facies contain poor fauna, widely dominated by nektonic organisms. This section is complete and one of the most conodont-rich for the Famennian of the north Gondwana-related area. The Upper Kellwasser event (Frasnian–Famennian boundary) and the Hangenberg (Devonian–Carboniferous boundary) have been lithologically identified. They are characterized by decimetre-thick black dysoxic to anoxic argillaceous sediments. The Condroz and annulata events, although not materialized by lithological changes, have been positioned due to the precise stratigraphy. The first event occurred during the deposition of condensed ferruginous facies (griotte limestones) and the second event during the deposition of micrites barren of benthic fauna. The combination of information from both facies and conodont biofacies changes allows a general sea-level curve through the entire Famennian for north Gondwana to be proposed for the first time. At Col des Tribes, the general trend is a slight deepening upwards from triangularis to trachytera zones, then a pronounced shallowing-upwards trend from upper trachytera to praesulcata zones. This curve correlates with the well-known reference curve from Euramerica concerning the late Famennian (trachytera to praesulcata Zones). There are some discrepancies in minor cycles which can be explained by tectonical phenomena at the onset of the edification of the Variscan belt in Europe

The Kulm Facies of the Montagne Noire (Mississippian, southern France)

“…Girard et al, 2013). Only the topmost unit of the group, the upper part of the "supragriottes" of Boyer et al (1974) and Lethiers & Feist (1991) is Tournaisian in age.…”

Assessing the composition of fragmented agglutinated foraminiferal assemblages in ancient sediments: comparison of counting and area-based methods in Famennian samples (Late Devonian)

“…One is located in Thuringia (Germany): the Buschteich (BU) section. Sedimentological studies have shown that CT and BU sections were deposited in an outer carbonated ramp (Girard et al, 2014(Girard et al, , 2017, LS-E being deposited in a more proximal environment (Casier et al, 2002). Along each section, some levels were selected to document contrasted depositional environments.…”

“…Seven levels were sampled along the CT section and seven along the BU section, and one level was sampled along LS-E . These levels have been attributed to five different facies, based on microfacies description (Girard et al, 2014(Girard et al, , 2017, which have been ranked along a theoretical depth transect (Fig. 2).…”

“…(1) Does the fragmentation vary with the paleoenvironmental setting? To tackle this question, we compare the size of each morphotype The microfacies ranking corresponds to a ranking of the samples along a theoretical water depth transect, based on microfacies description (Casier et al, 2002;Girard et al, 2014Girard et al, , 2017. Ages are given by the conodont zones (Ziegler and Sandberg, 1990).…”

“…These levels were chosen to document contrasted depositional settings. This was estimated by ranking the samples along a theoretical water depth transect, based on microfacies description in thin sections (Casier et al, 2002;Girard et al, 2014Girard et al, , 2017. To the right: mean area in square micrometers (calculated as the cumulated area of the morphotype divided by the number of item).…”