Diagenetic and palaeogeographic significance of clay, carbonate and other sedimentary components in the middle Devonian limestones of western Ardenne, France

Givetian deposits accumulated in a more than 300-m-thick succession on a carbonate platform developed on the passive margin of the so-called Rheic ocean. These rocks crop out in the Ardenne massif at Glageon in a structural context marked by small fault-controlled basins subjected to moderate overburden, tectonic and metamorphic constraints. Data on the clay mineral distribution, associated with detailed information on limestone facies/microfacies, as well as data on the depositional profile and sequence stratigraphic evolution of these rocks indicate strong carbonate diagenesis and moderate clay diagenesis, the latter being favoured by the early occurrence of the former, which prevented further fluid-rock interaction. The clay assemblage distribution, which roughly parallels the palaeomorphologic and palaeobathymetric shape of the Givetian continental margin, is organized in five successive zones indicating large-scale sequence stratigraphic evolution and the control of regional sea-level fluctuations. The clay and other sedimentary components provide additional information on the warm and variably humid climate, northern, relative to southern, terrigenous sources, the open sea relative to restricted depositional environments, the temporary tectonic rejuvenation of the continental hinterland and the chemical conditions allowing early diagenetic modifications.