Hiatuses and redeposits in the Tithonian-Berriasian transition at Le Chouet (Les Pras, La Drome, SE France): Sedimentological and biostratigraphical implications

Our new study of the Tithonian and lower Berriasian succession of Le Chouet (Les Pres, La Drome, France) better characterizes the lithological succession, the macro-and microfacies, and the stratigraphic ranges of some microfossils mostly calibrated on the calpionellid biozonation. On the lithological side, the Tithonian strata are dominantly characterized by thick-bedded breccias represent-ing debris flows and related calciturbidites whereas the Berriasian strata are typically white limestones that also comprises scattered intercalations of thin-bedded breccias and calciturbitides (including cryp-tic mud calciturbidites). In thin sections, these white limestones display mud-to wackestone textures and their allochems are mostly tiny bioclasts (e.g., radiolarians, calpionellids, saccocomids). Breccias are lithoclastic rudstones and/or floatstones with a matrix similar to the calciturbidites. Their lithoclasts are either extraclasts sensu stricto (i.e., material derived from updip shallow-water areas) or pseudoin-traclasts, representing reworked subautochthonous material (i.e., mud-and wackestone lithoclasts with radiolarians, saccocomids and/or calpionellids). In addition to the erosional features observed at the bases of the gravity flows, these pseudointraclasts document the intensity of submarine erosion. Locally they help to estimate the depths of erosion updip of the deposit. A number of bioclasts are re-worked from updip shallow-water areas; among them, it is worth mentioning the foraminifer Protope-neroplis ultragranulata (GORBATCHIK), the first occurrence of which is dated to late early Tithonian. Sac-cocomids are part of the dominating pelagic biota reported from the lower and lower upper Tithonian interval whereas calpionellids replace them in the uppermost Tithonian to lower Berriasian interval. In-tervals with saccocomids characteristic of zones 4-5 and zones 6-7 are respectively ascribed here to the lower Tithonian (4-5) and pro parte to the upper Tithonian (6-7). The biozonation of the calpionellid group sensu lato allows identification of the Boneti Subzone of the chitinoidellids, the Crassicollaria Zone with its four subzones (A0-A3), and the Alpina Zone with its first subzone (B1). On the basis of bio-stratigraphical and sedimentological data (including the rates of sedimentation), most zonal boundaries are located at the erosional bases of breccia or turbidite layers and thus coincide with hiatuses.

Automated summary

Our study focused on the Tithonian and lower Berriasian succession of Le Chouet in France, providing a better understanding of lithological characterization and the ranges of microfossils using calpionellid biozonation. The Tithonian strata are dominated by thick-bedded breccias and calciturbidites, while the Berriasian strata consist of mainly white limestones with intercalations of thin-bedded breccias and calciturbitides. Bioclasts found in these strata include radiolarians, calpionellids, and saccocomids. The study also revealed the presence of reworked material and erosion features within the sedimentary layers.