Castendyk, D. and Moore, A., Department of Geology, Hartwick College, Oneonta, NY 13820, castendykd@hartwick.edu & moorea@hartwick.edu

We measured a complete section of latest Triassic through Liassic carbonate strata at Bourg d'Oisans, France. Triassic evaporites form the basal detachment of most Alpine thrusts, and are conformably overlain by carbonate strata of Liassic age. These carbonates provide good markers for the reconstruction of Alpine thrust displacement. Autochthonous strata of the Bourg d'Oisans region of the Dauphine Alps show a facies pattern and faunal assemblage that resemble similarly aged allochthonous strata 100km south in the Provencal Alps. The Bourg d'Oisans section, when compared to sections previously measured at La Robine and Barles-Chine (Provence), will provide constraints on the displacement of Alpine thrusts in this region.
Measurements at three localities near Bourg d'Oisans allow us to compile a composite stratigraphic section appx. 2000 m thick that includes the Triassic-Jurassic boundary and strata of the entire Liassic epoch. The earliest Liassic strata are composed of carbonate turbidites--180 m of alternating layers of black marl and gray limestone. Middle Liassic strata are predominately dark gray marls (840 m). The upper Liassic strata consist of 954 m of dark gray to black marl. Triassic-Jurassic carbonates fill well-exposed channels cut into the Hercynian metamorphic basement of the Grandes Rousses massif and clearly indicate that these strata are autochthonous. Allochthonous strata of the Provence Alps bear much closer resemblence to the Bourg d'Oisans sequence than to authochthonous and parautochthonous Liassic carbonates exposed in that region. Comparison of our sections at Bourg d'Oisans with previously measured Liassic carbonates in the Provence Alps and sections published in the literature will allow us to reconstruct the Liassic depositional basin and better constrain estimates of crustal compression resulting from thrusting.

Key Words: Lias, stratigraphy, carbonate, France, Alps