HIGH RESOLUTION STRATIGRAPHY AND FACIES DIFFERENTIATION OF THE SHALLOW MARINE ANNOT-SANDSTONES, SOUTH-EAST FRANCE

High resolution stratigraphical analysis divides a rock succession int o the basic genetic units of stratigraphy which are here termed small scale stratigraphical cycles. Each cycle records the sedimentological response to an episode of shallowing and deepening. Assuming that thes e changes in water depth reflect changes in the shoreline position, th ey can be considered as regressive/transgressive episodes. Each cycle comprises a regressive and transgressive facies tract which will be va riably proportioned; in some examples a facies tract may only be repre sented by a hiatal surface of no deposition, erosion and/or bypass. In the Annot Sandstones of south-east France, variations in facies types , proportions and associations can be demonstrated both laterally and vertically through the succession. First, it is demonstrated that faci es variations occur within regressive or transgressive facies tracts a s a function of the stratigraphical stacking pattern of the cycles (i. e. landward, vertical or seaward stacked); this is termed 'vertical fa cies differentiation'. Second, the proportions of facies tracts and th eir constituent facies types within an individual cycle vary between m ore landward and more seaward palaeogeographical locations; this is te rmed 'lateral facies differentiation'. The upper Eocene/lower Oligocen e Annot sandstones outcrop in the Maritime Alps of south-east France, within the thin skinned outer fold and thrust belt of the Alpine arc. The sandstones are well exposed in the area of the Col de la Cayolle o n the north-west margin of the Argentera Massif, where lithostratigrap hical correlations are possible over 3-5 km in a NNW/SSE direction, pe rpendicular to the edge of the depositional basin. Traditionally, thes e outcrops have been interpreted as deep marine turbidite lobe sedimen ts; this study reflects a significant reinterpretation of this success ion as having been deposited in a shallow marine environment. Seven se dimentary sections were measured through the succession, which is divi ded into 10 small scale stratigraphical cycles. These cycles are descr ibed in terms of eight facies which are separated into their transgres sive or regressive facies tracts. In eight of the 10 cycles, the regre ssive facies tracts reflect the progradation of storm influenced braid deltas over shelf muds and silts. In two of the 10 cycles, the regres sive facies tracts reflect barrier inlet and wash-over sands interfing ering with back barrier deposits. These latter two cycles are located within landward stepping cycle sets; this is an example of vertical fa cies differentiation. Transgressive facies tracts locally reworked the upper surface of the regressive facies tract and also comprise barrie r and back barrier deposits. The facies succession within each cycle v aries according to its position with respect to the palaeoshoreline. T he more landward portion of an individual cycle comprises a deltaic sh oaling upward succession, culminating in coarse distributary channel c onglomerates, overlain by a transgressive barrier/inlet system with ex tensive back barrier deposits. Beyond the delta front, the more seawar d equivalent of individual cycles comprises an erosive base, with aggr adational massive pebbly sandstones sitting directly upon offshore het erolithics; these sandstones are interpreted as hyperconcentrated fluv ial effux into the nearshore environment. This grades upward into offs hore heterolithics and graded storm deposits representing the products of ravinement, which are then overlain by shelf mudstones. In summary , the more landward portions of cycles preserve predominantly repressi ve facies tracts, whereas the more seaward portions preserve aggradati onal to retrogradational strata of