Palynofacies of marginal marine deposits: the rhaetian of the east margin of the Massif Central (France)

Abstract The methodology presented concerns the definition of palynofacies. It develops 3 procedure stages based on multivariate analyses: 1 — define the palynomaceral facies, 2 — define and compare palynomorph facies with palynomaceral facies and 3 — exploit the two precedent categories of facies. The study deals with Rhaetian sedimentary cycles corresponding to the western limit boundary of the southeastern France intracratonic basin. Rhaetian strata are representative of paralic depositional environments, overlying Triassic fluvial deposits. On the palynomaceral sequence, that is revealed by multivariate analyses, the most buoyant particles are the needle-like phytoclasts. Crevasse splays, dewatering, drowned soils and restricted wave-influenced deposit facies yield them. The less buoyant particles are the black massive or polygonal phytoclasts. They were produced by crevasses, deltaic shales, distributary channels, palaeosoils, sheet-floods, shoals and shoreface facies. The bisaccate pollen Ovalipollis and the nonsaccate pollen Circumpolles are associated with needle-like particles. They are linked to deltaic shales, restricted deposits sheet-floods, shoal, shoreface and storm facies. The marine element Dapcodinium is not related to a particular palynomaceral type but could be compared to the lowest buoyant phytoclast. Deltaic plain and back-shoal lagoonal facies favour the concentration of Dapcodinium . The distribution of the small size dinoflagellate cysts ( Dapcodinium ) and large size dinoflagellate cysts ( Rhaetogonyaulax ) emphasizes the role of the size in the floatation competence. Base level-rises and highs are marked by amalgamated bioclastic deposits, fluvial channel fills, mixed siliciclastic-bioclastic amalgamated shoals, storm deposits or ravinement surfaces. Needle-like particles, Ovalipollis and Circumpolles are associated to these deposits. Base level-falls are represented by crevasse splay deposits, fluvial stream incisions, non-incising fluvial channels, sheet flood and stacked palaeosol facies. Black roundish or equidimensional translucent phytoclasts, Rhaetogonyaulax , short-spine Micrhystridium (acritarch) and smooth-walled spores are associated with these facies. In addition to to the energy factor, the water depth constrains both phytoclast and palynomorph sedimentation.