A multidisciplinary modeling approach to assess facies-dolomitization-porosity interdependence in a lower cretaceous platform (Northern spain)

An innovative methodology for diagenesis characterization and quantification is presented. It includes different geostatistical modeling workflows applied to a partially dolomitized carbonate platform. The case study consists of a Lower Cretaceous (upper Aptian) shallow-water carbonate platform from the Basque\u2013Cantabrian basin (northern Spain), in which a widespread burial dolomitization occurs. Previous studies at basin scale suggested that the flow of dolomitizing fluids through the carbonate succession was channeled by regional faults and that subsequently the dolomite distribution was partially controlled by depositional facies and their modifications after early meteoric diagenesis. Here, at reservoir scale, several carbonate facies were differentiated and grouped in five depositional environments. Two depositional sequences corresponding to transgressive\u2013regressive cycles and three stages of the platform evolution were distinguished. The statistical data treatment indicated that the dolomitization is mainly concentrated in the regressive part of the first sequence, corresponding to the second stage of the platform evolution. The most dolomitized environments are the inner platforms and the shoal. Facies from these shallower/proximal depositional environments were more exposed to early meteoric diagenesis, possibly controlling later dolomitization. The total macroscopic porosity is directly proportional to the degree of dolomitization: pores are most abundant in fully dolomitized portions of the succession, particularly in the rudist-bearing and grain-dominated facies. Abundant aragonitic shells (rudists, corals), easily leached or recrystallized during early meteoric diagenesis, could justify the higher moldic porosity in these facies. For geostatistical modeling purposes, several statistical rules were elaborated in order to associate to each depositional environment, in each of the three platform stages, different proportions of dolomitization and related pore abundance. A direct simulation of the distribution of depositional environments, degree of dolomitization, and pore abundance was achieved using a bi-plurigaussian simulation (PGS) algorithm. A nested-PGS algorithm was used to simulate the same parameters independently: dolomite and pore abundance were distributed within each depositional environment, based on the statistical rules previously defined. These simulations allowed three-dimensional (3D) visualization of the original depositional facies and textures affecting the distribution of dolomitization and pore abundance. Modeling using both bi-PGS and nested simulations accounted for the 3D dolomite body extension: the dolomitized succession is thicker in the north and thins toward the south, in agreement with evidence from mapping of the dolomite geobodies

Les Formations à Rudistes du Crétacé supérieur (Cénomanien moyen - Sénonien inférieur) du Domaine Prébétique (Sierra du Cuchillo, Région de Yecla, Espagne)

The Late Cretaceous Rudist bearing formations (Middle Cenomanian-Lower Senonian) of the Prebetic Domain (Sierra du Cuchillo, Yecla, Spain). In this paper, three rudist formations are studied. They were deposited during upper Cretaceous times in different carbonate platforms of the betic margin (Southeastern Spain). Each of them belongs to one of the three major depositional units recognized in this region for the uppermost Albian to lowermost Campanian interval. The upper Cenomanian and the lower Senonian are dated here by the first time in base of biostratigraphical data. This also shows the absence of marine sediments during Turonian, which, if exists, is composed just by a few meters of marls with paleosols. On the paleontological point of view, a new specie of the genus Distefanella is described. Paleoecological and paleobiogeographi-cal implications of the studied rudists are also discussed.Dans le Crétacé supérieur des zones externes du Bassin Bétique (région de Yecla, S.E. de l'Espagne), on étudie trois formations à rudistes développées chacune d'elles dans une des trois séquences majeures d'évolution de cette période. L'analyse détaillée biostratigraphique et paléoécologique permet, pour la première fois dans le Prébétique, de dater le Cénomanien supérieur et le Sénonien inférieur, et de montrer l'absence de sédimentation marine au Turonien (représenté par quelques mètres de marnes dolomitiques à paléosols). Du point de vue paléontologique une nouvelle espèce de Distefanella, d'âge cénomanien, est décrite. On discute, d'autre part, la signification paléoécologique et paléobiogéo-graphique des rudistes dans le contexte sédirnentaire des plates-ionnes carbonatées de cette époque.Martin-Chivelet J., Philip Jean, Tronchetti Guy. Les Formations à Rudistes du Crétacé supérieur (Cénomanien moyen - Sénonien inférieur) du Domaine Prébétique (Sierra du Cuchillo, Région de Yecla, Espagne). In: Géologie Méditerranéenne. Tome 17, numéro 2, 1990. pp. 139-151

Biostratigraphy of the Coniacian-Santonian carbonate platforms in the Jumilla-Yecla Altiplane (SE Spain)

Martin-Chivelet J., Luperto-Sinni E., Gimenez R. Biostratigraphy of the Coniacian-Santonian carbonate platforms in the Jumilla-Yecla Altiplane (SE Spain). In: Géologie Méditerranéenne. Tome 21, numéro 3-4, 1994. Perimediterranean carbonate platforms. First International Meeting. Marseille – France (5-8 septembre 1994) sous la direction de Jean-Pierre Masse. pp. 121-123