Abstract 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–Cantabrian 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–regressive 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.

Abstract Detailed geological mapping of a highly fractured Paleozoic (pre-Permian) basement and the scarce outcrops of overlying Permian–Mesozoic cover in the surroundings of the Duje Valley (Picos de Europa Unit, Cantabrian Mountains, NW Spain), together with new field data, have allowed the separation of four genetic fault sets in a polyorogenic area, affected by the Variscan and Alpine cycles. These fault sets are, from oldest to youngest: Variscan thrusts (late Carboniferous), late Variscan strike-slip faults (late Carboniferous–earliest Permian), Alpine normal faults (Permian–Mesozoic) and Alpine reverse faults (Cenozoic). A structural analysis is reported here, based on the joint use of geometric, kinematic and deformational features, cross-cutting and tectono – sedimentary relationships between the structures. This analysis has allowed the recognition and full characterization of the four fault sets. These types of structural analyses are useful for unravelling complex tectonic histories in regions where massive limestone lithologies make reconstructing the timing of fault activity difficult, especially if the basement is affected by late deformation events that are not recorded by cover outcrops.

Abstract The Tethyan belt extends throughout the circum-Mediterranean and eastward through Turkey, Iran, and Pakistan to China and Southeast Asia. The belt is characterized by rift zones with bimodal volcanic rocks and thick clastic sedimentary rock fill, passive-margin basins with platform carbonates, and calc-alkaline island-arc volcanic rock sequences. It is known primarily for its copper and gold endowment, but it includes several large and globally significant zinc-lead provinces. These include the Basque-Cantabrian basin (Réocin) in northern Spain, the Atlas zinc-lead district in Morocco, Algeria, and Tunisia, the zinc-lead-silver deposits in the Balkans—including the Trepča district extending south to Macedonia and Greece—the zinc districts in central Anatolia, Turkey, and Iran—such as Angouran and Mehdiabad—and deposits such as Padaeng, in Thailand, and Jinding, in southwestern China. Late Carboniferous to Triassic rifting in northern Gondwana and opening of the Neotethys Ocean marks the commencement of the most significant zinc-lead metallogenic cycle and initiated the break-up of Pangea. Rifting migrated eastward and broad Permian to Cenozoic carbonate shelf and passive-margin basin sequences were deposited. The thick carbonate sequences provided ideal trap settings for MVT deposits, with zinc- and lead-rich mineralizing fluid flow initiated by Cretaceous to Cenozoic inversion, collision, and uplift on the Tethyan margins. High-temperature carbonate-replacement and vein-type mineralization is also associated with magmatically induced hydrothermal activity during the Cenozoic compressional events. Unusual hybrid deposits involved both basinal and magmatic fluid inputs. Subsequent uplift and oxidation has resulted in the development of economically significant nonsulfide zinc deposits throughout the belt.