Ramon Salas

Mesozoic extensional tectonics, stratigraphy and crustal evolution during the Alpine cycle of the eastern Iberian basin

Abstract Sequence stratigraphy, subsidence analysis and the integration of the basin fill data allow to the identification of four successive evolutionary stages in the basins of the eastern Iberian margin during Mesozoic extension: (1) Triassic rift (Late Permian-Hettangian); (2) Early and Middle Jurassic postrift (Sinemurian-Oxfordian); (3) Late Jurassic and Early Cretaceous rift (Kimmeridgian-middle Albian); and (4) Late Cretaceous postrift (late Albian-Maastrichtian). The present-day crustal structure of the eastern Iberian Range and evidence of its evolution are deduced from the analysis of a new gravity map and other geophysical data. A regional gravity low along the Iberian Range is interpreted in terms of crustal thickening beneath the orogen as a result of the collision between the Ebro block and the Iberian plate during the Paleogene. The boundary between these blocks coincides with a magnetic lineament that is interpreted as an inherited signature of the thinning that occurred during Mesozoic extension. A geodynamic scenario for the crustal evolution of the eastern part of the Iberian Peninsula, based on the evaluation of Mesozoic extensional tectonics and an analysis of the available geophysical data, includes three main successive evolutionary stages: 1. (1) Mesozoic crustal thinning; 2. (2) Paleogene crustal thickening; 3. (3) Neogene crustal thinning. Based on new geological and geophysical arguments, this study offers an alternative and a more complete geodynamic history of the eastern Iberian basins related to the evolution of the Iberian plate and the Central-North Atlantic.

Sedimentary evolution of an Aptian syn-rift carbonate system (Maestrat Basin, E Spain): effects of accommodation and environmental change

We report an integrated study of an expanded and relatively complete syn-rift continental to epeiric marine succession of Aptian age, cropping out in the western Maestrat Basin (eastern Iberian Chain). Four transgressiveregressive sequences are recognized throughout this mixed carbonate-siliciclastic succession, with excellent age control provided by ammonite biostratigraphic data. The transgressive systems tracts consist mainly of alternations of marls and limestones rich in orbitolinids. The regressive systems tracts are essentially characterized by wave- and tidally influenced siliciclastic and carbonate deposits, and by the development of carbonate platforms with rudists, corals, orbitolinids and green algae. Carbon and oxygen isotope curves were established in order to identify the global d13C perturbations related to the Early Aptian Oceanic Anoxic Event (OAE1a). These perturbations commence with a horizon of coral rubble encrusted by Lithocodium aggregatum and Bacinella irregularis with widespread large-sized discoidal Palorbitolina lenticularis. Associated d18O values indicate high-frequency cooling-warming climatic cycles. The fault-controlled rapid syn-rift subsidence recorded during this stage was the most important factor in producing accommodation. However, the major transgressions, sea level falls and biotic changes recorded in the eastern Iberian Chain are in agreement with those registered in other contemporaneous basins of the Tethys. Thus, the resulting sedimentary succession faithfully reflects the major oceanographic and climatically-driven global changes that characterized this stage albeit within a context established by regional tectonics. Hence, this well-documented record of the evolution of an Aptian epicontinental sea provides a useful comparative case study for the analysis of other Aptian epeiric sedimentary successions.

Lower Aptian ammonite biostratigraphy in the Maestrat Basin (Eastern Iberian Chain, Eastern Spain). A Tethyan transgressive record enhanced by synrift subsidence

The present paper analyses the stratigraphic distribution of ammonites collected in the Lower Aptian sediments of the Maestrat Basin (E Spain). The faunal successions obtained from the systematic sampling of ten selected sections located in several sub basins led us to identify four biostratigraphic units (from base to top: Deshayesites oglanlensis, Deshayesites forbesi, Deshayesites deshayesi and Dufrenoyia furcata Zones) that are directly correlatable with the current Mediterranean standard zonation. This study further provides essential biochronologic information to accurately date the different lithostratigraphic units included in the interval studied. Thus, the upper part of the Xert Formation can be tentatively attributed to the lowermost Aptian (D. oglanlensis Zone). The Forcall Formation, which has yielded most of the ammonites, practically extends within most of the Lower Aptian. Its lower and middle parts (Cap de Vinyet and Barra de Morella Members) correspond to the upper part of the D. oglanlensis Zone and the lower part of the D. forbesi Zone, respectively. The base of the Morella la Vella Member (upper part of the Forcall Formation) includes the local record of Oceanic Anoxic Event 1a (OAE 1a) and correlates with the Roloboceras hambrovi horizon (middle/upper part of the D. forbesi Zone). The boundary between the Forcall Formation and the Villarroya de los Pinares Formation is diachronous and varies depending on the sub-basins. The base of the Villarroya de los Pinares Formation can be dated as the middle-upper part of the D. furcata Zone in the Galve, Perello and Salzedella sub-basins.

Expression of an oceanic anoxic event in a neritic setting: Lower Aptian coral rubble deposits from the western Maestrat Basin (Iberian Chain, Spain)

Abstract A singular lower Aptian lithofacies from the western Maestrat Basin (Iberian Chain) highlights the reaction of carbonate platform paleocommunities to natural disturbances of regional to global significance. It is composed mainly of sand- to cobble-sized coral rubble rigidly bound by Lithocodium aggregatum and is coeval with the early Aptian Oceanic Anoxic Event (OAE1a) and the intensified greenhouse conditions connected with this event. Severe storms induced by high atmospheric concentrations of CO2 had a recurrent catastrophic impact on coral populations, giving rise to sub-basin–wide coral rubble levels. Physical responses to elevated atmospheric CO2 levels, such as increased nutrient fluxes, together with low sedimentation rates, and the presence of a hard substratum, favored the mass occurrence of Lithocodium crusts, large flattened Palorbitolina lenticularis, and bioeroders such as lithophagid bivalves and endolithic sponges. These encrusted coral rubble deposits are here interpreted as records of chemical and physical disturbances linked to the OAE1a. Due to significant extension and normal faulting recorded in the lower Aptian of the western Maestrat Basin, however, earthquake-induced natural stresses might also have played a part in the generation and reworking of these coral rubble deposits.

SIMSAFADIM: three-dimensional simulation of stratigraphic architecture and facies distribution modeling of carbonate sediments

We present a three-dimensional simulation model for production, transport and deposition of carbonate sediment. Carbonate production is calculated from population dynamics of carbonate producing organisms. The population dynamics are simulated using a predator-prey model, which includes various effects such as competition with other species, internal competition, effects of mud and suspended carbonate sediments on carbonate producing organisms and depth dependent growth functions. Fluid flow is simulated as a steady-state potential flow using a finite-element model. Transport of suspended sediment is calculated including diffusive, dispersive and advective components. Deposition of suspended carbonate matter is calculated as a function of flow velocity, water depth and settling velocity of suspended carbonate matter. Its flexibility in representing ecologic processes and boundary conditions for flow and sediment transport permits the computer model to be applied to a wide range of possible situations in carbonate systems. A sample experiment is presented to demonstrate the capabilities of the model.

Simulating carbonate and mixed carbonate-clastic sedimentation using predator-prey models

Carbonate and mixed carbonate clastic sedimentation create a variety of facies types which reflect the population dynamics of carbonate-producing organisms and environmental conditions, under which carbonate sedimentation takes place. In this contribution a simulation model of carbonate and mixed carbonate—clastic sedimentation is presented that considers the population dynamics of the carbonate producing organisms and defines their evolution by simple ecological systems. These systems are represented mathematically by predator—prey models and include a variety of effects such as poisoning of carbonate-producing organisms under the presence of lime mud or clastic sediments and depth-dependent growth functions. In order to test the conceptual model, we apply data from the Lower Cretaceous Mola de Xert carbonate platform (Province Castellon, Spain). The simulated facies succession shows a good fit with the observed facies and demonstrates that predator—prey models can be adapted and calibrated to natural carbonate sequences. The model then is extended to two dimensions in space and tested for effects of sea-level changes on the geometrical and facial evolution of a carbonate deposit, applying data from the Mola de Xert carbonate platform.

Calcite/aragonite ratio fluctuations in Aptian rudist bivalves: Correlation with changing temperatures

Understanding how bivalves responded to past temperature fluctuations may help us to predict specific responses of complex calcifiers to future climate change. During the late-Early Aptian, aragonite-rich rudist bivalves decreased in abundance in northern Tethyan carbonate platforms, while rudists with a thickened calcitic outer shell layer came to dominate those of Iberia. Seawater cooling and variations in calcium carbonate saturation states may have controlled this faunal turnover. However, our understanding of how rudist lineages responded to changing environmental conditions is constrained by a lack of quantitative data on the evolution of thickness, size, and mineralogy of the shell. This study is based on volumetric measurements of the shell and shows the transition in lineages of the family Polyconitidae from aragonite-rich mineralogy in the earliest Aptian, to low-Mg calcite-dominated mineralogy in the middle Aptian, returning to aragonite-dominated composition in the latest Aptian. The platform biocalcification crisis that occurred at the Early-Late Aptian boundary in the Tethys was marked by a relative increase of calcite and a decrease in skeletal thickness and commissural diameters. The highest calcite/aragonite (Cc/A) ratios in polyconitid rudists accompanied the late Aptian cold episode, and the lowest values were reached during the warmer intervals of the earliest and latest Aptian. These results imply a correlation between Cc/A ratio values and temperature and suggest that some bivalves adapted to less favorable calcification conditions by changing calcite and aragonite proportions of their bimineralic shells and decreasing skeletal thickness, thereby reducing the metabolic cost of shell growth.

Subsidence analysis in thrust tectonics. Application to the southeastern Pyrenean foreland

Abstract This case-study conducted in the Pyrenees examines the application of 1D-subsidence analysis in thrust tectonics. By integrating subsidence analysis with sequence stratigraphy and structure, significant changes between the subsidence curves of the southeastern Pyrenean thrust sheets are seen to occur bearing a close relationship to regional unconformities and variations in the sedimentary record of each thrust sheet. A comparative study examining the correlation between the tectonic subsidence curves of the thrust sheets and those of the autochthon shows that the essential structure of the southward sequence of thrust sheets (Palaeozoic Axial Zone not included) was piggy-back developed in only 6 m.y. The northern Garrotxa antiformal stacks started to emplace ∼50.7 Ma ago, as can be interpreted from their linear-shaped curve and anomalously low subsidence rate (∼7 cm/ka), and preservation of continental platform, whereas the southern Cadi thrust sheet underwent strong subsidence acceleration (up to ∼60 cm/ky) related to the development of a deep starved continental slope. Comparison between coeval platform sections (with good palaeobathymetric constraints) and slope sections provides an estimate for slope palaeobathymetry up to 650–900 m. The Cadi thrust sheet was emplaced at about ∼49.5 Ma, as can be deduced from dramatic subsidence deceleration in its curves related to shallowing, resumption of siliciclastic sedimentation and broad erosion of the continental platform areas of the Cadi thrust sheet. Meanwhile, the curves of the Serrat thrust sheet and those of the autochthon recorded significant subsidence acceleration (∼30–40 cm/ka and ∼15 cm/ka, respectively). Finally, the Serrat thrust sheet was emplaced at ∼45 Ma, as can be inferred from the decelerated subsidence in its curve, associated with shallowing, emergence and broad molasse sedimentation, whereas in the foreland plate, the subsidence accelerated and was related to the onset of marine sedimentation.

LATE CHATTIAN PLATFORM CARBONATES WITH BENTHIC FORAMINIFERA AND CORALLINE ALGAE FROM THE SE IBERIAN PLATE

Abstract: The carbonate system studied represents an under-investigated sedimentary record formed in the western end of the Tethys during the Chattian relatively warm climate regime. These platform carbonates are examined with respect to rock fabrics, biostratigraphy, biostratinomy, paleoecology, and sequence stratigraphy. Dominant carbonate producers include scleractinian corals and echinoids, but the most prolific were symbiont-bearing benthic foraminifera and coralline algae. The presence of Miogypsinoides complanatus and Miogypsinoides formosensis indicates a late Chattian age (Shallow Benthic Zone 23). The depositional profile is consistent with a homoclinal ramp. The absence of a barrier margin and thus, of a lagoon, facilitated the transport and re-working of biogenic components throughout the platform. As a result, facies are rather homogeneous corresponding to a rudstone mainly formed by benthic foraminifera and coralline algae, which passes basinwards to deeper ramp to hemipelagic deposits rich in echinoids and planktonic foraminifera. Within this dominant facies, only subtle and gradual lateral variations on the relative abundance or absence of certain skeletal components or species are recognized, comprising two end members. A proximal biofacies of benthic foraminifera and coralline algae including corals in growth position, fragments of green algae, and seagrass dwellers where Eulepidina, Nummulites, and Operculina are absent, and a distal biofacies where corals, green algae, and seagrass dwellers are not present, but Eulepidina, Nummulites and Operculina are common. Carbonate deposition was controlled by long-term relative sea-level fluctuations including a Rupelian?–late Chattian transgression, a late Chattian regression, which ended in subaerial exposure of proximal ramp carbonates, and a latest Chattian to early Miocene transgression. The Chattian carbonate platform was finally drowned around the Oligocene/Miocene transition.

Geology of the Falcón Basin (NW Venezuela)

ABSTRACT This paper presents a geological map and cross-section of the Falcón Basin based both on published and unpublished work and on new data collected in the northern and southern basin margins. The geological map covers an area of 4600 km2 at 1:100,000 scale. The cross-section is oriented NNW-SSE, traversing perpendicular to the main structures. In general, the structure of the study area results from the inversion of a graben (Oligocene-early Miocene back-arc basin), that started in the middle Miocene due to the convergence between the Caribbean and South American plates. The map, the cross-section and the observations made in the field have been used to generate a tectonostratigraphic reconstruction of the Falcón Basin. The Oligocene-early Miocene sedimentary succession mapped and described is relevant to the hydrocarbon exploration in the Caribbean and in the Gulf of Venezuela, where new hydrocarbon resources have recently been discovered (i.e. Perla gas field).