Beatriz Bádenas

Transgressive–regressive cycles and Jurassic palaeogeography of northeast Iberia

Abstract A correlation and sequence stratigraphy study of Jurassic successions has been carried out in the main sedimentary basins of northeast Iberia, i.e., Asturias, Basque-Cantabrian, and Iberian basins, based on the identification of transgressive–regressive cycles. The development and palaeogeographic evolution of the epicontinental carbonate platforms of northeast Iberia were largely controlled by major tectonic activity at three main intervals, at the beginning of the Jurassic, in the Lower–Middle Jurassic transition, and during the uppermost Jurassic, respectively. During Early Jurassic times, northeast Iberia was the site of a single and large carbonate ramp opened to the north. This carbonate ramp suffered a progressive drowning, evolving from an inner to hemipelagic ramp systems, with the local development of suboxic environments in the deepest areas located to the north. During the Middle Jurassic, different open carbonate platforms were formed including the development of swells in intermediate areas. During the Upper Jurassic, the outer ramp areas were progressively moving to the east Iberian Basin, and the ammonite faunas showing a markedly Tethyan affinity thereafter. Three first order T–R cycles bounded by major discontinuities associated with significant time gaps are identified. They extend respectively from the latest Rhaetian to the Early Aalenian, from the Middle Aalenian to the Early Oxfordian and from the Early Oxfordian to the Late Berriasian. Major transgressive peaks occurred at the Middle Toarcian (Bifrons Zone), at the Late Bajocian (upper Niortense and Garantiana zones) and at the mid-Kimmeridgian (Divisum Zone). Each of the first order cycles includes four second-order T–R cycles. Cycles 1.1–1.4 are identified in the northern basins. Cycles 2.1–2.4 display some differences in age of transgressive peaks from one basin to another. Cycles 3.1–3.4 are mainly identified in the Iberian Basin. The correlation with other separated Boreal and Thethysian basins demonstrates that the number and age of T–R cycles varies from one basin to another and are mainly controlled by the local or regional tectonic development. The transgressive peaks may reflect episodes of eustatic rise during the Jurassic. However, their different age from one basin to another is explained by different subsidence evolution.

Proximal–distal facies relationships and sedimentary processes in a storm dominated carbonate ramp (Kimmeridgian, northwest of the Iberian Ranges, Spain)

Abstract Facies analysis of the upper Kimmeridgian rocks in the outcrops located near Ricla (Zaragoza province, northeast Spain) and the integration of the resultant data in a broader context (the northern part of the Iberian Basin), has produced two general models showing the facies distribution and the processes that controlled the sedimentation in the Kimmeridgian carbonate ramp. Using these two models the transition from shallow to relatively deep environments of the carbonate ramp is examined in detail. Model 1 corresponds to the development of a mixed carbonate-siliciclastic ramp during a slow rise and stillstand of sea level (Sequence 1-HST), whereas Model 2 represents the growth of a pure carbonate ramp during a rapid rise of sea level (Sequence 2-TST). Carbonate production was higher in the shallow ramp domains (coral reefs and oolitic shoals in Model 1 and reefs in Model 2) than in deeper domains, where there is no indication of significant pelagic or benthic production. The activity of unidirectional return flows induced by winter storms and hurricanes, played an important role in the redistribution of the sediment across the ramp, generating different coarse-grained deposits. In the inner and mid-ramp settings dunes, lower scale bedforms and tempestites occur in Model 1, and storm lobes, bars and tempestites in Model 2. Moreover, a significant bulk of the carbonate mud produced in shallow areas would eventually be resedimented in the outer ramp as suspended load in the density currents. Stillstand of sea level in Model 1 involved a rapid progradation of the inner and proximal mid-ramp carbonate and siliciclastic facies. The rapid relative sea level rise of Model 2 is determined by the dominance of the carbonate facies and by the presence of aggradational geometries in the transitional area between shallow and deep-ramp domains. The presence of relatively thick sections in the outer-ramp settings (instead of condensed sections, as observed in Model 1) during times of sea level rise (Model 2) can mainly be explained by the increase of the shallow production in the reef dominated areas.

Kimmeridgian palaeogeography and basin evolution of northeastern Iberia

Abstract Two sedimentary basins were developed during the Kimmeridgian in the northeastern part of Iberia: the Basque-Cantabrian Basin, to the northwest, and the Iberian Basin, to the east. These basins were mainly filled by carbonates deposited in a shallow epicontinental sea that was connected to the open marine realms of both the North Atlantic and the Western Tethys respectively. During the Late Jurassic, they were temporarily linked by means of the Soria Seaway. The uppermost Oxfordian to lowermost Tithonian of northeastern Iberia consists of two depositional sequences. Sequence J3.5 spans latest Oxfordian to early late Kimmeridgian times; Sequence J3.6 spans the late Kimmeridgian and early Tithonian. During Sequence J3.5 coralgal reefs were developed in the sedimentary domains of the Basque-Cantabrian Basin and the Soria Seaway, whereas the marginal areas of the Iberian Basin were dominated by oolitic shoals with variable siliciclastic influence. Outer ramp areas, located in the central and eastern part of the Iberian Basin, were dominated by carbonate muds and marls. During the late Kimmeridgian-earliest Tithonian shallow reefal and oolitic facies prograded over the micritic outer ramp facies. The sedimentation areas were reduced, and Sequence J3.6 was only deposited in the Iberian Basin. Most of the western margin of the Iberian Basin and the southern areas of the Soria Seaway were covered by reefal facies during this sequence. Major transgressive events in the Iberian Basin took place in the latest Oxfordian-early Kimmeridgian, and in the middle late Kimmeridgian, whereas eustatic falls in sea level are recognised at the onset of the late Kimmeridgian and at the Kimmeridgian–Tithonian transition. These events have also been described in other West European basins. Synsedimentary extensional tectonics is also evident, and has been related to the onset of the Late Jurassic-Early Cretaceous rifting stage. Synsedimentary normal faulting resulted in the presence of several troughs and highs within the basin. The tectonic uplift of the western basin margin explains the progressive basinwards shift of the shorelines, as observed in the Iberian Basin towards the end of the Jurassic.

Upper Jurassic thrombolite reservoir play, northeastern Gulf of Mexico

In the northeastern Gulf of Mexico, Upper Jurassic Smackover inner ramp, shallow-water thrombolite buildups developed on paleotopographic features in the eastern part of the Mississippi Interior Salt basin and in the Manila and Conecuh subbasins. These thrombolites attained a thickness of 58 m (190 ft) and were present in an area of as much as 6.2 km2 (2.4 mi2). Although these buildups have been exploration targets for some 30 yr, new field discoveries continue to be made in this region. Thrombolites were best developed on a hard substrate during a rise in sea level under initial zero to low background sedimentation rates in low-energy and eurytopic paleoenvironments. Extensive microbial growth occurred in response to available accommodation space. The demise of the thrombolites corresponded to changes in the paleoenvironmental conditions associated with an overall regression of the sea. The keys to drilling successful wildcat wells in the thrombolite reservoir play are to (1) use three-dimensional seismic reflection technology to find paleohighs and to determine whether potential thrombolite reservoir facies occur on the crest and/or flanks of these features and are above the oil-water contact; (2) use the characteristics of thrombolite bioherms and reefs as observed in outcrop to develop a three-dimensional geologic model to reconstruct the growth of thrombolite buildups on paleohighs for improved targeting of the preferred dendroidal and chaotic thrombolite reservoir facies; and (3) use the evaporative pumping mechanism instead of the seepage reflux or mixing zone models as a means for assessing potential dolomitization of the thrombolite boundstone.

Sequence stratigraphy and bedding rhythms of an outer ramp limestone succession (Late Kimmeridgian, Northeast Spain)

Facies, stratal and spectral analyses of an outer ramp lime mudstone succession (Aguilon, north Iberian Ranges, Spain) are presented in this work. The studied succession is Late Kimmeridgian (eudoxus and beckeri zones) in age and comprises the transgressive and highstand deposits of a third-order depositional sequence. A number of higher-order sequences (bundles and sets of bundles) have been identified based on the comparative analysis of the bedding planes. The bundles and sets of bundles show a well-defined stratal pattern. Spectral analysis has provided further independent confirmation of the cyclical nature of the bundles and sets of bundles defined from field analysis. The bundles have variable thickness (from 1 to 2 m) and are formed by up to 10 micritic beds. They have been related to sea- level changes controlled by the orbital precession cycle, affecting the shallow productivity area. A significant amount of the lime mudstones accumulated in outer ramp settings were derived from resedimentation of the shallow carbonate production areas. Many of the bundles show a lower interval with a thinning and fining-up trend, indicating a progressive decrease of the carbonate production (and carbonate export) during periods of high-frequency sea-level rise. The late transgressive and highstand deposits show sets of bundles (groups of five bundles, from 5 to 8 m) probably related to sea-level changes controlled by the short eccentricity cycle. The overall thickness and the stacking pattern observed in the sets of bundles are controlled by the long-term sea-level variation. The sets of bundles located in the late transgressive deposits show thinner micritic beds in their lower or middle part. The sets of bundles found in the highstand deposits are thinner and show a thickening-up and thinning-up trend. On the studied carbonate ramp, during periods of long-term sea-level rise, the overall carbonate production (and carbonate export) is high, although the superposition of the high-frequency sea-level rises may result in episodic flooding and drowning of the shallow ramp areas. During periods of long-term, early highstand of sea level, the overall carbonate production (and carbonate export) is more reduced, but it has maximum peaks during the transgressive (and early highstand) intervals of the high-frequency sea-level cycles. Sedimentation during the long-term sea- level fall (late highstand) was scarce and discontinuous in the outer ramp area, and resulted in the overall thickness reduction of the sets of bundles. D 2003 Elsevier Science B.V. All rights reserved.

Radiolarian productivity linked to climate conditions during the Pliensbachian–Aalenian in the Kermanshah Basin (West Iran)

The 40-m-thick Pliensbachian–Aalenian succession in Kermanshah (Kermanshah Basin; West Iran) includes three main radiolarian-bearing deposits: sponge spicule-radiolarian limestones, cherts, and pyroclastic deposits. Sedimentological and ichnological analyses of these facies reflect the different mechanisms of nutrient supply and proliferation of radiolarians. Pliensbachian p.p.—early Toarcian sponge spicule-radiolarian limestones with low proportions of radiolarians and scarce bioturbation (Chondrites) reflect low radiolarian productivity and accumulation in oxygen-deficient bottom waters. Their deposition was linked to the Pliensbachian—early Toarcian long-term warming, when the greenhouse-warm climate mode led to weak thermohaline circulation, stratified waters, and a well-developed pycnocline. However, a higher proportion of radiolarians is found in intercalated discrete pyroclastic deposits and in limestone beds located on top of coarse-grained internal wave deposits. These pulses of radiolarian productivity are related to an input of nutrients to surface waters due to volcanic eruptions and currents generated by internal waves propagating along the pycnocline. In contrast, middle Toarcian–Aalenian cherts with abundant radiolarians and ubiquitous bioturbation (Thalassinoides) were deposited in oxygenated bottom waters. High radiolarian productivity was related to the long-term middle Toarcian–Aalenian cooling trend and the greenhouse-cool climate. Biosiliceous production was linked to upwelling currents transporting cold deep waters rich in nutrients, which were driven by west-trending monsoon winds.

Barremian synrift sedimentation in the Oliete sub-basin (Iberian Basin, Spain): palaeogeographical evolution and distribution of vertebrate remains

A review of the onset of the synrift sedimentation and synsedimentary extensional tectonics of the Oliete sub-basin (northwestern Maestrazgo basin, East Spain) is presented here based on new data acquired after extensive sedimentological, structural and palaeontological analysis of the Barremian Blesa Fm. The lower boundary of the Blesa Fm is a prominent basal synrift unconformity overlying Jurassic units. This formation has been divided into three genetic stratigraphic sequences bounded by sub-basin-wide unconformities. The lower Blesa sequence (LBS) is characterized by distal alluvial to palustrine marls/clays grading upward to palustrine–lacustrine limestones. The LBS is bounded on top by a planar to irregular transgressive, hardened ferruginous surface, locally encrusted by oysters. Above this discontinuity, the middle Blesa sequence consists of oyster-rich limestones and marls deposited in a shallow restricted bay, which grade to distal alluvial and palustrine–lacustrine marls/clays and limestones towards the marginal areas of the basin. The boundary between the middle and upper Blesa sequence (UBS) is a regressive surface outlined by the local presence of an erosive conglomeratic bed. The UBS generally starts with red clays deposited in distal alluvial fan environments, which grade upwards to palustrine and lacustrine carbonates and marls/clays. The local presence of heterolithic alternations of clay with fine-to-medium sandstone and of cross-bedded sandstones indicates the local occurrence of siliciclastic coastal environments in the UBS. The upper boundary of the Blesa Fm is marked by widespread transgression, giving rise to the bioclastic limestones of the Alacón Fm. In the present paper, the stratigraphic position and palaeoenvironmental context of the abundant vertebrate remains found across the defined sequences within the Blesa Formation is reviewed. The results obtained are relevant for a further understanding of the tectosedimentary evolution of the studied basin. Successive stages of evolution are distinguished, including the initial uplift, breakup and erosion of the earlier Jurassic carbonate platform that took place during the Tithonian–Hauterivian; the onset of synrift sedimentation during the early Barremian, which was highly controlled by extensional faulting and differential block subsidence; the homogenization of the basin subsidence accompanied by the incursion of marine waters (sourced from southeastern areas) during the middle part of the Barremian; and the significant fall in base level, of possible climatic origin and also involving significant siliciclastic input in the northern areas of the Oliete sub-basin around the middle part of the late Barremian.ResumenEste trabajo es una revisión de la sedimentación sin-rift barremiense y la tectónica extensional en la subcuenca de Oliete (noroeste del Maestrazgo, este de España), a partir de datos previos y nuevos datos adquiridos después de un extenso análisis sedimentológico, estructural y paleontológico de la Fm. Blesa. El límite inferior de la Fm. Blesa es una discordancia basal sin-rift que recubre las unidades jurásicas. La unidad se ha dividido en tres secuencias genéticas delimitadas por discontinuidades en toda la subcuenca. La secuencia Blesa inferior (LBS) se caracteriza por margas/arcillas aluviales a palustres y calizas palustres-lacustres hacia techo. Su límite superior es una superficie transgresiva neta representada por una superficie ferruginosa irregular, localmente encostrada por ostras. La secuencia Blesa media (MBS) consiste en calizas y margas ricas en ostras depositadas en una bahía restringida poco profunda, que pasan lateralmente hacia áreas marginales de la cuenca a calizas palustres-lacustres y margas/arcillas aluviales distales. El límite con la secuencia Blesa superior (UBS) es una superficie regresiva erosiva asociada localmente a niveles conglomeráticos. La UBS comienza generalmente con arcillas rojas de abanicos aluviales distales, que hacia techo pasan calizas y margas/arcillas palustres-lacustres. La presencia local de alternancias heterolíticas de arcillas y areniscas de grano fino y medio, y de areniscas con estratificación cruzada, indica ambientes costeros siliciclásticos. El límite superior de la Fm. Blesa está marcado por una transgresión generalizada (calizas bioclásticas de la Fm. Alacón). En el presente trabajo, se revisa también la posición estratigráfica y el contexto paleoambiental de los abundantes restos de vertebrados encontrados teniendo como base el nuevo esquema de secuencias definido dentro de la Fm. Blesa. Los resultados obtenidos son relevantes para una mayor comprensión de la evolución tectosedimentaria de la subcuenca de Oliete. Se distinguen sucesivas etapas de evolución, incluyendo: 1) levantamiento inicial, ruptura y erosión del de las calizas de plataforma del Jurásico, que tuvo lugar durante el Titoniense-Hauteriviense; 2) inicio de la sedimentación durante el Barremiense inferior, controlada por fallas extensionales y hundimiento de bloques diferencial; 3) fase de hundimiento homogéneo acompañada por la incursión de aguas marinas (provenientes del sureste) durante la parte media del Barremiense; y 4) caída significativa en el nivel de base, de posible origen climático y también involucrando una importante entrada de siliciclásticos en las áreas del norte de la subcuenca, alrededor de la parte media del Barremiense superior.

Diagenetic evolution of a shallow marine Kimmeridgian carbonate ramp (Jabaloyas, NE Spain): implications for hydrocarbon reservoir quality

The upper Kimmeridgian outcrops in Jabaloyas (NE Spain) studied here have significant similarity in terms of carbonate ramp morphology and its facies architecture with Member D of the Upper Jurassic Arab Formation reservoirs in the Middle East. Geological models from analogue outcrops enhance or challenge the understanding of multi-scale sedimentological and diagenetic heterogeneities in the subsurface hydrocarbon reservoir models by providing morphometric parameters. For this purpose, conventional diagenetic studies (petrographic microscopy analysis and cathodoluminescence) have been performed to assess the impact of diagenetic modifications through burial. More than 50 thin sections have been used to define a full paragenetic sequence. Additional mineralogical mapping (Qemscan®) on a selection of thin sections serves as a calibration tool for semiquantitative analytic studies of every mineral phases and the proposed porosity evolution. This work unravels the whole paragenetic diagenetic processes and focused on those that occurred right after deposition to shallow burial (eogenesis). High-sequence stratigraphy allows linking these events to variations of the environmental domains that, in fact, respond most likely to sea-level fluctuations. In particular, it provides key parameters to frame the diagenetic overprint such as cementation processes plugging primary interparticle porosity and selective dissolution linked to master bounding surfaces: calcite meniscus cements in vadose zones and selective dissolution processes linked to firmgrounds. Ultimately, they offer valuable trends that would be potentially relevant to decipher and characterize reservoir parameters for the upscaling workflow of fabrics from microscopic to inter-well scale in carbonate hydrocarbon reservoirs.

Factors Controlling Reef fabric Distribution (Kimmeridgian Ramp, Iberian Basin) - Unravelling Reservoir Heterogeneities

The geological characterization of outcrops is increasingly used as a tool to better constrain the distribution of sub-seismic reservoir heterogeneities in mature oilfields. This approach applies to well-exposed late Kimmeridgian Jabaloyas outcrops (Teruel region, NE Spain) have a high potential, already used for inter-reef facies modelling at reservoir scale (i.e. analogue for Arab Fm in Middle East). The low angle carbonate ramp in Jabaloyas has been primarily studied in terms of high-frequency sequence stratigraphy and facies architecture. The 24 m thick succession shows an almost pure carbonate system with a high variety of buildups: thrombolite mounds, coral-microbial bioherms, branching coral biostromes, pure thrombolites and leiolites, oyster patches, stromatoporoid-Marinella algae meadows. Geometries and lateral distribution of the main buildups have been documented. Furthermore, recognition of successive sedimentary units and of micro- and macrofauna associations resulted in a better interpretation of the main physical and ecological factors controlling the fabric and distribution of the different bioconstructions. It will be used for up-scaling reservoir heterogeneities at sub-seismic scale for stratigraphical equivalent reservoirs.

Use of Surface Analogue for 3-D Geological Modelling of the Arab D Reservoirs - Example from Jabaloyas Outcrops (Eastern Spain)

The poster illustrates how an Upper Kimmeridgian analogue exposed in NE Spain has been used to characterise the internal heterogeneities of a low-angle carbonate ramp that includes the development of reef build-ups formed by colonial forms (corals, stromatoporoids), and microbial crusts with associated encrusting organisms. Results from this outcrop analogue have been applied for improving oil recovery from the Arab D reservoirs of a mature field in UAE. The well-exposed outcrops around the Jabaloyas village (Eastern Spain) have been used for detailed facies and sequence stratigraphic reconstructions within a 16–22 m thick series. These outcrops show strike and non-strike sections across a 12 km2 area (i.e. 4 x 3 km). Seventeen stratigraphic profiles were carried out to control vertical and lateral facies distribution. The facies follows an overall retrogradational-progradational trend with the development of low-energy peloidal-skeletal wackestone-packstone in the middle part of the sequence. Different types of grain-supported facies (ooidal, peloidal, intraclastic, skeletal) are found both in high-energy mid-ramp domains and inner ramp areas. The studied series is bounded by discontinuities that are traceable across a total of 17.5 km linear distance and encompasses coral-microbial build-ups 5 to 15 m high developed in mid-ramp setting during the stages of maximum accommodation gain. A total of 274 reefs have been mapped across the different reconstructed 2D transects. Most of them have pinnacle or conical geometry. Well-cemented discontinuity surfaces were used to identify four stages of sedimentary evolution, two of them including individual episode of reef growth. Some trends on the spatial density and on the fabric within each stage have been recorded. The overall distribution of the main facies were included in a full-field model (20 x 20 m grid increment) while the geometry, size and distribution of the reefs were better adjusted in sector models (1 x 1 m). These models assess the distribution of reservoir bodies and their connectivity. They are now used as a template for diagenesis modelling and constitute the geological input for simulation models.