Abstract An integrated tectonic and sequence stratigraphic analysis of the Cretaceous and Danian of the Danish Central Graben has led to significant new insights critical for our understanding of the chalk facies as a unique cool-water carbonate system, as well as for the evaluation of its potential remaining economic significance. A major regional unconformity in the middle of the Upper Cretaceous chalk has been dated as being of early Campanian age. It separates two distinctly different basin types: a thermal contraction early post-rift basin (Valanginian–Santonian), which was succeeded by an inversion tectonics-affected basin (Campanian–Danian). The infill patterns for these two basin types are dramatically different as a result of the changing influence of the tectonic, palaeoceanographic and eustatic controlling factors. Several new insights are reported for the Lower Cretaceous: a new depositional model for chalk deposition along the basin margins on shallow shelves, which impacts reservoir quality trends; recognition of a late Aptian long-lasting sea-level lowstand (which hosts lowstand sandstone reservoirs in other parts of the North Sea Basin); and, finally, the observation that Barremian–Aptian sequences can be correlated from the Boreal to the Tethyan domain. In contrast, the Late Cretaceous sedimentation patterns have a strong synsedimentary local tectonic overprint (inversion) that influenced palaeoceanography through the intensification of bottom currents and, as a result, the depositional facies. In this context, four different chalk depositional systems are distinguished in the Chalk Group, with specific palaeogeography, depositional features and sediment composition. The first formalization of the lithostratigraphic subdivision of the Chalk Group in the Danish Central Graben is proposed, as well as an addition to the Cromer Knoll Group.

Abstract The contributions in this volume originally formed a set of presentations at a conference on the same theme held in Mallorca, Spain in 2006. The goal of this conference was to investigate the potential to develop age or architecture specific reference models for carbonate systems and reservoirs similar to those successfully developed for siliciclastic systems. The conference focused on the Mesozoic and Cenozoic carbonate sequences of the Mediterranean and Middle East. These sequences were chosen for a number of reasons. Firstly, they represent sequence development in a variety of basin settings within a contiguous geographical entity, the former NeoTethys Ocean (Fig. 1 ). The sequences were also formed predominantly within tropical or sub-tropical climatic zones (cf. Schlager 2003 ). Finally, the high levels of industry and academic interest in the region have generated many excellent multidisciplinary studies of these sequences, based on both the comprehensive datasets of hydrocarbon-bearing strata and the excellent surface exposures in the region. In general, all Earth models underestimate the complexity of the subsurface and hence are intrinsically inaccurate. The value of developing such models, however, lies in the improved understanding of the processes controlling sequence development gained from their application (e.g. Ahr 1973 ; Read 1985 ; Burchette & Wright 1992 ; Handford & Loucks 1993 ; Pomar 2001 ; Bosence 2005 ). Extrapolating from data rich examples into areas where data coverage is poorer obliges us to distil out the generic from the specific and to propose

Abstract During the Mesozoic and Cenozoic Eras, regional tectonic processes, eustatic variations and the volume and distribution of non-carbonate sediment controlled the progressive expansion and rapid reduction of the accommodation space available for the deposition of carbonate sequences, in the area that is now the Mediterranean and Middle East. We present a simplified super-regional tectonostratigraphic history of this area from earliest Triassic time to the present day, to demonstrate the influence of these large-scale processes on the evolution of major Tethyan Mesozoic and Cenozoic carbonate sequences. The time period is divided into 11 tectonostratigraphic phases (TSP) two of which (1 and 11) are incomplete. Each TSP commenced with major changes in basin architecture in response to regional tectonic processes. Subsequent pulses of transgression and regression generated sequence stratigraphic hierarchies. These stratigraphic hierarchies reflect the interaction between regional and local tectonics, eustatic variations, carbonate growth processes, climate and non-carbonate sediment supply. A map is presented of a major second-order transgressive sequence (TST) within each TSP to illustrate the maximum extent of marine onlap. These maps also include the main plate configurations; active regional tectonic features and the resultant time averaged carbonate gross depositional systems that developed during the transgression. The sequence of maps illustrate that the volume of available accommodation space during the Mesozoic and Cenozoic Eras reached a maximum during the Late Cretaceous and has been progressively reduced during the Cenozoic Era to the present day minimum.

Abstract This paper describes the results of new stratigraphic correlations and petroleum systems analyses of the Triassic deposits in the Syrian Palmyrides. The correlations are based on well data and new palynological work which reconcile previous lithological and stratigraphic miscorrelations of Triassic sequences from this region. The sequences are subdivided into four Megacycles, which are directly related to the key elements of the petroleum systems of the Palmyrides. The hydrocarbon discoveries within these systems, the fluid contacts and hydrodynamics are explained with reference to the Megacycle subdivision. This subdivision is applied on a regional scale and is used to define the distribution of reservoir seal pairs for volumetric estimations.

Abstract Carbonate ramp systems are widespread throughout the geological record, but very few areas have seismic-scale, continuous and structurally undeformed outcrops that allow reliable interpretation of facies distributions and stacking patterns. The Amellago outcrop shows the detailed depositional and stratigraphic relationships of an ooid-dominated ramp system that is almost completely exposed along a dip profile (37 km long and 1000 m thick) in the Lower to Middle Jurassic of the southern High Atlas, Morocco. Ammonite and brachiopod fauna provide excellent biostratigraphic control on small scale stacking patterns. At Amellago, the evolution of depositional environments is evident at different scales of space and time during this period of tectonic quiescence dominated by thermal subsidence. An important observation is that the Amellago ramp system contains micrite-rich, ooid-free intervals that alternate with ooid-rich intervals. The ooid-rich intervals are mainly in the late transgressive and highstand system tracts, whereas the ooid-free intervals occur in the early transgressive phase. More than 25 such alternations were recorded in high frequency cycles and at the scale of one large cycle at the Aalenian/Bajocian transition. These compositional changes and the associated different ramp geometries are interpreted to result from the combined effects of eustatic sea level and climatic changes.

Abstract A synthesis of the sedimentary evolution of the Upper Jurassic carbonate epeiric ramps that developed in the northern part of the Iberian Basin (NE Spain) is presented. The facies distributions reconstructed from the analysis of a 200 km-long transect, show a transition from shallow to relatively deep sedimentation sites. The studied carbonate ramps record major long-term transgression, from mid-Oxfordian to mid-Kimmeridgian followed by progressive basinwards coastal shift until the major regressive event around the mid-Berriasian. Subsidence was relatively homogeneous across the northern Iberian Basin during most of the studied interval. Major episodes of differential subsidence occurred around the Oxfordian–Kimmeridgian transition and onwards from the mid-Tithonian. The sedimentary evolution and particular facies types of the successive Iberian carbonate ramps is described, considering five depositional sequences that have a long-term transgressive-regressive evolution. The Oxfordian sequence shows a sharp transition from shallow to deep ramp areas: from mixed siliciclastic-carbonate (ooidal, skeletal, peloidal) facies to condensed (i.e. spongiolithic, peloidal, glauconitic) facies in the open platform domain. In the two Kimmeridgian sequences (Kim1 and Kim2), the transition between shallow and deep areas is more gradual and thickness distribution across the ramp is more homogeneous. Coral-microbial reefs and oolitic-peloidal-skeletal shoals characterized the shallow areas. Towards the offshore domain, these facies grade rapidly to a tempestite-dominated lithofacies and then into thick lime mudstone successions (i.e. rhythmic marls-mudstone alternations). Shallow oncolitic-peloidal and skeletal facies covered wide areas of the carbonate ramp during the early Tithonian (Ti1 sequence) and graded basinwards to thick successions of well-bedded micrites. The middle Tithonian to lower Berriasian platform (Ti2 sequence) is only partly exposed and formed during a stage of more heterogeneous subsidence. It is characterized by a thick succession with metre-scale shallowing-upward sequences with local development of peritidal, algal-laminated caps. The factors that controlled the sedimentary evolution and major facies changes across the successive epeiric carbonate ramps are discussed by comparison to other Upper Jurassic platforms developed in the western Tethyan realm.

Abstract A 380 m thick Aptian platform to basin transition has been studied along a 16 km long transect of excellent and continuous outcrops in NE Spain. The series has been dated using biostratigraphy (foraminifera and ammonites) and carbon-isotope stratigraphy, and has been subdivided at four scales of depositional sequences. The Aptian marine succession is subdivided into two-large scale sequences separated by a middle Aptian sub-aerial exposure surface. A characteristic trend of the floral-faunal fossil assemblages is present, which evolves from orbitolinid-ooid dominated ramps in Sequence I-1, to a coral-stromatoporoid-microbialite dominated platform in Sequence I-2, to a rudist-dominated platform top in Sequence II-1, and finally to a second episode of orbitolinid-ooid dominated ramp system in Sequence II-2. There was an influx of siliciclastic sediments at the base and at the top of this succession. The detailed carbon-isotope curve measured along the Miravete section and covering almost the complete Aptian succession, is compared with published Aptian curves recorded in both basinal and carbonate platform settings along the northern and southern NeoTethys margins. It shows that the Galve sub-basin curve represents all the major isotope excursions of the lower and upper Aptian, in a dominantly shallow-water succession.

Abstract The Shu'aiba and Natih Formation carbonates are important hydrocarbon reservoirs in the Sultanate of Oman. They consist of stacked deepening and shallowing-upward depositional cycles within an extensive middle Cretaceous epeiric carbonate platform. Geological models for these units traditionally assume a layer-cake stratigraphy and a high lateral continuity of facies. This is based on the assumption that epeiric platforms consist of ramps with low depositional gradients, broad facies belts and gradual facies transitions. However, high-resolution 3D seismic data covering large areas of the platform have revealed a more complicated internal stratigraphic architecture and have led to a new geometrical model for these epeiric platform systems. The transgressive part of the cycles is dominated by a low angle ramp depositional profile with localized development of algal-dominated mounds. Differential carbonate growth led to a topography of shallow carbonate shoals and intra-platform ‘basins’ with water depths reaching several tens to 100 m. During the regressive part of the cycles these basins were progressively filled-in by prograding carbonate rudist shoal complexes with depositional slopes of 0.5° to more than 30°. Clinoform belts on seismic show a wide range of progradational geometries ranging from closely spaced, laterally continuous ‘tramlines’ to irregular wedges and noses. The cycle tops are characterized by bedrock incisions and the influx of fine clastic sediments that fill in remnants of the intra-platform basins. The seismic images show that previous stratigraphic models for these carbonates oversimplified and flattened the stratigraphy. As a result the stratigraphic trapping potential and the internal reservoir heterogeneity for these systems has been underestimated.

Abstract The Natih Formation (late Albian–early Turonian, Oman) corresponds to a very broad inner carbonate platform extending over more than 800 km between the Arabian Shield to the south and the Tethys continental margin to the north. Two types of channelized systems have developed recurrently on this inner carbonate platform: incisions corresponding to strictly erosive drainage systems which formed at the top of the sub-aerially-exposed platform during significant drops of relative sea level; tidal channels corresponding to partly erosive but mainly constructive/depositional systems which formed during phases of flooding of the inner platform. The comparative analysis of the basal surface and fill of incisions and tidal channels, based on the study of several outcrops in the Oman Mountains allows the recognition of the similarities and the main differences between these two types of channelized systems which both develop in an inner carbonate platform setting. One of the main criteria of differentiation is the stratigraphic context in which incisions and channels develop. Incisions develop at the top of regressive sequences, whereas the channels analysed here developed during phases of flooding or maximum flooding, during which higher energy processes such as tidal currents developed on the platform. The incision surface is clearly defined, with diagenetic effects such as silicification and dolomitization below, and with the systematic fill of subjacent burrows and cracks by sparitic calcite crystals. The basal erosion surface of channels is often multiple and composite, systematically burrowed, and associated with no significant diagenetic effect. Channels are generally less deep than incisions but their width is very similar. Incisions are longer than channels and present a section that is, on the whole, symmetrical and regular, whereas channels locally have one margin that is steeper and more erosive than the other. Finally, the less diagnostic parameter of differentiation is their fill. Indeed, incisions and channels are similarly filled during phases of flooding of the inner platform. Incisions and channels form significant heterogeneities at the reservoir scale. It is therefore necessary to be able to recognize these two types of channelized systems, in order to predict their geometry, extent and fill type, and the eventual occurrence of associated reservoir bodies in the more distal direction (forced regressive wedges/bioclastic shoals).

Abstract A high resolution sequence stratigraphic model has been constructed for the mid-Cretaceous Sarvak Formation (in the High Zagros region of SW Iran) which was deposited close to the eastern margin of the Arabian Plate. The exceptional outcrop quality, displaying the detailed facies patterns in the transition zone from carbonate platform to intra-shelf basin, offers the rare opportunity to distinguish between the relative control of carbonate sediment supply (S) and accommodation (A) on the depositional geometries of third- and fourth-order depositional sequences. Four third-order sequences have been distinguished in the Sarvak Formation, with a duration varying between 1.5 and 3 Ma, and a thickness of 50–150 m. These are in turn composed of fourth- and fifth-order sequences that form the stratigraphic building blocks of this carbonate system. A significant distinction has been made in the third-order sequences between the early transgression (e-TST) when the system was still flat, and corresponds to a ramp setting, and the late transgression (l-TST) when the carbonate platform to intra-shelf basin topography was created. The rate of accommodation creation is identified as the dominant factor controlling the morphology of the depositional profile, and, as such, the driving motor behind the dynamics of this type of carbonate system. The dip angle of the depositional profile has a major influence on: (1) the hydrodynamics of the system; (2) the type of carbonate sediment; and (3) the volume of carbonate sediment produced. A good correlation with the third-order sequences of the Natih Formation in Oman is demonstrated, which supports a dominant control by eustatic sea-level changes and a similar response of the carbonate system to changes in the rate of sea-level rise on the southern part of the Arabian Plate. This outcrop analogue can be considered as a good reference model for the Cenomanian–Turonian carbonate platform margins of the Arabian Plate, but also as a textbook example of the response of carbonate systems to sea-level fluctuations (relative influence of accommodation and sediment supply).

Abstract A regional sequence stratigraphic model is proposed for the Oligo-Miocene Asmari and Pabdeh Formations in the Dezful Embayment of SW Iran. The model is based on both new detailed sedimentological observations in outcrops, core and well logs, and an improved high-resolution chronostratigraphic framework constrained by Sr isotope stratigraphy and biostratigraphy. A better understanding of the stratigraphic architecture distinguishes four, geographically separated types of Asmari reservoirs. Three Oligocene sequences (of Rupelian, early Chattian and late Chattian age) and three Miocene sequences (of early Aquitanian, late Aquitanian and early Burdigalian age) have been distinguished, representing a period of 15.4 Ma. The stratigraphic architecture of these sequences is primarily controlled by glacio-eustatic sea-level fluctuations, which determined the distribution of carbonates, sandstones and anhydrites in this sedimentary system. Tectonic control became important in the Burdigalian with a regional tilt down towards the NE. The lithological heterogeneity, the complex geometries, and both early and late diagenetic alterations are the basis for a classification of four main stratigraphic reference types for the Asmari Reservoirs: Type 1, sandstone dominated; Type 2, mixed carbonate-siliciclastic; Type 3, mixed carbonate-anhydrite; and Type 4, carbonate dominated. The sequence stratigraphic model predicts how and when these types change laterally from one to another.

Abstract In south-central Turkey, a carbonate platform system of early middle Miocene age is exposed in three-dimensional outcrops displaying a rich variety of carbonate facies associated with exceptionally well-preserved depositional geometries. This paper presents a detailed reconstruction of the geometries and facies organization across the prograding margin of one intra-platform carbonate bank that grew during the Langhian on the Ermenek Platform. The total thickness of the margin is approximately 250 m, and it has prograded over a distance of 1.2 km. The geometrical pattern shows an alternation between sigmoid, sigmoid-oblique, and oblique accretionary units at different scales. Based on the facies distribution and the geometrical framework two large-scale depositional sequences and eight medium-scale depositional sequences were defined. The general evolution from a low-angle shelf geometry to a prograding flat-topped platform was associated with an evolution from oligophotic-dominated carbonate producers, such as large benthic foraminifera, molluscs, echinoderms, red algae and bryozoans at the base, to mesophotic and euphotic carbonate producer organisms, such as corals, red algae and porcellaneous small benthic foraminifera at the top. The eight medium cycles were defined primarily using the depositional geometries, since facies changes were observed only locally within these cycles. Several mechanisms influenced the stratigraphic architecture of this margin: (1) eustatic sea-level controlled the overall transgressive-regressive Langhian sequence, and two superposed large-scale sequences. Medium cycles were probably also influenced by higher frequency sea-level fluctuations; (b) climate change probably influenced the overall evolution of the faunal assemblage; and (c) antecedent topography determined the overall architecture of a shelf bordering a deeper basin.

Abstract The combination of sedimentological and diagenetic data is important for the characterization of carbonate pore systems. This is particularly true for carbonates that were affected by meteoric diagenesis during sub-aerial exposure, for instance at sea-level lowstands. This diagenetic environment is commonly believed to be associated with increases in porosity, permeability and pore-throat diameters. Using data from three localities, improvement or deterioration of reservoir parameters below karst unconformities were analysed with a three-fold approach. In the first step, meteoric dissolution was characterized and early to late diagenetic products were described. In the second step, sedimentological and diagenetic data were converted to petrophysical data. In the third step, modelled climate data, in particular the occurrence of monsoon cells, in conjunction with other control mechanisms, were considered to understand the processes that controlled meteoric dissolution and later pore infill. Three case studies were analysed: (1) Lower Triassic oolites (sedimentary rocks dominated by ooids) and microbialites of the Calvörde Formation (Buntsandstein Group, Germany); (2) stacked shallowing-upward cycles of carbonate platform deposits in the Middle–Upper Triassic Mahil Formation (Arabian plate, Oman), capped by palaeosols; and (3) an Upper Triassic coral patch reef and overlying strata (Adnet, Salzburg region, Austria). Data integration allowed the establishment of three scenarios of significantly different processes related to meteoric diagenesis below unconformities: (1) increase of porosity and permeability and their preservation through time; (2) increase of porosity and permeability and subsequent pore system occlusion; and (3) decrease of porosity and permeability and creation of a barrier for pore fluids. Knowledge of the time span involved in meteoric diagenesis and the nature of the climatic regime helped to explain the origins and control mechanisms of the meteoric pore systems. The study provided evidence that a well-connected, large karst system, typical of a humid climate, is likely to be sealed subsequently by sediment and cement. Under arid climatic conditions, tight palaeosols developed at the unconformity and small karst pore systems developed which had the potential to remain open during basin evolution. Depending on the aforementioned parameters, carbonates affected by meteoric diagenesis may either become tight rocks or reservoirs.

Abstract This paper describes an integrated field, petrographic and geochemical study of an Albian carbonate platform from the Basque-Cantabrian basin (northern Spain). It examines the distribution and evolution of porosity and the relationships between facies variations, sequences and variations in diagenesis. These platform carbonates were deposited on the footwall crests of active tilted blocks formed during continental rifting related to the Mesozoic opening of the Bay of Biscay and North Atlantic. The studied units document an early Albian aggradational steep-sloping platform and a late Albian, low-gradient expansive shelf separated by a hiatal unconformity spanning the middle–early late Albian ( c. 5 Ma). The late Albian platform unit also exhibits a major internal unconformity. Platform geometries and facies architecture were mainly controlled by tectonics, hydrodynamic energy level and water depth. Petrographic, cathodoluminescence and geochemical analyses suggest that early meteoric diagenesis developed during sub-aerial exposure in strata below these two major unconformities. The platform carbonates have been affected during burial by a number of diagenetic processes that include four phases of dissolution, several fracture generations, and six cement sequences with development of at least 13 calcite and dolomite cement zones (Z0–Z12). A contrasting diagenetic response from the different platform environments illustrates the role of primary sediment composition and unconformity development in controlling porosity and cement distribution. Limestone stabilization and cementation were relatively early processes that were mostly completed within the first kilometre of burial depth beneath the depositional surface. Below this burial depth, fluid circulation was concentrated along restricted pathways (fractures and fault zones). Migration of hydrothermal-related fluids along fault zones created localized dolomite patches and large-scale porosity associated with cavities and collapse breccias, but did not significantly increase the small-scale porosity.

Abstract The Barremian–Aptian upper Khami Group and Albian–Campanian Bangestan Group have been studied at outcrop in Lurestan, SW Iran. The upper Khami Group comprises a thin deltaic wedge (Gadvan Fm) transgressively overlain by shelfal carbonates (Dariyan Fm). The Dariyan Fm can be divided into lower and upper units separated by a major intra-Aptian fracture-controlled karst. The top of the Daryian Fm is capped by the Arabian plate-wide Aptian–Albian unconformity. The overlying Bangestan Group includes the Kazhdumi, Sarvak, Surgah and Ilam formations. The Kazhdumi Fm represents a mixed carbonate-clastic intrashelf basin succession, and passes laterally (towards the NE) into a low-angle Orbitolina- dominated muddy carbonate ramp/shoal (Mauddud Mbr). The Mauddud Mbr is capped by an angular unconformity and karst of latest Albian–earliest Cenomanian age. The overlying Sarvak Fm comprises both low-angle ramp and steeper dipping (5–10°) carbonate shelf/platform systems. Three regionally extensive karst surfaces are developed in the latest Cenomanian–Turonian interval of the Sarvak Fm, and are interpreted to be related to flexure of the Arabian plate margin due to the initiation of intra-oceanic deformation. The Surgah and Ilam Fm represent clastic and muddy carbonate ramp depositional systems respectively. Both The Khami and Bangestan groups have been affected by spectacularly exposed fracture-controlled dolomitization. Dolomite bodies are 100 m to several km in width, have plume-like geometry, with both fracture (fault/joint) and gradational diagenetic contacts with undolomitized country rock. Sheets of dolomite extend away from dolomite bodies along steeply dipping fault/joint zones, and as strata-bound bodies preferentially following specific depositional/diagenetic facies or stratal surfaces. There is a close link between primary depositional architecture/facies and secondary dolomitization. Vertical barriers to dolomitization are low permeability mudstones, below which dolomitizing fluids moved laterally. Where these barriers are cut by faults and fracture corridors, dolomitization can be observed to have advanced upwards, indicating that faults and joints were fluid migration conduits. Comparisons to Jurassic–Cenozoic dolomites elsewhere in Iran, Palaeozoic dolomites of North America and Neogene dolomites of the Gulf of Suez indicate striking textural, paragenetic and outcrop-scale similarities. These data imply a common fracture-controlled dolomitization process is applicable regardless of tectonic setting (compressional, transtensional and extensional).

Abstract Precipitation of dolomite cements in Jurassic carbonate platform sediments and slope breccias has been studied from well cores and outcrops of the central Southern Alps and central Apennines in Italy. In both areas, an initial, massive dolomite replacement was followed by multiphase precipitation of dolomite cements. The replacement occurred during burial, in a passive margin regime, in response to compaction-driven flow of formational fluids. This interpretation is based on results from fluid inclusion and stable isotope analyses which have been related to the thermal history. The dolomite cements precipitated when both areas were involved in collisional tectonics. In spite of the similar diagenetic evolution, the fluids causing dolomite cementation in each case were compositionally different. In the Alps a decrease in salinity was recorded from sea water to brackish fluids, whereas in the Apennines an increase in salinity from sea water up to >10% NaCl equivalent was recorded. The remarkable salinity differences in diagenetic fluids are considered to be related to the different sub-aerial relief of the two belts during dolomite precipitation. In the Alps, the dilution of fluids is related to the infiltration of meteoric waters from the mountain chain, that was widely emergent. In the Apennines, dolomite cements precipitated whilst the structural units were still widely submerged, preventing meteoric dilution of cementing fluids and promoting an increase in salinity through mixing with fluids rising from older evaporate-bearing layers. In both Alpine and Apennine cases, the same diagenetic trend is observed in thrust-fold belt and foreland basin units; in both structural systems the diagenetic events start precipitating dolomite cements in the inner part of the collision zone and then the diagenetic processes migrate towards the foreland basin along with the structural evolution of the area.

Abstract This volume contains a collection of stratigraphic and diagenetic case studies of Mesozoic and Cenozoic carbonate sequences from the Tethyan realm. High levels of industry and academic interest in the region have generated numerous multi-disciplinary studies of these sequences, a selection of which are presented in this volume. The studies presented are based on both comprehensive subsurface datasets from important hydrocarbon-bearing strata of the Middle East and the excellent surface exposures in the region of interest. The studies presented in this volume may serve as suitable starting points in the development of age and architecture specific carbonate reference models. Such models can form the basis of internally consistent models for carbonate deposition, sequence development and reservoir performance. Ideally such models, suitably scaled, will be equally applicable to academic studies, the exploration and development phases of the field life cycle and in the prediction of future reservoir performance.