Abstract This study focuses on the deformation history and hydrocarbon plays of Late Cretaceous carbonate reservoirs of the Cordoba Platform and adjacent Veracruz Basin. Here, the buried Laramide thrust front accounts for one of the most mature petroleum provinces of Mexico. Three regional structural cross sections across the Cordoba Platform have been constructed using available surface and subsurface geological and geophysical data, from the Sierra de Zongolica in the west to the Veracruz Basin in the east. Forward kinematic modeling of these transects, using the Thrustpack software, allowed reconstruction of the burial history of potential source rocks. One-dimensional and two-dimensional thermal modeling (using the Genex, Gentect, and Thrustpack models) allowed reconstruction of the petroleum generation history (i.e., the maturation history of potential source rocks) and the thermal evolution of carbonate reservoirs, wherein only conductive heat transfer was considered. Maximum temperatures in the Late Cretaceous reservoirs of the Cordoba Platform probably never exceeded 60°C. In contrast, the deeper duplexes located in the buried thrust front reached their maximum burial and peak temperature only very recently as a result of the Cenozoic subsidence history of the Veracruz Basin. This modeling showed that potential source rocks did not reach the oil window prior to post-Laramide episodes of burial. This means that hydrocarbons migrated essentially from east to west and upward from the Veracruz Basin and underthrusted foreland toward the productive duplexes of the buried Laramide thrust front. Microtectonic and diagenetic studies from outcrops helped in unraveling the importance of stylolite and (paleo)karst development and fracturing, and to better understand the structural control on the overall porosity and permeability of the reservoirs. Petrographic studies of outcrops and core material showed that the paleoenvironment accounts for the preservation of reasonably good matrix porosity in distinct lithofacies (i.e., in early dolomitized platform carbonates of the Orizaba and Guzmantla Formations, bioclastic wackestone to packstone in the Guzmantla Formation, and in slope breccias of the San Felipe Formation). An important factor controlling the development of secondary porosity in the Cordoba Platform carbonates appears to relate to two successive karstification episodes. The first episode was related either to global sea-level changes during the passive margin evolution or to the early development of a former Laramide flexural bulge, whereas the second karstification event postdates Laramide contractional episodes. Furthermore, hydraulic fracturing, which predates the development of bedding-parallel stylolites, is locally evidenced. They are interpreted to relate to vertical dewatering processes occurring in a dominantly extensional system. A second hydraulic fracturing postdates the bedding-parallel stylolites but predates the Layer Parallel Shortening (LPS) features. Overpressures during this second episode of hydraulic fracturing, which also locally affects the sealing strata, was mostly synchronous with the onset of the Laramide orogeny and occurred when the principal stress axis (σ 1) was already horizontal. Deformation features accounting for secondary porosity developed during the Laramide orogeny. These still act locally as vertical conduits for the fluids and eventually display fair-to-good porosity and permeability, especially in the extrados and near the lateral anticlinal closures or at places where their overall orientation is consistent with the post-Laramide (modern) stress pattern.

Abstract Once deeply buried rocks are elevated in thrust belts, the resulting effects on reservoir evolution, source-rock maturity, hydrocarbon phase and charge history pose major problems for thrust belt exploration. To understand the geometrical evolution and burial history of thrust belts, successive structural restorations and dynamic basin modelling are needed. The forward modelling program ‘Thrustpack’ provides a semi-quantitative way forward, and this paper presents a ‘Thrustpack’ case study. The area considered is Rio Horta in the western foothills of the Colombian Eastern Cordillera, where westward-directed frontal structures break out onto the foreland basin of the Middle Magdalena Valley. A large sub-thrust anticline underlies the frontal thrusts and provides a substantial exploration lead. Following conventional models of back-thrusting and ‘fish-tailing’, the structure can be interpreted as entirely late, post-dating the overlying thrusts and once buried by the entire sedimentary megasequence of the Magdalena foreland basin. This would imply that the prospective section had been buried to a depth of about 12 km before uplift, and suggest a hydrocarbon graveyard, or, at best, dry gas in fractured, tight rock and potential overpressure. If the structure formed early, there is a chance of preserving both original porosity and liquid hydrocarbon in the structure, and charge risk is lessened because hydrocarbons were able to migrate into a structure that already existed. Hints from geological maps and the (generally poor quality) seismic data suggest that this is the more likely situation. It is consistent with the idea of an evolving palaeo-landscape and a mountain front with a very long history, where the structure remained relatively elevated during later sedimentation and thrusting. The modelling of these two alternative possible structural histories in ‘Thrustpack’ tests their viability and quantifies the hydrocarbon maturation, migration history and porosity evolution. The model in which the structure develops early presents real exploration opportunity whereas the alternative presents unacceptable exploration risk.

Abstract A study of the southern Kirthar fold belt in Pakistan was undertaken to elucidate the hinterland structure and hydrocarbon prospectivity. Interpretation of structure and stratigraphy is difficult because of suboptimal seismic data, a lack of hinterland well data, and a transition from shelfal to basinal stratigraphy. An interpretation of two cross sections was made using outcrop and seismic data and well data from foreland discoveries. The Institut Français du Pétrole Thrustpack ® software was used to validate the structural model and provide data on the maturity of the source rock. The Kirthar fold belt is dominated by open and symmetrical folds that are driven by inversion of basement-involved Jurassic extensional faults. Thrusts have been interpreted with two detachments, thrusts with a shallow detachment in the Eocene mudstones and thrusts with a deeper detachment in the Lower Cretaceous source rock interval that involve the reservoir during deformation. The major mountain-building episode is interpreted as late Pliocene–Pleistocene, but there is evidence for earlier inversion dating from the late Paleocene associated with the emplacement of the Bela ophiolite and constrained by maturity data obtained from outcrop. Early inversion and uplift impacts the burial curve and, thus, the prospectivity of the area.

Abstract Major oil discoveries in foothill areas have recently focused the interest of exploration companies sub-Andean basins. The SUBTRAP consortium was initiated in order to unravel the petroleum system associated with sub-thrust carbonate and sandstone reservoirs in various foreland fold-and-thrust belts around the world. As an illustration of the methodology defined by the consortium, this paper summarizes the main results of the integrated study using surface and subsurface geological data and basin modelling tools along a regional transect from eastern Venezuela. The focus of the study was to understand the porosity reduction and, therefore, the origin of the palaeofluids in the Upper Cretaceous-Oligocene sandstone reservoirs of the El Furrial structure (Venezuela). Basin modelling was performed using the Thrustpack, Locace and Ceres tools. The temperature and nature of the fluids obtained by this modelling were compared to fluid inclusions and oxygen isotope data on quartz overgrowths. Four observations were made. From 65 Ma to 20 Ma fluids were at thermal equilibrium with the sediments. They were continuously expelled vertically toward the surface during compaction-driven de-watering processes. From 20 Ma to 12 Ma, as a result of the regional tilting and the deposition of the synflexural Naricual Formation, the Cretaceous and Oligocene sandstones of the El Furrial structure became efficient conduits for fluids circulating from the north. These thrust-driven fluids (’squeegee 1’) were at thermal equilibrium with the Cretaceous and Oligocene sandstones and seem to be correlated with the first generation of quartz overgrowths. This episode is characterized by an increase in the overpressure in the Oligocene and Upper Cretaceous sandstones correlated with a hydraulic fracturing of the sealing Carapita black shales. From 12 Ma to 8 Ma fluids were expelled laterally from the Cretaceous sediments of the Pirital hanging-wall unit located immediately north of the El Furrial structure (’squeegee 2’). These fluids were probably in chemical disequilibrium and their temperature was higher than the temperature of adjacent sediments. This probably resulted in additional, but minor, episodes of quartz precipitation. This hypothesis is consistent with the information obtained from oxygen isotope analyses, which suggest that subsequent generations of quartz cement probably formed from evolved basinal fluids. At around 8 Ma a reduction in the intensity of the flow and then an inversion of this flow marked the sealing of the southern structural closure. Closure of the northern flank occurred at around 5 Ma, as indicated by the present velocity of the fluids close to zero in the El Furrial reservoirs and the filling of the structure by hydrocarbons.

Abstract The main focus of this study is the origin of the paleofluids in the Late Cretaceous–Oligocene sandstone reservoirs of the El Furrial structure (Venezuela). Basin modeling was performed using Thrustpack®, Locace®, and Ceres® tools. The temperature and nature of the fluids obtained by this modeling were compared to fluid inclusions and oxygen isotope data on quartz overgrowth. Four stages should be considered in this area: (1) From 65 to 20 Ma: Fluids were at thermal equilibrium with the sediments. They were continuously expelled vertically toward the surface during compaction-driven dewatering processes. (2) From 20 to 12 Ma: As a result of the regional tilting and the deposition of the synflexural Naricual Formation, the Cretaceous and Oligocene sandstones of the El Furrial structure became efficient conduits for fluids circulating from the north. These fluids were at thermal equilibrium with the Cretaceous and Oligocene sandstones and seem to be correlated with the first generation of quartz overgrowths. This episode is characterized by an increase in the overpressure of the Oligocene and Upper Cretaceous sandstones that is correlated to a hydraulic fracturing of the sealing Carapita black shales. (3) From 12 to 8 Ma: Fluids were expelled laterally from the Cretaceous sediments of the Pirital hanging-wall unit that is located immediately north of the El Furrial structure. These fluids were likely in chemical disequilibrium, and their temperature was higher than the temperature of adjacent sediments, which probably resulted in additional but minor episodes of quartz precipitation. This hypothesis is consistent with the information obtained from oxygen isotope analyses, which suggest that subsequent generations of quartz cement probably formed from evolved basinal fluids. (4) A reduction of the intensity of the flow and then an inversion of this flow mark the sealing of the southern structural closure of the structure at about 8 Ma. Then, the closure of the northern flank occured at about 5 Ma, as indicated by a present velocity of the fluids close to zero in the El Furrial reservoirs and the filling of the structure by the hydrocarbons.

ABSTRACT Deep seismic profiles, recorded in the foothills of the Northern Emirates, image the thrust-belt architecture and document the wide underthrusting of Mesozoic sedimentary units in the footwall of the Hawasina–Sumeini allochthon in the Dibba Zone, beneath the Semail Ophiolite. Integrated structural and geophysical modeling helped to constrain the structural architecture of two regional transects crossing the foreland and adjacent foothills. 2-D forward kinematic and thermal modeling was performed with Thrustpack® along the transects, whereas CERES2D® complete petroleum system modeling was subsequently performed along the northern transect. One hundred twenty kilometers (75 mi) of convergence occurred from the Santonian to the end of Early Miocene, of which about 80 km (50 mi) correspond to the obduction of the Semail Ophiolite and Sumeini–Hawasina units over the Arabian margin, whereas the remaining approximately 40 km (25 mi) were accommodated by the fold-and-thrust structures of the Oman belt. Paleogene source rocks of the foredeep only reached the beginning of the oil window. In contrast, Mesozoic source rocks of the underthrusted foreland are overmature or in the gas window in the foothills, but still preserve hydrocarbon (HC) potential further west in the foreland. Frozen kitchens may still be preserved in the hinterland, due to the high thermal conductivity of its former ophiolitic cover.

Abstract Several advances have been made for the reconstruction of fluid circulations and diagenetic history in subthrusted petroleum reservoirs because of the combination of the in-situ microanalysis of hydrocarbon fluid inclusions by Synchrotron Fourier transform infrared spectroscopy and PVTX modeling coupled to diagenetic history and tectonic setting. Integrated study has been made in the Eocene Chorgali formation (North Potwar Basin, Pakistan), where the shallow-marine carbonates formed important fractured reservoirs. Hydrocarbon fluid inclusions recognized in authigenic quartz and calcite from hydroveins show atypical association of CO 2 -rich light oil depleted in H 2 O in sulfates-quartz-calcite along simultaneous dissolution recrystallization processes at micrometer scale. Synchrotron Fourier transform infrared spectroscopy analyses, microthermometry, and pressure-volume-temperature modeling led to the beginning of quartz and calcite recrystallization at no more than 75–85°C and 150–180 bar in conditions of sulfate-calcite transformation. Temperatures of 150°C measured in aqueous fluid inclusions from calcite hydroveins are in favor of a thermosulfatoreduction mechanism. Early diagenetic sulfates are reduced by organic acids, and CO 2 comes from organic matter decomposition and/or previous decarbonation. A second phase of quartz growth is evidenced by the homogeneous entrapment in fluid inclusions of more mature oil in 60% CH 4 and a large amount of water at temperatures reaching 150–170°C. This late production of CH 4 agrees with δ 13 C depletion (−20 and −36%o) measured in veins and the crystallization of saddle dolomite. Thrustpack ® modeling shows that the onset of hydrofracturing and quartz precipitation at 1.5 km (1 mi) depth and 15–10.8 Ma (middle Siwalik) began when temperatures of 65 ± 10°C were reached at the end of sedimentation in the basin. It lasted until 4–6 km (2.5–4 mi) depth at temperatures as much as 170°C and reached the development of the thrust sheet at 5 Ma. Thus, circulations of hydrocarbon-rich fluids may be considered in thermal equilibrium with host rocks in both cases. The oil could then be derived from source rocks in the deep Mesozoic formation for the first input. The second input originated from the deep part of the basin itself and mixed with tectonic and meteoric water along the circulation pathways. The fluids are mainly driven by tectonics. They are expelled from the hinterland farther to the north and move updip toward the south in the Chorgali conduits, below the Kuldana seals. The potential source rock for organic matter is known as type II and type III kerogens in coal and black shales from the Paleocene.

Abstract We modeled the kinematic evolution of two regional-scale transects through the Eastern Cordillera fold and thrust belt of Colombia and then calculated the conductive thermal state of key steps of the kinematic history using Thrustpack ® 4.0. The models were constrained by well, seismic, apatite fission-track, and thermal-maturity data. The main compressional structures in the Cordillera are controlled by Jurassic–Early Cretaceous normal faults of the Bogotá, Cocuy, and the paleo-Magdalena basins. The location of these Mesozoic extensional features strongly influenced thermal evolution. Although shortening and basin inversion started in the early Tertiary, the bulk of the deformation occurred during the Miocene to Holocene Andean orogeny. Rocks in different structural positions in the thrust belt have distinct thermal and maturation histories that determine the timing of hydrocarbon source rock maturation and the quality of sandstone reservoirs. The internal part of the Cordillera had high heat flow, with peak sedimentary burial and peak maturation during the Oligocene flexural phase. Local structures formed during this time and were followed by major uplift and denudation during the Andean orogeny. Hydrothermal circulation of basinal fluids, which was probably expulsed at the onset of structural inversion, led to extensive cementation of Albian reservoirs. In contrast, the Llanos foreland is characterized by continued flexural subsidence and syntectonic sedimentation up to the present time. Thermal maturation results from the combination of syntectonic sedimentation and tectonic burial. Quartz cementation appears to be linked to the appearance of abundant silica in the system from pressure solution during Andean shortening. The thermal regime of the western flank of the Cordillera is cooler than the interior of the range, whereas the structural history is more complex. Along our transect, an active kitchen is located in the west-vergent thrust belt of the Eastern Cordillera. In the Magdalena Valley, there are local kitchens only where a thick stratigraphic section is preserved. The main limitations of our thermal models are (1) the lack of constraints on the thickness and timing of deposition of the Eocene-Oligocene flexural deposits, which are sparsely preserved in the Eastern Cordillera; (2) the paucity of good-quality thermochronologic data to constrain the timing of erosion and rates of fault motion; and (3) the difficulty in modeling the effects of fluid circulation over this large and structurally complex region.

ABSTRACT The lithostratigraphic column of the Outer Albanides records a long geodynamic evolution. It began with a Liassic rifted margin made up of tilted fault blocks, carbonate platforms, and euxinic basins (Posidonia Schist) and evolved into a Paleogene flexed foreland, part of which inverted during the Neogene. The complex Mesozoic paleogeography accounts for the distribution of potential décollement levels and lateral changes in structural styles. Petroleum plays are numerous and result from the occurrence of various source rocks with contrasting burial histories and migration pathways. To document the respective timing of thrusting, petroleum generation, and trapping, that is, the critical timing of Albanian petroleum systems, we have reconstructed the kinematic and thermal evolution of two representative regional transects that cross the Peri-Adriatic Depression and the Kruja Zone, as well as the Ionian Basin, in the northern and southern segments of the Outer Albanides, respectively.

Abstract Basin modelling tools are now more efficient to reconstruct palinspastic structural cross sections and compute the history of temperature, pore-fluid pressure and fluid flow circulations in complex structural settings. In many cases and especially in areas where limited erosion occurred, the use of well logs, bottom hole temperatures (BHT) and palaeo-thermometers such as vitrinite reflectance (Ro) and Rock-Eval (Tmax) data is usually sufficient to calibrate the heat flow and geothermal gradients across a section. However, in the foothills domains erosion is a dominant process, challenging the reconstruction of reservoir rocks palaeo-burial and the corresponding calibration of their past thermal evolution. Often it is not possible to derive a single solution for palaeo-burial and palaeo-thermal gradient estimates in the foothills, if based solely on maturity ranks of the organic matter. Alternative methods are then required to narrow down the error bars in palaeo-burial estimates, and to secure more realistic predictions of hydrocarbon generation. Apatite fission tracks (AFT) can provide access to time–temperature paths and absolute ages for the crossing of the 120 °C isotherm and timing of the unroofing. Hydrocarbon-bearing fluid inclusions, when developing contemporaneously with aqueous inclusions, can provide a direct access to the pore-fluid temperature and pressure of cemented fractures or reservoir at the time of cementation and hydrocarbon trapping, on line with the tectonic evolution. Further attempts are also currently made to use calcite twins for constraining reservoir burial and palaeo-stress conditions during the main deformational episodes. Ultimately, the use of magnetic properties and petrographical measurements can also document the impact of tectonic stresses during the evolution of the layer parallel shortening (LPS). The methodology integrating these complementary constraints will be illustrated using reference case studies from Albania, sub-Andean basins in Colombia and Venezuela, segments of the North American Cordillera in Mexico and in the Canadian Rockies, as well as from the Middle East.

Abstract The structural deformation and the petroleum system of the southern Apennines thrust belt (SATB) are studied along a regional cross section traversing the Monte Alpi–Tempa Rossa fields. The SATB is interpreted as a system of three major structural blocks incorporating the basement and the sediments up to the Apulian platform deposits beneath an allochthonous complex. The Thrustpack® software has been used to reconstruct the successive geometries and their progressive burial under foredeep sediments and the allochthonous complex. The bottom of the Apulian platform and the basement are involved in the deformation, and the thickness of the Permian interval, drilled in the foreland, is extended regionally. The timing of the deformation is constrained by the ages of the Pliocene foredeep sediments drilled on top of the Apulian platform. This record was also instrumental to propose a flexure scenario of the migrating foredeep-forebulge system, in which the slope of the topography had to be maintained to a realistic value. These assumptions and boundary conditions were tested by successive, two-dimensional kinematic and thermal reconstructions until a satisfactory match could be obtained with the available temperatures and vitrinite reflectance data. A final good thermal calibration has been obtained for the structural blocks of Monte Alpi and Tempa Rossa. However, the relatively poor quality of the temperature and vitrinite data available for the most hinterland structure questions the conclusions about the validity of our proposed geometry and assumed accumulated thrust displacement. The methodology used in this work is a useful tool in exploration, because it forces one to improve and update structural scenarios and to provide the grounds for highlighting important data gathering to further enhance an evaluation of the hydrocarbon potential at a basin scale. This latter point will be described in a companion chapter.

Abstract Major oil discoveries in the foothills of the Venezuelan and Colombian Andes have recently focused the interest of exploration companies toward sub-Andean basins. Seismic, well, and core data from the El Furrial (Venezuela) and Cusiana (Colombia) productive fields have been integrated herein with other regional information to document the evolution of the thrust belt and the history of the petroleum systems, and to propose practical guidelines for prediction of sandstone reservoir quality in such a complex geodynamic environment. Although timing of deformation is slightly different in these areas of eastern Venezuela and Colombia, sedimentary and tectonic burial of the foreland autochthon in both regions led to the maturation of prolific Cretaceous marine source rocks, resulting in successive and diachronous hydrocarbon migration and trapping episodes. Early sedimentary burial at the current location of the Serranía del Interior (Venezuela) and the Eastern Cordillera (Colombia) resulted in long-range migration of early-generated hydrocarbons toward the foreland, forming the large accumulation of hydrocarbon along the Faja Petrolifera (Eastern Venezuela). Early entrapped hydrocarbons also have been preserved in pre-Andean prospects of the Andean foothills, as evidenced by the complex charge history of the Cusiana field. However, wide areas of source rocks in the Andean foothills and adjacent foreland reached the oil window only during the late Neogene and Pliocene-Quaternary, when maximum burial was attained. This produced a second migration episode, coeval with the growth of frontal anticlinal prospects. The main reservoir in Cusiana is fluvial sandstone of the Mirador Formation (Eocene); in El Furrial, it is sandstone of the Naricual-Merecure Formation (Oligocene). Pressure solution and quartz cementation decreased permeability of these sandstones. Results of studies of the anisotropy of the magnetic susceptibility (AMS), coupled with studies of fluid inclusions in quartz overgrowths and thermal modeling, demonstrate that sandstone reservoirs of these oil fields were compacted both vertically, by the load of the synflexural sequence, and horizontally, by tectonic stress (layer-parallel shortening) prior to being tectonically emplaced into the allochthon. Layer-parallel shortening by pressure solution is a major source of silica in the underthrust foreland. Venezuelan and Colombian sandstones still have reasonably good reservoir characteristics, although they have been buried to great depths. Overpressure that developed in these reservoirs as a result of rapid foredeep sedimentation probably caused a delay in compaction. Early carbonate cements also may have contributed locally to prevent compaction until secondary porosity developed as a result of dissolution of this early diagenetic phase. Finally, development of structural closures and hydrocarbon trapping has resulted progressively in the shutting down of the hydraulic system, preventing the transport of exotic silica by regional fluid flow.

Abstract The structural deformation and the source rock system evolution of the southern Apennines thrust belt (SATB) are studied along a regional structural profile traversing the Monte Alpi–Tempa Rossa oil fields. In part I (the accompanying chapter), the reconstruction of the structural evolution and the thermal history was addressed to calibrate the burial history of the source rocks along the cross section. Here in part II, the generation and expulsion of hydrocarbons were modeled to test a potential source rock interval and identify geometric factors explaining the observed differences in the nature of the oil found in the three major structural trends. Organic-rich, laminated limestones that were penetrated by a few wells in the region represent the best source rock candidate to date. The source interval shows total organic carbon (TOC) values as much as 4% and hydrogen index as much as 632 mg HC/g TOC. This source rock also contains high amounts of sulfur (3–6% in kerogen). Rock samples and asphaltenes isolated from the oil were analyzed to determine both primary bulk kerogen decomposition and compositional kerogen decomposition products. For the latter, the results include determination of the kinetics of dry gas (C 1), wet gas (C 2 –C 5), light oil (C 5 –C 14), and heavy oil (C 15+) components. The southern Apennines Cretaceous source rock behaves as a type I kerogen equivalent, consistent with the distribution of the activation energies dominated by a single activation energy. Most of the predicted generated and expelled hydrocarbons are heavy and light oils. Thermal conditions for secondary cracking of the generated oil into gas could have been reached only in the footwall of the major thrusts. The measured kinetic parameters allow the modeling of a favorable timing of trap formation with respect to hydrocarbon generation and expulsion. When the measured bulk and compositional kinetics are used in the modeling, no oil generation is reached in the Tempa Rossa trend. The model shows that the Tempa Rossa heavy-oil field has been filled by oil that was generated deeper in the surrounding of the structure. Compositional kinetic simulation is consistent with the results of the geochemical analyses performed on several oils from the region. The original oils in the reservoirs should have an API gravity of about 25° API. Only subsequent geological processes (uplift and erosion) provide the pressure-volume-temperature variation responsible for the compositional grading column at the present time. Finally, kerogen transformation ratio vs. depth shows that the three different transformation ratio-depth zones should be considered to fit the thermal history of the southern Apennines. This two-dimensional information can be used to predict the distribution of potential source rock kitchen areas in the surroundings of the modeled section to guide future exploration.

Abstract One-dimensional and two-dimensional basin modeling has been performed along a regional transect crossing the Córdoba Platform allochthons and the autochthonous Veracruz Basin in order to infer the burial and kinematic evolution and to determine timing of hydrocarbon migration and charge in this famous Mexican petroleum province. Vitrinite reflectance, Rock-Eval data, and bottom-hole temperatures have been used to calibrate the heat flow and thermal evolution of the Veracruz Basin, where no erosion occurred. The Córdoba Platform and Veracruz Basin in Eastern Mexico comprise the southern most extent of the Laramide foreland fold-and-thrust belt,which developed along the eastern border of the North American Cordillera from Late Cretaceous to Eocene. Unlike in the Canadian Rockies, where pre-orogenic strata are relatively isopachous, this segment of the North American craton has been strongly affected by the Jurassic rifting and opening of the Gulf of Mexico. Substantial thickness and facies changes between horsts and grabens control the lateral and vertical distribution of Mesozoic source rocks and hydrocarbon reservoirs. In the east, thick Paleogene and Neogene sequences in the Cordilleran foreland provide a continuous sedimentary record in the Veracruz Basin. In the west, however, the Middle Cretaceous carbonates of the Córdoba Platform generally constitute the main outcropping horizon in the adjacent thrust belt, making it difficult to reconstruct its burial evolution from the Laramide orogeny onward. Cemented veins were sampled in reservoir intervals of the thrust belt. Petrography, stable isotope analyses, and fluid inclusion studies (microthermetry, Synchroton Fourier Transform Infra-Red analyses) on these samples revealed the diagenetic history of the reservoirs. Where diagenetic phases could be constrained in time and with respect to the tectonic evolution, fluid inclusion temperatures provide an additional paleothermometer in areas where major erosion occurred. Pressure-temperature modeling of simultaneously entrapped aqueous and oil-bearing inclusions indicates more than 4.5 km of erosion of Late Cretaceous-Paleocene sequences in the thrust belt, which can be accommodated in palinspastic sections only by restoring a hypothetical foredeep basin. This implies that the current east-dipping attitude of the basement beneath the Córdoba Platform developed after Laramide deformation, accounting for a major change in paleofluid dynamics. Fluid flow and basin modeling of the Veracruz section has been performed using CERES2D to infer the paleofluid dynamic associated with the petroleum system evolution. Following the initial phase of geometric model building and calibration against the thermal and burial history inferred, the modeling accounted for the past migration pathways for both water and oil and gas fluids. Unlike in most other foreland fold-and-thrust belts, hydrocarbons generated in Jurassic source rocks from the Veracruz foreland are currently migrating westward toward the thrust belt, accounting for a post-Laramide charge of the frontal duplexes of the Cordilleran thrust belt.

ABSTRACT The Eastern Cordillera of Colombia is considered to be the result of compression and uplift during the late Miocene–Pliocene Andean orogeny. Nevertheless, detailed mapping carried out on a portion of the fold belt exposed along the western flank of the Eastern Cordillera suggests that deformation began in late Paleocene–early Eocene time, in the form of a west-vergent, forward-propagating fold-and-thrust belt. Several structures related to this event remain concealed beneath the late Paleocene–late Eocene unconformity, and synkinematic sediments are preserved locally within some of these thrust sheets. The relief generated during this deformational episode constrained the depositional axis of late Eocene fluvial sediments to run along the present-day crestal zone of the Eastern Cordillera. Onlapping basal Miocene molassic sediments on tilted middle Miocene fluvial deposits suggest that a series of seismically delineated intercutaneous wedges located at the thrust front formed in late Miocene time. These structures mark the onset of the Andean deformational episode. Thrusting polarity reversed during the latter event, that is, toward the hinterland, and Paleogene structures were reactivated. Additionally, the late Paleocene–early Eocene unconformity surface was folded and incorporated into north-plunging folds, and Cretaceous ex-tensional faults were inverted. As a result, the Eastern Cordillera developed its present pop-up, doubly vergent fold-belt geometry, flanked by thick molassic sequences that document the Miocene–Pliocene Andean orogeny. Regionally, the latest Campanian–Maastrichtian uplift of the Central Cordillera, Paleocene–early Eocene thrusting in the Middle Magdalena Valley and along the western flank of the Eastern Cordillera, and ultimately inversion and major uplift of the entire Eastern Cordillera in late Miocene–Pliocene time, attests to the eastward propagation of deformation from the Central toward the Eastern Cordillera. Kinematically, the driving element of deformation would have been the obliquely accreting western terranes of the Central and Western Cordilleras and the Panama arc. These transferred their easterly component of convergence to the Eastern Cordillera through a basal intracrustal detachment.