ABSTRACT The Papua New Guinea fold and thrust belt petroleum system is studied along a 200-km (124-mi)-long transect. The kinematic scenario includes the Jurassic rifting and passive margin, the erosion during the Upper Cretaceous related to the Coral Sea rifting and Pliocene–Pleistocene shortening, with an early growth of the Hedinia Anticline limiting lateral migration of oil in the adjacent Darai Plateau. Data from seven wells and two fields were used to calibrate section boundary conditions and properties. Apart from the high-pressure trend in the Kutubu/Moran structures, all data are well reproduced, and the modeled section appears quantitatively predictive. The modeling demonstrates three major pathways for water: (1) topographically driven flow from the onset of mountain building; (2) deep updip basinal flux, flowing along the tilted reservoirs; and (3) across fault escape from connected reservoir bodies. Type II or mixed type II/III is used to model the Triassic and Jurassic source rock. Maturation starts in the Middle Cretaceous and increases strongly during the late tectonic burial, with three main accumulations: (1) the deep part of the Mubi zone, with vertical migration along faults; (2) the Hedinia and Kutubu anticlines charged during Orubadi and Era deposition; and (3) the Darai Plateau.

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 Continental margins and their fossilized analogues are important repositories of natural resources. With better processing techniques and increased availability of high-resolution seismic and potential field data, imaging of present-day continental margins and their embedded sedimentary basins, in which the majority of these resources are located, has reached unprecedented levels of refinement and definition, as illustrated by papers in this volume. This, in turn, has led to greatly improved geological, geodynamic and numerical models for the crustal and mantle processes involved in continental-margin formation from the initial stages of rifting through to continental rupture and break-up, to the eventual development of a new ocean basin. Further informing these models, and contributing to a better understanding of the features imaged in the seismic and potential field data, are observations made on fossilized fragments of exhumed subcontinental mantle lithosphere and ocean–continent transition zones preserved in ophiolites and orogenic belts of both Palaeozoic and Mesozoic age from several different continents, including Europe, South Asia and Australasia.

Abstract This volume constitutes the proceedings of the American Association of Petroleum Geologists-Institut Francats du Petrole Hedberg conference entitled Deformation, Fluid Flow, and Reservoir Appraisal in Foreland Foldand Thrust Beltsheld on May 14-18, 2002, in Mondello, Sicily,with the participation of 80 earth scientists from the petroleum industry and universities. It comprises 21 papers, selected from among 38 oral and 13 poster presentations. Reservoir risk remains one of the key concerns to the exploration of deep subthrust prospects in foothill areas of fold and thrust belts. Case studies that have integrated structural geology, geochemistry, and reservoir petrology not only now provide a better understanding of the multiscale processes involved in reservoir damage (particularly small-scale deformation and cementation) but also have begun to identify the critical parameters that are likely to enhance secondary porosity and permeability in deeply buried sandstone and carbonate series. Recent progress in analytical resolution makes it more and more possible to approach the problems on a microscale level and link the evolution of rock properties to the geological history on a broader scale. Basin-scale numerical simulations now incorporate the kinematics and thermal evolution of fold and thrust belts, as well as reconstructions of the history of fluid flow and pore-fluid pressure. Basinmodeling techniques provide quantitative and predictive results based on both thermodynamics and mass-balance calculations of fluid-rock interactions at reservoir scale. Instantaneous fluid-flow values derived from such models can be used as boundary conditions for forward diagenetic simulations applied to a specific reservoir layer, particularly for those episodes of

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 Apatite fission-track (AFT) data from rocks above and below Lewis thrust fault lying in the footwall and hanging wall of Flathead normal fault record different thermal-history components, depending on individual structural and stratigraphic positions. Apatite fission-track temperature-history models (THMs) indicate that rapid cooling of the Lewis thrust sheet began at about 75 Ma. This cooling coincided with major displacement on the Lewis thrust. Subsequently, folding of the Lewis thrust sheet by underlying thrust duplex culminations formed the Akamina syncline, and a fossil AFT partial annealing zone was superimposed on the syncline. Apatite fission-track data from east of the Flathead graben record a subsequent cooling event during the middle Eocene onward that was coeval with extensional displacement on the Flathead fault and with accompanying uplift and erosion of its footwall. Apatite fission-track data from lower Oligocene sediments in the Flathead graben preserved the temperature history of the sediment source regions in the Lewis thrust sheet without significant subsequent annealing. A set of similar THMs that are consistent with the regional structural history can account for observed variations in AFT parameters at various levels, which are exposed in the Lewis thrust sheet and are penetrated below the thrust sheet by deep wells. From the onset of displacement on the Lewis thrust until the early Oligocene, paleogeothermal gradients in the thrust sheet (8.6–12°C/km) were lower than present values (~17°C/km). The changes in geothermal gradients are attributed to advective heat transfer by tectonically induced, topographically driven, deeply penetrating meteoric water flow. This is a complicated heat-transfer mechanism that can affect organic maturation history and petroleum systems in overthrust belts.

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 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 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 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 A structural analysis and petrographic investigation has been performed on veins in Cretaceous carbonates in the Cordoba Platform in eastern Mexico, which is part of the Laramide foreland fold and thrust belt (FFTB). This chapter focuses on the different episodes of vein formation, vein morphology, and possible mechanisms of vein formation. Vein (fracture) formation is interpreted in relation to the kinematic evolution of the FFTB. Evidence for the development of hydrofractures during this evolution is given. This study documents veins (fractures) related to Laramide FFTB development in the Cordoba Platform. These veins (fractures) are related to the kinematic evolution of the area and the inferred paleostress conditions. The kinematic evolution can be split up into three major stages: a precompression phase with platform development; a Laramide compressional stage, during which the FFTB developed; and finally, a late Basin and Range-related extension phase. Compound veins and densely spaced microveins record multiple fracturing events in a cyclic stress field during burial, most probably caused by changes in fluid pressure. They are interpreted in relation with early foreland flexuring. With rising compressional stress, less well-oriented veins and breccia veins develop because of a lowered differential stress in the prefolding stage. Progressive layer-parallel shortening (LPS) leads to a caterpillar-type scenario of fluid migration toward the foreland, eventually causing hydrofracturing, succeeded by pressure solution and development of vertical stylolitic planes. These LPS stylolites have the potential to be reopened during subsequent folding of the strata. In addition, older LPS-parallel planes and extrados fractures may open in anticlinal hinges. Shear-associated, shallow-dipping veins develop after LPS development, possibly because of bedding-parallel shear and/or thrust migration. Other post-LPS veins are steeply dipping and commonly reuse older vein orientations. Dark, banded veins, which are filled with a silt-sized and clay-sized material and lack significant cementation, are interpreted to reflect fracture planes along which recrystallization of matrix occurred. Many post-LPS dissolution-enlarged veins and breccias relate to telogenetic karstification. Post-LPS multiple brecciation just above a major thrust plane in the buried tectonic front area is interpreted to reflect the damage zone of that fault.

Abstract The Brooks Range is a north-directed fold and thrust belt that forms the southern boundary of the North Slope petroleum province in northern Alaska. Field-based studies have long recognized that large-magnitude, thin-skinned folding and thrusting in the Brooks Range occurred during arc-continent collision in the Middle Jurassic to Early Cretaceous (Neocomian). Folds and thrusts, however, also deform middle and Upper Cretaceous strata of the Colville foreland basin and thus record a younger phase of deformation that apatite fission-track data have shown to occur primarily during the early Tertiary (~60 and ~45 Ma). A structural and kinematic model that reconciles these observations is critical to understanding the petroleum system of the Brooks Range fold and thrust belt. New interpretations of outcrop and regional seismic reflection data indicate that from the modern mountain front northward to near the deformation front under the coastal plain, the basal thrust detachment for the orogen is located in the Jurassic and Lower Cretaceous Kingak Shale in the upper part of the regionally extensive, gently south-dipping, north-derived Mississippian to Early Cretaceous Ellesmerian sequence. The frontal part of the orogen lies in middle Cretaceous foreland basin strata and consists of a thin-skinned fold belt at the deformation front and a fully developed passive-roof duplex to the south. Near the mountain front, the orogen is composed of a stacked series of allochthons and thrust duplexes and associated Neocomian syntectonic deposits that are unconformably overlain by proximal foreland basin strata. The foreland basin strata and underlying deformed rocks are truncated by a younger generation of folds and thrusts. Vitrinite reflectance and stable isotope compositions of veins provide evidence of two fluid events in these rocks, including an earlier higher temperature (~250–300°C) event that was buffered by limestone and a younger, lower temperature (~150°C) event that had distinctly lower δ 13 C values as a result of oxidation of organic matter and/or methane. Zircon fission-track data from the host rocks of the veins show that the higher temperature fluid event occurred at 160–120 Ma, whereas the lower temperature event probably occurred at about 60–45 Ma. It is proposed that the Brooks Range consists of two superposed contractional orogens that used many of the same mechanically incompetent stratigraphic units (e.g., Kayak Shale, Kingak Shale) as sites of thrust detachment. The older orogen formed in a north-directed arc-continent collisional zone that was active from 160 to 120 Ma. This deformation produced a thin-skinned deformational wedge that is characterized by fartraveled allochthons with relatively low structural relief, because it involved a thin (1–4-km [0.6–2.5-mi]-thick) stratigraphic section. Deeper parts of the deformational wedge are envisioned to have contained relatively high-temperature fluids that presumably migrated from or through limestone-rich source areas in the underlying autochthon or from deeper parts of the orogen. The younger orogen, which formed initially at about 60 Ma and reactivated at 45 Ma, produced a thrust belt and frontal triangle zone with low amounts of shortening and relatively high structural relief, because it involved a structural section 5–10 km (3–6 mi) thick. Fluids associated with this deformation were relatively of lower temperature and suggest that hydrocarbon migration occurred at this time. We conclude that hydrocarbon generation from Triassic and Jurassic source strata and migration into stratigraphic traps occurred primarily by sedimentary burial principally at 100–90 Ma, between the times of the two major episodes of deformation. Subsequent sedimentary burial caused deep stratigraphic traps to become overmature, cracking oil to gas, and initiated some new hydrocarbon generation progressively higher in the section. Structural disruption of the traps in the early Tertiary released sequestered hydrocarbons. The hydrocarbons remigrated into newly formed structural traps, which formed at higher structural levels or were lost to the surface. Because of the generally high maturation of the Colville basin at the time of the deformation and remigration, most of the hydrocarbons available to fill traps were gas.

Abstract Beneath the Arctic coastal plain (commonly referred to as "the 1002 area") in the Arctic National Wildlife Refuge, northeastern Alaska, United States, seismic reflection data show that the northernmost and youngest part of the Brookian orogen is preserved as a Paleogene to Neogene system of blind and buried thrust-related structures. These structures involve Proterozoic to Miocene (and younger?) rocks that contain several potential petroleum reservoir facies. Thermal maturity data indicate that the deformed rocks are mature to overmature with respect to hydrocarbon generation. Oil seeps and stains in outcrops and shows in nearby wells indicate that oil has migrated through the region; geochemical studies have identified three potential petroleum systems. Hydrocarbons that were generated from Mesozoic source rocks in the deformed belt were apparently expelled and migrated northward in the Paleogene, before much of the deformation in this part of the orogen. It is also possible that Neogene petroleum, which was generated in Tertiary rocks offshore in the Arctic Ocean, migrated southward into Neogene structural traps at the thrust front. However, the hydrocarbon resource potential of this largely unexplored region of Alaska’s North Slope remains poorly known. In the western part of the 1002 area, the dominant style of thin-skinned thrusting is that of a passive-roof duplex, bounded below by a detachment (floor thrust) near the base of Lower Cretaceous and younger foreland basin deposits and bounded above by a north-dipping roof thrust near the base of the Eocene. East-west-trending, basement-involved thrusts produced the Sadlerochit Mountains to the south, and buried, basement-involved thrusts are also present north of the Sadlerochit Mountains, where they appear to feed displacement into the thin-skinned system. Locally, late basement-involved thrusts postdate the thin-skinned thrusting. Both the basement-involved thrusts and the thin-skinned passive-roof duplex were principally active in the Miocene. In the eastern part of the 1002 area, a northward-younging pattern of thin-skinned deformation is apparent. Converging patterns of Paleocene reflectors on the north flank of the Sabbath syncline indicate that the Aichilik high and the Sabbath syncline formed as a passive-roof duplex and piggyback basin, respectively, just behind the Paleocene deformation front. During the Eocene and possibly the Oligocene, thin-skinned thrusting advanced northward over the present location of the Niguanak high. A passive-roof duplex occupied the frontal part of this system. The Kingak and Hue shales exposed above the Niguanak high were transported into their present structural position during the Eocene to Oligocene motion on the long thrust ramps above the present south flank of the Niguanak high. Broad, basement-cored subsurface domes (Niguanak high and Aurora dome) formed near the deformation front in the Oligocene, deforming the overlying thin-skinned structures and feeding a new increment of displacement into thin-skinned structures directly to the north. Deformation continued through the Miocene above a detachment in the basement. Offshore seismicity and Holocene shortening documented by previous workers may indicate that contractional deformation continues to the present day.

Abstract The Linking Zone (northeast Spain) is a fold and thrust belt that, together with the Catalan Coastal Range and the Iberian Chain, constitutes the southern flank of the Ebro Basin. Compressive deformation occurred during the late Eocene-early Miocene, affecting a Hercynian basement, a Mesozoic cover, and syntectonic Tertiary conglomerates. The integration of the structural study of the fractures with the petrologic and geochemical study of the cements filling the fractures reveals two episodes of fluid circulation during compressive deformation. The first episode occurred during the early stages of the fold and thrust belt development and includes two different fluids responsible for precipitation of two types of calcite cement. The first type of calcite cement is characterized by δ 18 O ranging from −9 to −3.8‰ Peedee belemnite (PDB), δ 13 C ranging from −5.6 to −2.6‰ PDB, a 87 Sr/ 86 Sr ratio of 0.70768, between 440 and 3565 ppm of Mg, between 275 and 720 ppm of Fe, between 180 and 410 ppm of Mn, and Sr content always below 275 ppm (below the detection limit). The fluids precipitating these cements were meteoric fluids that were derived directly from the surface and circulating through the undeformed and highly porous Tertiary syntectonic conglomerates in an open paleohydrogeological system. The second type of calcite cement is characterized by δ 18 O ranging from −10.1 to −5.4‰ PDB, δ 13 C ranging from −7.5 to −3.5‰ PDB, a 87 Sr/ 86 Sr ratio ranging between 0.70759 and 0.70778, between 350 and 5150 ppm of Mg, Fe content as much as 11,490 ppm, Mn content below 180 ppm (below the detection limit), and Sr content as much as 795 ppm. The fluid that was precipitating these cements was originally a meteoric fluid that evolved to a formation water composition probably because of a high interaction with Mesozoic rocks. The Triassic shales and evaporites of the detachment levels served as barriers, forcing the fluids to move laterally above them. The second episode of fluid circulation occurred during the last stages of fold and thrust belt development, after the major uplift of the interior belt and formation of the relief. Two different fluids are recognized during this episode as being responsible for precipitation of two types of calcite cements. The first type of calcite cement is characterized by δ 18 O ranging from −3.4 to −3.3‰ PDB, δ 13 C ranging from −4.0 to −3.8‰ PDB, 87 Sr/ 86 Sr ratio of 0.70845, between 475 and 4200 ppm of Mg, Fe always below 275 ppm (below the detection limit), between 180 and 655 ppm of Mn, and between 280 and 850 ppm of Sr. The second type of calcite cement is characterized by δ 18 O ranging from −12.7 to −8.1% PDB, δ 13 C ranging from −6.4 to −3.9‰ PDB, a 87 Sr/ 86 Sr ratio ranging between 0.70792 and 0.70795, between 260 and 5240 ppm of Mg, Fe content as much as 1155 ppm, Mn content as much as 925 ppm, and Sr content as much as 925 ppm. These two groups of cements that precipitated from meteoric waters evolved to a formation water composition probably because of interaction with Mesozoic and Paleozoic rocks, being the low δ 18 O of the second probably because of high temperatures of precipitation. A late episode of meteoric fluid circulation, occurring during the Tertiary extension, is recorded by the calcite cements filling normal faults, which are characterized by δ 18 O ranging from −9.2 to −7.6‰ PDB, δ 13 C ranging from −2.6 to +1.1‰ PDB, 87 Sr/ 86 Sr ratio of 0.70788, between 870 and 2695 ppm of Mg, between 470 and 1420 ppm of Mn, and Fe and Sr always below the detection limit, which is 275 ppm for both. The study of the fluid-flow evolution during the Linking Zone fold and thrust belt development shows that the main factors controlling the fluid-flow dynamics are the existence of a high relief, whereas the host rocks and the type of structure are not important factors.

Abstract The data from oil-bearing Ukrainian basins outline the tectonic control of overpressure development in areas characterized by recent episodes of folding and active compression (dominantly horizontal stress regime). Based on the data presented, vertical compaction alone is not sufficient to account for the observed overpressure development. Tentatively, tectonic deformation is proposed as the dominant factor for overpressure development in sedimentary layers in recently folded regions. During folding, the opening of fractures results in local density decrease and helps in driving the migrating fluids, i.e., both hydrocarbon and formation waters, in the carrier beds toward the top of the structures. Ductile flow of shaly interbeds toward anticlinal closures can also enhance the sealing capacity of these layers. In the Ukrainian Carpathians and salt domes of the Dniepr-Donetz Basin, direct relationships have been evidenced to link and predict the amount of overpressure as a function of the amplitude of the folds. The use of measurements and of the monitoring of overpressures for evaluating the horizontal stress intensity and for the forecasting of earthquakes is also suggested.

Abstract Reservoir appraisal is commonly a difficult task in fold and thrust belts. Thrust-related folding leads to the development of meso- to microscopic brittle structures that can significantly alter the porosity and permeability properties of reservoir rocks, thus influencing fluid migration and accumulation. The aim of this chapter is to describe at different scales the deformation associated to the development of the Chaudrons thrust-related anticline (Corbières, France) and to discuss its influence on reservoir quality. Pervasive solution cleavage sets at high angle to bedding (ATB) were found and measured along the fold. In addition, collected core samples were used to measure the rock physical properties (anisotropy of magnetic susceptibility and anisotropy of the P-wave velocity). The distribution of deformation in the anticline was used to identify three different deformational panels: crest, rounded forelimb, and constantly steeping forelimb. The crest is characterized by the lowest cleavage intensity. Nonpenetrative solution cleavages and the magnetic foliation are orthogonal to bedding. In the rounded forelimb, bedding dip progressively rotates from 0 to 60°. Cleavage intensity progressively increases, and cleavage and magnetic foliation ATBs progressively increase from 80 to 120° and then remain constant in the steep forelimb. The timing of the development of mesoscale structures, as well as changes of physical properties occurring before and during folding, is also discussed.

Abstract In the Jurassic-lower Cretaceous sequence of central Apennines and their foreland (onshore and offshore Marche-Abruzzi regions), the dolomitization processes enhanced the petrophysical properties of the carbonate platform and slope series. The area experienced a first phase of passive-margin regime, from the Lower Jurassic to the Miocene: the Liassic carbonate platform underwent extensional tectonics that established the southern Apulian-Apennines persisting platforms and the northern Umbria-Marche basin; within the basin, differential subsidence rates created faulted horsts characterized by condensed series. From upper Miocene, the area entered the collision-margin phase when its eastern part was involved in the Apennines orogeny. The aim of this study was to analyze the dolomitization process in relation with the fluid-flow changes caused by the evolution of the geological framework. Dolomitized bodies are mainly located at the Jurassic-Early Cretaceous platform edges and in the paleohigh areas, particularly in the platform Calcare Massiccio and basinal Corniola formations, with minor extension to younger slope successions (up to Maiolica Formation). The petrographic observations evidenced a multiphase dolomitization of alternated dolomite replacement, dissolution, and recrystallization. The carbon and oxygen isotopic analyses suggest a seawater-derived diagenesis in a wide temperature range; this is confirmed by the fluid-inclusion analyses that detected a few stages of dolomitization events during a progressive heating of the carbonate series. The reconstructed paragenetic sequence is almost the same in all the studied successions, both in outcrop and subsurface. The data collected show that the dolomitization processes changed during the evolution of the area from a passive-margin domain to the collision-margin regime. In both phases, the interaction between the increasing burial temperature and the fluid migration paths, which is driven by the approaching orogenic wave, is suggested. The first dolomitization event (dolomite 1) is characterized by low homogenization temperature ( T h ) and is interpreted as a replacement of calcite precursor; its formation occurred during the passive-margin domain and is strongly dependent on the rate of subsidence of the different areas. The dolomite 1 time of generation varies from Cretaceous, in the highly subsiding areas of the thrust zone, to the Miocene in the paleohighs of the foreland. Dolomite overgrowths (dolomite 2) precipitated at higher temperatures. In the depocenters of thrust zone, those temperatures (as much as 130°C) were reached during maximum overburden during the upper Miocene, whereas in the foredeep and foreland areas, the high-temperature dolomitizing fluids seem to flow through faults during the orogenic phases (Pliocene). In the whole studied area, pore-filling dolomite cements (dolomite 4 and saddle dolomite) are supposed to be precipitated from heated fluids coming from deep strata along fault planes. Regional considerations and salinity data of the fluid inclusions support the hypothesis that the dolomitizing fluids of the last phases could come from Triassic evaporites that are present in the area and represent the detachment surface of the thrusts.

Abstract The Middle Devonian carbonates of the Slave Point Formation, Hamburg field, northwestern Alberta, are composed mainly of stromatoporoid and Amphipora floatstones and rudstones, with interbedded mudstone and grainstone facies characteristic of deposition in open to slightly restricted marine platform environments. These carbonates have undergone a complex diagenetic history, from shallow to deep burial, as represented by fracturing, calcite cementation, silicification, and dolomitization. Petrographically, four different types of dolomite have been identified (from early to late): (1) fine-crystalline matrix dolomite; (2) pseudomorphic dolomite; (3) medium-crystalline pervasive dolomite; and (4) saddle dolomite. Fine-crystalline dolomite (5–50 (μm) replaces the mud matrix and slightly penetrates the edges of allochems. It occurred in mud-supported facies and was precipitated by marine fluids. Oxygen isotope values range from −11.62 to −9.34‰ (Peedee belemnite), lower than postulated values for Devonian carbonates. The enriched 87 Sr/ 86 Sr isotope value from this phase (0.71002) suggests that later diagenetic fluids may have recrystallized this dolomite. Pseudomorphic dolomite (50–100 μm) replaces crinoids and occurs as single, large dolomite crystals. Its oxygen and carbon isotopic values range from −10.58 to −9.65 and +4.24 to +4.49‰, respectively. Medium-crystalline pervasive dolomite (10–100 μm) occurs along dissolution seams and obliterates all previous fabrics. It is proposed that this medium-crystalline dolomite formed during shallow to intermediate burial because of its association with dissolution seams and high iron content. The range of oxygen isotope values for this dolomite (−11.74 to −9.5‰) suggests precipitation from a warm fluid, possibly in a burial environment, and/or later recrystallization by hydrothermal fluids. The relatively wide range of carbon isotope values (+1.19 to +4.49‰) and enriched strontium isotope ratio (0.710020) suggests recrystallization. Saddle dolomite (250–2000 μm) partially to completely occludes void spaces (both fractures and vugs) and also occurs as a minor replacement mineral. The oxygen isotope values for saddle dolomite (−?13.95 to −?11.97‰), as well as the nonradiogenic to enriched strontium isotope ratios for saddle dolomite (0.70494 to 0.710351), and the fluid-inclusion data (homogenization temperature, T h , range between 125 and 161°C and estimated salinity, between 22.2 and 24.7 wt.% NaCl equivalent) indicate precipitation from hot, highly saline, hydrothermal fluids, which were probably expelled tectonically during the Late Devonian-Mississippian Antler thrust belt development.

Abstract Viscous remanent magnetization (VRM) recently acquired in the Earth’s magnetic field provides a compass to recover in-situ orientation of unoriented core material. This method was used to date a late chemical remanent magnetization (CRM) in Paleozoic carbonate rocks (Devonian to Mississippian) from the foreland of the western Canadian Cordillera. The paleomagnetic data showed three distinct components: (1) a low-temperature component, which is commonly removed at temperatures below 180°C and is assumed to be induced by drilling; (2) a medium-temperature component, which is commonly removed below 250–400°C, with a steep normal polarity direction; and (3) a high-temperature component, which is isolated above 250–400°C. In the foothills, high-temperature magnetizations always have steep reverse polarities, whereas in the Interior Plains, both normal and reverse polarities with more scattered inclinations are observed. The agreement between theoretical and laboratory blocking temperatures supports the interpretation that the medium-temperature component has recorded Earth’s magnetic field over the normal polarity Brunhes epoch as a VRM. The same approach for the high-temperature component led to the interpretation that the high unblocking temperatures indicate a CRM event that affected the Paleozoic carbonates long after deposition. This component is equivalent to the A component observed by Enkin et al. (2000) in exposed strata. By correcting declination values using the medium-temperature component, the direction of the high-temperature component in the Interior Plains is D = 330.4°, I = 74.3, k = 84, α 95 = 3.4°, N = 22 specimens, and in the foothills, it is D = 331.3°, I = 82.4°, k = 30, α 95 = 8.1° N = 12 specimens, corresponding to pole position consistent with the Late Cretaceous section of the North American apparent polar wander path.