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Calcite veins hosted by extension fractures and faults are common in the outcrop belt of the Austin Chalk – Eagle Ford – Buda stratigraphic section across south-central and west Texas, and contain aqueous and liquid hydrocarbon fluid inclusions. The hydrocarbon fluid inclusions in these thermally immature rocks indicate long-distance migration of oils from mature source rock down-dip and possibly from deeper units along faults. The widespread spatial distribution and extensive variety of oil types indicated by the fluid inclusion fluorescence suggest a protracted series of migration events – possibly from multiple source areas – rather than a single event. Oil inclusions in fault and fracture hosted calcite veins provide evidence of both strata-bound and cross-stratal oil migration along fault and fracture networks that are pervasive in the Austin Chalk, Eagle Ford, and Buda, as well as stratigraphically deeper units, in the subsurface and outcrop belt. Aqueous fluid inclusion microthermometry of the calcite veins provides evidence for significant exhumation of rocks in the Austin Chalk – Eagle Ford – Buda outcrop belt. Approximately 1.25–1.79 km of overburden was removed along the Balcones fault zone outcrop belt of south-central Texas, while in outcrop belt of the Devils River Uplift as much as 2.44–3.50 km of overburden was removed. In the productive region of the deeper basin down-dip from the outcrop belt, fluid inclusions in a deep core indicate that fluids were trapped during burial, but do not record maximum burial conditions. • Faults and fractures in immature Cretaceous strata of Texas host calcite veins. • Oil inclusion fluorescence in calcite veins records variety of trapped oils. • Protracted migration from distant and/or multiple source areas is indicated. • Migration from deep basin and/or deeper units along fault and fracture networks. • Exhumation across outcrop belt ranges from 1.25 to 3.50 km. [ABSTRACT FROM AUTHOR]

Small-scale synsedimentary folds in the Eagle Ford Formation in southwest Texas formed during deposition in a shallow epicratonic basin on the North American craton. These folds formed by slumping (i.e., gravity-driven deformation) and are characterized by (i) plastic deformation of limestone beds, (ii) discontinuous bedding and thickness changes of limestone beds, (iii) horizontal compactional fabric at high angle to folded bedding, (iv) low-angle or recumbent axial surfaces, and (v) erosion of slumped intervals and/or onlapping by resumed sedimentation. Exposures of the Eagle Ford near the northwest margin of the Maverick Basin reveal slump folds in 1–2 m thick zones with observed lateral extents of 10's to 100's of meters to >1 km – actual extents are likely much larger. Curvilinear fold hinges changing trend by >90° over short distances, indicating markedly non-cylindrical fold geometries. Bed thickness changes reflect flowage of unlithified sediment during slumping, and subsequent compaction. Previous descriptions of slump folds in the Eagle Ford Formation have focused on examples from the hydrodynamic facies of the basal portion, but slump folds are also present in pelagic facies of the upper Eagle Ford. Slump folding locally represents significant shortening (e.g., 50%) and thickening (e.g., 100%) of slumped intervals, with up-dip absence of the same interval represented by missing section, bed terminations, boudinage, and/or extensional faulting. Repeated slumping can result in significant cumulative updip thinning and downdip thickening along depositional slopes. Our experience working unconventional reservoirs in a variety of North American epicratonic basins indicates that slump folding is common and underrepresented in the literature. Criteria for recognizing slumping in the subsurface include a combination of discontinuous and contorted beds, thickening into fold hinges, compactional fabric postdating folds, and inverted or repeated section. Natural fracture networks may be less regular than in similar but flat-lying beds. Occurrence of slump folded intervals adds complexity and unpredictability to unconventional reservoirs, with implications for reservoir quality, drilling, and optimal stimulation during completion. • Synsedimentary slump folding is under-recognized in epicratonic basins, and influences unconventional reservoirs. • Slump folds in outcrops of the Eagle Ford Formation occur in both hydrodynamic and pelagic facies. • Slump folds are dominated by plastic deformation, even in layers that later became competent and brittle. • Compaction resulted in vertical thinning and locally an axial planar fabric in recumbent folds. • Outcrop fracture networks in slumped intervals are less regular than in similar but flat-lying beds. [ABSTRACT FROM AUTHOR]

The southern Newfoundland transform margin is a crustal-scale transfer zone that juxtaposes continental crust of the Grand Banks with the oceanic domain of the Fogo Basin, offshore SE Newfoundland. This crustal feature is generally accepted as a left-lateral transfer zone between the much-studied Scotian and Newfoundland margins, but relatively little is known about either its crustal-scale architecture or tectonic evolution. Interpretation of newly available regional seismic data from the Newfoundland Ridge and Fogo Basin, offshore Canada provides evidence for approximately 500 km of left-lateral displacement and associated segmented extension between the Late Triassic (210 Ma) and latest Jurassic (145 Ma) as a result of differential extension rates between the conjugate margins of Nova Scotia–Morocco and Newfoundland (Grand Banks)–Iberia. We show that the southern Newfoundland transform margin represents a 100–150 km wide zone of distributed left-lateral displacement across extended continental crust at the SW edge of the Grand Banks, and that crust beneath the Newfoundland Ridge and Fogo Basin is unlikely to be oceanic in origin. Kinematic restorations of regional cross sections and crustal area balancing provide the basis for map-based reconstructions of the area. Our results, which integrate existing plate reconstructions, crustal thickness data, and established age relationships, help to constrain the early structural evolution of the North Atlantic as the African and North American plates separated during Triassic to Jurassic rifting. • The southern Newfoundland transform margin represents a 100–150 km wide zone of distributed left-lateral displacement. • Differing extension rates between Nova Scotia–Morocco and Newfoundland–Iberia led to continental transform margin. • The Fogo Basin and Newfoundland Ridge are underlain by extended continental crust. • Diapirism of syn-rift Triassic evaporites is documented throughout the study area. • Diapirs formed as a result of primarily vertical salt movement from grabens and half-grabens in extended continental crust. [ABSTRACT FROM AUTHOR]

Interpretation of newly acquired modern broadband seismic reflection data and structural restoration of three regional, WNW-ESE oriented cross-sections across the Orphan Basin, Flemish Pass and Flemish Cap provide new insights into rift evolution and structural style in the area. Our results show that regional extension in the Orphan Basin and Flemish Pass area largely occurred between 170 Ma and 135 Ma, and later extension (135 Ma onwards) in the study area was accommodated east of Flemish Cap. Seismic stratigraphic mapping provides evidence for significant thicknesses of Jurassic strata throughout the Orphan Basin and Flemish Pass area, and structural interpretations highlight the importance of crustal-scale extensional detachment faults in controlling the geometry and position of Jurassic sub-basins at a range of scales. Stacked detachment surfaces and coincident extreme crustal attenuation (to ca. 3.1 km) are observed in eastern parts of the Orphan Basin in an area defined in this study as the Orphan Trough. Rifting style in the central, northern, and eastern parts of the Orphan Basin is dominated by low-angle detachment faulting with maximum extension perpendicular to the incipient rift axis. In contrast, structural geometries in the southwestern part of the basin are suggestive of transtensional deformation, and interplay of normal and strike-slip faulting. Results from map-based interpretation show that strike-slip faults within this transtensional zone are associated with displacement transfer between half-grabens of opposing polarity, rather than regional strike-slip displacement. These structures are interpreted as contemporaneous and kinematically linked to displacement along low-angle detachment surfaces elsewhere and are not attributed to distinct episodes of oblique extension. • Regional structural characterization of the Orphan Basin - Flemish Pass – Flemish Cap region. • Kinematic restoration and crustal area balancing of three laterally compatible, regional cross sections. • A single phase of protracted rifting from ca. 170 Ma to 135 Ma is interpreted in the Orphan Basin and Flemish Pass region. • Hyperextension, crustal-scale detachment surfaces and crustal attenuation associated with rift development. • Transtensional deformation in the southern part of the Orphan Basin compatible with rift-related extension. [ABSTRACT FROM AUTHOR]

The Orphan Basin and Flemish Pass region on the Newfoundland continental margin is a frontier area in terms of oil and gas exploration and remains poorly understood in terms of structural evolution and rift development. The area has few exploration wells and, until recently, sparse seismic data coverage. Existing gravity inversion and seismic refraction data from the area suggest that stretched continental crust in the Orphan Basin is highly attenuated (locally to < 5 km) but previously published structural restorations have been unable to fully restore the continental crust below the Orphan Basin to pre-deformed thicknesses (30–32 km). Here we perform a structural restoration of a regional, WNW-ESE oriented cross-section to investigate crustal structure, rifting style, and structural evolution of the Orphan Basin and Flemish Pass region. Interpretation is constrained by modern regional depth converted broadband 2D and 3D seismic reflection data, well data, and published gravity inversion results. Present-day crustal thicknesses are used as constraints for crustal area balancing and estimation of crustal thinning across the basin. We find that low-angle extensional detachments are widespread in the area, with offsets on individual structures of up to 42 km. Zones of attenuated continental crust are coincident with the presence of low-angle detachment surfaces displaying isostatic uplift of detachment footwalls. Comparison of total extension derived from crustal area balancing vs. structural restoration suggests approximately 39% of extension across the cross-section is unresolvable in seismic data. We attribute this to (i) ductile deformation prior to brittle faulting, (ii) subseismic-scale faulting, (iii) uncertainties in detachment breakaway positions, and (iv) unresolvable later offset of detachment surfaces. Widespread and relatively evenly distributed extension across the Orphan Basin and Flemish Pass region from Middle-Late Jurassic to Early Cretaceous influences sediment distribution across the region. Calibrated regional seismic mapping of the Orphan Basin suggests that significant thicknesses of Jurassic strata exist throughout the area, including in the northwestern part of the study area, where Kimmeridgian and Tithonian strata reach combined thicknesses of up to 4.9 km. • sSignificantthicknesses of Jurassic strataidentified throughout the Orphan Basin and Flemish Pass. • kinematic restoration and crustal area balancing used to constrain timing and amount of extension across the study area. • Structure dominated by low-angle extensional detachments with offsets on individual structures of up to 42 km. • Attenuated continental crust is coincident with low-angle detachment surfaces and isostatic uplift of detachment footwalls. [ABSTRACT FROM AUTHOR]