Abstract We present an updated synthesis of the widely accepted ‘single-arc Pacific-origin’ and ‘Yucatán-rotation’ models for Caribbean and Gulf of Mexico evolution, respectively. Fourteen palaeogeographic maps through time integrate new concepts and alterations to earlier models. Pre-Aptian maps are presented in a North American reference frame. Aptian and younger maps are presented in an Indo-Atlantic hot spot reference frame which demonstrates the surprising simplicity of Caribbean–American interaction. We use the Müller et al. ( Geology 21 : 275–278, 1993) reference frame because the motions of the Americas are smoothest in this reference frame, and because it does not differ significantly, at least since c. 90 Ma, from more recent ‘moving hot spot’ reference frames. The Caribbean oceanic lithosphere has moved little relative to the hot spots in the Cenozoic, but moved north at c. 50 km/Ma during the Cretaceous, while the American plates have drifted west much further and faster and thus are responsible for most Caribbean–American relative motion history. New or revised features of this model, generally driven by new data sets, include: (1) refined reconstruction of western Pangaea; (2) refined rotational motions of the Yucatán Block during the evolution of the Gulf of Mexico; (3) an origin for the Caribbean Arc that invokes Aptian conversion to a SW-dipping subduction zone of a trans-American plate boundary from Chortís to Ecuador that was part sinistral transform (northern Caribbean) and part pre-existing arc (eastern, southern Caribbean); (4) acknowledgement that the Caribbean basalt plateau may pertain to the palaeo-Galapagos hot spot, the occurrence of which was partly controlled by a Proto-Caribbean slab gap beneath the Caribbean Plate; (5) Campanian initiation of subduction at the Panama–Costa Rica Arc, although a sinistral transform boundary probably pre-dated subduction initiation here; (6) inception of a north-vergent crustal inversion zone along northern South America to account for Cenozoic convergence between the Americas ahead of the Caribbean Plate; (7) a fan-like, asymmetric rift opening model for the Grenada Basin, where the Margarita and Tobago footwall crustal slivers were exhumed from beneath the southeast Aves Ridge hanging wall; (8) an origin for the Early Cretaceous HP/LT metamorphism in the El Tambor units along the Motagua Fault Zone that relates to subduction of Farallon crust along western Mexico (and then translated along the trans-American plate boundary prior to onset of SW-dipping subduction beneath the Caribbean Arc) rather than to collision of Chortis with Southern Mexico; (9) Middle Miocene tectonic escape of Panamanian crustal slivers, followed by Late Miocene and Recent eastward movement of the ‘Panama Block’ that is faster than that of the Caribbean Plate, allowed by the inception of east–west trans-Costa Rica shear zones. The updated model integrates new concepts and global plate motion models in an internally consistent way, and can be used to test and guide more local research across the Gulf of Mexico, the Caribbean and northern South America. Using examples from the regional evolution, the processes of slab break off and flat slab subduction are assessed in relation to plate interactions in the hot spot reference frame.

Abstract The structure, stratigraphy and magmatic history of northern Peru, Ecuador and Colombia are only adequately explained by Pacific-origin models for the Caribbean Plate. Inter-American models for the origin of the Caribbean Plate cannot explain the contrasts between the Northern Andes and the Central Andes. Persistent large magnitude subduction, arc magmatism and compressional deformation typify the Central Andes, while the Northern Andes shows back-arc basin and passive margin formation followed by dextral oblique accretion of oceanic plateau basalt and island arc terranes with Caribbean affinity. Cretaceous separation between the Americas resulted in the development of a NNE-trending dextral–transpressive boundary between the Caribbean and northwestern South America, becoming more compressional when spreading in the Proto-Caribbean Seaway slowed towards the end of the Cretaceous. Dextral transpression started at 120–100 Ma, when the Caribbean Arc formed at the leading edge of the Caribbean Plate as a result of subduction zone polarity reversal at the site of the pre-existing Trans-American Arc, which had linked to Central America to South America in the vicinity of the present-day Peru–Ecuador border. Subsequent closure of the Andean Back-Arc Basin resulted in accretion of Caribbean terranes to western Colombia. Initiation of flat-slab subduction of the Caribbean Plate beneath Colombia at about 100 Ma is associated with limited magmatism, with no subsequent development of a magmatic arc. This was followed by northward-younging Maastrichtian to Eocene collision of the trailing edge Panama Arc. The triple junction where the Panama Arc joined the Peru–Chile trench was located west of present-day Ecuador as late as Eocene time, and the Talara, Tumbes and Manabi pull-apart basins directly relate to its northward migration. Features associated with the subduction of the Nazca Plate, such as active calc-alkaline volcanic arcs built on South American crust, only became established in Ecuador, and then Colombia, as the triple junction migrated to the north. Our model provides a comprehensive, regional and testable framework for analysing the as yet poorly understood collage of arc remnants, basement blocks and basins in the Northern Andes. Supplementary material: A detailed geological map is available at http://www.geolsoc.org.uk/SUP18364

Abstract The metamorphic rock sequences exposed on the Island of Margarita, Venezuela, located in the southeastern corner of the Caribbean Plate margin, are composed of a high-pressure/low-temperature (HP/LT) nucleus subducted to at least 50 km depth, now structurally overlain by lower-grade greenschist-facies units lacking any sign of high-pressure subduction-zone metamorphism. The HP/LT nucleus involves protoliths of both oceanic (metabasalts and intimately associated carbonaceous schists of the La Rinconada unit; peridotite massifs) and continental affinity (metapelites, marbles and gneisses of the Juan Griego unit). All HP/LT units were joined together prior to the peak of high-pressure metamorphism, as shown by their matching metamorphic pressure–temperature evolution. The metamorphic grade attained produced barroisite as the regional amphibole. Glaucophane is not known from Margarita. Contrary to a widely propagated assumption, there are no major nappe structures post-dating HP/LT metamorphism anywhere within the high-pressure nucleus of Margarita Island. U–Pb zircon dating of key tonalitic to granitic intrusive rocks provides the following constraints: (1) the Juan Griego unit is heterogeneous and contains Palaeozoic as well as probable Mesozoic protolith; (2) the peak of HP/LT metamorphism, that is maximum subduction, is younger than 116–106 Ma and older than 85 Ma, most probably c. 100–90 Ma, a time span during which the southeastern Caribbean/South American border was clearly a passive margin. The assembly of Margaritan protoliths and their HP/LT overprint occurred far to the west in northwestern South America, a scenario completely in accord with the details of the Pacific-origin model outlined by Pindell & Kennan. Juxtaposition of the greenschist-facies units occurred after exhumation into mid-crustal levels after c. 80 Ma.

Abstract Current models for the tectonic evolution of northeastern South America invoke a Palaeogene phase of inter-American convergence, followed by diachronous dextral oblique collision with the Caribbean Plate, becoming strongly transcurrent in the Late Miocene. Heavy mineral analysis of Cretaceous to Pleistocene rocks from eastern Venezuela, Barbados and Trinidad allow us to define six primary clastic domains, refine our palaeogeographic maps, and relate them to distinct stages of tectonic development: (1) Cretaceous passive margin of northern South America; (2) Palaeogene clastics related to the dynamics of the Proto-Caribbean Inversion Zone before collision with the Caribbean Plate; (3) Late Eocene–Oligocene southward-transgressive clastic sediments fringing the Caribbean foredeep during initial collision; (4) Oligocene–Middle Miocene axial fill of the Caribbean foredeep; (5) Late Eocene–Middle Miocene northern proximal sedimentary fringe of the Caribbean thrustfront; and (6) Late Miocene–Recent deltaic sediments flowing parallel to the orogen during its post-collisional, mainly transcurrent stage. Domain 1–3 sediments are highly mature, comprising primary Guayana Shield-derived sediment or recycled sediment of shield origin eroded from regional Palaeogene unconformities. In Trinidad, palinspastic restoration of Neogene deformation indicates that facies changes once interpreted as north to south are in fact west to east, reflecting progradation from the Maturín Basin into central Trinidad across the NW–SE trending Bohordal marginal offset, distorted by about 70 km of dextral shear through Trinidad. There is no mineralogical indication of a northern or northwestern erosional sediment source until Oligocene onset of Domain 4 sedimentation. Paleocene–Middle Eocene rocks of the Scotland Formation sandstones in Barbados do show an immature orogenic signature, in contrast to Venezuela–Trinidad Domain 2 sediments, this requires: (1) at least a bathymetric difference, if not a tectonic barrier, between them; and (2) that the Barbados deep-water depocentre was within turbidite transport distance of the Early Palaeogene orogenic source areas of western Venezuela and/or Colombia. Domains 4–6 (from Late Oligocene) show a strong direct or recycled influence of Caribbean Orogen igneous and metamorphic terranes in addition to substantial input from the shield areas to the south. The delay in the appearance of common Caribbean detritus in the east, relative to the Paleocene and Eocene appearance of Caribbean-influenced sands in the west, reflects the diachronous, eastward migration of Caribbean foredeep subsidence and sedimentation as a response to eastward-younging collision of the Caribbean Plate and the South American margin. Supplementary material: Location maps and detailed heavy mineral data tables are available at http://www.geolsoc.org.uk/SUP18365.

Abstract The tectonic evolution of the Cenozoic mountain ranges, fault systems and basins that comprise the roughly east-west Caribbean/ South America plate boundary zone from Colombia to Trinidad was controlled principally by highly-oblique dextral convergence between the Caribbean and South American Plates. The Caribbean Plate is pinned by the Central American and Lesser Antilles subduction zones and is stationary in a mantle reference frame whereas the South American Plate is moving westwards in that frame. The Caribbean Plate is of Pacific provenance and has, since early Cenozoic time, progressively invaded at an average rate of 20-25 mm/yr the Proto-Caribbean oceanic gap between North and South America, Thus, the Lesser Antilles are terminated southward by a dextral transpression zone that lengthened progressively throughout Cenozoic time. This zone showed strong partitioning between easi-west dextral strike slip faults, such as the Oca and El Pilar faults, and south-southeast ward-directed thrust nappes. The nappes loaded the South American craton to generate a coupled flexural foreland basin and peripheral bulge that migrated eastwards. At any time during this evolution, the zone between the thrust complex and the crest of the peripheral bulge was a zone of potential updip hydrocarbon migration, which moved eastwards in tandem with the relatively eastward migrating Caribbean Plate. Ln several cases, especially in Oligocene and younger Cenozoic times, E-W trending strike-slip and normal faults decoupled parts of the thrust load from the South American craton and allowed flexural recovery, the rapid uplift of coast ranges, and thick sedimentation in transtensional basins. All deformation in the Venezuela nappe pile pertaining to arc-continent collision between the Caribbean and South American crusts is of Cenozoic age and youngs from west to east. Our evolutionary tectonic reconstruction of the Caribbean/South American plate boundary zone is critically dependent upon a precise restoration of the geometry of northwest South America immediately before the Caribbean Plate began its relative eastward motion. This involved our determining the amounts of relative motion along the various faults and deformation zones of Colombia and Venezuela that have developed mainly since the late Oligocene. Retro-restoring motion on these faults allows a construction of the Cenozoic nappe front prior to 25 Ma and the shape of northwest South America prior to 60 Ma. Displacements include about 110 km of sinistral motion on the Santa Marta Fault Zone, up to 150 km of dextral slip in the Merida Andes zone, 25 km of shortening across the Sierra de Perijti, and at least 65 km and 90 km of dextral motion on the Oca Fault Zone in Colombia and Venezuela, respectively. On a retrodeformed paleogeographic grid which takes into account all of these restorations as well as removal of accreted tetranes, the paleogeographic development of Venezuela and Trinidad is traced through Cenozoic time, and important tectonic processes and controls on hydrocarbon accumulations are defined and discussed.

Abstract Approximately 5 km of Cretaceous and Paleogene strata are exposed in the Serranfa del Lnlerior of northeastern Venezuela, and the depositional settings and paleoenvironmental conditions of these strata have been investigated, leading to paleogeographic reconstructions spanning approximately 90 my of passive-margin sedimentation. Exposed Lower Cretaceous strata are generally shallow marine in origin and vary between siljciclasUc shelf deposits and bioherm-dominated, impure carbonate platform deposits. Neocomian-Aptian shelfal and carbonate-platform facies are widespread and comprise the Barranqufn Formation. A major, Early Cretaceous siliciclasiic fiuvio-deltaic system emanated from southwest of the Serranfa del Interior and was the source of the commonly coarse-grained Lower Cretaceous strata. In Early Albian time, a short-lived transgressive/regressive cycle led to deposition of the shaley, deep-shelf deposits of the Garcfa Formation. The E) Cantil Formation was deposited on a Early to early Middle Albian carbonate platform that had significant and variable silicjclaslic contamination (particularly in the southern Serranfa del Interior). The carbonate platform started retrograding southward in Early Albian time and was eventually succeeded by deeper marine deposition of glauconitic sand and shale of the Cbimana Formation. After a brief, Middle Albian progradational event (upper Chimana Formation), regional transgression led to primarily pelagic deposition in the Querecual Formation. Upper Cretaceous strata are notably more homogeneous and of deeper marine origin than Lower Cretaceous strata, and consist primarily of organic-rich, calcareous siltstone and muddy, micritic limestone. These slope deposits of the Querecual and San Antonio Formations are the petroleum source rocks for the Eastern Venezuela Basin. Deep-water (>200 m) sedimentation continued almost continuously from Late Albian until mid-Maastrichtian time, with (he exception of a minor, Santonian- Early Campanian influx of sand at the base of the San Antonio Formation. A voluminous influx of submarine fan sediments occurred in Late Maastrichtian time during deposition of the San Juan Formation. After transgression and monotonous dark shale deposition in the Vidono Formation, renewed progradation in Early Eocene time led to deposition of the glauconitic submarine fan deposits of the Caratas Formation. Shallowing of the depositional surface locally led to shelfal carbonate deposition at the top of the Caratas Formation in Middle Eocene time (the Tinajitas limestone). Passive-margin sedimentation was finished by the close of the Eocene Epoch, and was followed by foredeep sedimentation and eventually by uplift and exposure of the passive-margin strata within the Serranfa del Interior.

Abstract We performed zircon fission-track dating on twenty low-grade metamorphic rocks from the Northern Range and eight unmetamorphosed sandstones from the Central Range of Trinidad. Reset and partially reset zircon populations from the Northern Range gave a consistent fission-track age of 11.7 ± 1.1 Ma. This dates the cooling of the Northern Range through 240 ± 25°C. Assuming a geothermal gradient of 25°C km 1 which is unproved, and a constant rate of uplift, the Northern Range uplifted at an average rate of 0.7 to 1.0 mm yr 1 from the Late Miocene to Recent. If the uplift was not at a constant rate, then the true uplift rates may have been greater than 1.0 mm yr -1 . In areas of lower grade metamorphism, Northern Range zircon fission-track ages were not reset, and thus gave information on the provenance of the Cretaceous sediments. Permian and Late Jurassic fission-track ages determined for the Maastrichtian Galera Formation sandstones are interpreted to have been derived, respectively, from granitoids and rift-related volcanics along the northern South American margin. Albian and Early Silurian/Late Ordovician zircon fission-track ages from the Lower Cretaceous Toco Formation have no provenance local to Trinidad but may have been derived further west, possibly from the Caribbean island arc and northern Andes respectively. This difference between the two formations is entirely consistent with structural and stratigraphic work which show the Toco Formation to be part of the Sans Souci Group, an allochthonous terrane transported from the west with the Caribbean plate. The Galera Formation is part of the Northern Range Group, which makes up the majority of the Northern Range, and is inteipreted to have been deposited on the northern South American margin, probably within 400 km of its present location. Zircon fission-track ages from unmetamorphosed sandstones of central Trinidad’s Pointe-a-Pierre Formation constrain deposition of the formation to later than 34 Ma (Lower-Middle Oligocene or later). This is much younger than the faunally estimated Lower Eocene (55 Ma) depositional age, probably because the fauna, which are “arenaceous,” have been reworked. Similar zircon fission-track ages are found in central Trinidad’s Nariva Formation, which is faunally dated as Middle Oligocene to Middle Miocene age.

Abstract Passive-margin strata of Cretaceous through Eocene age are exposed in northeastern Venezuela and provide a rare opportunity for the study of the eustatic and tectonic controls of stratigraphic development. The sequence stratigraphy of these strata has been analyzed in conjunction with paleogeographic analysis, and seven regionally extensive sequence boundaries are identified between Hauterivian and late Eocene time: latest ? Hauterivian, two in Early-Middle Albian, Middle-Late Albian, Late Santonian, mid-Maastrichtian, and late middle Eocene. These sequence boundaries have an average spacing of ~ 16 my (typical of second-order sequences). Stratigraphic development and sequences were controlled by both tectonism and eustasy. Three tectonic episodes are most relevant to the stratigraphic development of the northeastern Venezuelan passive margin: (1) a Hauterivian (anomaly MIO) plate motion change between North America and South America-west Africa; (2) Aptian-Albian rifting and opening of the Equatorial Atlantic; and (3) Tertiary, eastward migration with respect to South America of the Caribbean plate. The effects of these tectonic events can at least partially account for Early Cretaceous and Eocene sedimentologic events and sequence development in northeastern Venezuela. Eustatic control of sequence stratigraphic, lithostratigraphic, and paleogeographic development is most probable in Late Cretaceous time. Eustatic fluctuations appear to be less frequent or of much smaller magnitude than is typically concluded from other more tectonically active areas.

Abstract The evolution of northeastern South America during Mesozoic times is here discussed and presented in nine paleogeographic maps. These maps are models that approximate true paleogeography because they meet the following requirements: (1) the geographic base of the maps is palinspasdcally retrodeformed and accounts for post-depositional deformation; (2) facies are interpreted and paleoenvironments are plotted in a continuous manner on the retrodeformed grid; (3) the maps represent genetically-related sequences or megasequences; and (4) depositional systems presented in the maps are coeval within the resolution of a revised biostratigraphy. The Mesozoic subsidence regime of northern South America allowed preservation of passive margin stratigraphic sequences formed during non-glacial times. In general, these sequences are of lower frequency than depositional sequences formed during glacial times or than sequences deposited in tectonically active settings such as foreland basins. This paper presents the regional framework for detailed sequence stratigraphic studies in northern South America.

Abstract Palinspastic paleogeographic maps of western and northern South America, including the entire 8500-km “Andean system” from Trinidad to Cape Horn, are presented for nine Mesozoic-Cenozoic time intervals. The maps show (1) the spatial record of formational lithostratigraphic units; (2) continental, shallow marine, and deeper marine paleoenvironments and the location of active magmatic arcs through time; (3) progressive structural and tectonic development; (4) relative motions of adjacent plates affecting the Andes; and (5) paleolatitude. Phases and causes of geologic development are summarized from the maps and other information. Depositional systems are related to tectonic evolution, with implications drawn for hydrocarbon systems and history. It is shown that tectonic, depositional, and hydrocarbon histories are closely interrelated, having occurred in fairly discrete pulses through time, each with its own significance to hydrocarbon potential.

ABSTRACT Existing interpretations of the major rock assemblages of the Florida basement (Cambrian Osceola Complex, Ordovician-Silurian Suwannee Basin sedimentary rocks, and Mesozoic Southwest Florida Volcanic Field) and basement structural features (Jay Fault-Bahamas Fracture Zone extensions and South Georgia Rift) indicate a history of initial evolution at a Gondwana continental margin, late Paleozoic coupling with North America, and eventual appendage as a peninsula following a fortuitous geometry of Triassic rifting. Reconciliation of this scenario, however, with the demonstrated spatial distribution of basement rock units and proposed concepts of motion on the Jay Fault is elusive without invoking unlikely initial configurations or tectonic behavior. Apprehensions concerning the shape of the extension into Florida of the South Georgia Rift, the presence of apparent elements of the Osceola Complex in the panhandle and southeastern Georgia, and lack of deformation within the Suwannee Basin sedimentary units can be tempered with a reconstruction of basement response to the closure of North America and Gondwana. A proposed sequence of events is contingent on deformational collision of Gondwana at and north of the North America Alabama Promontory followed by clockwise rotation and northwestward motion of Gondwana. En echelon right-lateral faults, including a precursory segment of the Jay Fault, progressively developed from east to west, facilitating closure at the Ouachita Orogen and displacing elements of a once-continuous continental margin to accommodate pivoting of Gondwana about the promontory. Thus, adjacent portions of the central Florida Osceola Complex to the northeast and southwest were fixed closer to the suture and bracketed the Suwannee Basin sequence. The subsequent development of Triassic basins in the Florida basement was constrained by the presence of offset basement blocks. Divergent motion of South America was accommodated by reactivated, but left-lateral and normal, motion along some of the initial Paleozoic faults. What previously had been described as the Jay Fault was actually a series of subparallel features, linked by embryonic spreading centers and perhaps converging near the present-day Osceola Complex. Accordingly, the Florida basement is a reflection of tectonic events attributable to a disruptive Paleozoic suturing process as well as Triassic rifting.

ABSTRACT New 240-fold, 24 km aperture, 2-ship seismic data tied to OBS refraction, gravity/magnetic and deep well data has been integrated with more conventional onshore and offshore seismic data to elucidate the deep structure and early history of the Texas rifted margin. We present a 330 km offshore composite seismic interpretation and cross-section from the Perdido foldbelt in Alaminos Canyon through a 200 km wide salt allochthon extending entirely across the Texas continental slope to the extensional growth fault complex in the Brazos shelf. Our data and interpretation are extended an additional 150 km onshore through Matagorda, Wharton and Colorado counties past the lower Cretaceous Sligo and Stuart City shelf edges. The Texas continental margin developed as an unstable progradational depositional complex built out over Jurassic transitional and oceanic mafic crust lying seaward of a detachment-faulted, rifted continental edge. Callovian Louann salt, up to 5 km thick in the cores of Perdido foldbelt anticlines, gradually thins northwestward. Autochthonous salt is thin or absent under the Texas shelf and coastal plain. A lower Cretaceous post-Callovian section 1.5 - 3.0 km thick underlies the prominent “MCU” event which can be traced in our data from the Cretaceous shelf edge into the Perdido foldbelt. A prominent sequence boundary at the top of the lower Eocene (49.5 m.y.) acts as a major decollement surface in the Texas coastal plain, largely decoupling a younger, greatly extended section overlying up to 6 km of upper Cretaceous, Paleocene and lower Eocene rocks. The 49.5 m.y. sequence boundary extends offshore underneath the allochthonous salt which intruded up-section across time lines and has accommodated massive amounts of updip extension from the early Tertiary to the present. Regional free-air gravity and OBS refraction data suggest the crust under the salt gradually thickens from 5 km (oceanic) in the Perdido foldbelt through 10 km (transitional?) under the Texas slope to 22 km (continental) under the coastal plain. No prominent magnetic anomaly distinguishes an oceanic/continental boundary. The oceanic crust is a magnetic “quiet zone”. The 300 nanotesla Houston magnetic anomaly overlies continental crust and may be speculatively attributed to a late Paleozoic (?) feature. Our data suggest that the presumably deepwater clastic packages under the salt allochthon are relatively simply-structured with huge volumes of unexplored and highly prospective section. The sub-allochthon play in the Texas slope must be considered as one of the last exploration frontiers left in the continental United States.

ABSTRACT A contour map on a prominent mid-Jurassic surface (MJS) outlines four crustal types in the northeastern Gulf of Mexico basin: 1) continental crust underlying northern Florida, 2) thick transitional crust characterized by large E-W trending basement highs and lows (Wiggins uplift, Apalachicola basin, Middle Ground arch-Southern platform, Tampa embayment, and Sarasota arch), 3) thin transitional crust underlying the West Florida basin, and 4) oceanic crust underlying the deep central Gulf basin. This basin configuration developed during the early breakup of Pangea, as South America-Africa separated from North America. Over much of the area the MJS is a prominent unconformity that truncates Late Triassic-Early Jurassic rift sediments as well as all older Paleozoic and Precambrian sedimentary, igneous and metamorphic rocks. It is overlain by mid-Jurassic pre-marine evaporites (Louann salt and equivalent rocks), which are thick in basinal areas and thin or absent over adjacent highs. The evaporites were deposited toward the end of the period of crustal attenuation and the formation of transitional crust but prior to the emplacement of oceanic crust. This crustal structure and basin configuralion of the MJS influenced the distribution and development of the overlying Upper Jurassic and Lower Cretaceous sequences. During Smackover time a broad shelf to prograding ramp partially filled the basinal areas, while scattered carbonate buildups developed along the surrounding basement highs. In areas of thick salt sediments thicken into small basins formed along listric growth faults caused by salt withdrawal (salt rollers). The shelf margins continued to prograde basinward during Haynesville time, depositing a thick section in the Tampa embayment, while a starved carbonate margin (Gilmer?) developed in the western Apalachicola basin. During the latest Jurassic-earliest Cretaceous (Cotton Valley time) a broad, dominantly clastic, prograding ramp filled the basins and overlapped the highs, while a deep-sea fan system developed in the adjacent West Florida basin. Cotton Valley deposition culminated with the development of the Knowles carbonate margin along a tectonic hinge-zone (THZ) at the thick/thin transitional crust boundary. During the Lower Cretaceous a rimmed carbonate margin controlled by the THZ continued to develop along the present-day Florida escarpment. This margin became steeply-dipping to the south, separating a broad carbonate platform from a relatively starved basin. To the north in the De Soto canyon area, the margin remained gently-dipping, reflecting the influence of a narrow shelf and the influx of terrigenous clastics to the adjacent slope. In the West Florida basin mounded and lobate geometries are interpreted as deep-sea fan systems. Low velocity channel fills on the adjacent platform suggest that siliciclastic sediments may have bypassed the Lower Cretaceous carbonate margin during sea level lowstands and been deposited as potential siliciclastic reservoir rocks within portions of the deep-sea fan systems. As the carbonate margin adjacent to the West Florida basin continued to aggrade and steepen during the Early Cretaceous, southward-flowing deep-sea currents intensified and became focused along the base of the margin, altering depositional patterns and processes and culminating in the deposition of a large southward-prograding contourite mound. Near the end of the Early Cretaceous, extremely intense currents, possibly due to sea level drops, preferentially eroded these lobes and mounds, culminating in the widespread mid-Cretaceous sequence boundary (MCSB). A subsequent rise in relative sea level terminally drowned the Lower Cretaceous platform margin and caused the retreat of the margins to more landward positions during the Upper Cretaceous.

ABSTRACT An attempt to reconcile the observed main tectonic elements in the southeastern Gulf of Mexico within the major constraints of the Gulf of Mexico evolution leads to a revised opening model for the basin. The kinematic part of the presented model proposes that during the rifting stage the Yucatan block translated southeastward along major transform zones in the western and eastern Gulf, respectively. During the drifting stage, however, it rotated counterclockwise to accommodate the Gulf of Mexico oceanic crust. The dynamic part of the model proposes a heterogeneous thinning of the lithosphere under the Gulf of Mexico during its rifting stage. The asymmetrical distribution of different crustal types under the Gulf of Mexico basin and sharp differences in the sedimentary record between the northern and southern gulf are the main arguments used to invoke the lithospheric simple shear model in interpreting the evolution of the basin’s conjugate passive margins. In the framework of this model, we interpret the northern and southern gulf margins as proximal and distal margins, respectively. The southeastern Gulf of Mexico is a deep seaway between Yucatan and Florida. In the framework of the Mesozoic evolution of the Gulf of Mexico basin, this area represents a major transform zone along which micro-plates (Yucatan block, Straits of Florida block) moved towards their present position, relative to North America, during the rifting and drifting stages of Gulf of Mexico opening. The southeastern Gulf of Mexico can be divided into three tectonically distinct domains, each reflecting different deformation styles and subsidence histories: A) The western domain (Area I) represents the eastern edge of the Yucatan block. It is an area where no significant Jurassic synrift deformation and subsidence occurred. The accumulation of thick Cretaceous to Cenozoic carbonate rocks in this area, however, indicates significant postrift thermal subsidence. B) The central domain (Area II), represented by the present-day deep seaway between Florida and Yucatan, is a deeply subsided, complex rifted area. Horst and graben features trend NW-SE, which are perpendicular to the major rift trends in the northern and southern Gulf of Mexico. The interpreted transform motions, along with the rift-trend direction define a transtensional deformation style for this area. C) The eastern domain (Area III) represents the south-western edge of the Straits of Florida block. Similar to the Yucatan block, it lacks major synrift deformation and it is extensively covered by Cretaceous and younger platform carbonates, related to the postrift thermal subsidence.

ABSTRACT In central and eastern Alabama, late Santonian to latest Maastrichtian (85 to 67 Ma) paleogeographic changes in both gross depositional-strike mode and specific latitudinal position of shoreline trend are directly related, respectively, to second- and third-order changes of sea level. The third-order sea-level changes are eustatic in origin with minor exceptions. Owing to relative tectonic stability of the Gulf passive margin over the Late Cretaceous eustacy has played a major role in depositional sequence development and thereby promoted a consistent and relatively predictable pattern in the paleogeographic distribution among a restricted number of depositional facies. In the study area, thirteen constituent depositional sequences are recognized. Analysis of their individual paleogeography and the facies relations within depositional sequences (both highstand systems tracts and transgressive systems tracts) permits successful prediction of intrasequence primary permeability ( i.e ., confined aquifer) distribution.

ABSTRACT Quantitative basin analysis techniques were used to study the structural history of Jurassic, Cretaceous, and Tertiary sediments in northern Louisiana, based on geological and geophysical data from 140 petroleum wells and 8 seismic lines. The uniformly distributed wells provide good control, on the regional scale, of the present day geometries of Cretaceous and Tertiary sediments. Seismic lines were used to identify deep Jurassic sediments, especially the Louann salt. The structural history in northern Louisiana can be separated into five major stages: (1) Jurassic rifting and extension; (2) Late Jurassic and Early Cretaceous subsidence; (3) mid-Cretaceous upwarping and westward tilting; (4) Late Cretaceous and Early Tertiary subsidence; and (5) Tertiary flexural downwarping. The regional tectonics and structures impact both the regional sediment deposition and lithology distribution. The hydrocarbon generation, migration and accumulation can be tied to the structural and depositional features. The dynamic salt movement associated with structural evolution could enhance the likelihood of hydrocarbon accumulations in sediments around salt diapirs.

ABSTRACT Cyclostratigraphy is the study of cyclic depositional patterns produced by climatic and tectonic processes ( Perlmutter and Matthews 1989 ). This paper describes a global scale quantitative cyclostratigraphic model which simulates carbonate growth patterns controlled by tectonic and climatic processes. The model uses seven factors simulating the effects of physical and chemical environments on the deposition rates of carbonate accumulations. These factors are sea level change, the rate of basement subsidence, food supply (influence of nutrient), available sunlight, temperature, salinity, and dissolved oxygen. The factors are considered as functions of climatic and tectonic processes. The model also integrates Milankovitch induced, short-term, climatic changes with the long-term, tectonic evolution of basins to examine the potential carbonate accumulation patterns. The two dimensional computer model results provided here show that: 1)Carbonate growth patterns in different climates and under different tectonic processes can be modeled quantitatively; 2) Carbonate production increases equatorward (latitude decreasing) due to both the temperature and nutrition supply increasing in tropical belts, and production changes because of the tropical belt expansion or contraction in different climatic periods; 3) When matched with the turbidity, the model describes different carbonate accumulation patterns in different climatic patterns; 4) At either abnormally high or low salinity, carbonate accumulation rates decline sharply, and the salinity becomes normal away from the strand line; 5) Cyclic sea level changes cause a cyclic change of carbonate accumulation. A case study is presented from the Texas Upper Pennsylvanian. The simulation results indicate that carbonate growth patterns observed from field, well or seismic data are accurately modeled by the quantitative procedure given here.

ABSTRACT The area of offshore Mobile Bay, Alabama is underlain by an extensive Jurassic salt deposit from the Louann Formation. Two procedures are given for estimating the original thickness of the Louann salt based on seismic information. The first procedure uses buoyancy pressure of the salt and empirical rock properties connected with fracture limits of rocks under pressure, to suggest a most likely salt thickness of 1600 ± 1400 ft. The second method uses the observed quasi-periodic amplitude variations of the Louann to estimate an original thickness of around 375 ft. An average of both estimates yields a mean thickness for the initial Louann salt of 1000 ± 500 ft.