CBTH Researchers at the
2016 UH Research Day and Industry Open House

CBTH Undergrads

• TITLE: GRAVITY MODELLING OF THE FLEXURAL RESPONSE OF LOADING OF THE NIGER AND AMAZON DELTAS ONTO THEIR UNDERLYING THINNED CONTINENTAL AND OCEANIC CRUST
  AUTHORS: Rasheed Ajala; Paul Mann
  ABSTRACT: The Niger and Amazon deltas occupy the rifted edges of conjugate margins presently located on opposite sides of the Equatorial Atlantic Ocean, so their underlying continental and oceanic crust is approximately the same age and thickness. The Amazon delta is considerably smaller than the Niger delta as it has limited surface expression due to the erosive effects of south to north ocean currents along the northeastern margin of South America. However, in the offshore area, the sedimentary wedges of both deltas are comparable in thickness with maximum thicknesses up to 12 km. This study uses gravity and seismic data to create gravity and flexural models that span the area of oceanic and thinned continental crust that underlies both deltas. These models help show the effect of the deltaic loads of both deltas on the lithosphere and are used to compare the flexural responses of their underlying crust. The results from these models show that the Niger delta is in near-isostatic equilibrium and the deltaic load is supported by a regional subsidence of its underlying crust. In contrast, the Amazon delta shows high amplitude isostatic gravity anomalies inferred to be a flexural response of its underlying crust. The load of the Amazon delta is supported by a highly thinned continental crust (~4.2 km), which has flexed by more than 2 km over a lateral distance of 500 km. I compare my proposed continent-ocean boundary inferred from the modeling of both deltas with the boundaries proposed by previous studies using other methods.



• TITLE: TECTONIC GEOMORPHOLOGY OF LARGE NORMAL FAULTS BOUNDING THE CUSCO RIFT BASIN WITHIN THE SOUTHERN PERUVIAN ANDES
  AUTHORS: Callum Byers; Paul Mann
  ABSTRACT: The Cusco rift basin is part of a subduction-related, intra-arc Neogene rift (Interandean basin) that extends from southern Colombia to southern Peru in the northern Andes. Located between the Eastern Cordillera and High Plateaus of southern Peru, the Cusco basin segment of the Interandean basin is bounded by a series of normal fault systems, mainly downthrown to the west and southwest. The region is also the location of a change in the geometry of the subducting slab of the Nazca plate that transitions from flat-slab subduction north of the Cusco area to a 30°-dipping subduction zone to the south. The Cusco normal fault system parallels the east-west-trending Apurimac river valley and is characterized by significant Upper Miocene footwall uplift of the Willkapampa Mountains that reach elevations of 6271 m and shows northward tilting to the southwest. Previous work has shown that the normal faults are dip-slip with up to 600 m of measured displacements, reflect north-south extension, and show Holocene displacements with some linked to destructive, historical earthquakes with documented normal fault ground offsets and earthquake focal mechanisms. I have constructed structural cross sections and river profiles across the entire area to demonstrate the flexural footwall effects of this large normal fault system on the plateau peneplain. To the northwest of Cusco, the Cordillera Blanca exhibits similarly high footwall topography caused by Late Miocene normal faults and a flexed lowland, hanging wall block. Previous work has attributed activation of the Cordillera Blanca detachment faults to the passing of the subhorizontal portion of the Nazca Ridge, a 1500 m bathymetric high, beneath the Cordillera Blanca region at 5 Ma. Southeast migration of this ridge suggests that the subhorizontal portion was initially subducted beneath the Cusco region of southern Peru during the Middle Pleistocene. I summarize previous tectonic models for the formation of these large, west dipping normal faults in the Cusco region and present that they formed in response to the passing of the Nazca Ridge.



• TITLE: GRAVITY AND BASIN MODELLING OF EAST AFRICA-MADAGASCAR CONJUGATE MARGINS: IMPLICATIONS FOR SOURCE ROCK MATURITY IN UNDEREXPLORED OFFSHORE BASINS
  AUTHORS: Matt Copley; Paul Mann
  ABSTRACT: The continental margin of East Africa is a rapidly emerging hydrocarbon province as demonstrated by Anadarko’s 150 Tcf gas discovery in the Rovuma delta in the offshore area of northern Mozambique. The objective of this study is to examine the underexplored East African margins of Somalia and Kenya and their conjugate margin in northern Madagascar. Rifting and oceanic spreading formed the West Somalia basin (WSB) during breakup of Gondwana from late Jurassic to early Cretaceous. Re-rifting of the area occurred as India rifted in a northeasterly direction from the eastern margin of Madagascar and formed the Mascarene basin. A northwest-southeast gravity transect across the East African margin in present-day Somalia supports a 79-km-wide band of thinned continental crust ranging from 12 to 3 km in thickness adjacent to oceanic crust in the West Somalia basin averaging 6.1 km in thickness. Published stratigraphic reports from both conjugate margins (including published information on the Jurassic-Cretaceous source rock interval) were used to create pseudo-wells whose porosity, temperature, and transformation ratios were modeled through time using Petromod. Both conjugates exhibit a similar subsidence history characterized by: 1) moderate subsidence during the Triassic and early Jurassic; 2) a rapid pulse of subsidence in the middle Jurassic; and 3) slow subsidence from the middle Jurassic to present with moderate events in the late Cretaceous, and Paleocene. Basin modeling shows that on both conjugate margins only Triassic sources reach maturity for the East African margin. For East Africa, expulsion begins in the early Cretaceous but does not reach a high transformation ratio until the Paleocene. For Madagascar, expulsion occurs later in the Eocene and does not reach a high transformation ratio. This likely occurs as a result of Madagascar’s more sediment-starved island location once it has separated from the more sediment-rich East African margin.



• TITLE: TESTING TWO MODELS OF THE EVOLUTION OF THE CARIBBEAN PLATE THROUGH COMPILATION OF JURASSIC TO RECENT RADIOMETRIC AGE DATES
  AUTHORS: Marie Kouassi; Paul Mann
  ABSTRACT: There are currently two tectonic models for the evolution of the Caribbean plate. The "in-situ" tectonic model proposes that the smaller Caribbean plate formed in the same location it occupies today between the North America and South America plates. The "single-arc Pacificorigin" model proposes that the Caribbean plate formed in the present-day area of the eastern Pacific and was transported over 1000 km to its present location by northeastward and eastward migration of the plate along subduction and strike-slip plate boundaries bounding it. Using ArcGIS tools, I compiled radiometric dates from ancient volcanic and plutonic rock and metamorphic complexes from all the subduction boundaries of the Caribbean plate to search for possible patterns of migration. Detrital zircon dates from sedimentary deposits were also compiled to infer the paleogeography and source areas of basins on the Caribbean plate during their deposition and can provide further clues for distinguishing the "in-situ" versus "Pacificorigin" tectonic models of the Caribbean plate. The results from the compilation show a pattern of eastward younging from Early Paleozoic to Late Cenozoic with record of continuous arc magmatism from c. 120 Ma to c. 45 Ma. This pattern is evidence of southwest to northeast and east to west motion of a single, northeast- or east-facing “Great Arc of the Caribbean” supportive of the "single-arc Pacific-origin" model.



• TITLE: DEFINING THE CONTINENT-OCEAN BOUNDARY AND ITS STRUCTURAL ROLE IN THE NORTHWESTERN GULF OF MEXICO FROM INTEGRATION OF SEISMIC REFLECTION AND GRAVITY DATA
  AUTHORS: David Lankford-Bravo; Paul Mann
  ABSTRACT: In the Gulf of Mexico (GOM), previous workers have used seismic reflection data to describe a deeply-buried sub-salt, “step-up fault” in the northeastern and north-central gulf where stretched continental crust abuts oceanic crust. From the previous studies, the vertical relief on this fault boundary varies from 1000 to 4000 meters with the oceanic (oceanward side) consistently being the upthrown fault block. Using 230 km of deep penetration seismic data, I have identified the western extension of this step-up fault in the subsalt area of northwestern GOM. In my area the fault exhibits up to 4000 m of vertical relief and is consistently upthrown on the oceanic side. I have also used gravity data to map the step-up fault that strikes N66E and extends 141 km as a continuous feature. In addition the step-up fault in this area of the northwestern GOM separates two distinctive structural provinces: the highly imbricated Port Isabel to the northwest and the less deformed Perdido foldbelt defined by large-wavelength folds structures. I propose that the continent-ocean boundary defined by the step-up fault that separates the two areas and acts as a basement ramp structure that controls the observed deformation seen at higher structural levels in both foldbelts.



• TITLE: CALCULATION OF REGIONAL GEOMORPHIC INDICES TO CONSTRAIN THE MECHANISMS OF TECTONIC UPLIFT AND ACTIVE DEFORMATION OF THE ISLAND OF PUERTO RICO
  AUTHORS: Sabrina Martinez; Paul Mann
  ABSTRACT: The island of Puerto Rico in the northern Caribbean covers an area of about 14,000 km2 and is 180 km long and 65 km wide and is densely populated by 3.4 million persons. The island is mountainous with an east-west-trending, central mountain range with its highest point of 1338 m in the geographic center of the island. The central range or Cordillera Central is flanked by narrow coastal plains on its northern and southern coasts. The origin of high topography in Puerto Rico has been attributed by previous workers to dynamic uplift of a large east-west trending anticline roughly coincident with the east-west topographic axis of the Cordillera Central and maintained by under thrust subducted slabs that converge roughly beneath the east-west axis of the island. To test the hypothesis that this topographic and structural axis is also the axis of active uplift, I have calculated geomorphic indices for 21 different watershed areas of the island that include over 50 different river systems. The geomorphic indices include a Hypsometric Integral and a Stream Length Gradient Index as defined by Stahler 1952 and Hack 1973 that assess tectonic activity based on stream and watershed behaviors. Results show that the most tectonically active watersheds correspond to the topographic axis of the island and support the idea of the anticlinal deformation of the island continuing to the present. I also compare these data to rock type and rainfall patterns to take into account these parameters on the geomorphic indices.



• TITLE: REVISED PLATE TECTONIC RECONSTRUCTIONS OF EARLY OPENING AND OCEANIC SPREADING HISTORY OF THE SOUTH ATLANTIC OCEAN
  AUTHORS: Andrew Steier; Paul Mann
  ABSTRACT: I have used GIS and GPlates plate reconstruction software to compile and analyze recent geologic and geophysical data to better constrain a continuous 130 Ma-present plate reconstruction for the rifting of South America and Africa and subsequent creation of oceanic crust in the South Atlantic. The plate tectonic opening models of the South Atlantic published in four previous studies differ in: 1) the initial continental fit based on locations of the continentocean boundary (COB) on both conjugate margins; 2) amounts of intracratonic deformation within South America and Africa during early rifting; 3) whether early rifting was symmetrical of asymmetrical; and 4) the time of early rifting in the Espirito Santo, Campos, and Santos basins. This study revises these models in the following areas: 1) using linear, basement shear zones in African and South American cratonic areas that act as "piercing points" to precisely match conjugate margins in the South Atlantic prior to breakup; 2) mapping radial dikes related to the Central Atlantic Magmatic Province (CAMP) to restore their original, sub-circular shape in North America, South America, and Africa; 3) analyzing recent marine satellite gravity to identify new fracture zones formed during early rifting (130-120 Ma) and improve the location of the COB and mapping of fracture zone trends in the oceanic crust (100 Ma-present); 4) using the improved maps of the COB to define areas of pre-breakup stretching in order to reduce continental overlap; 5) identifying upper-lower plate and volcanic-non-volcanic conjugate margins; 6) matching unique oil families on conjugate margins; and 7) realigning syn-rift salt basins on conjugate margins. The plate reconstructions of the previous authors were compared using GPlates modeling software. Layering these geologic and geophysical data onto the plate reconstructions reveals the strengths and weaknesses of each of the previously published models and allows me to propose a new plate kinematic model for South Atlantic early rifting and opening.

CBTH Beginning Graduate

• TITLE: SEISMIC STRATIGRAPHY AND STRUCTURE OF A LATE JURASSIC, SOUTHEASTWARD-PROPAGATING ZONE OF RIFTING AND OCEANIC SPREADING SEPARATING CONTINENTAL CRUST OF FLORIDA AND YUCATAN, SOUTHEASTERN GULF OF MEXICO
  AUTHORS: Pin Lin; Paul Mann
  ABSTRACT: The southeastern Gulf of Mexico (SEGOM) basin formed in the late Jurassic by rifting and the formation of a wedge-shaped area of oceanic crust that tapers from west to east indicative of a west-to-east propagating system of continental rifting and oceanic spreading. The V-shaped area of rifting and oceanic crust in SEGOM points to a pole of opening in Cuba and separates continental rocks of Precambrian and Paleozoic area now forming the deeply buried basements of Florida and the Yucatan platform. I use a grid of about 50,000 km2 of seismic reflection data tied to 7 DSDP Leg 77 wells to build an integrated stratigraphic and structural history of the SEGOM within the framework of the larger-scale opening of the entire GOM. Using these data, I have mapped the following seismic pre-, syn-, and post-rift seismic sequences: 1) Paleozoic and older, pre-rift, Paleozoic basement rocks; 2) Middle Jurassic (Callovian) Louann salt equivalents, that have not been previously well recognized in the SEGOM because the salt occurs in isolated areas rather than as a continuous salt sheet as in the northern and southern GOM; these salt deposits appear to have been deposited in sediment-starved rifts with the salt being reactivated by sediment loading during the early Cretaceous, passive margin phase; I see no evidence that salt was deposited above oceanic crust in the SEGOM and conclude that the salt phase preceded oceanic spreading; 3) Late Jurassic, syn-rift subdivided into a lower, clastic and non-marine sequence and an upper, carbonate sequence formed on rift-related structural highs; these rifts form a broad V-shaped pattern that mimic the shape of the adjacent oceanic crust; continent-ocean boundaries are observed on both the Yucatan and Florida conjugate margins and form “step up faults” separating the lower-standing continental crust from the higher-standing oceanic crust; and 4) earliest Cretaceous to recent, post-rift, passive margin deposits that reflect progressive subsidence and deepwater carbonate deposition in the northern and eastern part of SEGOM.

CBTH Advanced Graduate

• TITLE: NEW EVIDENCE FOR INTRAPLATE DEFORMATION IN THE WESTERN CARIBBEAN SEA: GRAVITY, MAGNETIC, EARTHQUAKE, TOMOGRAPHY, AND SEISMIC DATA EVIDENCE FOR AN ACTIVE MICROPLATE BOUNDARY ALONG THE SAN ANDRES RIFT
  AUTHORS: Luis Carlos Carvajal; Paul Mann
  ABSTRACT: The San Andres Rift (SAR), located in the Lower Nicaraguan Rise, is an active, 015°-trending, bathymetric and structural rift basin that extends for 346 km (214 mi). In this study, we used bathymetry, proprietary gravity and magnetic data, earthquake focal mechanisms, P-wave velocity anomaly tomography, and 980 Km (608.9 mi) of deep-penetration seismic reflection lines, in order to understand the processes that generate the current structural configuration of the San Andres Rift, and Neogene volcanism reported along the Nicaraguan Rise. Based on data observations, the SAR is structurally characterized by: 1) Normal, converging, high angle, dipslip faulting, 2) Block rotation, growth strata and negative flower structures, and 3) Bathymetric variations between the SAR flanks. Interpretations from 2D gravity and magnetic forward modeling and focal mechanisms, include: a) Different crustal affinity, thickness and deformation within the SAR expressed as surface lineaments, b) A negative gravity anomaly and high magnetism along the SAR attributed to crustal thinning with an elevated Moho surface, c) Seismicity takes place along the SAR axis with localized earthquake clusters and compression in its southwestern branch-line. We propose that Middle Miocene-Recent Cocos and Farallon slab roll-back, and Pleistocene Cocos Ridge collision are the crustal mechanisms responsible for regional intra-plate extension, eastward translation of strike-slip motion, and westward migration of Neogene volcanism in the Nicaraguan Rise.



• TITLE: GRAVITY COMPARISON OF OFFSHORE FLORIDA AND THE BLAKE PLATEAU AND ITS WEST AFRICAN CONJUGATE MARGIN
  AUTHORS: Naila Dowla; Paul Mann
  ABSTRACT: The outer continental shelf of the US East Coast, and northwest Africa are two underexplored conjugate margins with predicted reserves for the US East coast to be 3.3 billion barrels of oil and 32 TCF of gas within Cretaceous and Jurassic carbonate reservoirs charged by Jurassic carbonate source rocks. Predictions for the less studied conjugate margin of west Africa (Senegal to Guinea) vary widely for inferred source rocks ranging from in age Triassic to Oligocene sandstones and reservoir rocks ranging in age from Triassic to Late Cretaceous. In order to better estimate the hydrocarbon potential of both conjugate margins, crustal geometries of both conjugates have been compared to assess which margin is more favorable for hydrocarbon accumulation - or if both margins have equivalent potential. Margins with more favorable potential are generally considered those with wider rift zones with overlying sag basins and a thicker passive margin section. In the parlance of asymmetrical rifting, the margin with a wider rift zone is called here the upper plate, and the margin with a more narrow rift zone is called the lower plate. Two, 2D gravity profiles were created using refraction stations gathered from literature constrained with DSDP, IODP and ODP wells, as well as previously interpreted seismic data, and is integrated with the most recent satellite-derived worldwide gravity grid, to model the outer continental shelf basins up to 40 kms deep using gravity modelling software. This new gravity study indicates the wider, rifted margin of the Florida-Blake Plateau margin (possible rifted continental crust is 554 km wide with a thickness ranging from 22 to 12 km) may be more favorable for hydrocarbons than the more narrow and less extended margin of western Africa (rifted continental crust is 25 km wide with a thickness ranging from 25 to 11 km). The location of the proposed continent-ocean boundary is compared with the location of the boundary from previous studies.



• TITLE: DEEP STRUCTURE OF THE TOBAGO- BARBADOS RIDGE, LESSER ANTILLES, INFERRED FROM GRAVITY AND SEISMIC REFRACTION DATA
  AUTHORS: Shenelle Gomez; Paul Mann
  ABSTRACT: The north-south-trending Tobago-Barbados bathymetric ridge (TBR) extends 250 km from the island of Tobago and is underlain by an early Cretaceous, metamorphosed, arc basement. The TBR extends as a reduced bathymetric ridge as far north as the island of Barbados the is underlain by accreted, hydrocarbon-rich, Paleogene sedimentary rocks of the Barbados accretionary prism. This study improves the deep crustal characterization of this lithologic transition of the TBR from metamorphic rocks in the Tobago area to sedimentary rocks in the Barbados area by integrating data from: 1) three, ~500-1000-km-long gravity transects that I constructed across Tobago Forearc Basin (TFB) and TBR; and 2) publicly-available gravity and seismic refraction data. Three 120-200-km-long gravity transects were constructed across the trend of the TBR and one 500-km-long transect was constructed parallel to the axis of the ridge from the entire area. Gravity modeling confirms that the southern part of the ridge - which forms a single, well-defined bathymetry ridge and high gravity anomaly - is underlain by a 7-kmthick, upper crust of metamorphic rocks to 12.5N latitude that appear to be a direct continuation of the exposed metamorphic basement of Tobago. North of 12.5N, TBR becomes a more complex, multi-branched bathymetric ridge with a moderate gravity anomaly that extends for 126 km to the island of Barbados and is likely metasedimentary at depth. I propose that the metamorphic rocks of the southern TBR and metasedimentary rocks beneath the island of Barbados represent an unsubductable and elongate metamorphic terrane that was accreted around 110 Ma to the east-facing, proto-Caribbean subducton zone. As this event occurred in the Early Cretaceous, the terrane is now buried to a depth of 12 km. North of 12.5N, this same setting along the proto-Caribbean subduction zone is occupied by a co-linear belt of metasedimentary rocks with a distinctive gravity signature. In both areas, these rocks would have no source potential because of their low to intermediate metamorphic grade. Mature source rocks known from shallow oil wells and natural seeps in Barbados must exist at a higher level than these metasedimentary rocks inferred at depths of 10 km and greater.



• TITLE: STRUCTURAL ANALYSIS OF THE TAYRONA SOUTHERN CARIBBEAN DEFORMED BELT, OFFSHORE GUAJIRA PENINSULA, COLOMBIA
  AUTHORS: Stephen Leslie; Paul Mann
  ABSTRACT: The Southern Caribbean Deformed Belt (SCDB) is an accretionary prism that extends over 1300 km offshore of the Caribbean coastlines of Colombia and Venezuela. The SCDB defines the subduction boundary separating downgoing oceanic and oceanic plateau crust of the Caribbean plate beneath the Caribbean Sea from overriding, continental South American Plate in northern Colombia. The “Tayrona” portion of the SCDB is a ~500 km long, entirely submarine, section of the SCDB extending sub-parallel to the Colombian coastline located in deepwater offshore of the Guajira Peninsula and Santa Marta Massif. A grid of nineteen high quality 2D seismic reflection profiles (~2200 line km) provided by Spectrum Geophysical image the Tayrona SCDB and provides the basis for my structural analysis. Interpretation of the 2D seismic data in twoway time reveals at least nine major thrust related folds grouped inboard of the frontal thrust of the SCDB. The thickness of sediments along the top of the Caribbean plate outboard of the SCDB varies by an order of magnitude from west to east - with over 4 km of sediments in the western area proximal to the Magdalena Fan and ~400 m of sediments to the east towards the Aruba gap. The variability of sediment thickness directly influences the structure and style of folding and faulting along the Tayrona SCDB from west to east - most noticeably in the degree of shale diapirism that is apparent within the accretionary prism. Structural analysis of a series of seismic reflection profiles, converted from two-way time to depth, provides estimates of the degree of shortening that has occurred across the margin and also defines several phases of deformation that have occurred along the Tayrona SCDB.



• TITLE: ALONG-STRIKE VARIATIONS IN CRUSTAL ARCHITECTURE OF THE CONJUGATE MARGINS OF BRAZIL AND ANGOLA IN THE CENTRAL SOUTH ATLANTIC
  AUTHORS: Patrick Loureiro; Paul Mann; Dale Bird
  ABSTRACT:
The conjugate margins of Brazil and Angola have been the sites of some of the largest, and most productive oil fields in the world the past decade. While four decades of previous studies have produced several different models for early opening of the South Atlantic Ocean, there is no clear consensus on how these margins formed, their relative degrees of symmetry and asymmetry, and the deeper, crustal architectural constraints on the distribution of hydrocarbons on the conjugate margins. Low-pass filters applied to regional free-air gravity grids (Sandwell 2014) reveals a crustal signature imprinted by continental rifting during the Valanginian, and defined by a necking domain (zone of crustal thinning) and a distal domain (zone of thinned continental crust landward of the continent-ocean transition). Seismic reflection data from the conjugate basins of Brazil (Espirito Santo, Campos, Santos) and Angola (Kwanza, Benguela, Namibe) showed the presence of large listric normal faults and change in crustal seismic character at the transition between the necking and distal domain. My 2D gravity modeling of the conjugate basins is consistent with the observations from both the gravity grids and seismic reflection data. The gravity models match particularly well with the 10- km-wide zone of pronounced extension between the necking and distal domains which also underlies the pre-salt carbonate sag basin. The Santos basin (Brazil), Kwanza basin (Angola), and Benguela basin (Angola) all fall into the hyperextended lower plate domain, while their conjugates all exhibit narrow/ non-hyperextended crustal structures associated with upper plate margins formed during asymmetrical rifting. Lower plate margins range from 100-150 km (Kwanza, Santos, respectively) compared to their 30-50-km-wide upper plate, conjugate margins in west Africa (Namibe, Campos, respectively). The variations observed in crustal architecture along-strike can be attributed to reversals in the polarity of the upper and lower plates while across strike variations can be explained according to the relative widths of the necking and distal domains.


• TITLE: BASEMENT CONTROLS ON ALONG-STRIKE VARIABILITY OF THE VOLCANIC MARGINS OF URUGUAY AND SOUTHERN BRAZIL INFERRED FROM DEEP-PENETRATION SEISMIC REFLECTION DATA
  AUTHORS: Kyle Reuber; Paul Mann
  ABSTRACT: The present-day passive margins of offshore Uruguay and southern Brazil have been classified as volcanic margins that formed during the Aptian opening of the South Atlantic Ocean. For this study, I used 15,000 kms of 40-km-long record depth-migrated seismic data from a widelyspaced survey of the Punta de Este and Pelotas Basins of Uruguay and southern Brazil. Interpretation of these data indicate rapid, along-strike variations in the amounts of volcanic material and degree of continental stretching. Onshore basement rocks underlying the conjugate margins of South America and Western Africa include both Pan-African-Brasiliano foldbelts and stable cratons. Three lateral abrupt variations in the amount of syn-rift volcanism and the amount of continental stretching is observed from these data and correlates well with the type of basement that was rifted: 1) The northern extent of the Pelotas basin is underlain by nominally rifted basement, of the Dom Feliciano fold belt and is characterized by thick packages of seaward-dipping reflectors (SDR’s) and underlying, igneous crust. This 275 km-wide zone separates the continental and oceanic crustal domains; 2) the southern Pelotas Basin is underlain by the Polonio High, a prominent feature of the Uruguayan Shield. This margin segment shows evidence of minimal continental thinning and an 85km wide zone of SDRs and igneous crust west of the oceanic domain. 3) the southern Uruguayan Punta de Este Basin is the offshore domain of the Pampia fold belt and is characterized by moderately thinned continental crust, and variable amounts of igneous material. Evidence for rift related volcanism varies from minor occurrences to SDR packages reaching 13km in thickness. The implications for hydrocarbon exploration are primarily the existence of syn-rift targets and the variability along the margin. Regions where continental thinning has occurred, and where pre-existing fold-belts are present, have higher syn-rift prospectivity than regions where the transition from continental crust is abrupt.



• TITLE: LATE CRETACEOUS TO RECENT PALEOGEOGRAPHY AND SEQUENCE STRATIGRAPHY OF THE NICARAGUAN PLATFORM, WESTERN NICARAGUAN RISE: CONTROLS ON HYDROCARBON SOURCES, RESERVOIRS AND SEALS
  AUTHORS: Lucia Torrado; Paul Mann; Luis Carlos Carvajal; Javier Sanchez
  ABSTRACT: Late Cretaceous to Recent sediment deposition along the Nicaraguan platform, western Nicaraguan Rise, has evolved from a tectonically-controlled Late Cretaceous-Early Eocene mixed shallow to deep marine carbonate/siliciclastic shelf to an Early Miocene to Recent, tectonically-stable, shallow-marine carbonate platform. The Cenozoic sequence records three cycles of transgression and regression, starting with Early Eocene rodolitic/algal carbonate shelf that interfingered with marginal silicilastic sediments derived from exposed areas of Central America to the west. During the Middle Eocene, this mixed siliciclastic/carbonate platform shelf evolved into an entirely carbonate platform across which rimmed and isolated reefs formed. A Late Eocene forced regression resulted in widespread erosion and subaerial exposure along most of the platform and was recorded by a regional unconformity. The Oligocene-Early Miocene sedimentary record includes a southeastward-trending deltaic wedge that emanated from the proto-Coco River. Within this mainly clastic environment, restricted carbonate banks developed at the southernmost area of the platform. The Late Miocene to Recent marks a period of strong subsidence with development of small pinnacle reefs. The petroleum system elements of the Nicaraguan platform include: 1) Eocene fossiliferous limestone source rocks, 2) Early to Middle Eocene patch and pinnacle reefs, Middle Eocene calcareous turbidites and Oligocene fluvial-deltaic reservoirs, and 3) Seal intervals that include regional unconformities and Eocene-Oligocene intraformational shales.