South American Passive Margin Research Articles

The unsteady post-rift stage of the South American passive margin based on the tectono-sedimentary evolution of the onshore Paraíba Basin, NE Brazil

The post-rift tectono-sedimentary history of passive margins has been an issue of increased interest after the perception of their unsteady nature during the Neogene and Quaternary. The evolution of the eastern South America margin might be benefited from investigations of the sedimentary record in a number of marginal basins. The Paraíba Basin is of particular interest to discuss the post-rift evolution of the South American passive margin, because it represents the last bridge with the African plate. This work aims to analyze the post-rift sedimentary record of the onshore Paraíba Basin as a contribution to discuss the neotectonic history of the South American passive margin. Surface and subsurface data were integrated from outcrops, deep stratigraphic profiles, airborne geophysical maps and remote sensing products. The depositional and denudational processes in this basin were a result of tectonic subsidence and uplifting. Tectonics after the main rifting phase are indicated by abundant structures, including normal, reverse, and strike–slip faults, as well as folds that affected the Neogene and Late Pleistocene sedimentary deposits. The ductile and brittle deformation resulted mainly from multiple reactivations of E–W, NE–SW and NW–SE trending basement shear zones. The deformation mechanism included distension and compression under a strike–slip regime. Tectonic reactivations even during the late Pleistocene support an unsteady South Atlantic passive continental margin throughout the post–rifting stage.

Comparing contiguous high- and low-elevation continental margins: New (U-Th)/He constraints from South Brazil and an integration of the thermochronological record of the southeastern passive margin of South America

The southeastern coast of South America is an example of the complexity of passive continental margins, as it displays both high- and low-elevation segments despite sharing a similar pre-rift geological history and structural configuration. As such, it is a prime candidate for investigating debated questions concerning the evolution of passive margins, such as the tectonic mechanisms driving uplift, their relationship to rifting and continental break-up, and why some margins are elevated when others are not. In this contribution, we present new (U-Th)/He data from a low-altitude portion of the South American passive margin in South Brazil, the Sul-rio-grandense Shield, and interpret it in the context of the regional thermochronological record. New results produce widespread apparent ages and reveal a complex exhumation history from the early Paleozoic onwards, including reheating during Paleo-Mesozoic sedimentation. For most of the study area, however, final exhumation was achieved at the latest during the rifting and early opening of the South Atlantic Ocean (135 Ma to 100 Ma). In spite of the presence of major Neoproterozoic shear zones, the inherited NE-SW structural framework seems not to have strongly influenced the thermochronological record. The new data were integrated into a large compilation of apatite fission track and (U-Th)/He results from southeast South America, in order to compare regional trends and investigate possible tectonic controls in the exhumation history. Low-elevation areas of the passive margin consistently record complex pre-rift cooling histories, while high-elevation areas experienced significant Upper Cretaceous/Paleogene uplift associated with the reactivation of Neoproterozoic shear zones. Because the inherited structural features of both segments are similar, plate dynamics alone cannot be responsible for the variating response. Hence, mantellic processes associated with post-rift alkaline magmatism may have affected the contrasting exhumation histories. This process was probably controlled by important South Atlantic fracture zones.

Neotectonics in the South American passive margin: Evidence of Late Quaternary uplifting in the northern Paraiba Basin (NE Brazil)

The relief evolution of several areas of northeastern Brazil has been increasingly related to tectonic events. This is the case for the Paraíba Basin, where an abundance of faults and folds were recorded in Neogene and even Late Pleistocene-Holocene deposits. We tested whether dome-like morphologies in the northern sector of this basin, where geological exposures are scarce, were also formed by tectonic deformation. The work combined limited geological data with qualitative and quantitative analyses of the relief applying the 1 arc-second digital elevation model provided by the Shuttle Radar Topography Mission. The geomorphic indices of basin asymmetry factor (AF), swath topographic profiles, enhanced transverse hypsometry index (THi*) and normalized river long-profiles were used for validating a neotectonic origin for the dome-like morphologies. This interpretation was also supported by other morphological evidence of the dome relief, including: recurving channels featured in radial to recurved trellis patterns; tectonically-controlled drainage sub-basins; high relative relief values related to increased fluvial incision; and anomalous river long-profiles indicative of ungraded rivers. The domic structures were attributed to fault- and fold-related strike-slip deformation during the late Quaternary. This record supports the proposal that the South American passive margin remained under tectonic stress long after the main rifting in the late Jurassic-early Cretaceous.

(U‐Th)/He Thermochronology and Zircon Radiation Damage in the South American Passive Margin: Thermal Overprint of the Paraná LIP?

AbstractNew zircon and apatite (U‐Th)/He data (AHe and ZHe) from the crystalline basement of the South American passive margin in southern Brazil present a wide distribution of Phanerozoic apparent ages, recording its prerift evolution. Its geological significance can be investigated by modeling the influence of the accumulated radiation damages on the measured crystals in its He ages during a long upper crust residence. Despite the presence of a significant fault in the studied area, the samples essentially constrain a uniform thermal history for the entire study area. Zircon helium ages spread from 472 to 26 Ma and correlate strongly with the radioactive element content of the crystals. Although the region was probably covered by Paleozoic sediments of the Paraná Basin, the ZHe system experienced a more intense thermal overprint, most likely the onset of the Paraná Large Igneous Province (LIP), causing its dispersion. The nearby intrusion of a feeding system of the LIP, the Florianópolis Dyke Swarm, may have contributed for keeping geothermal gradients elevated for a period long enough to promote the observed reset. After the extrusion of the volcanism, the study area was probably covered by up to 2 km of basalt floods, imprinting temperatures above the AHe partial retention zone on the crystalline basement. These were eroded during rapid cooling between 75 and 55 Ma, as indicated by thermal modeling. Additional analyses with Raman spectroscopy were used for calculating radiation damage ages in the zircon crystals measured for (U‐Th)/He, resulting in a comparable set of ages.

Neotectonic record in South American passive margin based on morphostructural analysis of northern Paraíba Basin, Brazil

Neotectonic record in South American passive margin based on morphostructural analysis of northern Paraíba Basin, Brazil

The detrital record of Cretaceous to Pliocene sandstones across the NE South American margin

The Cretaceous to Pliocene erosional history of the NE South American margin depicts the increasing influence of the uplifting Caribbean Mountain belt. Petrographic analyses of 59 Cretaceous to Late Pliocene sandstone samples derived from across the islands of Trinidad and Barbados, demonstrate systematic mineralogical changes whereby Early Cretaceous arkosic arenites gave way to mature quartz arenites by the Late Cretaceous and Caribbean Mountain-derived lithic-rich arenites during the Neogene. Changes in the framework compositions are accompanied by changes in textural attributes, with Caribbean Mountain detritus being notably finer grained than cratonic input. Silica cements predominate in quartzose sandstones and sericitic and clay cements within litharenites. The changing mineralogical compositions record the gradual deformation of the northern South American passive margin and initiation of the Andean–Caribbean Mountain foreland basin system, with incipient orogenic detritus evident from the latest Eocene and unambiguous orogenic input by the Late Oligocene. The preponderance of finer grain sizes within deltaic Pliocene sandstones records the later fill of an established foredeep with sediments sourced primarily from erosion of the Andean hinterland. These interpretations agree with heavy mineral compositional changes and the timing of uplift from geo- and thermo-chronological data across the margin. Supplementary material : Qualitative descriptions, sample coordinates and raw point counts are available at https://doi.org/10.6084/m9.figshare.c.3659381

Topographic asymmetry of the South Atlantic from global models of mantle flow and lithospheric stretching

The relief of the South Atlantic is characterized by elevated passive continental margins along southern Africa and eastern Brazil, and by the bathymetric asymmetry of the southern oceanic basin where the western flank is much deeper than the eastern flank. We investigate the origin of these topographic features in the present and over time since the Jurassic with a model of global mantle flow and lithospheric deformation. The model progressively assimilates plate kinematics, plate boundaries and lithospheric age derived from global tectonic reconstructions with deforming plates, and predicts the evolution of mantle temperature, continental crustal thickness, long-wavelength dynamic topography, and isostatic topography. Mantle viscosity and the kinematics of the opening of the South Atlantic are adjustable parameters in thirteen model cases. Model predictions are compared to observables both for the present-day and in the past. Present-day predictions are compared to topography, mantle tomography, and an estimate of residual topography. Predictions for the past are compared to tectonic subsidence from backstripped borehole data along the South American passive margin, and to dynamic uplift as constrained by thermochronology in southern Africa. Comparison between model predictions and observations suggests that the first-order features of the topography of the South Atlantic are due to long-wavelength dynamic topography, rather than to asthenospheric processes. The uplift of southern Africa is best reproduced with a lower mantle that is at least 40 times more viscous than the upper mantle.

Contribution to the stratigraphy of the onshore Paraíba Basin, Brazil

Several publications have contributed to improve the stratigraphy of the Paraíba Basin in northeastern Brazil. However, the characterization and distribution of sedimentary units in onshore areas of this basin are still incomplete, despite their significance for reconstructing the tectono-sedimentary evolution of the South American passive margin. This work provides new information to differentiate among lithologically similar strata, otherwise entirely unrelated in time. This approach included morphological, sedimentological and stratigraphic descriptions based on surface and sub-surface data integrated with remote sensing, optically stimulated luminescence dating, U+Th/He dating of weathered goethite, and heavy mineral analysis. Based on this study, it was possible to show that Cretaceous units are constrained to the eastern part of the onshore Paraíba Basin. Except for a few outcrops of carbonatic rocks nearby the modern coastline, deposits of this age are not exposed to the surface in the study area. Instead, the sedimentary cover throughout the basin is constituted by mineralogically and chronologically distinctive deposits, inserted in the Barreiras Formation and mostly in the Post-Barreiras Sediments, of early/middle Miocene and Late Pleistocene-Holocene ages, respectively. The data presented in this work support tectonic deformation as a factor of great relevance to the distribution of the sedimentary units of the Paraíba Basin.

Late Quaternary sedimentation in the Paraíba Basin, Northeastern Brazil: Landform, sea level and tectonics in Eastern South America passive margin

Late Quaternary deposits in the northeastern Brazil have been scarcely investigated, despite their relevance to the discussion of the post-rift evolution of the South American passive margin within the context of landform, sea level and tectonic deformation. Sedimentological, stratigraphic and morphological characterization of these deposits, referred as Post-Barreiras Sediments, led to their distinction from underlying Early/Middle Miocene strata. Based on optically stimulated luminescence (OSL) dating, two sedimentary units (PB1 and PB2) were recognized and related to the time intervals between 74.8±9.3 and 30.8±6.9ka, and 8.8±0.9 and 1.8±0.2ka, respectively. Unit PB1 consists of indurated sandstones and breccias either with massive bedding or complex types of soft sediment deformation structures generated by contemporaneous seismic activity. Unit PB2 is composed of massive sands or sands related to structures developed by dissipation of dunes. The present work, focusing on the Post-Barreiras Sediments, discusses landform, sea level and tectonics of the eastern South American passive margin during the latest Quaternary. Non-deposition and sub-aerial exposure related to the Tortonian worldwide low sea level combined with tectonic quiescence followed the Miocene transgression. Tectonic deformation in the latest Pleistocene created space to accommodate unit PB1 in downthrown faulted blocks and, perhaps, also synclines produced by strike–slip deformation. Although deposition of this unit was simultaneous with the progressive fall in sea level that followed the Last Interglacial Maximum, punctuated rises combined with land subsidence led to marine deposition close to the modern coastline. Renewed subsidence in the Holocene gave rise to accommodation of the Post-Barreiras Sediments. Most of unit PB2 was deposited during the Holocene Transgression, but it is not composed of marine sediments, which suggests either an insignificant rise in relative sea level or aeolian reworking of thin transgressive sands. The data presented here lead to a review of the evolution of the South American passive margin based on assumptions of uniform sedimentation and undeformed planation surfaces over a wide coastal area of the northeastern Brazil.

Crustal structure of the Caribbean–northeastern South America arc‐continent collision zone

We present the results of a 568‐km‐long regional wide‐angle seismic profile conducted in the southeastern Caribbean that crosses an active island arc, a remnant arc, two basins possibly floored by oceanic crust, an allochthonous terrane of forearc affinity, and the passive margin of northern South America. The velocity structures of the Late Cretaceous Aves Ridge remnant arc and Miocene and younger Lesser Antilles arc are remarkably similar, which implies that magmatic processes have remained moderately steady over time. Crustal thickness is ∼26 km at the Aves Ridge and ∼24 km at the Lesser Antilles arc. In comparison to the Izu‐Bonin and Aleutian arcs, the Lesser Antilles arc is thinner and has no evidence for a lower crustal cumulate layer, which is consistent with the estimated low magma production rates of the Lesser Antilles arc. Crustal thickness beneath the Grenada and Tobago basins is 4–10 km, and the velocity structure suggests that these basins could be floored by oceanic crust. A decrease of ∼1 km/s in average seismic velocity of the upper crust is observed from NW to SE across the North Coast fault zone; we argue that this marks the suture between the far‐traveled Caribbean arc and the passive margin of the South American continent. Current strike‐slip motion between the Caribbean and South American plates is located ∼30 km to the south, and thus material originally deposited on the South American passive margin has now been transferred to the Caribbean plate.

Paleo-earthquakes in passive-margin settings, an example from the Paleocene of the Golfo San Jorge Basin, Argentina

Paleocene sedimentary rocks in the Golfo San Jorge Basin include the marine Salamanca Formation and the continental Río Chico Formation. Both units contain soft-sediment deformation features and evidence of contemporary tectonics, which include: 1) sediment-filled fissures, hosted in muddy marine sediments of the Salamanca Formation (“Fragmentosa” Section), where the sandy infill of the fissures took place from above; 2) synsedimentary normal faults in the uppermost levels of the Salamanca Formation, with vertical throws rarely exceeding 1 m; 3) fault-graded beds in the “Banco Negro Inferior” (marine–continental transition), which show a deformed sequence with small-scale normal faults at the bottom and intraformational breccias on top; and 4) liquefaction and/or fluidization pillars, “V” or funnel-shaped, with vertical extension of up to 5 m and preserved into fluvial channels of the Río Chico Formation. Deformed strata are bounded by undisturbed horizons and some of these features can be correlated along 60 km of exposures. The suite of soft-sediment deformation structures is considered a secondary evidence of synsedimentary paleo-earthquakes (seismites) in this portion of the South American passive margin. This work shows new evidence of syndepositional tectonic activity in the lowermost Paleogene of the Golfo San Jorge Basin.

Late Pleistocene tectonic-geomorphological development within a passive margin — The Cariatá trough, northeastern Brazil

Studies on the geomorphological evolution of the South American passive margin have been based on the pediplanation model, which predicts that its morphology is a response to regional uniform uplift and concomitant development of erosion surfaces. We combined remote sensing, geological mapping, lithostratigraphic and facies analyses, and luminescence dating in the Cariatá trough, northeastern Brazil, in order to determine how brittle tectonics and climate influenced colluviation and the shaping of local landforms in the Quaternary. Our work indicates that Cariatá is an asymmetrical trough ∼ 40 km long, ∼ 25 km wide, 250–550 m deep, and delimited by ENE–WSW-trending faults to the north and south. We recognized an ENE–WSW-oriented compression related to a strike-slip faulting regime, which corresponds to the present-day stress field in the region. This faulting event led to the deposition of colluvial fans, shed from adjacent uplifted crustal blocks, in a tectonically controlled depression. The colluvial succession is ∼ 45 m thick and presents two facies assemblages that filled the southern and, in particular, the northern borders of the trough: non-cohesive debrisflow and mudflow deposits. Optically stimulated luminescence dates of the sedimentary infill yielded ages at 224–128 ka and 45–28 ka, dominated by debrisflow and mudflow deposits, respectively. These ages may be over-estimated due to poor bleaching of colluvium, but they and our field data suggest that the margins of the trough were tectonically uplifted and eroded twice in the Late Pleistocene. The spasmodic colluvial accretion reflects the occurrence of high-magnitude, low-recurrence episodes probably associated with climate shifts in a semi-arid hillslope system. It follows that the present-day low-lying piedmont in which the Cariatá trough occurs is a juxtaposition of surfaces of various ages. This trough may have counterparts across the region. These conclusions do not corroborate the application of the cyclical pediplanation hypothesis in the area.

Tectonic controls of the right-lateral Burro Negro tear fault on Paleogene structure and stratigraphy, northeastern Maracaibo Basin

The northeastern Maracaibo Basin in western Venezuela was deformed by Paleogene thrusting and an associated tear fault (Burro Negro right-lateral strike-slip fault zone), related to Paleogene oblique collision between the Caribbean and South American plates. Two different tectonic models have been previously proposed for the thick Paleogene depocenter located along the northeastern margin of the Maracaibo Basin. The first model proposes that the depocenter is a foreland basin controlled by southwestward-directed overthrusting during a late Paleocene–middle Eocene oblique collision between the Caribbean and South American plates. The second model, supported by data presented in this study, proposes that the asymmetric Paleogene Maracaibo sedimentary wedge was controlled by strike-slip displacement along a right-lateral tear fault, separating southeast-directed thrust sheets to the east (Lara nappes) from a more stable platform area to the west (Maracaibo Basin).Regional seismic lines recorded to 5 s two-way traveltime reveal the structure of the asymmetric Paleogene depocenter in the northeastern part of the Maracaibo Basin. The approximately 100-km (62-mi)-long Burro Negro fault is a right-lateral strike-slip fault separating less deformed, inner- to outer-shelf rocks of the western Maracaibo Basin from highly deformed, deep-marine rocks of the eastern Maracaibo Basin. Seismic lines northeast of the Burro Negro fault zone show elongate, subsurface basins bounded by partially inverted reverse and strike-slip faults filled with about 3 km (1.8 mi) of Oligocene and Miocene clastic marine sedimentary rocks. Structural highs of Eocene rocks are characterized at depth on seismic reflection lines by chaotic seismic reflections that underlie the more coherently stratified Oligocene and Miocene subbasins. We interpret these structural highs as steeply dipping fault zones and shale diapirs activated during Eocene–Oligocene oblique plate convergence.The geology and overall structural configuration of the northeastern Maracaibo Basin and the Burro Negro fault zone support its origin as a right-lateral tear fault. In our model, the Burro Negro fault zone accommodated southeastward migration of the thrust front in the deep-water area east of the fault in the present-day Falcn region. The Paleogene clastic wedge of the Maracaibo Basin exhibits many common features of a classic foreland basin, including onlap onto an arch or forebulge located near the center of the present-day Lake Maracaibo. This paleogeographic coincidence of the Burro Negro fault zone and the Maracaibo shelf edge suggests that the paleotrend of the South American passive margin prior to collision was serrated in map view. West-to-east migration of the Caribbean–South America oblique collision formed progressively younger, parallel tear faults to the east of the Maracaibo Basin that may have formed by the same tectonic process as the Burro Negro fault zone.

Pliocene-Quaternary fault control of sedimentation and coastal plain morphology in NE Brazil

Although the last major tectonic event in the Brazilian passive margin was the South America–Africa breakup during the Mesozoic, there is pervasive evidence in northeastern Brazil for pronounced faulting since the late Tertiary. The faulting was partitioned between strike-slip and normal-slip and it reactivated Precambrian shear zones as well as generating new structures. A 040–060° -trending fault set and a 300–320° -trending set have strongly influenced both the deposition of alluvial and aeolian sediments and coastal evolution. Vertical throws have attained 260m since the Pliocene, and topographic breaks resulting from cumulative late Tertiary to Quaternary slip have attained 30–40m. Fault control of sediment deposition and coastal morphology may have affected the entire South American passive margin.

Fin d'analyse

The relief evolution of several areas of northeastern Brazil has been increasingly related to tectonic events. This is the case for the Paraíba Basin, where an abundance of faults and folds were recorded in Neogene and even Late Pleistocene-Holocene deposits. We tested whether dome-like morphologies in the northern sector of this basin, where geological exposures are scarce, were also formed by tectonic deformation. The work combined limited geological data with qualitative and quantitative analyses of the relief applying the 1 arc-second digital elevation model provided by the Shuttle Radar Topography Mission. The geomorphic indices of basin asymmetry factor (AF), swath topographic profiles, enhanced transverse hypsometry index (THi*) and normalized river long-profiles were used for validating a neotectonic origin for the dome-like morphologies. This interpretation was also supported by other morphological evidence of the dome relief, including: recurving channels featured in radial to recurved trellis patterns; tectonically-controlled drainage sub-basins; high relative relief values related to increased fluvial incision; and anomalous river long-profiles indicative of ungraded rivers. The domic structures were attributed to fault- and fold-related strike-slip deformation during the late Quaternary. This record supports the proposal that the South American passive margin remained under tectonic stress long after the main rifting in the late Jurassic-early Cretaceous.

Sea Level History Across the Northern South American Passive Margin: Eustatic vs. Tectonic Regulation: ABSTRACT

Sea Level History Across the Northern South American Passive Margin: Eustatic vs. Tectonic Regulation: ABSTRACT

Structure and deformation history of the northern range of Trinidad and adjacent areas

Conflicting models have been proposed for both the evolution of northern South America and the neotectonics of the south Caribbean plate boundary zone. The Trinidadian portion of the margin is particularly controversial, but surprisingly it has been little studied. We present a structural analysis of Trinidad's Northern Range, pertinent updates of the island's stratigraphy and sedimentology, and new zircon fission track age determinations, and use them to constrain Trinidad's geologic history, and to better understand the controlling tectonic processes. In our interpretation Trinidad's three E‐ENE striking ranges, which are separated by late Neogene‐Recent depocenters, expose (1) the Northern Range Group, generally greenschist‐metamorphosed Upper Jurassic to Cretaceous north facing continental slope sediments of the Northern Range, deposited on the northern South American passive margin 200–400 km to the WNW, and (2) the Trinidad Group, Cretaceous‐Paleogene shelf slope sediments of the central and southern Trinidad deposited less than 100 km WNW of their present location. A small allochthon composing the Sans Souci Group Cretaceous tholeiitic volcaniclastic, basaltic, and gabbroic rocks (Sans Souci Formation) and sediments (Toco Formation) now in the northeastern Northern Range, has been transported hundreds of kilometers from the west with the Caribbean Plate. Despite earlier references to Cretaceous orogenesis, all deformation in Trinidad is of Cenozoic age. The first deformation in the Northern Range (D1) formed north vergent nappes and induced greenschist metamorphism, probably in the Late Eocene or Oligocene. The nappes developed either by the underthrusting of the Proto‐Caribbean crust beneath South America due to convergence between North and South America, or as gravity slides caused by oversteepening induced by this convergence and/or the passage of the Caribbean Plate's peripheral bulge and arrival of its foredeep. Northern Range D2 deformation is south vergent and represents the incorporation of Northern Range metasediments into the Caribbean accretionary prism. The transition to D3 brittle transpressive right‐lateral strike‐slip faulting is interpreted to be due to the uplift and east‐southeastward transpressive emplacement of Northern Range/Caribbean prism rocks onto the South American stepped shelf. This emplacement formed the Miocene transpressive thrust belts and foreland basin in central and southern Trinidad. In the final phase of Northern Range deformation (D4) ∼E‐W normal faults and shear zones and conjugate NNW‐SSE and NE‐SW normal faults developed, and displacement on preexisting ∼E‐W right‐lateral strike‐slip faults continued. The 11 Ma Northern Range zircon fission track ages suggest rapid uplift from the Late Miocene to Recent. Late Miocene subsidence of the Tobago platform immediately to the north of the Northern Range, and greater than 3 km of normal, down to the north, displacement indicated for the North Coast Fault Zone separating the Northern Range and Tobago platform, leads us to postulate that the rapid uplift of the Northern Range was in response to the northward detachment of the Tobago platform from above the Northern Range, along the north‐dipping transtensional North Coast Fault Zone. This Late Miocene change in deformation style can be explained by a change from Caribbean/South American right‐lateral transpression to right‐lateral strike‐slip generally striking 080°. This has generally induced a component of extension on pre‐existing faults striking at greater than 080°, and a component of compression on faults striking at less than 080°.

Cretaceous Sequence Stratigraphy of the Northern South American Passive Margin: Implications for Tectonic Evolution

The passive margin of northern South America, from Colombia to northeastern Venezuela, was relatively stable through the Cretaceous and only broadly affected by the entry of the Caribbean Plate into the Protocaribbean Basin. This region offers a unique opportunity to test the relative effects of global sealevel change, autocyclic sedimentologic processed, and regional tectonics in shaping the stratigraphic record of Cretaceous passive margins. High-resolution stratigraphic studies of Colombia and Venezuela have established a precise system of regional chronology and correlation with resolution <1 Ma (50-500 ka for the middle Cretaceous). This allows precise separation of allocyclic and autocyclic controls on facies development. This new chronology integrates assemblage zone biostratigraphy with event/cycle chronostratigraphy. Newly measured Cretaceous sections in Venezuela and throughout Colombia are calibrated to this new chronology, and sequence stratigraphic units independently defined to the third-order of resolution. Graphic correlation of all sections is used to identify sequences with regional stratigraphic expression, and those which correlate to sequence stratigraphic standards of North America, Europe and the global cycles of Hag et al. (1988). 50-60 percent of the stratigraphic sequences across the South American passive margin correlate to other continents and to the global sequence stratigraphic standard, reflecting strong eustatic influencemore » on Cretaceous sedimentation across northern South America. The remaining sequences in this region reflect tectonic modification of the passive margin and autocyclic sedimentary processes.« less

Tectonics and Terranes of the Southeastern Caribbean

The southeastern Caribbean plate (Ca) is comprised of the following terranes: Tobago, Grenada Basin, St. Vincent, Araya-Margarita, and Paria-Trinidad-Barbardos (PTB). All are alient relative to South America (SA) east of Caracas except for PTB, which is of continental provenance and parautochthonous and lies within the principal movement zone of the Ca-Sa plate boundary. The Tobago terrane extends between the eastern Venezuelan coastline and the Grenada Basin. On its south, the Tobago terrane overrode PTB and the South American passive margin during Neogene oblique collision. The Mesozoic tectonostratigraphy of the Tobago terrane is not unlike that of the Colombian Basin, suggesting the Tobago may belong to the Pacific-derived Caribbean plate. The Grenada Basin terrane consists of Eocene and older oceanic crust that now occupies the southern Lesser Antilles arc platform and the southern Grenada Basin. Such crust abducted southward below the Tobago terrane in mid-Cenozoic time, probably taking up boundary-normal shortening during oblique collision of the Ca and Sa plates. The oceanic crust of the GB terrane arose by backarc spreading of unknown orientation. The St. Vincent terrane extends north in the Antilles from St. Vincent; it is defined by thick crust, perhaps an old arc basement. The Araya-Margarita terrane ismore » a probable subduction complex of Mesozoic age of metamorphism that has been transported far eastward from an unknown site with the Ca plate.« less

Molluscan Biozones, Event/Cycle Chronostratigraphy, and Sea Level History: A New Integrated Cretaceous Chronology for Northern South America

The Cretaceous marine basins of northern South America, in their evolution, record a dynamic interplay between regional and plate tectonics, sealevel history, changing paleo-ocean/paleoclimate systems, and the rates/patterns of sedimentation driven by both allocyclic and autocyclic processes. Regional interpretation of these complex interactions; and the evolution of the South American passive margin, requires a high-resolution stratigraphic system of dating and correlation. Because short-term events and dynamic processes shape the stratigraphic record, this chronology must have a resolution of 2 Ma/biozone. New efforts to establish a more refined chronology for South America involve: (a) High-resolution (cm-scale) event/cycle chronostratigraphic analyses of key Colombian and Venezuelan sections; (b) search for datable ash/bentonite beds; (c) detailed paleontologic collecting to firmly establish biostratigraphic ranges of mollusks and microplankton with high biostratigraphic potential, and to formulate regional assemblage zones; and (d) integration of these diverse data through graphic correlation to provide a new chronologic standard for the region.more » Initial results are presented: Middle Cretaceous biozones are now resolved to <500 ka/zone; a fine-scale sequence stratigraphy and sealevel history has been determined; numerous regional physical and chemostratigraphic event beds are identified; and climate-driven cyclostratigraphy has been resolved to at least 50 ka within the passive margin sequences of Colombia and Venezuela.« less