R-3 Repository :: Browsing by Author "Droxler, Andre W."

Browsing by Author "Droxler, Andre W."

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Calcium carbonate dissolution patterns at intermediate water depths of the tropical oceans during the Quaternary
(1994) Haddad, Geoffrey Allen; Droxler, Andre W.
This study presents mineralogic and stable isotopic records generated for piston cores and Ocean Drilling Program holes recovered from intermediate water depths (500 to 2500 meters) near carbonate platforms around the world. Study areas included the Bahamas (western North Atlantic Ocean), the Nicaragua Rise (Caribbean Sea), the Maldives (north equatorial Indian Ocean), and the Queensland Plateau (southwest Pacific Ocean). Mineralogic data includes percent fine aragonite content, percent fine Mg calcite content, pteropod (aragonitic holoplanktonic gastropods) abundance, percent whole pteropods, and for some cores, percent clear pteropods. Carbonate data were interpreted both in terms of carbonate input from the nearby banks and in terms of seafloor dissolution. Planktic foraminiferal $\delta\sp{18}$O records were used as the primary chronostratigraphic tool for all sites. Statistical analyses of four metastable CaCO$\sb3$ dissolution proxies yielded a composite dissolution index (CDI) that displays different dissolution histories for Bahama and Nicaragua Rise sediments over the last 200,000 years. These differences are not predicted by intermediate to deep water nutrient fractionation models (e.g., Boyle, 1988). A good correlation is observed between the Caribbean CDI record (this study) and CaCO$\sb3$ dissolution and benthic $\delta\sp{13}$C records from 4641 meters in the Venezuela Basin, Caribbean Sea (Cofer-Shabica, 1987). It is concluded that during the last 200,000 years, variable cross-equatorial flux of Antarctic Intermediate Water has strongly influenced Caribbean carbon chemistry at water depths greater than 1100 meters. The assumption, therefore, that deep Caribbean sediment cores reliably record nutrient and (CO$\sb3\sp{=}$) variations of average mid-depth Atlantic water may need re-evaluation. Over longer time scales, CaCO$\sb3$ dissolution records from intermediate water depths near the Bahamas, Maldives, and Queensland Plateau are similar to deep-water dissolution records. Dissolution occurred from thermocline to abyssal depths from 500,000 to 300,000 years ago (during the middle Brunhes Chron) and between 1,000,000 and 900,000 years ago revealing that whole-ocean changes in carbonate chemistry have occurred during the Quaternary. Enhanced CaCO$\sb3$ dissolution may be related to decreased Ca$\sp{2+}$ flux to the ocean (decreased glacial weathering) and increased neritic CaCO$\sb3$ production and accumulation during periods of elevated interglacial sea-level highstands.
Geologic evolution of conjugate volcanic passive margins: Pelotas Basin (Brazil) and offshore Namibia (Africa). Implication for global sea level changes
(1998) Abreu, Vitor dos Santos; Droxler, Andre W.
Volcanic passive margins are a major type of large igneous provinces, characterized by seaward dipping reflectors (SDRS), normally associated with subaerially emplaced basalt flows and intercalated at least in part with continental sediments. In the South Atlantic, volcanics extent laterally for hundreds of kilometers and can reach a thickness of about 15 kilometers. A number of questions related to their formation. Among them, the influence of hotspots, the timing of volcanic emplacement with respect to continental breakup and the nature of the crust associated with the volcanic wedge remain uncertain. The Walvis and Pelotas basins are particularly well imaged examples of volcanic passive margins, providing an unique opportunity to investigate the evolution of volcanic margins. The sedimentary infill of the Pelotas and Walvis basins directly resulted from the Jurassic to lower Cretaceous breakup of Pangea. In the Pelotas Basin along the Brazilian margin, forty eight sequence boundaries were identified based upon the analysis of 1,500 km of 2D reflection seismic profiles and four hydrocarbon exploration wells. These sequences form the sequence stratigraphic framework for the lower Cretaceous (Albian) to Cenozoic sedimentary succession and their age control is based upon calcareous nannofossils and planktonic foraminifera biostratigraphies. This local sequence stratigraphic framework is compared with the global chart (Haq et al., 1987) and the new cycle chart of Hardenbol et al. (in press). Positive oxygen isotope events defined in several deep-water DSDP/ODP sites are compared with the sequence boundaries defined in the Pelotas Basin, Exxon record (Haq et al., 1987), and new cycle chart (Hardenbol et al., in press). From the sequence stratigraphic analyses, a chronostratigraphic chart and an onlap curve were built. A relative sea-level curve for the upper Cretaceous and Cenozoic records was developed in the Pelotas Basin based on the variations in the coastal onlap. Magnitude of sea-level fluctuations were estimated in measuring the downward shift of coastal onlap in seismic profiles for each sequence boundary. A composite oxygen isotope record were built based upon benthonic foraminifera from DSDP/ODP sites and compared with the Antarctica glacial history, the eustatic curve of Haq et al. (1987), and the relative sea-level curve of the Pelotas Basin. A reasonable correlation results from the comparison between the relative sea-level curve derived from sequence stratigraphic studies and the composite oxygen isotope record. At least since the middle Eocene, positive isotope events correlate well with sequence boundaries. These correlation indicate that glacial eustasy has been the principal factor regulating stratal stacking patterns on a global scale since at least the middle Eocene. Oxygen isotope values for deep-water benthonic foraminifera during the Aptian to lower Albian stages and Campanian to Maastrichtian stages are similar to those observed during the middle Eocene. Due to the evidence for Antarctic glaciation during the middle Eocene, similarity between Cretaceous and Eocene isotope values could indicate the presence of polar ice as early as the Aptian.
Late Oligocene and Miocene evolution of the carbonate system in the Gulf of Martaban (northern Andaman Sea): Effects of eustacy, tectonics, and siliciclastic input; Comparison with the Maldives carbonate system
(2005) Mitra, Dipanjan; Droxler, Andre W.
Eustacy was the dominant factor influencing the Gulf of Martaban Field isolated platform, subdivided in Lower and Upper Martaban Limestones (LML) and (UML). LML was established on top of a faulted accretionary basement that influenced the LML late Oligocene growth. At the Oligocene-Miocene boundary, siliciclastic influx inhibited the carbonate growth, infilled a central trough, and covered the LML platform top, creating a relief on top of which grew the UML platform. This platform first aggraded and backstepped, and then drowned due to early Miocene high rates of sea level rise. The Maldives, because of its bigger size, greater growth potential, and lack of siliciclastic, kept up with those early Miocene rates, while Gulf of Martaban Field drowned.
Late Quaternary periplatform sediments and environments on the northeastern Nicaragua Rise, Caribbean Sea
(1992) Glaser, Karen Sullivan; Droxler, Andre W.
Four main factors control the accumulation of periplatform sediment on the northeastern Nicaragua Rise: (1) input of carbonate sediment; (2) input of siliciclastic sediment; (3) physical redistribution of sediment; and (4) partial dissolution of carbonate phases (aragonite and magnesian calcite). The intensity of these factors is directly influenced by climatic variations and associated sea-level fluctuations, creating the cyclic glacial/interglacial pattern characteristic of late Quaternary high resolution stratigraphy in periplatform sediments. During interglacial stages, the bank/shelf tops of the Nicaragua Rise were submerged. The northwestward flowing Caribbean Current swept neritic sediments off-bank to the periplatform environment where they accumulated, by settling through the water column or by sediment gravity flow, preferentially in downcurrent areas. These neritic sediments along with pelagic carbonates, form a thick wedge of highstand sediment on the upper slopes. Carbonate input was locally augmented by siliciclastic sediment input from Jamaica during peak sea-level highstands. Finally, neritic aragonite deposited in water depths below 1100 m was subject to partial dissolution. Glacial sea-level lowstands were characterized by bank/shelf top exposure and lower production, therefore, neritic carbonate input to the periplatform environment was reduced. Nannoplankton productivity shows little glacial/interglacial variation, while glacial foraminifer productivity was only half interglacial levels. Consequently, bulk sediment accumulation rates and turbidite frequencies are lower during glacial stages than in interglacial stages. Bank-top exposure restricted flow of the Caribbean Current to seaways between the banks and shelves. This flow constriction considerably increased flow rates, winnowing sediments in areas of Walton Basin with water depths shallower than 600 m today. Partial dissolution of aragonite may be associated with the formation of magnesian calcite cements in current winnowed sediments. The geometry of the late Quaternary sedimentary bodies, displayed on 3.5 kHz seismic lines, can be interpreted in a sequence stratigraphic framework for periplatform carbonate sediments. Lowstands are thin and overlain by thick accumulations of highstand sediments, all of which lap out on the steep bank/shelf margins. Transgressive systems tracts are too thin to be resolved on seismic data, but are revealed by subtle changes in interglacial sediment mineralogy.
Late Quaternary sediment accumulations and foraminiferal populations on the slopes of Gladden Basin (offshore Belize) and southern Ashmore Trough (Gulf of Papua) mixed siliciclastic-carbonate systems
(2007) Carson, Brooke Elizabeth; Droxler, Andre W.; Dickens, Gerald R.
The Belize margin, in the western Caribbean Sea, and Ashmore Trough, in the western Gulf of Papua, represent modern tropical mixed siliciclastic-carbonate depositional systems where significant masses of both river born terrigenous siliciclastics and neritic/pelagic carbonates accumulate at variables rates over space and time. This study examines variations in sedimentolgic and micropaleontologic parameters relative to late Quaternary sea level, climate, and paleoenvironment. This is accomplished through the evaluation of carbonate and siliciclastic accumulations, as well as planktic foraminiferal populations, of a 37.7 m giant piston core (MD02-2532) acquired from the slope of Gladden Basin adjacent to the Belize Barrier Reef, as well as benthic foraminiferal populations of two shorter (11.3 m) piston cores (MV-74 and MV-07/06) acquired on the slopes of Ashmore Trough, adjacent to the northern most extent of the Great Barrier Reef. Neritic carbonate fluxes to the slopes of Gladden Basin are largely regulated by sea level and consistent with well-established highstand shedding depositional concepts. Over the last ∼850 ka, neritic carbonate production (and export to the adjacent slopes) switches on when sea level floods the neritic carbonate regions and switches off when sea level falls and neritic carbonate regions are exposed. Siliciclastic accumulations are also controlled primarily by eustatic sea level fluctuations, with additional influences from local and regional variations in physiography, climate, and/or ocean currents. Planktic foraminiferal taxa of Gladden Basin are typical of tropical to subtropical populations and display significant variations in their downcore relative abundances, suggesting notable changes in surface water masses and oceanographic parameters over the last ∼630 ka. Temperature and salinity, often associated with glacial or interglacial intervals, appear to predominately influence the planktic foraminiferal populations. In Ashmore Trough, benthic foraminiferal relative abundances and multivariate analyses indicate three distinct assemblages whose proportions change over the last ∼83 ka. These assemblages signify distinct paleoenvironmental settings driven by organic carbon flux and sediment supply, as well as changes in sea level. Analysis of these late Quaternary mixed systems provides better understanding of their preservation in the rock record, particularly relative to sea level and sequence stratigraphic concepts.
Late Quaternary sediment dispersal and accumulation on slopes of the Great Barrier Reef mixed siliciclastic-carbonate depositional system, Gulf of Papua, Papua New Guinea and North Queensland Margin, Australia
(2007) Francis, Jason Michael; Dickens, Gerald R.; Droxler, Andre W.
The Great Barrier Reef (GBR) margin, located on the continental margin between Papua New Guinea and northeast Australia, is the largest extant example of a tropical mixed siliciclastic-carbonate depositional system. It is constructed by the combined input of terrigenous siliciclastic sediment delivered through riverine transport and biogenous carbonate sediment from neritic and pelagic production. This study investigates late Quaternary changes in sediment dispersal and accumulation on the slopes of this margin. Sedimentation across the GBR mixed system also serves as an important analog for understanding deposition on other extant and ancient systems and provides insight into global change, geochemical cycling, and resource management. Several concepts (e.g., reciprocal sedimentation, coeval sedimentation) have been proposed to explain spatial and temporal variations in siliciclastic and carbonate components. While these concepts are frequently used to evaluate ancient tropical mixed systems, they are rarely assessed in the Quaternary, an interval where the magnitude and timing of sea level are relatively well-constrained, and precise dating techniques can be used. These studies of the GBR mixed system integrate a full suite of data including core, seismic, and multi-beam bathymetry to gain a quantitative understanding of the GBR system and to evaluate reciprocal sedimentation concepts. Results indicate that slopes along the GBR margin have a complex depositional history. Sea level, climate, and margin physiography are all important depositional controls affecting timing, location, and mechanism of sediment dispersal. Reciprocal sedimentation can be used to predict carbonate accumulation. However, this approach must be combined with a firm understanding of sedimentary controls and processes to accurately predict siliciclastic accumulation along this margin.
Laurentide ice sheet meltwater influences and millennial-scale climate oscillations on the northwestern slope of the Gulf of Mexico during Marine Isotope Stage 6 and Termination II
(2009) O'Hayer, Walter Werley; Droxler, Andre W.; Dugan, Brandon
Sub-Milankovitch climate oscillations are well documented phenomena in the Gulf of Mexico during Marine Isotope Stage (MIS) 3 and Termination I, however very little is known about equivalent events during older time intervals. Basin 4 is located on the northwest slope of the Gulf of Mexico and has provided a detailed record of late MIS 6 and Termination II. The results of this study show that the delta18O record of planktonic foraminifer G. ruber contains millennial-scale climate oscillations during MIS 6, a series of meltwater spikes, and a climate reversal during Termination II. Paired delta18O -- Mg/Ca data across these events reveal that the unusually large amplitudes in the delta 18O record cannot be explained by sea surface temperature (SST) or ice volume, but rather are a response to isotopically light glacial meltwater from the paleo-Mississippi river. This conclusion supports the studies of similar oscillations during Termination I and MIS 3.
Nature and Evolution of Deep Water Carbonate Drifts in the past 3 Million years, Inner Sea of the Maldives Archipelago, Equatorial Indian Ocean
(2013-07-24) Lopez, Karem; Droxler, Andre W.; Anderson, John B.; Sawyer, Dale S.
The Maldives atolls, the very top of one of the largest modern carbonate platforms, occupy the central and largest part of the Chagos-Laccadives ridge located in the equatorial Indian Ocean. In the central part of the archipelago, the large atolls form tw
Neogene evolution of the Pedro Channel carbonate system, northern Nicaragua Rise
(1998) Cunningham, Andrew David; Droxler, Andre W.
Pedro Channel is the deepest, central-most seaway on the northern Nicaragua Rise. A revised bathymetric map illustrates a seafloor dissected by numerous canyons and gullies as well as portions of a drowned carbonate bank with keep-up bank morphology. The 3.5 kHz echogram data interpretation in Pedro Channel indicates the banks provide both a line and point source of sediment to the channel floor. Concentric facies belts along the bank margins illustrate the line source concept. Localized zones of coarser-grained deposits at the bases of canyons along the bank margins depict the point source concept. The synthetic seismograms for ODP Site 1000 have low correlation coefficients (0.321). Visual correlation of the synthetic seismogram with SCS data indicates a good correlation of seismic facies with various lithologic intervals. An interpretation of SCCS and MCS data reveals that periplatform sedimentation has dominated Pedro Channel from the early Miocene to recent. Dredge haul analysis suggests that a neritic carbonate bank drowned partially in the middle Oligocene and finally in the early Miocene. Erosion affects the edges of this drowned bank in the middle Miocene. Faults in Pedro Channel illustrate characteristics typical of sinistral strike-slip faults including vertical to sub-vertical faults, faults that splay upward, forced folds, and linear fault traces in map view. ODP Site 998 was selected over a small portion of the Cayman Rise on a small topographic high. Synthetic seismograms for ODP Site 998 have low correlation coefficients (0.168). Despite the low correlation coefficients, turbidite-rich core intervals correlate with SCS intervals having low continuity seismic reflectors. The predominantly pelagic sedimentation at this Site results in a generally continuous seismic reflection character. ODP Site 1001 is located just north of the Hess Escarpment. Synthetic seismograms have low correlation coefficients (0.335), but do permit correlation of SCS A$\sp{\prime\prime}$ and B$\sp{\prime\prime}$ horizons with an Eocene-Miocene unconformity and basaltic basement respectively. Hydrosweep data indicates that the Hess Escarpment is dissected by numerous canyons incising along faults. The northwest trending normal faults are suggestive of dextral strike-slip motion.
Origin and stratigraphic evolution of the Maldives (central Indian Ocean)
(1994) Aubert, Olivier; Droxler, Andre W.
The Maldive Ridge is a volcanic lineament overlain by locally 3.3 km of mostly shallow-water carbonate sediments. The Maldive basement appears on seismic profiles as a volcanic plateau generated during two distinct eruptive phases separated by an episode of tectonic deformation. This deformation created a series of en-echelon pull-apart structures along the ridge acoustic basement and can be related to intraplate compression following the initial stages of the India-Asia collision. The deformation possibly triggered the extrusion of the basaltic flows overlying the acoustic basement and constituting the lithologic basement of the Maldive carbonate system. Widespread neritic carbonate sedimentation was initiated during the Eocene when the broad and relatively flat volcanic substrate started sinking below sea level. In spite of the lava flow extrusion, the initial depressions corresponding to the structural pull-apart basins remained as deep internal seaways surrounded by reefal margins until the late Oligocene. The Eocene-Early Oligocene depositional signature remained essentially aggradational and corresponds to a first transgressive cycle associated with a second-order sea-level rise. In the mid-Oligocene, a pronounced sea-level fall matching the development of a major ice sheet in Antarctica restricted the sedimentation to the internal basins. During the following transgression, the neritic carbonate system temporarily kept up with the sea-level rise, but was finally drowned near the Oligocene-Miocene boundary. In the early Miocene, pelagic ooze deposition covered the Paleogene neritic system and transformed the central troughs into one single deep basin, the paleo-Inner Sea. During the Neogene, following the establishment of a reef framework near the present location of the platform edge, systematic progradations of carbonate bank margins toward the central Inner Sea basin correspond to a long-term sea-level fall associated with a second-order regressive cycle. Segmentation of the prograding complex into individual carbonate banks occurred through local channeling and drowning events. Finally, the late Pliocene-Pleistocene depositional signature is mainly aggradational and corresponds to a regional modification from flat-topped carbonate banks to atoll physiographies. The onset of high-frequency eustatic and climatic changes following the initiation of Northern Hemisphere glaciation explains this evolution.
Reconstruction of eastern Pacific climate variability using multiple geochemical tracers in Cocos Island corals
(2000) Houston, Robb Eldon; Droxler, Andre W.
Multiple isotopic and geochemical tracers were employed to unravel the complex history of recent environmental variability at Cocos Island. Downcore variations in delta18O, U/Ca, Sr/Ca, and Ba/Ca within coral skeletal aragonite correlate with environmental parameters such as temperature, precipitation, and advection of surface waters. U/Ca and Sr/Ca ratios were evaluated as potential paleothermometers in conjunction with delta 18O, and indicate a combined influence of temperature and precipitation on delta18O. Ba/Ca records indicate that this tracer may be a useful tracer for the advection of coastal waters from the Gulf of Panama and the strength of the NECC. Information regarding large-scale atmospheric and oceanic processes is also embedded within the records. Long-term trends are reproducible in coral records throughout the eastern Pacific and indicate significant changes in the tropical climate system. Records developed from Cocos Island suggest an increase in rainfall in conjunction with localized cooling during the past 100 years.
Tectonic and eustatic controls on the evolution of the Maldive carbonate platform
(2000) Belopolsky, Andrei Victorovich; Droxler, Andre W.
The Maldive Archipelago in the equatorial Indian Ocean is only the uppermost part of a more than 3-km thick carbonate platform. The Maldive platform contains a 50 Ma-long sedimentation record and has a relatively simple tectonic history. The interpretation of 6000 km of Shell 2-D seismic data and information from two industry and three ODP wells was the basis for the reconstruction of the platform evolution and assessment of controls on platform development. The evolution of the Maldives platform was essentially twofold. During the first stage (Eocene-early Oligocene), tectonic control played the dominant role in the establishment and geographic distribution of shallow water carbonates. A series of shallow water carbonate platforms were formed in the early Eocene on basement highs separated by two deep, narrow, and continuous graben systems. The platforms aggraded and backstepped in the Eocene and early Oligocene in response to relative sea level rise driven mostly by tectonic subsidence. The second stage of the platform evolution (late Oligocene-Quaternary) was predominantly controlled by sea level fluctuations. A significant fall in sea level at the early-late Oligocene transition, with a magnitude possibly up to a 100 m, was recorded in the paleo-bathymetry of the Shell ARI-1 well. In the late Oligocene and early Miocene, the platforms first aggraded, partially drowned, and later backstepped in response to a substantial long-term sea-level rise. At the end of the early Miocene, a series of aggrading flat top carbonate banks, a small remnant of the Eocene-Oligocene neritic carbonate system, were established on the periphery of the central basin, the predecessor of the modern Inner Sea of the Maldives. During the middle Miocene, the bank margins prograded for 10--15 km. The progradation was driven by five complete sea level cycles, with each cycle represented by a relative sea-level fall and a subsequent rise. The reconstructed late Oligocene-middle Miocene relative sea level history of the Maldives corresponds well with the newly-published ice-volume record based on the temperature-corrected benthic foraminifera oxygen isotope data. The late Oligocene-middle Miocene depositional geometries of the Maldive platform appear to have recorded eustatic sea-level fluctuations.
The Caribbean carbonate crash at the middle to late Miocene transition and the establishment of the modern global thermohaline circulation
(1999) Roth, Joy Michele; Droxler, Andre W.
The Caribbean carbonate crash was a time of increased regional carbonate dissolution at the middle to late Miocene transition. It is marked by five dissolution episodes, occurring from 12-10 Ma, characterized by significant reductions in carbonate mass accumulation rates (CO$\sb3$ MAR). We determined carbonate content and CO$\sb3$ MAR for sites 998-1000 over the middle to late Miocene interval. Stable isotope composition of benthic foraminifers is used to track changes in deep water masses. Carbonate mineralogies are determined for the shallow site 1000 (927 m water depth) to detect dissolution of metastable carbonates at sub-thermocline depths. The geochemical changes during the carbonate period are similar to those that occur during the Caribbean Quaternary interglacial stages, times when Antarctic Intermediate Water (AAIW) filled the Caribbean to abyssal depths. The initiation of North Atlantic Deep Water (NADW) production during this period, possibly caused by the partial closing of the Isthmus of Panama and the opening of Pedro Channel (northern Nicaragua Rise), led to reorganization of global thermohaline circulation. The increase of return flow that passes through the Caribbean may have brought corrosive AAIW into the Caribbean, causing dissolution of carbonate sediment at the sea floor.
The Cenozoic tectonostratigraphic evolution of the Belize margin, the origin of the Belize barrier reef, and sequence stratigraphy of the late Quaternary mixed siliciclastic-carbonate system
(2001) Ferro, Carlos Elmer; Droxler, Andre W.
The primary objectives of this study were to understand the origin of the Belize Barrier Reef and the sequence stratigraphy of the mixed siliciclastic-carbonate system. The data used consisted of 1,400 km of conventional multichannel seismic, 1,300 km of single-channel high resolution seismic, and information from nine wells. Conventional seismic shows elongated NNE-SSW highs and lows (Camels Basin, Camels Hump-Turneffe atoll, Gladden Basin, Glovers atoll-Lighthouse Island). The thrusted block of Camels Hump formed from buttressing of the Maya Mountains against the moving Caribbean plate during the Paleocene. Its load generated Camels Basin, whereas Gladden and Turneffe Basins formed as pull-aparts. The transtension produced the Turneffe and the Glovers-Lighthouse alignments whose tops as well as Camels Hump's were covered by carbonate platforms during the late Eocene/Oligocene. These carbonates were partially drowned in the early/middle Miocene. During the middle/late Miocene, tectonic enhancement of Camels Hump and Glovers highs triggered the collapse of their margins, shedding mass flow deposits. The late Pliocene/early Pleistocene sea-level fall moved the shoreline along the eastern flank of Camels Hump and in the northern Camels Basin where longshore currents redistributed the sediments. The Belize Barrier Reef became established on top of these lowstand siliciclastic coastal deposits in the middle of the Brunhes Epoch (about 0.45 Ma). Once the barrier reef was formed, it established the modern mixed siliciclastic-carbonate system. When sea-level dropped, about 120 m during the Last Glacial Maximum (18,000 years ago), the reef built during the previous interglacial highstand was karstified. The shelf lagoon became a fluvial plain drained by two incised valley systems. The northern fluvial system deposited a lowstand delta at the mouth of the English Cay Channel. This delta was partially reworked by longshore currents. The rise of sea-level slowed at about -65 to -70 m, 11,000 to 10,000 years ago (Younger Dryas) and is documented by a landward-stepped delta. As sea-level rise resumed, the incised valleys became filled with fluvial to estuarine sediments and, then, buried under marine marls. Flooding at about 7,000 years ago reactivated the reef.
The Paleocene of La Concepcion Field (Maracaibo Basin, Venezuela): Transition from Andean to Caribbean active margin
(2004) Marcha, Lanette Mary; Droxler, Andre W.
The Paleocene Guasare Formation of La Concepcion Field (Maracaibo Basin, Venezuela) consists of thin carbonates that were deposited in a dynamic near-shore marine setting greatly influenced by terrestrial siliclastics and muds. In seismic data, the Guasare Fm. shows uniform thickness and subparallel reflectors. Facies trends were not evident from the 3D seismic data set. Amplitude maps revealed one structurally-related anomaly. The regional setting of the Paleocene was clarified showing that Late Cretaceous foresets indicated a source from the Andean active margin to the west. These clinoforms were overlain by the Paleocene Guasare Formation and its western partial equivalent, the Marcelina Fm., a siliciclastic and coal sequence. Only the overlying Eocene Misoa Formation indicates a northeasterly clastic input and eastward thickening associated with the emplacement of the Lara nappes of the Caribbean active margin. This study is based on 3D seismic data, some well logs, and well cuttings. Cores were unavailable.

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