Lorena Moscardelli

Mass-transport complexes and associated processes in the offshore area of Trinidad and Venezuela

Mass-transport complexes (MTCs) form a significant component of the stratigraphic record in ancient and modern deep-water basins worldwide. One such basin, the deep-marine margin of eastern offshore Trinidad, situated along the obliquely converging boundary of the Caribbean and South American plates and proximal to the mouth of the Orinoco River, is characterized by catastrophic shelf-margin processes, intrusive and extrusive mobile shales, active tectonics, and possible migration and sequestration of hydrocarbons. Major structural elements found in the deep-water slope regions include large transpressional fault zones (i.e., Darien Ridge, Central Range, Los Bajos), along which mobile shales extrude to form sea-floor ridges; fault-cored anticlinal structures overlain by extrusive sea-floor mud volcanoes; shallow-rooted sediment bypass grabens near the shelf break; and normal and counterregional faults. A total of 10,708 km2 (4134-mi2) of merged three-dimensional (3-D) seismic surveys enable sub-sea-floor interpretation of several erosional surfaces that form the boundaries of enormous mass-transport complexes. The data show numerous episodes of MTC developments, which are characterized by chaotic, mounded seismic facies and fanlike geometry. Their extent (up to 2017 km2 [778 mi2]) and thickness (up to 250 m [820 ft]) is strongly influenced by sea-floor topography. Mass-transport flows show runout distances from the source area of 60–140 km (37–86 mi). Depositional architecture identified with these units includes (1) large-magnitude lateral erosional edges, (2) linear basal scours, and (3) side-wall failures. Mud volcanoes act as barriers to cross-slope mass sediment movements and form zones of shadowing on their downslope side that protect those regions from erosion. The subsequent erosional shadow remnants (ESRs) comprise preserved regions of older levee-channel complex sediments and are considered for the first time in this study as potential stratigraphic traps in deep-water deposits. Active tectonism in the region, high sedimentation rates associated with the Orinoco delta system, and abundant potential unstable hydrate suggest the viable presence of several higher frequency mechanisms at work for MTC generation than sea level fluctuations alone.

Deep-water polygonal fault systems as terrestrial analogs for large-scale Martian polygonal terrains

Discovery of giant polygonal terrains on Mars has prompted a 30-year debate over how they formed. The prevailing hypothesis is that small-scale Martian polygons formed by thermal contraction, as in terrestrial permafrost environments. Large-scale (>1 km) Martian polygons in the northern plains are visible in THEMIS, MOLA, Viking, and Mariner data, but how they formed remains enigmatic. We suggest that terrestrial deep-water marine polygons are morphological and perhaps genetic analogs to largescale Martian polygonal features. The terrestrial, deep-water polygons are imaged in three-dimensional seismic-reflection data acquired by the oil and gas industry in offshore Norway and the Gulf of Mexico. How deep-water polygonal fault systems form is a debated topic beyond the scope of this work. However, similarities between terrestrial deep-water polygonal fault systems and large-scale Martian polygonal terrains suggest that the latter could have formed during deep-water marine deposition. Deep-water polygonal faults form within fine-grained sediment at shallow burial depths. Increases in slope angles can trigger downslope disaggregation of deep-water polygons and mass wasting (forming debris flows). Physical models indicate that multidirectional extension can cause polygonal features to break up on a slope over a mobile substrate. Some knobby terrains in the Vastitas Borealis Formation seem to originate from disaggregation of large-scale Martian polygonal terrains. These analogies suggest a possible deep-water subaqueous origin for large-scale Martian polygonal terrains and support the idea of a late Hesperian–early Amazonian ocean on the northern plains of Mars.

Morphometry of mass-transport deposits as a predictive tool

Mass-transport deposits (MTDs) are gravity-induced units that represent an important component of modern and ancient deep-water stratigraphic successions. MTDs have been widely documented in the literature, but a comprehensive compilation of quantitative morphometric parameters associated with their external architecture is still lacking. This work presents a morphometric database that contains 332 data points that document the length, area, volume, and thickness of MTDs from different geologic ages and a variety of continental margins around the world. The compilation contains data collected from interpretations done by the authors in eastern offshore Trinidad and the Gulf of Mexico as well as from data mining from the peer-reviewed literature. Preliminary results indicate that there is a good correlation between a series of parameters that include the area, length, and volume of MTDs. On the other hand, the correlation between thickness and volume seems to be harder to document mainly due to lateral variations in thickness that are typical within MTDs. Data analysis suggests that previous qualitative classification of attached and detached MTDs can be validated by using a quantitative approach. This validation suggests that morphometric parameters associated with the architecture of MTDs can be used as a hint to link geologic setting, deposit geometry, and potential causal mechanisms. In addition, the defined morphometric relationships that were encountered between the different morphometric parameters (e.g., length and area) are useful to predict MTD dimensions in areas of the subsurface where data are limited and/or data quality is low. Likewise, these morphometric relationships can be used in outcrop studies where exposure of the MTD units is also limited.

Shelf-edge deltas along structurally complex margins: A case study from eastern offshore Trinidad

A 15,000-km2 (5792-mi2) three-dimensional seismic data survey that covers the shelf-slope transition of the eastern offshore Trinidad continental margin reveals the geometry and depositional history of the last maximum glacial lowstand shelf-margin succession. Despite the lack of well information at these shallow depths, the quality and continuity of the seismic data allow us to pursue a detailed seismic stratigraphic interpretation of the last lowstand margin succession. The basin-fill stratal architecture of the studied stratigraphic interval shows a great deal of lateral and vertical variability along the continental margin during the Pleistocene to Holocene. Three geomorphological elements controlled the character of the accommodation within the basin and were crucial in transporting, delivering, and storing sediment supply from shelf to slope areas: (1) the Columbus sedimentary pathway on the shelf, (2) bypass zones in the shelf-break region, and (3) deep-water depocenters. The location and geometry of these geomorphological elements within the basin are clearly controlled by underlying structures, transpressional to the north and gravity driven to the south. Migration of the paleo-Orinoco delta system across the shelf was also a key factor in defining the stratigraphic geometries that are observed within the shelf break. Development of shelf-edge versus outer-shelf deltaic systems on the continental margin was controlled by the nature of sediment supply at specific times, as well as by the availability of accommodation, although, to a lesser extent, to relative sea level fluctuations. The interpretation also showed that, for time-equivalent units, parts of the shelf-edge region could develop as an erosional margin (sediment bypass zones), whereas other parts of the shelf edge could behave as an accretionary margin (sediment accumulation). The sequence-stratigraphic interpretation that was attempted in this work also demonstrated that the characteristics of systems tracts can abruptly change along strike in the shelf-edge region for time-equivalent units. These changes can be misleading if a genetic interpretation is pursued only on the basis of the definition of system tracts in the shelf-edge region without the consideration of a complete regional framework.

Seismic geomorphology of early North Atlantic sediment waves, offshore northwest Africa

AbstractThe lower continental rise of Morocco’s Atlantic Margin contains three varying morphologies of buried deepwater sediment waves. The 3D mapping of a 1,064-km2 seismic survey acquired in the Safi Haute Mer seismic block revealed numerous linear features that range from small, less than 17-m-thick Jurassic-age amplitude striations up to 110-m-thick migrating Cretaceous contourite sediment waves. Early proto-Atlantic deposition in Safi Haute Mer initiated in the Triassic, with syn- and postrift accumulation in basement half-grabens basinward of the modern Moroccan salt front. Sedimentation continued through the Mesozoic with deposition of turbidites, progradation of clinoforms, and culminating in multiple Late Cretaceous, regionally expansive, mass-transport deposits (20,000  km2). Tertiary stratigraphy consists of multiple thin, pelagic drapes and unconformities. The complex history of sedimentation and tectonics gave rise to three styles of sediment waves found within the study area: (1) type J1 — s...

Boulders of the Vastitas Borealis Formation: Potential origin and implications for an ancient martian ocean

The hypothetical existence of a martian ocean that is based on identification of alleged paleoshorelines has been heavily contested during recent years. Despite the controversy surrounding the paleoshoreline interpretation, additional evidence supporting the idea of a late Hesperian–early Amazonian martian ocean has recently been documented in areas that were potentially covered by this body of water. Most of these observations have been made by the establishment of analogies between martian features within the northern plains and depositional elements from deep-water terrestrial environments (e.g., teardrop-shaped islands, large-scale polygonal terrains, and highalbedo mounds). This paper showcases a new terrestrial, deepwater analogy that also supports the existence of an ancient martian ocean. Boulder-size rocks that are contained within the Vastitas Borealis Formation (VBF) on the northern plains of Mars are compared with boulderand kilometer-scale blocks that have been transported subaqueously as part of mass-transport events in a multitude of terrestrial deep-water environments. These observations suggest that meter-scale rocks that make up part of the VBF might have been emplaced by catastrophic mass-transport events similar to those documented within continental margins on Earth.

Late Cretaceous Anoxia and Lateral Microfacies Changes in the Tres Esquinas Member, La Luna Formation, Western Venezuela

Abstract The Tres Esquinas Member of the La Luna Formation is a glauconite-rich phosphorite unit associated with changes that took place in depositional environments in the Maracaibo Basin at the end of the Late Cretaceous. The unit marks the end of La Luna Formation sedimentary cycle. This paper presents results of petrographic studies of samples from two sections, one outcrop (Río Guaruries), and one well core (Perijá), and from seismic profiles across the Perijá and Colón areas in the Maracaibo Basin. The Tres Esquinas Member is three meters thick in both locations. In the Río Guaruries outcrop, it contains an abundant foraminiferal fauna in addition to common allochemical material. Perijá core samples contain voluminous carbonate matrix, scarce allochemical materials, rare foraminifera, and poor definition of mineral facies, which may reflect higher-energy conditions on the sea floor. The deposition of the Tres Esquinas Member resulted from altered sea-floor topography during an episode of intense tectonic activity in the eastern part of the Maracaibo Basin. The modified shelf configuration ended anoxic conditions on the sea floor and led to increased erosion characteristic of the Tres Esquinas Member.

Deep-water erosional remnants in eastern offshore Trinidad as terrestrial analogs for teardrop-shaped islands on Mars: Implications for outflow channel formation

Discovery of geomorphological elements such as valleys and channel-like features on the surface of Mars has prompted debate over alternative origins for these morphologies, including erosion by lava, liquid CO 2 , glaciation, and mass wasting events. Similarities between Martian geomorphological elements and those of certain terrestrial environments suggest that water processes were involved in the formation of some visible Martian landscapes. Recent advances in three-dimensional seismic reflectivity imaging techniques, drawn mainly from oil and gas exploration activities in deep-water regions of the world, have allowed us to describe a variety of internal stratigraphic architectures that resemble some geomorphological features observed in the circum–Chryse Planitia region of Mars. For example, erosional shadow remnants that have been described as components of deep-water mass transport deposits in the eastern offshore margin of Trinidad closely resemble teardrop-shaped islands that have been described at the downstream end of outflow channels within the circum–Chryse Planitia region. These observations suggest that the teardrop-shaped islands might have been formed as a result of catastrophic submarine mass movements similar to those documented within continental margins on Earth.

Tsunamigenic Risks Associated with Mass Transport Complexes in Offshore Trinidad and Venezuela

The study area is situated along the obliquely converging boundary of the Caribbean and the South American plates and proximal to the Orinoco delta. Several Plio-Pleistocene-age seafloor destabilization events have been identified in the continental margin of eastern offshore Trinidad. These mass wasting processes are thought to have been of sufficient scale to produce tsunamigenic waves. This work concentrates on the modeling of mass-failure-event-generated tsunami waves in eastern offshore Trinidad. Three different models were generated on the basis of geomorphological characteristics and causal mechanisms of mass transport complexes (MTCs): (1) slope-attached, (2) shelf-attached and (3) detached MTCs. Present-day geologic conditions suggest that detached and slope-attached mass failure events (MFEs) are more likely to occur today. In addition, modeling results indicate that detached MFEs that can occur on the collapsing flanks of mud-volcano ridges represent a higher tsunamigenic risk. These modeling results are a first approach to try to establish a tsunamigenic risk assessment in the region.

Seismic geomorphological analysis and hydrocarbon potential of the Lower Cretaceous Cromer Knoll Group, Heidrun field, Norway

The Heidrun field, located on the Halten Terrace of the mid-Norwegian continental shelf, was one of the first giant oil fields found in the Norwegian Sea. Traditional reservoir intervals in the Heidrun field lie within the Jurassic synrift sequence. Most Norwegian continental shelf fields have been producing from these Jurassic reservoirs for the past 30 yr. Production has since declined in these mature fields, but recently, exploration for new reservoirs has resurged in this region. The Jurassic rifted fault blocks form a narrow continental shelf in Norway, thereby greatly reducing the areal extent for exploration and development within existing fields. As the rift axis is approached farther offshore, these Jurassic reservoirs become very deep, too risky to drill, and uneconomical. This risk has prompted exploration in more recent years of the shallower Cretaceous, postrift stratigraphic succession. Cretaceous turbidites have been found in the Norwegian and North Seas, and the discovery of the Agat field in the Norwegian North Sea confirms the existence of a working petroleum system capable of charging Cretaceous reservoirs. These Cretaceous reservoirs were deposited as slope- and basin-floor fans within a series of underfilled rifted deeps along the Norwegian continental shelf and are thought to be sourced from the localized erosion of Jurassic rifted highs. We use three-dimensional seismic and well data to document the geomorphology of a deep-water, Lower Cretaceous wedge (Cromer Knoll Group) within the hanging wall of a rift-related half graben formed on the Halten Terrace offshore mid-Norway. Seismic attribute extractions taken within this Lower Cretaceous wedge reveal the presence of several lobate to elongated bodies that seem to cascade over fault-bounded terraces associated with rifted structures. These high-amplitude, elongated bodies are interpreted as deep-water sedimentary conduits that are time equivalent to the Cretaceous basin-floor fans in more distal parts of the basin to the west. These half-graben fills have the potential to contain high-quality Cretaceous sandstones that might represent a potential new reservoir interval within the Heidrun field.