Mississippi Fan Research Articles

Sand wave fields beneath the Loop Current, Gulf of Mexico: reworking of fan sands

Extensive fields of large barchan-like sand waves and longitudinal sand ribbons have been mapped by deep-towed SeaMARC IA sidescan sonar on part of the middle and lower Mississippi Fan that lies in about 3200 m of water. The area is beneath the strongly flowing Loop Current. The bedforms have not been adequately sampled but probably consist of winnowed siliciclastic-foraminiferal sands. The size (about 200 m from wingtip to wingtip) and shape of the large barchans is consistent with a previously observed peak current speed of 30 cm/s, measured 25 m above the seabed. The types of small-scale bedforms and the scoured surfaces of chemical crusts, seen on nearby bottom photographs, indicate that near-bed currents in excess of 30 cm/s may sometimes occur. At the time of the survey the sand transport direction was to the northwest, in the opposite direction to the Loop Current but consistent with there being a deep boundary current along the foot of the Florida Escarpment. Some reworking of the underlying sandy turbidites and debris flow deposits is apparent on the sidescan sonar records. Reworking by deep-sea currents, resulting in erosion and in deposits characterised by coarsening upwards structures and cross-bedding, is a process that has been proposed for sand found in cores in shallower parts of the Gulf of Mexico. This process is more widespread than hitherto supposed.

Submarine landslides: advances and challenges

Due to the recent development of well-integrated surveying techniques of the sea floor, significant improvements were achieved in mapping and describing the morphology and architecture of submarine mass movements. Except for the occurrence of turbidity currents, the aquatic environment (marine and fresh water) experiences the same type of mass failure as that found on land. Submarine mass movements, however, can have run-out distances in excess of 100 km, so their impact on any offshore activity needs to be integrated over a wide area. This great mobility of submarine mass movements is still not very well understood, particularly for cases like the far-reaching debris flows mapped on the Mississippi Fan and the large submarine rock avalanches found around many volcanic islands. A major challenge ahead is the integration of mass movement mechanics in an appropriate evaluation of the hazard so that proper risk assessment methodologies can be developed and implemented for various human activities offshore, including the development of natural resources and the establishment of reliable communication corridors.Key words: submarine slides, hazards, risk assessment, morphology, mobility, tsunami.

ABSTRACT: High Resolution, 3-D Seismic Interpretation of a Late Pleistocene Mississippi Fan Channel, Northern Deep Gulf of Mexico

ABSTRACT: High Resolution, 3-D Seismic Interpretation of a Late Pleistocene Mississippi Fan Channel, Northern Deep Gulf of Mexico

Structural models of faulted detachment folds

Faulted detachment folds represent a common structural style in several hydrocarbon-producing fold and thrust belts, including the Zagros, Idaho-Wyoming-Utah, Carpathian, and Albanide belts, and several deep-water fold belts, including the Mississippi Fan and Per dido belts. These structures form in units with high competency contrasts and display a transition in deformational behavior from detachment folding to progressive fault propagation with increasing shortening. The structures first form by symmetric or asymmetric detachment folding, with the fold wavelength controlled by the thickness of the dominant units. Volumetric constraints require the movement of material from the synclines to the anticlines. Contin ued shortening results in tighter folds, with limb rotation by hinge migration, limb segment rotation, and internal shear. Rotation of limb segments between locked hinges results in thrust faults, which propagate through deformation zones on the frontlimb and possibly the backlimb. The faults may terminate both up and down section within brittle or ductile deformation zones. Eventually, a through going fault connects one of the major faults with the basal detach ment. Variations in the structural geometry are related to the rela tive thickness and competency of the units and the mechanisms of deformation. Because faulted detachment folds superficially resem ble fault-propagation folds, their geometry can be misinterpreted in areas of poor data quality. Characteristic features for distinguish ing these structures include (1) smaller variations in anticlinal length during fold evolution, (2) a more open and rounded fold geometry, (3) complex and nonuniform variations in fault slip, (4) a significant variation in deformational behavior among different units, and (5) fold-fault relationships indicating transition from folding to faulting, such as footwall synclines and decapitated fold geometries.

Gas hydrate and crude oil from the Mississippi Fan Foldbelt, downdip Gulf of Mexico Salt Basin: significance to petroleum system

Structure II gas hydrate, methane–ethane hydrate, and crude oil occur on the sea floor at ∼1920–1930 m water depth in Atwater Valley (AT) Block 425, near the juncture of the lower slope of the Gulf of Mexico Salt Basin and the abyssal plain. The site is in the eastern Mississippi Fan Foldbelt (MFF), a distinct structural province at the downdip limit of the Gulf of Mexico Salt Basin. The presence of thermogenic hydrocarbons confirms an active petroleum system in the deep eastern MFF. The hydrate-bound C2–C5 hydrocarbon gases of the MFF are isotopically distinct when compared to other gases from the upper and middle slope, being strongly depleted in 13C. The biomarkers (m/z=191 and 217) of oil inclusions from AT 425 gas hydrate are also distinct when compared to oils of the upper Gulf slope and the Smackover Trend. Biomarkers of AT 425 oil are consistent with a marine source rock deposited in an area of strong siliciclastic influx, with possible higher plant organic matter. The presence of a shale or mudstone source rock at the downdip limit of the Gulf raises new questions as to paleogeography during source rock deposition. Emergent highlands immediately to the south and east of the downdip limit of the Gulf of Mexico Salt Basin during the Mesozoic may explain the occurrence of the shale or mudstone source rock that gave rise to the gas and oil at AT 425.

ABSTRACT: Stratigraphic Studies Associated With The Ultradeepwater Play, Mississippi Fan Foldbelt, Gulf Of Mexico

ABSTRACT: Stratigraphic Studies Associated With The Ultradeepwater Play, Mississippi Fan Foldbelt, Gulf Of Mexico

ABSTRACT: Characterization, Origins, and Petroleum Potential of High-Amplitude Reflection Packets, HARPs, on the Middle and Lower Mississippi Fan

ABSTRACT: Characterization, Origins, and Petroleum Potential of High-Amplitude Reflection Packets, HARPs, on the Middle and Lower Mississippi Fan

ABSTRACT: Geologic Overview of the NE Mississippi Fan and Shelf to West Florida Terrace Region, Offshore Gulf of Mexico

Abstract This study is based on the joint venture (Schlumberger and TGS NOPEC) Phase 46, 16,000-line-mile 2D seismic and gravity/magnetic program that was acquired, processed, and interpreted from 1997-1999. It consists of a 2 2 mile grid (16,100 mi2), covering parts of Main Pass, Destin Dome, Viosca Knoll, Mississippi Canyon, Desoto Canyon, Atwater Valley, and Lloyd Ridge. Water depths range from 75 feet to over 10000 feet. Geological control from 44 biostratigraphy wells helped calibrate seven mapped horizons. In addition, a velocity cube was generated from this dataset. A Cretaceous carbonate shelf, a prominent escarpment to the southeast, dominates the east and northeast portions of the survey. It is overlain by primarily regressive Cenozoic clastics. West of the carbonate shelf is a Miocene to Plio-Pleistocene shelf /slope/fan complex. The shelf facies is developed in the northwest and progresses through slope to deepwater fan deposits toward the southeast. This complex contains numerous allochthonous salt bodies. In general, autochthonous salt structures are present east of the detached salt, underlying the slope fan complex. These continue eastward to the Cretaceous shelf edge. This region is becoming an increasingly attractive area to explore. For example, Crazy Horse in Mississippi Canyon (MC) Block 778 is a recent subsalt discovery within the study area.

Abstract: Significance of gas hydrates and oil seeps to Mississippi Fan Foldbelt Petroleum System

Abstract: Significance of gas hydrates and oil seeps to Mississippi Fan Foldbelt Petroleum System

Abstract: Into the Unknown, A History of the Discovery of the Giant Fields of the Western Mississippi Fan Foldbelt, Gulf of Mexico

ver the last 15 years, several giant petroleum accumulations have been discovered in the Mississippi Fan foldbelt, deep- water Gulf of Mexico. In the mid 1980s, initial work was driven by interest in the nature of sections at the edge of, and immedi- ately inboard of, the Sigsbee Escarpment. Outboard and counter-regional dip beneath an allochthonous salt canopy was recognized in early speculative 2D seismic transects.

Abstract: Calibration of Seismic Facies and influence of the Sigsbee Salt Canopy on Deposition of the Late Pleistocene Mississippi Fan, Deepwater Gulf of Mexico 

Abstract: Calibration of Seismic Facies and influence of the Sigsbee Salt Canopy on Deposition of the Late Pleistocene Mississippi Fan, Deepwater Gulf of Mexico 

Abstract: Tectonic Evolution and Mechanism of Folding of Mississippi Fan-Fold Belt System, Eastern Gulf of Mexico 

ABSTRACT Depth converted structural models constrained by 3-D seismic, gravity-magnetic and paleontological data over Atwater Valley and Mississippi Canyon protraction areas are used to address the tectonic evolution and mechanism of formation of the Eastern Mississippi Fan Fold Belt (EMFFB). The EMFFB is defined by a series of ENE-WSW trending salt cored detachment and break-thrust fold structures. The pronounced ENE-WSW linear strike orientation suggests interference with deeper basement fabric related to the rift stage opening of the Gulf of Mexico basin. The structural evolution of the EMFFB involves a complex interplay of basement geometry, salt tectonism, gravity gliding and gravity spreading related to the following four-stage evolution of the eastern Gulf of Mexico. 1) late Triassic-early Cretaceous rift phase, 2) mid-late Jurassic salt deposition, 3) Cretaceous-Oligocene early salt tectonism and gravity gliding, 4) mid Miocene-Pliocene silici-clastic progradation, gravity spreading, and formation of the EMFFB. Timing and mechanism of formation of the EMFFB has been addressed using palinspatically restored GeoSec depth sections, graphic correlation data, and growth strats relationships within and updip of the EMFFB. The EMFFB structures were triggered by gravity spreading, that resulted in adjustment of a 'super critical wedge' which slipped forward along a salt-basement decollement. This created the frontal EMFFB by basin inversion over pre-existing basement normal faults that acted as buttresses to the sliding wedge End_of_Record - Last_Page 2-------

Abstract: Dynamic Response of Deepwater Depositional Systems to Growth of the Mississippi Fan Fold Belt, Gulf of Mexico 

Abstract: Dynamic Response of Deepwater Depositional Systems to Growth of the Mississippi Fan Fold Belt, Gulf of Mexico 

Abstract: Late Miocene Mississippi Fan Fold Belt Effect on Deepwater Deposition in the Atwater Valley Area 

Abstract: Late Miocene Mississippi Fan Fold Belt Effect on Deepwater Deposition in the Atwater Valley Area 

Abstract: Comparison of the Mississippi Fan and Perdido Deepwater, Salt-cored Fold Belts, Northern Gulf of Mexico

Abstract: Comparison of the Mississippi Fan and Perdido Deepwater, Salt-cored Fold Belts, Northern Gulf of Mexico

Sequence Stratigraphy and Depositional History of the Eastern Mississippi Fan (Pleistocene), Northeastern Deep Gulf of Mexico

The eastern Mississippi Fan is a moderate-size, mud-dominated, Pleistocene submarine fan in the northeastern deep Gulf of Mexico. Analysis of 6900 km of multifold seismic data identified eight discrete depositional sequences interpreted to be coeval to the younger sequences in the western Mississippi Fan. All sequences consist of channel-levee deposits and slides. Channel-fill deposits are characterized by high-amplitude subparallel reflections, and levee-overbank deposits are characterized by interbedded subparallel to hummocky and mounded reflections. All sequences are affected by a series of volumetrically and areally large submarine slides, that are characterized by hummocky to chaotic reflections. Individual slides are up to 5000 km2 in area. The channel-levee systems within six of the sequences are derived from sediment sources located northwest in the Mississippi Canyon lease area. The channel-levee systems within the remaining two sequences are downfan continuations of systems in the western Mississippi Fan. These changing positions of the channels presumably reflect changes in the position of the shallow-marine depocenter that fed the fan throughout the Pleistocene. The eastern Mississippi Fan can serve as an exploration analog for mud-dominated turbidite systems with similar seismic facies and geometries. The fan has four potential reservoir facies: channel-fill sediments with sinuous to linear trends, thin-bedded sands in levee-overbank sediments, sheet sands deposited at the terminus of channels, and one possible basin-floor fan. Channel valley width/thickness ratio values range from 2.9 to 13/1 upfan to 2.9 to 8.8/1 downfan.

Three-dimensional geometry and evolution of a segmented detachment fold, Mississippi Fan foldbelt, Gulf of Mexico

The frontal fold of the deep-water Mississippi Fan foldbelt is used to investigate the relationships between folding and faulting in detachment folds. Seismic coverage shows the entire three-dimensional geometry, from termination to termination, and the deformation history as recorded by asymmetric growth strata on fold limbs. The fold is a salt-cored detachment fold cut by reverse faults on both limbs. Its three-dimensional geometry is complex, consisting of four separate culminations, each associated with a distinct fault or fault segment. Consequently, profile geometries vary significantly, but unsystematically, along strike. Data analysis and structural restoration suggest a three-stage evolution during Mio-Pliocene shortening: (1) preexisting, en-echelon salt pillows served as buckling instabilities for the initiation of detachment folds that experienced relatively minor lateral propagation during growth and linkage; (2) an increase in shortening rate was accommodated by break-thrust folding; and (3) the faults became inactive upon a decrease in shortening rate, such that further fold amplification occurred by rotation and uplift of the backlimb. There is a direct correlation between fold and fault geometries, and abundant evidence indicates that the geometries of individual fold segments dictated fault geometries.

Sediment Mass-Flow Processes on a Depositional Lobe, Outer Mississippi Fan

ABSTRACT SeaMARC 1A sidescan-sonar imagery and cores from the distal reaches of a depositional lobe on the Mississippi Fan show that channelized mass flow was the dominant mechanism for transport of silt and sand during the formation of this part of the fan. Sediments in these flows were rapidly deposited once outside of their confining channels. The depositional lobe is formed of a series of long, narrow sublobes composed of thin-bedded turbidites (normally graded siliciclastic sand and silt, 20 cm thick on average), debris-flow deposits (soft clay clasts up to 5 cm in diameter in a siliciclastic silt matrix, 48 cm thick on average), and background-sedimentation hemipelagic muds. The mass flows most likely originated from slope failure at the head of the Mississippi Canyon or on the outer ontinental shelf and flowed approximately 500 km to the distal reaches of the fan, with debris flow being the dominant flow type. An analysis that uses the geometry of the confining channels and strength properties of the debris-flow material shows that these thin debris flows could have traveled hundreds of kilometers on extremely small sea-floor slopes at low velocities if the flowing medium behaved as Bingham fluids and were steady-state phenomena.

Architectural Characteristics of Fine-Grained Submarine Fans: A Model Applicable to the Gulf of Mexico: ABSTRACT

ABSTRACT Submarine fan deposits in the Gulf of Mexico and in many areas of the Atlantic Ocean fall into the category of fine-grained, low overall sand/shale ratio basin-floor fans. Models published over the years that have been applied to either exploration or development are primarily based on sand-rich fans, most of which were deposited in active margin settings and are not applicable to the areas mentioned above. Observations from the excellent outcrops of the Permian Tanqua Karoo in the southwestern part of the Karoo Basin, South Africa, the Jackfork Formation (Pennsylvanian) in Arkansas, and the Deep Sea Drilling Project Leg 96 on the Mississippi Fan make it possible to construct a macro-scale model that addresses the architecture of both the macro- and meso-scale depositional features of fine-grained submarine fans deposited in generally unconfined settings. At the entrance to the basin floor in the base-of-slope area, the large conduit that was initially carved out across the basin slope, may start to widen. Most of the high- and low-density flows moving from the submarine canyon in the upslope area through the conduit (fan valley or upper fan channel), will be too small to occupy the entire width of the lower part of the conduit. The result is a complex build-up of channel fills incised into each other, forming amalgamated sandstone bodies interbedded with remnants of shale-rich levee-overbank deposits. Once in the basin proper the degree of erosion of flows will be reduced and channel-levee complexes result. The channel fills are primarily amalgamated sandstones whereas the levee-overbank deposits are often thin-bedded, low-contrast, low-resistivity sandstones with high porosity and permeability. The interbedded shales reduce vertical conductivity of fluids but proper production techniques make these deposits potentially very productive. The channels gradually become smaller and loose their influence to govern the direction of the head of density flows. A gradual widening of the deposits results, known as sheet sands or depositional lobes. They have high sand/shale ratios and the overall sheet sand deposition suggests lateral switching resulting from seafloor compensation rather than frequent channel progradation.

A coarse grained turbidite system with morphotectonic control (Middle Albian, Ondarroa, northern Iberia)

ABSTRACTThe Middle Albian Ondarroa turbidite system is a coarse grained, deep water unit which outcrops in the north‐eastern part of the Basque‐Cantabrian region, west of the Pyrenees. It is about 18 km long and 7 km wide, and shows an unusual ‘L’shape resulting from both a direct morphotectonic confinement and the presence of nearby shallow water carbonate buildups.Eight main facies have been distinguished within this turbidite system: (1) clast‐supported conglomerates; (2) mud‐supported conglomerates; (3) slump deposits; (4) normally graded pebbly sandstones; (5) cross stratified sandstones; (6) interbedded graded sandstones and mudstones; (7) interbedded non‐graded sandstones and mudstones: and (8) mudstones. Inner system, middle system, outer system and basin plain divisions have been distinguished. The inner turbidite system is characterized by stacked channel fill conglomerates and lesser sandy turbidites and mudstones. The middle system consists of sandy and conglomeratic fining upwards sequences, normally several metres thick. The outer system has alternating non‐channellized sandstones and mudstones, without any predictable vertical arrangement. The basin plain is characterized by mudstone‐siltstone laminations and lesser, randomly occurring thin bedded sandy turbidites.Three main channel fills make up the inner turbidite system. Although all of them can be compared with the valley channel fills of the modern Mississippi Fan, and thus their bases can be interpreted as sequence boundaries, only the lowermost and the uppermost channel bases are documented as allocyclic boundaries. The Ondarroa turbidite system was deposited in an immature passive margin subjected to transtensional movements. It filled a composite pull apart depression with coarse clastics derived from a narrow platform to the north of the present outcrops which was invaded by fan deltas. A major pattern of sinistral strike‐slip faulting linked to the opening of the Bay of Biscay is invoked to explain the Ondarroa turbidite system appearance and its tectonic confinement.