Mississippi Fan Research Articles

Sequence Stratigraphy, Facies Geometries, and Depositional History of the Mississippi Fan, Gulf of Mexico (1)

The Mississippi Fan is a large, mud-dominated submarine fan over 4 km thick that was deposited in the deep Gulf of Mexico during the late Pliocene and Pleistocene. Analysis of 19000 km of multifold seismic data across the fan defined 17 seismic sequences, each characterized by a series of channel, levee, and associated overbank deposits, along with other mass transport deposits. At the base of nine sequences are a series of seismic facies consisting of mounded, hummocky, chaotic, and subparallel reflections, which constitute 10-20% of the sediments in the sequence. These facies are externally mounded in cross section and occur in two general regions of the fan. In the upper and middle fan, they occur below channels and are elongated in shape, mimicking the channel's distr bution. In the middle to lower fan, they have a fan-shaped distribution, increasing in width downfan. These facies are interpreted to have formed as disorganized slides, debris flows, and turbidites, and are informally called mass transport complexes. Overlying this basal interval and characteristic of all sequences are well-developed channel-levee systems, which constitute 80-90% of the fan's sediments. Channels consist of high-amplitude, subparallel reflections. Levee sediments have subparallel reflections that have moderate to high amplitudes at the base changing upward to low amplitude. The vertical change in amplitude may reflect a decrease in the grain size and bed thickness of the levee sediments. Overbank sediments consist of interbedded subparallel to hummocky and mounded reflections, suggesting both turbidites derived from the channel, as well as slides and debris flows derived from the slope. Pliocene-Pleistocene eustatic cycles are interpreted to have been the major factor controlling the timing and style of sedimentation in the fan. Mass transport complexes are interpreted to have formed during a lowering of sea level, and reflect sediments derived from retrogressive slumping during the formation of submarine canyons in the upper slope and outer shelf. Channel-levee systems were deposited when sea level was near its lowest position and sediment derived from deltas was transported into the deep basin via submarine canyons. During highstands in sea level, a thin layer of hemipelagic sediment was deposited on the fan surface. The Mississippi Fan serves as an exploration model for mud-dominated submarine fans and has four prospective reservoir facies: channel sands with linear trends, unchannelized sands beyond the downdip terminus of the channel (possible lobes), potentially sand-prone levees immediately adjacent to initial channels deposited in some sequences, and limited parts of mass transport complexes.

Sequence Stratigraphy of Mississippi Fan Related to Oxygen Isotope Sea Level Index (1)

The techniques of sequence stratigraphy were applied to the analysis of stratal patterns on seismic data from the Mississippi Fan to outline a method for (1) understanding the processes and growth patterns of modern submarine fans and (2) predicting reservoir and seal for exploration in deep-water settings. We developed a sea level index from the oxygen isotope record for the last 3.5 m.y. tied to limited biostratigraphic control to provide a time framework within which the depositional patterns were analyzed. Analysis of the seismic data reveals that at least thirteen depositional sequences comprise the bulk of the Mississippi Fan section. The base of each sequence is defined by an erosional unconformity in a proximal position that can be traced regionally across the fan complex with its correlative conformity. Seismic facies analysis of individual sequences suggests that the Mississippi Fan is characterized by the cyclic stacking of individual lowstand systems tract deposits consisting dominantly of the lowstand basin-floor and lowstand slope fans. Lowstand slope fans consisting of leveed-channel complexes are volumetrically the greatest component of the Mississippi Fan. Lowstand basin-floor fans commonly are sandy and thin and are associated with the base of each depositional sequence. These fans are characterized by a mounded stratal geometry.

Crustal Types, Distribution of Salt and the Early Evolution of the Gulf of Mexico Basin: ABSTRACT

A new contour map on the top of basement shows the overall configuration of the entire Gulf of Mexico basin. Basement, as used here, is all rocks lying below (older than) the extensive Middle Jurassic (Callovian ) premarine evaporites (Louann Salt, etc.) plus the Late Jurassic oceanic crust in the deep part of the basin. The contour map combined with all other available geophysical data has been used to subdivide the gulf basin into four crustal types: continental, thick transitional, thin transitional, and oceanic crust. The broad region of transitional crust and the basic architecture of the basin shown by the map is believed to have formed mainly during a separate Middle Jurassic period of widespread attenuation of the entire gulf region. The area of thick transitional crust around the periphery of the northern gulf is characterized by broad basement highs and lows with wave lengths of 200-300 km. These features controlled the general distribution and thickness of salt and the overlying Jurassic through Lower Cretaceous rocks. In the area of thin transitional crust Mesozoic basins tend to be assymetrical and generally trend more parallel to the overall basin. The boundary between thin transitional crust and oceanic crust is characterizedmore » by various salt-related features. For example, the northwest and north-central boundaries are defined by two northeast trending salt-cored foldbelts, the Perdido and Mississippi fan foldbelts, respectively. The offset between the two foldbelts may represent a major transform boundary related to the northwest opening of the gulf basin. All these data put important constraints on models for early gulf evolution.« less

Seismic Stratigraphy of the Modern Mississippi Fan Turbidite Systems: ABSTRACT

Seismic Stratigraphy of the Modern Mississippi Fan Turbidite Systems: ABSTRACT

Comparison of GLORIA and SeaMARC I Side-Scan Sonar Images on the Lower Mississippi Fan, Eastern Gulf of Mexico: ABSTRACT

Comparison of GLORIA and SeaMARC I Side-Scan Sonar Images on the Lower Mississippi Fan, Eastern Gulf of Mexico: ABSTRACT

Sequence stratigraphy of the Mississippi fan (Plio-Pleistocene), Gulf of Mexico

The Mississippi Fan is a large, mud-dominated submarine fan over 4 km thick, deposited in the deep Gulf of Mexico during the late Pliocene and Pleistocene. Analysis of 19,000 km of multifold seismic data defined 17 seismic sequences, each characterized by channel, levee, and associated overbank deposits, as well as mass transport deposits. At the base of nine sequences are a series of seismic facies consisting of mounded, hummocky, chaotic, and subparallel reflections, which constitute 10–20% of the sediments in each the sequences. These facies are externally mounded and occur in two general regions of the fan: (1) in the upper and middle fan they are elongate in shape and mimic the channel's distribution; (2) in the middle fan to lower fan they are characterized by a fan-shaped distribution, increasing in width downfan. These facies are interpreted to have formed as disorganized slides, debris flows, and turbidites (informally called “mass transport complexes”).

Influence of relative sea level changes on the construction of the Mississippi Fan

A conceptual sea-level-driven depositional model for individual fanlobes (channel-overbank systems) of the Mississippi Fan does not permit direct application of the sequence stratigraphic principles of Vail and colleagues. Deep Sea Drilling Project Leg 96 results suggest that, during initial relative lowering of sea level, the canyon and upper fan channel were formed; excavated fine-grained slope sediments may have formed a debris flow deposit base for the fanlobe. Continued lowering produced constructional channel-levee-overbank deposits. Rising relative sea level inhibited input of coarse clastics, and channel depressions filled with muds. A blanket of (hemi)pelagics represents relative high sea level stand.

Petroleum Potential of Mississippi Fan: Exploration Analogs to Flex Trend Reservoirs: ABSTRACT

The Mississippi fan is a large mud-dominated submarine fan over 4 km thick that was deposited in the deep Gulf of Mexico during the late Pliocene and Pleistocene. The fan contains deep-water sediments coeval to the Flex Trend turbidite reservoirs deposited in the continental slope to the north. The fan reflects turbidite deposition in an unconfined basin, in contrast to the confined intraslope basins. Analysis of 19,000 km of multifold seismic data across the fan defined 17 seismic sequences, each characterized by a series of channel, levee, and associated overbank deposits and other mass transport deposits. At the base of nine sequences is a series of seismic facies consisting of mounded, hummocky, chaotic, and subparallel reflections which constitute 10-20% of the sediments of each sequence. These facies are externally mounded in cross section and occur in two general regions of the fan. In the upper and middle fan, they occur below channels and are elongate in shape, mimicking the channel's distribution. In the middle to lower fan, they have a fan-shaped distribution, increasing in width downfan. These facies are interpreted to have formed as disorganized slides, debris flows, and turbidites and are informally called mass complexes. The Mississippi fan hasmore » four prospective reservoir intervals and serves as a possible exploration model for Flex trend reservoirs: channel sands with linear trends, unchannelized sands beyond the terminus of the channel downdip that are areally widespread, potentially sandprone levees immediately adjacent to initial channels deposited in some sequences, and limited portions of mass transport complexes. Large structural traps are present where the fan has been deformed by salt and the Mississippi fan foldbelt.« less

Characterization and Depositional History of Muddy Lithotypes, Mississippi Fan: ABSTRACT

Characterization and Depositional History of Muddy Lithotypes, Mississippi Fan: ABSTRACT

Structural Origin and Evolution of Mississippi Fan Foldbelt, Gulf of Mexico: ABSTRACT

Structural Origin and Evolution of Mississippi Fan Foldbelt, Gulf of Mexico: ABSTRACT

Comparison of turbidite facies associations in modern passive-margin Mississippi fan with ancient active-margin fans

Our comparison of the modern passive-margin Mississippi fan (DSDP Leg 96) with ancient active-margin fans (e.g. Eocene Hecho Group, Spain) reveals major differences in turbidite facies associations (Mutti and Ricci Lucchi scheme) and in seismic characteristics in the lower fan area. The lower (outer) Mississippi fan is composed of channel (Facies B and F) and non-channel facies (C? and D), whereas ancient fans are characterized by non-channelized, thickening-upward, depositional lobe facies (C and D). An absence of depositional lobes in the lower Mississippi fan is also suggested by a lack of convex-upward (mounded) seismic reflections with bidirectional downlap. Continuous seismic reflections of the lower Mississippi fan may represent “sheet sands”, but not those of true depositional lobes with mounded character. Extensive channelization in modern passive-margin fans appears to be a product of the lateral shifting of a major sinuous distributary system, developed as a consequence of low gradients and the transport of sediment with a relatively low sand/mud ratio. In contrast, channels in active-margin fans are short and of low sinuosity as a result of high gradients and the transport of sediment with a relatively high sand/mud ratio. The turbidite facies association scheme, which was developed exclusively from ancient active-margin fans, should be applied to mature passive-margin fans with qualifications because of the differences in spatial distribution of turbidite facies and their associations.

Distribution and seismic facies of Mississippi fan channels

Analysis of a closely spaced grid of multifold seismic data across the upper Pliocene-Pleistocene Mississippi fan in the deep Gulf of Mexico allows for the first time a detailed description of a large part of the fan. Mapping of the 17 channel-levee systems show considerable variability in parameters such as size, location, geometry, lateral migration, aggradation, sinuosity, and downfan bifurcation, which suggests that multiple factors control channel evolution. The youngest channel, cored during Deep Sea Drilling Project Leg 96, refects only style in channel evolution. Such complexity in large, mud-dominated, submarine fan systems must be considered in evaluating fan models and interpreting ancient fan systems.

Morphology of Florida Escarpment Chemosynthetic Brine Seep Community Sites: Deep-Tow, Seabeam, and GLORIA Surveys: ABSTRACT

The Florida Escarpment near 26/degree/N was surveyed with Deep-Tow, Seabeam, and GLORIA in the area where chemosynthetic communities were discovered via ALVIN in the abyssal Gulf of Mexico. Seabeam bathymetry and GLORIA images indicate that the escarpment is a generally straight cliff with average slopes of about 45/degree/ from 2200 to more than 3250 m. The escarpment's face is cut by 2-km wide box canyons whose head walls are as steep as the intervening escarpment's face. The shapes of these canyons are difficult to explain with the traditional models of canyon formation. Sidescan sonar images and bottom photographs reveal that the escarpment's face is composed of a series of long, straight bedding-plain terraces which are truncated along nearly vertical orthogonal joints. Exposure of these truncated strata indicate the face of the escarpment is eroded. The contact between the basal escarpment and the flat-lying abyssal hemipelagic sediments is abrupt. Basal talus is uncommon because the abyssal floor is part of the distal Mississippi fan which is rapidly burying the escarpment. However, where talus occurs, it is in tongues of angular megabreccia of meter- and larger-sized blocks which indicate periodic catastrophic collapse. Sidescan images reveal bands of contrast in the reflective texturemore » of the sea floor that extends 10-20 m from the base along more than 10% of the surveyed area. Photographic surveys show that these areas are associated with communities of abundant organisms. Apparently chemosynthetic communities line extensive sections of the escarpment base where reduced brines seep out into the sea floor. The morphology suggests joints and deep seeps are controlling factors in scarp retreat.« less

Comparison of Modern Mississippi Fan with Selected Ancient Fans: ABSTRACT

Comparison of Modern Mississippi Fan with Selected Ancient Fans: ABSTRACT

Neogene-Holocene Mixed Carbonate-Siliciclastic Deposition in Eastern Gulf of Mexico with Earlier Analogs: ABSTRACT

The Neogene to Holocene history of the eastern Gulf of Mexico reveals a complex interplay between carbonate and siliciclastic sedimentation that may help interpret and explain many ancient deposits. Well data from the Florida Panhandle have been correlated with over 1,900 mi of high-resolution seismic reflection profiles collected on a 2-mi grid as part of a major geophysical program sponsored by GECO Geophysical Company, Inc. Data show a shift from flat carbonate sequences to prograding sequences about a major Neogene unconformity. Below that unconformity, carbonate sedimentation was dominant; afterward sediments became progressively more siliciclastic, grading into the Apalachicola delta and a surficial quartz sand sheet. The quartz sand grades laterally into the west Florida carbonate margin, bounded on the east by fine quartz sand beaches and terrace deposits of the Florida peninsula and on the west by the massive siliciclastic Mississippi fan. Siliciclastic sediments must have advanced and retreated across the carbonate shelf with sea level rise and fall. DSDP Leg 9 cores and seismic profiles suggest that, periodically, portions of the west Florida and probably Yucatan margins have failed, injecting massive carbonate gravity deposits into the deep Gulf of Mexico. These deposits have become intercalated into the Mississippi fan.more » Examples of quartz sandfilled channels in carbonate rocks and carbonate gravity deposits within siliciclastic (e.g., south Pyrenean basin and some deposits of the Permian basin) are found in the ancient record where they provide excellent isochronous marker beds as well as good potential reservoirs for hydrocarbons.« less

Hydrocarbons in Mississippi Fan and intraslope basin sediments

Aliphatic and aromatic hydrocarbons in sediments of the middle and lower Mississippi Fan and two intraslope basins in the Gulf of Mexico are derived from terrestrial organic matter and thermogenic, mature hydrocarbons. The terrestrial hydrocarbon component consists primarily of terrigenous, plant biowaxes ( n-alkanes with 21 to 33 carbons). The occurrence of thermogenic hydrocarbons in immature near-surface sediments, their molecular distributions and concentration variations with depth suggest that the majority of these mature hydrocarbons have migrated from a source much deeper in the sediment column. A portion of the thermogenic hydrocarbons may be derived from recycled material and includes phenanthrene, methyl phenanthrenes, chrysene and benzopyrenes. The migrated, thermogenic hydrocarbons include normal and isoprenoid alkanes with less than 21 carbons, naphthalene, methyl naphthalenes, ethyl naphthalenes and other aromatics of similar volatility ( i.e., biphenyl, acenaphthene and fluorene). Triterpane, sterane and aromatized sterane distributions suggest that the thermogenic hydrocarbons at both sites have a common source and are overprinted with immature sediment hydrocarbons. The biomarker distributions and carbon isotopic compositions of the thermogenic hydrocarbons are atypical for petroleum produced in the Gulf of Mexico. Molecular distributions of the hydrocarbons are constant, regardless of the present depth of occurrence, suggesting that they have migrated in a separate phase. The upward migration of hydrocarbons from deeper sources is a wide-spread phenomenon in the Gulf of Mexico with several documented cases of massive seepage (visible oil) as well as the more diffuse permeation of Pleistocene sediments of the Mississippi Fan and two intraslopes reported here.

Deepwater Fans

Technology Today Series articles provide useful summary informationon both classic and emerging concepts in petroleum engineering. Purpose: To provide the general reader with a basic understanding of a significantconcept, technique, or development within a specific area of technology. An increasing share of the world's oil and Las reserves is being found indeepwater fans that contain an accumulation of turbidite deposits. These fansoccur in two major locales: off mountainous, coastal, tectonically active areaswith steep slopes and off major deltas with gentler but unstable slopes (seeFig. 1). They may also occur in lakes, such as Lake Geneva. Most submarine fansare believed to be derived from sediments and debris laid down at or near anincrease in slope. These sediments are unstable. and their movement may betriggered during earthquakes, storms, or floods, causing them to move suddenlyto deeper waters. These dense masses of sediments flow down the basin slope andalong the ocean floors in turbidity currents that cut gullies and channels intoexisting deposits and that subsequently fan out on the gently sloping basinfloor, where they come to rest. Later, as currents in the basin return to thenormal slow fallout of finer particles, increasing amounts of clays are laiddown particles, increasing amounts of clays are laid down over the turbiditesto seal the deposit. Fan deposits can be observed and mapped from (good-quality seismic data. Although individual turbidite flows are usually thinner than can be resolved byseismic reflections, it is generally possible to map the internal reflectionpattern and to possible to map the internal reflection pattern and to definedepositional lobes. Such a detailed analysis may be important in the earlyevaluation of the field and in platform location. Log correlation within thefan complex is difficult: consequently, every effort should be made to obtainhigh-resolution seismic data in a grid of very closely spaced lines to definethe internal geometry of the fan. Three-dimensional surveys may be justifiedbecause of the need to migrate steep depositional dips. Our seismic example (Fig. 2) is the large Frigg field in the north-centralNorth Sea. Gas is in reservoirs of Eocene quartz sands, and the fan is veryquartz-rich. The most probable source of sediments for the fan lies to thewest, many miles away. Lateral continuity of the individual turbidite beds orchannels deposited during a single cycle may range from a few hundred tothousands of feet along the channels and hundreds of feet across their widths. Some fans are composed of many lateral and vertical sequences of turbidite bedsor channels and may cover very large areas. For example, the Mississippi fan inthe Gulf of Mexico covers 300 000 km2 [115,830 sq miles]. Vertical continuity. between beds on a fan is usually extremely poor because of the lenticulargeometry, of the sands and the continuity of the intervening silt/clay beds. The idealized vertical sequence of a single turbidite flow in Fig. 3 showsclean gravel and coarser sand at the base, sand laminated by silt or clay inthe upper part, and a thicker layer of silt or clay at the top. Gamma ray logresponses of sequences of beds are shown in Fig. 4 for the channels and for thedistal edges of the fans. The pay in the channels typically appears as blockyin clean sands or bell-shaped as the shale content increases upward. Individuallaminae of shales are usually too thin to be seen on the logs. P. 402

Sedimentological significance of strain and sonic velocity anisotropy in fine-grained turbiditic and hemipelagic deep-sea sediments — An example from the Mississippi Fan

In visually homogeneous and compositionally similar argillaceous sediment of the Mississippi Fan, depositional processes (turbiditic versus hemipelagic sedimentation) are reflected in the anisotropy of strain as well as in sonic velocity. The correspondence between the mode of deposition and anisotropy was observed in single beds as well as in entire depositional sequences. In single beds, the turbiditic part (as opposed to the pelagic portion) is characterized by an anisotropy within bedding and a comparatively low anisotropy between vertical and horizontal directions; as current influence decreases, anisotropy within bedding disappears, while anisotropy in vertical versus horizontal directions increases. Because of rapid sedimentation, the sediments are not influenced by bioturbation that would distort the primary fabric. In depositional sequences, the anisotropy pattern depends on the type of sequence; in fining-upward sequences, anisotropy in vertical versus horizontal directions increases upsection and anisotropy within bedding is less frequent. This pattern is explained by the decreasing influence of turbidity currents on sediment fabric and an increasing proportion of quietly accumulated, hemipelagic deposits. In coarsening-upward sequences the inverse trends are found. The general correspondence between trends in lithology and anisotropy only documents relative changes in the predominant depositional process within a specific fan sub-environment. On an absolute scale, values of both types of anisotropy differ from site to site; a clear pattern within the fan is found. Thus, anisotropy determinations provide useful supplementary information for interpreting fan environments. Compaction generally leads to an increasing anisotropy, but the relative differences in anisotropy between turbiditic and hemipelagic sediments are not significantly affected.

Seismic Stratigraphic Comparison of DSDP Leg 96 Results with Older Mississippi Fan Lobes, Gulf of Mexico: ABSTRACT

DSDP Leg 96 drilled the youngest depositional lobe of the Mississippi fan at nine sites. These sites were designed to provide a set of reference cores to help explain the development of Quaternary and older submarine fans. The youngest fan lobe is dominated by a single, sinuous aggradational channel system, characterized by high-amplitude reflections that represent channel-lag gravels and sands, while adjacent laterally continuous reflections correspond to fine-grained overbank sediments. Analysis of 12,000 km of multifold seismic data from the Mississippi fan provides a method for comparing the drilling results with the seismic stratigraphy of the nine older Mississippi fan lobes. Sinuous channels and associated facies are present in all older lobes in the middle fan area, although there is a greater diversity in channel/overbank distribution and interpreted depositional processes. For example, four of the lobes have several coeval channels that are fed by separate submarine canyons in the slope, and a bifurcating channel pattern caused by channel avulsion is present in six different lobes along the middle and lower fan. In addition, an important seismic facies consisting of mounded, hummocky, and chaotic reflections is present at the base of six older lobes. This facies is more areally restricted thanmore » the overlying, well-developed channel/overbank deposits and is interpreted to represent coarse-grained channel sediments deposited during lowering sea level. Although Leg 96 drilling provides sedimentologic information that can be used for comparison with other fans, this seismic stratigraphic study of the entire Mississippi fan suggests that additional processes were operating that were not explained by the drilling results.« less

Hydrocarbons in Mississippi Fan and intraslope basin sediments : Kennicutt, M.C. II, G.J. Denoux, J.M. Brooks and W.A. Sandberg, 1987. Geochim. cosmochim. Acta, 51(6):1457–1466

Hydrocarbons in Mississippi Fan and intraslope basin sediments : Kennicutt, M.C. II, G.J. Denoux, J.M. Brooks and W.A. Sandberg, 1987. Geochim. cosmochim. Acta, 51(6):1457–1466