Shelf-edge Bank Research Articles

Seasonal Occurrence, Horizontal Movements, and Habitat Use Patterns of Whale Sharks (Rhincodon typus) in the Gulf of Mexico

In the northern Gulf of Mexico (GOM), whale sharks (Rhincodon typus) form large aggregations at continental shelf-edge banks during summer; however, knowledge of movements once they leave aggregation sites is limited. Here we report on the seasonal occurrence of whale sharks in the northern GOM based on over 800 whale shark sightings from 1989 to 2016, as well as the movements of 42 whale sharks tagged with satellite-linked and popup satellite archival transmitting tags from 2008 to 2015. Sightings data were most numerous during summer and fall often with aggregations of individuals reported along the continental shelf break. Most sharks (66%) were tagged during this time at Ewing Bank, a known aggregation site off the coast of Louisiana. Whale shark track duration ranged from three to 366 days and all tagged individuals, which ranged from 4.5 to 12.0 m in total length, remained within the GOM. Sightings data revealed that whale sharks occurred primarily in continental shelf and shelf-edge waters (81%) whereas tag data revealed the sharks primarily inhabited continental slope and open ocean waters (91%) of the GOM. Much of their time spent in open ocean waters was associated with the edge of the Loop Current and associated mesoscale eddies. During cooler months, there was a net movement southward, corresponding with the time of reduced sighting reports. Several sharks migrated to the southwest GOM during fall and winter, suggesting this region could be important overwintering habitat and possibly represents another seasonal aggregation site. The three long-term tracked whale sharks exhibited interannual site fidelity, returning one year later to the vicinity where they were originally tagged. The increased habitat use of north central GOM waters by whale sharks as summer foraging grounds and potential interannual site fidelity to Ewing Bank demonstrate the importance of this region for this species.

Movement patterns and habitat use of tiger sharks (Galeocerdo cuvier) across ontogeny in the Gulf of Mexico.

The tiger shark (Galeocerdo cuvier) is globally distributed with established coastal and open-ocean movement patterns in many portions of its range. While all life stages of tiger sharks are known to occur in the Gulf of Mexico (GoM), variability in habitat use and movement patterns over ontogeny have never been quantified in this large marine ecosystem. To address this data gap we fitted 56 tiger sharks with Smart Position and Temperature transmitting tags between 2010 and 2018 and examined seasonal and spatial distribution patterns across the GoM. Additionally, we analyzed overlap of core habitats (i.e., 50% kernel density estimates) among individuals relative to large benthic features (oil and gas platforms, natural banks, bathymetric breaks). Our analyses revealed significant ontogenetic and seasonal differences in distribution patterns as well as across-shelf (i.e., regional) and sex-linked variability in movement rates. Presumably sub-adult and adult sharks achieved significantly higher movement rates and used off-shelf deeper habitats at greater proportions than juvenile sharks, particularly during the fall and winter seasons. Further, female maximum rate of movement was higher than males when accounting for size. Additionally, we found evidence of core regions encompassing the National Oceanographic and Atmospheric Administration designated Habitat Areas of Particular Concern (i.e., shelf-edge banks) during cooler months, particularly by females, as well as 2,504 oil and gas platforms. These data provide a baseline for future assessments of environmental impacts, such as climate variability or oil spills, on tiger shark movements and distribution in the region. Future research may benefit from combining alternative tracking tools, such as acoustic telemetry and genetic approaches, which can facilitate long-term assessment of the species’ movement dynamics and better elucidate the ecological significance of the core habitats identified here.

Comparative Evolution of Pennsylvanian Platform Margins in Oklahoma and North-Central Texas

Pennsylvanian evolution of the Midland basin's eastern shelf and the northern shelves of the Anadarko and Arkoma basins demonstrates a strongly contrasting pattern with regard to the facies composition and stability of the shelf margin. For the Midland basin a carbonate ramp system developed adjacent to the Eastern shelf during the early Desmoinesian but received no coarse-grained clastic sediment until after the central Fort Worth basin was completely filled by Ouachita orogenic debris in the late Desmoinesian. At that time, a distinct north-south hingeline formed between the shelf and incipient Midland basin that allowed for subsequent vertical accretion of a Missourian-age double bank system. Due to the absence of active deltaic depocenters across the southern two-thirds of the shelf, the Missourian shelf margin did not prograde basinward nor did a submarine fan system develop adjacent to this reciprocal bank complex. Later, during the Virgilian, a single shelf-edge bank and submarine fan complex prograded the shelf edge westward. The shelf edges for the Anadarko and Arkoma basins demonstrate a significantly different pattern. Only during the late Desmoinesian (Marmaton Group) did a shelf-edge bank develop in association with shelf-slope reciprocal sedimentation. For the Anadarko basin, widespread submarine fans, fed from a northeasterlymore » cratonic source, are first seen with Red Fork deposition. Post-Tonkawa cyclic sedimentation prograded the shelf edge southward and gave rise to a more carbonate-dominated shelf sequence. In virtually all instances the regressive submarine fan units indicate eustatic lowstands of sea level.« less

Response of a Passive Continental Margin Carbonate Slope to Closing of a Mesozoic Ocean Basin--Mayhah Formation and Qumayrah Facies of Muti Formation, Oman: ABSTRACT

The Jurassic to Cretaceous Mayhah Formation formed along the passive continental margin slope between the extensive shallow-marine Arabian carbonate platform and the deep-oceanic Hawasina basin (South Tethys Sea). Near Wadi Qumayrah, it is overlain by preorogenic and synorogenic sediments of the Cretaceous Qumayrah facies of the Muti Formation. These strata record the response of the platform margin to Late Cretaceous basin closing. Redeposited Jurassic oolitic calcarenite, megabreccia, and other calcirudite formed an apron along an east-facing platform margin. Redeposited limestone and slump deposits become uncommon upsection, suggesting basinal sedimentation; perhaps this basin developed ramp-like margins along which mass movements were unlikely. A well-documented Tithonian to Early Cretaceous drowning of the platform led to the deposition of bedded chert in this marginal basin. The chert is primarily silicified limestone, indicating a shallower depositional setting (above the CCD) than for equivalent red radiolarian chert at the type locality, Jebel Sumeini. Basinal carbonate sedimentation became reestablished in the post-Valaginian. In the uppermost Mayhah Formation, slump deposits and intraformational breccias indicate steepening of the slope, perhaps due to tectonic downbowing associated with basin closing. Cenomanian to Coniacian chert and siliceous mudstone of the Qumayrah facies formed below the CCD. This could signify tectonically inducedmore » deepening of the ocean basin, upwelling in a relatively narrow ocean basin, and/or shallowing of the CCD. Calcirudite and calciturbidite in the unit were derived from an uplifted shelf edge and local coeval rudist banks. A thick, lenticular synorogenic megabreccia may have been derived from adjacent eroded anticlines.« less

Morphology and Evolution of Mesozoic Carbonate Paleoshelf Edge, Eastern Baltimore Canyon Trough: ABSTRACT

Deep-water petroleum exploration on the US Atlantic continental slope provided information about a Late Jurassic-Early Cretaceous shelf-edge carbonate trend. Well data and seismic interpretation indicate a ridgelike limestone buildup of probably Valanginian age at the crest. One well, penetrating over 1200 ft of this unit, shows that the buildup consists of bioclastic grainstone, packstone, wackestone, rudstone, and possible minor boundstone. Lobate metazoans several centimeters in size may be framework elements. However, more than 80% of this unit is bioclastic debris consisting mostly of coated grains, suggesting that the buildup is dominantly a shelf-edge carbonate debris accumulation. Immediately shoreward, a topographically lower tabular facies, locally 8-10 mi wide, interfingers landward with terrigenous clastics. This back-bank carbonate facies is lithologically, biologically, and genetically similar to the shelf-edge buildup, but appears to be Berriasian-Berjocian. Overlying the back-bank unit, lithologically immature Barremian-Valanginian continental clastic rocks form a seaward-thinning wedge, whose apex meets the top of the shelf-edge carbonate bank. In places, this terrigenous unit may have covered and spilled over the buildup onto the paleoslope during the Barremian and Hauterivian. Unconformably overlying the clastic wedge, an Aptian blanketlike grainstone, packstone, and wackestone unit 200-400 ft thick contains a distinctive biotic assemblage, including calpionellids, tubiphytes,more » and sparse heexactinellids. It is concluded that during the aptian marine regression, the terrigenous clastic unit was beveled by erosion to its present wedge configuration. The blanketlike carbonate unit was deposited on the resulting topographic surface during the subsequent Aptian transgression.« less

Depositional Systems and Shelf-Slope Relations on Cratonic Basin Margin, Uppermost Pennsylvanian of North-Central Texas

The Eastern shelf was a constructional platform developed on the margin of the sediment-starved Midland basin during Late Pennsylvanian and Early Permian times. A mixed terrigenous-carbonate sedimentary province characterized the shelf during most of its history. Sediments were derived from highlands on the east and northeast. Along the outcrop belt in north-central Texas, uppermost Pennsylvanian beds comprise the Harpersville Formation, a boundary-defined rock stratigraphic unit within the Cisco Group. Harpersville facies extend westward into the subsurface 50-60 mi (80-96 km), where they grade into equivalent shelf-margin carbonate and slope terrigenous facies. Preserved relief between the shelf margin and basin floor ranges from 600 to 1,100 ft (180-330 m) with dips ra ging up to 5 degrees. Three component depositional systems, recognized on the basis of gross lithologic composition and position relative to the shelf edges, are the Cisco fluvial-deltaic system, the Sylvester shelf-edge bank system, and the Sweetwater slope system. The Cisco fluvial-deltaic system is composed of fluvial-deltaic facies and associated interdeltaic embayment facies. Eight deltaic lobes have been mapped. The Sweetwater slope system is composed of several slope wedges, or fans, each of which includes shelf-margin, slope-trough, and distal-slope sandstone facies, as well as slope mudstone facies. Terrigenous sediments were transported across the shelf by prograding fluvial-deltaic channels that locally extended through the Sylvester shelf-edge bank system and onto the slope where deposition in he deeper basin constructed submarine fans. The Eastern shelf prograded into the Midland basin through contemporaneous, local upbuilding by fluvial, deltaic, and shelf-edge bank deposition and outbuilding by slope-fan deposition. Sites of shelf construction and outbuilding shifted through time in response to sedimentary and structurally controlled abandonment of major delta lobes. Extrabasinal controls such as eustatic sea-level changes were of secondary importance in developing the depositional fabric of the Harpersville shelf sequence. Petroleum is found in all three depositional systems. Principal productive facies include fluvial, distributary-channel, and distributary-mouth bar sandstones of the fluvial-deltaic system and distal slope and shelf-margin sandstones of the slope system. The complex, lenticular geometry of these thin deltaic sandstones affords maximum opportunity for development of stratigraphic and combination traps. Coal beds, consisting of detrital plant debris, are present within inter-deltaic embayment facies.

Upper Paleozoic Fluvial-Deltaic, Shelf, and Slope Depositional Systems in a Cratonic Basin, West-Central Texas: ABSTRACT

Upper Pennsylvanian and Lower Permian rocks on the eastern flank of the West Texas basin were deposited within fluvial-deltaic, shelf-edge bank, and slope depositional systems. The Cisco fluvial-deltaic system consists of numerous 100- to 200-ft-thick packages of dip-fed facies flanked by strike-fed interdeltaic embayment facies. Fluvial deposits include tabular and belted sandstone bodies characterized by braided and coarse-grained, meander-belt sequences. Fine-grained multistory meander-belt facies exhibiting general fining upward point-bar sequences commonly occur high in the system, pointing to decreasing sediment supply from the Ouachita Mountains and Fort Worth Piedmont. Fluvial channels normally cut subjacent deltaic facies and may lie on rocks of previous depositi nal episodes. Cisco deltaic facies are progradational, coarsening upward prodelta, delta-front, channel-mouth bar, and distributary channel units, and aggradational crevasse splays and delta-plain facies (coal, mudstones, or organic-rich clays); local destructional sandstone bars may fringe the delta. Interdeltaic embayment facies flank delta lobes and include mudstones, sheet sandstones, limestones, and impure detrital coals. Sheet sandstones may reflect strike-fed strandplain accretion or locally reworked delta-front sandstones. The Sylvester shelf-edge bank system occupies a position along the shelf to basin break in paleoslope. The system is composed predominantly of carbonate units that intertongue updip with fluvial-deltaic facies and downdip with slope facies. Individual units range from 100 to 400 ft thick; carbonate facies End_Page 1906------------------------------ thicken upward and basinward because terrigenous sediment supplied to the fluvial-deltaic system diminished. The Sweetwater slope system, studied intensively by W. E. Galloway, is composed of numerous broad, coalescing to restricted wedges of mudstone and sandstone averaging 1,000 ft thick. Slope wedges are bounded by carbonate aprons and the wedges thin upward and basinward in response to decreasing terrigenous sediment supply. Sandstone distribution within slope wedges forms fan-shaped patterns that are elongate perpendicular to shelf edges. Principal slope units include shelf-margin, slope-trough, and distal-slope fan facies. Deposition was sporadic, probably by turbidity currents and associated traction carpets. The slope system was fed by major delta distributaries that prograded to the shelf edge, or by tidal or storm currents that transported sediment through local breaches in the ban system. Destructional processes such as slumping, sliding, and minor canyon development alternated with periods of active slope construction. The eastern flank of the West Texas basin was, therefore, filled by simultaneous upbuilding (fluvial-deltaic and shelf-edge bank deposition) and outbuilding (slope deposition); some slope destructional activity followed episodes of outbuilding. Sites of deltaic and complementary slope deposition shifted widely in response to subtle variations in subsidence and normal avulsion of drainage systems. Fluvial, deltaic, and slope sandstones provide a variety of petroleum reservoirs and stratigraphic traps; early and late compactional and structural traps can be postulated from second-order compactional and structural mapping. End_of_Article - Last_Page 1907------------

Depositional Systems of Cisco Group: Their Relation to Reservoir Distribution and Petroleum Production on Eastern Shelf, Midland Basin: ABSTRACT

The Cisco Group is a mixed terrigenous clastic and carbonate rock stratigraphic unit deposited on the Eastern shelf, a late Paleozoic constructional platform developed on the margin of the sediment-starved Midland basin. Detailed facies mapping of the Harpersville format, a boundary-defined unit within the Cisco Group, outlines 3 depositional systems that are differentiated by gross lithologic composition and position relative to the equivalent shelf edges. They are the (1) Cisco fluvial-deltaic system, (2) Sylvester shelf-edge bank system, and (3) Sweetwater slope system. The Cisco fluvial-deltaic system is composed of dip-fed fluvial and deltaic facies and associated strike-fed interdeltaic embayment facies. The Sylvester shelf-edge bank system consists of an offlapping series of elongated, prismatic limestone banks that lie along the shelf margin. The Sweetwater slope system is composed of numerous slope wedges, or fans, which include shelf-margin, slope-trough, and distal-slope sandstone facies. The eastern shelf prograded into the Midland basin by local upbuilding through fluvial, deltaic, and shelf-edge bank deposition contemporaneous with outbuilding by slope-fan deposition. Oil pools are found in all 3 depositional systems. Productive facies include fluvial, distributary channel, and distributary-mouth bar sandstones of the fluvial-deltaic system and distal-slope and shelf-margin sandstones of the slope system. Production is concentrated in areas where 2 broad, subparallel, structurally-related NE-SW trends intersect the mapped fluvial-deltaic lobes. The complex, lenticular geometry of these thin deltaic sandstones affords maximum opportunity for development of stratigraphic and combination traps. End_of_Article - Last_Page 619------------

Shelf-Edge Submarine Banks in Gulf of Mexico--Their Paleoecology and Biostratigraphy: ABSTRACT

A series of submarine banks along the outer edge of the northern Gulf continental shelf are occupied by reefal foraminiferal assemblages. The majority of specimens at these localities are dead, but a sparse living community is present on the shallowest banks. The reefal assemblages contain many species that have not been reported previously from the Gulf of Mexico, but most are well known from shallow reefs in the Caribbean. Cores recovered from the tops of the banks reveal the paleoecologic and biostratigraphic record of sea level fluctuations during the late Quaternary. The mutual presence of large planktonic and benthonic faunules in the same core samples provides direct means for equating paleobathymetric and paleothermal changes that resulted from glacial-interglacia climatic events. End_of_Article - Last_Page 1902------------

Facies of Cisco-Equivalent Slope Deposition Systems and Their Role in Construction of Eastern Shelf: ABSTRACT

Uppermost Pennsylvanian rocks of the Eastern shelf, a paleogeographic feature of the eastern flank of the Midland basin, consist of 3 depositional systems. (1) The Cisco fluvial-deltaic system extends across the updip part of the shelf and consists of fluvial to deltaic facies flanked by interdeltaic embayment facies. (2) Downdip, along the margin of the shelf, the Sylvester shelf-edge bank system separates relatively flat-lying shelf units from slope deposits. (3) The Sweetwater slope system is composed of numerous broad, coalescing to restricted wedges of sediment 800 to 1,200 ft thick. The terrigenous wedges are bounded by carbonate aprons that extend upslope into the shelf-edge banks. Sandstone distribution within the slope wedges forms fan-shaped maxima that are elon ate perpendicular to the shelf edges and grades from relatively narrow, restricted belts upslope to irregular, broad patches downslope. Principal facies include shelf-margin sandstone, which caps the slope wedges, slope-trough sandstone, which extends through the body of the slope wedge, and distal-slope sandstone. Slope-trough facies include thinly interbedded sandstone and mudstone and medium to thick-bedded, graded sandstone units. Sedimentary structures and textures indicate sporadic deposition, probably by turbidity currents and associated traction carpets, and by subsequent reworking. The slope system was fed from distal parts of the largest delta distributaries that prograded to the shelf edge, or where tidal or storm currents swept sediment through local breaches in the bank system. Sediment moved downslope by gravity transport mechanisms. The Eastern shelf was constructed by both simultaneous upbuilding (fluvial-deltaic and shelf-edge bank deposition) and outbuilding (slope deposition). Sites of deposition shifted widely across the shelf and slope in response to subtle variations in subsidence and consequent abandonment of active delta lobes. Petroleum production is limited to lower slope-trough, distal-slope, and shelf-margin sandstones. The small number of fields in the slope system may be the result of (1) low permeability, characteristic of slope sandstones, (2) updip migration of petroleum through slope sandstone facies into facies of other systems, or (3) insufficient drilling. End_of_Article - Last_Page 153------------

Virgil and Wolfcamp Fluvial, Deltaic, and Inter-Deltaic Embayment Depositional Systems in North and West-Central Texas: ABSTRACT

Virgil and lower Wolfcamp sediments on the Eastern shelf were deposited within 3 depositional systems--Bowie fluvial system, Cisco delta system, and Lake Hubbard interdeltaic embayment system--which are the subjects of this report. Complementary shelf-edge bank, slope, and basin systems, to be discussed by William E. Galloway, complete the facies tract. Bowie fluvial facies compose tabular and belted sandstone bodies characterized by braided and coarse-grained meander-belt sequences and sedimentary structures. Fine-grained meander-belt facies generally becoming finer upward, lateral accretionary point bar deposits, and characteristic sedimentary structures commonly occur high in the Bowie fluvial system, indicating decreasing tectonic activity in source areas. Basal fluvial channel facies normally cut subjacent deltaic facies and may overlie rocks of previous depositional episodes. Cisco deltaic facies are composed of prograding, prodelta mudstones that become coarser upward, delta front, channel-mouth bar and distributary channel sandstones, and aggradational crevasse splay facies, delta-plain mudstones, and coal or organic-rich clays. Local sandstone bars of destructional origin may fringe the delta facies. Lake Hubbard interdeltaic embayment facies flank deltaic lobes and are composed of mudstone, thin extensive sheet sandstone, and thin impure detrital coal. Some sheet sandstones reflect strandplain accretion, but more commonly they are reworked delta-front sands. Deltas prograded rapidly westward across the slowly subsiding Eastern shelf. Sediments from the east supplied crevassing delta lobes until avulsion of over-extended systems occurred. Delta construction, accompanied by deposition of complementary facies within nearby interdelta embayments, restricted open-shelf limestone facies to areas downslope or in areas of abandoned deltas. Channels were cut deeply into subjacent facies as prograding deltas extended fluvial erosion and deposition far across older deltaic facies. Marine processes slowly modified abandoned, compacting, and subsiding deltas. Winnowed sediment was swept into interdeltaic embayment mudflats and strandplains. In the absence of local terrigenous sediment, shelf limestones transgressed upslope and along the coast to coale ce over marsh-stabilized deltaic and interdeltaic areas. All environments could occur simultaneously, shifting with distribution of delta sites to produce repetitive End_Page 151------------------------------ sequences of thin superposed depositional systems. Deposition of fluvial and deltaic facies was rapid; deposition of destructional and transgressive facies represents most of the time consumed by deposition. Depositional systems shifted westward through time as the eastern flank of the basin was filled. End_of_Article - Last_Page 152------------