Abstract The Oxfordian Smackover Formation is generally acknowledged to be a hydrocarbon source for numerous reservoirs in the Gulf of Mexico, both onshore and offshore. More than 25 wells in the eastern Gulf of Mexico have penetrated the Smackover since 2003. Offshore, the Smackover consists predominantly of limestone and shale containing thin organic layers. Immediately above the lower Smackover is a widespread shale marker. This thin shale is correlated as the base of the upper Smackover Formation, which consists of interbedded shale and limestone. This study will demonstrate that the lower Smackover Formation in the eastern Gulf of Mexico (Mississippi Canyon and De Soto Canyon offshore areas) is composed of a series of seven units that occur in the same sequence in virtually every well in which the lower Smackover has been encountered. Although the seven individual units can be resolved readily with the proper wireline suite, each has a sub-seismic thickness. The overall thickness of the lower Smackover is about 300 +/-100 feet. Unlike the lower Smackover, the surrounding Mesozoic formations, from Cotton Valley to Norphlet, vary greatly in thickness in the eastern Gulf. The initial correlations of the units in the lower Smackover were made by comparing the gamma ray, resistivity, and density log patterns with the computed mineralogy of Elemental Capture Spectroscopy (ECS) wireline logs. It was immediately obvious that the same sequence of beds/units was present in the lower Smackover in well after well. Within the lower Smackover Formation is a conspicuous zone characterized by iron-bearing minerals having a matrix density in excess of 3.0 g/cm 3 throughout. However, X-Ray Diffraction (XRD) data from rotary sidewall cores was necessary to validate the mineralogy. Because the mineralogy of the ECS log is a model-based calculation from the elemental concentrations of iron, calcium, aluminum, etc,. rather than a direct measurement, the modeled mineralogy can be inaccurate as was the case in the bottom two units. Mineralogy of the seven units has been verified by XRD analyses, albeit from a limited number of rotary sidewall cores obtained in only five wells. The top three units are limestones which vary in carbonate, clay, and pyrite content. The fourth and fifth units contain significant amounts of high density minerals, particularly siderite and pyrite. The sixth zone is dominated by anhydrite. The seventh unit is a hematite-rich shale and its base is an unconformity. Although wireline data are plentiful, analysis of the seven units within the lower Smackover is hampered by the limited amount of rock data and the complete lack of whole core. Many depositional and geochemical questions suggested by the unusual mineralogy and sequence of beds remain unanswered.

Abstract A biostratigraphical review of eight exploration boreholes located within the De Soto Canyon protraction area in the Gulf of Mexico yields a repeatable and predictive evolutionary and paleoecological sequence with implications to paleogeography. The Oxfordian section within these boreholes contains primitive planktic foraminifera such as Globuligerina oxfordiana. Near the end of the Kimmeridgian (or slightly above the nannofossil Calcivascularis cassidyi extinction), nannofossils are of low abundance, and dominated by Cyclagelosphaera spp. Weakly developed benthic foraminifera abundance gives rise to Reinholdella A which is coincident with a nannofossil dominance switch to Polycostella spp. Planktic foraminifera are not observed in this section In the overlying section, the extinction of nanno-fossil genus Polycostella , the origination and dominance of Nannoconus , and minute benthic foraminifera gradually increase. Here, the suggested datum, Polycostella beckmanii extinction, is observed consistently higher than the Reinholdella A extinction in the early Tithonian. The fossil assemblage change through this section suggests a change in water masses, which has implications to major reorganization in oceanic circulation. The Lower Cretaceous continues with multiple nannofossil originations that persist into the Valangin-ian. Here, a significant, diverse, and abundant benthic foraminifera and ostracod assemblage occurs in multiple, rapid abundance increases followed by gradual upward decreases, suggesting cyclical change in the shallower, upslope paleoenvironments. The cause of cyclical changes is unclear and may be the result of sea level change, progradation, and/or changes in ocean composition. The Hauterivian to Aptian section varies greatly in thickness with the maximum thickness in the northern De Soto Canyon area and thinning to the south. Nannoconus continues to dominate the nannofossil assemblage through the Aptian; benthic foraminifera and ostracods disappear rapidly during the Hauterivian and remaining sparse until the Albian when there is an increase of Nezzazata spp. The significance of these fossil sequences and respective assemblages are discussed in a paleoecological and paleogeographical context, which has implications to depositional history and correlation.

Abstract As part of a larger intercollegiate effort to reconstruct late Triassic, presalt sediment provenance and routing environments for the Gulf of Mexico sedimentary basin, an integrated geochronologic approach leveraging more traditional biostratigraphic, sedimentologic, and sequence stratigraphic provenance constraints from geologic cores, cuttings, and geophysical well logs was initiated. This paper presents the initial results of this ongoing study and details detrital zircon U-Pb extraction methodologies while Inductively Coupled Plasma Mass Spectrometry analyses are pending. Eagle Mills Formation sandstone samples were collected from well core and cuttings, at five sub-crop locations extending from Texas to South Carolina to the West Florida shelf, in preparation for U-Pb detrital zircon provenance analysis. Prior to separation of detrital zircon grains, a sedimentologic-stratigraphic analysis was conducted including detailed core description, well log evaluation, and thin-section petrography assessment. These findings confirm a hypothesis that late Triassic Eagle Mills siliciclastics were derived from the erosion of an active horst-graben rift block topography with associated igneous intrusives. Specifically, preliminary results reveal pervasive very finegrained mottled gray to red bed sandstone lithology confirming synrift continental alluvium having little or no marine component, and probable deposition in a warm, humid environment but with increasing aridity. Classic fluvial facies features are highlighted including depositional cross strata typifying dynamic braided to meandering channel belts and alluvial floodplain deposits. Less common siltstone and shale lithologies were likely deposited amidst lower energy subfacies including potential shallow lakes, marshes, and/or ephemeral ponds. Bioturbated trace fossils were only rarely preserved, and there was no evidence of marine or eolian facies incursion. Igneous magmatism was prevalent in most subsurface Eagle Mills Formation samples including intrusive diabase, basalt flows, and volcanic ash.

Abstract Large parts of the De Soto Canyon Salt Basin are unexplored, and structural and petroleum system models may facilitate continued hydrocarbon exploration, as well as the development of geologic CO 2 storage programs. The basin contains four structural provinces: (1) Destin fault system, (2) salt pillow province, (3) diapir province, and (4) salt roller province. The Destin fault system bounds half grabens that formed near the updip limit of salt. The faults have variable displacement and were active mainly during the Cretaceous. Broad salt pillows occur basinward of the Destin fault system, and the largest of these structures forms the core of Destin Dome. Salt pillows basinward of Destin Dome began forming shortly after Smackover deposition, whereas Destin Dome largely post-dates the Destin fault system. The diapir province is in the structurally deepest part of the salt basin, and diapirism occurred from the Jurassic into the Tertiary. The salt roller province contains a complex array of normal faults and rollover structures that record gravitational shelf spreading during Jurassic time. Petroleum systems analysis indicates that the basin contains a distinctive suite of source rocks, sealing strata, reservoir strata, and trap types. Exploration efforts have thus far proven successful in structures that formed before or during hydrocarbon expulsion, and many such structures remain untested.

Abstract The petroleum geology of the Mississippi Canyon, Atwater Valley, western DeSoto and western Lloyd Ridge protraction areas, offshore northern Gulf of Mexico, is controlled by the interaction of salt tectonics and high sedimentation rate during the Neogene, and has resulted resulting in a complex distribution of reservoirs and traps. Seventy-eight fields/discoveries are evaluated and comprise structures with four-way closures (18), three-way closures (46), and stratigraphic traps (14). Three of these discoveries are in Upper Jurassic eolian reservoirs, the remainder are in Neogene deep-water reservoirs. The tectonic-stratigraphic evolution of the area is analyzed at eleven discrete intervals between 24 Ma and Present. The analyses show how the allochthonous salt systems evolved over time, and their effect on sedimentation patterns and sub-basin evolution. The study area includes some of the largest fields in the northern deep Gulf of Mexico. Thunder Horse produces from an anticlinal (turtle) structure that developed with a basement-controlled allochthonous system. The greater Mars-Ursa sub-basin has nine fields with > 1.5 BBBOE EUR, including Mars, Ursa and Princess, that developed with a counterregional allochthonous salt system. The remaining fields have considerably smaller reserves, which are controlled by the area within closure and number of reservoir intervals. Many of the smaller fields are produced from one well subsea tiebacks. Most of fields in the study area are contained within sheet-like or wedge-shaped stratigraphic intervals and have four-way or three-way trapping configurations. These findings reflect the profound effect that mobile salt has had on the petroleum geology of the region.