ABSTRACT Paleocene Lower Wilcox Group sedimentation rates are three times the Cenozoic average for the Gulf of Mexico region and are attributed to Laramide tectonism within the Laramide–Rocky Mountains region. These increased rates likely represent the erosion of easily weathered Phanerozoic strata that blanketed the Laramide-age basement-cored uplifts. Geologic observations and U-Pb geochronology are not sufficient to fully address this hypothesis alone, so we conducted 439 Lu-Hf isotopic analyses on detrital zircons from eight samples from the San Juan Basin and five samples from the Gulf of Mexico Basin. Focusing on the zircons younger than 300 Ma allowed us to make direct comparisons to the eight principal components that comprise the North American Cordilleran magmatic arc: (1) Coast Mountains batholith; (2) North Cascades Range; (3) Idaho batholith; (4) Sierra Nevada batholith; (5) Laramide porphyry copper province; (6) Transverse Ranges; (7) Peninsular Ranges; and (8) Sierra Madre Occidental. The εHf ( t ) results range from +8.9 to –27.0 for the San Juan Basin samples and from +13.0 to –26.6 for the Gulf of Mexico samples. Using the San Juan Basin samples as a proxy for the eroded Mesozoic cover that was shed from the Laramide uplifts, we show that much of the sediment entering the Gulf of Mexico through the Houston and Mississippi embayments during the late Paleocene was derived from reworked cover from the greater Laramide–Rocky Mountains region. However, the Gulf of Mexico samples also include a distinct juvenile suite (εHf [ t ] ranging from +13 to +5) of zircons ranging in age from ca. 220 to 55 Ma that we traced to the Coast Mountains batholith in British Columbia, Canada. This transcontinental connection indicates an extension to the headwaters of the previously defined paleo-Mississippi drainage basin from ca. 58 to 56 Ma. Therefore, we propose a through-going fluvial system (referred to here as the “Coast Mountains River”) that was routed from the Coast Mountains batholith to the Gulf of Mexico. This expands the previously defined paleo-Mississippi drainage basin area by an estimated 280,000 km 2 . Our comprehensive Hf isotopic compilation of the North American Cordilleran magmatic arc also provides a benchmark εHf ( t ) versus U-Pb age plot, which can be used to determine provenance of detrital zircons (85–50 Ma) at the scale of specific region(s) within the Cordillera based on their εHf ( t ) values.

Abstract An understanding of trap and fault seal quality is critical for assessing hydrocarbon prospectivity. To achieve this, modern analytical techniques leverage well data and conventional industry-standard 3D seismic data to evaluate the trap, and any faults displacing the reservoir and top seal intervals. Above all, geological interpretation provides the framework of trap and fault seal analyses, but can be hindered by the data resolution, quality and acquisition style of the conventional seismic data. Furthermore, limiting the analysis to only the petroleum system at depth may lead to erroneous perceptions because interpreting overburden features, such as shallow faults or gas chimneys, can provide valuable observations with respect to container performance, and can to help validate trap and fault seal predictions. A supplement to conventional 3D data are high-resolution 3D seismic (HR3D) data, which provide detailed images of the overburden geology. This study utilizes an HR3D seismic volume in the San Luis Pass area of the Texas inner shelf, where shallow fault tips and a sizeable gas chimney are interpreted over an unsuccessful hydrocarbon prospect. Static post-drill fault seal and trap analyses suggest that the primary fault displacing the structural closure could have withheld columns of gas c. 100 m high, but disagree with our HR3D seismic interpretations and dry-well analyses. From our results, we hypothesize that tertiary gas migration through fault conduits reduced the hydrocarbon column in the prospective Early Miocene reservoir, and may have resulted from continued movement along the intersecting faults. Overall, this study reinforces the importance of understanding the overburden geology and geohistory of faulted prospects, and demonstrates the utility of pre-drill HR3D acquisition when conducting trap and fault seal analyses.

Published estimates for the original volume of Mid-Jurassic Louann evaporites found throughout the entire Gulf of Mexico Basin vary widely. Volume totals derived from both map data and actual volume numbers, range from about 10,500 km 3 (2,500 mi 3 ) to 839,000 km 3 (200,000 mi 3 ), an 80 fold variation. Little new information has been published during the past twenty-five years to address this disparity. But gaining knowledge of the present day volume of salt would be an important metric if debates concerning the origin of the salt and the nature of the Gulf of Mexico Basin during salt deposition are to be reconciled. A methodology now exists to estimate more accurately and quantitatively the volume of salt present in a given area. Multiple, recent generations of 3-D seismic depth volumes in the offshore Gulf of Mexico require that salt velocities be inserted. This vital processing step includes a systematic picking and interpretation of the tops and bases of all salt bodies encountered. The resulting models of salt velocity allow salt volume in the 3-D data sets to be calculated. Combining the salt volumes calculated from multiple seismic surveys offers new stratigraphic insights across large portions of the original salt basin. A comparison of salt volumes derived from seismic data cubes and volumes derived from published maps can now be made. The comparisons should give some suggestion as to the accuracy of the map data. By extrapolation it should also give a more accurate and quantitative estimation of the original salt volume deposited in the Gulf of Mexico basin.

Abstract We cannot hope to predict Mesozoic depositional processes and sediment properties well enough to plan effective regional exploration strategies without considering the big picture of Gulf of Mexico deposystem evolution. The two critical big picture elements are the kinematics and timing of the Yucatan Block's detachment and separation from North America and the various major expansions and contractions and the ultimate disappearance of the Western Interior Seaway. Although a number of authors, including this one, have speculated on the timing of separation of Yucatan from North America ( Fillon, 2007a ), no definitive evidence exists: i.e. , drilled samples of the ocean crust and the sediments directly overlying it. Without that unambiguous information we must infer the paleogeographic evolution of the early Gulf of Mexico Basin from deposystem architecture by asking questions such as when do Gulf of Mexico deposystems transition from architectures consistent with deposition in a youthful blockfaulted basin underlain by actively attenuating continental crust to deposition in a mature basin having stable margins surrounding a central region underlain by subsiding ocean crust. An understanding of the paleogeography and paleoceanography of the Gulf of Mexico Basin derived from deposystem architecture can help provide answers to crustal kinematic questions and to more exploration focused questions such as: where, and in section of what age should we look to find facies similar to the organic rich, generative Haynesville Shale facies of eastern Texas and western Louisiana. Although we all know something about the Western Interior Seaway, most of us working on the Mesozoic of the Gulf of Mexico Basin have not spent much time considering what effects it might have had on the prospectivity of Gulf of Mexico deposystems. Through much of Albian and Late Cretaceous time the Western Interior Seaway connected the Gulf of Mexico Basin with the Arctic Ocean Basin. The effects of the establishment and intermittent blocking of this major seaway connecting arctic and tropical water masses on global paleoceanography, on global paleoenvironments, and locally on onshore and offshore Gulf Basin deposystems cannot be ignored in our quest to understand the Mesozoic of the Gulf Rim. This paper is a “big picture” review of Gulf of Mexico Basin deposystem evolution within the Late Jurassic (Oxfordian)–Late Cretaceous (Maastrichtian) interval. Seventeen Mesozoic chronosequences are defined therein based on chronostratigraphic data garnered from over 130,000 industry well and pseudowell penetrations of Mesozoic section in the Gulf of Mexico Basin region. Examination of the collected data suggests that grouping the seventeen Gulf of Mexico Mesozoic chronosequences into seven super-chronose-quences optimally distinguishes key phases of deposystem and basin evolution. The oldest super-chronosequence defined in this study, dubbed “MG,” encompasses ca. 16.45 Ma of Norphlet through lowermost Cotton Valley Late Jurassic deposition. Sediment distribution and accumulation rates within the MG interval clearly define the rectilinear configuration of the earliest Gulf of Mexico Basin. This early basin geometry is consistent with fault controlled attenuation and foundering of North American continental crust, associated flooding, and rapid depositional infill concurrent with the earliest detachment of the Mayan (Yucatan) crustal block from North America. The Yucatan block, although showing an affinity with South American (Amazonian) terranes ( Martens, 2009 ), was left attached to the North American plate when North America began pulling away from Gondwana during the initial breakup of Pangea ( Fillon, 2007a ). The next younger super-chronosequence, “MF,” contains a. ca. 13.47 Ma record of Cotton Valley, Bossier, Knowles limestone., Late Tithonian through mid Hauterivian, deposition. The “MF” interval reflects the same rectilinear outline as the “MG,” but is marked by decreased accumulation rates, suggesting that the fault bounded crustal attenuation, rapid sediment infill phase had markedly slowed. The ca. 9.4 Ma of Hosston, Sligo, Sunniland limestone, James limestone, mid-Hauterivian through Early Aptian section contained within the succeeding “ME” super-chronosequence records modification of the early rectilinear basin outline by a temporary reactivation of attenuation and foundering in the western portion of the Gulf of Mexico Basin. “ME” sediment distribution patterns also indicate development of a depositional continental margin and accumulation of true continental margin type deltaic and reef systems. These observations suggest that during this interval a deep continental basin, probably floored by ocean crust, was beginning to form outboard of the attenuated continental crust. Sediment distribution and accumulation rates within the ca. 23.5 Ma Rodessa through lower Washita, Early Aptian through Early Cenomanian “MD” super-chronosequence reflect growth of the Wisconsin interior seaway and a stable phase of relatively low accumulation rates throughout the entire Gulf of Mexico Basin deposystem. During this interval, deposition was very likely influenced by a vigorous tidal and thermohaline current circulation driven by strong temperature contrasts within the Gulf of Mexico–Wisconsin interior seaway–Arctic Ocean connection. The next younger super-chronosequence, “MC,” contains a ca. ca. 16.0 Ma record of Dantzler, Washita, Lower Pine Key, Eutaw, Woodbine, Eagle Ford, Austin, and Early Cenomanian through Late Santonian (Late Cretaceous) deposition. During this phase, there is a marked reduction of accumulation rates in the north-western portion of the basin, attributable perhaps to expansion of the Western interior seaway and continued subsidence of the old Gulf of Mexico Basin margin. Associated small, perhaps tidal submarine delta-like depopods developed, perhaps in response to the regional Western interior seaway transgression ( Blakey, 2014 ). These delta-like depocenters appear to define a new basin margin presaging the modern curved shape of western Gulf of Mexico so familiar to us today. Here also we see the first unambiguous evidence of abyssal deposition in the deepest portion of the Gulf of Mexico Basin underlain by ocean crust. The succeeding ca. 12.82 Ma interval of Late Santonian through Early Maastrichtian upper Pine Key, upper Selma, upper Austin, Taylor, Olmos, Saratoga, and low accumulation rate mainly chalk and marl deposition contained within the “MB” super-chronosequence provides evidence of transgressive onlap associated with an expanding and deepening interior seaway during “MB” time. “MB” onlap has the effect of temporarily reemphasizing structural trends inherited from crustal attenuation that took place during “ME” time. Finally, the ca. 5.4 Ma long terminal Mesozoic “MA” super-chronosequence consists of Maastrichtian, Navarro equivalent, low accumulation rate marls deposited along the basin margin. These low accumulation rate basin rim sediments and low accumulation rate slope sediments are punctuated by high accumulation rate canyon fill and lobe-shaped slope depopods which are probably attributable to sediment reworking, transport and deposition by transitional Cretaceous-Paleogene (K/P) interval mega-tsunami backwash flows immediately following the Chicxulub impact. Higher accumulation rates in the deeper parts of the basin underlain by ocean crust are also consistent with high volume backwash flows.

Abstract The Mesozoic Gulf of Mexico Basin is considered in this discussion as the set of contiguous, Triassic and Jurassic sub-basins directly involved in the counterclockwise rotation of the Yucatan Block from North America in the Late Jurassic. The rifting and seafloor spreading history of the basin is less well understood than analogous salt basins of the Atlantic margins, largely because the base salt surface is significantly deeper and has hereto widely been considered acoustic basement. In 2012, 17,000 km of 2D PSDM reflection seismic data ( SuperCache ) were acquired across the deep water of the U.S. Gulf of Mexico. The unique acquisition configuration of long-offset, powerful source, and deep-tow of both source and receivers was designed to optimize the imaging of the presalt architecture of the basin to a depth of 40 km. On these seismic data, the base of the salt and its correlative unconformity, continental and oceanic basement, and the Moho are evident. In combination with vintage, reflection seismic data, shipboard and regional gravity data, and regional refraction profiles, a crustal interpretation has been extended to the greater Gulf of Mexico Basin. The continental crustal architecture is described in terms of crustal thinning: from low (<30%) to transitional (>70%). Synkinematic sequences are recognized within the Late Triassic to the Middle Oxfordian (~70 my). The final break-up phase occurred within 15 my, ending with a basin-wide open marine transgression and initial emplacement of oceanic crust at 160±1 Ma; continued extension may have occurred in the eastern part of the basin in the latest Jurassic. The basin margins are considered to be intermediate between magmapoor and volcanic end-members. The ocean crust tapers from a maximum width of 700 km in the west, where it is anomalously thin, to anomalously thick as it approaches the pole of rotation in the Straits of Florida. The architecture of extinct spreading valleys and fracture zones is analogous to the modern, slow spreading mid-Atlantic ocean, suggesting that spreading continued until the latest Jurassic (~142 Ma), possibly as late as within the early Cretaceous (~132 Ma).

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 Detrital zircon from the Upper Jurassic Norphlet Formation in the vicinity of Mobile Bay, AL reflects a Laurentian provenance, with U-Pb age populations including dominant Paleozoic (265-490 Ma) and Grenville (950-1250 Ma) age. Twenty-three zircon grains from a sandstone sample recovered from the upper part of the Norphlet formation in well permit# 9863-OS-46-B show a population of 850-920 Ma zircon that is not observed in stratigraphically older samples. As there are very few sources for zircon of this age in southeastern United States, we interpret derivation from either the Goiás magmatic arc of Brazil; the conglomeratic sandstone of the eastern Yucatan peninsula; and/or Mixteca terrain of Mexico as probable sources. Previous study of 850-920 Ma zircon grains from the Goiás magmatic arc shows an origin from a depleted mantle without any crustal contamination (Hf (t) = +8 to +12); however, the same age zircons in eastern Yucatan and Mixteca terrain indicate crystallization from magmas having a strong crustal signature (Hf (t) = -3.2 to -3.8). Detrital Neoproterozoic zircon grains in the Norphlet Formation shows a wide Hf (t) range (-5.1 to +11.9) for the 850-920 Ma zircons, indicating sediments influx to the Gulf of Mexico basin during late Norphlet time was a mix of material from all of these sources during the Norphlet deposition. We propose that sediments from the Goiás magmatic arc probably were transported to the Mixteca terrain through a paleo-fluvial system; given the proximity of Mixteca terrain to southern North America during Late-Early Jurassic, we infer that erosion of Mixteca terrane sedimentary rocks supplied sediment to the Norphlet erg in the eastern Gulf of Mexico. Alternately, the Neoproterozoic grains may have been derived directly from the Goiás arc and transported to the eastern Gulf of Mexico by a proto-Orinoco river that developed during Jurassic-Early Cretaceous time.

Abstract This study provides an assessment of two source-to-sink sediment routing systems of the Early Cretaceous and highlights sedimentologic changes that occurred in response to major tectonic reorganization of the eastern Gulf of Mexico during the Valanginian-Hauterivian stages. Depth-imaged 2D and 3D seismic data, well log correlation, sand grain size, and detrital zircon U-Pb data obtained from the Valanginian intervals of the cores of a key well, facilitates source-to-sink analysis of Early Cretaceous deep-water deposits, as well as construction of a new depositional model of Hosston equivalent-siliciclastics previously investigated only in the western Gulf of Mexico onshore areas. U-Pb dating of detrital zircon grains suggests that Hosston siliciclastics observed in the 200-km-long base-of-slope sandy progradational delta-fed apron at the Florida Escarpment originated in a peninsular Florida source terrane – the Ocala Arch. Interpretation of 3D seismic data with nearby well control also allows conclusions to be drawn about the Appalachian-sourced Hosston fan system in Mississippi Canyon. This Appa-lachian-sourced sandy fan is believed to have terminated updip of a series of salt-related asymmetric expulsion rollovers, although we know sediment accommodation in these inverted basins was not confined to the Valanginian-Hauterivian age Hosston interval and extended from the Jurassic Cotton Valley-Bossier supersequence to the Late Cretaceous Navarro-Taylor supersequence. Two plausible models of Appa-lachian-sourced fan length are considered, incorporating calculations of salt rafting to estimate a best-case scenario fan length of 90-km, while a more probable fan geometry is determined from seismic observations and well control, yielding a Valanginian-Hauterivian submarine fan of 70-km length. The study presents a new paleogeographic model, with special focus on the eastern Gulf of Mexico and the interpreted sand-prone fan and progradational delta-fed apron. It also provides a robust model for source to sink transport during a critical phase of Gulf of Mexico basin evolution. The shorter fan length calculated in this study suggest the majority of asymmetric expulsion rollovers in Mississippi Canyon are either sandstone-poor or were sourced from a different, likely younger, source-to-sink system ( e.g. , Late Cretaceous, Cenomanian-Turonian-age Tuscaloosa fluvial system).