Abstract A generalized stratigraphic framework for the upper Jurassic is suggested, in which the name Haynesville Formation is utilized, and the name Lower Cotton Valley Lime is suppressed in favor of the Gilmer, where appropriate. Eustatic sea-level fluctuations have resulted in patterns of sedimentation common to upper Jurassic sequences across the entire northern Gulf of Mexico region and hence indicate the wide applicability of this generalized stratigraphic framework. The presently accepted model of the Smackover-Haynesville sedimentation must be modified to take into account sea-level fluctuations, subsidence, and sediment availability. The model developed here is simply one of lower Smackover basin fill during a rapid transgressive phase and upper Smackover regional shoaling during a sea-level stillstand in which sedimentation was in equilibrium with subsidence. The lower and upper Smackover are not necessarily time equivalent, but represent two separate sedimentologic sea-level regimens. The Haynesville Formation is thought to be a separate sedimentologic package that was deposited during the next sea-level rise; the Gilmer Limestone formed a shelf-margin barrier behind which the lagoonal Buckner evaporites were deposited. The evaporites graded landward into quartzose clastics. Predictable regional porosity patterns have developed in the Smackover-Haynesville, in response to early diagenetic overprints, controlled largely by eustatic sea-level subsidence interactions. These patterns include: updip oomoldic porosity in a regional meteoric-water system developed during the upper Smackover sea-level stillstand; downdip porosity preservation under marine conditions along the shelf margin; regional dolomitization associated with reflux of evaporitive waters from the Buckner lagoon behind the Gilmer shelf-margin barrier. Structural hydrocarbon traps associated with salt movement are the most common type of Late Jurassic trap. Buckner evaporites or Haynesville shales usually form the seals in the Late Jurassic reservoirs. Jurassic source rocks are probably lower Smackover limestones and Norphlet shales. Sourcing is generally local with migration into updip areas, particularly where regional dolomitization has occurred. The time of migration, which is a key factor in a viable Smackover exploration strategy, varies across the Gulf in response to the subsidence history of each individual basin. Future Jurassic exploration will center on south Texas, the Gilmer shelf margin, and the updip Smackover along the bounding graben fault systems. Most production will be gas, but some oil should occur along the updip faulted fairways.

Abstract Recent discoveries in the Late Jurassic Haynesville and Bossier shales have dramatically increased unconventional gas exploration activity in the mature petroleum provinces of eastern Texas and northern Louisiana. The Haynesville and Lower Bossier shales comprise the uppermost units of a transgressive systems tract of a second-order supersequence, which spans the interval from the top of the Werner Anhydrite/Louann Salt equivalent to the upper Cotton Valley clastics. Depositional variations within the shales are a function of higher-order sequences that resulted from eustatic sea-level fluctuations, paleobasin physiography, and the interplay of local subsidence and sediment input rates. The antecedent topography shaped by underlying carbonates of the Gilmer (Haynesville) Lime (Forgotson and Forgotson, 1976) and subsequent sediment budgets strongly influenced (1) facies development and stacking patterns that vary along the northern rim of the young Gulf of Mexico (GOM) Basin during Haynesville and Bossier time, and (2) the depositional processes, total organic carbon richness, and preservation of the self-sourcing Haynesville and Bossier Shale units. The Haynesville Shale depositional system is an example of a competing carbonate and clastic system that contains contemporaneous retrogradational and progradational facies. In the western part of the system, which is carbonate-dominated and fairly restricted from siliciclastic input, the time-equivalent Gilmer (Haynesville) Lime consists of backstepping carbonate facies. In contrast, to the east, strong progradational stacking patterns, comprised of mainly siliciclastic facies assemblages, dominate in northern Louisiana and western Mississippi because of increased sediment supply from the ancestral Mississippi River, which outpaced subsidence and eustasy. Hence, major bounding stratigraphic events such as higher-order maximum flooding surfaces and condensed sections critical for shale gas exploration appear to change facies laterally whereas the second-order maximum flooding surface, or the turn from retrograding to prograding stacking patterns, appears diachronous along depositional strike. During Bossier time, the youngest carbonates were drowned and siliciclastics became increasingly dominant, expanding westward from northern Louisiana into eastern Texas and ultimately across most of the northern GOM shelf as the Cotton Valley Sandstones and its distal shale equivalents. Depending on the paleophysiography of the depositional shelf setting, some areas of the Haynesville-Bossier system were restricted and relatively sediment starved. These correspond with areas of total organic carbon enrichment and, in turn, lower shale gas exploration risk.

Abstract The Haynesville Shale, an Upper Jurassic (Kimmeridgian) age calcareous and locally organic-rich mudrock, is one of many prominent shale gas plays in North America. As shale plays increase in importance, the ability to define basin-wide, robust, and stable stratigraphic frameworks using data derived from well-bores becomes increasingly critical. Here, the technique of chemostratigraphy is used to define a stratigraphic framework that extends through ten wells ranging from eastern Texas to northwestern Louisiana. Stratigraphic variations in inorganic geochemistry allow clear differentiation of Haynesville Shale from the underlying Smackover Formation, the Gilmer Lime, and the overlying Bossier Formation. More importantly, however, interpretation of the results allows two chemostratigraphic packages and four geochemically distinct units to be defined and correlated within the Haynesville Shale. The lithostratigraphic units are geochemically differentiated using variations in SiO 2 , Al 2 O 3 , MgO, Zr, and Nb, whereas the units within the Haynesville Shale are defined using changes in CaO, Al 2 O 3 , MgO, Fe 2 O 3 , Rb/K 2 O and Th/U values, and V enrichments. By integrating the geochemistry with x-ray diffraction and total organic carbon (TOC) results, it becomes apparent that the driving forces behind the changing geochemistry within the Haynesville Shale are the amounts of anoxia in the lower portion of the Haynesville Shale and of CaO input in the upper portion. Cyclical fluctuations in the relative abundances of Zr and Nb are interpreted to represent transgressive—regressive cycles—and provide enhanced correlation within the Haynesville Shale. By combining stratigraphic changes in Zr/Nb values with V enrichments, it is shown that the most severe period of anoxia is associated with the transgressive portion of the oldest cycle. Importantly, this suggests that this stratigraphic horizon is where maximum TOC can be expected. Lateral changes in geochemistry within the Haynesville Shale demonstrate that terrigenous input was highest in the northwest sector of the basin, primarily in East Texas, and anoxia was greatest in the east of the basin, primarily in Louisiana.

Abstract Ancestral Gulf Coast Basin architecture controls much of the Jurassic Haynesville shale mudstone trend. Basement blocks developed during Early and Middle Jurassic rifting and overlain by a variable thickness of Louann Salt ultimately formed the foundation of large Haynesville (Gilmer) carbonate platforms that provide boundaries to the Haynesville organic shale trend. Salt movement influenced by basement features created local fairways of salt deflation, which received thicker Haynesville organic shale sequence and experienced less subsequent disruption. Available data sets indicate that salt movement in the Sabine uplift area terminated during the Late Jurassic. Therefore, post-Jurassic faulting was minimized, preventing hydrocarbon loss from the Haynesville organic shale reservoirs.

Abstract The subsurface Upper Jurassic Haynesville and Bossier Formations comprise three facies associations along the eastern slope of the Gilmer Platform. The lower Haynesville facies association consists of three facies produced by mass-wasting processes: (1) calcirudite/calcarenite, (2) mud-clast calcarenite, and (3) laminated calcisiltite intercalated with laminated calcareous mudrock and bioturbated calcareous mudrock. These facies were deposited by (1) hyperconcentrated density flows/transitional concentrated density flows, (2) hydrated turbidity flows, and (3) distal settling from turbidity flows, respectively. These mass-wasting deposits are the deeper water equivalents of the shallower water Haynesville Lime. The sedimentary dynamics of the mass-wasting processes produced TOC (total organic content)-rich accumulations downslope in the deeper parts of the basin. The upper Haynesville facies association also consists of three facies: (1) TOC-rich laminated calcareous mudrock, (2) bioturbated calcareous mudrock, and (3) bioturbated mud-clast calcisiltite. These facies were derived from marine snow deposited and reworked as sediment drifts by bottom currents above and below the oxycline. The Bossier Formation facies association contains (1) massive argillaceous mudrock, (2) bioturbated argillaceous mudrock, and (3) argillaceous claystone. These facies are interpreted as prodelta deposits intercalated with sediment deposited by settling from flood plumes. TOC is relatively high despite sedimentary dilution from deltaic input, indicating high primary productivity of organic matter at the time of deposition. TOC-rich accumulations comparable to the Haynesville Shale are observed in the Bossier Formation on Sabine Island and may exist wherever detrital sediment input has been reduced or diverted by currents. The lower Haynesville was deposited as an upwards-deepening succession during a second-order transgression that started after deposition of the Smackover Formation. Because the upper Haynesville was deposited as a sediment drift with an internally complex sedimentary geometry, no internal cyclicity is apparent, and the position of the second-order maximum flooding surface cannot be established. Deposition of the Bossier marks a significant turnaround when deltaic sediments prograded from the north and buried the mass-wasting and sediment-drift deposits. The distal setting of the facies, evidence of deposition below storm-wave base, the pelagic source of the sediment, and the sedimentary processes involved make application of sequence stratigraphic concepts to the deposits problematic.