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In this study, the stable isotope and trace element geochemistries of meteoric cements in Pleistocene limestones from Enewetak Atoll (western Pacific Ocean), Cat Island (Bahamas), and Yucatan were characterized to help interpret similar cements in ancient rocks. Meteoric calcite cements have a narrow range of δ18O values and a broad range of δ13C values in each geographical province. These Pleistocene cements were precipitated from water with stable oxygen isotopic compositions similar to modern rainwater in each location. Enewetak calcite cements have a mean δ18O composition of −6.5%0 (PDB) and δ13C values ranging from −9.6 to +0.4%0 (PDB). Sparry calcite cements from Cat Island have a mean δ18O composition of −4.1%0 and δ13C values ranging from −6.3 to + 1.1%0. Sparry cements from Yucatan have a mean δ18O composition of −5.7%0 and δ13C values of −8.0 to −2.7%0. The mean δ18O values of these Pleistocene meteoric calcite cements vary by 2.4%0 due to climatic variations not related directly to latitude. The δ13C compositions of meteoric cements are distinctly lower than those of the depositional sediments. Variations in δ13C are not simply a function of distance below an exposure surface. Meteoric phreatic cements often have δ13C compositions of less than —4.0%0, which suggests that soil‐derived CO2 and organic material were washed into the water table penecontemporaneous with precipitation of phreatic cements. Concentrations of strontium and magnesium are quite variable within and between the three geographical provinces. Mean strontium concentrations for sparry calcite cements are, for Enewetak Atoll, 620 ppm (σ= 510 ppm); for Cat Island, 1200 ppm (σ= 980 ppm); and for Yucatan, 700 ppm (σ= 390 ppm). Equant cements, intraskeletal cements, and Bahamian cements have higher mean strontium concentrations than other cements. Equant and intraskeletal cements probably precipitated in more closed or stagnant aqueous environments. Bahamian depositional sediments had higher strontium concentrations which probably caused high strontium concentrations in their cements. Magnesium concentrations in Pleistocene meteoric cements are similar in samples from Enewetak Atoll (mean =1.00 mol% MgCO3; σ= 0.60 mol% MgCO3) and Cat Island (mean = 0.84 mol% MgCO3; σ= 0.52mol% MgCO3) but Yucatan samples have higher magnesium concentrations (mean = 2.20 mol% MgCO3: σ= 0.84mol% MgCO3). Higher magnesium concentrations in some Yucatan cements probably reflect precipitation in environments where sea water mixed with fresh water.

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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.