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 This field trip examines exposures of transgressive and highstand marine deposits of the Sabinetown transgression that forms the upper part of the Calvert Bluff Formation of the Wilcox Group in the outcrop belt. The horizon of maximum flood in the Sabinetown transgression at Bastrop contains molluscs and diverse vertebrate fossils characteristic of open marine environments. The highstand deposits coarsen upward and are capped with a well-developed paleosol. These deposits are dated as early Eocene.

Small deposits of Neoproterozoic ironstone in the New Jersey Highlands are hosted by the Chestnut Hill Formation, a terrestrial sequence of siliciclastic rocks, sparsely preserved felsic and mafic volcanic and tuffaceous rocks, and thin limestone metamorphosed at greenschist-facies conditions. Sediments of the Chestnut Hill Formation were deposited in alluvial, fluvial, and lacustrine environments in a series of fault-bounded subbasins along the Iapetan eastern Laurentian margin. Ironstone occurs mainly in the upper part of the sequence in sandstones, quartzites, fine-grained tuffs, tuffaceous sediments, and carbonate-bearing beds. Ore is massive to banded and contains the assemblage hematite ± magnetite, which is locally associated with tourmaline and Fe silicates + sericite + calcite + chlorite ± quartz. Ironstone alternates with clastic bands, and sedimentary structures in ore bands and clastic bands are consistent with alternating chemical and clastic sedimentation deposited synchronously. Chestnut Hill rocks exhibit geochemical compositions that are dissimilar to typical sedimentary and volcanic rocks. They display evidence for two stages of post-diagenetic alteration. The first stage involved widespread potassium metasomatism, which produced increased values of K, Ba, and Rb that are not correlated with increased Fe or other hydrothermal elements. The metasomatizing fluid may have been basinal water heated during emplacement of Chestnut Hill volcanic rocks. The second stage produced alteration of Chestnut Hill rocks, and also Mesoproterozoic rocks along the footwall contact of the deposits, by hydrothermal fluids likely from a volcanogenic source. The ironstone deposits were formed by hydrothermal processes related to extension during formation of continental rift subbasins in the New Jersey Highlands. Iron was sourced from Fe-rich Mesoproterozoic rocks at depth, where it was leached by hydrothermal fluids that migrated upward along extensional faults. Iron and other metals were precipitated in permeable basin sediments and chemically favorable volcanic rocks, as well as precipitated directly as chemical sediment.