Browsing by Subject "Sedimentation and deposition--Mexico, Gulf of"
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Item Depositional and structural evolution of the middle Miocene depositional episode, east-central Gulf of Mexico(2003-12) Combellas Bigott, Ricardo Ignacio, 1974-; Galloway, William E.Item Lithium, boron, and barium in formation waters and sediments, Northwestern Gulf of Mexico Sedimentary Basin(1989) Macpherson, Gwendolyn Lee, 1953-; Land, Lynton StuartLithium, boron and barium, found in varying abundances in formation waters of the Gulf of Mexico Sedimentary Basin (Gulf Basin), have contrasting origins and are useful in assessing the open or closed nature of hydrocarbon-producing aquifers in Texas and Louisiana. Dissolved barium concentrations are controlled primarily by barite. Barium contents of sandstones show that either the barium content of dissolved or albitized detrital feldspars was considerably higher than in detrital feldspars which remain unaltered or that the original feldspar content of the sandstones was higher than that of the least altered sandstone analyzed. Boron and lithium contents are more difficult to attribute to local diagenesis. Most formation waters contain low concentrations of lithium (less than 10 mg/L) ascribable to feldspar diagenesis, except that whole-rock sandstones increase in lithium content with increasing diagenetic alteration. Formation waters from deep reservoirs contain very high concentrations of lithium for which there is no apparent local source. These waters do not resemble waters residual from either marine or non-marine evaporite deposition. Boron in most formation waters cannot originate exclusively from organic matter unless organic matter contents are much higher than have been measured, nor does it come from volcanic sediments because these are abundant only in the South Texas region while high boron contents are not geographically restricted. Formation waters from deep reservoirs contain very high concentrations of boron which probably come from deeper in the Basin because clay minerals, the major reservoir of boron, show no systematic decrease in boron content with depth. The 𝛿¹¹B of these waters is light (to +11%₀) and shows that the boron is not seawater boron (+40%₀) or boron from Jurassic evaporites (+31%₀). The 𝛿¹¹B of other formation waters lies between the value for sea water and the light boron. The Gulf Basin is nearly open with respect to lithium and boron but closed with respect to barium. The high concentrations of lithium and boron probably originate deeper than the sampled part of the Gulf Basin and may be products of metamorphic processes. The source of the barium in formation waters is detrital feldspars.Item Upper Miocene depositional history of the Central Gulf of Mexico basin(2004) Wu, Xinxia; Galloway, William E.The Upper Miocene (late Middle to early late Miocene) depositional episode, defined by two widespread, transgressive deposits associated with biostratigraphic tops Textularia W (12.0 Ma) and Robulus E (6.2 Ma), records a long-lived family of sediment dispersal systems that persisted for nearly 6 m.y. with little modification. It corresponds to a prolonged lowstand after a dramatic sea-level fall at the end of the middle Miocene and is punctuated by three additional flooding events associated with Cibcides carstensi, Discorbis 12 and Cristellaria K biostratigraphic tops, which subdivide the Upper Miocene depositional episode into four secondary depositional episodes. In the east-central Gulf of Mexico, the Upper Miocene genetic sequence records extensive continental margin offlap, primarily centered on the ancestral Tennessee River and Mississippi River dispersal axes. Thickest sediments were deposited in the Tennessee River delta beneath modern SE Louisiana. The composite fluvial-dominated, wave-modified Tennessee and Mississippi delta system rapidly built beyond the subjacent Middle Miocene shelf margin to construct a sandy delta-fed apron that ultimately spilled distal sandy turbidites onto the adjacent basin floor. Margin outbuilding was locally and briefly interrupted by hyper-subsidence due to salt withdrawal and consequent slope mass wasting, forming numerous depocenters separated by salt massifs and ridges, and various linked structural systems. A broad, but relatively thin, sandy strandplain and clastic shelf succession, supplied by reworking of the deltaic deposits, extends both eastward and westward from the delta system. Abundant strike-reworked sediment locally prograded the strandplain to the shelf edge, with slope offlap exceeding 30 mi (50 km). A large volume of sand continuously bypassed the confined minibasin and upper slope at the flank of active deltaic depocenters into the Mississippi Canyon, Atwater Valley and Green Canyon OCS areas throughout the entire Upper Miocene, forming a linked, long-lived McAVLU intraslope and abyssal fan system in the primary minibasin corridor of the lower slope and basin floor. Sand bypass and subsequent deposition was dominantly through the slope canyon and intraslope fan systems developed in the east-central Gulf. Canyons, fan valleys, leveed channels, gravity mass transport complexes and structural conduits that focused sediment flow provide various sediment transport elements.