http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
xiii, 196 leaves : illustrations ; 29 cm
Cored Miocene, Pleistocene, and Holocene Gulf of Mexico sediments (ranging in depth from 0 to 3,700 meters below sea floor) consist of interbedded sands, silts, and muds with varying degrees of consolidation. Samples selected from these sediments were studied for their mineralogy and diagenesis. Rapid deposition, lack of tectonism, and modest temperature increase (maximum temperature: 91°C), has resulted in limited diagenesis. The Miocene sediments represent various sub-environments of the ancestral Mississippi River delta complex; Pleistocene and Holocene sediments are continental shelf, slope, and Mississippi Fan deposits. Sands are fine- to very fine-grained feldspathic litharenites with abundant (average 18%) matrix fines and minor (average 4.4%) carbonate clasts and shell fragments. The authigenic phases are dominated by carbonates, including calcite, dolomite, and siderite. Carbonate diagenesis is a continuing process, forming (1) disseminated authigenic micron-sized (<30 μm) siderite or ferroan carbonate grains in muddy, organic-rich marine sediments or (2) scattered thin (<15 cm), poikilotopic, calcite- or dolomite-cemented bands in thicker, unconsolidated marine sands. The cemented bands grew during burial through dissolution of detrital carbonate and reprecipitation at the margins of cemented zones. These bands may represent a substrate for extensive cementation during later diagenesis. The mineralogy, chemistry, and texture of carbonate are controlled in part by organic matter diagenesis; the majority of authigenic carbonate formed under sulfidic or methanic conditions. Pore fluids in mudstones were expelled into adjacent sand due to compaction dewatering. Due in part to this fluid flow, different authigenic assemblages were developed in muds and sands. Minor authigenic phases include pyrite, clay minerals, feldspar, and a tentatively identified zeolite, possibly clinoptilolite. Pyrite occurs during sulfidic diagenesis in organic-rich, muddy sediments, typically associated with authigenic carbonates. Authigenic clay is restricted to thin alteration rims on detrital silicate grains. Zeolite and feldspar are rare and may represent precursors of later cements in the sands. No significant silica authigenesis was observed, suggesting the action of inhibiting solutes or phases. The smectite to illite transformation has not yet affected the mudstones, although potassium fixation in smectite interlayers and a decrease in cation exchange capacity may have occurred.