Browsing by Subject "stratigraphy"
Now showing 1 - 5 of 5
Results Per Page
Sort Options
Item Acoustic characteristics of bay bottom sediments in Lavaca Bay, TX(Texas A&M University, 2005-08-29) Patch, Mary CatherineThe purpose of this study is to examine the sediment stratigraphy and oyster reefs of Lavaca Bay. There has been little previous research on the bay??s stratigraphy, and information from this study is important for industry and resources management. The Lavaca Bay estuary is a drowned river valley containing a history of estuary development in the late Pleistocene and Holocene. We used a chirp sonar to gather acoustic reflection profiles, which were classified to categorize and trace reflectors. The data were plotted to make maps of the distribution of various reflection types and contour maps of reflector surfaces. The maps were compared with previous studies of Lavaca Bay and Galveston Bay to aid interpretation. The vertical sediment stratigraphy showed two main reflector packages. The upper package, bay bottom to ~25 m depth, is mostly acoustically transparent with a few, semi-continuous, prominent reflectors in the upper 5-10 m. The lower package ranges from 15-40 m depth with several strong reflectors sometimes underlain by unconformities. To classify reflector characteristics, the upper package was divided into two categories, each with 4 sub-categories: 1) surface reflectors??weak, medium, strong, and ringing, which describe the general acoustic return of the bay bottom, and 2) strong, shallow reflectors??surface strong, mounds, buried strong, andburied multiples, which describe strong acoustic returns in the upper 5 m of stratigraphy. Within the lower package, four categories were recognized: 1) subbottom reflectors/horizons, occurring ~20-40 m depth, 2) deep wipeout (incoherent/wipeout zone), ~10-30 m depth, 3) clinoforms, ~5-30 m depth, and 4) terraces, ~10-30 m depth. The data interpretation agrees with previous studies suggesting Lavaca Bay filled beginning with coarse sediment and grading to finer sediment. In addition, the surface type reflectors are indicative of bottom type, the strong, shallow reflectors are largely indicative of oyster reef/shell, and the subbottom reflectors are related to the Pleistocene and bay fill. The location/extent of oyster reefs in the bay does not agree well with previous studies, suggesting either oysters do not grow over older ones or differences between the chirp sonar response and other methods significantly differentiate the interpretation of their locations/extents.Item Geoarchaeological Investigation of the Coats-Hines Site (40WM31), Williamson County, Tennessee(2013-07-24) Schmalle, Kayla AnneThe Coats-Hines site (40WM31) is a potential pre-Clovis site located in Franklin, Tennessee. The site rests, geographically, at the convergence of the Central Basin and Western Highland Rim. The site was discovered during the construction of a nearby golf course when a salvage team uncovered a mature female mastodon.. The site was later excavated in 1994-1995, during which time two additional mastodons were uncovered, in direct association with lithic artifacts. Preliminary radiocarbon dates reveal the site was deposited during the late Pleistocene epoch at roughly 12,000^(14)C yr BP. During the summer of 2012, the site was excavated with the goal of determining the depositional setting of the site and geographic region, as well as establishing the antiquity of the archaeological remains. The site geology was determined through field interpretation and texturing, micromorphological analysis, laboratory particle size analysis, and radiocarbon dating. Sedimentation at the site is a combination of cherty colluvium from upslope as well as alluvium. Four chronostratigraphic sequences of sedimentation were determined to have occurred during the last glacial, the Pleistocene-Holocene transition, the Holocene, and modern time periods. The volume, distribution, and composition of the nine defined stratigraphic units are dependent on the fluctuations occurring in the climate during these time periods. The climate changes and rates of deposition occurring at Coats-Hines were correlated to similar sites in the region. The Coats-Hines site was surveyed along the wet-weather drainage that bounds the site during in the spring of 2013. A channel unconformity was discovered, likely dating to the Pleistocene-Holocene transition and providing context to the 1994/1995 excavation.Item Neogene stratigraphic relationships within the Nam Con Son Basin, offshore Vietnam resulting from tectonics, eustasy, and sediment flux(2009-05-15) Wright, Christine M.The South China Sea is a region of significant importance in terms of the records of SE Asian tectonics, including Tibetan Plateau uplift, and the onset and evolution of the East Asian monsoon. The Mekong River has been a dominant sediment source since at least late Miocene time and has headwaters on the eastern Tibetan Plateau. Understanding the Pliocene to Recent stratigraphy of the paleo-Mekong Delta and associated shelf-edge deposits aids in understanding changes in accommodation, sea level, and sediment supply. This record might then be useful in interpreting the longterm history of basin evolution in the Nam Con Son Basin. Nine sequence boundaries and associated sequences are recognized along the late Miocene to latest Pleistocene shelf in the East Nam Con Son Basin. Age constraints were assigned to key stratigraphic horizons by correlating sequence boundaries with published sea level curves. Accommodation in the study area is controlled by shelf -edge compaction, rift-related thermal subsidence, non-rift-related anomalous subsidence,Two primary sources supplied sediment to the southwestern South China Sea during Pliocene to Recent time and likely include the paleo-Mekong Delta and a fluviodeltaic system originating from the Sunda Shelf, such as the Molengraaff River. Changes in thickness, area, and location of Pliocene to Recent shelf-edge delta deposits reflect changes in accommodation and sediment supply over time, as well as progradation of the shelf edge during Pliocene to Recent time and avulsion of the shelf edge delta. Anomalous subsidence of LGM shelf edge deposits is estimated at approximately 40-50 m deeper than expected. The current depth of the LGM deltaic wedge may indicate renewed rapid tectonic subsidence during the last 18,000 yrs, possible compaction effects or a combination of these. eustatic change, and shelf edge faulting.Item Sequence Stratigraphy and Detrital Zircon Geochronology of the Swan Peak Quartzite, Southeastern Idaho(2012-02-14) Wulf, Tracy DavidThe supermature Middle-Late Ordovician Swan Peak quartz arenite was deposited on the western Laurentia passive margin and is very fine to fine grained, well-rounded, well-sorted, and silica-cemented. Laurentia was positioned over the equator during the Middle-Late Ordovician, suggesting that basement rock along the Transcontinental Arch was intensely eroded in a humid climate to produce this and other coeval quartz arenites. To determine provenance for the Swan Peak Quartzite, zircon grains were analyzed using LA-ICP-MS and the results were constrained within a sequence stratigraphic framework. Depositional environments of the Swan Peak Quartzite record an offshore-to-onshore transition with five facies (A-E). Facies A only occurs at the base of the Bear Lake section and may record an incised valley or localized embayment. It is the deepest water facies in the succession containing shale and quartz arenite interbeds. Facies B through E are interpreted as lower, middle, upper shoreface/foreshore depositional environments, respectively, based on primary sedimentary structures and bioturbation. Detrital zircon age spectra of the Swan Peak Quartzite have four distinct populations: the two main populations are at 1.8 - 2.0 Ga (Paleoproterozoic) and between 2.5 - 3.0 Ga (Archean), with a smaller, but persistent, population at 2.0 - 2.1 Ga, and a very minor 0.8 - 1.2 Ga (Mesoproterozoic) population occurring mainly in the tops of the measured sections. The base of each section has a larger Archean peak whereas the top of each section is predominantly Paleoproterozoic grains. Zircon data have overlap and similarity values ranging between 0.531 - 0.771 and 0.506 - 0.881, respectively, which indicates zircon age spectra of the Swan Peak Quartzite is similar to other Cordilleran Ordovician quartzites and that recycling of heterogeneous underlying sedimentary rocks was minimal. The Wyoming Craton (2.5 - 2.8 Ga) and the Trans-Hudson Orogen (1.8 - 2.0 Ga) provinces near the paleoequator likely provided the majority of zircons in the Swan Peak Quartzite. The source for the 2.0 - 2.1 Ga grains is currently unknown and the 0.8 - 1.2 Ga grains are interpreted to reflect Mesoproterozoic Laurentian tectonism. Sediment input varied in response to sea level fluctuations. Longshore transport was likely an important process in redistributing grains along the coastline during later deposition of the Swan Peak Quartzite.Item Tephrochronology and Stratigraphy of Eocene and Oligocene Volcanic Ashes of East and Central Texas(2013-12-02) Heintz, MindiSedimentary formations of east and central Texas contain many Eocene to Oligocene volcanic ash beds, with some of the younger ash layers containing hydrated but otherwise unaltered glass shards. This study analyzed samples of 15 volcanic ash beds using neutron activation analysis (NAA) of bulk ash and glass shards, inductively coupled plasma mass spectrometry (ICPMS) of bulk ash, and electron microprobe analysis of both apatite phenocrysts and glass shards to characterize their geochemistry. ^(40)Ar/^(39)Ar dating of single sanidine phenocrysts gives an age of 30.64 ?0.03 Ma for the youngest (Sam Rayburn) sample to 41.79 ?0.02 Ma for the oldest (Hurricane Bayou) sample. The nine radiometric dates obtained by this study serve to better constrain the ages of the Claiborne and Jackson Groups and the Catahoula Formation of Texas with the Conquista and Hurricane Bayou ash beds being possible calibration points for the Eocene/Oligocene and Lutetian/Bartonian boundaries, respectively. Geochemical fingerprinting, particularly apatite phenocryst chemistry, supports the correlation of the Little Brazos volcanic ash in Brazos County to volcanic ash deposits in Houston County, Texas, and provides supporting evidence for equivalence to the St. Johns bentonite in Louisiana. Geochemical fingerprinting also suggests equivalence of the Caddell (Koppe Bridge) volcanic ash to deposits within the Gonzales County bentonite mines of south-central Texas. Major element electron microprobe data from seven samples of volcanic glass shards indicate the ash was produced from sub-alkaline rhyolitic volcanism and the trace-element characteristics of all 15 ashes are consistent with subduction-related sources. Rare earth element (REE) data indicates light rare earth element (LREE) enrichment with a moderate Europium anomaly. The Sierra Madre Occidental of Mexico is the likely source area, but the Trans-Pecos of Texas and Mogollon-Datil of New Mexico cannot be definitively ruled out as possible eruptive source regions.