A dearth of reliably-dated paleolake records from the southern Basin and Range has limited knowledge of past water balance changes there, precluding a more complete understanding of late Pleistocene atmospheric circulation across western North America. Paleoshorelines in closed basins throughout the region can provide accurately dated records of local effective moisture variations, representing a largely untapped source of paleohydrologic information. This dissertation presents paleohydrologic reconstructions from depositional successions in two basins at 32°N, approximately 100 km apart: Willcox basin, in southeastern Arizona, and Playas Valley, in southwestern New Mexico. Also presented are the results of ¹⁴C dating of charcoal samples from the El Fin del Mundo Clovis archaeological site, in northwestern Sonora, Mexico. In depth analysis of these results allowed constraint of the "small sample effect" on the charcoal ages, found to be smaller than 1σ of analytical uncertainty. The magnitude of the problem in ages from miniscule shell samples in the Willcox and Playas chronologies was found to be similar. The successions record moist pluvial conditions from ~20-13 ka in Playas, and>37-11 ka in Willcox, with most dates younger than 19 ka--before which there is no solid evidence for lake transgressions. There is clear evidence for overlapping highstands between ~18.3 and 17.9 ka and a brief highstand of Cochise at ~12.9 ka, coinciding with Heinrich events H1b and H0, respectively. Temporal concordance between wet periods and perturbations in the North Atlantic ocean and/or southern Laurentide ice sheet supports the idea that abrupt paleoclimatic changes in the southwestern U.S. occurred in response to large-scale atmospheric linkages to the northern high latitudes. The H1b highstands fill a hiatus in ¹⁴C dates compiled from paleoshorelines throughout the western U.S., and correspond to the first part of a lowstand in paleo-Lake Estancia (35°N), in north-central New Mexico. Anti-phasing within New Mexico suggests that the newly documented highstands resulted from an increase in southerly-sourced precipitation. This is consistent with paleoenvironmental evidence from southern Arizona and New Mexico that points toward periodic intensification of the summer monsoon during the late Pleistocene.

No description available.

The Bahamian Archipelago is one of the few locations in the world where ooid formation is actively occurring. Ooid cortices from six locations in the region were incrementally dissolved and analyzed for 14C, δ18O, δ13C, Mg/Ca and Sr/Ca ratios. Ooids were examined under SEM after each step in the incremental analyses to characterize the nature of dissolution. Radiocarbon dating indicates that surface ooids began forming across the Archipelago between 1000 and 2800 yr BP and continue to form today. The ooids have the same pattern of microboring alteration across the region. The surface and outer cortex of the ooids are punctuated with unfilled microborings, whereas the inner cortex contains two morphologies of aragonite cement filling the microborings. The two morphologies of cement form in association with two different species of cyanobacteria, one is Solentia sp. the other is interpreted to be Hyella sp.. The chemistry of ooids from across the region is remarkably similar. δ18O and δ13C values for all samples vary directly, having a slope of approximately 1. The outer cortex has low δ18O and δ13C values of -3.4‰ and 0.2‰ respectively, whereas the δ18O and δ13C values of the inner cortex are high with values of 1.9‰ and 6.8‰ respectively. The presence of aragonite cement in microborings in the inner cortex increases the overall isotopic composition of both oxygen and carbon in the ooid, causing it to appear close to equilibrium with seawater. The isotopic variation in δ18O and δ13C within the cortex can be characterized as a mixing line between the low values in the unaltered ooid laminae and the aragonite cement in the microborings. The most exterior portion of the ooid has very high Mg/Ca values and is interpreted as an amorphous calcium carbonate (ACC) coating. There are two other phases in the cortex, both being aragonite. The outer cortex has a higher Mg/Ca ratio and lower Sr/Ca ratio than the inner cortex. This difference in chemistry is a result of the presence of aragonite cement in the inner cortex. Stable isotopic and trace element results coupled with SEM investigations indicate that microbes do not play a role in ooid formation, but instead alter the texture and chemistry of ooids after they have formed. This alteration occurs throughout the entire shoal region. A new model of ooid formation is proposed whereby a veneer of ACC precipitates on an ooid while it is at the sediment-water interface (the active phase). This veneer of ACC later recrystallizes to aragonite needles, possibly nucleating on organic material and a new cortex layer is formed. Observations from this study lead to a deeper understanding of the chemical processes involved in ooid genesis, which allows for a better understanding of paleoenvironments hosting ooid formation. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2009-01-27 13:29:42.765

Isotopes and hydrochemistry were used to define groundwater flow systems and better understand the hydrogeological setting of the Karijini National Park within the Central Pilbara region, this study was initiated because of the near proximity of the Marandoo iron ore mine to the National Park. Based on the stable isotope composition of the water samples, two main groups of water can be identified. Groundwater is characterised by depleted δD and δ¹⁸O, suggesting no significant evaporation effect. Surface water on the other hand is more enriched in δD and δ¹⁸O due to evaporation. The relatively high concentration of Cl- compared to rainfall and depleted δD and δ¹⁸O values of groundwater indicate that recharge of the aquifers is occurring during intense rainfall events when rapid infiltration occurs. Evapotranspiration then acts to concentrate ionic species prior to recharge. The presence of CFCs in the groundwater indicates the presence of modern recharge water. Relationships between various ionic species has shown that infiltration through the Tertiary sequence and subsquent dissolution of carbonate minerals is main influence on increasing concentrations of Ca²⁺ , Mg²⁺ , HCO₃⁻ . The TDS concentration of the groundwater in the Marra-Mamba Iron Formation that hosts the Marandoo ore body is higher than most of the water bodies surrounding the mining area. This suggests that either significant chemical modification is occuring or it is recharged by different mechanisms to that of the Karijini groundwater. Relationships between the major ion concentration and catchment area, surficial Tertiary cover and distance between recharge and discharge were identified. The results show that the hydrochemistry of the water discharging at each location within the National Park can be justified by groundwater evolution within it’s own catchment.

The structural framework of the northern Gulf of Mexico coastal zone is characterized by numerous growth fault systems. Neotectonic processes in coastal marshes in this region have been shown to be important drivers of relative sea-level rise as well as having significant influence on marsh accretion processes. One active growth fault has been identified at East Matagorda Peninsula, Texas. To characterize the Holocene behavior of this fault and the consequent sedimentary responses, a suite of fallout radionuclides (7Be, 137Cs, 210Pb) and radiocarbon, supplemented by sediment physical property data have been used to determine sediment mixing depths, rates of accumulation, and geochronology. Correlation of time-equivalent stratigraphic boundaries reveals a maximum total Holocene offset of ~1 meter. Determination of slip rates from these values reveals a linear trend of displacement as a function of distance along the fault trace with maximum slip occurring to the southwest and minimum slip to the northeast. Sediment accumulation rates from the downthrown station nearest to the fault trace display a dramatic increase over the last 30 years. Sediment bulk density and grain size data suggest an interaction between fault-driven geomorphic change and sedimentation where a migrating land-water interface has influenced the type of sediment accumulation here.

名古屋大学年代測定総合研究センターシンポジウム報告

第23回名古屋大学年代測定総合研究センターシンポジウム平成22(2010)年度報告

Submerged caves, locally referred to as cenotes, can be found throughout the Yucatan Peninsula of Mexico. These nutrient poor, aphotic “underground estuaries” lack photosynthetic primary productivity, but are often found underlying high primary productivity areas such as mangroves and tropical forests. Adjacent ecosystems contribute organic carbon to the cave systems via percolation, where it is then utilized by the obligate, cave-dwelling fish and invertebrates. Another potential pathway through which organic carbon can enter the cave food web is through chemosynthesis. Chemoautotrophic sulfur-oxidizing or nitrifying bacteria have been found in the hydrogen sulfide layer or in the sediments of some anchialine caves. Our study utilizes 13C/12C and 15N/14N stable isotopes as well as 14C radiocarbon dating to determine and compare the sources of organic matter entering a coastal anchialine cave (Cenote Aak Kimin) versus an inland cave (Cenote Maya Blue) in the Yucatan Peninsula. Stable isotopes have long been employed in tropic investigations. This study, however, is the first to utilize radiocarbon isotopes in anchialine caves. The use of both stable and radiocarbon isotopes as source indicators provides greater discrimination in systems that contain numerous carbon sources or indistinct trophic levels, particularly to distinguish between chemoautotrophic versus photosynthetically derived carbon. Results indicate that chemosynthetically derived organic carbon contributes substantially to the diet of some crustaceans, such as the stygobitic shrimp Typhlatya, while other species remain dependent on detrital inputs. Depleted δ13C values and aged radiocarbon values (as low as -47.51‰ and 1840 yrs. for Typhlatya spp.) in comparison to particulate and sediment δ13C values (lowest -32.07‰ and -28.43‰, respectively). A comparison of isotopic values between Cenote Aak Kimin and Cenote Maya Blue suggests that the trophic web of the coastal cave incorporates more photosynthetic or detrital carbon, while the inland cave, with more depleted 13C and 14C values, relies more heavily on chemoautotrophic carbon. Within both systems, however, distinct photosynthetic and chemoautotrophic levels were identified. Water quality parameters, especially dissolved oxygen and pH, support the hypothesis of bacterial activity at the halocline. Anchialine systems in the Yucatan Peninsula are threatened due to increases in tourism, development, and pollution. Quantifying and qualifying the inputs of organic carbon is vital for the management and conservation of the area’s freshwater resources.

Thesis (M.S.)--University of Hawaii at Manoa, 2006. / Includes bibliographical references (leaves 165-166). / xii, 166 leaves, bound col. ill., maps 29 cm

Isotopes and hydrochemistry were used to define groundwater flow systems and better understand the hydrogeological setting of the Karijini National Park within the Central Pilbara region, this study was initiated because of the near proximity of the Marandoo iron ore mine to the National Park. Based on the stable isotope composition of the water samples, two main groups of water can be identified. Groundwater is characterised by depleted δD and δ¹⁸O, suggesting no significant evaporation effect. Surface water on the other hand is more enriched in δD and δ¹⁸O due to evaporation. The relatively high concentration of Cl- compared to rainfall and depleted δD and δ¹⁸O values of groundwater indicate that recharge of the aquifers is occurring during intense rainfall events when rapid infiltration occurs. Evapotranspiration then acts to concentrate ionic species prior to recharge. The presence of CFCs in the groundwater indicates the presence of modern recharge water. Relationships between various ionic species has shown that infiltration through the Tertiary sequence and subsquent dissolution of carbonate minerals is main influence on increasing concentrations of Ca²⁺ , Mg²⁺ , HCO₃⁻ . The TDS concentration of the groundwater in the Marra-Mamba Iron Formation that hosts the Marandoo ore body is higher than most of the water bodies surrounding the mining area. This suggests that either significant chemical modification is occuring or it is recharged by different mechanisms to that of the Karijini groundwater. Relationships between the major ion concentration and catchment area, surficial Tertiary cover and distance between recharge and discharge were identified. The results show that the hydrochemistry of the water discharging at each location within the National Park can be justified by groundwater evolution within it’s own catchment.