Thesis (Ph. D.)--University of Wisconsin--Madison, 1974. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

<p> Eight dissolution caves from the Helderberg Plateau in Schoharie County, New York were studied to investigate unusual sediment packages previously interpreted to be deposits laid down during stagnant ice-cover conditions of the Wisconsin glaciation. The sediment package, consisting of white finely laminated silts and clays are overlain by coarse gravels, in turn overlain by dark silts and clays. Analysis of 63 sediment samples was inconclusive in terms of organic content, but indicated a higher degree of fine-grained calcite material in the white clays than in the overlying units. The caves with the white clays exist only within the footprint of Glacial Lake Schoharie, with lower elevation caves containing a thicker white clay sequence, a measure of the duration of lake cover. The sediment sequence represents glacial rock flour formed under stagnant lake conditions, overlain by outwash deposits emplaced during lake termination, and more recent sediment from soil-loss deposition.</p>

Thesis (Ph. D.)--University of Wisconsin--Madison, 1963. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

The record of the changing composition of planktonic foraminifer assemblages constitutes a record of changes in the hydrography of the upper water column. A priori knowledge of the ecology and paleoecology of prominent taxa is used to interpret past changes in the hydrography of the upper water column, particularly the position of the seasonal thermocline. In this study planktonic foraminifers have been counted at five sites in the equatorial Pacific (ODP Site 806, 807, 847 and 852) and Atlantic (ODP Site 925). The initial sampling interval at all sites is $\sim$9.5 m ($\sim$250 kyr) through approximately the last 6 m.y. In the first paper the results of low-resolution faunal counts of four sites are presented in the depth domain. In the upper Miocene both eastern and western samples contained 60% thermocline dwellers and 40% mixed-layer dwellers. At the western sites the mixed-layer dwellers increase until they constitute 80% of the assemblage in the Pleistocene. At ODP Site 847 thermocline dwellers increase in the Pleistocene to comprise $>$80% of the assemblage. In the second paper data from ODP Sites 806 and 847 was placed in the time domain and higher-resolution sampling ($\sim$20 cm = $\sim$10 kyr) was carried out through two intervals (4.35-4.10 Ma and 3.15-2.90 Ma). The disappearance of thermocline-dwelling Neogene globoturborotalitids at ODP Site 806 coincides with the reduction of late Miocene Antarctic ice volume and southeast tradewind strength, the end of the biogenic bloom in the Pacific and the beginning of the closing of the Central American Seaway. The expansion of thermocline dweller Neogloboquadrina dutertrei at ODP Site 847 follows the onset of large-scale Northern Hemisphere glaciaton. The third paper explores the relationship between isotopic data for three species (Globigerinoides sacculifer, Neogloboquadrina dutertrei and Globorotalia crassaformis) and faunal count data. Assemblage composition at ODP Site 925 is principally affected by the intensity of downwelling associated with the ITCZ, which moves steadily equatorward from the early Pliocene to the early Pleistocene due to the cooling of the Northern relative to the Southern Hemisphere.

Multi-proxy sediment records from four lakes in the Venezuelan Andes document changes in tropical climate over timescales of decades to millennia. The results are grouped into three topics: the Little Ice Age, the Holocene climate history, and atmospheric moisture balance of South America from oxygen isotopes. A 1500-year reconstruction of climate history and glaciation indicates four glacial advances occurred between 1250 and 1810 A.D. These advances are coincident with solar activity minima. Temperature declines of 2.3 to 3.4° C and precipitation increases of 25 to 70% are required to produce the observed glacial responses. These results highlight the sensitivity of high-altitude tropical regions to relatively small changes in radiative forcing, implying even greater responses to future anthropogenic forcing. On longer timescales, the Venezuelan Andes were generally wetter during the early Holocene. The middle Holocene was a time of low lake levels and reduced moisture balance whereas the late Holocene was wetter, with the wettest period occurring during the Little Ice Age. The pattern of millennial climate variability in Venezuela appears to be either a wet-dry-wet (Andes) or dry-wet-dry (lowlands) sequence. Comparison with climate records from North, Central and South America suggests this pattern is widespread near the northern and southern edges of the tropical monsoon climate regime and along the Andes near the equatorial Pacific. The isotopic composition of Andean precipitation reflects evaporation conditions over the Atlantic Ocean, moisture recycling over the South American lowlands and uplift to the Andes. The isotopic composition of precipitation in the Venezuelan Andes, reconstructed from lake sediment diatom oxygen isotope records, show a 2.4 ‰ decrease during the Holocene. This decrease reflects a reduction in the moisture entering South America which reaches the Andes. Ice cores from Peru and Bolivia exhibit similar isotopic trends. Direct orbital changes in solar insolation cannot explain the synchronous trends in both climatic and isotopic histories throughout the neotropics. However, sea surface temperature variation in the tropical Pacific may explain these trends because modern interannual variability in this region has similar effects in both hemispheres.

Thesis supervisor: E. Arthur Bettis, III. Includes bibliographic references (p. 102-107).

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