Thesis (M. Sc.)--University of Canterbury, 2008. / Typescript (photocopy). One map in pocket. Includes bibliographical references (leaves 131-145). Also available via the World Wide Web.

Quaking aspen (Populus tremuloides) has the largest natural distribution of any tree native to North America, ranging from Alaska through the breadth of Canada and south to mid-Mexico. The Laurentide ice sheet occupied most of the current range of P. tremuloides until the late Pleistocene epoch, so this species has undergone a significant, geologically recent range expansion. Surprisingly, range-wide patterns of genetic variation in P. tremuloides have never been described. Using a sample set representing the full longitudinal and latitudinal extent of the species distribution, I have conducted a phylogeographic analysis for P. tremuloides. Preliminary results comparing both nuclear and chloroplast DNA sequences revealed surprisingly low levels of divergence across the range. Because of this remarkably shallow genetic divergence among aspen populations, I used a set of rapidly-evolving molecular markers (microsatellites) to describe patterns of gene flow and diversity and to correlate those patterns with landscape features and histories. I analyzed eight microsatellite loci in 794 individuals from 30 sampling sites. From this multilocus data set, I identified pronounced genetic structuring across the range. Strikingly, sampling sites representing the southwestern portion of the range, the western United States and Mexico, form a distinct cluster. Sites within this southwestern cluster display dramatically reduced within-site genetic diversity but elevated regional genetic diversity, which suggests that populations in the southwestern portion of the range make up a stable edge persisting through multiple climate oscillations. Based on the uniqueness of the southwestern cluster and the climatic differences between the southwest and northern portions of the range, I propose that the southwestern cluster may represent a distinct ecotype. I also identified hotspots of diversity that correspond with potential refugia during the last glacial maximum but additional work is needed to refine these patterns. Further, my findings provide a solid foundation for a range of future studies on adaptive genetic and trait variation in this species.

<p>Development of a predictive model for the distribution of diagenetic alterations and related evolution of reservoir quality of sandstones was achieved by integrating the knowledge of diagenesis to sequence stratigraphy. This approach allows a better elucidation of the distribution of eogenetic alterations within sequence stratigraphy, because changes in the relative sea level induce changes to: (i) pore water chemistry, (ii) residence time of sediments under certain near-surface geochemical conditions, (iii) variations in the detrital composition, and (iv) amounts and type of organic matter.</p><p>This thesis revealed that eogenetic alterations, which are linked to sequence stratigraphy and have an impact on reservoir quality evolution, include formation of: (i) pseudomatrix and mechanically infiltrated clays in fluvial sandstones of the lowstand and highstand systems tracts (LST and HST, respectively), (ii) kaolinite in tide-dominated deltaic and foreshore-shoreface sandstones of HST, Gilbert-type deltaic sandstones of LST and fluvial deltaic sandstones of LST, (iii) kaolinite and mechanically infiltrated clays in sandstones lying below sequence boundary, (iv) K-feldspar overgrowths in fluvial deltaic LST, (v) glaucony towards the top of fluvial deltaic LST immediately below and at transgressive surface (TS) and in foreshore and shoreface transgressive systems tracts (TST) below parasequence boundaries (PB) and maximum flooding surface (MFS), (vi) framboidal pyrite and extensive cementation by calcite and dolomite in foreshore and shoreface and tide-dominated deltaic TST, and shoreface and tidal flat HST bioclastic-rich arenites particularly in the vicinity of PB, TS and MFS, (vii) pervasive cementation by iron oxide in shoreface-offshore and shoreface sandstones of TST immediately below the MFS, (viii) zeolites and palygroskite in shoreface sandstones of TST and HST, particularly above PB, and (ix) cementation by siderite in Gilbert-type deltaic sandstones of LST, tide-dominated deltaic and foreshore-shoreface sandstones of HST and in tide-dominated deltaic sandstones of TST, particularly at MFS. Moreover, this thesis revealed that the distribution of eogenetic alterations strongly control, and thus provide information for constraining the distribution patterns of mesogenetic alterations, such as illitization of mechanically infiltrated clays and dickitization of kaolinite, and hence of related reservoir quality evolution of sandstones during progressive burial.</p>

Development of a predictive model for the distribution of diagenetic alterations and related evolution of reservoir quality of sandstones was achieved by integrating the knowledge of diagenesis to sequence stratigraphy. This approach allows a better elucidation of the distribution of eogenetic alterations within sequence stratigraphy, because changes in the relative sea level induce changes to: (i) pore water chemistry, (ii) residence time of sediments under certain near-surface geochemical conditions, (iii) variations in the detrital composition, and (iv) amounts and type of organic matter. This thesis revealed that eogenetic alterations, which are linked to sequence stratigraphy and have an impact on reservoir quality evolution, include formation of: (i) pseudomatrix and mechanically infiltrated clays in fluvial sandstones of the lowstand and highstand systems tracts (LST and HST, respectively), (ii) kaolinite in tide-dominated deltaic and foreshore-shoreface sandstones of HST, Gilbert-type deltaic sandstones of LST and fluvial deltaic sandstones of LST, (iii) kaolinite and mechanically infiltrated clays in sandstones lying below sequence boundary, (iv) K-feldspar overgrowths in fluvial deltaic LST, (v) glaucony towards the top of fluvial deltaic LST immediately below and at transgressive surface (TS) and in foreshore and shoreface transgressive systems tracts (TST) below parasequence boundaries (PB) and maximum flooding surface (MFS), (vi) framboidal pyrite and extensive cementation by calcite and dolomite in foreshore and shoreface and tide-dominated deltaic TST, and shoreface and tidal flat HST bioclastic-rich arenites particularly in the vicinity of PB, TS and MFS, (vii) pervasive cementation by iron oxide in shoreface-offshore and shoreface sandstones of TST immediately below the MFS, (viii) zeolites and palygroskite in shoreface sandstones of TST and HST, particularly above PB, and (ix) cementation by siderite in Gilbert-type deltaic sandstones of LST, tide-dominated deltaic and foreshore-shoreface sandstones of HST and in tide-dominated deltaic sandstones of TST, particularly at MFS. Moreover, this thesis revealed that the distribution of eogenetic alterations strongly control, and thus provide information for constraining the distribution patterns of mesogenetic alterations, such as illitization of mechanically infiltrated clays and dickitization of kaolinite, and hence of related reservoir quality evolution of sandstones during progressive burial.

This thesis develops a better knowledge of the extent and timing of glaciations in southern Argentina throughout the Quaternary. It provides a detailed understanding of successive major glacial outlet lobes in the Lago Pueyrredón valley. The glacial and glaciofluvial deposits in the valley, as elsewhere in the region, are extremely well-preserved and reflect punctuated glacial advances between ~ 1.1 Ma and ~ 17 ka. Several intermediate glaciations are undated, constrained by the limited time frame of radiocarbon age dating, the limited potential volcanic sites for K-Ar or 40Ar/39Ar age dating, and erosion and exhumation problems associated with cosmogenic-nuclide surface exposure ages on moraines. This thesis provides a new chronology for the mid-Quaternary glaciations based on methodological advances in cosmogenic-nuclide surface exposure age dating. This is done by deriving ages from glacial outwash terrace sediment and demonstrating their reliability. The work shows that for younger (i.e., last glacial) moraines, well-constrained ages can be derived from the common-practice of dating large boulders on the moraine surface. However, on older moraines, the ages so-derived become considerably scattered. This is interpreted to be caused primarily by boulder exhumation as a consequence of moraine erosion, resulting in shorter residence of some boulders at the surface relative to the moraine formation date. By contrast, glacial outwash surfaces in this area, if carefully chosen, can be shown to have undergone little aggradation or erosion, and thus have had long and consistent surface exposure since formation. Provided these surfaces can be stratigraphically linked with the glacial limits, they can provide good surface exposure ages. This has been convincingly confirmed in one location by a sequence of ages obtained from a 10Be concentration depth-profile which demonstrate the surface stability and lack of inherited nuclides. Using these methods, cosmogenic 10Be and 26Al surface exposure ages indicate successive major advances occurred at ~ 1.2 Ma, ~ 600 ka, ~ 260 ka and ~27 – 17.5 ka. These are correlated with global marine and ice core records.