No description available.

No description available.

Patterns of fossil diagenesis caused by groundwater leaching provide insight into how shells are altered. This study analyzes fossils in unconsolidated terrigenous sediments from the Virginia Coastal Plain, unlike previous studies conducted mostly in carbonate terranes. The vertical and lateral distribution of diagenetic states was mapped in an outcrop (63 m by 2.1 m) of the Yorktown Formation. A paleostream channel located at one end was incised during the Pleistocene and filled with sediments of the Shirley Formation. The Tabb Formation unconformably overlies the outcrop. Acidic groundwater caused the observed patterns of fossil and sediment diagenesis. These patterns include zones of fossil alteration, diagenetic stratification of the sediment, and fossil diagenesis on a microstructural level. Groundwater movement, controlled by the presence of the paleochannel, caused diagenetic alteration or complete dissolution of the fossils, and possibly caused precipitation of fine-grained iron oxyhydroxides. All carbonate material in the vicinity of the paleochannel is completely dissolved away, although iron oxyhydroxide coatings of fossils remain. Away from the paleochannel Crepidula fornicata (gastropod; aragonite), Ostrea sp. (bivalve; calcite), Balanus sp. (barnacle; calcite), and bryozoans (calcite) are found in parallel zones of alteration that dip toward the paleochannel and cut across horizontal sedimentologic and fossiliferous layers. Groundwater also leached the Yorktown sediments. This alteration caused a diagenetic stratification of the sediment, with unaltered greenish-gray silty fine sand along the base of the outcrop, overlain by leached yellowish-brown silty fine sand and areas of concentrated iron oxyhydroxides. The preservation of both aragonitic and calcitic shells was affected by groundwater movement. Original aragonitic shell material is found as chalky, uncrystallized specimens or neomorphosed shells, or is completely dissolved with only molds or ghosts remaining. Neomorphosed specimens typically consist of calcite-replaced shell material with pockets of original aragonite, and sparry calcite filling empty shell cavities. Original calcitic shell material is either chalky or unaltered. Chalky shells range from relatively hard to soft and pasty. Crepidula shells of intermediate chalkiness tend to separate into thin flakes, caused by dissolution along growth surfaces. Chalkiness of pasty shells is caused by dissolution of shell material (without recrystallization) and not simply loss of organic matrix. SEM photos of Crepidula reveal the more porous and leached appearance of chalky shells in contrast with hard; unaltered shells. The presence of chalky aragonitic and calcitic shells indicates that chalky textures are, to some degree, independent of mineralogy and microstructure. / M.S.

No description available.

This diploma thesis summarizes results of the detailed morphometric analysis of extensive fossil materials of the genus Myotis from the upper Pliocene deposits of Javoříčské caves (Czech Republic) and Urwista cave (Poland). Patterns of phenotype variation of particular fossil populations were analyzed with aid of uni- and multivariation techniques, compared with type series of fossil taxa described from MN15 site Gundersheim and a comparative series of extant European species. Nine fossil and 10 extant species were identified and further reexamined in terms of their phenotype variation and possible phylogenetic relations. The phenotype structure of fossil assemblages were compared to that of Gundersheim and extant European fauna: samples from Urwista cave show clear resemblances to the former one, those from Javoříčské cave exhibit certain similarities to the extant European fauna despite clear differences in variation patterns of particular species. Technical preparation, documentation by photographic material, measurement and statistical analysis is included in this work. Key words: bats, Pliocene, phenotype dynamics, community structure

Geologic mapping, basin analysis, and tephrochronologic analysis in the Clifton quadrangle of southeast Idaho indicates that the modern Basin-and-Range topography is only a few million years old and that the bulk of Cenozoic extension was accommodated by slip on an older low-angle normal-fault system, the Bannock detachment system. The detachment system was active between ~12 and < 4 Ma and accommodated ~50 % extension. Cross-cutting relationships show that the master detachment fault, the Clifton fault, is the youngest low-angle normal fault of the system, was active at a low angle, and has not been rotated to a low-dip angle through time. Map patterns and relationships indicate that the hanging wall to the detachment system began as a cohesive block that later broke up along listric and planar normal faults that either sole into or are cut by the master detachment fault. The Miocene-Pliocene Salt Lake Formation, a syntectonic, basin-fill deposit of the Bannock detachment system, was deposited during three sub-episodes of extension on the detachment system. Depositional systems within the Salt Lake Formation evolved from saline/alkaline lakes to fresh water lakes and streams to braided streams in response to the changing structural configuration of rift basins in the hanging wall of the detachment system. After breakup of the hanging wall began, the master detachment fault excised part of the hanging wall and cut hanging-wall deposits and structures. The structural geometry of the Bannock detachment system strongly resembles that of detachments documented in metamorphic core complexes. Therefore, we interpret the Bannock detachment system as a proto-metamorphic core complex, akin to the Sevier Desert detachment fault. The Bannock detachment system also collapsed the Cache-Pocatello culmination of the dormant Sevier fold-and-thrust belt, much like the Sevier Desert detachment collapsed the Sevier culmination. Structures of the Bannock detachment system are overprinted by a second episode of extension accommodated by E- and NE-trending normal faults that may be related to subsidence along the Yellowstone hotspot track and a third episode of extension accommodated by high-angle, Basin-and-Range normal faults. This last episode of extension began no earlier than 4-5 Ma and continues today.

Basalt outcrops in Curlew Valley consist of vii several flow remnants and eruptive centers situated along the valley margins. Basalt is also found in association with salic rocks that erupted in the central portion of The basalts are of probable Pliocene age and the valley. were erupted during a period of active extensional tectonics. Since their emplacement, and downfaulted. the basalts have been extensively eroded The present morphology reflects the erosional and depositional processes of prehistoric Lake Bonneville. Twelve samples were analyzed chemically for major oxides, trace elements, and rare-earth elements. The basalts form a hypersthene normative series ranging from olivine tholeiite to tholeiite. Based on chemical data, the basalts form three distinct groups. Comparison of the major oxides shows two of the groups forming a differentiation sequence separate from the third group. Trace element and rare-earth element data indicate that the three chemical groups are related to a common source but that two batches of magma probably emanated from this source. Pyrolite, spinel lherzolite, and garnet lherzolite were evaluated as hypothetical mantle materials from which a parent magma might be derived through partial melting. Based on rare-earth element profiles, garnet lherzolite appears to be the most likely source material for deriving the basalts. The trace element and rare-earth element data do not show any anomalies that would suggest contamination from crustal material. Comparison of chemical data shows that the Curlew Valley basalts are genetically similar to basalts from the Kelton and Rozel Point-Black Mountain areas, southwest and southeast of the study area, respectively. The Curlew Valley basalts are chemically similar to olivine tholeiites from the Snake River Plain and Blackfoot Reservoir areas in Idaho, but they do not show much similarity to basalts near Snowville, Utah, northeast of the study area. The Curlew Valley basalts are generally more iron rich and less alkalic than other basaltic rocks from the eastern Basin and Range Province.

Mesoamerica is considered a biodiversity hot spot with levels of endemism and species diversity likely underestimated. For mammals, the patterns of diversification of Mesoamerican taxa still are controversial. Reasons for this include the region's complex geologic history, and the relatively recent timing of such geological events. Previous studies, however, support the view that substantial migration between North (NA) and South America (SA) occurred prior or/and during the Great American Biotic Interchange (GABI) ~3.5 Ma. This was followed by repeated periods of isolation during Pleistocene climatic oscillations, which produced most of the diversification in the region. From a North American origin, the subfamily Sigmodontinae migrated to SA, where most of its present day diversity exists. The taxonomic history of this subfamily, and of Oryzomynii, its largest tribe, has been exceptionally complex. Recently, extensive studies have helped to clarify genealogical relationships among major clades, but have left the evolutionary histories of several groups unresolved. Such is the case for the genus Handleyomys that includes nine species; seven of which are endemic to Mesoamerica; and of its phylogenetic position among closely related genera Euryoryzomys, Hylaeamys, Oecomys, Nephelomys and Transandinomys. The results supported the monophyly of Handleyomys, and four clades with inter-generic levels of divergence within the genus, three of these clades restricted to Mesoamerica (the alfaroi, chapmani and melanotis species groups). Furthermore, the estimated time for the split of the Mesoamerican Handleyomys is on average, 2.0 Myr older than the proposed migrations to NA during the GABI. In addition, the position of Handleyomys as the sister clade to Euryoryzomys, Hylaeamys, Oecomys, Nephelomys and Transandinomys was well supported, as it was a biogeographic hypotheses that depicted a polyphyletic origin for these genera and Handleyomys 5.5-6.0 Ma. The integrative approach implemented in this dissertation allowed the development of more biologically realistic hypothesis than has previously been conducted in Mesoamerica, where half of the endemic mammals are listed under the IUCN Red list; and where mammals with small ranges, which are the most vulnerable to extinction, are found largely outside reserves. The continued decline of the ecosystems health in this region calls for a more precise account of its biodiversity for its proper conservation; and for rigorous biogeographic studies for its management, since the region also serves as a biological corridor for intercontinental connectivity.

Graduation date: 1987

The northern Los Angeles basin is influenced by two structural styles: the west-trending compressional Transverse Ranges to the north, and the strike-slip Peninsular Ranges to the south. The interaction of these two structural styles has resulted in a complex fold/fault belt at the northern margin of the Los Angeles basin, which deforms a variable sequence of late Miocene through Quaternary marine strata. Subsurface mapping of Quaternary marine gravels by electric-log correlation documents the latest phase of deformation in the northern Los Angeles basin. The Quaternary marine gravels are folded at the Wilshire arch, the Hollywood basin, the central trough, the Newport-Inglewood fault, and the Santa Monica fault. The west-plunging Wilshire arch, which follows Wilshire Boulevard east of the Newport- Inglewood fault, is a broad fold identified and named in this study. Deformation of the Wilshire arch, which is underlain and caused by the potentially-seismogenic Wilshire fault, began around 0.8 - 1.0 Ma. A fault-bend fold model, based on the shape of the Wilshire arch, indicates a dip-slip rate of 1.5 - 1.9 mm/yr for the Wilshire fault, whereas a three-dimensional elastic dislocation model indicates a right-reverse slip rate of 2.6 - 3.2 mm/year for the Wilshire fault. The finer-grained marine Pliocene strata include the late Pliocene to early Pleistocene Pico member, and the early Pliocene Repetto member, of the Fernando Formation. Thickness and lithology variations in the Pico and Repetto strata, which were influenced by syndepositional structures, indicate that the entire Pliocene and the latest Miocene were characterized by compression. The primary structure present throughout the Pliocene is a south-dipping monocline, which was underlain and caused by a deep reverse fault, dipping ~55 - 60° to the north, referred to here as the Monocline fault. Relative subsidence of the central trough resulted in deposition of up to 7000 ft (2135 m) of Pico strata, and up to 5000 ft (1525 m) of Repetto strata, compared to zero deposition on the monoclinal high. In the western part of the study area, the south-dipping monocline is interrupted by the secondary East Beverly Hills fold, which may be a rabbit-ear fold that accommodates excess volume by bedding-parallel slip. The East Beverly Hills fold was active in the latest Miocene through Pliocene, and was most active during early Pliocene Repetto deposition. In the eastern part of the study area, the monocline is interrupted by the Las Cienegas fold, which formed in the hangingwall of the Las Cienegas fault. The Las Cienegas fault was a normal fault in the late Miocene, and was reactivated in the Pliocene as a steep reverse fault. Folding and uplift on the Las Cienegas anticline occurred throughout the Pliocene, with the greatest amount occurring during lower and lower-middle Pico deposition. / Graduation date: 1994