No description available.

<p> Three studies on Cordilleran foreland basin deposits in the western U.S.A. constitute this dissertation. These studies differ in scale, time and discipline. The first two studies include basin analysis, flexural modeling and detailed stratigraphic analysis of Upper Cretaceous depocenters and strata in the western U.S.A. The third study consists of detrital zircon U-Pb analysis (DZ U-Pb) and thermochronology, both zircon (U-Th)/He and apatite fission track (AFT), of Upper Jurassic to Upper Cretaceous foreland-basin conglomerates and sandstones. Five electronic supplementary files are a part of this dissertation and are available online; these include 3 raw data files (Appendix_A_raw_isopach_data.txt, Appendix_C_DZ_Data.xls, Appendix_C_U-Pb_apatite.xls), 1 oversized stratigraphic cross section (Appendix_B_figure_5.pdf), and 1 figure containing apatite U-Pb concordia plots (Appendix_C_Concordia.pdf).</p><p> <b>Appendix A</b> is a combination of detailed isopach maps of the Upper Cretaceous Western Interior, flexural modeling and a comparison to dynamic subsidence models as applied to the region. Using these new isopach maps and modeling, I place the previously recognized but poorly constrained shift from flexural to non-flexural subsidence at 81 Ma.</p><p> <b>Appendix B</b> is a detailed stratigraphic study of the Upper Cretaceous, (Campanian, ~76 Ma) Sego Sandstone Member of the Mesaverde Group in northwestern Colorado, an area where little research has been done on this formation.</p><p> <b>Appendix C</b> is a geo-thermochronologic study to measure the lag time of Upper Jurassic to Upper Cretaceous conglomerates and sandstones in the Cordilleran foreland basin. The maximum depositional ages using DZ U-Pb match existing biostratigraphic age controls. AFT is an effective thermochronometer for Lower to Upper Cretaceous foreland stratigraphy and indicates that source material was exhumed from >4&ndash;5 km depth in the Cordilleran orogenic belt between 118 and 66 Ma, and zircon (U-Th)/He suggests that it was exhumed from &lt;8&ndash;9 km depth. Apatite U-Pb analyses indicate that volcanic contamination is a significant issue, without which, one cannot exclude the possibility that the youngest detrital AFT population is contaminated with significant amounts of volcanogenic apatite and does not represent source exhumation. AFT lag times are &lt;5 Myr with relatively steady-state to slightly increasing exhumation rates. Lag time measurements indicate exhumation rates of ~0.9->>1 km/Myr.</p>

The Start-Perranporth Zone is one of a number of E-W trending zones in S.W. England, which are characterised by an anomalous and structurally complex deformation history, and which are thought to reflect the influence of pre-existing basin architecture. The SPZ straddles the Start Complex in S. Devon, and is approximately coincident with the northern margin of the Gramscatho Basin in S. Cornwall. It appears to coincide with significant sedimentological, geochemical and metamorphic transitions, and may mark the site of a pre- to Early Devonian terrane boundary. This terrane boundary may have formed the northern margin to a series of small possibly transtensional basins, including the Start and Gramscatho Basins, in which thick successions accumulated prior to inversion during the Variscan orogeny. The pelitic sequences in these basins (Gramscatho Group sandstones, Start greyschists) are geochemically similar to one another, and to other Rhenohercynian basinal sequences in mainland Europe. Both the Gramscatho and Start basins are characterised by the presence of incipient ocean crust (Lizard ophiolite, Start greenschists), with a strongly depleted N-type MORB signature and evidence of ridge-related sub-oceanic early deformation. The interlayered green and grey schists of the Start Complex are separated from the shallow marine Meadfoot shales to the north by a steep north dipping normal fault, the Start Boundary Fault, which bears evidence of a long-lived movement history. This fault is intimately associated with large volumes of highly altered and replaced basic intrusives, and appears to be the surface manifestation of the basin bounding fault at depth. Approaching the SBF, the strain intensifies, primary folds tighten, the primary cleavage steepens to sub-vertical and mineral stretching lineations switch from SSE plunging (sub-parallel to the Variscan transport direction) to sub-horizontal approximately E-W trending. Immediately adjacent to the SBF, sheath folds occur, suggesting very high along strike shear strains. Small scale structures, e.g. shear bands, refold relationships, etc. consistently indicate that dextral simple shear is important during Variscan shortening. Similar, though somewhat more cryptic, evidence for dextral shear is also seen in the L. Devonian shales north of the SBF. In S. Cornwall there is a similar focusing of high strain along the northern Gramscatho margin, with a tightening of folds, a backsteepening of the primary cleavage, and the development of overprinting late crenulations. Primary stretching lineations lie E-W. There is no evidence for sheath folding on either coast, although broad phyllonite zones bearing dextrally asymmetric quartz augen provide evidence of long-lived dextral shear. Many of the high strain fabrics on the east coast are absent, probably faulted out along a major NW-SE dextral strike-slip fault (the Pentewan Fault).The small scale structural evidence along this zone consistently indicates that dextral transpression was the dominant deformation mechanism during Variscan orogenesis. The structural transitions are also suggestive of fault butttressing, e.g. secondary backfolding, backthrusting, etc. and it appears that the ~E-W trending basin bounding fault acted as an oblique buttress to the NNW directed Variscan nappes, the high angle obliquity of this collision inducing dextral transpression in the shortening cover sequence. This fault buttressing mechanism readily accounts for all of the observed anomalous small scale structures, and the marked along strike persistence of the anomalous zone.

The thesis examines the geology and geomorphology of the town of Maratea, southern Italy, and their efffect on the development of the town. Maratea is situated at the mouth of a fault-controlled valley surrounded by high limestone mountains of Jurassic and Triassic age. Recent ground movements are associated with a 2km long fault plane scarp which runs along the eastern flank of the valley and the limestone strata above the Town Centre are affected by an excellent example of a deep-seated slope deformation known as a sackung. Six limestone blocks are located in the valley floor below the fault plane scarp and in addition the area is affected by earthquakes associated with the evolution of the Apennine chain. The area has experienced two phases of neotectonic activity. Evidence from the literature places the first of these at somewhere between 2.0 MY BP and 0.7 MY BP. Subsequently the valley was deepened by a further phase of neotectonic activity, fixed by a U-series date obtained by the author, at 46.4 +/-3.5 x 103 yrs BP. Since then landslide movements have predominated. The fault plane scarp is being exhumed from beneath covering deposits and lichenometric dating, based on the species Aspicilia calcarea, shows that up to 15m of scarp face has been exposed in the last 300 - 600 years. The movements are periodically accelerated by earthquake shaking. The limestone blocks are found to be stable features, although a piece of one block, which has broken away from the main block has tilted at various times. The dates of tilting have been determined by sectioning stalactites growing on the block and dating their observed growth phases by a first-order 14C method. Tilting apparently occurred at 2400 +/-300 yrs BP and within the last 400 years. Finally a questionnaire survey covering all 1008 buildings in Maratea indicated that earthquake shaking, exacerbated by the highly variable sub-surface geology of the valley, is the primary cause of damage. These preliminary findings reinforce the case for detailed neotectonic research as a prelude to development in unstable tectonic environments.

No description available.

No description available.

No description available.

No description available.

Processing, interpretation, and modelling studies incorporating reflection seismic, VSP, and wireline data from onshore metamorphic basement in Aberdeen formed the basis for investigating the origins of unexpected sequences of coherent, laterally extensive seismic reflections, gently dipping to the NNE and occupying most of the crystalline upper crust. Wireline analysis from a vertical well drilled to 4800' in the metamorphic basement incorporated evaluation of formation lithology and fracturing. In absence of core, wireline characteristics were correlated with formation lithology using crossplots and histograms. Computed stratigraphy incorporating quartz-schist, mica-schist and igneous units agreed with cuttings analysis, outcrop geology, wireline characteristics, and known paleo-evironment of deposition. 1463 fractures counted on the FMS log showed significant NW-SE strikes and steep dips (40-50°) to the NEW. The significant fracture orientations may be an expression of the stress field affecting Scotland. Re-processing of the vibroseis seismic profiles using optimum parameters resulted in significant improvements despite limitations in the accuracy of RMS velocity estimations induced by survey characteristics. Two of the three profiles showed poor signal to noise ratio in consequence of traffic noise contamination of the data. Reflections were categorised into three kinds: (1) parallel, inclined, laterally extensive, sometimes weakly coherent, single packed reflections related to the syndepositional characteristics of the formation (metasedimentary and basic igneous units); (2) discordant, irregular, high amplitude, double or multiple peaked and usually short spaced reflections related to the post-depositional characteristics of the formation (fracture zone and acidic igneous units); and (3) two sequence boundaries, the upper of which was interpreted, on the basis of regional evidence, as both a stratigraphic boundary as well as a thrust plane. The NNE thickening and dip of the metasedimentary wedges defined by the sequence boundaries appeared to contradict inferred regional structure of the upper crust dictated by the recumbently folded Tay Nappe.

<p> Foreland and forearc basins are large sediment repositories that form in response to tectonic loading and lithospheric flexure during orogenesis along convergent plate boundaries. In addition to their numerous valuable natural resources, these systems preserve important geologic information regarding the timing and intensity of deformation, uplift and erosion history, and subsidence history along collisional margins, and, in ancient systems, may provide more macroscopic information regarding climate, plate motion, and eustatic sea level fluctuations. This thesis presents two studies focused in the Paleozoic Appalachian foreland basin system along the eastern United States and in the Mesozoic to Cenozoic Matanuska forearc basin system in south-central Alaska. </p><p> Strata of the Appalachian foreland basin system preserve the dynamic history of orogenesis and sediment dispersal along the east Laurentian margin, recording multiple episodes of deformation and basin development during Paleozoic time. A well-exposed, >600 m thick measured stratigraphic section of the Pine Mountain thrust sheet at Pound Gap, Kentucky affords one of the most complete exposures of Upper Devonian through Middle Pennsylvanian strata in the basin. These strata provide a window into which the foreland basin's development during two major collisional events known as the Acadian-Neoacadian and the Alleghanian orogenies can be observed. Lithofacies analysis of four major sedimentary successions observed in hanging wall strata record the upward transition from (1) a submarine deltaic fan complex developed on a distal to proximal prodelta in Late Devonian to Middle Mississippian time, to (2) a Middle to Late Mississippian carbonate bank system developed on a slowly subsiding, distal foreland ramp, which was drowned by (3) Late Mississippian renewed clastic influx to a tidally influenced, coastal deltaic complex to fluvial delta plain system unconformably overlain by (4) a fluvial braided river complex. Four samples of Lower Mississippian to Middle Pennsylvanian sandstone were collected from the hanging wall (n = 3) and footwall (n = 1) of the Pine Mountain thrust sheet at Pound Gap to determine sediment provenance in this long-lived foreland basin system. Paleocurrent indicators considered in the context of the regional foreland basin system suggest transverse regional drainage during the development of Early and Late Mississippian delta complexes. Eustatic fall during the early stages of the Alleghanian orogeny to the east saw a shift in regional drainage with the development of a southwestward-flowing and axial braided river system in Early Pennsylvanian time followed by Middle Mississippian transgression of a fluvio-deltaic complex. Detrital zircon U-Pb age data from Lower Mississippian to Lower Pennsylvanian sandstone support regional interpretations of sediment sourcing from probably recycled foreland basin strata along the east Laurentian margin, whereas compositionally immature Middle Pennsylvanian sediment was sourced by a limited distribution of east Laurentia sources reflecting thrust belt migration into the adjacent foreland basin system during Alleghanian orogenesis. </p><p> In addition, the stratigraphy of the foreland basin system in the central Appalachian basin is significantly different compared to the stratigraphic record that is typified for foreland basin systems and suggests that the Carboniferous Appalachian foreland basin system investigated in this study does not fit the typical foreland basin model that is used widely today for both ancient and modern systems. Possible factors that produce the observed discrepancies between the central Appalachian and typical foreland basin systems may include differences in the timing, type, and frequency of orogenic events leading to foreland basin development, related variations in the rheology of the underlying lithosphere, and whether forebulge migration is mechanically static or mobile. </p><p> The Cordilleran margin of south-central Alaska is an area of active convergence where the Pacific plate is being subducted at a low angle beneath the North American plate. In the Matanuska Valley of south-central Alaska, the geology of the Mesozoic to Cenozoic Matanuska forearc basin system records a complex collisional history along the margin from Cretaceous to Miocene time and provides an opportunity to study how shallow-angle subduction affects upper plate processes. Paleocene-Eocene low-angle subduction of an eastward migrating spreading ridge and Oligocene oceanic plateau subduction caused uplift, deformation, and slab window magmatic intrusion and volcanism in the Matanuska Valley region, thereby modifying the depositional environment and structure of the forearc system. In this study, detailed field mapping in the Matanuska Valley region and structural analysis of Paleocene-Eocene nonmarine sedimentary strata are utilized to better understand the structural response of the forearc basin system to multi-stage flat-slab subduction beneath an accreted continental margin, a process observed along multiple modern convergent margins. Four geologic maps and structural cross-sections from key areas along the peripheries of the Matanuska Valley area and one regional cross-section across the forearc system are presented to delineate its local structural configuration and to contribute to a more complete understanding of how sedimentary and tectonic processes along modern convergent margins may be or have been impacted by shallow-angle type and related subduction processes.</p>