The biotic crisis of the Late Devonian Period involved three distinct peaks of extinction intensity and preferentially eliminated reef taxa. By the end of the second peak, the Frasnian-Famennian (F-F) boundary, the dominant constructor guild member of the mid-Paleozoic, the stromatoporoids, had ceased reef construction in most parts of the world. An undescribed stromatoporoid bioherm in the Dugway Range, west-central Utah, is one of the few locations where stromatoporoids continued building reefs into the mid-Famennian. The sections are well-constrained biostratigraphically using both conodonts and stromatoporoids and range from the latest Frasnian to the Early Carboniferous. The reefal faunas are depauperate and dominated by labechiids and stylostromids, as is characteristic of most Famennian bioconstructions. In this region, reefal development was episodic with reefal units interbedded with units lacking reef taxa. The stromatoporoid survivors belong to long-ranging clades, and may represent "extinction-resistant" taxa. Both were fairly minor constituents of Frasnian reef communities.

Tracking the phases of Cenozoic deformation in the Eastern Cordillera of Colombia has proven to be a challenging task. Clear disagreements remain in interpretations of the timing of uplift of the Eastern Cordillera, possibly based on difficulties in distinguishing first-cycle Central Cordillera grains from recycled Eastern Cordillera clasts. This thesis focuses on the Eocene-Pliocene sedimentary record of the eastern foothills of the Eastern Cordillera at a latitude of 6°N, integrating basin analysis with several provenance techniques in order to date the activation of several thrust systems. Based on assessments of depositional environments and sediment dispersal patterns together with mineralogical and geochronological provenance, the onset of uplift in the axial zone of the Eastern Cordillera is constrained to be Oligocene. Prior to uplift, deposition in the eastern foothills was sourced from the eastern craton. Following the Oligocene episode, a continuous eastward advance of deformation is documented. An early Miocene episode probably reactivated the easternmost Cretaceous rift boundary along the eastern side of the Eastern Cordillera. Subsequent footwall shortcuts of those faults initiated activity in the middle to late Miocene, creating an intermontane (piggyback) basin in the eastern foothills at that time. In the preferred interpretation, this in-sequence history of thrust activation represents the main phases of deformation in the Eastern Cordillera from Eocene to Pliocene time, with neotectonic activity recording continued shortening. / text

Not available / text

This is a summary report on some existing results and methods regarding the problem of determining the basins of attraction of dynamical systems (in particular, two-dimensional diffeomorphisms) when there is a coexistence of attractors. Based on the work of Helena Nusse and James Yorke, it presents existence and characterization results for a certain kind of basin boundaries (namely, the Wada boundaries). The key feature of their approach is to redefine the idea of a basin boundary by introducing the notion of a `basin cell', which bypasses the problem of exactly locating the attractor of a system, which is often either not well-defined or hard to locate in practice. Moreover, the basin cells and their boundaries are characterized by utilizing the stable and unstable manifolds of the system, which are easier to locate by numerical methods, and thus their method provides both numerically verifiable characteristics and algorithms for computation. / text

Detailed mapping (1:6,000) of Lower Ordovician through Lower Pennsylvanian strata, exposed in the vicinity of the Sunshine Springs thrust fault, shows that the thrust ramps up-section twice in a direction parallel or subparallel with the thrusting, and that the geometry of folds can be attributed to their proximity to the two closely spaced ramps. The lower ramp is a frontal ramp which originated as a forelimb thrust through the overturned limb of a tight anticline-syncline fold couplet. The upper ramp cuts up-section through a thin, upper Paleozoic flysch sequence where the Sunshine Springs thrust becomes imbricated. Directly above the lower ramp, in the upper plate, is a broad symmetrical anticline which has a geometry similar to a fault-bend fold. Forward of the lower ramp is a large wavelength, flat-bottomed syncline, and behind the lower ramp is a series of tight to isoclinal overturned folds. As a result of fault-bend folding and continued shortening of the ramp region, upper plate folds characteristically have a larger amplitude than folds of the lower plate. Just forward of the lower ramp in the footwall is the tightly folded and truncated syncline of the syncline-anticline fold couplet. The rest of the lower plate section is only mildly deformed. A composite, down-structure cross section drawn parallel with the direction of thrusting shows that the Peña Colorada synclinorium has been transported along the Sunshine Springs thrust approximately 3.8 km. Shortening, as deduced from folding in this study alone, is 20 percent, and when the shortening by the thrust is also considered, the total amount of shortening equals 52 percent. A major left-lateral strike-slip system, trending WNW, approximately parallel with the thrusting direction, offsets the Sunshine Springs thrust fault. Strike-slip and dip-slip displacements can be calculated from a displaced fold axis of the lower plate syncline, and are 335 m and 90 m, respectively. In the vicinity of this strike-slip system, the axial traces of folds change from a dominantly southwesterly trend to a more southerly trend. The regional extent of the fault system within the Marathon Basin, and its correspondence with the change in major fold axes orientations suggests that the fault zone is a regional tear which formed in response to the impingement of the Marathon thrust front against the Diablo Platform during the Pennsylvanian Period. / text

The Weber Basin Water Conservancy District is a state institution, but its primary function is collecting money for the U.S. Bureau of reclamation, to pay for the Weber Basin Project. Different classes of water users pay markedly different fees for identical Project services. More than half of the water developed by the Project is not used consumptively, yet supply facilities continue to be built in the Basin because they are less expensive to their owners than prices charged for the underused capacity of the Project. Paradoxically, some Basin residents are bitterly resentful to both the District and the Bureau, claiming that water rights formerly their own have, by means of the Project, been stolen. That is, both the enemies and the proponents of the Project adhere to the Western orthodoxy that water is scarce and drought imminent. The principal difficulty of this investigation lay in identifying the nature of the problem, for the situation seemed full of contradictions. Consequently, the primary contribution of the dissertation is an explanation of Basin circumstances that accounts for arresting observations without inconsistency or contradiction. The most important hypotheses are, therefore, empirical, or historical and institutional. Economics, according to Richard T. Ely and Frank H. Knight, is a set of principles concerning what ought to be, not empirical descriptions of what is. Consistent with that perspective, once the nature of the problem is clear, applications of economic principles is a prescriptive judgement of how the problem may be resolved. The most important empirical hypotheses are as follows: Water is not scarce in the Weber Basin; neither are storage and conveyance facilities. All are abundant, even redundant. Nevertheless in combination with certain institutional arrangements and sustained propaganda campaign, this very abundance contributes to persistence of the attitude that water is scarce. Redundant facilities thereby encourage even more unneeded development. What appears on first examination to be a case of misallocated water resources by discriminatory prices, turns out to be a problem of distributing the burden of paying for excessive, unwanted public works. Water itself is a free good in the Basin. Actual distribution of the repayment burden is partly ideological and partly pragmatic; partly a political choice and partly a bureaucratic decision; partly a manifestation of agrarian policy and partly what the traffic will bear. If water is free, it is not an economic good, and not a subject for economic analysis. The Basin has an ample water supply, but water may nevertheless be locally and periodically scarce. The water problem is therefore one of conveyance and timing. Control of timing requires storage. Conveyance requires energy, as well as aqueducts. In the Weber Basin, conveyance energy may be either the controlled flow of falling (mountain) water, or electrically powered pumps tapping abundant groundwater reservoirs. The water development problem is therefore, an issue of alternative capital facilities for the control and delivery of water (itself abundant). Efficient resource allocation in water development is consequently relevant at the investment level; it is not a matter of pricing water. In this case, the major investment decisions have already been implemented, and the problem is one of evaluating distribution of the repayment burden. The relevant economics literature is principles of equitable taxation, and of public utilities' pricing. Application to the basin situation produces a conclusion that present arrangements are as equitable as could be devised. Further redundant investment (inefficient use of resources), however, could be avoided if the State Engineer's Office took a harder line on requests to drill new wells. The information provided in this work could be the basis for making such a program popularly acceptable.

No description available.

No description available.

The Xigaze forearc basin in southern Tibet, one of the largest and best-preserved forearc basins on Earth, records upper-plate processes active prior to and following the inter-continental collision between India and Asia. However, the understanding of the timing and mechanisms of forearc development and its evolution following collision is spatially and temporally limited. Fundamental questions remain concerning how the basin formed, its paleogeography prior to collision, its subsidence history and the thermal history of the basin following the initial and ongoing continent-continent collision. Answering these questions is important to reconstructing upper plate dynamics during active subduction of oceanic and continental lithosphere. This dissertation addresses the Early Cretaceous to Pliocene history of the Xigaze forearc, using field mapping, sedimentology, sandstone modal petrography, geohistory analysis, U-Pb detrital zircon geochronology, and low-temperature thermochronology (apatite and zircon (U-Th/He)). Appendix A documents the sedimentology and stratigraphy of Lower Cretaceous to Paleocene strata to identify the relationship between the Yarlung-Tsangpo ophiolite and Xigaze forearc basin, reconstruct the sedimentary environments of the southern margin of Asia during the initial to middle stages of forearc deposition, and use the basin history to evaluate the mechanisms controlling forearc subsidence. In Appendix B, analysis of Eocene sedimentary strata, the youngest preserved in the forearc basin, constrains the timing of collision between Asia and the Tethyan Himalaya (India) to be no later than 58-54 Ma based on the similarity of the U-Pb detrital zircon age spectra and sandstone compositions between the Xigaze forearc and strata deposited atop the passive margin of the Tethyan Himalayan at that time. Apatite and zircon (U-Th)/He thermochronologic results in Appendix C constrain the maximum burial temperature of the basin following collision to ~140-200 °C, which corresponds to depths attainable by sedimentation in the forearc and a Paleogene forearc successor basin. This integrated dataset also identifies the initial stage of post-collisional exhumation during the Early Miocene (~ 20-15 Ma), followed by accelerated cooling during the Late Miocene to Early Pliocene (~ 10-4 Ma). These results suggest the presence of a paleo-Yarlung River and/or intensification of the Asian monsoon during the Early to Late Miocene. The Pliocene cooling signal is the youngest reported to date along the IYSZ and likely reflects increased river incision of the Yarlung-Tsangpo driven by accelerated orogen-parallel extension across structures which cross-cut the IYSZ. Robust interpretation of thermochronologic data requires knowledge about the geologic factors and intrinsic properties of the minerals. Appendix D of this dissertation examines intragranular zonation as a source of anomalously young zircon (U-Th)/He ages from leucogranites that intrude Greater Himalayan Sequence rocks at Ronbguk Valley, north of Mt. Everest. Depth profile laser ablation ICP-MS analysis was used to quantify the U-Th concentration profiles of a series of zoned, single, whole zircon grains and to apply a grain specific zonation-dependent age correction. Zircon grains corrected for zonation yield zircon He ages of 15-17 Ma, in agreement with AFT, ZFT and mica ⁴⁰Ar/³⁹Ar ages from the region. This study highlights the importance of characterizing intragranular zonation, especially in complex, zoned zircons that are typical of crustal melts and high-grade metamorphic rocks. Appendix E synthesis the results from Appendices A-C in the context of a global comparison with other ancient and preserved forearc basins. Results from the Xigaze forearc basin are compared to general models for forearc basin formation, subsidence trends, and preservation. The results show similarities between the Xigaze forearc basin and modern forearc basins, such as the Japan forearc off Honshu Island. The mechanisms driving tectonic subsidence are addressed, but remain an area of frontier research in continental dynamics.

The Canterbury Basin is located on a passive margin on the east coast of the South Island, developed by the rifting of the New Zealand continental fragment from Antarctica in the Late Cretaceous. Well cuttings produced during petroleum exploration in the offshore Canterbury Basin have been examined for secondary minerals and textures. Minerals and textures have been identified primarily from optical examination in reflected light, with a particular focus on producing high-resolution images. Additional identifications are made using thin sections, SEM, XRD and XRF analysis. The focus of this study is the Clipper-1 well in the Clipper sub-basin as it contains the most abundant mineralisation and covers the full depth of the Canterbury Basin sedimentary sequence. Examination of cuttings from this well has revealed intrusive igneous carbonates and native metals including iron, aluminium and copper. The trace element concentrations in the igneous carbonates indicates they are derived from crustal material. Textures indicating fluidisation and recrystallisation of sedimentary material are also present. The proposed mechanism for producing these unusual mineral assemblages is a late Pliocene or younger mafic intrusion into the schist basement of the Canterbury Basin. The igneous carbonates are inferred to be derived from melting of carbonates in the schist. The native metals have been produced from melt due to highly reducing conditions produced by interaction of the intrusion with coal and limestone. The combination of native metals and igneous carbonates with a conspicuous absence of typical silicate igneous rocks is inferred to represent a new type of intrusive environment that has not previously been described in the scientific literature.