Ocean Gateways and Glaciation: Planktic Foraminiferal Records from the Southern Ocean, Equatorial Pacific, and Caribbean

Ocean gateway changes, once the best mechanism for driving abrupt climatic change, have fallen from favor. They have been largely replaced within the literature by changes in CO2 concentration and orbital forcing. This dissertation looks at three intervals of relative stability (Oligocene), prolonged change (Plio-Pleistocene), or transient events (Oligocene/Miocene boundary) in order to better understand the oceanographic circumstances which govern ‘events’ in the paleoceanographic record. Chapter 1 discusses the chronostratigraphy of Integrated Ocean Drilling Program (IODP) Site U1396 (Expedition 340) in the Caribbean Sea. A combination of paleomagnetostratigraphy, biostratigraphy, astrochronology, and correlation to Marine Isotope Stages (MIS) allows a high-resolution age model to be constructed. Sedimentation rates are calculated for the paleomagnetic and MIS age models, and with and without volcanic sediments. The findings agree with shipboard determination of slowing sedimentation toward the present, and suggest either increased winnowing due to bottom-water flow or changes in productivity altering the biotic flux at the site. Chapter 2 reexamines the Oligocene at Ocean Drilling Project (ODP) Sites 803 and 628 with revised taxonomic concepts. There are disagreements between the global compilations of macroevolutionary rates and the rates calculated at Site 803, though several hypotheses are discussed to explain the findings. A series of illustrations are presented to aid in taxonomic identification through this difficult interval. Chapter 3 focuses on the Mi-1 event, discussing several new records: Deep Sea Drilling Program Site 78, ODP Site 803 (both equatorial Pacific Ocean), and ODP Site 744 (southern Kerguelen Plateau). After reviewing the leading hypotheses for Mi-1, the three new sites are used to test the paleoproductivity hypothesis, and use those records to investigate the importance of different orbital parameters. Lastly, the foram fragmentation index is employed to examine changes in the lysocline at the sites, demonstrating that there are dramatic global changes in the lysocline throughout the leadup to Mi-1. While carbonate sequestering carbon through the lysocline changes (or infact deepening Calcite Compensation Depth) cannot explain abrupt cooling events on their own (e.g., Coxall et al., 2005), a narrative discussion of the leadup to Mi-1 puts the lysocline changes in context with findings at other sites

A revised Plio-Pleistocene age model and paleoceanography of the northeastern Caribbean Sea: IODP Site U1396 off Montserrat, Lesser Antilles

Site U1396 was piston cored as a part of Integrated Ocean Drilling Project Expedition 340 to establish a long record for Lesser Antilles volcanism. A ~150 m sediment succession was recovered from three holes on a bathymetric high ~33 km southwest of Montserrat. A series of shipboard and newly-generated chronostratigraphic tools (biostratigraphy, magnetostratigraphy, astrochronology, and stable isotope chemostratigraphy) were employed to generate an integrated age model. Two possible chronostratigraphic interpretations for the Brunhes chron are presented, with hypotheses to explain the discrepancies seen between this study and Wall-Palmer et al. (2014). The recent Wade et al. (2011) planktic foraminiferal biostratigraphic calibration is tested, revealing good agreement between primary datums observed at Site U1396 and calibrated ages, but significant mismatches for some secondary datums. Sedimentation rates are calculated, both including and excluding the contribution of discrete volcanic sediment layers within the succession. Rates are found to be ‘pulsed’ or highly variable within the Pliocene interval, declining through the 1.5-2.4 Ma interval, and then lower through the Pleistocene. Different explanations for the trends in the sedimentation rates are discussed, including orbitally-forced biogenic production spikes, elevated contributions of cryptotephra (dispersed ash), and changes in bottom water sources and flow rates with increased winnowing in the area of Site U1396 into the Pleistocene

Numeričko i eksperimentalno modeliranje nosivih elemenata teške metalurške opreme

Carrying structures of heavy metallurgical equipments are during their operation often exposed to extreme loading. The short-term overloading of the structure results to high stresses in locations of their concentrations. By repeating of these phenomena is decreased the life-time of the structure and eventually this leads to local failures in their carrying elements. In the paper are on examples described advantages of using numerical and experimental methods of mechanical system modelling that is exploited for identification of overloading in carrying elements of metallurgical equipments or for detection of damage causes.Nosivi elementi teške metalurške opreme tijekom eksploatacije često su izloženi ekstremnim opterećenjima. Njihova kratkotrajna preopterećenja izazivaju visoka naprezanja na mjestima koncentracije. Ponavljanje ove pojave izaziva skraćenje životnog vijeka konstrukcije i moguća lokalna oštećenja nosivih elemenata. U ovom članku, na dva primjera su prikazane prednosti primjene numeričkih i eksperimentalnih metoda modeliranja mehaničkog sustava u otkrivanju preopterećenja ili uzroka oštećenja nosivih elemenata metalurške opreme

Permeability and pressure measurements in Lesser Antilles submarine slides: Evidence for pressure-driven slow-slip failure

Recent studies hypothesize that some submarine slides fail via pressure-driven slow-slip deformation. To test this hypothesis, this study derives pore pressures in failed and adjacent unfailed deep marine sediments by integrating rock physics models, physical property measurements on recovered sediment core, and wireline logs. Two drill sites (U1394 and U1399) drilled through interpreted slide debris; a third (U1395) drilled into normal marine sediment. Near-hydrostatic fluid pressure exists in sediments at site U1395. In contrast, results at both sites U1394 and U1399 indicate elevated pore fluid pressures in some sediment. We suggest that high pore pressure at the base of a submarine slide deposit at site U1394 results from slide shearing. High pore pressure exists throughout much of site U1399, and Mohr circle analysis suggests that only slight changes in the stress regime will trigger motion. Consolidation tests and permeability measurements indicate moderately low (~10⁻¹⁶–10⁻¹⁷ m²) permeability and overconsolidation in fine-grained slide debris, implying that these sediments act as seals. Three mechanisms, in isolation or in combination, may produce the observed elevated pore fluid pressures at site U1399: (1) rapid sedimentation, (2) lateral fluid flow, and (3) shearing that causes sediments to contract, increasing pore pressure. Our preferred hypothesis is this third mechanism because it explains both elevated fluid pressure and sediment overconsolidation without requiring high sedimentation rates. Our combined analysis of subsurface pore pressures, drilling data, and regional seismic images indicates that slope failure offshore Martinique is perhaps an ongoing, creep-like process where small stress changes trigger motion

Age Model-Site 78.csv

Age model for the Site 7

Age Model-Site 522.csv

Age model for Site 52

Thermal vacancies and phase separation in bcc mixtures of helium-3 and helium-4

Thermal vacancy concentrations in crystals of 3He-4He mixtures have been determined from accurate measurements of the temperature dependence of the x-ray lattice parameter. A new x-ray diffractometer-position sensitive detector system is used to make measurements of the absolute lattice parameter of the helium crystals with an accuracy of 300 ppm, and measurements of changes in lattice parameter to better than 60 ppm. The phase separation of the concentrated 3He-4He mixtures has been studied in detail with the x-ray measurements. Vacancy concentrations in crystals with 99%, 51%, 28%, 12%, and 0% 3He have been determined. The vacancy data in the nearly pure 3He crystals confirm previous x-ray results from pure 3He. The first direct measurements of vacancies in pure hcp 4He' are reported, along with study of vacancies in bcc 4He . The vacancy concentrations in the 51% and 28% 3He mixed crystals are found to be as large as 5%. Progress is made toward characterization of the detailed temperature dependence of the vacancy concentration in all the crystals. The low temperature x-ray molar volumes of the crystals are determined to better than 0.1%. Vacancy volumes of formation are inferred by several methods. Phase separation has been studied in mixed crystals with concentrations of 51%, 28%, and 12% 3He and melting pressures between 3.0 and 6.1 MPa. The phase separation temperatures determined in this work are in general agreement with previous work. The pressure dependence of Tc, the phase separation temperature for a 50% mixture, is found to be linear: dTc /dP = -34 mdeg/MPa. The x-ray measurements are used to make several comments on the low temperature phase diagram of the helium mixtures.U of I OnlyThesi

Age Model-Site 1218.csv

Age Model for Site 121