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

Heat flow in the Lesser Antilles island arc and adjacent back arc Grenada basin

Using temperature gradients measured in 10 holes at 6 sites, we generate the first high fidelity heat flow measurements from Integrated Ocean Drilling Program drill holes across the northern and central Lesser Antilles arc and back arc Grenada basin. The implied heat flow, after correcting for bathymetry and sedimentation effects, ranges from about 0.1 W/m² on the crest of the arc, midway between the volcanic islands of Montserrat and Guadeloupe, to 15 km from the crest in the back arc direction. Combined with previous measurements, we find that the magnitude and spatial pattern of heat flow are similar to those at continental arcs. The heat flow in the Grenada basin to the west of the active arc is 0.06 W/m², a factor of 2 lower than that found in the previous and most recent study. There is no thermal evidence for significant shallow fluid advection at any of these sites. Present-day volcanism is confined to the region with the highest heat flow.American Geophysical Union – Geochemistry, Geophysics, Geosystems. This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/gc/.Keywords: volcanic arc., Lesser Antilles, IODP, heat flow, back arc, Grenada basinKeywords: volcanic arc., Lesser Antilles, IODP, heat flow, back arc, Grenada basi

Late Pleistocene stratigraphy of IODP Site U1396 and compiled chronology offshore of south and south west Montserrat, Lesser Antilles

Marine sediments around volcanic islands contain an archive of volcaniclastic deposits, which can be used to reconstruct the volcanic history of an area. Such records hold many advantages over often incomplete terrestrial data sets. This includes the potential for precise and continuous dating of intervening sediment packages, which allow a correlatable and temporally constrained stratigraphic framework to be constructed across multiple marine sediment cores. Here we discuss a marine record of eruptive and mass-wasting events spanning ~250 ka offshore of Montserrat, using new data from IODP Expedition 340, as well as previously collected cores. By using a combination of high-resolution oxygen isotope stratigraphy, AMS radiocarbon dating, biostratigraphy of foraminifera and calcareous nannofossils, and clast componentry, we identify five major events at Soufriere Hills volcano since 250 ka. Lateral correlations of these events across sediment cores collected offshore of the south and south west of Montserrat have improved our understanding of the timing, extent and associations between events in this area. Correlations reveal that powerful and potentially erosive density-currents traveled at least 33 km offshore and demonstrate that marine deposits, produced by eruption-fed and mass-wasting events on volcanic islands, are heterogeneous in their spatial distribution. Thus, multiple drilling/coring sites are needed to reconstruct the full chronostratigraphy of volcanic islands. This multidisciplinary study will be vital to interpreting the chaotic records of submarine landslides at other sites drilled during Expedition 340 and provides a framework that can be applied to the stratigraphic analysis of sediments surrounding other volcanic islands.Keywords: Debris avalanche, Pyroclastic flows, Late quaternary, Submarine evidenc

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

Macroevolutionary history of the planktic foraminifera

Planktic foraminifera are an abundant component of deep-sea sediment and are critical to geohistorical research, primarily because as a biological and geochemical system they are sensitive to coupled bio-hydro-lithosphere interactions. They are also well sampled and studied throughout their evolutionary history. Here, we combine a synoptic global compilation of planktic foraminifera with a stochastic null model of taxonomic turnover to identify statistically significant increases in macroevolutionary rates. There are three taxonomic diversifications and two distinct extinctions in the history of the group. The well-known Cretaceous–Paleogene extinction is of unprecedented magnitude and abruptness and is linked to rapid environmental perturbations associated with bolide impact. The Eocene–Oligocene boundary extinction occurs due to a combination of factors related to a major reorganization of the global climate system. Changes in ocean stratification, seawater chemistry, and global climate recur as primary determinants of both macroevolutionary turnover in planktic foraminifera and spatiotemporal patterns of deep-sea sedimentation over the past 130 Myr. </jats:p

Rock and Paleomagnetic data from IODP Site 340-U1396

Sedimentary magnetic data along the revised stratigraphic splice from IODP Site U1396. The dataset includes the meters composite depth scale, three age models, and sedimentation rate. Sediment classification is from the shipboard data. Rock magnetic properties (MS, karm, karm/k, MDFarm) and paleomagnetic properties (optimized ChRM inclination, inclination anomaly, optimized ChRM declination, VGP Latitude, MAD values) are provided for every cm along the splice. NRM/ARMslope values provide a proxy for RPI and are presented with the R-value following filtering as outlined in the associated publication