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No description available.

Shatsky Rise is oceanic plateau in the northwest part of the Pacific Ocean, and the formation of Shatsky Rise is poorly known. To get a better understanding of the formation Integrated Ocean Drilling Program (IODP) Expedition 324 drilled five sites: Sites U1347 and U1348 on Tamu Massif, Site U1349 and U1350 on Ori Massif, and Site U1346. Paleomagnetic measurements of the basaltic flows recovered can give insight into the timing and paleolatitude of each site. Relating the change in principle component inclination over depth at each site to the paleosecular variation of the geomagnetic field can better constrain the timing of the eruptions. Measurements were carried out by different sources during IODP Expedition 324 and after. This study is an amalgamation of the results from Sites U1346, U1347, U1349, and U1350. Samples from each site were divided into half and demagnetized using alternating field (AF) demagnetization and thermal (TH) demagnetization. After the drilling overprint was removed most samples displayed univectorial decay in the orthogonal vector plot. AF demagnetized samples displayed a low median destructive field (MDF) behavior, <10 mT, and a moderate MDF behavior, >10-20 mT. Thermal demagnetized samples displayed three behaviors: a rapid decline in magnetic intensity after moderate temperature steps behavior, a linear decline in magnetic intensity behavior, and some samples displayed a small segment of self-reversal at 300°-350°. Using the Cox and Gordon (1984) method Sites U1346, U1347, and U1349 displayed very little variation in principal component inclinations over depth, implying a relatively rapid lava emplacement of 10^2-10^3 years. Site U1350 display more variation, implying a longer eruptive time frame of 10^4-10^5years. With the assumption of a normal polarity the paleolatitude estimates are -11.0° +22.2°/-21.4° for Site U1346, 11.3° 27.4°/-28.5° for Site U1347, -5.0° +20.8°/-20.6° for Site U1349 and 1.6° ±7.7 ° for Site U1350. The site paleolatitudes imply that Ori Massif (Sites U1350 and U1349) formed at the equator and Tamu Massif (Site U1347) and Shirshov Massif (Site U1346) formed slightly north and south of the equator respectively. All results are consistent with the interpretation that Shatsky Rise formed near the equator.

The several million years preceding the Cretaceous/Paleogene (K/Pg) boundary has been the focus of many studies. Changes in ocean circulation and sea level, extinctions, and major volcanic events have all been documented for this interval. Important research questions these changes raise include the climate dynamics during the warm, but not hot, time after the decay of the Late Cretaceous greenhouse interval and the stability of ecosystems prior to the mass extinctions at the end-Cretaceous. I document several biotic perturbations as well as changes in ocean circulation during the Maastrichtian stage of the latest Cretaceous that question whether the biosphere was being preconditioned for the end-Cretaceous extinction. The first event at Shatsky Rise in the tropical North Pacific was the brief acme of inoceramid clams at ~71 Ma, followed by their abrupt extinction during the “mid-Maastrichtian event” at 70.1 Ma. The second is an intriguing dissolution event that began ~67.8 Ma at Ocean Drilling Program Site 1209 (2387 m). The dissolution event is marked by very poor planktic foraminiferal preservation and sharply reduced calcareous plankton diversity. The shift into the dissolution interval was initially gradual, then rapid. Within the late Maastrichtian dissolution interval, the planktic/benthic (P/B) ratio is low, planktic foraminifera are highly fragmented, larger taxa are mostly absent, small taxa are relatively abundant, and planktic foraminifera and nannofossil species richness are low. The event is followed by an abrupt recovery in carbonate preservation ~300 kyr prior to the K/Pg boundary. Was the dissolution event caused by a change in deep water circulation, migration of the site out of the high productivity tropical belt, or ocean acidification associated with Deccan Traps volcanism? Our data show that changing deep water masses, coupled with reduced productivity and associated decrease in pelagic carbonate flux was responsible for the dissolution interval, while Deccan Traps volcanism may have caused surface ocean acidification ~200-kyr prior to the K/Pg mass extinction event.

Well-preserved and diverse assemblages of late Campanian-Maastrichtian age (76.5-65.5 Ma) planktic foraminifera from Ocean Drilling Program Sites 1209 and 1210 on Shatsky Rise provide an excellent source of data to better understand the environmental and biotic changes of the end-Cretaceous Period in the tropical Pacific. A thorough taxonomic and biostratigraphic study of planktic foraminifera has revealed significant differences in species ranges when compared to detailed studies from the western North Atlantic and eastern South Atlantic. These observations are attributed to site locations with different ocean current and productivity conditions. During the globally recognized “mid-Maastrichtian Event”, inoceramid clams, rare at Shatsky Rise, dramatically increased (~69.3 Ma) before suddenly going extinct (69.1 Ma). This Inoceramid Acme Event (IAE), occurs during high sedimentation rates (~21.8-m/myr) and is indicated in planktic foraminifera by a 0.50‰ positive shift in δ18O values (~2 °C cooling), a 0.24‰ negative shift in δ13C values of and high species richness. A simultaneous decrease in both the δ18O and δ13C gradients between surface and thermocline dwelling planktic foraminifera indicate the IAE was possibly initiated by an increase in surface productivity due to the upwelling of cooler, nutrient-rich waters. A dissolution event was identified at ~66.1 Ma lasting to the Cretaceous/Paleogene boundary (65.5 Ma) and is characterized by chalky, highly fragmented planktic foraminifera, increased dissolution of larger Globotruncanids, increased small (< 63 μm) planktic foraminifera, large and increasingly abundant benthic foraminifera, a sharp decrease in species richness and increased sedimentation rates (~19.9-m/myr). This event follows a transitional interval at ~66.7 Ma where preservation is highly variable. The dissolution event, reported in previous studies at Shatsky Rise (Caron, 1975; Premoli Silva et al., 2005), is not reported in the North and South Atlantic but may help to explain the high diachroneity in species occurrences between ocean basins. These events may indicate that the calcite carbonate compensation depth (CCD) shoaled to shallower depths than previously reported (Theirstein, 1979) due to changing deep or intermediate water mass sources. Alternatively, the timing the dissolution is approximately coincident with the main pulse of Deccan Trap volcanism on the Indian subcontinent suggesting a possible link through ocean acidification.

Global climate is controlled by two factors, the amount of heat energy received from the sun (solar insolation) and the way that heat is distributed Earth's surface. Solar insolation varies on timescales of 10s to 100s of thousands of years due to changes in the path of Earth's orbit about the sun (Milankovitch cycles). Earth's internal boundary conditions, such as paleogeography, the presence/absence of polar icecaps, atmospheric/oceanic chemistry and sea level, provide distribution and feedback mechanisms for the incoming heat. Variations in these internal boundary conditions may happen abruptly or, as in the case of plate tectonics, take millions of years. We use geochemical and sedimentological techniques to investigate the response of ocean chemistry, regional aridity and atmospheric and oceanic circulation patterns to climate change during both greenhouse and icehouse climates. To explore the connection between orbitally-forced changes in solar insolation, continental aridity and wind, we generated a high-resolution dust record for ~58 Myr old deep-sea sediments from Shatsky Rise. Our data provide the first evidence of a correlation between dust flux to the deep sea and orbital cycles during the Early Paleogene, indicating dust supply (regional aridity) responded to orbital forcing during the last major interval of greenhouse climate. The change in dust flux was comparable to that during icehouse climates implying subtle variations in solar insolation have a similar impact on climate during intervals of over-all warmth as they do during glacial-interglacial states. The Carboniferous Period (359-299 Ma) marks a critical time in Earth's history when a series of tectonic and biological events caused a shift in the mean climate state from a global "greenhouse" to an "icehouse". Geochemical records extracted from sedimentary rocks deposited in shallow epicontinental seaways are increasingly being used to infer relationships between tectonism, carbon cycling and climate and therefore are assumed to reflect global ocean processes. We analyzed radiogenic isotopes in biogenic apatite along a North American transect to constrain the degree of geochemical coupling between the epicontinental seas and the open ocean. Our results argue strongly for decoupling of North American seaways from the open ocean by latest Mississippian time.