Palaeomagnetic, astrochronological, and environmental magnetic perspective on Oligocene-Miocene climate, using drift sediments from the northwest Atlantic Ocean

Van Peer, Tim (2017) Palaeomagnetic, astrochronological, and environmental magnetic perspective on Oligocene-Miocene climate, using drift sediments from the northwest Atlantic Ocean. University of Southampton, Doctoral Thesis, 217pp.

Record type: Thesis (Doctoral)

Abstract

The Antarctic ice sheet oscillated between nearly deglaciated and near-‐modern proportions, sometimes within ~110 kyr, during transient glacial phases of the Oligocene-‐Miocene icehouse world (5.33-‐33.9 Ma). Ice sheet hysteresis is closely coupled with carbon-‐cycle feedback mechanisms that are strongly affected by ocean circulation. However, the absence of high-‐resolution records representing the North Atlantic end member, a key region driving modern climate variability and ocean circulation, hamper full understanding of Oligocene-‐Miocene ocean circulation and climate. In this thesis, I integrate palaeomagnetic, X-‐ray fluorescence (XRF), and environmental magnetic records to date and reconstruct current variability from contourite drift sediments, recovered at Integrated Ocean Drilling Program (IODP) Site U1406 (northwest Atlantic). The revised splice ensures stratigraphic continuity for the studied section. The presented novel palaeomagnetic data processing protocol, which is applicable to all weakly magnetised sediments, ensures the use of only high quality directional data for the construction of a reliable magnetostratigraphy between Chrons C6Ar – C9n (21-‐27 Ma). Astronomical tuning using XRF-‐based ln(Ca/K), a proxy for CaCO3 content, provides independent dates for the identified geomagnetic reversals. I determine the best age estimates of reversals using a set of criteria to reconcile the Oligocene-‐Miocene geomagnetic polarity time scale. Congruent obliquity-‐paced CaCO3 cycles at Ocean Drilling Program Site 926 (equatorial Atlantic) and IODP Site U1406 suggest that one corrosive bottom water mass influences the CaCO3 content of the boreal Atlantic. The location and occurrence of contourite drift sediments at IODP Site U1406 advocates that the Deep Western Boundary Current (DWBC) is the candidate for such corrosive bottom waters. DWBC variability around the Oligocene-‐Miocene Transition (~23 Ma) is traced using the detrital magnetic fraction, containing titanohaematite, recognised through detailed rock and environmental magnetic measurements. During the last ca. 1 Myr of the Oligocene, the decrease in CaCO3-‐corrected concentration and coercivity of titanohaematite indicates an invigorated DWBC. If these characteristics of the DWBC are substantiated, this will have major implications for CO2 reconstructions on orbital time scales and Oligocene-‐Miocene climate models.

Text

Van Peer, Tim_PhD_Thesis_Nov_17_ - Author's Original

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