Data report: paleomagnetism and rock magnetism of sediments from offshore Canterbury Basin, IODP Expedition 317

Abstract

Paleomagnetic and rock magnetic analyses were conducted on discrete samples from sediments drilled during Integrated Ocean Drilling Program Expedition 317 in the Canterbury Basin offshore New Zealand to assess the nature of magnetic remanence and to evaluate the directional data for a magnetic reversal stratigraphy. The sediments consist of relatively coarse grained lithologies from shelf to slope settings. The presence of several hiatuses, together with very low core recovery in some intervals as well as drillingrelated magnetic overprints, prevented establishment of a good shipboard magnetostratigraphy. In an effort to overcome some of the magnetic shortcomings and to substantiate shipboard measurements (overprints and partial demagnetization to 20 mT), natural remanent magnetization and subsequent full stepwise alternating field or thermal demagnetization measurements were taken on 765 individual discrete samples from Holes U1351B (131 samples), U1352B/U1352C (485 samples), U1353B (54 samples), and U1354B/U1354C (95 samples). Some rock magnetic measurements, including thermomagnetic curves, were taken on a few representative samples to acquire information on the magnetic carriers. The remanence intensity of the sediments is relatively low (usually 10–3 to 10–5 A/m) and often displays unstable behavior upon demagnetization. Demagnetization data have been separated into four different classes based on their quality. Classes 1 and 2 are of sufficient quality to be used for magnetostratigraphic purposes and represent ~40% of the studied samples (although some of them could still represent a steep magnetic drilling overprint). Considering the calculated characteristic remanent magnetization inclination, a number of polarity zones can be defined. However, the fragmentary nature of the data set, mostly related to core recovery in addition to detected and undetected sedimentary hiatuses, makes determination of the precise position of the reversal boundaries and their correlation to the geomagnetic polarity timescale a difficult task. Nevertheless, when combined shipboard and postcruise discrete measurements are placed within biostratigraphic constraints, some magnetostratigraphic insights can potentially refine the available age model. These insights include the identification of the Matuyama/Brunhes boundary (C1r1r/C1n, 0.778 Ma) at all four sites, the Gauss/Matuyama boundary (C2An.1n/C2r.2r, 2.581 Ma) in Hole U1351B, and also the position of the Olduvai Subchron (C2n, 1.778–1.945 Ma) in Hole U1351B, which relates to the position of the classical Pliocene/Pleistocene boundary.