Quaternary magnetic and oxygen isotope stratigraphy in diatom-rich sediments of the southern Gardar Drift (IODP Site U1304, North Atlantic)

Abstract

The sediment sequence from Integrated Ocean Drilling Program (IODP) Site U1304 (53°03.40′N, 33°31.78′W; water depth, 3024 m) on the southern Gardar Drift, North Atlantic Ocean, covers the last ∼1.8 Myr with a mean sedimentation rate of ∼15 cm/kyr. At Site U1304, paleomagnetic directional and relative paleointensity (RPI) records have been generated for the last ∼1.5 Myr, and benthic oxygen isotope data for the last ∼1 Myr. The age model for Site U1304 was established by matching δ18O and RPI data to calibrated reference records. Prominent intervals of diatom mats at Site U1304 are associated with the latter stages of interglacial marine isotope stages (MIS) 9, 11, 13, 15, 21, 27 and 35, and with the weak glacial of MIS 14. The deposition of diatom mats, and associated diluted magnetic mineral concentrations, leads to weak magnetizations and susceptibilities in these intervals. Comparison of histograms of paleomagnetic directions and RPI from diatom-rich sediments and from surrounding silty clays indicates that, although results from diatom-rich sediments are more scattered, the occurrence of diatom mats does not appreciably distort the paleomagnetic directional and RPI records. Site U1304 sediments record the Matuyama/Brunhes boundary (∼772 ka), the Jaramillo Subchron (∼993–1071 ka) and the Cobb Mountain Subchron (∼1193–1219 ka), as well as three apparent geomagnetic excursions in the Matuyama Chron, interpreted as the “Kamikatsura/Santa Rosa”, “Punaruu”, and “Gardar” excursions, at ∼888 ka, ∼1124 ka, and ∼1463 ka, respectively. The Site U1304 RPI record can be correlated with the PISO-1500 RPI stack and with other high-resolution RPI records from the North Atlantic Ocean. Wavelet analyses performed on the Site U1304 RPI record and a new high-resolution North Atlantic paleointensity stack for the last 1500 kyr (HINAPIS-1500), comprising Ocean Drilling Program (ODP) Sites 983, 984 and IODP Sites U1306 and U1304, did not reveal significant orbital power.