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Depth of post-depositional remanence acquisition in deep-sea sediments: a case study of the Brunhes-Matuyama reversal and oxygen isotopic Stage 19.1

deMenocal, Peter B.; Ruddiman, William F.; Kent, Dennis V.

Although post-depositional remanent magnetization (PDRM) in deep-sea sediments appears to be acquired during the earliest stages of sediment compaction, the natural variability of the PDRM lock-in depth in deep-sea sediments is poorly understood and as yet unquantified. Here we consider variations in the relative stratigraphic positions of oxygen isotopic interglacial Stage 19.1 and the Brunhes-Matuyama (B/M) Chronozone reversal for eight deep-sea sediment cores. Results from a similar study of the displacement between a widespread microtektite layer and the B/M boundary are also included [1]. The PDRM lock-in depth and the temporal relationships between the B/M and Stage 19.1 datums can be determined from the offsets between the paleomagnetic and the isotopic (and microtektite) stratigraphies. For cores with sedimentation rates greater than 1 cm kyr−1, the depth offset between the paleomagnetic and isotopic datums is a linear function of sedimentation rate. A simple model (r2 = 0.77) demonstrates that (1) PDRM acquisition occurs ∼ 16 cm below the sediment surface, and (2) the B/M reversal occurs 6 kyr (±2 kyr) after the Stage 19.1 datum, and the Stage 19.1 datum occurs 9 kyr (±3 kyr) after the deposition of the Australasian microtektite strewnfield. This example argues against simple geophysical models linking geomagnetic field reversals to climate change or impact events. The B/M boundary is anomalously deep (30–50 cm) in very low accumulation rate sediments ( < 1 cm kyr−1) and this may reflect the unusual physical properties of these sediments. A review of the geotechnical literature suggests that very low accumulation rate sediments have sufficient time to develop enhanced interparticle rigidity (structural strength) which inhibits early compaction and, hence, PDRM acquisition.



Also Published In

Earth and Planetary Science Letters

More About This Work

Academic Units
Lamont-Doherty Earth Observatory
Biology and Paleo Environment
Published Here
December 6, 2011