10Be Distributions in Deep Sea Drilling Project Site 576 and Site 578 Sediments Studied by Accelerator Mass Spectrometry

Abstract

Extension of the 10 Be geochronology for deep-sea sediments beyond the limit of late Pliocene age found in published works has been attempted. The results obtained on sediments from Deep Sea Drilling Project (DSDP) Sites 576 and 578 of Leg 86 suggest the feasibility of dating sediments as old as 12 to 15 m.y. At both sites, there have been large changes in sedimentation rate, with the Pleistocene sediments accumulating several times faster than those of the Pliocene, which in turn were deposited several times more rapidly than the late Miocene sediments. The Pleistocene-Pliocene section is considerably thicker in Hole 578 than in Hole 576B: the respective depths for the 7-m.y. time boundary in the two holes are ~ 125 and ~25 m. These 10 Be-based age estimates are in agreement with the paleomagnetic stratigraphies established for the two sites. The suggested enhancement in the oceanic deposition of 10 Be before 7 to 9 m.y. ago, as noticed in manganese crusts, has found tentative support from the present sedimentary records. A preliminary search for 10 Be production variation during a geomagnetic field reversal has been conducted. In Hole 578, an enhanced 10 Be concentration is found in a sample close to the Brunhes/Matuyama reversal boundary. More detailed and systematic measurements are required to confirm this observation, which bears on the detailed behavior of the geomagnetic field during the reversal.

Meteoric 10Be Reveals a Young, Active Accretionary Prism and Structurally Complex Décollement in the Vicinity of the 2011 Tohoku Earthquake Rupture

“…This approach assumes that N o in seafloor sediments remained within this range over the time period of investigation. Our calculated N o values are consistent with 10 Be concentrations measured in “zero‐aged” surface seafloor sediments in the western Pacific outboard of the Japan trench (Ku et al, ; Lao et al, ; Morris, Valentine, et al, ) and those back‐calculated from 0–5 Ma sediments cored at DSDP Site 436, suggesting this assumption is valid (Tables and ).…”

10Be and 9Be concentrations in the deep sea sediments at Site 925, Ceara Rise, in the western equatorial Atlantic: implication of 10Be flux change

“…It is well known that the variation of 10 Be concentration in ocean sediment is also controlled by the 10 Be production rate in the atmosphere. Measurements of 10 Be profiles in the deep-sea sediments across geomagnetic reversals have shown that the 10 Be production rate was influenced by variations in the geomagnetic intensity (Raisbeck et al, 1979(Raisbeck et al, , 1985Ku et al, 1985;Eisenhauer et al, 1987;Henken-Mellies et al, 1990;Kent and Schneider, 1995). Thus, the data of 10 Be flux variation in the sediments also includes the effect of changes in 10 Be production rate in the atmosphere.…”

“…The detailed 10 Be and 9 Be content record in marine sediments has been investigated as a potential geochronological tool (Tanaka and Inoue 1979;Bourles et al, 1989, Beets et al, 1991 and as a proxy monitor of variations in solar activity and geomagnetic field intensity (Raisebeck et al, 1979(Raisebeck et al, , 1985Ku et al, 1985;Raisebeck and Yiou 1988;Henken-Mellies et al, 1990;Kent and Schneider, 1995). Furthermore, the radionuclide 10 Be (half life = 1.5 ´ 10 6 yr) has also been used in flux studies as a geochemical and a sedimentological tracer (Brown 1987;Sharma et al, 1987).…”

Applications of Cosmogenic 10Be to Problems in the Earth Sciences

“…The authors worry that this increase may be due to hydrothermal input or the effects of diagenesis, but subsequent work (Boudes et al 1989b) suggests that such effects are sm all and cannot explain the discrepancy. It may be that the authigenic 'OBerBe ratio is recording changes in lOBe supply due to changing ocean circulation patterns, as seen in nodules at � 6-7 Ma, and tentatively identified at 6.8 Ma in other sediments from the North Pacific (Ku et al 1985). Bourles et al (l989a,b) leave unresolved the question of whether total or authigenic ratios provide a better dating tool; where it can be quantitatively extracted, the authigenic component has a clear and relatively simple relationship to seawater and is pr obably a better candidate for geochronology and tr acer studies, except where the goal is to evaluate input from the continents.…”