Diagenetic magnetic enhancement of sapropels from the eastern Mediterranean Sea

Author(s): Roberts, Andrew P.; Stoner, Joseph S.; Richter, Carl
Author Affiliation(s): Primary:
University of Southampton, Department of Oceanography, Southampton, United Kingdom
Volume Title: Fifth decade of Mediterranean paleoclimate and sapropel studies
Volume Author(s): Rohling, Eelco J., editor
Source: Fifth decade of Mediterranean paleoclimate and sapropel studies, edited by Eelco J. Rohling. Marine Geology, 153(1-4), p.103-116. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0025-3227 CODEN: MAGEA6
Note: In English. 71 refs.A collection of papers dedicated to the memory of Colette Vergnaud-Grazzini and Robert Kidd; illus., incl. sketch map
Summary: Diagenetic dissolution of magnetic minerals has been widely observed in organic-rich sediments from many environments. Organic-rich sediments from the eastern Mediterranean Sea (sapropels), recovered during Leg 160 of the Ocean Drilling Program, reveal a surprising catalogue of magnetic properties. Sapropels, from all sites studied across the eastern Mediterranean Sea, are strongly magnetic and the magnetization is directly proportional to the organic carbon content. The magnetization of the sapropels is dominated by a low-coercivity, probably single domain magnetic mineral (with an inverse magnetic fabric) that exhibits a clear decay in magnetic properties when exposed to air. During heating, the magnetic particles irreversibly break down between 360 and 400°C. The contrast between the magnetic properties of sapropels and surrounding sediments is marked, with remanence intensities of sapropels often being more than three orders of magnitude higher than those of underlying sediments. The contrast between the magnetic properties of sapropels and the surrounding sediments is apparently controlled by non-steady-state diagenesis: sulphate-reducing conditions dominated during sapropel deposition, while overlying sediments were deposited under oxic conditions. The mineral responsible for the magnetic properties of sapropels is most likely to have formed under sulphate-reducing conditions that existed during times of sapropel formation. Attempts to identify this mineral have been unsuccessful, but several lines of evidence point toward an unknown ferrimagnetic iron sulphide phase. The influence of diagenesis on the magnetic properties of cyclically-deposited eastern Mediterranean sedimentary sequences suggests that magnetic parameters may be a useful proxy for diagenesis in these sediments. Abstract Copyright (1999) Elsevier, B.V.
Year of Publication: 1999
Research Program: ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Cenozoic; Diagenesis; East Mediterranean; Geochemistry; Iron sulfides; Isothermal remanent magnetization; Leg 160; Magnetic intensity; Magnetic minerals; Magnetic properties; Magnetization; Marine sediments; Mediterranean Sea; Natural remanent magnetization; Neogene; Ocean Drilling Program; Organic compounds; Paleomagnetism; Reduction; Remanent magnetization; Sapropel; Saturation magnetization; Sediments; Sulfides; Tertiary
Coordinates: N334212 N370209 E0324513 E0131040
Record ID: 1999015181
Copyright Information: GeoRef, Copyright 2017 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands