Mineral magnetic signatures in a long core from Lake Qarun, Middle Egypt

• Published in: Journal of paleolimnology 2008-10, Vol.40 (3), p.835-849
• Main Authors: Foster, I. D. L., Oldfield, F., Flower, R. J., Keatings, K.
• Format: Article
• Language: English
• Subjects: Climate Change; Earth and Environmental Science; Earth Sciences; Fluvial sediments; Freshwater & Marine Ecology; Geology; High temperature; Lakes; Low temperature; Magnetism; Mineralogy; Organic matter; Original Paper; Paleolimnology; Paleontology; Particle size; Physical Geography; Sedimentation rates; Sedimentology; Sediments
• ISSN: 0921-2728; 1573-0417
• DOI: 10.1007/s10933-008-9202-x

The analysis and interpretation of changes in mineral magnetic signatures from a long (ca. 8.2 m) sedimentary sequence recovered from Lake Qarun, Middle Egypt in 2003 spanning a timescale of approximately the last 2,000 years is reported. A suite of mass specific susceptibility and magnetic remanence measurements were made at irregular intervals downcore on 39 samples. These samples were selected on the basis of trends and abrupt changes in whole-core magnetic susceptibility measured using a Bartington ® MS2E sensor and were analysed for low and high temperature loss on ignition and their particle size distribution. Trends in all mineral magnetic concentration parameters are remarkably similar and were initially used to divide the core into three magnetically distinct zones. The upper and lower sections of the core (0–119 cm and 445–822 cm depth) are characterised by low values for all magnetic concentration parameters. Between 153 and 380 cm depth, concentration parameters are considerably higher, although somewhat variable. The S ratio and percentage loss of remanence after 24 h (IRM loss ) follow a different trend and are inversely related to each other. A low S ratio (4%. On the basis of these parameters, the core can be divided into four zones, and differences in magnetic mineralogy between these four zones were confirmed by measurement of IRM acquisition curves. The major difference between concentration parameters and ratios or percentage loss of IRM lies in the identification of an additional zone below 619 cm depth where the S ratio is high and IRM loss is low. There is little evidence to suggest that the magnetic signatures are controlled by particle size or by trends in organic matter and/or carbonate content. The signatures appear to be predominantly detrital and show little evidence of post-depositional alteration through dissolution or authigenic addition of bacterial magnetite or greigite. Analysis of Saharan dust deposition rates in Northern Egypt suggests that atmospheric fallout is likely to make only a very minor contribution (