MINERAL-MAGNETIC PROXIES OF EROSION OXIDATION CYCLES IN TROPICAL MAAR-LAKE SEDIMENTS (LAKE TRITRIVAKELY, MADAGASCAR) - PALEOENVIRONMENTAL IMPLICATIONS/

Mineral-magnetic measurements were performed on the upper 16m of five piston-cored sedimentary sequences from Lake Tritrivakely, Madagascar. AMS C-14 dating and correlation of the five magnetic susceptibility r ecords allowed establishment of a composite sedimentary record of the last 46 kyr. Our data suggest that mineral-magnetic changes result fro m changes in concentration of strongly ferrimagnetic terrigenous miner als and from preservation/dissolution cycles of detrital iron oxides ( primarily high-coercivity Fe(III) phases such as hematite) in alternat ely oxic and anoxic depositional environments, High-coercivity iron ox ide phases are restricted to stratigraphic intervals that are interpre ted to represent dry periods with oxic conditions. Comparison with oth er paleoenvironmental proxies (pollen, total organic carbon, lithology ) suggests that the sediments record relatively humid conditions befor e 22 kyr BP, and relatively dry conditions during the Last Glacial Max imum (LGM) and the early Holocene. Such results contrast with the prev ious observations of relatively dry glacial conditions and humid mid-H olocene conditions in the summer rainfall area of East and SE Africa. (C) 1998 Elsevier Science B.V.