Inhaltsbereich
Erlongwan – Sediment magnetism
Detailed paleo- and rock magnetic investigations were carried out on two 23 m long sediment cores from Erlongwan maar lake, NE China. The completely laminated sediment sequence of the lake is interrupted by 410 graded layers with thicknesses between 0.1 and 150 cm. Measurements of the anisotropy of the magnetic susceptibility revealed that these layers have not disturbed the sediment structure in general, but only in intervals where their thicknesses exceeds 50 cm.
Geographical position and simplified geological map of the Long Gang Volcanic Field (LGVF). The coring location in Erlongwan maar lake is marked by a dot on the topographical map.
The age model for Erlongwan is based on 15 AMS 14C-datings on bulk sediment; showing that the sediment profile spans the last 37 ka cal. BP. Magnetite of PSD-size was identified as the main magnetic carrier mineral by temperature dependent measurements of the saturation magnetization and determination of hysteresis parameters. The minerogenic components in the laminated sediments and the graded layers are nearly identical, and their rock magnetic characteristics reflect the prevailing conditions, anoxic or oxic, during deposition. Comparison of different rock magnetic parameters indicative for magnetic grain size and coercitivity revealed, that the S-ratio which is known to reflect the presence of high coercive minerals, is grain size indicative in sediments with a monomineralic magnetic composition. Although one of the sediment cores has been slightly deformed during core recovery, similar inclination and declination records could be obtained by standard paleomagnetic methods. The stacked inclination and declination records show both variations similar to those known from paleosecular variation (PSV) records from Lake Biwa, Japan.
Lithozones, records of the concentration dependent parameters intensity of the anhysteretic remanent magnetization (JARM), low field magnetic susceptibility (kLF), and intensity of the saturation isothermal remanent magnetization (JSIRM), and records of parameters indicative for magnetic grain size and coercitivity: median destructive field of the ARM (MDFARM), S-ratio, JARM/JSIRM and JSIRM/kLF, for core ERL-B versus composite depth. S-ratio = 0.5 × (1 - IRM-0.3T / SIRM1.5T). Graded layers ³ 10 cm thickness are marked by khaki shaded areas.
Comparison of the stacked inclination and declination records from Erlongwan maar lake with the Holocene records from Lake Biwa [Ali et al., 1999] . The letters denote correlatable features. Both records are presented versus their calibrated 14C-ages.
Backer: DFG
Employee: Dr. Ute Frank, Dr. Jens Mingram, Dr. Georg Schettler, Dr. Peter Dulski
Partner: Haitao You, Institute of Geology & Geophysics, Chinese Academy of Sciences