0000000000405136
AUTHOR
R. Oberhänsli
Natural and anthropogenic influences on the geochemistry of Quaternary lake sediments from Holzmaar, Germany
The accumulation of heavy metals and trace elements has been investigated in a well laminated sequence of Holocene and late Pleistocene lake sediments composed of diatomaceous gyttja, tuff and silt and clay sediments. Varve chronology of the annually deposited gyttja yielded a continuous high-resolution time sequence and allowed the absolute age dating of the sediment. Fluxes of elements remained largely uniform from the late Pleistocene into the Holocene. Higher trace element and heavy metal fluxes occur from 2322 to 862 VT years ago (VT: varve time, years before 1950) and reached their maxima in the uppermost sediments (<845 VT years ago). These increasing element fluxes correlate with in…
Geochemistry, PbPb single zircon ages and NdSr isotope composition of Precambrian rocks from southern and eastern Ethiopia: implications for crustal evolution in East Africa
Abstract Geochemical and isotope data for granitoid rocks from southern and eastern Ethiopia delineate the presumed margin of the Pan-African juvenile terrain of the Arabian-Nubian Shield against an older crustal segment of unknown origin extending from eastern Ethiopia to northern Somalia. Granitoids from southern Ethiopia have higher Na2O and Na 2 0 K 2 O and lower Cr and Ni than granitoids with comparable SiO2 values from eastern Ethiopia. In southern Ethiopia three periods of magmatism are identified on the basis on single zircon 207 Pb 206 Pb evaporation ages, namely at ∼850, ∼750-700 and ∼650-550 Ma, and these correlate well with events documented from other parts of Ethiopia and the …
Environmental geology and geochemistry of lake sediments (Holzmaar, Eifwl, Germany)
Quaternary sediments of the lake Holzmaar comprise a well laminated, undisturbed sequence of diatomaceous gyttja, silt, clay laminites and tuff layers. The annually deposited gyttja has been dated by varve chronology yielding a continuous high-resolution time sequence for the Holocene and early Pleistocene. These organic-rich sediments provide an unique paleolimnological record on climatic changes, forest fires, volcanic eruptions, and anthropogenic influences on the sediment composition. Volcanic activity produced thin tephra layers (Laacher See Tephra 11,200±120 radiocarbon yrs BP; Ulmener Maar Tephra 9435±70 radiocarbon yrs BP) in the sedimentary column which possess elevated Ba, Sr, Zr,…