Paleolimnology of a Late Pleistocene-Holocene Crater Lake from the Golan Heights, Eastern Mediterranean

Abstract

ABSTRACT A deep sediment core from Birket Ram, a Late Pleistocene-Holocene crater lake in the Golan Heights, was examined. The sediments rest on volcanic rocks at 81 m depth, and represent entire lake history. The core consists of 2 major zones: A lower zone (81-42.5 m) composed principally of diatomite and an upper zone consisting mainly of fine grained, clastic sediments. The diatoms in the diatomite zone include exclusively centric, planktonic forms, indicating a rather deep, quiet, stratified, slightly alkaline lake, eutrophic (Stephanodiscus astraea) for most of the time, with some oligotrophic (Cyclotella ocellata) intervals. Most of the diatomite is varved, with couplets of an average thickness of 0.6 mm, consisting of dark diatom laminae alternating with calcite laminae. The major clay mineral in the elastic zone is a nontronitic smectite similar to the clay alteration product of some pyroclastic layers found intercalated amidst the diatomite zone. Microgranular (6-63 µm) siderite is present in the 32.5-21 m section of the zone, close to an organic C enrichment at 21-20.5 m. Mainly pennate, benthic diatom forms were identified in this zone. This composition is interpreted as indicating a shallow, at times marshy phase of the lake. Acidophilous diatom species at 42.5-32.5 m depth suggest a neutral or even acidic water body introducing the shallow water phase. From a radiocarbon dating at 24.5 m, giving 29.300 + 4000 Y.B.P., an average sedimentation rate of 0.8 mm/y for the elastic sediments was calculated. The formation of the lake is assumed to ave taken place about 100.000 Y.B.P., the transition from the deep into the shallow phase, possibly indicating a climatic shift, about 50.000 Y.B.P.