Seismostratigraphy and sediment studies of Lake Hestvatn, southern Iceland: implications for the deglacial history of the region

Core 95-HV was obtained from Lake Hestvatn, southern Iceland, after a seism ic survey had identified a sediment sequence over 45 m thick in the lake. T he core penetrated ca. 25 m into the sediment correlating with seismostrati graphic unit 2 of alternating seismic facies, with semi-parallel reflectors of high amplitude and chaotic reflectors. Detailed sedimentological, chemi cal, magnetic and chronostratigraphical analyses on core 95-HV, combined wi th interpretation of the seismic survey, show considerable changes in the s edimentary environment between ca. 10300 and 9000 C-14 yr BP (reservoir cor rected). The lowermost ca. 12 m of the core was deposited in a marine envir onment during energy shifts from a very rapid accumulation of sandy turbidi te units to slower deposition of suspended fine-grained sediments. The turb idite units, thought to have originated from catastrophic outburst floods ( jokulhlaup), contributed greatly to the high sediment accumulation rate at the Younger Dryas-Preboreal transition. Further change in the sedimentary e nvironments is evidenced by the deposition of organic-rich lake sediment wi th abundant tephra layers, starting at ca. 9000 yr BP (seismostratigraphic unit 3). The study shows that the inland glacier did not override the site of Hestvatn during the time of sediment deposition in the lake basin. Copyr ight (C) 2001 John Wiley & Sons, Ltd.