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 seismic survey had identified a sediment sequence over 45 m thick in the lake. The core penetrated ca. 25 m into the sediment correlating with seismostratigraphic unit 2 of alternating seismic facies, with semi‐parallel reflectors of high amplitude and chaotic reflectors. Detailed sedimentological, chemical, magnetic and chronostratigraphical analyses on core 95‐HV, combined with interpretation of the seismic survey, show considerable changes in the sedimentary environment between ca. 10300 and 9000 14C yr BP (reservoir corrected). The lowermost ca. 12 m of the core was deposited in a marine environment during energy shifts from a very rapid accumulation of sandy turbidite units to slower deposition of suspended fine‐grained sediments. The turbidite units, thought to have originated from catastrophic outburst floods (jökulhlaup), contributed greatly to the high sediment accumulation rate at the Younger Dryas–Preboreal transition. Further change in the sedimentary environments is evidenced by the deposition of organic‐rich lake sediment with 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. Copyright © 2001 John Wiley & Sons, Ltd.

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