Abstract:
Several reworked tephra layers in gravity-flow deposits are present in
lacustrine core sediments collected from Hotel and Rudy lakes on King George
Island, South Shetland Islands, W. Antarctica. The tephra record is more
abundant in a long Hotel Lake core (515 cm long). This study uses volcanic
glass samples from five tephra layers of Hotel Lake and from one tephra layer
of Rudy Lake.
... Morphologically, tephras are mixtures of basaltic and pumice
shards, both having various degrees of vesicularity. Major element analyses of
glass shards reveal that the majority of the glass fragments belong to basic
glass (< 60 wt.% SiO2), compositionally ranging from basalt to low-silica
andesite and subalkaline series medium-K tholeiites, probably sourced from
Deception Island located 130 km southwest of King George Island. Less than 20%
of tephra belongs to silicic glass and occurs in three tephra horizons E of
Hotel Lake. However, source volcano(es) for about 10% of basic tephra and
silicic tephra are not readily identified from nearby volcanic centers. Except
for the studied tephra in Rudy Lake, all tephra samples in Hotel Lake are not
ashfall deposits but reworked and re-deposited pyroclasts derived from
retreating ice sheet, resulting in the occurrence of geochemically equivalent
tephra samples in different tephra horizons. The dating of the studied tephra
horizons represents the timing of deglaciation rather than that of volcanic
eruptions. The result of this study implies that combined with sedimentological
information more chemical criterion is necessary to study tephrochronology and
regional correlation and to understand paleoenvironmental changes using tephra. 
