Late Quaternary distal tephra-fall deposits in lacustrine sediments, Kenai Peninsula, Alaska

Abstract

Tephra-fall deposits from Cook Inlet volcanoes were detected in sediment cores from Tustumena and Paradox Lakes, Kenai Peninsula, Alaska, using magnetic susceptibility and petrography. The ages of tephra layers were estimated using 21 14C ages on macrofossils. Tephras layers are typically fine, gray ash, 1–5 mm thick, and composed of varying proportions of glass shards, pumice, and glass-coated phenocrysts. Of the two lakes, Paradox Lake contained a higher frequency of tephra (0.8 tephra/100 yr; 109 over the 13,200-yr record). The unusually large number of tephra in this lake relative to others previously studied in the area is attributed to the lake's physiography, sedimentology, and limnology. The frequency of ash fall was not constant through the Holocene. In Paradox Lake, tephra layers are absent between ca. 800–2200, 3800–4800, and 9000–10,300 cal yr BP, despite continuously layered lacustrine sediment. In contrast, between 5000 and 9000 cal yr BP, an average of 1.7 tephra layers are present per 100 yr. The peak period of tephra fall (7000–9000 cal yr BP; 2.6 tephra/100 yr) in Paradox Lake is consistent with the increase in volcanism between 7000 and 9000 yr ago recorded in the Greenland ice cores.

Tephrochronology and its application: A review

“…Such cores (or sections) thus complement the dry-land records and enable tephra distribution patterns, usually shown as isopachs, which are lines depicting deposits of equal thickness, to be mapped with improved accuracy over much greater distances than previously attainable (Fig. 7) (Lowe, 1988b;Rodbell et al, 2002;de Fontaine et al, 2007). Tephras preserved in marine sediments also provide an enhanced record of their distal distribution (e.g., Froggatt et al, 1986;Carey, 1997;Lacasse et al, 1998;Shane et al, 2006), although thicknesses may not directly reflect an eruptive signal, and the distinction between "primary" tephra layers, deposited in a single continuous event from ash fallout onto the sea surface (thence to be delivered to the sea bed) and "secondary" deposits from syndepositional turbidity currents developed by slumping of previously deposited ash, may not be attainable (Manville and Wilson, 2004).…”

“…Some techniques are destructive, others are not (Gehrels et al, 2008). They include ground penetrating radar (Lowe, 1985), magnetic susceptibility and remanent magnetisation (Hodgson et al, 1998;Takemura et al, 2000;Carter et al, 2002;Rasmussen et al, 2003;de Fontaine et al, 2007;Gomez et al, 2007;Venuti and Verosub, 2010), X-radiography (Lowe, 1988b;Turner et al, 2008b;Marshall et al, 2010), X-ray fluorescence (XRF) (Hogg and McCraw, 1983;Gehrels et al, 2008) including XRF-based core scanning (Vogel et al, 2009;Révillon et al, 2010), and scanning Xray analytical microscopy (Katsuta et al, 2007). Further techniques include spectrophotometry (reflectance, luminescence) (Caseldine et al, 1999;Gehrels et al, 2008), high-resolution micropetrography (de Vleeschouwer et al, 2008), high-resolution trace-element analysis by instrumental neutron activation analysis (INAA) (Lim et al, 2008), and measurements of particle size distribution, total organic carbon, and loss-on-ignition (Gehrels et al, 2006(Gehrels et al, , 2008Payne and Gehrels, 2010;Pyne-O"Donnell, in press).…”

“…(3) age-equivalence (Lacasse et al, 1998;Wulf et al, 2004;Kristjánsdóttir et al, 2007;Placzek et al, 2009); and (4) age-modelling of sediment sequences de Fontaine et al, 2007;Lowe et al, 2007) (Table 4). …”

Construction of volcanic records from marine sediment cores: A review and case study (Montserrat, West Indies)

“…de Fontaine et al, 2007;Bertrand et al, 2008). These tephrostratigraphic studies are presented with a range of interpretational challenges, which are much less of an issue than for studies examining distal tephra deposits.…”

“…As a consequence, dispersed explosive-eruption products (tephra) sampled within marine-and lake-sediment cores are widely used to reconstruct explosive eruption records of volcanoes (e.g. Paterne et al, 1988;Ortega-Guerrero and Newton, 1998;Wulf et al, 2004;de Fontaine et al, 2007;Bertrand et al, 2008;Gudmundsdóttir et al, 2012). In making such reconstructions, it is important that explosive eruption deposits are correctly identified, and can be discriminated from volcaniclastic sediments deposited via other mechanisms (e.g.…”