Tephra layers

Brown F. H., Sarna-Wojcicki A. M., Meyer C. E., and Haileab B. (1992) Correlation of Phocene and Pleistocene tephra layers between the Turkana Basin of East Africa and the Gulf of Aden. Quat. Int. 13/14, 55—67. 

Locally, there may be a frequent occurrence of tephra layers and significant concentrations of finely dispersed volcaniclastic material in deep-sea sediments especially in the proximal zones of volcanic activity, like in marginal zones of the modern Pacific Ocean. In a recent evaluation of tephra input into the Pacific Ocean sediments based on DSDP and ODP data Straub and Schmincke (1998) estimate that the minimum proportion of volcanic tephra corresponds to 23 vol.% of the existing Pacific oceanic sediments. 

Palais JM (1985) Tephra layers and ice chemistry in the Byrd-Station ice core, Antarctica. Ph.D. dissertation. Dept. Geol. Minertil., The Ohio State University, Columbus, OH... 

Tephra layers in ice cores are typically overlain by ice that contains elevated sulfate concentrations and excess hydrogen ions (H ). These chemostiatigraphic relationships occur because the sulfur dioxide gas... 

The effect of the volcanic eruptions during the 19th and 20th centuries on the tanperature of the atmosphoe was evaluated in a series of papers by Self et al. (1981), Newell (1981), Robok (1981), and Walker (1981), all of whom published their contribulions in volume 11 of the Journal of Volcanology and Geothermal Research. The occurrence of tephra layers in the East Antarctic ice sheet is the subject of reports by Keys et al. (1977), Koeberl et al. (1987), Palais and Sigurdsson (1989), and Faure et al. (1994, with assistance from Mary Davis and Keith Henderson). 

The ice core drilled in 1983/84 at South Pole Station contained a 3-mm tephra layer at a depth of 303.44 m (Palais et al. 1987). The tephra are composed of vesic-nlar glass with crystals of quartz, pyroxene, and pla-gioclase. The bulk chemical composition of these tephra plots close to the boundary between the andesite and benmoreite fields in Fig. 17.44 in strong contrast to the tephra in the cores at Byrd Station and Dome C (See also Koeberl 1990, Table 1). 

The Vostok tephra are very similar in composition to the tephra in the South-Pole core and closely resemble the andesite in Candlemas and Bellingshausen islands of the South Sandwich Islands in Fig. 17.46 (57°45 S, 026°30 W) (Tomblin 1979 Baker 1978). The distance between these islands and Vostok station is about 4,500 km (Palais et al. 1987 Kyle et al. 1984). In spite of the dispersion during transport through the atmosphere, the thickness of the tephra layer in the Vostok core is 5 cm at a depth of 101 m giving it an assigned age of 3,300 years. Therefore, the volcanic ash erupted by volcanoes in the South Sandwich Islands may have formed a large plume over East Antarctica. If so, this ash layer may be a useful stratigraphic marker in the East Antarctic ice sheet (Kyle et al. 1984). 

The tephra layers exposed on the ice fields west of the AUan HiUs were mapped by Dunbar (1995a, b) who also attanpted to date anorthoclase crystals contained within them by the Ar/ Ar method. The outcrop patterns of these tephra layers in Fig. 17.48 demonstrate their linear continuity and the structural deformation of the ice in this area. The same investigators also sampled dnst layers on other ice fields associated with the AUan HiUs, such as the ice around the Elephant and Redding moraines, the Ear Western, Ear Northern, and Meteorite City ice fields, ice adjacent to Carapace Nunatak, and other localities on the margin of the East Antarctic ice sheet in southern Victoria Land. 

Fig. 17.47 The Lewis Cliff ice tongue contains several tephra layers and englacial clasts that emerge as the surrounding ice sublimates. A dirt layer occurs at the weU-defined contact between pale blue ice and dark blue ice. The contact appears to be a fault in the ice (Photo by G. Faure)...

The ice fields adjacent to the Allan Hills, where a large number of meteorite specimens have been collected, also contain tephra layers. The outcrop patterns of these layers indicate that the ice was extensively deformed as it flowed over and around the subglacial foothills of the Transantarctic Mountains. A small deposit of black spherules embedded in the ice near the Allan Hills was attributed to the passage through the atmosphere of a stony meteorite. This deposit reminds us that the East Antarctic ice sheet contains extraterrestrial particles and specimens of meteorites in addition to terrigenous dust and volcanic ash. 

Kyle PR, Jezek PA, Mosley-Thompson E, Thompson LG (1981) Tephra layers in the Byrd Station ice core and the Dome C ice core, Antarctica, and their climatic importance. J Volcanol Geotherm Res 11 29-39... 

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