Tephrochronology of the Brooks River Archaeological District, Katmai National Park and Preserve, Alaska: what can and cannot be done with tephra deposits

Abstract

The Brooks River Archaeological District (BRAD) in Katmai National Park and Preserve is a classical site for the study of early humans in Alaska. Because of proximity to the active Aleutian volcanic arc, there are numerous tephra deposits in the BRAD, which are potentially useful for correlating among sites of archaeological investigations. Microprobe analyses of glass separates show, however, that most of these tephra deposits are heterogeneous mixtures of multiple glass populations. Some glasses are highly similar to pyroclasts of Aniakchak Crater (160 km to the south), others are similar to pyroclasts in the nearby Valley of Ten Thousand Smokes, and some are similar to no other tephra samples from the Alaska Peninsula. Moreover, tephra deposits in any one archaeological study site are not always similar to those from nearby sites, indicating inconsistent preservation of these mainly thin, fine-grained deposits. At least 15, late Holocene tephra deposits are inferred at the BRAD. Their heterogeneity is the result of either eruptions of mixed or heterogeneous magmas, like the 1912 Katmai eruption, or secondary mixing of closely succeeding tephra deposits. Because most cannot be reliably distinguished from one another on the basis of megascopic properties, their utility for correlations is limited. At least one deposit can be reliably identified because of its thickness (10 cm) and colour stratification. Early humans seem not to have been significantly affected by these tephra falls, which is not surprising in view of the resilience exhibited by both plants and animals following the 1912 Katmai eruption.

The Middle Stone Age of the northern Kenyan Rift: age and context of new archaeological sites from the Kapedo Tuffs

“…This is in part due to the wide recognition of the many potential sources of withinsample compositional variation, which include instrumental error, postdepositional weathering and selective element leaching, heterogeneous batches of parent magma, the inclusion of older deposits during eruption and magma ascent, and reworking by fluvial or other processes (e.g., Hunt and Hill, 1993;Orton, 1996;Feibel, 1999a;Riehle et al, 2000;Donoghue et al, 2007). In general, the strongest correlations are those that show concordance between multiple independent datasets, including stratigraphic, fossil, chronological, and geochemical evidence.…”

K-bentonites, volcanic ash preservation, and implications for Early to Middle Devonian volcanism in the Acadian orogen, eastern North America

“…Alternatively, condensation due to low background sedimentation rates may, under some conditions, enhance the preservation of volcanic materials (Loutit et al, 1988;Rea et al, 1993;Huff et al, 1999;Riehle et al, 2000). The effect may be especially enhanced in situations of relatively high volcanic ash input rates.…”

Effects of tephra deposition on mire vegetation: a field experiment in Hokkaido, Japan

“…There are different views on how severe and how long lasting the effects of tephra deposition on ecosystems are (Crowley et al . 1994; Riehle et al . 2000).…”