Broken Mammoth Archaeological Project - Stratigraphy and Chronology

The stratigraphy at the Broken Mammoth and other sites in the Shaw Creek region consists of a series of aeolian sediments (sand and loess) overlying a frost-shattered and weathered felsic gneiss bedrock of the Yukon-Tanana crystalline terrane. The sediments and soils at the sites contain a record of past environmental changes in east-central Alaska. For example, the Broken Mammoth, Mead, and Swan Point stratigraphy documents the change from a full glacial, deflational environment at the close of the Pleistocene to one of alternating episodes of aeolian deposition and soil formation during the Holocene.

View Broken Mammoth Stratigraphy and C14 Dates
View Swan Point Site Stratigraphy and C14 Dates
View Mead Site Stratigraphy and C14 Dates

Paleosol complexes associated with the two earliest human occupations (c.11,500 yr. BP and c. 10,400 yr. BP), are indicative of stable occupation surfaces. This interpretation correlates with the regional pollen record, specifically the latter part of the "Birch Period" (an open shrubland that included dwarf birch and willow) and the "Populus-Salix Zone" (described as open Populus woodland and birch-shrub tundra). After about 9,000 years ago, this shrubland changed to a woodland that included spruce and alder species. Faunal remains of Red squirrel and porcupine from the Broken Mammoth Site, suggest the process of forestation may have begun slightly prior to 9,500 years ago. Shortly thereafter, windier conditions may have become reestablished, as loess accumulation appears to have accelerated until about 7,000 years ago. After which, more modern conditions appear to have prevailed, with the modern forest soil established sometime after 5,000 years ago.