Paleoindian environmental change and landscape response in Barger Gulch, Middle Park, Colorado

Abstract

Middle Park, a high‐altitude basin in the Southern Rocky Mountains of north‐central Colorado, contains at least 59 known Paleoindian localities. At Barger Gulch Locality B, an extensive Folsom assemblage (˜10,500 14C yr B.P.) occurs within a buried soil. Radiocarbon ages of charcoal and soil organic matter, as well as stratigraphic positions of artifacts, indicate the soil is a composite of a truncated, latest‐Pleistocene soil and a younger mollic epipedon formed between ˜6000 and 5200 14C yr B.P. and partially welded onto the older soil following erosion and truncation. Radiocarbon ages from an alluvial terrace adjacent to the excavation area indicate that erosion followed by aggradation occurred between ˜10,200 and 9700 14C yr B.P., and that the erosion is likely related to truncation of the latest‐Pleistocene soil. Erosion along the main axis of Barger Gulch occurring between ˜10,000 and 9700 14C yr B.P. was followed by rapid aggradation between ˜9700 and 9550 14C yr B.P., which, along with the erosion at Locality B, coincides with the abrupt onset of monsoonal precipitation following cooling in the region ˜11,000–10,000 14C yr B.P. during the Younger Dryas oscillation. Buried soils dated between ˜9500 and 8000 14C yr B.P. indicate relative landscape stability and soil formation throughout Middle Park. Morphological characteristics displayed by early Holocene soils suggest pedogenesis under parkland vegetation in areas currently characterized by sagebrush steppe. The expansion of forest cover into lower elevations during the early Holocene may have resulted in lower productivity in regards to mammalian fauna, and may partly explain the abundance of early Paleoindian sites (˜11,000–10,000 14C yr B.P., 76%) relative to late Paleoindian sites (˜10,000–8000 14C yr B.P., 24%) documented in Middle Park. © 2005 Wiley Periodicals, Inc.

Comparisons and Interpretations of Charcoal and Organic Matter Radiocarbon Ages from Buried Soils in North-Central Colorado, USA

“…All of the 14 C ages from buried Kremmling surface soil horizons occur between 9000 and 4000 BP, while the buried surface horizon at JCS 05-1 produced entirely late Holocene ages (Table 3; Figures 4 and 5). Surovell et al (2005) c Originally published by Mayer et al (2007) d Originally published by Mayer et al (2005) The HT and HA samples from the Kremmling soil in the main block of the Barger Gulch excavation area show the same relationship as the LT and HA fractions, though they are in closer agreement relative to most SOM pairs (Table 4, Figures 4 and 5). While no charcoal samples were recovered in direct association with the SOM samples, the Kremmling soil A horizon in the Barger Gulch Locality B excavation area produced charcoal ages of ~9500 BP and ~6900 BP from lower and upper samples, respectively Surovell et al 2005).…”

“…Determining the age of the soil is important for understanding landscape evolution and Holocene environmental change, which have archaeological implications. Middle Park contains an abundance of Paleoindian archaeological components (Kornfeld and Frison 2000), some of which occur in buried soils (Kornfeld et al 1999;Mayer et al 2005Mayer et al , 2007Surovell et al 2005). Table 1 The goals of this study are threefold.…”

Shallow site archaeology: Artifact dispersal, stratigraphy, and radiocarbon dating at the Barger Gulch locality B Folsom Site, Middle Park, Colorado

“…14 C yr B.P., an age estimate roughly comparable to that identified by Mayer et al (2005) using independent lines of evidence from other stratigraphic sections.…”

“…The association of Folsom artifacts with what was believed to be a soil-organic-matter radiocarbon date of 9420 Ϯ 50 (Beta-109464) from the base of Stratum 3 suggested to us that the buried A and B horizons represented a Younger Dryas soil commonly found at Paleoindian sites across the western Plains and Rocky Mountains (e.g., Irwin-Williams et al, 1973;Reider, 1980Reider, , 1990Haynes, 1993). In his initial study of the site, however, Reider (1998), like Mayer et al (2005) felt that the A horizon formed in Stratum 3 was welded to a truncated late-Pleistocene B horizon developed in Stratum 1. The question has important implications for the Folsom archaeology at the site because the occupation surface, as we define it, correlates with this contact in vertical space.…”

“…Samples were collected in 2.5-cm increments from Profile 02-4 (see Mayer et al, 2005, for a detailed stratigraphic description) on the eastern side of the excavation block. Each sample underwent particle size analysis using the pipette method (Singer and Janitsky, 1986) and sonic sifting for sand fractions, percent carbonate using a Chittick apparatus, and percent organic carbon content using the Walkley-Black method.…”