Stratigraphy Cultural Deposits Research Statement Field and Lab Methods Conclusions References
Natural Deposits
Stratigraphy at the Darkmold site is quite complex. The site is located on a small glacial kame terrace along west side of the Animas River Valley. The underlying Cutler Formation is exposed below and above the site and in the excavations along the west end of the site. In these exposures, two beds are visible−arkosic sandstone and siltstone. Natural undercutting and slope failure may have caused the step-like exposures visible at the site. Similar exposures of inset benches are common features along the valley walls.
After terrace formation, postglacial sediments were deposited along the surface.The disparity in size grades from coarse sand and pebbles to large boulders suggests a fluvioglacial origin. These sediments were probably not the result of direct glacial activity, rather they were deposited from meltwaters from the receding glaciers. Striations were noted on several large boulders, and the striations support a glacial origin. Episodic deposition has resulted in irregular strata, complicated facies changes, and differential soil development.
The glacial deposits are covered with slope-wash sediments or colluvium of sandy loam sediments with pebbles and occasional rounded cobbles. The rounded cobbles occur in fluvioglacial deposits upslope of the site. The red color and sandy texture indicate that the parent material is the Permian Cutler Formation.
At the site, soil formation is
largely the result of relief, climate, and parent material.
The site is situated on a slope and it
receives a more or less constant supply of slope-wash sediments or colluvium.
Colluvium, derived from weathered Cutler
Sandstone, is the parent material for soil formation at the site. Of lesser
importance are eolian and fluvioglacial
sediments. The site is mantled with a thick layer of sandy clay loam in which soil pedogensis has been active since the beginning of the Holocene. A thick soil
profile with some evidence of buried soils is exposed along the backwall. Soils
here mostly display a thick Bt horizon with a cumulative A horizon, a B horizon
formed in cultural colluvium, and a buried Bt horizon with accumulations of
calcium carbonate (Btkb). Beneath the Btkb horizon is a layer of fluvioglacial
sediments. This cobbly sandy loam unconformably overlies the Permian sandstone,
with a major hiatus of 250,000,000 years.
The Cutler Formation in Hidden Valley West of Durango
Students working on stratigraphic sections at the Darkmold Site.