Lyndsay M. DiPietro

Dry Creek Revisited: New Excavations, Radiocarbon Dates, and Site Formation Inform on the Peopling of Eastern Beringia

The multicomponent Dry Creek site, located in the Nenana Valley, central Alaska, is arguably one of the most important archaeological sites in Beringia. Original work in the 1970s identified two separate cultural layers, called Components 1 and 2, thought to date to the terminal Pleistocene and suggesting that the site was visited by Upper Paleolithic huntergatherers between about 13,000 and 12,000 calendar years before present (cal B.P.). The oldest of these became the typeassemblage for the Nenana complex. Recently, some have questioned the geoarchaeological integrity of the sites early deposits, suggesting that the separated cultural layers resulted from natural postdepositional disturbances. In 2011, we revisited Dry Creek to independently assess the sites age and formation. Here we present our findings and reaffirm original interpretations of clear separation of two terminal Pleistocene cultural occupations. For the first time, we report direct radiocarbon dates on cultural features associated with both occupation zones, one dating to 13,485-13,305 and the other to 11,060-10,590 cal B.P.

Anatomy of a Sub-Cambrian Paleosol in Wisconsin: Mass Fluxes of Chemical Weathering and Climatic Conditions in North America during Formation of the Cambrian Great Unconformity

A paleosol beneath the Upper Cambrian Mount Simon Sandstone in Wisconsin provides an opportunity to evaluate the characteristics of Cambrian weathering in a subtropical climate, having been located at 20°S paleolatitude 500 My ago. The 285-cm-thick paleosol resulted from advanced chemical weathering of a gabbroic protolith, recording a total mass loss of 50%. Weathering of hornblende and plagioclase produced a pedogenic assemblage of quartz, chlorite, kaolinite, goethite, and, in the lowest part of the profile, siderite. Despite the paucity of quartz in the protolith and 40% removal of SiO2 from the profile, quartz constitutes 11%–23% of the pedogenic mineral assemblage. Like many other Precambrian and Cambrian paleosols in the Lake Superior region, the paleosol experienced potassium metasomatism, now containing 10%–25% mixed-layer illite-vermiculite and 5%–44% potassium feldspar. Estimates of mean annual precipitation and mean annual temperature are 1777 mm y−1 and 20.1°C, respectively, which are consistent with a paleolatitude of 20°S. For an atmospheric CO2 concentration of 4000–6000 ppm at 550–500 Ma, the duration of weathering is constrained to have been between 20,000 and 100,000 y. When the effects of erosion and influence of protolith composition are considered, the degree, or maturity, of weathering for the Wisconsin paleosol and four other sub-Cambrian paleosols is comparable to that for two modern soils in subtropical and temperate climates, despite the lack of land plants in Cambrian time. Such correspondent degrees of weathering likely result from the effects of elevated levels of atmospheric CO2 and microbial activity on weathering in Cambrian time.