Lake Records of Northern Plains Paleoindian and Early Archaic Environments: The "Park Oasis" Hypothesis

Article excerpt

Fossil pollen and other proxies from lake sediments are used to reconstruct past dynamics in vegetation, climate and local availability of potable water for the northeastern Plains, thereby providing a landscape context to re-assess local Paleoindian and Early Archaic subsistence strategies and settlement patterns. Presented are pollen and plant macrofossil data from two lakes in North Dakota and discussion of these results in the context of published paleoenvironmental and archaeological data for the region. Aridity has characterized the regional climate since deglaciation. From 12,000 to 10,000 ^sup 14^C yr B.P., this aridity was counter-balanced by glacial meltwater saturating much of the landscape, which supported a vegetation of white spruce parkland. The regional water table lowered after 10,000 ^sup 14^C yr B.P. As some lakes went dry or became saline others received ground-water input, thereby creating scattered "oases" in a deciduous parkland, which would have attracted prehistoric people and game alike. Grassland became widespread by 9000 ^sup 14^C yr B.P. Alternating arid and moist intervals characterized the mid-Holocene Altithermal, but some oases existed in the region. This paper supports the hypothesis proposed by some archaeologists for the persistence of human occupation of the northern Plains during the Altithermal except, perhaps, during the severest droughts.

Keywords: pollen, drought, Paleoindian, Archaic, Altithermal

Archaeological records typically reconstruct detailed snapshots of local environmental conditions and human-environment interactions for discrete time intervals and thus have notable chronological gaps. In contrast, the analysis of proxy indicators from lake sediments (e.g., pollen, diatoms) provides continuous records of past vegetation, climatic and hydrologic changes since the formation of these lake basins after deglaciation (so long as water levels are maintained). Lake-sediment data offer both local and regional reconstructions of past environmental changes and thus provide the landscape setting for which site-specific archaeological records may be evaluated.

Unfortunately, paleolacustrine records are limited to where lakes and wetlands exist, which precludes most of the Great Plains. Lakes are common, however, in areas occupied by glaciers during the Late Wisconsinan: the eastern part of the northern Plains (Laurentide Ice Sheet) and higher elevation areas within the Inter-montane West (Cordilleran Ice Sheet). My case study is the northeastern Plains, that area of eastern South Dakota, eastern and northern North Dakota, and eastern Montana in the USA and the Canadian prairies (southern parts of Alberta, Saskatchewan and Manitoba). Even though this glaciated region contains numerous lakes, ponds, and ephemeral wetlands, perennial lakes are still rare, because of the semiarid to subhumid climate. Most existing wetlands are saline playas and "sloughs" (also known as "prairie potholes" and "prairie marshes"), which fill with water after snowmelt and spring rains but are often dry by late summer. However, many of these sloughs provide truncated fossil records from the time the basins formed after déglaciation until the mid-Holocene (Yansa 1998, 2006). In these contexts, the fossils are preserved in saturated sediments below the water table and the fossils in the overlying sediments have been destroyed by oxidation and decay.

In this paper, I present a detailed comparison of pollen and plant macrofossil (seeds, fruits, leaves, buds and wood) data from two lake sites in North Dakota that represent different physiographic areas in order to distinguish between regional climate changes and local conditions of geology and hydrology. Coldwater Lake is a kettle lake situated on the Missouri Coteau upland, whereas the Wendel site was once a paleolake located on the lower-elevation Glaciated Till Plain (Figure 1). The Wendel site offers a truncated fossil record from ca. …