No abstract

This paper presents the biotic, sedimentary, geomorphic, and climatic history of the upper part of the Roberts Creek Basin, northeastern Iowa for the late—glacial and Holocene, and compares these records with a C—O isotopic sequence from Coldwater Cave, 60 km northwest of Roberts Creek. The biotic record (pollen, vascular plant and bryophyte macrofossils, and insects) is preserved in floodplain alluvium that underlies three constructional surfaces separated by low scarps. Each surface is underlain by a lithologically and temporally distinct alluvial fill. The highest surface is underlain by the Gunder Member of the Deforest Formation, dating from 11 000 to 4000 yr BP; beneath the intermediate level is the Roberts Creek Member, dating from 4000 to 400 yr BP; and the lowest level is underlain by the Camp Creek Member, deposited during the last 380 yr. Pollen and plant macrofossils in the alluvial fill show that a typical late—glacial spruce forest was replaced by Quercus and Ulmus in the early Holocene. This early—to—middle Holocene forest became dominated by mesic elements such as Acer saccharum, Tilia americana, Ostrya virginiana, and Carpinus caroliniana as late as 5500 yr BP; in contrast, the closest sites to the west and north were at their warmest and driest and were covered by prairie vegetation between 6500 and 5500 yr BP. After 5500 yr BP, the forest in the Roberts Creek area was replaced by prairie, as indicated by a rich assemblage of plant macrofossils, although only Ambrosia and Poaceae became abundant in the pollen record. The return of Quercus ≈ 3000 BP (while nonarboreal pollen percentages remained relatively high) indicates that oak savanna prevailed with little change until settlement time. The bryophyte assemblages strongly support the vascular plant record. Rich fen species characteristic of boreal habitats occur only in the late—glacial. They are replaced by a number of deciduous—forest elements when early—to—middle Holocene forests were present, but mosses of forest habitats completely disappear when prairie became dominant. A few deciduous—forest taxa return during the late—Holocene, when oak savanna prevailed. The C—O isotopic record from stalagmite s in Coldwater Cave indicates a relatively stable environment from ≈ 8000 to 5100 yr BP, when the δ13C values indicate a change in vegetation dominated by C3 (predominantly forest) to C4 (predominantly prairie) plants. About 4900 yr BP, the rise in 18O values indicates a temperature increase of ≈ 1.5°C. The fact that the vegetational change suggested by the δ13C values preceded the temperature increase suggests that fire may have been an important factor in converting forest to prairie. Abundant charred seeds and other plant material at Roberts Creek 4830 yr BP support this hypothesis. The 18O values remain constant from ≈ 5100 to ≈ 3000 yr BP, but the δ13C values gradually rise, indicating that soil formed under forest takes at least 2000 yr for its carbon to reach equilibrium after replacement by prairie vegetation. The return of oak to form sav...

Wisconsinan full-glacial silts filling a swale exposed in Conklin Quarry, Johnson Co., Iowa, contain a large and diverse biota that includes pollen, bryophytes, vascular-plant macrofossils, small mammals, molluscs, and insects. Radiocarbon dates on wood from the top, middle and bottom of the swale fill respectively were 1671 0 k 270, 17 170 k 205, and 18090 k 190 yr BP. The pollen diagram is dominated by Picea (spruce), Pinus (pine), and Cyperaceae (sedge), and it records low pollen accumulation rates. Plant macrofossils include a number of tundra species along with Picea and Larix (larch) needles and small pieces of wood. The insect fauna contains many species now confined to the forest-tundra thnsition zone of northwestern Yukon and Alaska. Small mammals include the tundra indicators Dicrostonyx (collared lernming), and prodably Microtus rniurus (singing vole) together with boreal forest taxa. The molluscs include extinct and relict species and show the widest range in present geographic distribution, but Rocky Mountain and especially northern elements predominate in the swale fill. All these lines of evidence lead to consistent palaeoclimatological interpretation and palaeoecoiogical reconstruction.The dominant habitats represented by the biota and sedimentary environment collectively included open calcareous silty to sandy or gravelly upland sites, minerotrophic fens (wetlands), pond-or stream-side clayey to sandy shores, and shallow (possibly ephemeral), cold, clear-water ponds. Mean July temperatures were probably 11" to 13°C cooler than at present. The biota indicates that a Picea-Larix krummholz with extensive tundra openings was present in southeastern Iowa between 18090 and 16 71 0 yr BP.

a b s t r a c tA long standing research approach in island Oceania is the examination of community and regional level patterning of archaeological remains. However, these efforts are impeded by heavy vegetation and rugged terrain, which limit the implementation and productivity of traditional archaeological methods. Aerial lidar data provide an opportunity to survey large archaeological landscapes effectively and efficiently in these environments. In this paper, we present the results of a lidar-based survey and analysis of community-level spatial patterning for at sites in the Manu'a Group of American Samoa. Using lidar data in conjunction with pedestrian survey results, we first established the suitability of lidar for identifying archaeological features, and then applied the technique to a previously unexamined landscape. We were able to record archaeological remains and analyse the data to discern spatial patterning in their distribution. The patterning of these remains is broadly comparable, though not identical, to that of three other settlement zones on Olosega and the adjacent island of Ofu, which previously were intensively surveyed. The differences in the characteristics and distribution of structural features within and between these four settlement zones may reflect differences in social status and ranking.