Les Sirkin

The Portwashingtonian warm interval in the northern Atlantic coastal plain

Stratified and deformed masses of marine sediment that range in age from 43,800 to 21,750 yr were deposited in the Woodfordian moraine on western Long Island, New York. Reconstruction of the geologic history of these sediments provides further evidence of a mid-Wisconsinan warm interval, the Portwashingtonian warm interval (new name), that is represented by warm climate, temperate forests, and relative sea level comparable to modern sea level.

Late Pleistocene and Holocene deglaciation and environments of the southern Chugach Mountains, Alaska

The description of late Pleistocene and Holocene deglaciation and environments in the Copper River–Chugach Mountains region is based on surficial geology as well as on pollen analysis and radiocarbon dating of core samples. The results of this study indicate that late Pleistocene glaciers extended well beyond the present coastal plain. Deglaciation began in the lower Copper River valley prior to 14,000 yr B.P. and in the Bremner and Tasnuna River valleys about 10,000 and 9000 yr B.P., respectively. Cirque glaciers formed marginal moraines at an elevation of ∼560 m in the Tasnuna Valley ∼8800 yr B.P. On the basis of the pollen record, shrub-herb tundra characterized the initial late wisconsinan vegetation. Tundra was succeeded first by alder-dominated vegetation and then by spruce forest. The late-glacial pollen zones indicate a time-transgressive colonization of the river valleys and mountain slopes inland from the coast.

LATE PLEISTOCENE VEGETATION AND ENVIRONMENTS IN THE MIDDLE ATLANTIC REGION

The mid-Atlantic region has proven to be important in the reconstruction of late Quaternary stratigraphy and environments. This region includes both glaciated and unglaciated terrain and deposits of terrestrial and marine origin ( F I G U R E 1). Reconstructions have been greatly enhanced by palynological investigation of a variety of sediments and stratigraphic units. Studies in the glaciated areas north of the late Wisconsin end moraines have demonstrated changes in vegetation and climate and have been useful in interpreting the age of glacial deposits and the nature of glacial recession. South of the end moraines the record of late Pleistocene environments has been extended back to the Sangamon Interglacial, and it includes the major changes in vegetation, climate, and sea level that have occurred since that time. In both the glaciated and unglaciated areas, greater awareness of Quaternary stratigraphy can be useful in the interpretation of archaeological sites. Pollen studies have also contributed a more or less standard sequence of pollen zones that are applicable to environmental and archaeological reconstructions in this region. In the absence of radiometric data, pollen analyses from a new site can be compared with the standard zonation in order to determine regional vegetation, climate, and approximate geologic age. Even though the standard zonation has evolved independently of archaeological studies, these correlations can be effective in providing chronologic and environmental data in archaeological research. The archaeological record for the mid-Atlantic region appears to be limited, however, to the late and postglacial. Whether Paleoindians were present here during or before the late Wisconsin glaciation has not been established, even though evidence exists for early Wisconsin migration elsewhere in North America. Such evidence may also be forthcoming in this region as archaeological activity increases. This paper covers the major geologic and environmental changes that have occurred in the mid-Atlantic region between Sangamon and postglacial time. The discussion emphasizes stratigraphic units and their associated microfloras, from which the environmental inferences are made. The predominant pollen assemblages are cited in order to document major vegetational changes.

Late Quaternary stratigraphy and environments of the West Mexican coastal plain

Abstract The geomorphic events that formed the west Mexican coastal plain and the stratigraphy and chronology for those events based on soils, pollen zones, and radiocarbon ages are discussed. Three phases of geomorphic development are recognized. The Alluvial Phase represents deposition of the coastal bajada during the Neogene; oxisols and saprolites have formed on this surface. The Teacapan Peninsula Phase began during the Sangamonian Inter‐glacial with deposition of the spit; an ultisol and an alfisol have developed on the peninsula. In the Prograding Beach Phase, beginning about 13,000 B.P., four sequences of beach ridges were deposited during eustatic sea level rise and periodic uplift. On the resulting ridge and swale topography are four soil units, three inceptisols on the initial, early, and middle beaches and an entisol on the late beach. The pollen stratigraphy and chronology are based on samples from eleven cores, twelve radiocarbon dates, and calculated deposition rates. The alternation in dom...

Block Island, Rhode Island: Evidence of fluctuation of the late Pleistocene ice margin

Superimposed drift sheets on Block Island provide evidence of two advances of the late Pleistocene glacial margin. The lower Montauk Drift crops out as two till units separated by a deformed stratified unit or till over outwash. It closely resembles the drift at Montauk Point, Long Island. This complex unit was probably deposited by a glacial lobe that moved across the Narragansett Bay region. The upper New Shoreham Drift forms the morainal topography of the island and was probably derived from a glacial lobe that crossed the Connecticut region. The stratigraphy indicates that an oscillating early Wisconsinan ice sheet deposited the Montauk Drift and subsequently receded from its terminal position. Laminated silt, sand, and clay (varves?) were deposited in a proglacial lake, and irregularly stratified silt was deposited as alluvium adjacent to the end moraine. With the advance of the late Wisconsinan glacier, the New Shoreham Drift was deposited. This ice overrode and deformed existing drift and created a drumlin field and prominent morainal topography.