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Salt marshes are common globally in low-lying coastal environments. Their geological settings and ecosystems vary widely by latitude and climatic settings (Chapman, 1960). Allen (2000) provides a comprehensive sketch of European salt marshes, while Rogers and Woodroffe (2014) give a recent summary of the subject. Woodwell et al. (1973) suggest that there are more than 38 million hectares (380,000 km2) of salt marshes worldwide, but specific delineation of distributions is incomplete, particularly in Asia, Africa, and South America. That area is greater than the total area of coastal American states from New Jersey to South Carolina. This chapter concentrates on the east coast of North America as containing examples of well-studied environments, with a few additional examples.
Los Morteros (8°39'54"S, 78°42 '00"W) is located in coastal, northern Peru, one of the six original centers of world civilization. The site consists of a large, sand-covered, isolated prominence situated on a Mid-Holocene shoreline, ∽5 km from the present coast. Preceramic archaeological deposits (4040±75 to 4656±60 14C yr BP or ∽3600–5500 cal yr BP) cap this feature, which has been identified by prior researchers as a sand-draped, bedrock-cored landform or a relict dune deposit. Because neither explanation is geomorphologically probable, we used ground-penetrating radar (GPR) and high-resolution mapping to assess the mound's interior structure. Our results indicate an anthropogenic origin for Los Morteros, potentially placing it among the earliest monumental structures in prehistoric South America. The extremely arid setting raises new questions about the purpose and the logistics of early mound construction in this region. This work demonstrates the value of an integrated Quaternary sciences approach to assess long-term landscape change and to understand the interaction between humans and the environment.
Alternative kinetic models for amino acid racemization in Pleistocene molluscan samples are compared by examination of results for samples from marine Pleistocene deposits in California, Washington, and Florida. Linear kinetic models previously have been applied to the Florida samples [ Mitterer, R.M. (1975). Earth and Planetary Science Letters 28 , 275–282.] because these kinetics were observed in laboratory pyrolysis experiments with the particular genus involved (Mercenaria). Nonlinear kinetic models, extrapolated from deep-sea foraminifera racemization kinetics, are applied to samples of Protothaca and Saxidomus from California and Washington and seem more consistent with their local chronologic and stratigraphic control. Average or effective diagenetic temperatures can be estimated by each of these models if reliably dated samples are available. Linear models applied to such samples from California and Florida suggest average diagenetic temperatures that are cooler (by as much as 10°C) than would be inferred from available paleoclimatic records. Nonlinear kinetic models yield estimates of average diagenetic temperatures that are more consistent with these records: full-glacial (i.e., approximately 18,000 yr BP) temperature reductions of between 2 and 6°C are inferred for coastal California and southern Florida. The nonlinear kinetic model is used to expand (by a factor of 2.5 to 3.0) the time scale proposed by Mitterer (1975) for five marine Pleistocene units of Florida.
Reconstructions of glacioisostatic rebound based on relative sea level in Maine and adjacent Canada do not agree well with existing geophysical models. In order to understand these discrepancies better, we investigated the lake-level history of 40-km-long Moosehead Lake in northwestern Maine. Glacioisostasy has affected the level of Moosehead Lake since deglaciation ca. 12,500 14C yr B.P. Lowstand features at the southeastern end and an abandoned outlet at the northwestern end of the lake indicate that the lake basin was tilted down to the northwest, toward the retreating ice sheet, by 0.7 m/km at 10,000 14C yr B.P. Water level then rose rapidly in the southeastern end of the lake, and the northwestern outlet was abandoned, indicating rapid relaxation of landscape tilt. Lowstand features at the northwestern end of the lake suggest that the lake basin was tilted to the southeast at ca. 8750 14C yr B.P., possibly as the result of a migrating isostatic forebulge. After 8000 14C yr B.P., water level at the southeastern end was again below present lake level and rose gradually thereafter. We found no evidence suggesting that postglacial climate change significantly affected lake level. The rebound history inferred from lake-level data is consistent with previous interpretations of nearby relative sea-level data, which indicate a significantly steeper and faster-moving ice-proximal depression and ice-distal forebulge than geophysical models predict.
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