Non-glacial Sediments Research Articles

Amino acid analysis of Pleistocene marine molluscs from the Gower Peninsula

The Gower Peninsula, South Wales is a particularly important area, where marine, terrestrial, glacial and non-glacial sediments occur in stratigraphical sequence1. The establishment of a Pleistocene aminostratigraphy where stratigraphical relationships are well established would make it possible to include Pleistocene deposits elsewhere in this stratotypic framework thereby expanding it. Sampling of sites in Devon, Cornwall, Dorset and Sussex is now being carried out to extend aminostratigraphical correlation of the Pleistocene beaches of southern Britain. Extensive sampling of the Pleistocene beaches of the Gower Peninsula, was carried out during 1981 when specimens of Patella vulgata (Linnaeus) and Nucella lapillus (Linnaeus) were collected for amino acid analysis (Fig. 1). Amino acid analysis is fundamental to the identification of mixed-age populations which, it has been discovered, are common in most beach deposits. This is particularly important because successive high sea-level stands have probably occupied the coast on several occasions, leaving only one extensively reworked deposit as evidence for several marine incursions. If a molluscan fauna was associated with each high stand of sea-level and has been preserved in part, the multiple occupation of these sites can be confirmed and their relative ages resolved.

The nature of the Late Paleozoic glaciation in Gondwana as determined from an analysis of garnets and other heavy minerals: Discussion

Gravenor (1979) has used chattermark trails found upon the surfaces of detrital garnet grains as palaeoenvironmental indicators of both the degree and multiplicity of glaciation in an area. Such a practice of using this microtexture analysis to authenticate ancient deposits (developed from Folk (1975); Gravenor et al. (1978)) may prove erroneous or, at the least, questionable in the light of scanning electron microscope theory (Margolis and Kennett 1971; Whalley and Krinsley 1974). In addition, some problems recently identified regarding the origin of these chattermark trails (Bull 1977; Rocha-Campos and Krauspenhar 1978) need to be considered. A major aim of Gravenor (1979, p. 1138) was . . to examine the evidence provided by an analysis of heavy minerals, particularly garnets . . . to provide an explanation for certain of the controversial aspects of this (the Gondwana) glaciation. (our parentheses). The evidence cited depended heavily upon the acceptance that chattermark trails are not only mechanically formed but that they are glacially formed. We wish to question the hypothesis of formation of grinding as the sole mechanism of chattermark genesis and in support of these views we shall draw upon recent results that we have obtained from analysis of garnet and quartz grains taken from deposits (Table 1). More detailed presentation of these data and their implications to chattermark formation is presently in preparation (Bull et al. , in preparation). The deposits were taken from beaches on Freetown Peninsula, Sierra Leone, and from Cape Comorin beach and dune complex, Tamilnadu State, southern India. In both instances, fieldwork and literature searches have shown that the deposits sampled are not likely to have been affected either by ancient or more modern modification. Those samples from the Freetown Peninsula have derived from Archaean granitic rocks either from the north-central Sierra Leone or possibly from the south along the West African coastline. Those samples taken from Cape Comorin have also derived from more ancient basement rocks (gneiss, granulite, and charnockite) of the Ghats Mountains to the west. The implications of our findings (Table 1) are that chattermark trails can seemingly be found in the same or higher percentages upon quartz and garnet grains from nonglacial sediments as those identified from sediments by Gravenor. Furthermore, these results are compatible with those of RochaCampos and Krauspenhar (1978) who considered the features to be formed in a subaqueous environment with later chemical etching. The samples taken from both India and Sierra Leone have, at one time or another, been subjected to modification in the beach environment. Whether the textures are mechanically formed in subaqueous environments later to be chemically etched or indeed solely the result of chemical action requires further consideration (Bull et al., in preparation). Nevertheless, it can be shown that chattermark trails are not exclusively formed by modification (whatever glacial modification is: see Whalley and Krinsley (1974)). Most certainly, glaciers do impart chattermark trails upon grains, however, great caution must be exercised in using these textures for environmental reconstruction. By considering that chattermark trails were at

Pre-Olympia Pleistocene Stratigraphy and Chronology in the Central Puget Lowland, Washington

Drifts of two pre-Olympia glaciations separated by nonglacial sediments are widespread in the central Puget Lowland of western Washington. The Double Bluff Drift (older) and Possession Drift represent advances of the Puget lobe of the Cordilleran ice sheet more than 40,000 years ago. The nonglacial Whidbey Formation between the drifts was formed in streams and lakes. During its deposition, climate was initially cool and moist, as inferred from pollen in peat beds, but subsequently it became much like that of the present in the lowland. The Possession Drift is tentatively correlated with glacial deposits of Salmon Springs age in the southern part of the lowland. The Whidbey Formation may correlate with nonglacial deposits between two Salmon Springs Drifts or with the Puyallup Formation.

Late Pleistocene Stratigraphy and Chronology in Southwestern British Columbia and Northwestern Washington

Six geologic-climate units are proposed for the late Pleistocene sequence in southwestern British Columbia and northwestern Washington. They include two major units, the Olympia Interglaciation and the Fraser Glaciation, and four subdivisions of the latter—the Evans Creek, Vashon, and Sumas Stades, and the Everson Interstade. The Olympia Interglaciation is a nonglacial episode that started at least 36,000 years B.P. and continued until the advance of Cordilleran glacier ice during the Fraser Glaciation. During the Evans Creek Stade, alpine glaciers formed in the mountains of western Washington and British Columbia while nonglacial sediments were still being deposited in the southern Puget Lowland. Further growth of glaciers in British Columbia resulted in the formation of the Cordilleran ice sheet. This ice entered the northern end of the area after 25,000 years B.P. but did not reach the southern end until after 15,000 years B.P. The Vashon Stade of the Fraser Glaciation began with this advance of Cordilleran ice into the lowlands. It ended with the beginning of marine and glaciomarine conditions there, which commenced in the southern Puget Lowland about 13,500 years B.P. and in the Strait of Georgia about 13,000 years B.P. The episode represented by the marine conditions is called the Everson Interstade and lasted about 2000 years, during which the sea contained much floating ice. The Interstade ended when the land rose with respect to the sea level forcing withdrawal of the sea and the disappearance of floating ice in most of northwestern Washington and southwestern British Columbia; in the eastern part of the Fraser Lowland this event coincided with the advance of a valley glacier during the Sumas Stade.

Early Pleistocene Sediments in Indiana

Exposures of both glacial and non-glacial sediments that are correlated with Kansan and Yarmouth stages have been discovered recently in southern Indiana. Distribution of Kansan stage till indicates that the Kansan glacier probably covered about the same amount of the state as did the Illinoian ice. A paleosol on Kansan stage till is leached of carbonates to a depth of 9-11 feet. Fossiliferous proglacial loess conformably underlies the Kansan stage till at one locality and is named the Cagle silt. Assemblages of mollusks recovered from the Cagle silt and from the top of an alluvial silt of Yarmouth age indicate that at both times the climate in south-central Indiana was cool and moist, probably resembling the present-day climate in central Ontario.