Showing papers on "Varve published in 1975"

Sedimentation in Lillooet Lake, British Columbia

Abstract: Sediment from Lillooet River Basin, 3580 sq km of alpine and subalpine landscape, 7% of which is glacier-covered, is deposited in Lillooet Lake. During the summer when the lake is stratified by temperature and suspended sediment content, processes of interflow and underflow distribute sediment throughout the lake and give rise to a distinctive sedimentary sequence of varved silts and clays interspaced irregularly with massive beds of coarser grained sediments up to 120 mm thick. Coarse sediment deposited on the proximal delta slope is redistributed by infrequent slumps; mounds of slumped material cover the foreset slopes to their base at 120 m depth. Thickness of varves is related to the annual inflow to the lake, and continuous records of water temperature near the lake bottom indicate that the numerous laminae within varves are due to intermittent underflow events.

The palaeomagnetism of varved clays from Blekinge, southern Sweden

Abstract: I have studied the palaeomagnetism of two clay cores collected from southern Blekinge and have used the Swedish varve chronology and the shore-level-displacement record to assign absolute dates to the magnetic parameters. The results provide an accurate, annual record of part of the Laschamp geomagnetic event and indicate that the virtual magnetic pole was reversed between 10,153 and 10,127 years B.C. A cycle of palaeo-intensity with a period of 24 ± 2 y. has been found in the varved clay, while several clear cycles of magnetic inclination occur in the postglacial fraction of one core with a period of 2860 ± 200 y. My data suggest the possibility of a more recent geomagnetic excursion around 790 B.C., which I call the Starno event.

Report on annually laminated sediment in lake Järlasjön, Nacka, Stockholm

Abstract: Annual laminations — varves — in sediment cores from Jarlasjon are described on the basis of microscopic examination and X-radiographic analysis. Dates are inferred from varve-counting and Cs-137 analysis. Four clay layers, which can be related to building-excavations in the surroundings of the lake, are exactly dated. Chemical changes in the recent sediment and in the sediment deposited around the isolation of the lake are discussed.

Turbidite Origin of Glaciolacustrine Sediments, Woodcock Lake, Pennsylvania

Abstract: Laminated silt- and clay-size sediments exposed in cutbanks along Woodcock Creek in northwestern Pennsylvania are of glaciolacustrine origin. The presence of convolutions and graded laminae indicate that deposition of these sediments was by turbidity currents. Small-scale cross-bedding in some of the coarser sediments within the laminae suggests that deposition of an individual graded lamination required no more than a few days' time. Thus, although these sediments superficially appear to be annual varves, they are in fact rhythmites. The turbidity currents primarily responsible for the deposition and deformation of the laminated sediments probably originated from an outwash stream which flowed into an ice-dammed lake which temporarily occupied Woodcock. Creek Valley sometime during Pleistocene time. As the sediment-laden stream entered the lake, sand- and gravel-size sediments were deposited, forming a delta-kame which presently exists. along the valley wall about km from the exposed lake sediments. When the stream currents which flowed across the delta reached the delta front, they had a higher density (suspended-sediment load) than the lake water. Thus, the stream currents flowed down the delta face onto the prodelta slope as turbidity currents. These turbidity c rrents are believed to have deposited the graded laminae now exposed along the valley bottom.

Grain-Size Distribution within Glacial Varves

Abstract: Climatic variations lasting a few days can produce variations in the coarseness of the grain size within the summer phase of glacial varve couplets. Studies of size distribution made with a Quantimet 720 make it possible to resolve these variations in grain size. This allows correlations between varves in the same basin of deposition on the basis of internal features as well as on sequences of varve thicknesses. Similarly improved correlations between basins will be possible. The internal structures of varves are now a potential factor in determining climatic cycles or periods of less than one year.