Sediment yields, lithofacies architecture and mudrock characteristics in glacimarine environments

Sediment yields, lithofacies architecture and mudrock characteristics in glacimarine environments
Cai, J.
Northern Illinois University, DeKalb
466 p., Illus.
Sedimentation rates, glacial signatures on particle shapes and lithofacies architectures of glacimarine deposits are the three foci of this study. Sediment-trap data collected in Tarr Inlet, Glacier Bay, Alaska, show that sedimentation rates in a temperate glacial fjord are extremely high, and decrease exponentially with increasing distance from tidewater termini by the relationship: y = 319.29 exp($-$3.20 $\times$ 10$\sp{-4}$x) where y is sedimentation rate (cm/a) and x is distance (m). Average rates measured from sediment traps during 1989-1991 in Tarr Inlet were at least 4.5 cm/day within 2 km of the termini, and about 0.01 cm/day at 15 km away. An estimated total volume of about $\rm 2.1\times 10\sp9\ m\sp3$ sediment has accumulated in the fjord since deglaciation in about 1892, at an annual rate of about 2.5 to $\rm 3.0\times 10\sp7\ m\sp3/a.$ Results from this study indicate that the shape of quartz silt particles is dependent upon their origin, and demonstrate that Fourier shape analysis of quartz silt can be used to identify particles of glacial origin, and to detect the first sign of iceberg rafting and glaciation at sea level from fine-grained sediments. Fourier shapes were determined on about 60,000 quartz silt grains (25-63 $\mu$m) from 143 samples, collected from Grand Pacific and Margerie Glaciers and streams around and within Tarr Inlet. The analyses show that quartz silt from supra-/englacial debris is more angular and elongate than that from both basal debris and stream sediments. Ice-proximal sediment has a larger component of basal debris, and ice-distal sediment has a higher supraglacial (iceberg-rafted) component. Lithofacies architectures of glacimarine deposits are studied by seismic facies analysis of sediment fill in the fjord of Glacier Bay. Examination of single-channel, high-resolution, seismic-reflection profiles allows the recognition of 8 seismic facies, and the interpretation of 14 lithofacies. Seismic stratigraphy indicates that the retreat of tidewater termini in Glacier Bay was discontinuous, and retreat rates varied greatly. Although the overall retreat rate was very fast, the termini had many short periods of quasi-stability, when morainal banks were formed. Terminus retreat was often slowed, or a quasi-stability was established, when bedrock highs, mid fjord islands, and fjord narrowing, dividing and elbows were encountered.
Ph.D. dissertation
Minerals Data and Information Rescue in Alaska (MDIRA)