Lithofacies and seismic-reflection interpretation of temperate glacimarine sedimentation in Tarr inlet, Glacier bay, Alaska

High-resolution seismic-reflection profiles of sediment fill within Tarr Inlet of Glacier Bay, Alaska, show seismic facies changes with increasing distance from the glacial termini. Five types of seismic facies are recognized from analysis of Huntec and minisparker records, and seven lithofacies are determined from detailed sedimentologic study of gravity-, vibro- and box-cores, and bottom grab samples. Lithofacies and seismic facies associations, and fjord-floor morphology allow us to divide the fjord into three sedimentary environments: ice-proximal, iceberg-zone and ice-distal. The ice-proximal environment, characterized by a morainal-bank depositional system, can be subdivided into bank-back, bank-core and bank-front subenvironments, each of which is characterized by a different depositional subsystem. A bank-back subsystem shows chaotic seismic facies with a mounded surface, which we infer consists mainly of unsorted diamicton and poorly sorted coarse-grained sediments. A bank-core depositional subsystem is a mixture of diamicton, rubble, gravel, sand and mud. Seismic-reflection records of this subsystem are characterized by chaotic seismic facies with abundant hyperbolic diffractions and a hummocky surface. A bank-front depositional subsystem consists of mainly stratified and massive sand, and is characterized by internal hummocky facies on seismic-reflection records with significant surface relief and sediment gravity flow channels. The depositional system formed in the iceberg-zone environment consists of rhythmically laminated mud interbedded with thin beds of weakly stratified diamicton and stratified or massive sand and silt. On seismic-reflection profiles, this depositional system is characterized by discontinuously stratified facies with multiple channels on the surface in the proximal zone and a single channel on the largely flat sediment surface in the distal zone. The depositional system formed in the ice-distal environment consists of interbedded homogeneous or laminated mud and massive or stratified sand and coarse silt. This depositional system shows continuously stratified seismic facies with smooth and flat surfaces on minisparker records, and continuously stratified seismic facies which are interlayered with thin weakly stratified facies on Huntec records. (C) 1997 Elsevier Science B.V.