LAMINATED SEDIMENTS IN GLACIMARINE ENVIRONMENTS: DIAGNOSTIC CRITERIA FOR THEIR INTERPRETATION

Abstract

Fine-grained laminated deposits are often reported from contemporary and ancient glacimarine sedimentary sequences. Laminated glacimarine sediments form by a variety of processes, including suspension settling from turbid overflow plumes, turbidity current deposition and contour current activity. Subglacial deformation of pre-existing sediments may also produce laminated deposits in the form of glacitectonite and deformation till. The development of diagnostic criteria for genetic discrimination of laminated glacimarine sediments is important, both for their correct interpretation in sedimentary sequences, and also for the accurate reconstruction of former glacier extent and geometry, as laminated sediments may form in subglacial, ice-proximal and ice-distal environments. This paper reviews the processes by which laminated glacimarine sediments form and their resulting sedimentology. The aim is to provide a synthesis of diagnostic sedimentological criteria for laminated glacimarine deposits that will assist in the interpretation of such sediments in the geological record. Laminated sediments are genetically differentiated on the basis of sedimentary structures, bedding contacts, stratigraphic relationships and macrofaunal content/bioturbation. These attributes also facilitate discrimination between glacimarine and glacilacustrine rhythmites. The paper concludes by discussing the glaciological significance of laminated glacimarine sediments in terms of glacier hydrology, reconstructions of former ice-dynamics, and basal thermal regime.