SILT AGGREGATES IN LAMINATED MARINE SEDIMENT PRODUCED BY AGGLUTINATEDFORAMINIFERA

Fabric studies of Miocene to Holocene hemipelagic and pelagic marine s ediments by means of backscattered electron imagery reveal the common presence of exotic aggregates of well to poorly sorted silt-size parti cles, New observations of silt aggregates associated with readily iden tifiable multi-chambered agglutinated foraminifera, when combined with recent experimental insights into the chamber-building activities of these organisms, provide a new model for the formation of these aggreg ates. Some silt aggregates of well-sorted grains appear to represent t he collapsed or compacted tests of agglutinated foraminifera, Aggregat es of poorly sorted, silt-size material probably represent the discard ed ''detritic covers'' that agglutinated foraminifera erect around the mselves while constructing a new chamber. These remnant tests and detr itic covers are likely to be preserved in settings of low bottom-water oxygenation where bioturbation is limited or absent, The long stratig raphic range (Cambrian to Recent) and diverse habitats (hyposaline lag oons to abyssal environments) occupied by agglutinated foraminifera su ggest that they may be an important, but hitherto unrecognized, contri butor to the production of early fabrics in fine-grained marine sedime nts, Their presence may provide unique evidence on the concentration o f dissolved oxygen in the bottom waters.