Abstract

Fabric studies of Miocene to Holocene hemipelagic and pelagic marine sediments by means of backscattered electron imagery reveal the common presence of exotic aggregates of well to poorly sorted silt-size particles. New observations of silt aggregates associated with readily identifiable 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 aggregates. Some silt aggregates of well-sorted grains appear to represent the collapsed or compacted tests of agglutinated foraminifera. Aggregates of poorly sorted, silt-size material probably represent the discarded "detritic covers" that agglutinated foraminifera erect around themselves while constructing a new chamber. These remnant tests and detritic covers are likely to be preserved in settings of low bottom-water oxygenation where bioturbation is limited or absent. The long stratigraphic range (Cambrian to Recent) and diverse habitats (hyposaline lagoons to abyssal environments) occupied by agglutinated foraminifera suggest that they may be an important, but hitherto unrecognized, contributor to the production of early fabrics in fine-grained marine sediments. Their presence may provide unique evidence on the concentration of dissolved oxygen in the bottom waters.

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