MICROFABRIC AND TAPHONOMIC ANALYSIS IN DETERMINING SEDIMENTARY PROCESSES IN MARINE MUDSTONES - EXAMPLE FROM SILURIAN OF NEW-YORK

Microfabric evidence from mudstones combined with taphonomic informati on provides important clues to sedimentary processes. The microfabric of the Lewiston Member, Rochester Shale (Silurian, Wenlockian) of New York has yielded evidence of episodic sedimentation from storm-generat ed sediment plumes or tempestites. A cardhouse arrangement of clay fla kes in the mudstones indicates rapid deposition of flocculated clay. I n addition, taphonomic observations such as the presence of articulate d crinoids buried in life position also indicate rapid burial by the f locculated clay sediment. Four intervals of Lewiston mudstones show ev idence of periods of ''background sedimentation'' during which skeleta l debris slowly accumulated. These conditions were punctuated by brief events of deposition from a storm-generated, silty clay sediment plum e that rapidly (hours to days) covered the depositional site. This stu dy provides an example of the utility of an integrated microfabric and taphonomic analysis in determining the nature of mudstone depositiona l processes.