INSIGHTS INTO GRAVITATIONAL COMPACTION HISTORY BY STRAIN ANALYSIS: EXAMPLE FROM THE UPPER DEVONIAN OF WESTERN NEW YORK STATE

摘要

The gravitational compaction history of black, shale deposits of the Upper Devonian Hanover shale-Dunkirk shale succession, western New York State, was determined by applying H.C. Sorby's approach to the quantification of compaction strain in sedimentary rocks. Specifically, the organic-rich clay was compacted on average -9% before having been buried more than a few tens of cm, by which time Planolites-making organisms were working through the sediment. Concomitant with and following biotiirbation, the burrows and host laminated black shale experienced -37% (± 9%) additional compaction strain as determined by analysis of flattened burrows. The moderately wide range in post-bioturbation compaction of the Planolites traces indicates that biotiirbation occurred while the sediment was compacting. Mechanical compaction of the laminated black shale is manifested by a strongly planar platy grain microfabric. The burrow fill, however, failed to acquire the anisotropic microfabric.