An SEM Study of Microfabrics from the Irish Chalk

Abstract

Sediment compaction and subsequent cementation must be considered important mechanisms for the reduction of porosity in the fine grained rocks studied. Evidence for early post-depositional compaction includes micrite grain flow around large bioclasts and grain orientation. Fracture of delicate grains causing some displacement was observed with suturing or serration at the grain boundaries between broken fragments of microfossils. Styolites cutting through grains and matrix suggests continued compaction. Geopetal structures and veins with incorporated whole microfossils indicate some grain support from partial cementation. Micrite veins with crystal orientation parallel to the trend of the vein may represent anastomosis tubes for the dewatering of the sediment.