Sedimentary and Diagenetic Structures and Textures in Turbiditic and Hemiturbiditic Strata as Revealed by Whole-Core X-Radiography, Middle Valley, Northern Juan de Fuca Ridge

Abstract

Whole-core X-radiography of siliciclastic and clastic sulfide strata from Middle Valley, northern Juan de Fuca Ridge revealed primary, biogenic, and diagenetic structures and textures that were not evident during visual core examination. These textures and structures document a history of fine-grained turbidite sedimentation overprinted by several phases of carbonate and sulfide diagenesis. The X-radiographs reveal primary sedimentary structures in mud-rich units that allow us to distinguish between mud turbidites and pelagic deposits. They reveal three distinct ichnofauna assemblages that record depositional environments with different levels of oxygen and different sedimentation rates as well as eight major carbonate and pyrite diagenetic morphologies. The X-radiographs delineate the extent of metalliferous turbidites and debris flows at Site 856. Further analysis of the structures and textures illuminated by X-radiographi c techniques will permit detailed interpretations of the sedimentary and diagenetic history of sedimentation in this sedimented rift valley.