Firmground ichnofabrics in deep-water sequence stratigraphy, Tertiary clinoform-toe deposits, New Jersey slope

Sixteen erosional surfaces are recognized in a 144-m-thick condensed packag e of Tertiary (Eocene-Pliocene) clinoform-toe sediments recovered at ODP Si te 1073 on the New Jersey slope. Most of these surfaces are associated with significant hiatuses or extremely condensed intervals defined by Sr isotop es or biostratigraphic data, and many can be linked to sequence boundaries defined in. onshore and shelf seismic studies. AIL surfaces define the base s of fining upward sequences; they separate clay or biogenic muds below fro m authigenic glauconitic sandy muds or sands above. The entire Tertiary pac kage is thoroughly bioturbated and dominated by ichnotaxa representing soft ground conditions. Burrow densities, burrow preservation, and the relative importance of certain ichnotaxa vary through the Tertiary package, reflecti ng changes in water depth, relative degree of condensation, and associated glaucony authigenesis, all related to margin progradation. Nonetheless, whe n. individual sequences are considered little or no change in softground ic hnofossil assemblages is recognized across bounding surfaces. However most surfaces are marked clearly by firmground Thalassinoides, burrow systems th at penetrate deeply (up to 2 m) into subjacent clays and are characterized by extremely sharp walls and coarser glauconitic fills. In shallower shelf sequences, firmground ichnofabrics develop at sequence boundaries in respon se to subaerial exposure and transgressive ravinement. In contrast, the Ter tiary firmgrounds on the New Jersey margin, formed in deep water in, respon se to phases of rapid transgression and net erosion; consolidated mud subst rates were exhumed as a result of sediment starvation and bottom-current wi nnowing, facilitated by bioerosion, at or near the bases of slope clinoform s. These observations extend the previously established sequence stratigrap hic utility of the substrate-controlled Glossifungites ichnofacies to deepe r water facies.