Abstract:
Ocean Drilling Program (ODP) Leg 210 drilled the western half of a Newfoundland-Iberian conjugate-margin transect. At ODP Site 1276, the goal was to drill through the drift succession into synrift deposits. Only part of the drift history was successfully cored, but it contained a surprising quantity and variety of sandy gravity flow deposits within a nearly continuous record of Oligocene to Albian sedimentation. These deposits provide some insight into the petrology and reservoir potential of possible counterparts in upslope sections on this segment of the Newfoundland margin. Thin sections were prepared from 114 samples of Site 1276 gravity deposits, which were first impregnated with blue-dyed epoxy for porosity recognition. The samples are complex mixtures of sand-sized terrigenous and carbonate debris and thus range from sandstone to grainstone end members. Possible sources of sand-sized material include: 1) the continental margin to the southwest (Avalon Uplift) and north (Flemish Cap); 2) extrabasinal sources from the northern gateway and/or the conjugate Iberian margin; 3) intrabasinal basement highs; 4) and the Newfoundland Seamounts to the south. Gravity deposits in the Cenozoic section are dominantly composed of biogenic debris, with lesser terrigenous components and glauconite. Carbonate cement is pervasive to common with microporosity limited to bioclasts and matrix. Where spiculitic, there is development of secondary porosity and opaline to chalcedonic cements. In general, underlying Cretaceous gravity deposits contain more terrigenous debris, are cemented by poikilotopic carbonate, and exhibit evidence of secondary dissolution of feldspar grains. Locally, cement is absent and intragranular primary porosity is preserved.