The most direct and productive method to test our hypotheses about basement structure and the deep reflection sequence in the Newfoundland transition zone was to drill a deep hole (up to ~2200 m) into that zone. Such a hole would also recover an expanded Cretaceous and Tertiary sedimentary record with which to investigate the paleoceanographic history in this gateway region. The prime site that was selected to accomplish these objectives was Site 1276 (proposed Site NNB01A), located in the westernmost edge of the abyssal plain at the foot of the Newfoundland continental rise. In the event that our basement and deep sedimentary objectives could not be achieved at this site and sufficient drilling time remained during Leg 210, we also developed a series of alternate sites that extend seaward onto known oceanic crust and could be drilled in order to partially satisfy our objectives.
Depths of major seismic horizons, including basement, were predicted from semblance velocity analysis of MCS reflection data obtained along the drilling transect during the SCREECH site survey program in 2000. This analysis indicated that the major drilling objectives at proposed Site NNB01A (i.e., U and basement) were at depths of ~1860 and ~2080 meters below seafloor (mbsf), respectively (Table T1). Sampling to these great depths in one drilling leg was considered to be an ambitious goal, but the objectives were deemed to be achievable by following a plan of drilling, casing, and logging the hole as shown in Figure F15. To improve our chances of meeting the objectives within the time available for drilling, it was agreed that the upper 800 m of the hole would be drilled without coring. Thus, we expected that the first sediments recovered from the hole would be of Oligocene age, above Horizon Au.
Actual hole conditions and time constraints necessitated modification of this plan in real time during Leg 210. Nonetheless, we were able to follow part of the drilling and casing plan at Site 1276 (Fig. F16) and we achieved a significant part of our objectives. In addition, we drilled a short hole ~95 m into basement at Site 1277 (proposed Site NNB04A). Table T2 summarizes drilling and coring at Sites 1276 and 1277, and a time breakdown of operations while on site is shown in Figure F17. Drilling results of both sites are summarized below.