11. Site 12521

Shipboard Scientific Party2

INTRODUCTION

Site 1252 (proposed Site HR5a) was drilled in ~1040 m of water ~4.5 km northeast of the southern summit of Hydrate Ridge. The site is located on the western flank of a secondary anticline that is located east of the crest of Hydrate Ridge. The sediments in the core of the anticline appear to be continuous with the accretionary complex sediments sampled near the base of Site 1244, ~1.5 km to the west. Although there is an anomalously bright bottom-simulating reflector (BSR) at a depth of ~170 meters below seafloor (mbsf) within the core of the anticline, the BSR disappears abruptly and does not extend beneath Site 1252 (see Fig. F8 in the "Leg 204 Summary" chapter). Sediments onlapping the anticline from the west can be correlated with sediments sampled at Site 1251.

The principal objectives at Site 1252 were the following:

  1. Sample the sediments in the core of the anticline to determine whether they are compositionally and biostratigraphically similar to those at the base of Site 1244.
  2. Determine the structure of these sediments in order to constrain the mode of growth of the anticline/diapir.
  3. Determine whether hydrates are present ~150 m from a strong BSR but where no BSR is present.
  4. Provide age constraints on the geological history recorded by seismic stratigraphy.

This is the only site at which we did not acquire logging-while-drilling (LWD) data. One hole was drilled at Site 1252 (Fig. F1), comprising 28 cores to 260 mbsf.

1Examples of how to reference the whole or part of this volume can be found under "Citations" in the preliminary pages of the volume.
2Shipboard Scientific Party addresses can be found under "Shipboard Scientific Party" in the preliminary pages of the volume.

Ms 204 IR-111

NEXT