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doi:10.2204/iodp.proc.317.103.2011

Site U1351¹

Expedition 317 Scientists²

Background and objectives

Hole U1351A

• Position: 44°53.0307′S, 171°50.4037′E

• Start hole: 0931 h, 18 November 2009

• End hole: 2330 h, 18 November 2009

• Time on hole (d): 0.58

• Seafloor (drill pipe measurement from rig floor, m DRF): 133.3 (APC mudline)

• Distance between rig floor and sea level (m): 11.0

• Water depth (drill pipe measurement from sea level, m): 122.3

• Total depth (drill pipe measurement from rig floor, m DRF): 161.3

• Total penetration (m DSF): 28.0

• Total length of cored section (m): 28.0

• Total core recovered (m): 27.3

• Core recovery (%): 98

• Total number of cores: 6

Hole U1351B

• Position: 44°53.0422′S, 171°50.4065′E

• Start hole: 2330 h, 19 November 2009

• End hole: 1800 h, 25 November 2009

• Time on hole (d): 6.77

• Seafloor (drill pipe measurement from rig floor, m DRF): 132.7 (APC mudline)

• Distance between rig floor and sea level (m): 11.0

• Water depth (drill pipe measurement from sea level, m): 121.7

• Total depth (drill pipe measurement from rig floor, m DRF): 1163.3

• Total penetration (m DSF): 1030.6

• Total length of cored section (m): 1030.6

• Total core recovered (m): 304.5

• Core recovery (%): 30

• Total number of cores: 116

Hole U1351C

• Position: 44°53.0572′S, 171°50.4057′E

• Start hole: 1800 h, 25 November 2009

• End hole: 0200 h, 30 November 2009

• Time on hole (d): 4.33

• Seafloor (drill pipe measurement from rig floor, m DRF): 132.7 (by proxy, Hole U1351B)

• Distance between rig floor and sea level (m): 11.0

• Water depth (drill pipe measurement from sea level, m): 121.7

• Total depth (drill pipe measurement from rig floor, m DRF): 1100.0

• Total penetration (m DSF): 967.3

• Total length of cored section (m): 0.00

• Total core recovered (m): 0.0

• Core recovery (%): 0.0

• Total number of cores: 0

Integrated Ocean Drilling Program (IODP) Site U1351 (proposed Site CB-03B) is located on the outer shelf (122 m water depth) within the Canterbury Bight and is the most basinward shelf site of the Canterbury Basin drilling transect. This location was chosen as a primary site in response to an Environmental Protection and Safety Panel (EPSP) request (December 2005) to avoid the high seismic amplitudes observed at ~1.05 s two-way traveltime at proposed Site CB-03A. Site U1351 is located on dip seismic Profile EW00-01-66, updip from Site CB-03A (Fig. F1). Because of the move from Site CB-03A, there is no EW00-01 crossing strike profile at Site U1351. However, this site is located on crossing strike Profile CB-82-25, a line acquired for hydrocarbon exploration purposes in 1982 (Figs. F1, F2).

In order to determine the impact of global sea level change on deposition cyclicity, it is important to drill each sedimentary sequence in at least two locations: landward of the rollover or clinoform break representing the paleoshelf edge, where paleowater depths critical for eustatic amplitude estimates are best constrained by benthic foraminiferal biofacies, and on paleoslopes, where increased pelagic microfossil abundance provides optimal age control. Obtaining such information for a number of prograding sequences requires a transect of boreholes crossing the margin in the dip direction.

Furthermore, the facies, paleoenvironments, and depositional processes associated with sequence stratigraphic models of prograding continental margins, where sequences are best resolved seismically, have yet to be adequately constrained by scientific ocean drilling. Prediction of the distribution of sediments within sequences is highly model dependent (e.g., systems tract models of Posamentier et al., 1988; Vail et al., 1991). These models offer great potential for understanding oil and gas resources and for ground water–pollution remediation issues. However, the fundamental assumptions and predictive capabilities of these models can only be tested by drilling on shallow continental shelves within a well-defined seismic stratigraphic framework.

Operations at Site U1351 began in accordance with the proposed drilling strategy, which stipulated that drilling should begin at the deepwater end of the shelf transect if weather conditions allowed. The distal location of this site allowed the initial attempt at shelf drilling to occur at the deepest water depth of any of the proposed shelf sites and at a location where sediments were presumably finer grained than at more proximal proposed shelf sites such as Site U1353 (proposed Site CB-01A). This approach provided experience in shelf sediment drilling before drilling was attempted at more challenging inboard shelf sites. The planned maximum penetration was 1249 m. Actual penetration was 1031 m drilling depth below seafloor (DSF) in Hole U1351B.

Nineteen regional seismic surfaces interpreted as seismic sequence boundaries (U1–U19) have been identified in the middle Miocene to recent shelf-slope sediment prism (Lu and Fulthorpe, 2004). Seismic sequence boundaries U6–U19 were penetrated at Site U1351. Upper Miocene–lower Pliocene sequence boundaries (below U10) feature smooth onlapped paleoshelves and rounded rollovers with sigmoid internal reflection geometries. In contrast, middle Pliocene–Holocene sequence boundaries (U10 and above) display eroded and incised downlapped paleoshelves and more pronounced rollovers with oblique reflection geometries. Drilling tested the hypothesis that these contrasting characteristics occur because paleoshelves below U10 were not subaerially exposed at lowstand, whereas those above U10 were exposed, probably because of increasing eustatic amplitudes during the Pliocene–Holocene.

The principal objectives at Site U1351 were as follows:

1. To sample facies landward of, but close to, rollovers of progradational sequence boundaries, particularly U8–U19. A particular goal was to use benthic foraminiferal biofacies to estimate paleowater depths both above and below sequence boundaries. This information will be used to calculate eustatic amplitudes using two-dimensional backstripping.
2. To sample slope facies of U4–U7 to provide age control.
3. To investigate facies, paleoenvironments, and depositional processes associated with the sequence stratigraphic model on a prograding continental margin where sequence architecture is well constrained by seismic imaging.

¹Expedition 317 Scientists, 2011. Site U1351. In Fulthorpe, C.S., Hoyanagi, K., Blum, P., and the Expedition 317 Scientists, Proc. IODP, 317: Tokyo (Integrated Ocean Drilling Program Management International, Inc.). doi:10.2204/iodp.proc.317.103.2011

²Expedition 317 Scientists' addresses.

Publication: 4 January 2011
MS 317-103

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