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doi:10.2204/iodp.proc.308.108.2006

Downhole measurements

Downhole measurements at Site U1324 were used to characterize pressure, temperature, and rock properties within the mudstone-dominated sedimentary section above the Blue Unit.

Logging while drilling and measurement while drilling

Operations

LWD/MWD operations in Hole U1324A used the same BHA, tool configuration, and protocols as those for at Sites U1322 and U1323. (see “Downhole measurements” and “Summary of operations” in the “Site U1322” chapter). Batteries were replaced in the LWD tools prior to drilling. The hole was initiated with a rapid jet-in to 8 mbsf before retrieving the VIT camera. After the VIT camera was recovered, bit rotation and pump rates of 50 rpm and 60 gpm were used to 25 mbsf while maintaining an ROP of 30 m/h. From 25 to 35 mbsf, pump rates were increased gradually to 400 gpm. Below 35 to ~612 mbsf, an ROP of 30 m/h and pump rates of at least 400 gpm were maintained. The interval from 472 to 612 mbsf was drilled using 10.5 ppg mud (seawater, sepiolite, and barite). One sand interval >1.5 m was encountered, and as result the hole was cemented according to IODP Expedition 308 operations protocol.

Logging data quality

Figure F41 shows the LWD quality control logs. The target ROP of 30 m/h (±5 m/h) was achieved except during jet-in (Fig. F41). The density-derived caliper log (DCAV) documents good borehole conditions from 130 to 612 mbsf (Fig. F41). Enlarged borehole dimensions, however, existed from 378 to 420 and 509 to 520 mbsf. The bulk density correction (IDDR) for the entire borehole varies from –0.1 to 0.2 g/cm³ (mean = 0.02 g/cm³) (Fig. F41), which was larger than in previous holes. The largest variations are concentrated in enlarged borehole intervals.

LWD logs were depth-shifted by identifying the seafloor in the gamma ray data. For Hole U1324B, the gamma ray pick for the seafloor was at 1466.5 mbrf, 0.4 m deeper than the drillers depth. The rig floor logging datum was located 10.6 m above sea level.

Annular pressure while drilling and equivalent circulating density

Pressure within the borehole was monitored during MWD/LWD operations (see discussion in “Array resistivity compensated tool” in “Downhole measurements” in the “Methods” chapter) as annular pressure while drilling in excess of hydrostatic (APWD*) and equivalent circulating density referenced to the seafloor (ECD_rsf). ECD_rsf decreases from 0 to 300 mbsf and then gradually increases from 300 to 470 mbsf (Fig. F42). APWD* gradually increases with depth from 0 to 470 mbsf. At 470 mbsf, 10.5 ppg mud (seawater, sepiolite, and barite) was circulated while drilling. The weighted mud created step increases in ECD_rsf and APWD*.

LWD results

Operations in Hole U1324A drilled through a series of interbedded clay, mud, and sand units as well as several MTDs from 0 to 612 mbsf. The hole quality from 0 to 65 mbsf is highly variable, with caliper measurements reaching at least 42 cm. Below 65 mbsf, the caliper measured an average hole diameter of 25.9 cm, with washouts at ~244, 328, 378, and 509 mbsf.

The GeoVision Resistivity (GVR) tool gamma ray log has minor variations through lithostratigraphic Unit I. Lithostratigraphic Unit I was predominantly composed of clay and mud with rare occurrences of silt and sand. Gamma radiation in lithostratigraphic Unit I increases with depth, and the most significant deviation occurs at ~160 mbsf, which corresponds to seismic Reflector S30 (Fig. F43). This interval is characterized by lower gamma radiation and is interpreted as a silty sand layer. Lithostratigraphic Unit II, predominantly composed of interbedded silt and very fine sand with beds and laminae of mud and clay, shows more gamma ray variability than lithostratigraphic Unit I. Gamma radiation ranges from 26.4 to 92.4 gAPI, which suggests distinct changes in lithology from sand-rich to mud intervals (Fig. F43).

GVR deep button resistivity increases from 0.3 to 2.2 Ωm from the seafloor to 365 mbsf (Fig. F43). Variations in deep resistivity are interpreted as occurrences of sand and silt within lithostratigraphic Unit I. The GVR shallow button resistivity shows larger variations above 100 mbsf, due to variable hole conditions that are most likely caused by drilling disturbances (Fig. F43). Deep resistivity measurements show a wider range of values within lithostratigraphic Unit II (365–608 mbsf), where resistivity varies from 0.5 to 3.6 Ωm (mean = 1.5 Ωm). These variations reflect greater sand content within lithostratigraphic Unit II.

Vision Density Neutron (VDN) bulk density increases from 1.0 g/cm³ near the seafloor to 2.2 g/cm³ near the bottom of the hole (Fig. F43). A comparison of LWD bulk density with core MAD measurements shows an excellent correlation throughout most of the hole except for washed-out intervals in lithostratigraphic Subunits IIA and IIC (Fig. F43). Neutron porosity decreases from 86.5% to 38%, with the largest downhole porosity fluctuations occurring in sand-rich intervals within lithostratigraphic Subunit IIA (Fig. F43). The photoelectric factor log from Hole U1324B follows similar trends as those observed in the gamma ray profile except below 472 mbsf, when of heavy mud containing barite affected the measurements (Fig. F43).

Resistivity images show deformation in the hemipelagic drape and distal turbidites drilled in Hole U1324A (Fig. F43). Lithostratigraphic Subunit ID is composed of faulted and contorted reddish brown and greenish gray clay (see “Lithostratigraphy”). Resistivity images in Subunits ID and IE reveal dipping beds (5°–55°) throughout these intervals that are consistent with core observations (Fig. F44). Steep deformed beds with dips as high as 65°, corresponding to the top of lithostratigraphic Subunit IE, exist just above seismic Reflector S30 (Fig. F44).

Lithostratigraphic Unit II shows large amounts of deformation as contorted and faulted beds indicative of downslope remobilization (Fig. F45). This unit is interpreted as MTDs (see “Lithostratigraphy”). Steep dips and folds in the resistivity images suggest the presence of overturned beds in lithostratigraphic Subunit IIA. Scoured surfaces, interpreted as erosional episodes, are imaged in lithostratigraphic Subunit IIC (Fig. F46). A fold with an east-west-trending axis found in lithostratigraphic Subunit IID confirms significant deformation in this subunit (Fig. F47). Most of the deformation features observed within Hole U1324A trend in an east-west direction, with the majority dipping to the north.

Wireline logging

Operations

Wireline tools were deployed in Hole U1324A to obtain velocity data (Fig. F48). A tool string consisting of the HNGS, DSI, and GPIT was deployed first (see “Downhole measurements” in the “Methods” chapter), with the drill pipe at ~54 mbsf. A downhole log was recorded at 550 m/h from the seafloor to 59 mbsf. The tool string was then stuck either with the lower DSI centralizer on the lockable float valve or the go-devil at the end of the tool string hitting the borehole wall. We pulled the pipe up 5 m and then successfully lowered the tool string into the borehole. The pipe was left at 49 mbsf. We started the first logging pass from 507 mbsf. We measured gamma radiation, including spectral data, and P- and S-wave (P&S) mode at 15 Hz sampling rate. Logging proceeded at 275 m/h to 84 mbsf. We then lowered the tool string for a second pass starting from 509.5 mbsf. The second pass recorded gamma radiation, P&S, low-frequency lower dipole, and Stoneley modes at 15 Hz sampling rate.

The second wireline tool string deployed consisted of the Well Seismic Tool for a check shot survey (see “Downhole logging” in the “Methods” chapter).

Sixteen stations were targeted at ~25 m intervals (Table T15). The generator-injector gun had a 45 in³ generator chamber volume and a 105 in³ injector chamber volume and a total pressure of 2000 psi. The recording length was 5 s with a 1 ms sampling rate and a 40 ms delay. The rig floor preparations for wireline logging operations began on 19 June 2005 at 1905 h and were completed by 20 June at 1255 h.

Logging data quality

The wireline data were depth-shifted based on a seafloor depth of 1066.5 mbsf determined by gamma ray logs. HNGS data were not corrected for borehole diameter variations or mud weight.

Wireline results

HNGS gamma ray measurements are in good agreement with those of the GVR. The spectral measurements (⁴⁰K, ²³²Th, and ²³⁸U isotopes) show that the decay of ²³²Th is the primary gamma ray contributor (Fig. F48.) The range of ²³²Th values measured in Hole U1324A fall within values reported for illite and smectite (Rider, 1996).

In Hole U1324A we collected wireline sonic data and check shot data to evaluate velocity between 83.8 and 498.9 mbsf (Table T15; Fig. F48). Compressional wave velocities (wireline log) to 501.9 mbsf generally increase from 1486 to 1834 m/s with depth, whereas the interval velocities from the check shot increase from 1583 to 1852 m/s (Fig. F48).

Before obtaining velocity measurements at Site U1324, the only available time-depth information for the Ursa Basin site was based on nearby check shot surveys (see Equation 1 in the “Site U1322” chapter). This time-to-depth conversion is plotted with check shot and sonic log data (Fig. F49).

Core-log-seismic integration

Lithostratigraphic Unit I (0–364.7 mbsf) is described as hemipelagic drape and very distal turbidites from channel-levee systems to the west and is divided into seven subunits (see “Lithostratigraphy”). Lithostratigraphic Unit II (364.7–600.8 mbsf) includes four subunits and marks a change in lithology that includes interbedded silt and very fine sand with beds and laminae of mud and clay. Several MTDs within this unit are potentially associated with the depositional environment of the Southwest Pass Canyon channel-levee system (see “Lithostratigraphy”).

Most of the lithostratigraphic subdivisions correlate with log responses (Fig. F50). Based on gamma radiation, resistivity, bulk density, and compressional wave velocity log responses, five fining-upward and fining-downward sequences were identified within lithostratigraphic Unit II. This correlates well with variations in sand content in cores. Four out of five of these zones correlate closely with the tops of lithostratigraphic subunits; the exception is from 400 to 422 mbsf within lithostratigraphic Subunit IIA and seems to be the thickest sand sequence (Fig. F51).

We used LWD density data and the wireline sonic log to construct a synthetic seismogram for Hole U1324B (Fig. F50). Reflection coefficients were calculated using the LWD density data and a constant compressional wave velocity of 1600 m/s from 0 to 50 mbsf and the wireline velocity below 50 mbsf. A 150 Hz minimum-phase, Ricker wavelet was convolved with the reflection coefficients to create the synthetic seismogram. The correlation of events between the synthetic seismogram and the high-resolution seismic indicates that the time-depth model is appropriate for these sediments. An accurate time-depth model allows correlation of seismic reflections with observations in core and logging data.

A decrease in gamma radiation and bulk density correlates with seismic Reflector S10 (Figs. F24, F51). The top of lithostratigraphic Subunit ID is defined by an increase in velocity and a subtle change in resistivity (Figs. F50, F51). The top of lithostratigraphic Subunit IE is interpreted as a transition from an overlying MTD to a series clay laminae and thin beds enriched in foraminifers and nannofossils (see “Lithostratigraphy”). The upper part of this subunit is characterized by high gamma radiation, low density, and low velocity. A low-density zone correlates with seismic Reflector S30 (Figs. F50, F51). Seismic reflectors S40-1324 and S50-1324 correlate with zones interpreted as potential low-relief channels containing silt and sand deposits. The synthetic seismogram shows an apparent offset with the regional seismic data suggesting that the shallow velocity may have been too fast (Fig. F50). The synthetic seismogram matches the frequency and amplitude of signals observed in the seismic data except in lithostratigraphic Unit II, where the high-amplitude reflections, due to low densities, are frequent. These low densities may be the result of degraded borehole conditions.

Temperature and pressure measurements

In situ measurements made with the APCT tool, the T2P, and the DVTPP documented overpressure and a low thermal gradient relative to Site U1322.

Advanced piston corer temperature tool

The APCT tool was deployed four times in Hole U1324B (Table T16). Temperature was measured in the sediment for 10 min to establish the temperature decay curve. Extrapolation of the temperature decay curve with an assumed thermal conductivity of 1.2 W/(m·K) was used to estimate in situ formation temperatures. The first deployment at 51.3 mbsf (Core 308-U1324B-6H) provided an in situ temperature of 5.66°C (Fig. F52). The second deployment (79.8 mbsf; Core 308-U1324B-9H) yielded an equilibrium temperature of 6.32°C (Fig. F53). The third deployment was at 108.3 mbsf (Core 308-U1324B-12H) and yielded an equilibrium temperature of 6.40°C (Fig. F54). The final deployment occurred at 136.3 mbsf (Core 308-U1324B-15H) and provided a formation temperature of 7.50°C (Fig. F55).

Temperature/Dual Pressure Probe

Twelve deployments of the T2P were completed at Site 1324 (Table T16). These measurements provided numerous constraints on in situ temperature and some constraints on formation pressures.

T2P Deployment 5

All sensors recorded an increase during penetration into the formation during T2P Deployment 5 (Table T17; Fig. F56). The tip pressure decreased after penetration and achieved nearly constant pressure at 11.0 MPa. The hydrostatic reference was 11.13 MPa. The shaft sensor recorded a small pressure increase followed by minimal dissipation to 11.9 MPa. A pressure difference between the tip and shaft was recorded while lowering the tool downhole. The temperature record was continuous and smooth to its final temperature of 5.57°C. Data recording stopped upon pulling the tool out of the formation. At the rig floor, it was noted that the T2P tip was bent and the thermistor and bottom porous stone were missing from the tool. We believe the tool was bent during penetration and broken when pulling the tool out of the formation. Data may not reflect in situ conditions because of probe damage.

T2P Deployment 6

Pressure and temperature data for T2P Deployment 6 show multiple pulses and decays (Table T18; Fig. F57). The first increase in all sensors occurred when the CDS landed in the BHA, the second increase in the tip and shaft pressure coincided with pushing into the formation, and the third increase occurred when circulation began (Table T18; Fig. F57). The tip pressure went subhydrostatic (hydrostatic pressure = 11.51 MPa), after which it slowly increased to 11.7 MPa. Subhydrostatic pressure may have resulted from an internal leak or a small void near the tip caused when the drill bit was picked up. The shaft pressure dissipated to 12.7 MPa. The temperature was decreasing when the tool was recovered and did not reach an equilibrium value. This continual decrease in temperature suggested there was a leak in the system that removed heat.

T2P Deployment 7

During T2P Deployment 7, pressure and temperature responded to initial landing of the CDS in the BHA, pushing into to the formation, and circulation of drilling fluid (Table T19; Fig. F58). The tip pressure decreased to 12.0 MPa; however, the response was erratic. The shaft had a small pressure increase and declined to a final pressure of 13.3 MPa. Hydrostatic pressure was 11.80 MPa. The small shaft pressure increase may have indicated incomplete penetration into the formation. The temperature data provided an in situ temperature estimate of 6.81°C.

T2P Deployment 8

The tip pressure and temperature increased with penetration during T2P Deployment 8 (Table T20; Fig. F59). The tip pressure eventually increased to 12.4 MPa. The hydrostatic reference was 11.99 MPa. The temperature profile equilibrated to a formation temperature of 7.20°C. The shaft pressure response was erratic throughout the deployment, with multiple step increases and decreases in pressure that were not associated with deployment events. Because of the poor pressure readings the tool was disassembled and reassembled to establish good seals and electrical connections.

T2P Deployment 9

T2P Deployment 9 exhibited large pressure and temperature responses when the tool landed in the BHA and when it penetrated the formation (Table T21; Fig. F60). These responses were immediately followed by decreases. We interpreted that the tool was coupled with the drill bit; therefore, when the bit was picked up, the tool was pulled out of the sediment. A large offset between the tip and shaft pressure was also a problem. Because of deployment and calibration problems, no in situ conditions could be evaluated.

T2P Deployment 10

T2P Deployment 10 is documented in Table T22. An electronic problem that occurred after placing the tool on the rig floor precluded collection of any downhole data. Upon recovery of the tool, it was determined that the connection between the sensors and the data acquisition system was poor. To remedy this problem, the tool was dismantled, all connections were cleaned, and the tool was reassembled.

T2P Deployment 11

T2P Deployment 11 tested the sensors and data acquisition system. The probe was not pushed into the sediment (Table T23). Data recorded for the deployment show excellent agreement between the tip and shaft pressure sensors (Fig. F61). Two pressure decreases occurred at the tip. These may have been caused by the tip being partly embedded in the sediment. The shaft did not penetrate the formation. Overall, the Deployment 10 confirmed that the electronic failure from T2P deployment had been fixed.

T2P Deployment 12

T2P Deployment 12 showed pressure and temperature increases during landing of the CDS in the BHA and during penetration into the formation (Table T24; Fig. F62). The tip pressure decreased rapidly and then slowly dissipated to 11.0 MPa (hydrostatic pressure = 11.10 MPa). The shaft pressure increased and then dissipated to 11.4 MPa. From the slow dissipation of shaft pressure we inferred low permeability of the sediments. The temperature profile recorded a final temperature of 5.46°C, which was assumed to represent in situ conditions.

T2P Deployment 13

All sensors increased with penetration into the sediment during T2P Deployment 13 (Table T25; Fig. F63). Pressures then dissipated until the tool was pulled out of the formation. The tip had a pressure decrease coincident with picking up the bit. End pressures of 12.0 MPa (tip) and 12.2 MPa (shaft) exceeded hydrostatic pressure (11.61 MPa). The temperature profile exhibited decay to an estimated in situ temperature of 6.40°C.

T2P Deployment 14

Similar to Deployment 13, pressure and temperature increased with penetration into the sediment, followed by dissipation curves during T2P Deployment 14 (Table T26; Fig. F64). All sensors recorded a perturbation while in the formation that could not be attributed to deployment activities (Table T26). After this perturbation, temperature and shaft pressure continued to dissipate. The tip pressure had a larger decrease followed by a pressure increase. The end pressures of 12.7 MPa (tip) and 13.0 MPa (shaft) exceed hydrostatic (12.11 MPa). The temperature (7.31°C) appeared to be in equilibrium with the formation.

T2P Deployment 15

T2P Deployment 15 provided useful shaft pressure and temperature data; however, tip pressure data were less reliable. All data increased during penetration followed by dissipation curves (Table T27; Fig. F65). No data were recorded during retrieval of the tool from the sediment. The tip pressure decreased after penetration, then recovered and dissipated to 13.8 MPa. The shaft pressure dissipated to 14.3 MPa. Hydrostatic pressure was 12.61 MPa. The temperature decay was rapid to 8.27°C. We interpreted this to be the formation temperature. When the tool reached the rig floor, it was confirmed that the tip was bent and the drive tube was loose. The loosening of the drive tube most likely caused the failure to record data during tool retrieval.

T2P Deployment 16

The pressure and temperature data are excellent for T2P Deployment 16 (Table T28; Fig. F66). Pressure and temperature increased during penetration, which was followed by continuous dissipation curves. The end pressure of 13.9 MPa (tip) may have been in equilibrium with the formation. The hydrostatic reference was 13.62 MPa. Temperature equilibrated with the formation at 9.97°C.

Davis-Villinger Temperature-Pressure Probe

Thirteen DVTPP deployments were competed at Site U1324 (229.1–608.1 mbsf) to provide additional constraints on formation pressure and temperature (Table T16).

DVTPP Deployment 3

After penetration during DVTPP Deployment 3, the pressure rapidly decreased followed by a slow pressure increase (Fig. F67). It was believed an internal leak or a pressure drop caused by a void when picking up the drill string, caused this response. The slow, continuous pressure increase most likely indicated the latter. A final pressure of 13.1 MPa was nearly constant and may be near in situ conditions; hydrostatic pressure was 12.92 MPa. The temperature profile provided an equilibrium temperature of 9.52°C (Fig. F67).

DVTPP Deployment 4

Similar to DVTPP Deployment 3, the temperature record provided in situ conditions during DVTPP Deployment 4 (11.68°C), whereas the pressure record was problematic (Fig. F68). Pressure decreased rapidly after insertion and then had increase/​decrease cycles. We interpreted this was caused by an internal leak; as the pressure reached a high value, fluid pressure leaked into the tool pressure housing, which in turn caused a rapid decrease; the pressure then slowly increased until it leaked again. This prompted a rebuild of the DVTPP to seal internal leaks.

DVTPP Deployment 5

No data were recorded for DVTPP Deployment 5.

DVTPP Deployment 6

DVTPP Deployment 6 provided an equilibrium temperature (12.96°C) (Fig. F69). Pressure increased with penetration and then decreased rapidly when the bit was picked up from the bottom of the hole. A slow pressure rebound was then recorded. It was believed the tool was partly pulled up with the drill bit, and this created a void around the pressure sensor. As the void equilibrated with the formation, pressure increased to 14.9 MPa, which is less than hydrostatic pressure (15.28 MPa). Pressure was still increasing when the DVTPP was retrieved.

DVTPP Deployment 7

During DVTPP Deployment 7 the temperature profile had a type dissipation curve but the pressure profile exhibited a low-pressure excursion after picking up the bit off the bottom of the hole (Fig. F70). The equilibrium temperature was estimated to be 13.46°C. The pressure decreased to a value significantly below hydrostatic (hydrostatic pressure = 15.57 MPa) and then slowly increased to 12.9 MPa. The increase may have reflected charging of a void with formation fluids. Fluid pressure was still increasing at the end of the experiment.

DVTPP Deployment 8

In DVTPP Deployment 8 the temperature spiked at penetration followed by decay to an in situ temperature of 13.84°C (Fig. F71). The pressure record for this deployment was significantly less than hydrostatic (hydrostatic = 15.86 MPa) and did not record any penetration pressure or dissipation (Fig. F71). This poor pressure result prompted a change in the DVTPP being deployed while the tool used in this deployment was rebuilt.

DVTPP Deployment 9

A programming error occurred during DVTPP Deployment 9. No data were recorded.

DVTPP Deployment 10

Pressure and temperature dissipation profiles increased with penetration and then decreased during DVTPP Deployment 10 (Fig. F72). Temperature followed a decay curve to a formation temperature of 15.81°C. Pressure dissipated while the tool was in the formation, but only to 19.9 MPa, in contrast to hydrostatic pressure of 16.75 MPa. The pressure dissipation was far from reaching equilibrium.

DVTPP Deployment 11

The temperature and pressure sensors recorded unreliable data during DVTPP Deployment 11 (Fig. F73).

DVTPP Deployment 12

During DVTPP Deployment 12, pressure increased during penetration, then quickly declined, and then recovered rapidly. The pressure ultimately dissipated to 18.9 MPa (Fig. F74). This dissipation was not yet in equilibrium with the formation. The temperature increased rapidly during penetration and then dissipated. The equilibrium temperature was 17.16°C (Fig. F74).

DVTPP Deployment 13

Pressure and temperature profiles were recorded during and after penetration during DVTPP Deployment 13 (Fig. F75). Temperature decayed to an in situ value of 11.11°C. The pressure profile dissipated to 14.7 MPa but had not yet equilibrated with the formation. Hydrostatic pressure was 13.12 MPa.

DVTPP Deployment 14

During DVTPP Deployment 14, pressure and temperature data had regular profiles. Pressure increased slightly during penetration and then dropped rapidly to 15.8 MPa (Fig. F76), which exceeded hydrostatic (14.67 MPa). Temperature increased rapidly and then decreased rapidly when the bit was picked up off the bottom of the hole. Near the end of the deployment, temperature increased to a final value of 11.2°C. No explanation was available for the small temperature increase at the end of the deployment.

DVTPP Deployment 15

Similar to DVTPP Deployment 14, during DVTPP Deployment 15, pressure increased, then decreased, and slowly increased to 16.9 MPa (Fig. F77), which exceeded hydrostatic pressure (15.68 MPa). The temperature reading was more problematic than DVTPP Deployment 14. The end temperature of 13.63°C most likely is not representative of in situ conditions.

Temperature and pressure summary

APCT, T2P, and DVTPP measurements help constrain the thermal gradient and the pressure field at Site U1324. Temperature measurements increased approximately linearly with depth (Fig. F78). Regression of temperatures provided a thermal gradient of 18.4°C/km. The largest scatter between the data and the average gradient occurred between 200 and 400 mbsf and below 550 mbsf. In the 200–400 mbsf interval, deviations may reflect lithology variation, deployment duration, or coupling between the probe and the sediment.

Two summaries of the pressure field were extracted from pressure measurements. The first included the pressure data (Fig. F79) where both pressure increases during penetration and dissipation curves were recorded. These data provided a maximum estimate of pressure, as complete dissipation was not achieved. Deviations of the last measured pressure (Fig. F79) and the in situ pressure were a function of the initial pressure spike (a function of probe geometry) and the amount of time the tool was left in the formation (Table T16).

The second pressure interpretation included reliable dissipation pressures (Fig. F79) and pressures measured that were interpreted as recovery from a void created near the tip of the probe. In multiple deployments, it was interpreted that a void was created near the tip of the probe when the drill bit was picked up. The pressure then rebounded as the void started to equilibrate with the formation fluid. The pressures (Fig. F80) were the final pressures measured by the probe prior to removal from the formation and represent a minimum bound on pressure. These data, although not finalized, were interpreted to document fluid overpressure from 50 to 608 mbsf at Site U1324.

Summary

Site U1324 logging data provided a detailed picture of the bedding style and lithofacies overlying the Blue Unit. Detailed core-log data integration at Sites U1322 and U1323 will enable refinement of the interpretation, but our preliminary interpretation provided the following insights:

• The main lithostratigraphic units defined in cores correlate with variations in LWD and wireline logs responses.
• Gamma ray, resistivity, bulk density, and compressional wave velocity log responses define five intervals within lithostratigraphic Unit II that are associated with fining-upward and fining-downward sequences.
• Resistivity images show significant deformation (dipping beds from 5° to 55°) of the overlying hemipelagic drape and distal turbidites from the Southwest Pass Canyon sediments. Steeply deformed beds with dips as high as 65° and folded and faulted beds suggest downslope remobilization as MTDs. Resistivity images show evidence of these MTDs in lithostratigraphic Subunit IIA, where steep dips and folds suggest a succession of sand-silt-mud laminae. Most of the deformation features observed in Hole U1324A trend in an east-west direction with the majority dipping to the north.
• A correlation between seismic data, well logs, and synthetic seismograms shows a good match between seismic reflectors. In the case of lithostratigraphic Subunit IE, faulted and contorted clay units with steeply dipping beds show an acoustically transparent nature in both the seismic data and the synthetic model.
• In situ temperature and pressure measurements documented overpressure and a low thermal gradient at Site U1324. Successful fluid pressure measurements yield λ* values between 0.2 and 0.6 at the end of the deployment:

λ* = (P – P_h)/(σ_v – P_h),

where

• P = pressure,
• P_h = hydrostatic pressure, and
• σ_v = total vertical stress.
• A thermal gradient of 18.4°C/km was established for temperature data.

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