METHODS

One-dimensional (vertical) consolidation tests were completed on seven samples recovered from Sites 1020 and 1021. Whole-round samples, 10 cm long, were cut from the core sections, capped, sealed in wax, and stored in refrigerated seawater until testing. The tests were conducted in two back-pressured consolidometers at the Bedford Institute of Oceanography. The application of back pressure redissolves air bubbles trapped within the sample. The samples were back pressured for a minimum of 12 hr before incremental loading was started. A standard load increment ratio of one was used, and the samples were double drained (top and bottom). The measured and derived index properties (Table 1), determined before the start of each test, were similar to those obtained at sea, indicating that no desiccation of the samples occurred during transport and storage. In addition, no disturbance was observed during sample preparation.

The consolidation test measures the change in sample height over a series of increasing (loading) and decreasing (unloading) stresses. The change in sample height is used to calculate the volume change expressed as void ratio. The consolidation results, plotted as a consolidation curve (Fig. 1), are used to determine the coefficient of expansion (C_r) defined as the log-linear slope of the rebound portion of the curve. The elastic rebound causes the bulk density and dry density to decrease while porosity and void ratio increases. The elastic rebound does not change the grain density or pore-fluid density. Discrete laboratory index data were corrected using the coefficient of expansion. Void ratio values were corrected to in situ values as follows:

, (1)

where e_c is the corrected void ratio, e_i is the laboratory-determined void ratio, and P´_o is the effective overburden stress calculated using

, (2)

where d is the discrete measurement interval (mbsf), _c is the laboratory-determined bulk density, and _w is the pore-fluid density. Porosity values were corrected using the following phase relationship:

n_c = e_c / (1 + e_c ). (3)

Bulk density (_c) and dry density (_dc) data were corrected to in situ valves using corrected void ratio (e_c), grain density (_g), pore-fluid density (_w), and the following phase relationships:

, and (4)

_dc = _g / (1 + e_c ). (5)

The corrected bulk density values can be used for constructing synthetic seismograms, determining in situ stress conditions, and correlating with downhole logging data. Corrected dry density data can be used in determination of mass accumulation rates.

The change in void ratio over one core length is geometrically related to the increase in core length or core expansion (MacKillop et al., 1995). The core length expansion (L) in meters over discrete measurement intervals was calculated from the elastic change in void ratio as follows:

L = e (L_o - nL_o), (6)

where n is the core porosity and L_o is the recovered length of core. The L over discrete measurement intervals is then accumulated and added to the mbsf scale. The accumulated length in meters below seafloor is then compared with the mcd scale.