The two intervals of the laminated Ethmodiscus oozes that were embedded and analyzed (intervals 167-1010C-5H-4, 79-88 cm, and 167-1010E-5H-2, 24-43 cm) are of similar stratigraphic thickness and have similar macroscopic and microscopic sediment fabric (Fig. 1, Fig. 2). It is likely that they represent the same sediment interval recovered in each core. When sample intervals from the two different cores are converted to the same depth scale, using the shipboard-defined meters composite depth (mcd), the laminated oozes occur at 44.15-44.24 mcd in Hole 1010C and 43.92-44.11 mcd in Hole 1010E (Shipboard Scientific Party, 1997).
Low-magnification BSEI photomosaics reveal an irregular alternation between (1) bright, very low porosity, horizontal to subhorizontal burrows (marked "x" on Fig. 1, Fig. 2) filled with silt, clays, coccoliths, and discoasters (Fig. 4B); (2) dark, porous laminae rich in Ethmodiscus fragments (Fig. 3A-3E); and (3) bright, low-porosity mixed-sediment laminae comprising silt grains and clays, coccoliths, and discoasters (Fig. 4A). Core photographs and BSEI photomosaics show that the top 4 and 9 cm of the Ethmodiscus ooze interval in Holes 1010C and 1010E, respectively, are dominated by macroscopic burrows (Fig. 1, Fig. 2). High-magnification BSEI analysis further shows that the burrows push between the darker, more porous layers of Ethmodiscus fragments, displacing the fragments (Fig. 4C). Burrows are filled with sediment that is similar in nature to nannofossil clay that is found above and below the laminated interval (Shipboard Scientific Party, 1997) and to mixed-sediment laminae (compare Fig. 4A, 4B). The margins of the burrows are very sharp (Fig. 4C, 4D) with a clear demarcation between the burrow and the Ethmodiscus fragments. Beneath the top 4 and 9 cm, the burrows become much less common and appear to be mainly restricted to the most porous, Ethmodiscus-rich laminae (marked "bl" on Fig. 2C).
Ethmodiscus laminae are porous and are defined by dark laminae/patches on the BSEI photomosaics (Fig. 1, Fig. 2). The laminae range in thickness from 0.05 to 4.73 mm, with an average thickness of 0.67 mm (N = 152); however, the thickness is influenced by the presence or absence of burrows within laminae (see individual burrows marked "x" on Fig. 2A). The brightness of the Ethmodiscus laminae on the photomosaics also ranges from being slightly less bright than the mixed-sediment laminae (Fig. 3A) to very dark (Fig. 3C); the darker the image, the greater the abundance of Ethmodiscus fragments relative to other sediment components. The darker laminae in the lower, well-laminated portion of the Ethmodiscus ooze interval tend to have concentrations of burrows within them (marked "bl" on Fig. 2C). One particular short interval of Ethmodiscus laminations contains rare pyritized frustules (Fig. 3E; marked "p" on Fig. 2A); otherwise, pyrite is relatively commonly dispersed within the laminae.
The mixed-sediment laminae are of similar composition to the nannofossil clay in which the Ethmodiscus ooze interval is found (Shipboard Scientific Party, 1997). Mixed-sediment laminations have a porosity intermediate between the low-porosity burrows and the higher porosity Ethmodiscus laminae. Laminae contain coccoliths, discoasters, carbonate grains, foraminifers, clays, and quartz and feldspar silt grains (Fig. 4A). There appears to be a gradation from laminae that are pure mixed-sediment laminae (Fig. 4A), to laminations that are mixed sediment with a few Ethmodiscus fragments (Fig. 3A), to Ethmodiscus laminae with mixed sediment (Fig. 3B), and to laminae that are pure Ethmodiscus fragments (Fig. 3C, 3D). In the absence of burrows, the Ethmodiscus and mixed-sediment laminae appear to alternate cyclically (Fig. 3F; marked "cy" on Fig. 2A, 2C).