(Table 1) Typical trace-fossil occurrences in DSDP Holes 56-436 and 56-435A

Trace fossils are in places abundant in cores from DSDP Leg 56 sites. They are particularly rich in the pelagic-clay sequence at Site 436. Some significant trace fossils, including Zoophycos, Teichichnus, Chondrites, rind and solid burrows, and pellet-armored rods, are described. The ichnofauna, except for pellet-armored rods in diatomaceous mudstone of the landward trench slope, is characterized by cosmopolitan bathyal to abyssal forms.

(Table 1) Quantitative mineralogy at DSDP Holes 59-447A and 59-450

The authigenic minerals contained in the altered basal intervals of volcaniclastic sediments from Sites 447 and 450 of Deep Sea Drilling Project Leg 59 are dioctahedral smectite (with variable crystallinity), phillipsite, and sanidine. Sanidine seems the most widespread and common product of basal alteration in the Philippine Sea marginal basins. The neomorphic mineral suites may have been produced by (1) halmyrolisis of the volcaniclastic sediments; (2) halmyrolisis of the underlying basalts; or (3) hydrothermalism associated with basaltic intrusions. At Site 450, other authigenic minerals occur (carbonates, analcime, clinoptilolite, Fe-Mn oxides), and the basal paragenesis is consistent with a hydro thermal origin. Such a process could have produced temperatures up to 200 °C in the tuffs lying as much as 2 meters above the contact with a basaltic intrusion. Products of low-temperature alteration, however, are also present in the altered interval of this site.

A magneto-mineralogical study of basalt at DSDP Leg 73 Holes

The basalts in Holes 519A, 522B, and 524 were studied for intensity of natural remanent magnetization, magnetic hysteresis, magnetic susceptibility, stability of isothermal remanence, and thermomagnetic behavior. Some of these properties are sensitive to both the composition and the microstructure of the magnetic minerals, others to composition only. Thus it is possible to separate the two effects and to trace the variation of effective magnetic grain size and degree of alteration within a lithologic unit or over a yet larger distance or time interval. The flow in Hole 519A is highly maghemitized at the top, the degree of maghemitization decreasing with depth in the flow. Effective grain size increases with increasing depth. Electron microprobe analysis of the titanomaghemite grains in these samples provides no support for the leaching out of iron during alteration. The pillows and flows in Hole 522B are distributed among a number of cooling units, and no systematic downhole variations are apparent. The inferred magneto-petrology is consistent with the cooling and alteration history that might be expected within the units. The upper and lower sills in Hole 524 are more uniform and have a larger concentration of well-developed magnetic mineral grains than the pillows and flows in Holes 519A and 522B. Maghemitization appears to have developed from the boundaries of the sills that are in contact with the sediments between the sills.