Initial Reports of the Deep Sea Drilling Project - Volume 67

This volume covers Leg 67 of the cruises of the Drilling Vessel Glomar Challenger. The Oaxaca transect, located off southern Mexico and drilled during Leg 66, sampled a truncated margin and subduction complex. In contrast, the Guatemala transect was selected for Leg 67 because accretion was thought to have continued in this area during most of the Tertiary. Selection of this transect arises in part from the fact that it includes a portion of the San José Canyon, thus layers of hemipelagic drape may have been stripped away by erosion, allowing quicker access to deep horizons. By studying the continental margin off Guatemala we hoped to strengthen the tie between offshore and onshore geology, to describe the stratigraphic sequence from the continental slope to the subducting oceanic plate beneath, to recover in ash layers a record of Central American volcanism, and to test the hypotheses describing active-margin tectonics. Specifically, the Guatemalan transect was chosen to sample and to map the geology of the "type region" for the Trench-Slope Model. During Leg 67, 15 holes were drilled at 7 sites located in three tectonic environments: Holes 496, 497, 498, 498A, 494, and 494A (in order of increasing water depth) on the continental slope, Holes 499, 499A, 499B, 499C, 499D, 500, 500A, and 500B on the floor of the Middle America Trench, and Hole 495 located on the Cocos Plate. Leg 67 began in Manzanillo, Mexico in May 1979 and ended in Puntarenas, Costa Rica in June 1979.