(Table 1) Suspected gas hydrate occurrence on DSDP Leg 66 Holes

Evidence for naturally occurring methane hydrates was collected at three drill sites off the southern Mexico continental margin. The hydrates are manifested either by ice inclusions or, more often, as frozen porous volcanic ash and fine sands interlayered with muds. Gas generation from the ice inclusions and interstitial water of the frozen sediment was as high as about 7 ml of gas/ml of water. One large sample immediately placed in a sealed container released about 20 ml of gas/ml of water. All of these values are higher than may be accounted for by gas solubility at in situ conditions. Measured thermal gradients place the bottom-simulating reflection (BSR) in this area very near the phase boundary for the methane hydrate system. This is consistent with earlier interpretations that the BSR is related to the hydrate/gas phase boundary