PLEISTOCENE DEPOSITS IN PIERRE SAINT-MARTIN CAVE, FRENCH PYRENEES

Pleistocene deposits in alpine Pierre Saint-Martin cave are preserved in an abandoned river gallery. The deposits, 300 m long and 25 m high, are composed of a lower unit of fallen blocks overlain by debris flow s, a main unit of laminated clay, and a series of river terraces inset into these units. The lower and main units are each overlain by spele othems. The lower unit represents a cold period, probably isotope stag e 10. Corroded speleothems above it have given U/Th ages greater than 300,000-330,000 yr B.P. The main unit, with carbonate-rich varves devo id of pollen, represents a glaciation that occurred before 225,000 yr B.P. and probably correlates with stage 8, even though such a glaciati on has not been previously recognized in the Pyrenees. The river terra ces, covered by many noncorroded speleothems, probably formed during s tage 7 (U/Th ages between 194,000 and 211,000-225,000 yr B.P.). Subseq uent sinking of an underground river protected the deposits from erosi on. (C) 1998 University of Washington.