Pleistocene Deposits in Pierre Saint-Martin Cave, French Pyrenees

Abstract

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 flows, 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 speleothems. The lower unit represents a cold period, probably isotope stage 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 devoid of pollen, represents a glaciation that occurred before 225,000 yr B.P. and probably correlates with stage 8, even though such a glaciation has not been previously recognized in the Pyrenees. The river terraces, covered by many noncorroded speleothems, probably formed during stage 7 (U/Th ages between 194,000 and 211,000–225,000 yr B.P.). Subsequent sinking of an underground river protected the deposits from erosion.