Abstract:
In the Alpi Apuane (Tuscany, Italy), Late Pliocene to Pleistocene karst landforms are preserved as relict phreatic caves, which were formed in a geomorphic setting very different from that of the present day. The largest karst drainage basin in the region, the Frigido, hosts cave systems with a vertical development totalling 1600 m. Abandoned phreatic cave passages preserved within this and neighbouring basins indicate that former base-levels were situated at up to ~1000 m above the modern valley floors. The passages constitute morphostratigraphic markers that can be used to reconstruct the uplift history of the Apuane. Their vertical distribution suggests two major phases of base-level standstill--one at 1000-1200 m a.s.l. and one at 600-700 m a.s.l. Some of the passages situated at the latter level contain >5 m thick flowstones whose top-beds have an age exceeding the limits of U/Th alpha spectrometric dating (>350 ka). Cave morphology and chronological constraints obtained from speleothems suggest that an important uplift event occurred during the Middle Pleistocene following a period of tectonic standstill of probable latest Early Pleistocene age. Active spring caves close to present-day valley floors contain speleothems whose ages exceed 100 ka, implying that no significant downcutting of the seaward valleys, and consequently no tectonic uplift, has occurred during Late Pleistocene