Late-glacial to Holocene biogenic moonmilk and calcareous tufa deposits from caves in Trentino (NE-Italy): environment of precipitation and paleoclimatic significance

Abstract

: Flowstones and coatings consisting of biogenic moonmilk and calcareous tufa are commonly associated with macrocrystalline speleothems in several caves of the Trento Province. Biogenic moonmilk is most common in caves located at middle to high elevation, from 1400 m a.s.l.up to the timberline (1900-2000 m), whereas calcareous tufa flowstones occur in caves set at low and middle elevation, from the valley bottom up to the upper limit of the deciduous forest (1400-1500 m). Most of these flowstones are fossil and exhibit evidences of erosion. 14C dating on both moonmilk and calcareous tufa, and U/Th dating on associated macrocrystalline stalagmites, allowed for the recognition of three depositional phases which can be correlated with the following environmental and climatic events at the surface: (1) - Between 12,000 and 9,000 year B.P., macrocrystalline and calcareous tufa speleothems started to form in caves at low elevation. (2) - Between 9,000 and 5,000 year B.P., the maximum deposition of moonmilk flowstones and, probably, of calcareous tufa flowstones, occurred. This time span corresponds to the Holocene climatic optimum, i.e. to an increase in both temperature and precipitation that promoted intense pedogenesis and the consequent increase in carbonate dissolution above the cave and speleothem precipitation within the caves. (3) - At about 5,000 B.P. moonmilk deposition stopped in caves located at high-altitude. This event corresponds to a dramatic drop in calcareous tufa deposition in low-altitude caves and is probably related to an abrupt climatic deterioration and strong soil erosion at the surface.