Ancient speleothem giant preserved in a high-Alpine cave (Dolomites, N Italy): rare insights into the Neogene

Conturines cave opens at 2775 m a.s.l. in the Dolomites (Northern Italy), hundreds of meters above the modern tree line. The cave is about 200 m long and comprises a single ascending paleophreatic conduit. The entrance of the cave is located at the base of the headwall of a former glacial cirque, testifying its pre-Pleistocene origin. Large parts of the cave floor are covered by an extensive (up to 3.5 m thick) flowstone and large stalagmite formations are present in the inner part of the passage, where the flowstone starts. All these large formations are inactive, partly corroded and dissected by fractures. The catchment area is a sharp ridge devoid of vegetation and soil, and the dripping water in the cave is undersaturated with respect to calcite, leading to the slow demise of these large speleothems.

 

Several drill cores covering the entire stratigraphy of the flowstone were obtained along the course of the gallery, the longest reaching bedrock at 3.5 m depth. Multi-proxy analyses of the two longest cores drilled approximately 5 m apart in the proximal part of the flowstone replicate well. Multiple magnetic reversals are preserved in the flowstone stratigraphy. According to preliminary U-Pb dating, speleothem deposition began ca. 5.5 - 5.0 Ma ago, likely coincident with the end of the Messinian Salinity Crisis in the Mediterranean, and continued intermittently until around 3 Ma. This uplifted ancient speleothem record provides a rare window into the Neogene at high resolution.