ABSTRACT In this study, we discuss the results from different luminescence dating methods applied to four samples of Pleistocene slack-water sediments from the Frasassi hypogenic cave system, in the northeastern Apennines of Italy. Two samples came from a well-sorted, fine sand deposit in the Grotta Grande del Vento cave (SDS site), while two others were taken from a borehole through a clayey deposit in the adjacent Caverna del Carbone cave (CDC site). Both sites are located at an elevation of ~235 m above sea level (asl), which corresponds to ~30 m above the thalweg of the Sentino River flowing through the Frasassi Gorge outside the cave. In the Frasassi multistory cave system, the elevation of 235 ± 5 m asl corresponds to the third karst level or “floor,” the minimum age of which from speleothem U-Th dating is ca. 130 ± 15 ka. The luminescence ages for the two samples from the SDS site are in good agreement with each other within error, just like the two samples from the CDC profile. Different luminescence dating protocols were used to determine the ages for each individual sample. By applying this comparative approach, and taking the luminescence characteristics of the samples into consideration (quartz optically stimulated luminescence, different feldspar luminescence signals), the ages could be based on the most robust measurement protocol. The ages presented here were all derived from measurements using the post-infrared infrared signal of potassium-rich feldspar stimulated at a temperature of 225 °C (pIRIR225). Incomplete bleaching of the luminescence signal prior to deposition, leading to age overestimation when not detected and corrected for, was not a significant factor for the samples under investigation, because ages calculated for luminescence signals with different bleachability yielded results in agreement within error. Bleaching can therefore be assumed to have been sufficient before the samples entered the cave system. The ages determined for both sites are reliable from a methodological standpoint. The pIRIR225 luminescence dates from the SDS sand range between 129 and 101 ka and are consistent with the minimum age for the third cave floor (~235 m asl) as obtained from previous U-Th dating. In contrast, the pIRIR225 luminescence dates obtained from the clay-rich CDC deposit range from 217 to 158 ka, which is consistent with the minimum age for the fifth subhorizontal cave level when measured from the modern water table, found at ~65 m above the present river thalweg. This apparent discrepancy may be due to the fact that the present entrance of the CDC cave was incised by the river on the south side of Frasassi Gorge sometime during the Eemian interglacial period (marine isotope stage [MIS] 5e), but, being part of a hypogenic karst system in an uplifting tectonic structure, the actual third floor was preexisting, thus anteceding the river incision. On the other hand, the fifth floor of the cave system, some 30 m above the third floor, was incised sometime during the interglacial MIS 7 at around 200 ka, at a time when the saturated phreatic third floor had already been formed and thus was capable of collecting the fine suspension sediment settling from muddy river water flooding the cave.

ABSTRACT In this paper, we present old and new data about our integrated interdisciplinary stratigraphic study of sedimentary deposits preserved in the Grotta dei Baffoni Cave of the Frasassi hypogenic cave complex, including sedimentological, paleontological, archaeometric, and radiometric analyses. This research work allowed us to reconstruct the geologic, environmental, and human history of this part of the northeastern Apennines of Italy for the past 200,000 years, from the late Middle Pleistocene to the Present. Accumulation of alluvial sediment began in this cave ~200,000 years ago, when an entrance was breached by the Sentino River during its process of incision and deepening of the Frasassi Gorge coupled with regional tectonic uplift. Flooding of the cave went on until the entrance sill of the cave was lifted up to an elevation that could no longer be reached by the river, sometime in the mid–Late Pleistocene. After this, windblown dust (i.e., loess) and coarser carbonate clasts derived from the disintegration of the vaults due to cryogenic processes and/or seismically induced collapses of the limestone vaults, accumulated on this now-dry underground environment. The stratigraphy of an ~4-m-thick sedimentary deposit accumulated in the vast atrium room of the cave was measured, sampled, and documented in two excavation trenches in 1952 by archaeologist Anton Mario Radmilli. By collecting a dozen stratigraphically located osteological finds for 14 C dating, and revisiting artifacts collected by Radmilli, which are archived respectively in the Museum of Natural History of Verona and in the National Museum of Archaeology of Ancona, we assessed that the cave was frequented by wild animals, such as cave bear and ibex, starting in the mid–Late Pleistocene. Dating of charcoal particles from subsurface sediments in the inner part of the cave suggested that fires were lit in this cave by Epigravettian visitors during the Younger Dryas cold period. Scarce archaeological evidence nevertheless suggests that man began using this underground environment for worship practices probably in the early Neolithic. Human bones in the lower part of one of Radmilli's excavations yielded early Eneolithic ages. No other human bones were found in overlying levels of this excavation, but the typology of animal bones and associated ceramic artifacts, corroborated by our 14 C dates, suggest that this cave was utilized as a worship or ritual place until the early Middle Bronze Age. After that, the cave was sporadically used as a shelter for herders until recent times.

Deep phreatic shafts and travertine-capped sinkholes characterize Sistema Zacatón, an isolated karst area in northeastern Mexico. At a depth of at least 329 m, El Zacatón is the deepest known underwater pit in the world. Hypogenic karst development related to volcanism is proposed to have formed El Zacatón and is thought to have diminished since the late Quaternary peak activity. The resulting geomorphic overprint of Zacatón displays features similar to hydrothermal groundwater systems throughout the world. Other karst areas in northeastern Mexico are known for deep pits and high-flow springs rising from great depths, but differ from Zacatón in the speleogenetic processes that developed the caves. Sótano de Las Golondrinas (378 m), 200 km to the southwest of Zacatón, is among the deepest air-filled shafts in the world. The Nacimiento del Río Mante, 100 km to the west, is a large artesian spring that extends a minimum of 270 m below the water table. Although these three world-class karst systems all formed in Cretaceous limestone and are located relatively close together, there are significant differences in lithology, tectonic setting, and geomorphic features. Geochemical, microbiological, and geomorphologic data for Zacatón indicate that cave formation processes are similar to those observed in other volcanically influenced systems.