The microstratigraphic record of abrupt climate changes in cave sediments of the Western Mediterranean

Abstract

The purpose of this paper is to illustrate how calcareous sediments from Pleistocene and Holocene rockshelters and open caves of the Western Mediterranean can provide a stratigraphic record of abrupt climate change. The method proposed here is based on microstratigraphic examination of sedimentary sequences using microscopic techniques. The most important processes for characterizing the sensitivity of each cave to climate variables are: (1) the modes and rate of carbonate sediment production, (2) the nature and intensity of the pedogenic processes responsible for the synchronous alteration of carbonate materials (either those derived from the cave walls or those deposited on the ground surface), and (3) the supply of allogenic sediments, particularly by eolian activity. The cave sediment sequences presented record the marked coolings known as Dansgaard-Oeschger stadials and Heinrich events that occurred during the Pleistocene and the Holocene, as demonstrated by the high resolution records from ice and deep sea cores. At Abric Romanì in northeastern Spain, a series of sharp climatic deteriorations of increasing severity is shown to have occurred synchronously with the transition from the Middle to the Upper Paleolithic, with a period of seasonal frost and strong winds at ca. 37,000 yr B.P., tentatively correlated with Heinrich event 4. At Pigeon Cave, Taforalt (northern Morocco), the transition from the Aterian to IberoMaurusian/Epipalaeolithic cultures is dated to around 24,000-20,000 yr B.P. and is punctuated by a series of short cold pulses with evidence for seasonal freezing, soil erosion, and minimal evapotranspiration. In El Miron cave in north-central Spain, the exceptional nature of the Younger Dryas cooling produced a marked destabilization of the cave walls and roof. At El Miron, the stratigraphic evidence for sediment removal due to the rapid percolation of snow melt under a degraded soil cover allows us to reconstruct the nature of the negative excursion at ca. 8200 yr B.P. This example also illustrates how climate-controlled pedogenic processes can create a stratigraphic signature which has often been confused with a sedimentary hiatus. We conclude that cave sediments provide a valuable record of Pleistocene and Holocene climate changes. In appropriate contexts, these sequences allow us to examine the ecological stress generated by these unique global events at a local and regional level and improve our understanding of the complex anthropological processes that occurred at the same time.

The sedimentary records in Mediterranean rockshelters and caves: Archives of environmental change

“…Coarse-grained rockshelter deposits with comparable clast morphologies and geomorphological contexts have been recorded in sites throughout the northern Mediterranean region where frost action is still evident today. Interestingly, at 750 m above sea level in the mountains of eastern Morocco, Courty and Vallverdu (2001) report evidence for intensive cryoclastic cave wall fragmentation during the Pleistocene that produced deposits that are rather similar to the cryoclastic deposits found in rockshelters of western Europe. Laville (1976) presents his definition of "macrothermoclastism," which is a process associated with an annual freeze -thaw cycle (where an extended period of freezing produces large, angular rock fragments) and "microthermoclastism" associated with less extreme diurnal freeze -thaw cycles and the production of smaller rock fragments.…”

“…Rockshelter environments may form important slackwater sedimentation zones and such deposits have been reported at Boila in the Voidomatis basin (Hamlin et al, 2000;Woodward et al, 2001). Fine sediments are commonly deposited by fluvial processes in active karst settings (see Table II) when sediment-laden flows from the internal karst drainage deposit their loads in cave passages and shelter openings (see Courty and Vallverdu, 2001). 5.…”

“…The degree of interaction or coupling with the internal karst system can exert an important control on sediment transport pathways (Figure 2), on the ratio of allogenic to autogenic fine sediment delivery, and on the sensitivity of a given site to climatic changes and how these are manifest in the sedimentary record (Woodward, 1997b;Courty and Vallverdu, 2001). Rockshelters and caves have been classified in several ways (see Ford and Williams, 1989), but in this context, most sites can be described as either Active Karst Settings (AKS) or Passive Karst Settings (PKS), and some of the characteristics of such sites are listed in Table II.…”

“…Thus, not all of the approaches currently employed in the study of rockshelter and cave sediment records will yield unequivocal paleoclimatic signals in all contexts. Theopetra Cave in Thessaly (Karkanas, this issue) and Pigeon Cave in Morocco (Courty and Vallverdu, 2001) may be described as Active Karst Settings, and these sites and their sedimentary records display many of the characteristics listed for this group in Table II. Indeed, it is interesting to note that both sites contain important paleoclimatic records that have been pieced together from detailed micromorphological analysis of a range of primary and secondary microstratigraphic features.…”

“…However, the paleoclimatic significance of the sedimentary records in these specialized depositional zones has been widely debated (Collcutt, 1979;Farrand, 1985Farrand, , 1988Bailey and Woodward, 1997;Goldberg, 1992;Goldberg and Bar-Yosef, 1998;Macphail and Goldberg, 2000;Courty and Vallverdu, 2001), and the methods employed for intersite correlation have also proved controversial (see Turner and Hannon, 1988).…”