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Birds of Indian Subcontinent

Radiocarbon-Dated Molluscan Successions from the Holocene of Central Spain

Publication Type:Journal Article
Year of Publication:1991
Authors:PREECE, RC
Journal:Journal of Biogeography
Volume:18
Issue:4
Date Published:1991
ISBN Number:03050270
Keywords:Meleagris, Meleagris gallopavo, Phasianidae
Abstract:The molluscan successions from thick calcareous sediments exposed in the Rio Henares valley near Baides, central Spain, have been analysed. The main sequence comprises a thick unit of bedded silts, with occasional interbedded gravels and sands. These silts accumulated in a marsh on the river floodplain between 9940 ± 120 BP and 6210 ± 854 BP. Pollen spectra from this period are completely dominated by Pinus which reaches frequencies of $\thicksim 80%$ . The silts have yielded a hygrophilous fauna which includes several taxa which today are scare or very local. These include Vallonia enniensis (Gredler) and towards the top Vertigo moulinsiana (Dupuy) and V. agustior Jeffreys. This unit is overlain by tufa containing an aquatic community that includes some brackish elements. A date of 5160± 90 BP has been obtained from charcoal from a palaeosol representing a pause in tufa growth when the surface was invaded by species of dry ground. The tufa is overlain by slope deposits containing re-worked elements from the tufa, mixed with a xerophilous fauna that includes Zebrina detrita (Muller) and Orculella bulgarica (Hesse). The latter species is particularly noteworthy because it is only known as fossils or from dead shells from a few scattered localities in southern Europe, Turkey and Soviet Asia. The comparatively young data of 2640 ± 70 BP from this sequence suggests that it may well persist in this part of Spain. A further section, immediately south of the others, represents a much drier facies with a higher proportion of xerophiles including Trochoidea geyeri (Soos), Truncatellina callicratis (Scacchi) and in the upper levels Granaria braunii (Rossmassler). Because of the effects of facies, the sections could not be correlated using molluscan biostratigraphy but their relationships have been established by radiocarbon dating charcoal using accelerator mass spectrometry. These are the first detailed molluscan successions of this age to be analysed from the Iberaian peninsula. A preliminary study of the modern fauna revealed several taxa that were not recovered from the deposits. Their absence must either be due to the sediments reflecting a different depositional facies or else these species may be recent arrivals to the area. Unlike comparable profiles reported elsewhere in northern Europe, these successions do not reveal the progressive replacement of open-ground communities by those of woodland. Instead open-ground and marsh faunas persisted at this site throughout the Holocene. As this occurs at quite a high elevation $(\thicksim900 m)$ in the Spanish meseta, it remains to be seen to what extent it represents the situation generally in Iberia.
URL:http://www.jstor.org/stable/2845483
Short Title:Journal of Biogeography
Taxonomic name: 
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