Mid-Pleistocene to Recent ostracod record in slack water deposits of the Frasassi gorge and cave system as a prospective proxy for palaeoenvironmental reconstruction


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January 2017


To trace environmental changes of the tectonically active Frasassi area in the northeastern Apennines of Italy, thedistribution of ostracod valves was studied in a series in slack water deposits collected from both caves and river banks, representing various time windows from lower Middle Pleistocene to Holocene, and allowing comparison with the modern ostracod assemblages in the Sentino River.The studied sediment sequences: BDR (BucodeiRovi cave, ca.780 ka), GBV (Grottadella Beata Vergine – ca. 650-450 ka), CDC and SDS (Caverna del Carbone and Sala dellaSabia – ca. 80-115 ka) and SBH (Sbif House fluvial swamp deposit – ca. 30 ka),as well as TRO (lake and river overbank deposits of the Esino River – 3.7 and 2.0 ka) yielded nearly 800 subfossil valves ofca. 25 ostracod species, of which all but threeare known to live today in the Sentino River or Frasassi Cave system. Due to thefragmentary and/or immature nature of recovered valves,their specific determination proved difficult in several samples and resulted in lumping under generic level. Neverthelessthe species accumulation curvesestimating the total species richness show that not many more taxa would be observed by increasing the number of samples. However, species/taxa richness of individual sediment samples was generally low and varied from 3 (in some samples of BDR and GBV) to 12 (CDC) with a mean  SD of 5.9  3.0. The most common and abundant taxa in the studied sediment samples were Candona spp. ex gr. neglecta (33.8% of the analyzed valves, present in 15 out of 16 studied samples), Potamocypris spp. (26.8%, 14) and Ilyocypris spp. (20.6%, 16), which also constituted the indicator taxa of each of the studied site/age palaeoassemblages. Due to variationsin mutual proportions of these taxa,the site/age sequences differed significantly in the taxonomic structure of their ostracod palaeoassemblages (PERMANOVA pMC = 0.011-0.025) and could be successfully discriminated (100% allocation success by Canonical Analysis of Principal Coordinates). For instance the SD

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