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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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Abstract

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 SDS assemblage with valve oxygen isotope composition of 18O = -5‰ recovered from sediment OSL dated at 115 17 kais clearly dominated by Potamocypris spp. (69%) and different from the somewhat younger CDC assemblage with 18O signature = -3‰ where C. neglecta group dominated (34%) whereas Potamocypris spp. relative abundance was on average only 15%. Such preliminary associations should, however, be interpreted cautiously and further study is needed (integrating also pollen analysis and more stable oxygen isotope measurements) to prove a cause-and-effect relationship between the recorded differences in ostracod palaeoassemblage successions and major glacial/interglacial environmental and climatic changes. Finally, the structure and species composition of the palaeoassemblages differed also significantly from modern ostracod assemblages from the Sentino R. and sulphidic spring (PERMANOVA pMC = 0.001-0.049). The main disparity has to be attributedto the lack of Prionocypriszenkeri in the fossil assemblages, which is a clear dominant today in the Sentino R. As P. zenkeri is a relatively large species (compared to Candona spp., Ilyocypris spp. and Potamocypris spp.), this difference may be due to the sorting effect and/or breakage of large valves, which were left unidentified and not analyzed in the fossil material. Additionally, valves of stygobitic species were found in sediment samples recovered from the caves, while these species do not occur today in surface riverine habitats of the Frasassi area.
Geophysical Research Abstracts
Vol. 14, EGU2012-11662-2, 2012
EGU General Assembly 2012
© Author(s) 2012
A comparison of modern and fossil ostracods from Frasassi Cave system
(northeastern Apennines, Italy) to infer past environmental conditions
S. Iepure (1,2), T. Namiotko (3), A. Montanari (4), E. Brugiapaglia (5), M. Mainiero (6), S. Mariani (7), and M.
Fiebig (8)
(1) IMDEA Water, Spain (sanda.iepure@imdea.org), (2) “Emil Racovita” Institute of Speleology, Romanian Academy, Cluj,
Romania, siepure@hasdeu.ubbcluj.ro, (3) Laboratory of Limnozoology, Department of Genetics, University of Gdansk,
Poland, (4) Osservatorio Geologico di Coldigioco, Cda. Coldigioco 4, 62021 Apiro, Italy, (5) Dipartimento di Scienze
Animali, Vegetali e dell’Ambiente, Facoltà di Agraria, Università degli Studi del Molise, Campobasso, Italy, (6) Federazione
Speleologica Marchigiana, P.zza della Repubblica 1, 60035 Jesi, Italy, (7) Gruppo Speleologico CAI Fabriano, Via Alfieri 9,
60044 Fabriano, Italy, (8) Dept. of Structural Engineering and Natural Hazards, University of Vienna, Austria
Cave water and sediments from an extensive sulfidic, chemioautotrophic subterranean ecosystem in the hypogenic
karst complex of Frasassi (northeastern Apennines of Italy) was analysed for modern and fossil ostracode
assemblages. 22 extant and 16 extinct ostracode species make of this continental sulphidic ecosystem one of the
richest worldwide. Both modern and fossil assemblages show the expected pattern of species diversity after the
simulation procedure for taxonomic distinctness, which indicates no major extinction events since the Pleistocene.
Extant species display patchy distribution according to habitat heterogeneity within the sulphidic environment.
Fossil assemblages from a 3 m thick fluvial deposit trapped near the entrance of the Caverna del Carbone
(CDC) at about 30 m above present river level, and a fine sand deposit resting at about the same elevation in
Sala Duecento (SDS) within the Grotta Grande del Vento preliminarily dated with OSL at 111±17 ka are being
investigated. The former deposit has yet to be dated but it represents probably a normal stratigraphic succession
spanning a few tens of kyr, which was deposited when the cave entrance was at the reach of fluvial flooding,
potentially recording the transition from the last interglacial Riss-Würm to the glacial Würm. Sediment samples
from the SDS site yielded an ostracode assemblage represented by 12 species with a d18O signature of -5hand
a well-diversified palinoflora assemblage indicating a transitional condition between steppe and temperate forest.
The top sediment from the CDC site is characterized by a less diversified ostracode assemblage represented by
8 species, d18O of -3hand a poorly diversified palinoflora dominated by herbaceous plants and lesser pines,
indicating a colder environment in the early stage of the last glacial. Additional information on the geometric
morphometry approach of B-splines method applied to extant and fossil specimens of the hypogean Mixtacandona
ostracode was used to identify microevolutionary patterns and environmentally cued variation. Analyses indicate
the presence of one morphotype of a new species A of the group Mixtacandona riongessa, and three distinctive
morphotypes of a species B of the group M. laisi-chappuisi occurring in stratigraphically distinct fluvial-cave
sediments. Apparent difference in the disparity level between these species could be associated with their survival
in different environmental conditions. Species A is found nowadays living exclusively in sulphidic cave waters,
and was present in the system since at least the end of the last interglacial.
The extraordinary high taxonomic and morphological diversity of ostracods reflects in situ evolutionary
processes that have occurred under the cumulative effect of high environmental energy availability of subterranean
sulphidic ecosystems, heterogeneous environmental conditions, and spatial and temporal isolation.
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