Interpretation of Pleistocene deposits from Magoula (northwestern Peloponnesus, Greece)

• Κύριος συγγραφέας: Καρανίκα, Κωνσταντίνα
• Άλλοι συγγραφείς: Ηλιόπουλος, Γεώργιος
• Μορφή: Thesis
• Γλώσσα: English
• Έκδοση: 2020
• Θέματα: Paleoenvironment; Pleistocene; Magoula; Παλαιοοικολογία; Πλειστόκαινο; Μαγούλα

This work involves the palaeoecological study of Pleistocene deposits from Magoula (northwestern Peloponnesus, Greece), based on the analysis of microfaunal elements. The study area has been chosen not only as a site of significant palaeontological interest where plant fossils, mammal bones and a wide range of different kinds of invertebrate and microfossils occur, but also for its tectonic position at the Rio –Antirio basin. The former basin bridges the Patraikos and Corinth Grabens. Microfaunal analyses were carried out on 267 samples collected every 20-40cm from two natural sections in the area of Magoula. From the first section (section M), which has a total thickness of 31.30 meters, 133 samples were processed, whereas from the second section (section K) with a total thickness of 27.20 meters, 134 samples. Sediment samples were wet sieved with tap water through 500 and 63 μm mesh sieves. Microfossils were sorted from the dried residues and subsequently were studied under the stereoscope. Species were determined based on previous studies of Mediterranean benthic taxa. The collected data were analyzed, relative abundance diagrams were prepared for each species using the software C2. Furthermore, taphonomic indices (Right/Left valve ratio, Sex ratio, Adult/Juvenile ratio and Carapace/Disarticulated Valves ratio) were calculated for most of the abundant species of ostracods. Also, stratigraphic columns were plotted according to collected section log data. Considering both the stratigraphic and the micropalaeontological analysis results, a detailed palaeoenvironmental reconstruction took place. In section M, according to microfaunal analysis, 4 ostracod taxa (Cyprideis torosa (both un-noded and noded morphotypes), Candona neglecta, Ilyocypris gibba, Aurila convexa) were recorded in the studied samples. The most abundant were C. torosa and C. neglecta. Two benthic foraminifera taxa (Ammonia tepida and Haynesina depressula), as well as some charophyte gyrogonites, freshwater gastropod opercula and fragments (Bithynia sp. and Valavata cristata) were identified as well. These data suggest that an initially lagoon system, turned gradually into a lagoonal river mouth environment (barren layers) due to sea level drop, and finally when sea level rose, it became again a lagoonal environment influenced by a river system with strong freshwater influxes. Moreover, the relative abundance diagrams and the taphonomic indices in combination with the stratigraphic column characterize a possible flood event at 24.10-24.30 meters. Thus paleoenvironmental changes occurred due to eustatism. In section K, according to the microfaunal analysis, 6 ostracod taxa (C. torosa (un-noded morphotypes), C. neglecta, Loxoconcha elliptica, Cytheridea neapolitana, Leptocythere rara and A. convexa were recorded in the studied samples, 6 benthic foraminifera taxa (A. beccarii, Ammonia tepida, H. depressula, Elphidium advenum, Elphidium crispum and Quinqueloculina seminula), as well as some brackish gastropods (Hydrobia acuta) brackish bivalves and fragments (Cerastoderma glaucum and Mytilidae) were identified as well. Palaeonvironmental changes occurred due to eustatism. Initially a lagoon system, turned gradually into an open lagoon environment due to sea level rise, and finally when sea level dropped became again a lagoonal environment influenced by a river system with freshwater influxes. The distance between section M and section K is only 138 meters, however, there is no connection between the two referred palaeoenvironments. The small distance between the two sections and the difference of the determined palaeoenvironments indicate the effect of a fault, with a total throw of at least 58.5 metres.