GEOCHEMICAL AND SCLEROCHRONOLOGICAL ANALYSES OF THE LOWER PLEISTOCENE MACROFAUNA OF WESTERN EMILIA (NORTHERN ITALY): PALAEOENVIRONMENTAL AND PALAEOCLIMATIC IMPLICATIONS
Tesi di Dottorato
Data di Pubblicazione:
2015
Citazione:
GEOCHEMICAL AND SCLEROCHRONOLOGICAL ANALYSES OF THE LOWER PLEISTOCENE MACROFAUNA OF WESTERN EMILIA (NORTHERN ITALY): PALAEOENVIRONMENTAL AND PALAEOCLIMATIC IMPLICATIONS / G. Crippa ; tutor: L. Angiolini ; coordinator: E. Erba. DIPARTIMENTO DI SCIENZE DELLA TERRA "ARDITO DESIO", 2015 Feb 11. 27. ciclo, Anno Accademico 2014. [10.13130/crippa-gaia_phd2015-02-11].
Abstract:
The Early Pleistocene is a time interval characterized by several climatic oscillations which has its lower and upper boundaries coinciding respectively with the beginning of the Northern Hemisphere Glaciation and the Middle Pleistocene Transition. The Mediterranean area was strongly affected by the Early Pleistocene climatic changes. One of the most important biotic event is here represented by the appearance of the boreal guests (e.g. the bivalve Arctica islandica and the foraminifer Hyalinea balthica) at the beginning of the Calabrian Stage, suggesting significant cooling of the Mediterranean Sea, which is also confirmed by a change in the pollen flora indicating cold climatic conditions.
The Arda River marine succession, cropping out in Western Emilia, Northern Italy, is very rich in macrofossils and it covers without significant gaps the Early Pleistocene. It thus represents an ideal setting where to study the climatic oscillations of this time interval.
This study, combining sedimentology, taxonomy, palaeoecology, biostratigraphy and geochemistry and sclerochemistry of bivalve shells, provides an integrated investigation of the palaeoenvironmental and palaeoclimatic conditions accompanying these major climatic changes in the Arda section.
The Arda marine succession is 237.40 m-thick and consists of sandstones, siltstones and mudstones deposited in a tectonically active setting during phases of advance of fan deltas; it is bounded at the top by continental conglomerates indicating a major sea level drop and the establishment of a continental environment with vertebrate faunas and fresh water mollusks.
The taxonomic analysis of the macrofauna allows to identify 159 taxa, of which bivalves are dominant with 105 taxa, followed by gastropods (44 taxa) and a few corals (3 taxa) and serpulids (2 taxa); brachiopods, echinoids, barnacles, bryozoans and scaphopods do also occur. The comparative sedimentological and palaeoecological analysis shows that the Arda marine succession deposited in an infralittoral to a shallow circalittoral environment, where the maximum depth of the succession should not have exceeded 40-50 m. This comparative analysis confirms also the general regressive trend of the studied marine succession, punctuated by eight lower order transgressive and regressive cycles; however, no evidence of subaerial exposure or shift to water depths exceeding 50 m has been recorded, framing the depositional depth through the transgressive and regressive cycles between 5 m and 50 m of depth.
According to mollusk and nannofossil biostratigraphy the Arda River section has a late Gelasian-Calabrian (Early Pleistocene) age. The main mollusk bioevents comprise the last occurrences of Chama placentina, Glycymeris inflata and Aequipecten scabrella in the basal part of the section, the first occurrence of Arctica islandica at 103.70 m from the base and the last occurrence of the gastropods Nassarius prysmaticus and Turritella tricarinata in the upper part of the section. The identified nannofossil zones range from Zone CNPL7 to the lower part of Zone CNPL9.
The palaeoclimatic significance of the Arda biota has been investigated at two different levels: first the analyses of its mollusk fauna and of its pollen content and then a more detailed research involving geochemistry and sclerochemistry of the bivalve shells.
The occurrence of boreal guests, such as Arctica islandica, Pseudamussium septemradiatum and possibly also Mytilus edulis, from 103 m upward, suggests that a climatic change occurred in the Arda marine succession with a shift to colder seawater temperatures. However, aside from the occurrence of boreal guests, the fauna is mainly dominated by eurythermal species having a cosmopolitan distribution, lacking the str
Tipologia IRIS:
Tesi di dottorato
Elenco autori:
G. Crippa
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