LATE ALBIAN-CENOMANIAN PLANKTONIC FORAMINIFERAL BIOSTRATIGRAPHY, TAXONOMY AND PALEOCEANOGRAPHIC INFERENCES
Tesi di Dottorato
Data di Pubblicazione:
2017
Citazione:
LATE ALBIAN-CENOMANIAN PLANKTONIC FORAMINIFERAL BIOSTRATIGRAPHY, TAXONOMY AND PALEOCEANOGRAPHIC INFERENCES / S.e. Gilardoni ; tutor: M. R. Petrizzo ; coordinator: E. Erba. DIPARTIMENTO DI SCIENZE DELLA TERRA "ARDITO DESIO", 2017 Feb 24. 29. ciclo, Anno Accademico 2016. [10.13130/gilardoni-silvia-elena_phd2017-02-24].
Abstract:
The mid-Cretaceous period (about 120 Ma to 80 Ma) was characterized by unusually warm climate, low thermal gradient between latitudes and by a series of Oceanic Anoxic Events (OAEs) promoting deposition of black shales (e.g. Bréhéret, 1988; Gale et al., 1996; Coccioni, 2001; Bornemann et al., 2005; Gambacorta et al., 2014, among others). During the late Albian-Cenomanian (~105-93 Ma), a major radiation of planktonic foraminifera did occur for the first time in their evolutionary history and was marked by the appearance of novel morphologies (biserial taxa and single-keeled trochospiral taxa with supplementary apertures) and by the development of new and more complex wall textures (macroperforate, muricate and costellate) on planispiral and trochospiral taxa that lasted until the end of the Cretaceous (González-Donoso et al., 2008; Lipson-Benitah, 2008; Georgescu and Huber, 2006, 2009; Huber and Leckie, 2011). However, the often imprecise usage of the key taxonomic criteria for species identification (morphology vs. wall texture) and/or broad species concept used for the identification of some upper Albian-Cenomanian species have lead to uncertainties in the planktonic foraminiferal biozonation.
This study is aimed 1) to review the upper Albian-Cenomanian planktonic foraminiferal species in order to clarify the key taxonomic features of some often misidentified species (e.g., Th. reicheli, R. cushmani, R. montsalvensis); 2) to refine the planktonic foraminiferal biozonation according to the revised taxonomy; 3) to describe the planktonic foraminiferal preferred trophic regime in the upper Albian-Cenomanian interval through the observation and comparison of relative abundances and diversity of species with inferred similar depth ecology; and 4) to clarify the planktonic foraminiferal response to the upper Albian Oceanic Anoxic Event 1d (OAE1d) (Erbacher and Thurow, 1997) and to the Mid Cenomanian Event (MCE) (Ernst et al., 1983).
The upper Albian-Cenomanian samples analyzed were selected from different sedimentary basins:
1) the Umbria-Marche Basin (Monte Petrano and Le Brecce sections) and 2) the Mazagan Plateau (Deep Sea Drilling Program - DSDP Leg 79, Sites 547A and 545).
All the studied sections include the Albian/Cenomanian boundary and the OAE1d (Leckie, 1984; Nederbragt et al., 2001; Gambacorta et al., 2014, 2015, 2016).
In addition, the Monte Petrano section also records the MCE (Coccioni and Galeotti, 2003; Gambacorta et al., 2014, 2015, 2016).
Samples from the Umbria-Marche Basin were processed using a technique with acetic acid, while those from the Mazagan Plateau were prepared with the standard methodology. A scanning electron microscope (SEM) was used to document the species and to observe the wall texture at higher magnification. Finally, quantitative analysis were performed for the Monte Petrano and Site 547A to document variations in abundance of species and genera respect to the total planktonic foraminifera, and, consequently, to evaluate the evolutionary trends and the changes in the assemblages composition.
Five Biozones and one Subzone (Robaszynski and Caron, 1995) were identified, specifically from base to top: Pseudothalmanninella ticinensis Zone, Thalmanninella appenninica Zone, Planomalina buxtorfi Subzone, Thalmanninella globotruncanoides Zone, Thalmanninella reicheli Zone and Rotalipora cushmani Zone.
Moreover, the LO (lowest occurrence) of Th. appenninica, the LO of P. buxtorfi, the LO of P. libyca, the LO of Th. brotzeni, the LO of Th. globotruncanoides, the LO of Th. greenhornensis, and the LO of R. cushmani are identified to be potentially useful bioevents for regional and global correlations by comparing the results from this study with data reported from the literature (Mont Risou sec
Tipologia IRIS:
Tesi di dottorato
Keywords:
micropalaeontology; planktonic foraminifera; taxonomy; biostratigraphy; paleoceanography; Albian-Cenomanian;
Elenco autori:
S.E. Gilardoni
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