Calcareous nannofossils in the basal Zanclean of the Eastern Mediterranean Sea: remarks on paleoceanography and sapropel formation

Abstract

This paper presents the results of a study on nannofossil assemblages in the uppermost Messinian and basal Zanclean sediments recovered from Ocean Drilling Program (ODP) Holes 969B (south of Crete) and 967A (north of the Eratosthenes Seamount) located in the Eastern Mediterranean Sea. Focus of the research is on (1) the micropaleontological signature of the basically nonmarine facies of the uppermost Messinian interval; (2) the correlation of the Messinian/Zanclean boundary outside the Mediterranean by means of nannofossil biostratigraphy; and (3) the mechanism of sapropel formation in the earliest Pliocene. The main results are summarized as follows:1. The Messinian sediments are characterized by assemblages dominated by diagenetic resistant and long-ranging Neogene species, absence of typical upper Tortonian-Messinian species, high abundance of reworked taxa of Cenozoic and Cretaceous age, and high abundance of gypsum crystals and dolomite. All evidence listed above point to the absence of a primary marine signature in the nannofossil assemblages of the sediments. A noticeable exception, constituted by anomalous abundance of Sphenolithus spp., which suggests a possible (marginal) marine signature, is documented.2. The recovery of some specimens of Triquetrorhabdulus rugosus and of Ceratolithus acutus overlapping each other in the basal Zanclean suggests that, contrary to what has been reported by most authors, the last appearance datum (LAD) of T. rugosus and the first appearance datum (FAD) of C. acutus do not exactly coincide. This was already reported from the Ceara Rise (ODP Leg 154), where the FAD of C. acutus was found immediately below the cyclostratigraphically correlated position of the Messinian/Zanclean boundary. These closely spaced bioevents can be considered as a valuable tool, in addition to magnetostratigraphy and astrocyclostratigraphy, for the recognition and worldwide traceability of the Messinian/Zanclean boundary.3. Based on a model by Molfino and McIntyre, fluctuation in abundance of Florisphaera profunda, a peculiar nannoplankton species living in the lower part of the photic zone, is interpreted to represent nutrient availability within different levels of the photic zone. Thus, positive peaks of F. profunda were connected by the author to the presence of a deep chlorophyll maximum (DCM) at times of sapropel formation, a concept previously introduced by Rohling and Gieskes for the mid-Pleistocene to Holocene time interval.Abundance peaks of Florisphaera profunda are recorded in all five sapropel layers recovered in the basal Zanclean of ODP Hole 969B. Therefore, the DCM model may be tentatively applied also to the earliest Pliocene and probably to the whole sapropel sequence of the Mediterranean area, since the late Miocene.The recovery of abundance peaks of Discoaster pentaradiatus in most sapropels (together with the decreased abundance of Coccolithus pelagicus in some of them), suggests that these sapropels probably correlate with the marls (and not the limestones) of the rhy...

Pliocene Mediterranean Foraminiferal Biostratigraphy: A Synthesis and Application to the Paleoenvironmental Evolution of Northwestern Italy

“…Biostratigraphic events for global correlations are mainly provided by calcareous nannofossils: the Discoaster quinqueramus LO, dated at 5.537 Ma, and the first occurrence of Ceratolithus acutus dated at 5.37 Ma in the equatorial Atlantic slightly predating the Messinian/Zanclean boundary (Backman & Raffi, 1997). The disappearance of Triquetrorhabdulus rugosus was recorded in Mediterranean deep-sea cores (Castradori, 1998;Di Stefano et al, 1996) and in the equatorial Atlantic (Backman & Raffi, 1997) at 5.23 Ma. Planktonic foraminiferal events, such as the Sphaeroidinellopsis spp.…”

“…The Gelasian stage was proposed by Rio et al (1994;1998) to represent the uppermost and third interval of the Pliocene Series, corresponding to the strong climatic deterioration due to orbitally controlled glacial cycles in the Northern Hemisphere. The stage was named from the Greek name of the town of Gela, near to the Monte S. Nicola section where the Gelasian GSSP was established.…”

“…acme within complete successions (Di www.intechopen.com Stefano et al, 1996;Iaccarino et al, 1999b). A short hiatus in the basal Pliocene of Moncucco T. was therefore inferred, also on the basis of Triquetrorhabdulus rugosus absence, a calcareous nannofossil taxon usually recorded in the lowermost Zanclean (Castradori, 1998); 3) the Globorotalia scitula dextral Common Occurrence (CO), a "delayed invasion event", was recorded in sample 8 of the Moncucco T. section and in the basal Early Pliocene of the Western Mediterranean (Iaccarino et al, 1999b); 4) the re-immigration of the epibathyal to mesobathyal benthic foraminifer Siphonina reticulata, and the subsequent re-entry of the deep, oxyphilic benthic Cibicidoides robertsonianus, nearly synchronous events, recognized at considerable geographic distance (Iaccarino et al, 1999b;Pierre et al, 2006;Spezzaferri et al, 1998) in the Mediterranean basin. The re-immigration of bathyal benthic species, disappeared from the Mediterranean before the Messinian Salinity Crisis (Kouwenhoven et al, 1999), was related to the establishment of deep oceanic-type conditions during the early Zanclean (Hasegawa et al, 1990;Spezzaferri et al, 1998).…”

Zanclean/Piacenzian transition on Cyprus (SE Mediterranean): calcareous nannofossil evidence of sapropel formation

“…Higher values of F. profunda have been previously documented in other Pliocene sapropels (Zanclean age) from the Mediterranean region (Castradori 1998), connecting the increased abundance of the species with the development of DCM. Similarly, Negri et al (2003) observed the same pattern of a well-developed DCM favouring F. profunda during the deposition of Pleistocene sapropels.…”

“…Calcareous nannofossils are one of the most important pelagic sediment micro-components (Müller 1985;De Kaenel and Villa 1996;Castradori 1998;Negri et al 1999a, b;Negri and Villa 2000;Vázque et al 2000), used mainly for biostratigraphy and paleoceanographic reconstructions. Calcareous nannofossil biostratigraphy historically provides first-order age control in many outcrops and cores.…”