Agata Di Stefano

ASTROCHRONOLOGICAL CALIBRATION OF THE UPPER SERRAVALLIAN/LOWER TORTONIAN SEDIMENTARY SEQUENCE AT TREMITI ISLANDS(ADRIATIC SEA, SOUTHERN ITALY)

A high resolution cyclostratigraphic study was carried out on a cyclicaly bedded succession of late Middle Miocene deep marine deposits from the Tremiti Islands, Adriatic sea (Italy). Astronomical calibration of the sedimentary cycles provides absolute ages for different calcareous plankton bioevents, widely used for intra Mediterranean correlation, in the interval between 11.12 and 12.60 Ma. The sedimentary record of the S. nicola composite section consists of an alternation of indurated, withish coloured, CaCo3 rich and grey less indurated, CaCo3 poor marly beds, at times replaced by red coloured CaCo3 poor marls. Results of direct correlation between the La 90 (1,1) solution of the insolation curve and the cyclic lithologic patterns occurring in the studied sections, combined with results of spectral methodologies applied on the climate sensitive data (CaCo3 and Globigerinoides ) showed that the classic Milankovitch periodicity can be represented through the modulation forcing of the studied sedimentary records.

Late Quaternary oceanic fronts along Chatham Rise indicated by phytoplankton assemblages, and refined calcareous nannofossil stratigraphy for the mid-latitude SW Pacific

Abstract A quantitative analysis was carried out of planktonic diatoms (biogenic opal) and calcareous nannofossils (biogenic calcite) in late Quaternary sediments (MIS 1–6) from four cores along a N–S transect east of New Zealand from 39°50′S to 50°04′S across the E–W-trending submarine ridge, the Chatham Rise. This was done to trace movements of oceanic fronts and to improve calcareous nannofossil stratigraphy for the last 130 000 yr in the SW Pacific. Sites ODP 1123 and Q 858 are below present day subtropical surface waters north of Chatham Rise. Site DSDP 594 is below present-day mixed temperate–subantarctic surface water south of the rise, and site ODP 1120 is below subantarctic surface water. The more diverse and opportunistic planktonic diatoms provided marker species for subtropical surface waters ( Alveus marina , Fragilariopsis doliolus , Rhizosolenia bergonii and Azpeitia nodulifer ) and others for subantarctic surface waters ( Nitzschia kerguelensis , Thalassiosira lentiginosa ). Application of these tracers permits the following conclusions: (1) subtropical conditions persisted north of Chatham Rise throughout the past 130 000 yr, in spite of the cooling of surface waters during colder periods; (2) during warm times (MIS 5 and MIS 3, and in MIS 1), the sporadic occurrence of subtropical species south of Chatham Rise indicates occasional admixture of subtropical surface waters that far south; (3) subantarctic waters extended to the southern slopes of the Chatham Rise during MIS 5b, late MIS 5a to early MIS 4, during the warmer time intervals in early MIS 3, and during latest MIS 3 to early MIS 2; (4) subantarctic frontal conditions existed over southern Chatham Rise during early MIS 4 and late MIS 3 to early MIS 2; and (5) it is probable that during cooler times, MIS 6, MIS 5b, and in MIS 2, intensified particle transport from the Bounty Trough to the northern flank of Chatham Rise occurred by intensified boundary currents. The larger abundance fluctuations in both microfossil groups at the sites south of Chatham Rise than north of Chatham Rise reflect northward shifts of the Circumpolar Subantarctic Water (CSW) and a contemporaneous disappearance of Australasian Subantarctic Water (ASW), implying an elevated temperature gradient between the surface water masses north and south of the Chatham Rise at the times of such northward shifts of CSW. Calcareous nannofossils are less diverse than diatoms, and are less specialised. Some calcareous nannofossil species show abundance shifts at the same time at different latitudes. Two of these abundance shifts can be used for correlation between subtropical and subantarctic sediments in the SW Pacific: (1) reversal in the relative abundance of Calcidiscus leptoporus and Coccolithus pelagicus associated with the MIS 2/1 boundary; and (2) drop in abundance of Gephyrocapsa muellerae or medium-sized Gephyrocapsa at the MIS 4/3 boundary. An additional abundance shift seems to be restricted to subtropical to mixed temperate–subtropical–subantarctic surface waters: (3) increase in abundance of G. muellerae or medium-sized Gephyrocapsa at the beginning of MIS 2 below the Okareka tephra.

HIGH RESOLUTION CALCAREOUS PLANKTON BIOSTRATIGRAPHY OF THE SERRAVALLIAN SUCCESSION OF THE TREMITI ISLANDS (ADRIATIC SEA, ITALY)

The planktonic foraminifer and calcareous nannofossil content of two Middle Miocene sections of the Tremiti Islands (Southern Adriatic Sea) have been studied. The two sections are composed of marly limestones rich in calcareous plankton which show cyclic alternations of indurated (higher carbonate content) whitish and less indurated grey or reddish beds. The two sections represent a succession with a total thickness of 38 m. Samples have been collected at a mean spacing of 10-15 cm; qualitative analyses were performed on one sample per meter but quantitative analyses were made for each sample. The abundance fluctuations of several marker species proved to be a very useful tool to correlate the two sections. The astronomical calibration of the sedimentary cycles provided absolute ages for all the recognised calcareous plankton bioevents.

Stratigraphic features of the Maltese Archipelago: a synthesis

The present study gathers a large amount of both existing and unpublished biostratigraphic data, which allows a detailed and complete definition of the stratigraphic features of the late Oligocene–late Miocene Maltese Archipelago sedimentary succession, recording in turn the tectonic and eustatic history of the Central Mediterranean region. We selected five sections in the Malta Island and three in Gozo, representative of the entire sedimentary succession, affected by well-known erosional surfaces, correlated to low-stands of the sea level, often associated with phoshatic layers, linked to the subsequent high-stands. The sedimentary interval, and thus the associated hiatuses, was constrained both by the bio-chronostratigraphic attribution and by the comparison with the third-order succession of the New Jersey passive margin, which shows strict analogy with the geodynamic context in which the Maltese succession deposited. The diachroneity at the base of the formations in the different sections, and the presence of intraformational unconformity/hiatuses, highlighted the role of the tectonic, which depicted a complex sedimentary basin, characterized by more distal versus more marginal sectors. Furthermore, the possibility to compare the sedimentary succession with the oxygen isotope curve connects the sedimentation interruptions, recorded within the Maltese Archipelago deposits, to global cooling events.

Integrated micropalaeontological study (ostracods and calcareous plankton) of the Langhian western Hyblean successions (Sicily, Italy)

Abstract Four sections cropping out in the Hyblean Plateau (SE Sicily) were studied biostratigraphically and palaeoecologically. The investigated succession was referred to the early–late Langhian on the basis of both the planktonic foraminifers (lowermost part of the Praeorbulina glomerosa sicana Subzone–lowermost part of the Orbulina universa Subzone) and the calcareous nannofossils (uppermost part of the MNN4a Zone–lowermost part of the MNN5b Subzone). All the biozonal markers were recorded and further significant events were identified. The most remarkable ones are two paracmes of Paragloborotalia siakensis within the P. glomerosa sicana Subzone and the distribution of Helicosphaera waltrans, which characterises the upper part of the MNN5a Subzone. The ostracod palaeoecological analysis indicated a progressive and gradual trend from thermospheric to psychrospheric conditions and probably a basin deepening (from upper to lower epibathyal). The flowing of deep Atlantic waters into the basin is documented by the entry of the psychrospheric species Agrenocythere hazelae within the upper part of the P. glomerosa sicana Subzone. Only in the late Langhian, however, were typical psychrospheric conditions probably reached. These data provide evidence that oceanic deep water masses reached the Central Mediterranean, passing through both the western connections to the Atlantic Ocean and the African–Sicilian threshold, during a great part of the Langhian.

Tectonics and sedimentation of the Lower and Middle Pleistocene mixed siliciclastic/bioclastic sedimentary successions of the Ionian Peloritani Mts (NE Sicily, Southern Italy): the onset of opening of the Messina Strait

Biostratigraphic analyses carried out on siliciclastic/bioclastic deposits discontinuously cropping out along the Ionian flank of NE Sicily, indicate that they form two sedimentary events of Early and Middle Pleistocene, respec tively. Vertical facies successions, showing transgressive trends, suggest that sedimentation occurred within semi-enclosed marine embayments, where sublittoral coastal wedges developed on steep ramp-type shelves. Sediments accumulated in shoreface to offshore transitions along steep bottom profiles. This depositional scenario was strongly conditioned by the tectonic activity of the rift zone linking Western Calabria and Eastern Sicily. The effects of glacio-eustatism were also recognized. According to our reconstruction, the study area was controlled by a transfer fault system which affected the coastal margin producing major episodes of uplift and subsidence. Block-faulting was responsible for significant cannibalization and recycling of older deposits during the Middle Pleistocene. Such a tectonic setting can be considered the precursor scenario for the formation of the Messina Strait between Calabria and Sicily. This narrow, linear basin influences the hydrodynamic setting of sublittoral deposits along the Ionian coast of Sicily, giving rise to strong flood/ebb tidal currents. The uppermost part of the Middle Pleistocene succession recognized in the study area is indeed dominated by tide-influenced associations of sedimentary structures which most likely record the first stage of the opening of this ‘seaway’ of the central Mediterranean Sea.

New insights on the Oligo-Miocene succession bearing phosphatic layers of the Maltese Archipelago

The Maltese Archipelago sedimentary succession is nowadays very well studied and known, mostly due to the excellent exposures of the outcrops, the well-preserved calcareous microfossil content, and the cyclic lithological pattern of most of the stratigraphic intervals. Therefore, the Maltese sediments have been studied to establish updated calcareous plankton biostratigraphic schemes, and the Ras il Pellegrin section, along the western coast of Malta Island, has been chosen to host the Global Stratigraphic Section and Point of the Serravallian Stage. This paper focuses on the Maltese Oligo-Miocene succession bearing well-developed phosphatic beds, with particular attention to the evaluation of the associated sedimentary hiatuses. To achieve this goal, the calcareous nannofossils content of the marine sediments inter-bedded to the phosphatic horizons has been analysed in two key sections: Il Blata (W of the Malta Island) and Qammieh (N of the Malta Island). Furthermore, the good correspondence of the examined succession with the third-order sequences of the New Jersey passive margin, allowed a more refined definition of the intervals characterized by absence of normal marine sedimentation. Dissimilarities in the number of the phosphatic horizons characterizing the two sections have been explained supposing different locations of the two depositional areas within the sedimentary basin, probably affected by local syn-sedimentary tectonic activity. Finally, the correlation of the two investigated successions with the stable Oxygen isotope curve provided relationships between the origin of the phosphatic layers and global sea-level changes.

Quaternary marine terraces and fault activity in the northern mainland sectors of the Messina Strait (southern Italy)

The Strait of Messina area has been affected by strong uplift, which caused the development of spectacular sequences of Pleistocene coastal marine terraces. A new detailed mapping of the terraced surfaces has been carried out on both sides of the northern sector of the Strait. In the Calabrian side, a complete sequence of ten fluvial-coastal terraces has been recognized at elevations ranging from 40 to 520 m a.s.l. and dated from 60 to 330 ka. The series is partly displaced by normal faults bordering the structural high of Campo Piale and the estimated uplift rates change in time and space in response to the fault activity. They range from 1.5 mm/yr for the period 330-200 ka, on the Campo Piale high, to 0.8 mm/yr for the period 125-60 ka, on the hanging wall of the Scilla Fault that borders the Campo Piale high to the north. The constant elevation of the I order terrace suggests an uniform uplift rate of 1.4 mm/yr along the Villa San Giovanni coastal area and the termination of the western sector of the Scilla Fault, even though the offshore activity of segments belonging to the same system is not excluded. In the Sicilian side, six orders of terraces have been recognized on the Capo Peloro promontory. Their inner edges range in elevation from 30 m to 170 m a.s.l., the age attribution varies from 60 to 240 ka. The series is tilted of ~10-15° southward due to the activity of the Mortelle Fault, bounding the promontory to north. The elevation of inner edges suggests that the uplift process, characterized by rate of 0.8 mm/yr, has undergone an acceleration during the late Pleistocene, probably related to activity of offshore structures.