The origin of rhythmic bedding in the Pliocene Trubi Formation of Sicily, southern Italy

Continental deposits from the early Pliocene lacustrine Ptolemais basin in NW Greece display rhythmical alternations of lignite and marl beds. Three parallel sections from this area are studied using magnetostratigraphy and cyclostratigraphy. The presence of the greater part of the Gilbert Chron enables the recognition of astronomical periodicities in the succession. Especially the precessional influence is evident, as it determines the lithological cycles. The continental Ptolemais composite section is correlated to the most recent astronomical time scale -and thus to the marine reference section: the Rossello composite from Sicily [C.G. Langereis, F.J. Hilgen, The Rossello composite: a Mediterranean and global reference section for the Early to early Late Pliocene, Earth Planet. Sci. Lett. 104 (1991) 211-225] -on a bed-to-bed scale. It is concluded that lignite corresponds to an insolation minimum (beige layer in the Rossello composite), and marl to an insolation maximum (grey layer in the Rossello composite). This implies a precipitation increase during insolation maxima in early Pliocene continental Greece.

Section: Phase Relation Between Lithology and Insolationsupporting

confidence: 56%

Magnetostratigraphy-based astronomical tuning of the early Pliocene lacustrine sediments of Ptolemais (NW Greece) and bed-to-bed correlation with the marine record

Vugt

Steenbrink

Langereis

et al. 1998

“…On Sicily these small-scale cycles are generally quadripartite due to the intercalation of an additional, beige-coloured, CaCO3-poor marl-bed in the white marls. The small-scale cycles were found to have an average duration of approximately 20 ka and have been interpreted in terms of climatic variations that are induced by the orbital cycle of precession [1,12,15].…”

Section: Lithostratigraphymentioning

confidence: 99%

The age of the Miocene-Pliocene boundary in the Capo Rossello area (Sicily)

Hilgen

Langereis²

1988

Detailed correlations of magnetostratigraphy, biostratigraphy and lithostratigraphy reveal that the basal Pliocene is equally complete in the Eraclea Minoa and Capo Rossello sections (Sicily) and the Singa section (Calabria), and that, in accordance with the model of the Pliocene flooding event in the Mediterranean, the deposition of the pelagic marls of the Trubi Formation started synchronously on Sicily and in adjacent Calabria. In addition, the data obtained from the Trubi in the Eraclea Minoa section allows the age of the Miocene-Pliocene boundary to be adjusted slightly from 4.83-4.84 [1] to 4.86 Ma because downward extrapolation of both sedimentation rate and average duration of small-scale sedimentary cycles in the Trubi yields this age for the boundary in this section. Linearly interpolated ages for the top of the Sphaeroidinellopsis acme and the first substantial increase in Globorotalia margaritae (the FOD of this species is non-existent in the Mediterranean Pliocene) at Eraclea Minoa arrive at 4.74 and 4.63 Ma respectively.Because of the detailed magnetostratigraphy and the very accurate dating of the Miocene-Pliocene boundary, it is preferable to select the Eraclea Minoa section as the boundary stratotype rather than the Capo Rossello section.Finally, this age of 4.86 Ma for the Miocene-Pliocene boundary suggests that the beginning of the Pliocene is connected with the termination of a series of latest Miocene glaciations and that the re-establishment of open marine conditions in the Mediterranean might be of glacio-eustatic origin.

“…The average sedimentation rate can be accurately determined on the basis of the astronomically calibrated polarity time scale (APTS) [13] and is 5.0 cm/kyr in the lower Thvera section and 4.4 cm/kyr in the upper Thvera section. The marls of the Trubi formation mainly consist of carbonates (60-80% CaCO 3) and a mixture of clay minerals [14]. Hilgen [15] recognized a long succession of small-scale sedimentary cycles--the so-called quadruplets.…”

Section: Geological Setting and Samplingmentioning

confidence: 99%

“…The zero level of the upper Thvera record is at the top of the gray layer of cycle 15. The white marls have a higher carbonate content, while the grey and beige marls are relatively poor in carbonate [16], probably due to increased continental run-off (grey) or increased African wind-blown input (beige) [14]. tion points at fields of 100-200 mT, indicating that a low coercivity mineral has reached the saturation remanence.…”

Section: Rock Magnetismmentioning

confidence: 99%

“…The sedimentation rate during the deposition of the grey and beige marls could be somewhat higher due to increased continental run-off and a constant carbonate flux [14], or somewhat lower due to increased carbonate production in the white marls while the flux of the non-carbonate fraction is constant [31]. The difference in ages between the midpoints of two subsequent grey layers [13] is the time during which one quadruplet is deposited.…”

Section: The Sicilian Lower and Upper Tht~era Recordsmentioning

confidence: 99%

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The upper and lower Thvera sedimentary geomagnetic reversal records from southern Sicily

Hoof¹,

Langereis²

1992

Detailed paleomagnetic records of the upper and lower Thvera polarity transitions have been determined from Pliocenc marine marls in southern Sicily. The dominant magnetic mineral is fine grained magnetite. The two transitions have VGP paths following a great circle passing South America and the west coast of North America. There are strong indications that the VGP paths result from smoothing of the non-antipodal stable directions before and after the transitions. The upper Thvera transitional record is preceded by two excursions and followed by a third one. The first excursion is a sedimentary artefact caused by post-depositional migration of magnetic minerals and the third one by is caused by weathering of the sediment. The upper Thvera transition from Sicily is compared with the record from Calabria, about 250 km away. The two records show similarities as well as differences: both transitions have identical VGP paths, but in Calabria the transition is recorded lower in the sediment, the first and third excursions have different characters and the second one is not present. Apparently the registration of transitions of the Earth's magnetic field in sediments is strongly influenced by smoothing and diagenetic processes after deposition.