Integrated stratigraphy and astronomical calibration of the Serravallian/Tortonian boundary section at Monte Gibliscemi (Sicily, Italy)

Results are presented of an integrated stratigraphic (calcareous plankton biostratigraphy, cyclostratigraphy and magnetostratigraphy) study of the Serravallian=Tortonian (S=T) boundary section of Monte Gibliscemi (Sicily, Italy). Astronomical calibration of the sedimentary cycles provides absolute ages for calcareous plankton bio-events in the interval between 9.8 and 12.1 Ma. The first occurrence (FO) of Neogloboquadrina acostaensis, usually taken to delimit the S=T boundary, is dated astronomically at 11.781 Ma, pre-dating the migratory arrival of the species at low latitudes in the Atlantic by almost 2 million years. In contrast to delayed low-latitude arrival of N. acostaensis, Paragloborotalia mayeri shows a delayed low-latitude extinction of slightly more than 0.7 million years with respect to the Mediterranean (last occurrence (LO) at 10.49 Ma at Ceara Rise; LO at 11.205 Ma in the Mediterranean). The Discoaster hamatus FO, dated at 10.150 Ma, is clearly delayed with respect to the open ocean. The ages of D. kugleri first and last common occurrence (FCO and LCO), Catinaster coalitus FO, Coccolithus miopelagicus last (regular) occurrence (L(R)O) and the D. hamatus=neohamatus cross-over, however, are in good to excellent agreement with astronomically tuned ages for the same events at Ceara Rise (tropical Atlantic), suggesting that both independently established timescales are consistent with one another. The lack of a reliable magnetostratigraphy hampers a direct comparison with the geomagnetic polarity timescale of Cande and Kent (1995; CK95), but ages of calcareous nannofossil events suggests that CK95 is significantly younger over the studied time interval. Approximate astronomical ages for the polarity reversals were obtained by exporting astronomical ages of selected nannofossil events from Ceara Rise (and the Mediterranean) to eastern equatorial Pacific ODP Leg 138 Site 845, which has a reliable magnetostratigraphy. Our data from the Rio Mazzapiedi-Castellania section reveal that the base of the Tortonian stratotype corresponds almost exactly with the first regular occurrence (FRO) of N. acostaensis s.s. as defined in the present study, dated at 10.554 Ma. An extrapolated age of 11.8 Ma calculated for the top of the Serravallian stratotype indicates that there is a gap between the top of the Serravallian and the base of the Tortonian stratotype, potentially rendering all bio-events in the interval between 11.8 and 10.554 Ma suitable for delimiting the S=T boundary. Despite the tectonic deformation and the lack of a magnetostratigraphy, Gibliscemi remains a candidate to define the S=T boundary by means of the Tortonian global boundary stratotype section and point (GSSP)

The 'Tortonian salinity crisis' of the eastern Betics (Spain)

The late Miocene depositional history of the Lorca and Fortuna basins, both occupying an internal position in the eastern Betics of Spain, is marked by a regressive sequence from open marine marls, via diatomites and evaporites, to continental sediments. Based on facies similarities, these evaporites have often been correlated to the well-known Mediterranean evaporites of the Messinian salinity crisis, although this correlation was never substantiated by reliable chronological data. In this paper, we present an integrated stratigraphy of this regressive sequence which shows that the evaporites of the Lorca and Fortuna basins are entirely of late Tortonian age and as such have no relation with the Messinian salinity crisis. The main phase of basin restriction, resulting in deposition of diatomites and evaporites, took place at 7.8 Ma, while the last marine deposits (massive evaporites of the Lorca basin) are dated at 7.6 Ma. Consequently, this `Tortonian salinity crisis' of the eastern Betics had a duration of approximately 200 kyr, while continental deposition prevailed throughout the entire Messinian as also revealed by the fossil mammal record. The `Tortonian salinity crisis' of the eastern Betics is obviously related to a local phase of basin restriction caused by uplift of the metamorphic complexes at the basin margins, probably in concert with strike-slip activity along SW-NE trending fault systems. The development of a submarine sill is of crucial importance for the increase in salinity because it allows marine waters to continuously enter the basin at the surface while it restricts or prevents the outflow of dense saline waters at depth. Furthermore, we show that evaporite and diatomite cyclicity in these restricted basins is predominantly related to precession controlled circum-Mediterranean climate changes and that glacio-eustatic sea level changes only play a minor role. It is remarkable that the lithological sequence of the Tortonian salinity crisis mimics in many aspects that of the Messinian salinity crisis. This suggests that the diatomaceous facies is an essential part of the lithological sequence associated with basin restriction

Comment on: 'A late Pleistocene clockwise rotation phase of Zakynthos (Greece) and implications for the evolution of the western Aegean Arc'

In a recent paper, Duermeijer et al. [1] report new palaeomagnetic results from the island of Zakynthos (Greece). In many cases, these authors have re-sampled the original sites of Laj et al. [2] and the results are virtually identical to those of the earlier study except for much more precise biostratigraphic age control. Three middle Pleistocene sites (Bochali, Zakynthos town and Porto Roma) which were not sampled by Laj et al. document signi¢cant clockwise rotations. From the results obtained from these three new sites, the authors conclude that the 25° clockwise rotation of Zakynthos described by Laj et al. as affecting the entire western Hellenic margin more or less progressively over the last 5 Myr is much more recent (early Pleistocene)

A Late Pleistocene clockwise rotation phase of Zakynthos (Greece) and implications for the evolution of the western Aegean arc

Palaeomagnetic measurements have been carried out on Eocene to Pleistocene sediments on the Ionian island of Zakynthos, NW Greece. Magnetostratigraphic constraints, biostratigraphic analyses of planktonic foraminifera and calcareous nannofossils provide a reliable time frame for these deposits. The results show that no significant rotation occurred between 8.11 and 0.77 Ma, but that Zakynthos underwent a 21.6º 7.4º clockwise rotation between 0.77 Ma and Recent. Thus, our data indicate a rapid rotational event, in contrast to continuous rotation since 5 Ma as previously postulated [Laj et al., Tectonophysics 86 (1982) 45 67]. We speculate this late Pleistocene tectonic rotation phase to be linked to rapid uplift in the Greek region which results from rebound processes caused by (African) slab detachment underneath the Ionian islands. Ó 1999 Elsevier Science B.V. All rights reserved

Planktonic foraminiferal biostratigraphy of the late Neogene of Crete (Greece)

A planktonic foraminiferal zonation is established for the Middle/Upper Miocene - Pliocene interval in Crete. It is based upon the investigation of samples from 29 sections. Eight zones are distinguished. A comparison with samples from other Neogene sections from Italy, Spain, Algeria, and the islands of Karpathos, Malta and Gozo shows that the Cretan zonation is valid for intra - Mediterranean correlations. The zonal schemes established by Bizon (1967: Western Greece) and Cita (1973: DSDP cores, Leg 13) seem to be rather different from the Cretan zonation. This is certainly due to different paleontological criteria applied by these authors and different limiting species concepts rather than significant differences in the planktonic foraminiferal successions. Clues for correlating our zonal scheme with Blow's standard zonation (1969) appear to be limited. The Late Neogene sediments in Crete are thought to range from Zone N 15 to Zone N 21. The study of the faunas of some Late Neogene stratotypes, including those of the Tortonian, Messinian, Andalusian, Tabianian and Piacenzian, enables the positioning of our Cretan zonation within the chronostratigraphic scale. The systematic part of the study deals with some 40 taxa. Attention is paid to their horizontal and vertical variation. For wall structure investigations the Scanning Electron Microscope has been used

Planktonic foraminiferal biostratigraphy of the late Neogene of Crete (Greece)

A planktonic foraminiferal zonation is established for the Middle/Upper Miocene - Pliocene interval in Crete. It is based upon the investigation of samples from 29 sections. Eight zones are distinguished. A comparison with samples from other Neogene sections from Italy, Spain, Algeria, and the islands of Karpathos, Malta and Gozo shows that the Cretan zonation is valid for intra - Mediterranean correlations. The zonal schemes established by Bizon (1967: Western Greece) and Cita (1973: DSDP cores, Leg 13) seem to be rather different from the Cretan zonation. This is certainly due to different paleontological criteria applied by these authors and different limiting species concepts rather than significant differences in the planktonic foraminiferal successions. Clues for correlating our zonal scheme with Blow's standard zonation (1969) appear to be limited. The Late Neogene sediments in Crete are thought to range from Zone N 15 to Zone N 21. The study of the faunas of some Late Neogene stratotypes, including those of the Tortonian, Messinian, Andalusian, Tabianian and Piacenzian, enables the positioning of our Cretan zonation within the chronostratigraphic scale. The systematic part of the study deals with some 40 taxa. Attention is paid to their horizontal and vertical variation. For wall structure investigations the Scanning Electron Microscope has been used

The Messinian on Gavdos (Greece) and the status of currently used ages for the onset of the MSC and gypsum precipitation

The Upper Tortonian and Messinian in the already classic Metochia section on Gavdos Island (Greece) is made up of deep marine, laminated and homogeneous marls with the latter being replaced by evaporitic limestones at the very top of the section. Previous tuning of the section to the La90 time series of northern summer insolation provided ages for sedimentary cycles, polarity reversals, and bioevents. Earlier work on foraminifers and stable isotopes focused on the last 2.45 Myr of the Tortonian and the first 470 kyr of the Messinian. This study extends the stable isotope record and the set of semi-quantitative data on planktonic foraminifers into the youngest 820 kyr of the section which include the precursor and initial stages of the Messinian Salinity Crisis (MSC). New and old foraminiferal oxygen and carbon isotope data have been combined into a ~25 kyr resolution record for the entire pre-evaporitic Messinian and show a major change at 6.74 ± 0.04 Ma which we interpret to reflect an abrupt change in salinity from normal marine to hypersaline and thus marks the prelude to the MSC. Field and thin-section observations on the limestones in the top of the section confirm their evaporitic origin and suggests that salinities has risen to values of >70 psu. We further discuss the biotic response to the two-step salinity increase during the Messinian. Tuning provides an age of 6.00 Ma for the base of the first evaporitic limestone on Gavdos and this age is therefore the age for the onset of the MSC in this part of the Mediterranean. An evaluation of the published ages for the MSC onset in sections Perales (SE Spain), Monticino (N Italy), and Falconara (Sicily) shows that the onset in Falconara, just as on Gavdos, begins at ~6.00 Ma with calcium carbonate precipitation, whereas in Perales and Monticino, onset begins at 5.97 Ma (similar to the currently used age of 5.971 Ma) with gypsum precipitation, i.e. some 30 kyr later than the onset of the MSC on Gavdos and Sicily (Falconara)

Late miocene magnetobiostratigraphy of Crete

Six Upper Miocene marine clay sections on Crete (Greece) have been subjected to a detailed magnetobiostratigraphic analysis. Six correlatable polarity zones are recognized and these demonstrate the regional synchrony of planktonic foraminiferal biohorizons. By way of correlation to the magnetic polarity time-scale of Lowrie and Alvarez (1981), the Cretan sequence is assigned to polarity chronozones 5 (anomaly 3A) and 6. The new chronology provides an age of 5.6 Ma for the first occurrence datum (FOD) of the Globorotalia conomiozea group in the Mediterranean, an age of 6.0 Ma for the FOD of G. menardii form 5 and an age of 6.6 Ma for the last occurrence datum (LOD) of G. menardii form 4. Correlating the polarity record of the New Zealand Blind River section (Kennett and Watkins, 1974), with the magnetic polarity time-scale provides an age of 6.0 Ma for the evolutionary appearance of Globorotalia conomiozea, which is in complete agreement with the age of 6.1 ± 0.1 Ma given by Loutit and Kennett (1979). The demonstrated diachrony of 0.4 Ma between the New Zealand FOD of G. conomiozea and its Mediterranean counterpart is explicable in view of the different nature of the two events, the one in New Zealand being evolutionary and the one in the Mediterranean migrational. The FOD of the G. conomiozea group in the*Tortonian/Messinian boundary stratotype section coincides with the level proposed by Colalongo et al. (1979) to mark the base of the Messinian. Since the FOD of the G. conomiozea group in Crete and in Sicily are most probably time-equivalent, the age of the Tortonian/Messinian boundary is fixed at 5.6 Ma. The youngest sediments incorporated in this study extend into the Gilbert chronozone and antedate the main evaporitic phase. Consequently, the Messinian evaporitic body is younger than the base of the Gilbert chronozone, the age of which is fixed at 5.3 Ma. Adopting an age of 5.0 Ma for the Miocene/Pliocene boundary would imply that evaporites and post-evaporitic Lago Mare sediments were deposited in some 300,000 years and suggests that in the central parts of the Mediterranean basins evaporites must have accumulated at rates of some 3 m per 1000 years

Mass wasting and uplift on Crete and Karpathos (Greece) during the early Pliocene related to beginning of south Aegean left-lateral strike slip tectonics

Reconstruction of the vertical motion history of Crete and Karpathos (southeastern Aegean region, Greece) from the Messinian to Recent revealed a previously poorly documented late Messinian phase of strong subsidence with rates of 50–100 cm/k.y. followed by stasis during the first 250 k.y. of the Pliocene and then by uplift of 500–700 m during the late early to early middle Pliocene. Uplift continued up to Recent albeit at a slower pace and at different rates in different areas. The lower Pliocene in Crete and Karpathos is characterized by widespread occurrences of mass-wasting deposits, which were emplaced over a period of time spanning the first 1.35 m.y. of the Pliocene. The origin of these mass-wasting deposits has long been enigmatic but is here related to uplift which started in Crete as early as ca 5 Ma. It is suggested that the beginning uplift following strong subsidence of various fault blocks until late in the Messinian is related to the onset of south Aegean strike-slip faulting. We postulate that small-scale tilting of fault blocks by trans-tensional strike-slip faulting and increased seismic activity generated slope failures and subsequent sliding of poorly cemented lower Pliocene and uppermost Messinian Lago Mare sediments overlying the terminal Miocene erosional unconformity. The absence of mass-wasting deposits after 3.98 Ma, while uplift continued, is most likely the result of progressive compaction and cementation of the increasingly deeper buried Lago Mare and lower Pliocene sediments, thereby preventing slope failure to a depth of the terminal Miocene unconformity. Hiatuses in some places in Crete and on Karpathos, however, indicate that slope failures continued to occur although on a smaller scale and less frequent than before. Connecting the change from subsidence to uplift in the earliest Pliocene with the onset of left-lateral, strike-slip tectonics in the southeastern Aegean arc would make this major strike-slip system much older (by ~2 m.y.) than the generally accepted age of middle to late Pliocene. A recently postulated scenario of “Subduction Transform Edge Propagator” (STEP) faulting to explain the south Aegean strike-slip system predicts rates, distribution, and amount of uplift as rebound to south-westward retreat of the subducted slab along a transform fault zone that is in line with our findings on Crete and Karpathos and explains the absence of compressional structures associated with the uplift, as well as the ongoing southwestward motion of Crete

Mass wasting and uplift on Crete and Karpathos during the early Pliocene related to initiation of south Aegean left-lateral strike slip tectonics

Reconstruction of the vertical motion history of Crete and Karpathos (southeastern Aegean region, Greece) from the Messinian to Recent revealed a previously poorly documented late Messinian phase of strong subsidence with rates of 50-100 cm/k.y. followed by stasis during the first 250 k.y. of the Pliocene and then by uplift of 500-700 m during the late early to early middle Pliocene. Uplift continued up to Recent albeit at a slower pace and at different rates in different areas. The lower Pliocene in Crete and Karpathos is characterized by widespread occurrences of mass-wasting deposits, which were emplaced over a period of time spanning the first 1.35 m.y. of the Pliocene. The origin of these mass-wasting deposits has long been enigmatic but is here related to uplift which started in Crete as early as ca 5 Ma. It is suggested that the beginning uplift following strong subsidence of various fault blocks until late in the Messinian is related to the onset of south Aegean strike-slip faulting. We postulate that small-scale tilting of fault blocks by transtensional strike-slip faulting and increased seismic activity generated slope failures and subsequent sliding of poorly cemented lower Pliocene and uppermost Messinian Lago Mare sediments overlying the terminal Miocene erosional unconformity. The absence of mass-wasting deposits after 3.98 Ma, while uplift continued, is most likely the result of progressive compaction and cementation of the increasingly deeper buried Lago Mare and lower Pliocene sediments, thereby preventing slope failure to a depth of the terminal Mocene unconformity. Matuses in some places in Crete and on Karpathos, however, indicate that slope failures continued to occur although on a smaller scale and less frequent than before. Connecting the change from subsidence to uplift in the earliest Pliocene with the onset of left-lateral, strike-slip tectonics in the southeastern Aegean arc would make this major strike-slip system much older (by ∼2 m.y.) than the generally accepted age of middle to late Pliocene. A recently postulated scenario of "Subduction Transform Edge Propagator" (STEP) faulting to explain the south Aegean strike-slip system predicts rates, distribution, and amount of uplift as rebound to south-westward retreat of the subducted slab along a transform fault zone that is in line with our findings on Crete and Karpathos and explains the absence of compressional structures associated with the uplift, as well as the ongoing southwestward motion of Crete. © 2008 Geological Society of America