Magnetostratigraphy of the Zobzit and Koudiat Zarga sections (Taza-Guercif basin, Morocco): implications for the evolution of the Rifian Corridor

Magnetostratigraphic analyses for two Neogene `post-nappes' successions of the Taza-Guercif basin enable a reliable correlation of the sedimentary sequence to the astronomical polarity time scale. Rock magnetic analyses indicate that hematite is the dominant carrier of the magnetisation in the marine marls of the Melloulou Formation, whereas both magnetite and hematite contribute to the NRM of the near-shore and continental sediments of the Kef Ed Deba and Bou Irhardaiene Formations. Anisotropy of magnetic susceptibility (AMS) measurements indicate that the maximum axes of the magnetic fabric are aligned in a direction SW-NE. This suggests that the AMS is tectonically induced, related to SE-NW compression, in agreement with the major fold and fault systems in the basin. Our magnetostratigraphic correlation shows that the oldest marine sediments in the basin, which are related to the development of the Rifian Corridor, are dated at approximately 8 Ma. Between 7.2 and 7.1 Ma, just after the Tortonian/Messinian boundary, an important shallowing of the Taza-Guercif basin takes place. This shallowing phase is primarily related to active tectonics, although a small glacio-eustatic sea level lowering also took place. Our results indicate that at least the Taza-Guercif basin, and perhaps the entire Rifian Corridor, became emerged at an age between 6.7 and 6.0 Ma. Continental deposits, separated from the underlying deposits by a considerable hiatus of 700 kyr, extend into the Pliocene (up to 4.7 Ma)

Astronomical dating of a tectonic rotation on Sicily and consequences for the timing and extent of a middle Pliocene deformation phase

A detailed palaeomagnetic study of long and continuous middle Pliocene sections from the Caltanisetta basin on Sicily reveals a differential clockwise rotation occurring around 3.21 Ma. The rotation appears to be a rapid event (80,000100,000 years) which suggests that the responsible tectonic processes also occur rapidly. Its timing corresponds closely to the transition from the Trubi to the Narbone Formation at 3.19 Ma. This transition marks a major change in sedimentary environment on Sicily and in Calabria, and it is coeval, for instance, with the onset of sapropel formation in the eastern Mediterranean. Apparently it marks a synchronous and centraleastern Mediterranean-wide event. Data from the oldest sediments overlying the Tyrrhenian basement (ODP Leg 107) suggest an acceleration in opening of the Tyrrhenian Sea during the middle Pliocene. We speculate that this acceleration is related to a transpressional event in the Sicilian fold-and-thrust belt and extension which formed troughs in the foreland, the Strait of Sicily. Thrust imbrication accompanying the transpressional event on Sicily induced the middle Pliocene clockwise rotation and resulted in shallowing of the Caltanisetta basin causing the change in sedimentation regime characterised by the TrubiNarbone transition. Following this middle Pliocene tectonic phase, no rotation took place in the southern Apennines, Calabria and Sicily until the middle Pleistocene (1.00.7 Ma). Ó 1998 Elsevier Science B.V. All rights reserved

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

During the 80s, a number of seminal papers were published by the Gif-sur-Yvette group of Carlo Laj and co-workers, on the late Neogene palaeomagnetic rotations of the Aegean and, in particular, of the Aegean Arc system. These studies shed new light on the tectonic evolution of the region (e.g. [1,2]). Then, similar work on the Calabrian^ Sicilian arc system established that major tectonic rotations were of very young (middle Pleistocene) age [3], and it became clear to us that it was warranted to have a closer and more detailed look at the tectonic history of the Aegean Arc. In particular, the advent of more accurate, astronomically calibrated time scales during the 90s provided the opportunity to correlate tectonic (or other, e.g. climatic) events over a large geographical area, and to constrain their age and duration and hence their (a)synchrony. This would aid in testing a dynamical model of subduction- related geodynamics of the (central) Mediterranean area [4]. Many studies, e.g. on numerical modelling of stress patterns, tomography, vertical motions and depot centre migration, and on tectonostratigraphy, have aided in testing this hypothesis (see [5] for references). Meanwhile, the accurate time control has provided increasing evidence for relatively short periods of rapid, pulsed tectonic rotations (see [5] for references and discussion). This is in contrast to a more continuous deformation over a longer time interval, as was earlier suggested by Laj et al. [1] for the western Aegean Arc

Post-early Messinian counterclockwise rotations on Crete: implications for Late Miocene to Recent kinematics of the southern Hellenic arc

Most geodynamical models for the kinematics of the central Mediterranean recognise that major tectonic rotations must have played an important role during the Neogene. The Hellenic arc is believed to have been subjected to clockwise rotations in the west and counterclockwise rotations in the east, while the southern part (Crete) shows no rotations (Kissel and Laj, 1988). Many qualitative and quantitative models are based on the idea that Crete did not rotate. We present new palaeomagnetic data which show that post-early Messinian counterclockwise rotations have occurred on Crete. The amount of counterclockwise rotation generally varies between 10º and 20º, but in central Crete much larger rotations (up to 40º counterclockwise) were found. Only a few sections did not show any rotation. The anisotropy of magnetic susceptibility (AMS) shows lineations, which are consistently WNWESE throughout Crete, indicating post-rotational WNW-ESE extension, or NNE-SSE compression. The observed counterclockwise rotations are consistent with the results of tectonic modelling by Ten Veen and Meijer (1998). The latter study compares the late-Middle Miocene to Recent kinematics with modelled intra-plate stresses for various possible distributions of plate boundary forces. Observations reveal that motion along left-lateral and right-lateral faults occurred during the Pliocene. The model analysis shows these motions to be consistent with transform resistance along the eastern segment of the overriding margin. The counterclockwise block rotations observed by us are probably a consequence of displacements along the left-lateral and right-lateral faults and could reflect a similar tectonic regime that involved transform resistance. Ó 1998 Elsevier Science B.V. All rights reserved

Neogene evolution of the Aegean arc: paleomagnetic and geodetic evidence for a rapid and young rotation phase

New paleomagnetic data of the entire Aegean outer-arc are presented. The results indicate a young Pleistocene and rapid clockwise rotation phase in the western Aegean arc, covering at least Zakynthos and the Peloponessos. The eastern Aegean arc, incorporating Kassos, Karpathos and Rhodos, also experienced Pleistocene anticlockwise rotations. The anisotropies of the magnetic susceptibility (AMS) data are in agreement with arc-parallel extension in the south and south-eastern Aegean arc and arc-normal compression in the north-west, in agreement with structural and geodetic observations. We compare the paleomagnetic results with the present-day pattern of rotation as computed from geodetic data, and we find good agreement. The onset of the Pleistocene rotations coincides with the beginning of uplift and a change in the stress pattern of extension. We compare our findings with existing models for the Aegean area

Paleomagnetism and astronomically induced cyclicity of the Armantes section; a Miocene continental red sequence in the Calatayud-Daroca basin (Central Sapin)

The Armantes section is a red-bed sequence consisting of a regular altemation (10 m scale) of reddish silts and pink/white limestones.In between these limestones, a smaller-scale bedding (2-3 m scale) is intercalated, characterised by varying carbonate content and related differences in erosion resistance. An earlier correlation of the magnetic polarity sequence of the Armantes section to the geomagnetic polarity time scale (GPTS) suggested a periodicity of 111 kyr for the large-scale cyclicity (Krijgsman et al., 1994b). The carbonate, gamma-ray and susceptibility records indicate that 4 to 5 small-scale cycles are developed in one large-scale cycle, showing that the small-scale cyclicity is related to precession and thus caused by climate forcing. We suggest that the precipitation of the carbonates is most likely related to rising ground-water levels and an increase of evaporation. This implies that the thick limestone beds would correlate to eccentricity maxima and the smaller-scale limestone beds to precession minima. Rock magnetic experiments show that the NRM in the Armantes section results from the presence of hematite and magnetite/maghemite.The relative contribution of hematite is strongly related to the lithology. Hematite is the dominant carrier in the limestones, while in the silts magnetite/maghemite prevail

Про необхідність використання іноземного досвіду мікрострахування та гарантування кредитів малому підприємству в Україні

У статті йдеться про світовий досвід використання гарантійних установ для підтримки малого підприємництва. Проаналізовано основні параметри діяльності фондів гарантування кредитів та інститутів мікрострахування. Визначено можливості впровадження схем гарантування та мікрострахування підприємств малого бізнесу в Україні. Ключові слова: кредит, фінансування, підприємництво, малий бізнес, гарантія, фонд, банківська система, страхування, забезпечення, мікрострахування.В статье исследован мировой опыт использования гарантийных учреждений для поддержки малого предпринимательства. Проанализированы основные параметры деятельности фондов гарантирования кредитов и институтов микрострахования. Определены возможности внедрения схем гарантирования и микрострахование предприятий малого бизнеса в Украине. Ключевые слова: кредит, финансирование, предпринимательство, малый бизнес, гарантия, фонд, банковская система, страхование, обеспечение, микрострахование.In the article research of world experience of the use of guarantee establishments is conducted for support of small enterprise. The basic parameters of activity of funds of guaranteeing of credits are analysed and institutes of mikroinsurance. Possibilities of introduction of charts of guaranteeing are certain and mikroinsurance of enterprises of small business in Ukraine. Key words: credit, finance, entrepreneurship, small business, the guarantee fund, banking, insurance, security, micro-insurance

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

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. Ó 1998 Elsevier Science B.V. All rights reserved

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