Syn-Collision Folding and Multi-Layers Detachment in the Molassic Basin, Northeastern Tunisia

Tunisia had been the place of various tectonic episodes which have drawn the actual structural map of the country. The Neogene period was the most active period in which the collision contributed to the mountain ranges formation such as the Atlassic chain. The contrast of mechanical behavior between the different sedimentary units of the cover and the substratum is a determining factor that has controlled the deformation style of many folding structures. Detachment folding has been studied on the basis of field and seismic data examples from the Northeastern Tunisia. We discuss different aspects of detachment to constrain the chronology of structural events and understand the cover‒substratum relationship during the major folding phases. In the present paper, we found that the deformation style admitted previously do not reflect adequately the tectonic structure of Kechabta Neogene basin (North of Tunisia). The cover-substratum relationship study at this area revealed two major shortening phases; the first had been happened during the Upper Tortonian and the second in the Lower Quaternary. The resulting folding style is characterized by disharmonic and multi-layers detachment phenomena produced by incompetent evaporitic sequences. The two described folding phases are superimposed and testify at a large scale the continental collision which controls the North African margin during the Late Miocene to the Quaternary.

A reappraisal of the stratigraphy of the upper Miocene unit X in the Maaseik core, eastern Campine area (northern Belgium)

The stratigraphy of the Tortonian-Messinian sequence from the Maaseik core, located on the shoulder of the Roer Valley Graben (RVG) in the eastern Campine area in northern Belgium, was improved. The analysis of the marine palynomorphs (dinoflagellate cysts and acritarchs) from the uppermost part of the Breda Formation, the unnamed unit X and the basal part of the Lower Waubach Member led to the recognition of the mid to upper Tortonian Hystrichosphaeropsis obscura biozone. Therefore deposition of this entire analyzed sequence took place sometime between 8.8 to 7.6 Ma. Paleoenvironmental interpretation of the palynomorphs points to shallow marine conditions and most probably a stressed environment during the deposition of unit X. A comparison with the time equivalent stratigraphy in the nearby Belgian Campine, the Dutch RVG and the German Lower Rhine Basin allowed the identification of the Inden Formation and required a shift in the base of the Kieseloolite Formation compared to the earlier lithostratigraphic interpretation of the Maaseik core. The regional stratigraphic scheme shows the progressive northwestward extension of the river facies from the Lower Rhine during the late Tortonian.

Paleoecological observations of the corals reefs of the upper Tortonian between Viannos - Ierapetra provinces (SE Crete)

The fossilized association as well as the pétrographie material coming from a sedimentary basin (ca. 30 km2) situated at the SE part of Crete, between the Provinces Viannos and Ierapetra are studied. The fossiliferous regions are in the area of the villages Myrtos, Mournies and Gdochia. Among an important number of fossils (154 taxons): 83 Foraminifers, 19 Bivalves, 24 Gastropods, Ostracods, 3 Echinoids, 13 Anthozoans, 1 Scaphopods, 6 Bryozoans, 2 Algues etc. there are some characteristic species of the Upper Tortonian age- especially Gl. obliquus extremus (zone of G. numerosa)- found in these sediments known up today generally as Miocene. The Tortonian age are based also on the occurrence of the species: Spondylus concentricus, Chlamys submalvinea, Chlamys solarium, Gryphaea gingensis, Gryphaea gryphoides crassissima, Turritella formata pseudoimbricata, Terebralia bidentata bidentata, Pontes collegniana, Palaeoplesiastraea desmoulinsi, Tarbellastraea carryensis, Thegioastraea rosacea etc. Based on the faunal and floral association and their morphofunctional analysis, their conditions of existence etc. the author attempts to interpret the paleoenvironmental conditions during the timespan of the Upper Tortonian, like as patch reefs or micro-atolls and lagoons.

LATE MIOCENE CALCAREOUS NANNOFOSSIL STRATIGRAPHY AND BIOEVENTS CORRELATION: KALIDONIA CASE SECTION (NW CRETE, GREECE)

Calcareous nannofossils are widely used for biostratigraphic correlations. Quantitative approaches enable better understanding of reliability of bioevents. In order to refine the late Miocene stratigraphy ofNW Crete, the deposits of Kalidonia basin along its type section are here investigated. It was possible to distinguish the Tortonian/Messinian boundary by NNlla & NNllb, CN9a & CN9b, MNNlla & MNNllb biozones. Reticulofenestra pseudoumbilicus PB (Paracme Beginning) and R. rotaria FO (First Occurrence) proved to act as additional significant biohorizons improving the stratigraphie evolution of the studied paleobasin and providing a tight biochronologic framework. The Kalidonia section fully covers an undisturbed marine depositional cycle from the upper Tortonian to upper Messinian, where a predominant deep water fades (DWF) is followed by transitional sediments (TF) and the sequence closes at the top by a reefal-bioclastic fades (RF) relative to the 'Calcare di Base ' in Italy indicating the 'Messinian Salinity Crisis Event.

First record of buccinid genus Chauvetia (Mollusca: Gastropoda) from the fossil record of the New World (Miocene, Venezuela) and its paleobiogeographic implications

Until now, the buccinid genus Chauvetia was considered of European or West African origin, and is still endemic to these areas today. This paper describes the oldest representative of the genus, Chauvetia inopinata nov. sp., from the upper Burdigalian-lower Langhian transition Cantaure Formation of Venezuela. This surprising record suggests a New World tropical origin to the genus and subsequent immigration to the Old World before the earliest known Old World record, which is upper Tortonian. We postulate that this pre-late Tortonian (pre-8.12–7.42 Ma) dispersal of the tropical Gatunian west-Atlantic Chauvetia into the tropical East Atlantic European-West African Province most probably happened during the 10.71–9.36 Ma interval (early–mid Tortonian) during which the Circum-Tropical Current weakened, and the northward Intra-Caribbean Current had started, enhancing the Gulf Stream and the North Atlantic Current. This new data constitutes compelling evidence of a pre-Pliocene eastward dispersal of New World shallow marine organisms across the Atlantic.

Borings in gneiss boulders in the Miocene (Upper Tortonian) of the Sorbas Basin, SE Spain

Marine invertebrate borings are very rare in crystalline rocks, providing evidence of particular strategies producers use to colonise these unfavourable substrates. In the Sorbas Basin (Almería, southern Spain), Upper Miocene transgressive successions contain blocks of metamorphic and igneous rocks of the Nevado–Filabride Complex of the Betic Cordillera. Ichnological analysis of the embedded blocks shows the presence of two types of macroborings located in gneiss boulders, revealed to be an extraordinary case worldwide. The most abundant are regular hemispherical depressions ascribed reservedly to the well-known, mostly bivalve boringGastrochaenolites. The second one is a pouch-like depression, tapering downward, elliptical in outline, and clearly different to other non-circular-in-outline, pouch-shaped macroborings. Thus, a new ichnogenus and ichnospeciesCuenulites sorbasensishas been defined. According to the overall shape, an endolithic or semi-endolithic bivalve using chemical means to bore is suggested as the tracemaker. Colonisation could be determined by sea-level coastal dynamics, with decreasing energy during advancing transgression allowing boring, which was then stopped due to supply of fine-grained sediment that killed the borers.