Synsedimentary tectonics and sedimentation in the Tertiary Piedmont Basin, Northwestern Italy

The Late Oligocene/Early Miocene tectonic and sedimentary evolution of the eastern sector of the Langhe Sub-Basin (Tertiary Piedmont Basin) is proposed and discussed. The area is located between the villages of Roccaverano and Mombaldone, along the western side of the Bormida di Spigno River Valley (see attached geologic map). Synsedimentary tectonics strongly influenced the geologic evolution of the region during the time span examined, being particularly evident at three specific "times" that were chosen as models. During "Time 1" (Late Oligocene) gentle anticlines, aligned WNW-ESE and NW-SE, started to form, affecting only hemipelagic mudstones and creating structural highs that controlled the areal distribution of both turbidites (i.e. T. Ovrano High) and a thick pelitic slump sheet (i.e. M. Pisone High). During "Time 2" (Aquitanian) the C. Mazzurini Half-Graben developed, separated by W-E and WNW-ESE growth faults from the M. Ovrano High to the north and gradually connecting, through a gently sloping ramp, with the Rocchetta High to the south. Turbidity currents and debris flows were channeled into the half-graben, while hemipelagic limestones were deposited onto the adjacent higher areas. During "Time 3" (Early Burdigalian) the depocenter of the depression shifted southward, while the half-graben evolved into a wide trough (Piantivello Trough) characterized by turbidites. Subsequently, the strongly irregular topography was progressively leveled to the quite homogeneous landscape on which the Cortemilia Formation (Late Burdigalian) was deposited

Néotectonique des fonds sous-marins de la Dorsale Méditerranéenne en mer Ionienne au cours du Pléistocene moyen et supérieur

The «area 3» (i. e. an océanographie investigation area) of the Mediterranean Ridge is typical of the Ionian Sea «cobblestone topography». It has been the objet of the R/V campaigns .'Melville (1978), Eastward (1978) and Bannock (1981). The bathymetrical and geological data gathered during these three cruises allow the determination of the age and the interpretation of the genesis of the two enigmatic landforms of the submarine bottoms : the «Ares crater» and the «Prometheus dome». The karstic (or submarine karst) origin — direct or indirect - proposed as hypothesis in order to explain this closed depression hollow, cannot be maintained anymore. Actually this is the result of the extrusion to the surface of the Mid-Cretaceous «argille scagliose». The diapirism affecting the incompétent material squeezed from deep levels of the sedimentary cover, looks as being attributable to the compression undergone by the Mediterranean Ridge. The event is post Pliocene/ lower Pleistocene which found themselves affected and earlier than sapropel S 8 that fossilizes the extrusion, within the depression. This extrusion is diachronous since the Prometheus dome - made of the same materiel — results from an even earlier setting, slightly anterior to 40 000 BP.«L'area 3» (si tratta di un perimetro di investigazione oceanografica) délia Dorsale Mediterranea e molto rappresentativa délia «cobblestone topography» nel Mar Ionio. Qui si sono fatte le campagne délie navi oceanografiche : Melville (1978), Eastward (1978) e Bannock (1981). I dati délia batimetria e délia geologia, raccolti nelle tre crociere, permettono di determinare l'età e di spiegare la genesi délie due forme di relievo enigmatiche dei fondi sottomarini : il «cratère» di Ares e il «duomo» di Prometeo. L'origine carsica (o didisso- luzione), diretta o indiretta - dato per ipotesi per spiegare questa depressione chiusa - non puo essere mante- nuta. Essa risulta dall'estrusione délie «argille scagliose» del Cretaceo medio. Il diapirismo che assumo questo materiale incompétente, uscito dei livelli profondi délia copertura sedimentaria, sembra imputabile alla compres- sione che affetta la Dorsale Mediterranea. Questo avvenimento è posteriore al Pliocene e al Pleistocene inferiore (che sono interessati) e anteriore al sapropel S 8 che fossilizza l'estrusione, nel seno délia depressione. Questa estrusione è diachrona poiche il duomo di Prometeo, formato da questo stesso materiale, risulta da una messa in posto ancora più récente, poco anteriore a 40 000 BP.Le «secteur 3» (il s'agit d'un périmètre d'investigation océanographique) de la Dorsale Méditerranéenne est très représentatif de la «cobblestone topography» en Mer Ionienne. Il a fait l'objet de trois campagnes de recherches des navires océanographiques : Melville (1978), Eastward (1978) et Bannock (1981). Les données bathy métriques et géologiques recueillies au cours de ces trois croisières permettent de déterminer l'âge et d'interpréter la genèse de deux formes de relief énigmatique s des fonds sous-marins : le «cratère» d'Ares et le «dôme» de Prométhée. L'origine karstique (ou dissolvante), directe ou indirecte - avancée à titre d'hypothèse pour expliquer cette dépression fermée — ne peut plus être retenue. Celle-ci résulte, en effet, de l'extrusion en surface des «argille scagliose» du Crétacé moyen. Le diapirisme qui affecte ce matériel incompétent, issu des niveaux profonds de la couverture sédimentaire, paraît imputable à la compression subie par la Dorsale Méditerranéenne au cours du Quaternaire. L'événement est postérieur au Pliocène et au Pleistocene inférieur qui se trouvent affectés par la déformation et antérieur au sapropèle S 8 qui fossilise l'extrusion au sein de la dépression (carotte 23). Cette extrusion est diachrone puisque le dôme de Prométhée, constitué de ce même matériel, résulte d'une mise en place encore plus récente, légèrement antérieure à 40 000 BP.Malinverno A., Parisi E., Salvatorini G., Clauzon Georges, Cita M. B., Bossio A., Broglia C., Camerlenghi A., Catrullo D., Colombo A., Croce M., Giambastiani M., Gnaccolini M., Kastens K., Mac Coy F. Néotectonique des fonds sous-marins de la Dorsale Méditerranéenne en mer Ionienne au cours du Pléistocene moyen et supérieur. In: Méditerranée, troisième série, tome 48, 2-1983. Evolution récente des paysages de la péninsule hellénique. pp. 51-63