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 (Teriary 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.

THE BEGINNING OF THE PIEDMONT TERTIARY BASIN HISTORY: SOME OBSERVATIONS ON THE "ALTO MONFERRATO" AREA

The main features of the Oligocene Molare Fm. cropping out in the "Alto Monferrato" area (Piedmont Tertiary Basin, Northern Italy) are briefly summarized. Lithofacies associations and sandstone composition allow to outline the initial stage of the PTB history in the examined area

SEDIMENTAZIONE CICLICA NEL TRIAS LOMBARDO: OSSERVAZIONI E PROSPETTIVE

High-frequency cycles are widespread in the whole Triassic succession of Lombardy (Southern Alps). These cycles characterize depositional environments ranging from continental to shallow marine to basinal, with carbonate or mixed sedimentation; their thickness is from several metres to a few millimetres. They are inferred to be the result of cyclic phenomena such as eustatic and/or tectonically controlled sea level oscillations and long term to seasonal climatic changes. The time interval covered by each of these cycles spans from the "Milankovian band" to annual. The examined Triassic succession has been arranged in depositional sequences, tentatively correlated with the third order cycles of Haq et al. (1988)

THE STRATIGRAPHIC RECORD OF OLIGOCENE-EARLY MIOCENE EVENTS AT THE SOUTH-WESTERN END OF THE PIEDMONT TERTIARY BASIN

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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

ANATOMY OF A SEMIARID COASTAL SYSTEM: THE UPPER CARNIAN OF LOMBARDY (ITALY)

The mixed terrigenous-carbonate-evaporitic  S.Giovanni Bianco  Formation  and dolomitic Campolungo  Tongue  (upper part of the Breno Formation),  generally 2OO  to  3OO  m thick, are assigned  to the Late Carnian.  They  respectively  overlie lagoonal limestones  (Gorno  Fm.)  and peritidal  carbonates  (Annunciata Member of the Breno Fm.), and underlie  intraformational  breccias  and recrystallized  limestones  (Castro Fm.). Recognition of an unconformity,  ascribed  to a relative  fall of sea-level (sequence  boundary), allowed  us to subdivide the Upper  Carnian  succession  into two parts. ln the lower part (SGBL),  six lithosomes  were recognized. Red  to green  alluvial  clastics in the south-east  and south-west  pass northward  to mixed terrigenous-carbonate  coastal sediments  and finally to dolostones  deposited  in carbonate tidal flats. In the proximal sections  of the Brescia  Prealps,  renewed  north-westward  progradation  of alluvial redbeds  with  intercalated  calclithite conglomerates  points to a stage of teconic uplift. A distinct  increase  in quartz, representing a regional  petrographic  marker  followed  all  across Lombardy, indicates  deepening  of erosion  into the metamorphic wallrocks  of the volcanic  belt. A major hiatus  at the top of the SGB1  is best documented  in the northern  Presolana  area by a silcrete crust directly overlying  the Julian Annunciata Member of the Breno Formation.  In the Brembana  Valley area, the discontinuity occurs within  a greenish  siliciclastic  coastal  plain  succession, and may be traced at the top of a marker  interval of interbedded  reddish siltstones  and sandstones. The upper part (SGB2) consists  of four lithosomes. Greenish sandstones  and siltstones,  accumulating  in coastal  plains in  the south-west,  passed  northward  to mudrocks and dolostones.  In the southernmost  Camonica Valley  area,  mudrocks  are locally interbedded  with  calcarenites  containing  bored or pedogenized  lithoclasts ripped from the underlying sequence and varied  bioclasts,  restifiying to relatively  open shallow-marine conditions  during transgression. Next, thick gypsum  accumulated in coasral  salinas  barred  by locally oolitic  platform carbonates to the north. Rare sandstone lenses  occurring  in the Brembana Valley at the top of the unit conrain  exclusive rhyolitic  detritus,  indicating either  a terminal phase of explosive  volcanism  or erosion of older  felsic volcanic products

AN ANOXIC INTRAPLATFORM BASIN IN THE MIDDLE TRIASSIC OF LOMBARDY (SOUTHERN ALPS, ITALY): ANATOMY OF A HYDROCARBON SOURCE

The Ladinian rocks of Central Lombardy consist of carbonate platforms (Esino Formation) subdivided by intraplatform troughs represented either by dark, well bedded limestones, marls and dolomites of poorly oxic to anoxic environment (Perledo-Varenna and Lierna Formations), or by grey nodular cherty limestones (Buchenstein Formation). Subsidence and deposition rates were high ( >100 m/MA), both on the carbonate platform and in the anoxic intraplatform troughs. Sedimentological study of the anoxic intraplatform rocks in the Grigne Mountains has identified 12 main lithofacies with mudstone/ wackestones, both massive and laminated, forming more than 2/3 of the total thickness. Packstones and carbonate breccias, all originating or fed from the neighbouring shallow carbonate platforms, represent 6 % of the total thickness in the basin. Also the dominating micrite is thought to have originated by overproduction on the carbonate platform. Concerning the depositional processes, almost 3/4 of the total thickness is interpreted x re-sedimented. Dolomitization is widespread in the marginal parts of the basin. No benthonic macrofauna is present, and only sporadically the bottom oxygen content was sufficient to support a non skeletal infauna. Two depositional sequences have been detected, both causing emersion on the carbonare platform. The younger emersion was severe and the platform/basin system ceased to exist. The Grigne Mountains are presently arranged in three main tectonically stacked sheets. Vitrinite Reflectance, Illite Crystallinity Index, and Conodont Alteration Index, all suggest an increase of temperature within the sheets, from south to north, i.e. from the geometrically deeper to the more elevated, which has reached the field of deep diagenesis or even anchimetamorphism

Contrasting styles of (U)HP rock exhumation along the Cenozoic Adria-Europe plate boundary (Western Alps, Calabria, Corsica)

Since the first discovery of ultrahigh pressure (UHP) rocks 30 years ago in the Western Alps, the mechanisms for exhumation of (U)HP terranes worldwide are still debated. In the western Mediterranean, the presently accepted model of synconvergent exhumation (e.g., the channel-flow model) is in conflict with parts of the geologic record. We synthesize regional geologic data and present alternative exhumation mechanisms that consider the role of divergence within subduction zones. These mechanisms, i.e., (i) the motion of the upper plate away from the trench and (ii) the rollback of the lower plate, are discussed in detail with particular reference to the Cenozoic Adria-Europe plate boundary, and along three different transects (Western Alps, Calabria-Sardinia, and Corsica-Northern Apennines). In the Western Alps, (U)HP rocks were exhumed from the greatest depth at the rear of the accretionary wedge during motion of the upper plate away from the trench. Exhumation was extremely fast, and associated with very low geothermal gradients. In Calabria, HP rocks were exhumed from shallower depths and at lower rates during rollback of the Adriatic plate, with repeated exhumation pulses progressively younging toward the foreland. Both mechanisms were active to create boundary divergence along the Corsica-Northern Apennines transect, where European southeastward subduction was progressively replaced along strike by Adriatic northwestward subduction. The tectonic scenario depicted for the Western Alps trench during Eocene exhumation of (U)HP rocks correlates well with present-day eastern Papua New Guinea, which is presented as a modern analog of the Paleogene Adria-Europe plate boundary

The oldest ceratosaurian (Dinosauria: Theropoda), from the Lower Jurassic of Italy, sheds light on the evolution of the three-fingered hand of birds

The homology of the tridactyl hand of birds is a still debated subject, with both paleontological and developmental evidence used in support of alternative identity patterns in the avian fingers. With its simplified phalangeal morphology, the Late Jurassic ceratosaurian Limusaurus has been argued to support a II–III–IV digital identity in birds and a complex pattern of homeotic transformations in three-fingered (tetanuran) theropods. We report a new large-bodied theropod, Saltriovenator zanellai gen. et sp. nov., based on a partial skeleton from the marine Saltrio Formation (Sinemurian, lowermost Jurassic) of Lombardy (Northern Italy). Taphonomical analyses show bone bioerosion by marine invertebrates (first record for dinosaurian remains) and suggest a complex history for the carcass before being deposited on a well-oxygenated and well-illuminated sea bottom. Saltriovenator shows a mosaic of features seen in four-fingered theropods and in basal tetanurans. Phylogenetic analysis supports sister taxon relationships between the new Italian theropod and the younger Early Jurassic Berberosaurus from Morocco, in a lineage which is the basalmost of Ceratosauria. Compared to the atrophied hand of later members of Ceratosauria, Saltriovenator demonstrates that a fully functional hand, well-adapted for struggling and grasping, was primitively present in ceratosaurians. Ancestral state reconstruction along the avian stem supports 2-3-4-1-X and 2-3-4-0-X as the manual phalangeal formulae at the roots of Ceratosauria and Tetanurae, confirming the I–II–III pattern in the homology of the avian fingers. Accordingly, the peculiar hand of Limusaurus represents a derived condition restricted to late-diverging ceratosaurians and cannot help in elucidating the origin of the three-fingered condition of tetanurans. The evolution of the tridactyl hand of birds is explained by step-wise lateral simplification among non-tetanuran theropod dinosaurs, followed by a single primary axis shift from digit position 4 to 3 at the root of Tetanurae once the fourth finger was completely lost, which allowed independent losses of the vestigial fourth metacarpal among allosaurians, tyrannosauroids, and maniraptoromorphs. With an estimated body length of 7.5 m, Saltriovenator is the largest and most robust theropod from the Early Jurassic, pre-dating the occurrence in theropods of a body mass approaching 1,000 Kg by over 25 My. The radiation of larger and relatively stockier averostran theropods earlier than previously known may represent one of the factors that ignited the trend toward gigantism in Early Jurassic sauropods

LA FORMAZIONE Dl GORNO NEI DINTORNI Dl DOSSENA E Dl GORNO (PREALPI BERGAMASCHE) ANALISI Dl UNA LAGUNA TRIASSICA

A Triassic lagoon has been identified in the Bergamasc Alps, northern Italy. It is bordered, to the south, by a volcanic mainland, with fluviatile and deltaic depositional systems, and northwards by a peritidal carbonate platform. The Triassic lagoon is characterized by mixed terrigenous and  carbonate sedimentation. Four main zones have been distinguished: Zone 1a is situated near the mouthes of the rivers and corresponds to the subaqueous part. of the  delta. Feldspatic litharenites and siltstones prevail in this area. Zone lb represents near—shore lagoonal areas situated far from the "entry—points" of the sands. This zone is characterized by intrabacinal carbonate deposits (oolitic grainstones are relatively frequent). Terrigenous mudstones are also frequent, whereas hybrid arenites and feldspatic litharenites are subordinate. Zone II is the transition zone between the area la and the central part of the lagoon. Terrigenous mudstones and intrabacinal carbonate packstones, wackestones and mudstones prevail. Feldspatic litharenites are locally frequent. Zone III represents the central part of the lagoon and is almost exclusively characterized by wackestones, carbonate mudstones and marls