153 research outputs found
Geology and sedimentary facies of the Pliocene succession of the Baronia Mountains (Ariano Basin, southern Italy)
An up to 1500 m-thick clastic succession, the late Zanclean Baronia Synthem, has been analysed in detail in the Ariano wedge-top Basin (southern Apennine, Italy). In the Baronia Mountains the studied sediments are well exposed and laterally mappable due to young uplift and exhumation and rest unconformably on a complexly deformed pre-Pliocene substratum formed by Triassic to Miocene allochthonous units. The Baronia Synthem has been resolved into seven facies associations that are representative of distinct fluvial, deltaic, nearshore and offshore depositional environments and can be grouped into lowstand, transgressive, and highstand systems tracts. Using an integrated approach comprising original geological field mapping at 1:10,000 scale, conventional sedimentary facies analysis and a sequence stratigraphic approach, this paper provides a detailed description and interpretation of facies associations and new insights on the stratigraphic architecture and the geological history of this portion of the basin fill
Superficial and deep-seated gravity-driven deformation horizons within basinal succession: the case study of Maiolica Formation, Gargano Promontory, Southern Italy
Gravitational phenomena on the paleoslope of continental margins play a significant role both in redistribution
of sediment and formation of new structural features within sedimentary basins worldwide. Mass-transport
deposits (MTDs) represent important heterogeneities within the succession and occur on various scales (tens of
centimetres to hundreds of metres). Small- to medium-scale MTDs (up to tens of meters) act as layers of different petrophysical properties, whereas large-scale MTDs (tens to hundreds of meters) form both stratigraphic and structural discontinuities (faults, thrusts, erosional surfaces, dykes or injections) within the succession.
The Maiolica Formation, Early Cretaceous deep basinal succession cropping out in Gargano Promontory of
Southeast Italy is represented by undisturbed intervals of flat-lying thin-bedded, cherty micritic limestone
interstratified with intervals of lithologically similar, but structurally distorted beds. For this reason, the studied
outcrops provide a good opportunity to characterize the geometry and the internal deformation of small- and
medium-scale carbonate MTDs. At the outcrop scale, small- to medium-sized MTDs can be simply identified
as sheets of deformed strata alternated with packages of undeformed beds. However, several observed features such as folded stylolites with radially oriented peaks within some of these deformed packages and the presence of large vertical clastic-dyke-like bodies in the succession suggest that some of these deformed packages represent deep-seated basal gliding horizons of large-scale MTDs.
In this study, we present MTDs on two different scales that have a crucial influence on the evolution of slope
to basinal successions. Moreover, we define the features that distinguish superficial MTDs from the deep-seated
gravity-driven deformation horizons within basinal carbonates
Evolution of the Gelasian (Pleistocene) slope turbidite systems of southern Marche (Peri-Adriatic basin, central Italy)
Examples of slope channels and canyons being diverted by structurally related sea-floor topography are commonly found both on the modern seabed and in the subsurface, in deep-water fold and thrust belts but their depositional histories have rarely been documented using examples from outcrop. The synthesis of outcrop (original geological field mapping at 1:10,000 scale) and subsurface data sets from the early Pleistocene stratigraphic succession of the Peri-Adriatic basin provides a window into the overall evolutionary pattern of large intraslope turbidite systems that, during the Gelasian (2.58–1.80 Ma), shed Apennine-derived clastic sediments into the adjacent deep-water basin. Trends from mapping and paleocurrent indicators converge to indicate that the sea-floor bathymetric expression of a thrust-related anticline, the north-trending Jesi-Nereto-Zaccheo structure, likely influenced the downslope transport direction of gravity flows and sediment dispersal pattern. During early and middle Gelasian time, coarse-grained turbidite deposition occurred on the western flank of the intraslope anticline by westerly sourced, northward-flowing turbidity currents, indicating that the opposing sea-floor topography was sufficient to cause the diversion of turbidite systems, forcing them to travel near parallel to the east-facing regional paleoslope for significant distances. By very late Gelasian time, the intraslope accommodation space on the western flank of the anticline had filled and turbidites were dispersed through dip-oriented conduits incising across the crest of the underlying structure
Internal architecture of mass-transport deposits in basinal carbonates : A case study from southern Italy
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Submarine slope degradation and aggradation and the stratigraphic evolution of channel-levee systems
Two seismic-scale submarine channel–levee systems exposed in the Karoo Basin, South Africa provide insights into slope conduit evolution. Component channel fills in a levee-confined channel system (Unit C) and an entrenched channel system (Unit D) follow common stacking patterns; initial horizontal stacking (lateral migration) is followed by vertical stacking (aggradation). This architecture is a response to an equilibrium profile shift from low accommodation (slope degradation, composite erosion surface formation, external levee development, sediment bypass) through at-grade conditions (horizontal stacking and widening) to high accommodation (slope aggradation, vertical stacking, internal levee development). This architecture is likely common to other channel–levee systems
Distinguishing tectonically-and gravity-driven synsedimentary deformation structures along the Apulian platform margin (Gargano Promontory, southern Italy)
Acknowledgements This work has been supported by Reservoir Characterisation Project (www.rechproject.com) and FAR Project 2014 "Characterisation and modelling of natural reservoirs of geofluids in fractured carbonate rocks", funded by the University of Camerino, coordinator Emanuele Tondi.Peer reviewedPostprin
Inside baleen: Exceptional microstructure preservation in a late Miocene whale skeleton from Peru
Exceptionally preserved delicate baleen microstructures have been found in association with the skeleton of a late Miocene balaenopteroid whale in a dolomite concretion of the Pisco Formation, Peru. Microanalytical data (scanning electron microscopy, electron probe microanalysis, X-ray diffraction) on fossil baleen are provided and the results are discussed in terms of their taphonomic and paleoecological implications. Baleen fossilization modes at this site include molding of plates and tubules, and phosphatization. A rapid formation of the concretion was fundamental for fossilization. We suggest that the whale foundered in a soft sediment chemically favorable to rapid dolomite precipitation, allowing the preservation of delicate structures. Morphometric considerations on the baleen plates and bristles coupled with the reconstructed calcification of the latter permit speculation on the trophic preferences of this balaenopteroid whale: the densely spaced plates and the fine and calcified bristles provide evidence for feeding on small-sized plankton, as does the modern sei whale
Looking for the key to preservation of fossil marine vertebrates in the Pisco Formation of Peru: new insights from a small dolphin skeleton
The upper Neogene Pisco Formation of Peru is known worldwide as one of the most significant Cenozoic
marine vertebrate Konservatt-Lagerstätten, even featuring cetacean specimens that retain remains of soft tissues or
stomach contents. Previous works showed that biomediated precipitation of dolomite concretions around large-sized
decaying carcasses was one of the most relevant processes responsible for exceptional fossil preservation. In turn, little is
known about the modes of fossilization of well-preserved small-sized vertebrates, which are rather common in the Pisco
Formation, but mostly do not exhibit dolomite concretions. We report on a cetacean specimen, identified as belonging
to the extinct short-snouted, small dolphin species Brachydelphis mazeasi (Pontoporiidae), preserved within a late
Miocene sandy deposit at the site of Pampa Corre Viento. This specimen consists of a moderately disarticulated partial
skeleton exhibiting well-mineralized bones; it is not enclosed within a dolomite concretion, being however delimited
by an evident dark boundary in the host sediment. Scanning electron microscopy and microanalytical investigations
identify Mn-oxides and apatite as early diagenetic minerals around the skeleton. We argue that a rapid burial of the
specimen was pivotal for the preservation of the bones, and allowed the early establishment of anoxic processes for
degradation of organic matter. Coupled with availability of P in porewater, the reducing conditions and the lowered
pH allowed precipitation of Ca-phosphate while increasing Mn solubility close to the pontoporiid carcass. Mn-oxides
precipitated at the redox boundary, the latter defining the outer edge of the volume of sediment affected by altered
chemical conditions due to the decaying processes. The permeability of the sediment and the small size of the carcass
were possible factors unfavorable to extensive sulfate reduction, thus preventing the formation of a dolomite concretion
and allowing bone phosphatization. This record emphasizes the role of conditions favorable to bone mineralization in
absence of an isolating carbonate concretion, in cases of high quality preservation of small-sized vertebrates observed
in the Pisco Formation. The observation of patterns in the distribution of diagenetic minerals in the sediment enclosing
vertebrate remains without, or with limited carbonate concretions provides insights into early taphonomic processes
Stratigraphic framework of the late Miocene to Pliocene Pisco Formation at Cerro Colorado (Ica Desert, Peru)
This paper describes a 200 m-thick section of the Pisco Formation exposed at Cerro
Colorado, an important fossiliferous site in the Ica desert. In order to properly place the
fauna in its correct relative position, this study establishes the stratigraphic framework
within which the different fossil-bearing intervals of this site can be compared and may
prove invaluable in future high-resolution studies on the faunal change. Most of the Pisco
Formation deposits exposed at Cerro Colorado consist of gently dipping fine-grained
sandstones, diatomaceous siltstones and diatomites with minor ash layers and dolomites
deposited within nearshore and offshore settings. To facilitate detailed stratigraphic
correlations within the Pisco strata for a 30 km2 area, eight marker beds have been defined
and large-scale (1:10,000 scale) geological mapping conducted to determine fault positions,
styles and offsets. The geological map shows that there are two important angular
unconformities in the study area. The first one is the interformational basal unconformity of
the Pisco Formation against folded, faulted, and planated Oligo-Miocene rocks of the
Chilcatay Formation. The second is a low-angle intraformational erosional discontinuity of
up to 48 angular discordance that allows the subdivision of the Pisco stratigraphy exposed in
the study area into two informal allomembers. Dating of the exposed succession by diatom
biostratigraphy suggests that the age of the lower allomember is late Miocene, whereas the
upper allomember is late Miocene or younger
Paleoceanographic Implications of Diatom Seasonal Laminations in the Upper Miocene Pisco Formation (Ica Desert, Peru) and Their Clues on the Development of the Pisco Fossil-Lagerstätte
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