107 research outputs found
The pre-Variscan Sequence of the Carnic Alps (Italy-Austria)
No full textThe Pre-Variscan Sequence of the Carnic Alps is exposed across the state border between north-east Italy and Austria. It includes Middle Ordovician to lower Pennsylvanian rocks that, although affected by both Variscan and Alpine orogenesesorogeny, preserve continuous and non-metamorphosed successionssequences. Depositional settings vary from shallow water to open marine environments. Remarkable is the presence of the largest Devonian reefs of Europe, and related deposits from back reef to fore-reef and basin. The field trip is organized as a pre-congress excursion of the 90th congress of the Italian Geological Society (Trieste, September 2021) and includes three days to visit the main localities of the central sector of the Carnic Alps, focusing on various aspects of stratigraphy, palaeontology and tectonics of the sequence
Hints at diapirism in Arabia Terra craters, Mars
No full textArabia Terra is a region of Mars located at the boundary between the southern highlands and the northern lowlands
and classically dominated by heavily cratered terrain. Unlike the rest of the topographic dichotomy on the planet,
in Arabia Terra the elevation transition is very gentle, falling of 4 km over a distance of 2500 km (average
slope = 0.0016). Most of the impact craters within the region display a central bulge, bearing a well preserved
stratification and a wide range of smaller morphologies like pitted cones, mounds and knobs (Franchi et al. 2013).
Images acquired by HiRISE and CTX cameras on board MRO provided a comprehensive dataset in which also
these small features can be easily recognized. These are tens of meters of diameter and tens of meters high, and
many of them show an apical orifice. They are interpreted to have worked as pathways for subsurface fluid flow
(e.g. Pondrelli et al., 2011; Rossi et al., 2008). Indeed an active underground fluid flow activity in Arabia Terra It
has been recently hypothesized (e.g. Andrews-Hanna et al, 2011) , being crater central bulges a place of sulfate
precipitation, due to local water table emergence (e.g. Franchi et al., 2013).
To date, there is no clear explanation for occurrence of central bulges surrounded by prominent depressions in
Arabia craters. In addition, in Firsoff and Crommelin craters it is possible to recognize folds and outward dipping
strata on the central bulges and their surroundings. Interestingly, a few craters with a prominent bulged floor
elsewhere in Arabia Terra do not display stratification and are not explainable as impact related structures as their
expected pristine central peak derived by hydrocode modelling is 2km lower and one third the diameter than
the actual topography (Pozzobon et al., 2013). All these evidences are not consistent with a typical lacustrine
stratigraphic environment, whether interested by sulfate precipitation or not, and suggest active deformation after
or during bulge sequences deposition.
One or – more likely - multiple layers of sulfates below the shallower levels of Arabia Terra surface need, in our
opinion, to be hypothesized in order to explain all these contrasting observations. Indeed impact cratering on
such an evaporate bearing layered target might have provided the ideal conditions of faulting, interconnectivity of
evaporatic beds and lithostatic load release to allow diapirs ascent, In turn diapirism could have been responsible
for central bulging as testified by outward dipping strata on stratified bulges, broad un-stratified bulges and folding
(see Jackson and Vendeville, 1994 for typical salt tectonics). The depth of the fluid source calculated with a fractal
method (Pozzobon et al., 2013) using the position of the small widespread mounds within Firsoff and Crommelin
craters can give a hint of the average depth of the evaportic horizons (4 km).
As further developments we plan to test and quantify our model to take into account geological evidences, possible
kinematics, rheology and stratigraphic constrains
Geology of Aeolis Dorsa alluvial sedimentary basin, Mars
No full textAeolis Dorsa is a topographic depression, ∼800 km east of Gale Crater, located along the Mars’ dichotomy boundary. This area hosts a set of fluvial sedimentary rocks displaying an exceptional record of depositional environments and fluvial channels patterns that suggest the presence of a large amount of surface and/or subsurface water. We interpreted the plain as an ancient waterlogged environment, a sedimentary basin passing into distal depositional environments. Regional mapping of the area revealed the presence of a large-scale fluvial system that points to a long-term and extensive hydrological cycle. A significant wet period with changing environmental conditions in Hesperian/Amazonian occurred in the study area diverging from the present-day climate. Our map (Main Map) contributes to the understanding of past climatic conditions on Mars. Moreover, it provides an interesting perspective for future missions looking for evidence of present-day and/or past extraterrestrial organisms as the life as we know it needs liquid water
Lochkovian (Lower Devonian) conodonts from Rio Malinfier Section (Carnic Alps, Italy).
No full textConodont data from the Rio Malinfier section, located in the Cason di Lanza area (Carnic Alps, Italy) are presented. Twelve taxa belonging to eight genera (Ancyrodelloides, Dvorakia, Icriodus, Lanea, Oulodus, Ozarkodina, Pseudooneotodus and Zieglerodina) allow to state a middle Lochkovian (Lower Devonian) age for the section. The lithological boundary between the Nölbling and the La Valute formations is dated to the transitans Zone
GEOLOGY OF MOUNT ZERMULA MASSIF (CARNIC ALPS, NE ITALY)
No full textIn Mt Zermula area rocks of Ordovician to Carboniferous age belonging to the Pre-Variscan sequence of the Carnic Alps crop out. The whole area was overturned during the Variscan orogeny and the higher parts of Mt Zermula represent Devonian shallow water rocks thrusted on top of an Upper Ordovician to Lower Carboniferous succession showing mostly basin to slope depositional environments. This distal sequence is well exposed in the southern flank of Mt Zermula and in the eastern and western sides of the study area. The lithostratigraphic units and their relationships are described. A geological map of the southern part of Mt Zermula is provided, as well as a stratigraphic scheme
Application of Sequence-Stratigraphic Concepts to Mars: Eberswalde Crater
No full textSedimentary deposits within Eberswalde Crater are generally inter- preted as having formed in a fluviolacustrine depositional environment. The Eberswalde fan delta consists of five lobes (four deltaic), the relative stratigraphy of which can be unravelled through simple cross-cutting relationships, allowing inferences to be made of the approximate water level from the transition between delta plain and delta front. Switching between different lobes is inferred to have been controlled by allogenic control. We distinguish three water-level fluctuations, possibly associated with system tracts, on which a higher order regressive trend is superimposed. The three lower-order cycles may partly reflect control by transient and/or localized processes, but the cyclic behaviour suggests the presence of climatic control
Fluvio–Lacustrine Sedimentation and Tectonic Influence, Lunae Planum (Mars)
No full textThis area of Lunae Planum (centred around 4°S and 298°E) has been studied by various authors, who have described the presence of exhumed channels (sinuous lineations), Light Layered Deposits (LLD), and detected hydrated sul- phates associated with LLDs. We performed sedimentological, geomorphological, and stratigraphic analyses of the LLDs and produced geological maps of the area. The geological maps can serve as a guide for scientific or landing site analyses, and they represent a tool for making lateral correlations and for detecting different units in the vertical dimension. Our aim is to contribute to the debate about processes associated with the presence of water, the factors controlling these processes, and the residence time of liquid water on the surface of Mars. The significant element that emerges from this work is the complex evolutionary history of the study area and, to our knowledge, the area represents a unique example on Mars of clear evidence of tectonic influence on sedimentation
Conodont diversity across the late Eifelian Kačák Episode of the southern Alpine realm (central Carnic Alps, Austria/Italy)
No full textThe polyphased Kačák Episode near the Eifelian-Givetian boundary (Middle Devonian), well documented globally, resembles other global biotic extinction events driven by climate change. High-resolution conodont biodiversity patterns from shallow marine, slope and pelagic bathymetric settings within the same basin from the Carnic Alps showthatwhile conodonts experienced diversification during the latest Eifelian ensensis Biozone, assemblages suffered extinction during the early Givetian hemiansatus Biozone. Although a similar general pattern is observed in different bathymetric settings there is a changed taxonomic composition of conodont assemblages across the stage boundary. Based on microfacies analysis this change is contemporaneous with changes in palaeoenvironmental conditions in the earliest Givetian
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