1,721,113 research outputs found
Biostratigraphy and high-resolution sequence stratigraphy in shallow water Cretaceous carbonates (San Lorenzello, Southern Italy).
No full textBiostratigraphy and high-resolution sequence stratigraphy in shallow water Cretaceous carbonates (San Lorenzello, Southern Italy.
No full textEarly Cretaceous dendritic shrub-like fabric in karstified peritidal carbonates from southern Italy
No full textLower Cretaceous (Valanginian) dendritic microfabrics occur in karstic cavities within fine-grained shallowmarine
platform carbonates at San Lorenzello, southern Italy. They form dense micritic masses and clusters,
generally oriented perpendicularly to cavity surfaces, surrounded by layered sparry cement. Individual dendrites,
typically sub-millimetric in size, have highly irregular margins and form distinctive shrub-like masses ranging
from compact and squat, to elongate and highly branched. The centimetric and irregularly elongate cavities
appear to have formed through subaerial exposure, and are almost entirely filled by the micritic dendrites and
associated sparry crusts. In size, shape and micritic composition, the dendrites broadly resemble a variety of
similar fabrics, including hot spring travertine shrubs and calcified microfossils such as Cambrian Angusticellularia,
which has analogs in present-day lacustrine calcified cyanobacteria. However, the San Lorenzello dendrites differ
in occupying small cavities. This cryptic microkarstic dripstone setting, together with the often regular spacing
and appearance of these dendritic fabrics, may be more consistent with an abiotic origin. These comparisons underscore
the challenge of interpreting microdendritic carbonates fabrics in general
Carbonate ecosystem and environmental evolution during the Valanginian–Barremian: Discussion on possible controlling factors in the Apennine Carbonate Platform record (Italy)
No full textShallow-water carbonate records are often characterised by low stratigraphic resolution and poor chronostratigraphic calibration despite abundant and diversified fossil content. We present here a stratigraphic study of a Valanginian–Barremian carbonate platform section, exposed in the southern Apennines (Italy). In the San Lorenzello section, we produced a high-resolution dataset integrating sedimentology, biostratigraphy, cyclostratigraphy and sequence stratigraphy to investigate how neritic biofacies responded to palaeonvironmental and palaeoclimatic changes in the time interval after the Weissert event. Fossil assemblages and lithofacies characteristics allowed the reconstruction of the paleoenvironmental history of the section, which is part of a shallow carbonate platform influenced by waves activity, storm events and sea-level changes. The latter induced cyclic emersions of this flat-topped subtropical platform, witnessed by karstification and pedogenesis. Investigations lead to a refinement of the previous biostratigraphy, also producing a close agreement between the biostratigraphic and C-isotope position of the Valanginian–Hauterivian boundary. Numerous green algae and benthic foraminifera bioevents have been identified and six biozones have been defined and anchored to the southern Tethys biozonal schemes. We used biostratigraphy and previous C-isotope stratigraphy to correlate local to global stratigraphic events and to discuss controlling factors influenced this carbonate platform system. An eustatic control on the hierarchical organization of the superbundles, also interpreted in terms of depositional sequences, is evidenced. Most Trangressive/Regressive Facies Trends (T/RFTs) boundaries have been correlated with the “global” Sequence Boundaries and to the Cretaceous eustatic curve. A correspondence between calcareous algae and benthic foraminiferal turnover phases and long-term eustatic events is also shown
Accurate algorithms for identifying the median ranking when dealing with weak and partial rankings under the Kemeny axiomatic approach
No full textPreference rankings virtually appear in all elds of science (political sciences, behavioral sciences, machine learning, decision making and so on). The well-know social choice problem consists in trying to find a reasonable procedure to use the aggregate preferences or rankings expressed by subjects to reach a collective decision. This turns out to be equivalent to estimate the consensus (central) ranking from data and it is known to be a NP-hard problem. A useful solution has been proposed by Emond and Mason in 2002 through the Branch-and-Bound algorithm (BB) within the Kemeny and Snell axiomatic framework. As a matter of fact, BB is a time demanding procedure when the complexity of the problem becomes untractable, i.e. a large number of objects, with weak and partial rankings, in presence of a low degree of consensus. As an alternative, we propose an accurate heuristic algorithm called FAST that finds at least one of the consensus ranking solutions found by BB saving a lot of computational time. In addition, we show that the building
block of FAST is an algorithm called QUICK that finds already one of the
BB solutions so that it can be fruitfully considered to speed up even more
the overall searching procedure if the number of objects is low. Simulation
studies and applications on real data allows to show the accuracy and the
computational eciency of our proposal
Microstratigraphic approach to sequence stratigraphy of shallow water carbonates. Lower Cretaceous, Southern Apennines.
No full text1. Quantizzazione del tempo geologico. L’Esempio del limite Valanginiano/Hauteriviano (Cretacico inferiore) misurato con metodi di cronostratigrafia orbitale.
No full textMicrostratigraphic approach to sequence stratigraphy of shallow water carbonates. Lower Cretaceous, Southern Apennines.
No full textSedimentologic and stratigraphic evidences of eustatic control on shallow-water carbonates, Early Cretaceous, Southern Italy.
No full textQuantizzazione del tempo geologico. L’Esempio del limite Valanginiano/Hauteriviano (Cretacico inferiore) misurato con metodi di cronostratigrafia orbitale.
No full textCD-Rom, 4pp
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