Freeform surfaces from single curved panels Pottmann, Helmut; Schiftner, Alexander; Bo, Pengbo ...
ACM transactions on graphics,
08/2008, Volume:
27, Issue:
3
Journal Article
Peer reviewed
Open access
Motivated by applications in architecture and manufacturing, we discuss the problem of covering a freeform surface by single curved panels. This leads to the new concept of semi-discrete surface ...representation, which constitutes a link between smooth and discrete surfaces. The basic entity we are working with is the developable strip model. It is the semi-discrete equivalent of a quad mesh with planar faces, or a conjugate parametrization of a smooth surface. We present a B-spline based optimization framework for efficient computing with D-strip models. In particular we study conical and circular models, which semi-discretize the network of principal curvature lines, and which enjoy elegant geometric properties. Together with geodesic models and cylindrical models they offer a rich source of solutions for surface panelization problems.
The present study gathers a large amount of both existing and unpublished biostratigraphic data, which allows a detailed and complete definition of the stratigraphic features of the late ...Oligocene–late Miocene Maltese Archipelago sedimentary succession, recording in turn the tectonic and eustatic history of the Central Mediterranean region. We selected five sections in the Malta Island and three in Gozo, representative of the entire sedimentary succession, affected by well-known erosional surfaces, correlated to low-stands of the sea level, often associated with phoshatic layers, linked to the subsequent high-stands. The sedimentary interval, and thus the associated hiatuses, was constrained both by the bio-chronostratigraphic attribution and by the comparison with the third-order succession of the New Jersey passive margin, which shows strict analogy with the geodynamic context in which the Maltese succession deposited. The diachroneity at the base of the formations in the different sections, and the presence of intraformational unconformity/hiatuses, highlighted the role of the tectonic, which depicted a complex sedimentary basin, characterized by more distal versus more marginal sectors. Furthermore, the possibility to compare the sedimentary succession with the oxygen isotope curve connects the sedimentation interruptions, recorded within the Maltese Archipelago deposits, to global cooling events.
During a cycle of sea-level variation, coastal environments develop in different position of the continental shelf following seaward and landward shift of the coastline. They vary widely in ...character, reflecting the wide range of process-regimes that are brought about during the different stages of sea-level variations. Within this scenario, the morphology of continental shelves, mainly resulting from the combined effect of tectonic activity and eustatism, plays an important role in controlling the features and the preservation of coastal environments. Coastal deposits formed along continental shelves in the past, during different stages of sea-level changes, consist of discontinuous and thin depositional bodies, thus their reconstruction can be best carried out through the interpretation of high-resolution seismic data. Such a research approach is adopted in the present study to investigate a portion of the continental shelf of the southernmost sector of SE Sicily, in the offshore of Marzamemi village (Syracuse). The interpretation of high-resolution “Sparker” profiles allowed us to reconstruct the evolution of alluvial and lagoonal environments, established on a substratum of Pliocene or more ancient marine deposits, with the detection of several seismic units and unconformity surfaces, which have been related to alternating sedimentation and erosional processes, depicting the sea-level change framework of glacial-interglacial phases, from the late Pleistocene onward.
The middle Miocene is marked by a changeover from a warm climatic period (Miocene Climatic Optimum, ~17-14.7 Ma), to a transitional phase (Middle Miocene Climatic Transition), culminating in a cold ...stage (Icehouse Mode, ~13.8 Ma). This period is associated with a positive excursion of δ13C (“Monterey Excursion”), showing a series of δ13C maxima (CM events) highlighted by cooling peaks in the δ18O values (Mi events). DSDP Site 372 obtained a high-resolution record of the middle Miocene of the western Mediterranean (Balearic Islands), and represents one of the best marine sedimentary records for the considered time interval. In this study, high-resolution stable isotope and quantitative calcareous plankton records for the Langhian to the early Serravallian time interval are presented. The stable oxygen and carbon isotope records allowed us to recognize and chronologically frame the Mi and CM events falling between 15.82 and 13.04 Ma.
Furthermore, by integrating the stable isotope data with those obtained by the quantitative analyses of the calcareous plankton content, the three-folded climatic and environmental evolution was outlined for the considered time interval in the Mediterranean region.
During the first stage (Miocene Climatic Optimum = MCO; from 17 up to 14.55 Ma), an initial warm-surface-water, oligotrophic, high salinity and restricted environment is followed by an open marine setting (starting from 15.18 Ma) within still warm-surface-water and oligotrophic conditions. The re-opening of the connections between the Mediterranean Sea and the Indian Ocean would have likely triggered this latter environmental change.
From 14.55 to 13.75 Ma (second stage; Middle Miocene Climatic Transition; MMCT) an initial (up to 14.05 Ma) temperate-warm-surface-water and eutrophic environment occurred, followed by the onset of warm-surface-water, oligotrophic and slightly restricted marine conditions.
The third stage (Icehouse Mode = IHM; from 13.75 Ma onwards) points to the development of a cold-water, eutrophic, high salinity environment in an open-marine setting.
•We considered a DSDP site in the western Mediterranean Sea (Balearic islands).•We recognized the middle Miocene climatic evolution through stable isotope analyses.•We outlined the surface-water conditions based on calcareous plankton paleoecology.
The abundant and diverse calcareous nannofossil assemblages found in the sediments of two ODP cores from the Western (Site 975B, South Balearic Basin) and Eastern (Site 969B, Mediterranean Ridge) ...Mediterranean Sea have been taken into account for the paleoenvironmental reconstruction of the surface water conditions during the first 490kyrs immediately following the end of the Messinian Salinity Crisis, chronostratigraphically settled at 5.332Ma. The areal distribution of the calcareous nannofossils is closely linked to their ecological and environmental affinities, mostly driven by temperature, salinity, nutrients or other chemical parameters of the water masses. Hence, taxa (or groups of taxa) showing well-known ecological behaviors were considered, and different environmental evolutions were recognized for the two sectors of the Mediterranean Basin during the early Zanclean (early Pliocene). Specifically, in the Western Mediterranean a switching from a warm and oligotrophic water environment, showing normal open-marine conditions, to a colder and eutrophic one, characterized by a decrease in salinity rates and the development of a more restricted environment, can be recorded. Conversely, in the Eastern Mediterranean the environmental setting immediately following the MSC is indicative of temperate waters and normal open-marine conditions, which evolves, in the younger layers, to a warmer environment characterized by high salinity rates and typical of a restricted marine context. The timing of the environmental transitions recognized at the two sites has been set through the Principal Component Analysis. Taxa and groups of taxa reflecting precise ecological affinities have been handled together and a transition interval have been defined between 5.20/5.15Ma and 5.06/4.98Ma, and between 5.10Ma and 4.92Ma in the Western and Eastern Mediterranean, respectively.
•We considered the calcareous nannofossil assemblages of two Mediterranean ODP sites.•We outlined the surface water properties based on nannofossil paleoecology.•We showed the differences between West and East Mediterranean in the early Pliocene.•The environmental parameters driving the changes were emphasized by the PC analysis.•We rebuilt the 490kyrs-environmental evolution of two key-areas of the Mediterranean.
The accumulation of large boulders related to waves generated by either tsunamis or extreme storm events have been observed in different areas of the Mediterranean Sea. Along the eastern low-lying ...rocky coasts of Malta, five sites with large boulder deposits have been investigated, measured and mapped. These boulders have been detached and moved from the nearshore and the lowest parts of the coast by sea wave action. In the Sicily–Malta channel, heavy storms are common and originate from the NE and NW winds. Conversely, few tsunamis have been recorded in historical documents to have reached the Maltese archipelago. We present a multi-disciplinary study, which aims to define the characteristics of these boulder accumulations, in order to assess the coastal geo-hazard implications triggered by the sheer ability of extreme waves to detach and move large rocky blocks inland. The wave heights required to transport 77 coastal boulders were calculated using various hydrodynamic equations. Particular attention was given to the quantification of the input parameters required in the workings of these equations, such as size, density and distance from the coast. In addition, accelerator mass spectrometry (AMS) 14C ages were determined from selected samples of marine organisms encrusted on some of the coastal boulders. The combination of the results obtained both by the hydrodynamic equations, which provided values comparable with those observed and measured during the storms, and radiocarbon dating suggests that the majority of the boulders have been detached and moved by intense storm waves. These boulders testify to the existence of a real hazard for the coasts of Malta, i.e. that of very high storm waves, which, during exceptional storms, are able to detach large blocks of volumes exceeding 10 m3 from the coastal edge and the nearshore bottom, and also to transport them inland. Nevertheless, the occurrence of one or more tsunami events cannot be ruled out, since radiocarbon dating of some marine organisms did reveal ages which may be related to historically known tsunamis in the Mediterranean region, such as the ones in AD 963, 1329, 1693 and 1743.
The assessment of the vulnerability of a site to tsunami events should take into consideration the geomorphological setting, which is strongly determined by the stratigraphic framework of the area. ...Lampedusa island is located in the central portion of the Sicilian Channel (Mediterranean Sea, Italy), where a significant incidence of tsunamis (with wave runup above 15 m) caused by earthquakes and submarine landslides has been historically documented. This work shows the geomorphological and stratigraphic differences between the western and south-eastern sectors of Lampedusa island. This update to the geological characterization of the island was used to create 3D flooding maps according to runup steps of 5 m, 10 m, and 15 m, thus showing a homogeneous involvement of the south-eastern sector of Lampedusa. Furthermore, our study aims to provide a geomorphological-stratigraphic base for a mathematical-statistical model to create coastal flooding maps due to tsunami waves. As such, this tool is useful for evaluation of strategic infrastructure for the security of the island and the improvement of risk management in civil protection.
Understanding whether a system was unconfined, and deposited on a relatively unstructured basin-floor, or was confined by actively deforming substrate is important for the prediction of turbidite ...stratigraphy. Here we consider the Numidian turbidite system (Oligocene-Miocene) of Sicily - for many the type example of thick structureless submarine sandstones. New mapping and detailed sedimentology in the Nebrodi and Madonie Mountains (northern Sicily), allied to existing and new biostratigraphic data, challenge conventional interpretations for the Numidian system as a whole. Rather than having been deposited within an unstructured foredeep by relatively unconfined flows, we show that Numidian deposition was confined by active structures. These governed the routing of turbidity currents to create sand fairways and associated facies variations. The controlling structures include thrust-related folds together with inherited basin-floor faults. Existing models suggest that facies variations between adjacent outcrops on Sicily (and elsewhere) result from long-range stratigraphic variations being juxtaposed by later large-displacement thrusts. Our research reveals a much simpler tectonic structure but a more complex stratigraphic arrangement for the Numidian on Sicily - a characteristic of confined turbidite systems.
•New mapping, sedimentology and biostratigraphy data for Numidian of northern Sicily.•Numidian turbidite system of northern Sicily is Burdigalian in age.•Numidian system confined by active thrusts and inherited structures.•System shows short-range facies variations related to confining basin geometry.•Degree of post-Numidian thrust disruption in N Sicily previously over-estimated.
The quantitative analysis of the calcareous nannofossil content yield in the 600 m thick succession drilled at ODP Site 1123 (offshore New Zealand), considered as a reference section for the Southern ...Ocean region, allowed the recognition of 43 bioevents distributed along the last 20 Myr. The correlation with the excellent magnetostratigraphic record resulted in the attribution of numerical ages for the position of the detected horizons. Many of the marker species used in previous zonation were detected also at ODP Site 1123, but others revealed to be absent or of scarce applicability. On the other hand, the good applicability of additional events was verified and proved to be useful for the biostratigraphic subdivision and correlation. The obtained average bio- and chronostratigraphic resolution is about 0.6 Myr along the whole section, which increases to about 0.3 in the Pliocene–Holocene time interval. The final result is a detailed southern mid-to-high latitude nannofossil biochronology for the last 20 Myr, which confirms that the ODP Site 1123 succession represents a reference section for the Southern Ocean.
Understanding ancient deep‐water sedimentary systems that accumulated at complex plate boundaries requires confronting the stratigraphic record of deformed sedimentary successions by tracking ...sand‐fairways and identifying original relationships in later deformed sequences. Here, we investigate the Numidian turbidite system (early to mid‐Miocene) of Central‐East Sicily to explore a deep‐water sedimentary system deposited at an active thrust belt on the Central Mediterranean. Turbidites include multi‐metre thick‐bedded, ultra‐mature quartz sandstones that were sourced from North Africa and are now deformed and dismembered within the Apennine‐Maghrebian orogen. To date, much research has focused on the little‐deformed sections that sample discrete parts of the original turbidite pathways. Yet the bulk of these systems are represented by deformed successions and these have attracted little modern sedimentological and stratigraphic investigation. We present new data based on field mapping, sedimentological/structural fieldwork, and biostratigraphy (planktonic foraminifera and nannofossils) that focus on the Numidian turbidites of Central‐East Sicily. Thickness and facies variations, together with evidence of large‐scale sediment bypass and local substrate reworking, characterize the Numidian turbidites of the study area, consistent with a partially confined turbidite system. Our work demonstrates that the Numidian turbidite system accumulated across active structures and these provided tortuous, evolving corridors through which turbidity currents were routed, transporting coarse sand over many hundreds of km. These results provide insight on structurally confined turbidites in analogous tectonic settings and demonstrate the need to seek sedimentological and stratigraphic data from deformed and dismembered parts of deep‐water systems.
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