In un paese come l`Italia, caratterizzato da una forte densità abitativa

Scuola di Dottorato in Scienze della Terra,
Dipartimento di Geoscienze, Università degli Studi di Padova – A.A. 2010-2011
DEMISE AND RECOVERY OF CARNIAN PLATFORMS: LARGE SCALE GEOMETRIES
AND MECHANISMS OF PRECIPITATION
Ph.D. candidate: GIOVANNI GATTOLIN, I course
Tutor: Dr. Nereo Preto
Co-tutor: Dr. Anna Breda
Cycle: XXVI
Abstract
During Middle Triassic, the Western Tethys was characterized by a complex paleogeography, featuring isolated carbonate
platforms and carbonate - siliciclastic deep basins. This complexity disappeared as a late Early Carnian global climatic event
increased significantly the terrigenous input to marginal basins and determined their infilling, leading to the formation of a
epeiric sea in W Tethys. The carbonate platform grown in this setting (Dolomia Principale) developed depositional geometries
on the scale of hundreds to thousands of km.
The transition from isolated carbonate buildups to the epeiric platform of the Dolomia Principale implied a major crisis of
carbonate platforms, during which the mode of carbonate precipitation changed dramatically. To depict how the changes of
shallow water carbonate precipitation influenced the depositional geometries of carbonate platforms, a quantitative three
dimensional acquisition (laser scanner, photogrammetry) of the geometry of sedimentary bodies deposited before, during and
after the Carnian crisis, coupled with facies analysis, is being performed.
Introduction
From Anisian to Carnian, high relief-isolated carbonate platforms of the Dolomites were dominated by
microbialites (Blendinger 1994; Russo et al., 1997; Keim and Schlager 1999; 2001). Those platforms
developed extreme depositional geometries, with carbonate slopes steeper than the angle of repose of
gravel, and often the lack of clear clinoforms, because the slope itself was the site of primary carbonate
production.
At the end of the Early Carnian, a climatic event, known as the Carnian Pluvial Event (CPE, Simms and
Ruffel 1989; Preto et al., 2010), resulted in a major crisis of carbonate factories. Shallow water carbonate
systems of the Dolomites switched from microbial dominated to carbonates with skeletal associations and
geometries typical of C-factories sensu Schlager (Preto and Hinnov, 2003).
The subsequent recovery of carbonate factories led to the deposition of the Dolomia Principale. This huge
carbonate platform developed depositional geometries on the scale of hundreds to thousands of kilometers
(from Switzerland to Hungary) and, together with its periplatform deposits, constituted the largest
carbonate system of the western Tethysian domain from Late Carnian to the end of Triassic (and later).
Aim
What exactly happened to carbonate platforms during the Carnian crisis, is still only partially understood.
In particular, detailed studies on the geometry of these carbonate platforms are missing.
This study aims to investigate how the changes of the mode of precipitation in shallow water carbonate
systems influenced the depositional geometries, through a quantitative three dimensional acquisition
(through laser scanning and photogrammetric techniques) and 3D geo-modeling.
Selected outcrops for the 1st year
The Lower Carnian interval was surveyed on the southern walls of the Tofana di Rozes (Falzarego valleyCortina d'Ampezzo, BL), that exposes a platform-to-basin transect of pre- and post-crisis platforms (Preto
and Hinnov, 2003; Breda et al., 2009). The other selected site is the ca. 30 m thick prograding carbonate
body deposited during the Carnian crisis cropping out at Rif. Dibona (Preto and Hinnov, 2003).
Methods
The geometry of the selected carbonate body cropping out at Rifugio Dibona was acquired through
terrestrial LIDAR while for Tofana di Rozes, due to outcrops conditions, photogrammetry was preferred.
The LIDAR and photogrammetric data were processed to produce a 3D geometrical models of the
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Scuola di Dottorato in Scienze della Terra,
Dipartimento di Geoscienze, Università degli Studi di Padova – A.A. 2010-2011
outcrops. At Tofana di Rozes mapping of the studied area was carried out with the aid of a handheld PC
coupled with a differential GPS. At both sites rock samples were taken for thin-sections analysis. Facies
and facies associations were defined in the field and through petrographic analysis, using standard
carbonate sedimentology methods (e.g., Tucker and Wright, 1990; Flügel, 2004). At the moment 3D
models of selected carbonate bodies are being built. The workflow to a 3D geological model goes as
follows: (1) a volume of interest is identified, (2) facies association boundaries are traced on the
geometrical model, basing on visible bedding planes, stratigraphic logs, and surfaces traced in the field
where available, then (3) such traces are interpolated to generate surfaces, and finally (4) the resulting
volumes are populated with geological parameters of interest.
Preliminary results and future plans
At Tofana di Rozes the debated limit between Cassian Dolomite and the first member of Heiligkreuz Fm.
was identified with confidence. This finding, together with field observations, geometrical model
acquisition and elaboration permitted to define a sedimentological model for the basal part of Heiligkreuz
Fm. that will be reproduced on a 3D model. It consists of numerous tens-hundreds of meters large
carbonate mounds grown on a pre-existing inclined surface, and intercalated with an alternation of
skeletal carbonates (grainstones and packstones) and siltites-arenites. This system soon evolved into a
carbonate-clastic ramp. To define the precise age of the onset of the Heiligkreuz Fm. carbon isotope
stratigraphy and palynostratigraphic analyses will be carried out.
At Rifugio Dibona a sedimentological model of the ca. 30 m thick prograding body is being defined and
modeled on the basis of LIDAR and petrographic analysis. As at Tofana, this interval comprises
carbonate mounds with skeletal intra-mound sediments; the prograding body we are studying is part of
the intra-mound unit. To better characterize sedimentary facies constituting this body,
catodoluminescence and porosity estimations (based on image analysis of petrographic thin sections) will
be carried out.
Field data suggest that even if carbonate bodies cropping out at Tofana di Rozes and Rif. Dibona are
really neighbouring (1,5 Km far from each other) and practically coeval, they were independent at time of
deposition, having provenances from opposite sides of the basin.
Facies mapping and analysis, geometry acquisition via photogrammetry and 3D modeling will be applied
to the Dolomia Principale margin and slope (De Zanche et al., 2000; Gianolla et al., 2003) cropping out at
Portella Pass (Cave del Predil, Tarvisio, UD).
References
BLENDINGER, W. (1994). The carbonate factory if Middle Triassic buildups in the Dolomites, Italy: a
quantitative analysis. Sedimentology, 41, 1147-1159.
BREDA, A., PRETO, N., ROGHI, G., FURIN, S., MENEGUOLO, R., RAGAZZI, E., FEDELE, P.,
GIANOLLA, P. (2009). The Carnian Pluvial Event in the Tofane area (Cortina d'Ampezzo, Dolomites,
Italy). Geo Alp, 6, 80-115.
DE ZANCHE V., GIANOLLA P., ROGHI G. (2000). Carnian stratigraphy in the Raibl/Cave del Predil
area (Julian Alps, Italy). Eclogae geologicae Helvetiae, 93, 331-347.
FLÜGEL, E. (2004). Microfacies of carbonate rocks. Springer-Verlag, Berlin-Heidelberg (Germany), 976
pp.
GIANOLLA P., DE ZANCHE V., ROGHI G. (2003). An Upper Tuvalian (Triassic) platform-basin
system in the Julian Alps: the start-up of the Dolomia Principale (Southern Alps, Italy). Facies,
49,135-150.
KEIM, L. and SCHLAGER, W. (1999). Automicrite facies on steep slopes (Triassic, Dolomites, Italy).
Facies, 41, 15-25.
KEIM, L. and SCHLAGER, W. (2001). Quantitative compositional analysis of a Triassic carbonate
platform (Southern Alps, Italy). Sedimentary Geology, 139, 261-283.
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Scuola di Dottorato in Scienze della Terra,
Dipartimento di Geoscienze, Università degli Studi di Padova – A.A. 2010-2011
PRETO, N. and HINNOV, L.A. (2003). Unravelling the origin of shallow-water cyclothems in the Upper
Triassic Dürrenstein Fm. (Dolomites, Italy). Journal of Sedimentary Research, 73, 774-789.
RUSSO, F., NERI, C., MASTANDREA, A. AND BARACCA, A. (1997). The mud mound nature of the
Cassian platform margins of the Dolomites. A case history: The Cipit boulders from Punta Grohmann
(Sasso Piatto Massif, Northern Italy). Facies, 36, 25-36.
SIMMS, M.J., RUFFELL, A.H. (1989). Synchroneity of climatic change and extinctions in the Late
Triassic. Geology, 17, 65–268.
TUCKER, M.E. and WRIGHT, V.P. (1990). Carbonate sedimentology. Blackwell, Oxford, 492 pp.
SUMMARY LAST YEAR’S ACTIVITY
Courses:
SALMASO L., ARBORETTI R., CORAIN L., BONNINI S. “Statistica Applicata alla Sperimentazione Scientifica (Edizione
2011)”, Centro Studi per l'Ambiente Alpino, Università degli Studi di Padova.
PRETO N. “Petrologia dei Carbonati Avanzata”, Dipertimento di Geoscienze, Università degli Studi di Padova.
REMONDINO F., RIZZI A., MENNA F., AGUGIARO G. “Fotogrammetria e 3D Laser Scanning”, Dipartimento di
Geoscienze, Università degli Studi di Padova.
JENKYNS H.C. “Elements, Isotopes and Organic Matter in Chemostratigraphy: Applications, Limitations and Implications for
Global Environmental Change”, Dipartimento di Scienze della Terra, Università di Ferrara.
DANIELETTO E. and BOESSO S. “Corso introduzione alla biblioteca” e “Gestire le bibliografie con Refworks”, Biblioteca
del Dipartimento di Geoscienze, Università degli Studi di Padova.
Communications:
MARANGON A., GATTOLIN G., FRANCESCHI M., PRETO N. (2011). Il Latemar, un atollo tropicale di 240 milioni di
anni fa. Expo delle Dolomiti, Longarone (BL).
PRETO N., DAL CORSO J., GATTOLIN G., ROGHI G., BIRGEL D., PANCOST R., PECKMANN J., WESTPHAL H.
(2011). Organic compounds in shales and carbonates of the "upper Cassian beds" (Heiligkreuz Fm.) of the Dolomites: a
preliminary report. Cassian beds Workshop, Bozen.
PRETO N., BIRGEL D., GATTOLIN G., MONTINARO A., PECKMANN J., WESTPHAL H. (2011). Extreme
supersaturation promoted whitings in Early Triassic seawater. 28th IAS Meeting, Zaragoza.
FRANCESCHI M., PRETO N., GATTOLIN G., MARANGON A., VISEUR S., PALERMO D., NARDON S. (2011). 3D
modeling of a complex carbonate platform: the case of the Latemar (Middle Triassic, Dolomites). 28th IAS Meeting, Zaragoza.
MARANGON A., GATTOLIN G., FRANCESCHI M., DELLA PORTA G., PRETO N. (2011). An upper Anisian microbial
platform: the Latemar (Western Dolomites, Italy). 28th IAS Meeting, Zaragoza.
Posters:
JALIL N.E., BELVEDERE M., BREDA A., GATTOLIN G., DYKE G.J. (2011). A varied ichnocoenosis in the Cretaceous
Kem Kem beds of Morocco. SVP 71th annual meeting, Las Vegas.
GIANOLLA P., STEFANI M., PRETO N., GATTOLIN G., MARTELLI A. (2011). Start-up carbonate mounds, their
selective survival, and subsequent Middle Triassic platforms in the Dolomites. 28th IAS Meeting, Zaragoza.
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Scuola di Dottorato in Scienze della Terra,
Dipartimento di Geoscienze, Università degli Studi di Padova – A.A. 2010-2011
Publications:
PRETO N., BIRGEL D., GATTOLIN G., MONTINARO A., PECKMANN J., WESTPHAL H. (2011). Extreme
supersaturation promoted whitings in Early Triassic seawater. EPSL, submitted.
MARANGON A., GATTOLIN G., DELLA PORTA G., PRETO N. (2011). The Latemar: a flat-topped, steep fronted
platform dominated by microbialites and synsedimentary cements. Sedimentary Geology, 240 (3-4), 97-114.
PRETO N., FRANCESCHI M., GATTOLIN G., MASSIRONI M., RIVA A., GRAMIGNA P., BERTOLDI L., NARDON S.
(2011). The Latemar: a Middle Triassic polygonal fault-block platform controlled by synsedimentary tectonics. Sedimentary
Geology 234 (1-4), 1-18.
Congresses and Workshops:
Workshop on the Cassian beds (Upper Triassic), Bozen , 28–29 July 2011.
Teaching activities:
Teaching assistant: 25 hours, “Laboratorio di Cartografia”, Laurea di primo livello in Scienze Geologiche (2010/2011).
Other:
Awarded of the “Geosed contributo giovani 2011” (1000€) for the project “Depositional geometry, facies analysis and 3D
geo-modeling of the Dolomia Principale platform margin at Cave del Predil (Udine, Italy)”
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