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| Titel |
Record of the end-Triassic crisis in south-western Sicily: palaeoenvironmental changes reflected by the carbonate facies architecture. |
| VerfasserIn |
M. S. Cacciatore, P. Di Stefano |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250024202
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| Zusammenfassung |
| The Sciacca-Monti Sicani area, in south-western Sicily, offers a regional example of the
facies architecture in an Upper Triassic/Lower Jurassic carbonate shelf margin to slope
zone. It allows us to evaluate the interplay of different controlling factors on the
sedimentary dynamics of a South Tethyan basin margin across the Triassic/Jurassic
boundary.
In this segment of the Maghrebian thrust and fold belt, the Triassic/Jurassic facies
associations and their spatial relationships were restored by the correlation of selected
sections from several structural units.
The Triassic carbonate shelf consists of thick successions of peritidal-lagoonal cycles
(Sciacca Fm.). Our studies reveal that a NW-SE trending Dachstein-type reef edged the shelf
of the platform towards east. This implies the contiguity of the carbonate shelf with a
high-energy, open-marine environment, providing the optimum oligotrophic life conditions
for sponge-coral-algae communities. A terminal complex, consisting of chaetetid-dominated
boundstones, characterizes the Rhaetian topmost zone of the reef, probably because of the
end-Triassic biotic crisis.
A sharp discontinuity surface on top of the uppermost Triassic platform strata (Triasina
facies) is overprinted in places by karstic dissolution. It is interpreted as a result of a Late
Rhaetian sea-level fall. A lowering of the sea-level is also supported by the presence of fine
skeletal grainstones in the slope–basinal successions. This implies a downslope forced
shedding of reef-derived biodetritus, favoured probably by the shifting of the active
bioconstruction to the outer shelf margin/upper slope.
Around the Rhaetian–Hettangian boundary, a widespread clastic carbonate wedge was
formed downslope by the cannibalization of the Upper Triassic reef. The selective source of
clastics (Upper Triassic reef extraclasts) suggests, as trigger mechanisms, margin collapses
coupled to an intense wave erosion of the reef limestones during the lowstand stage.
Transtensional tectonics activity along the shelf edge, inducing margin retreats, is
documented by local angular unconformities, so we cannot exclude the contribution of brittle
deformations to the the production of clastic materials.
The aggradation of Thaumatoporella-mollusc bearing peritidal cycles in the shelf and of
oolitic-bioclastic sands along the shelf-edge indicate the recovery of the carbonate
productivity during Early Jurassic times coupled to a sea-level rise during Hettangian times.
Moreover an intense shedding of carbonate sands in the adjacent slope and peribasinal areas
is recorded in all the studied deep-water successions.
In the distal slope zone the observed switching of the intrabasinal carbonate supply from
scarce biodetritus containing reef-derived foraminifers (e.g. Galeanella, Siculocosta
and others) to abundant oolitic and skeletal sands, bearing Aeolisaccus sp. and
Siphovalvulina gibraltarensis, can be used as a proxy of the Triassic/Jurassic boundary. |
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