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Rend. Online Soc. Geol. It., Vol. 17 (2011) - (DOI 10.3301/ROL.2011.16)

Downslope-migrating sandwave in the Chattian carbonate ramp of Majella (Central Apennines, Italy)

M. Brandano (*), (****), L. Lipparini (**), A. Romi (***), V. Campagnoni (**) & L. Tomassetti (*)


(*) Sapienza University of Rome, 00185-Rome, Italy.
(**) Medoilgas Italia S.p.A. (MOG Group), 00166-Rome, Italy.
(***) Schlumberger Information Solutions, 20097-Milan, Italy.
(****) IGAG-CNR, Area della Ricerca di Roma, Via Salaria km 29,300, 00016 Monterotondo Stazione, Rome-Italy.


The reconstruction of depositional models in spatial dimensions by means of integrating quantitative field studies with digital outcrop models is becoming a new tool to gain new insights to extract depositional geometries and facies architectures in the example where they are unobtainable.
We investigated the Chattian interval of Bolognano Formation in the northern sector of Majella Mountain (Central Apennines). This formation consists of four lithostratigraphic units. The Chattian interval is represented by cross-bedded lepidocyclina calcarenites dominated by larger benthic foraminifers (Nephrolepidina, Amphistegina), bryozoan fragments, red algae debris.
This lithostratigraphic unit is overlaid by bioturbated planktonic marly limestones that unconformably are overlied by the third unit represented by cross bedded bryozoan limestone. The skeletal fraction is dominated by bryozoan, mollusc and echinoid fragments and rarely by larger benthic foraminifers. The uppermost unit consists of red algal marly limestones dominated by red algal nodules and bivalves. A 30 cm thick Heterostegina rich bed is interposed between the last two units.
The aim of the present work is to present sedimentological analysis on facies, structures and geometries of lepidocyclina calcarenites and the generation of a 3D geological model that permits to understand the architecture of this unit of Majella platform and their relationship with facies distribution.
Four lithofacies have been recognized in the lepidocyclina calcarenites: Planar cross-bedded grainstone (lithofacies A); Moderate angle cross-bedded grainstone (lithofacies B); Sigmoidal cross-bedded (lithofacies C); Horizontal bedded bioturbated marly packtone to wackestone (lithofacies D).
The sediment is composed of bryozoans, LBF (Nephrolepidina, Eulepidina, Amphistegina, Operculina, Heterostegina) and abraded and fragmented plates of echinoids, red algae debris and bivalve fragments. The abundance of well preserved bryozoan colonies as well as LBF specimens suggests a parauthoctonous origin of the sediment in a middle ramp environment. Sedimentary structures of the recognized lithofacies indicate high hydrodynamic conditions in the proximal sector of the middle ramp evolving to low hydrodynamic conditions in the transition between middle to outer ramp.
The bedforms of the proximal middle ramp (lithofacies A e B) formed under fluctuations in the current strength and/or direction (from N to W), while lithofacies C formed in the distal part of the middle ramp under slight variations in flow strength and direction (N).
The lepidocyclina calcarenites represents a middle ramp environment characterized by a field of basinward migrating dunes 10 x 15 km wide.

KEY WORDS:   Oligocene, carbonate ramp, lithofacies, submarine dune.

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