Quantification des flux sédimentaires et de la subsidence du bassin ...

tel-00790852, version 1 - 21 Feb 2013
F. Bache et al.
nazzolo units. The Zanclean GSSP was eventually established
at the base of the Trubi (van Couvering et al.,
2000).
At Eraclea Minoa, two sections located on both sides of
the Zanclean GSSP were studied (Londeix et al., 2007;
Popescu et al., 2009) (Fig. 9c and d).
Section 1 (Fig. 9e and f) starts with clays and diatomitic
turbidites underlying the highest gypsum bed of the
Sicilian Upper Evaporites. This bed is overlain by the
Lago Mare Unit (7.80 m thick), constituted by clay
deposits, which includes in its upper part three characteristic
layers (two dreissenid coquina layers, 25 and 40 cm
thick respectively, and a 32 cm thick white sand layer
between the two previous layers). The Lago Mare Unit is
followed by the silty Arenazzolo Unit (5.60 m thick) comprising
6.5 dark–light alternations (Figs 9e and 10a). The
upper part of this section corresponds to the Trubi Unit
and is constituted by cyclic carbonates and marls. The
position of the Zanclean GSSP, placed at the base of the
Trubi Unit, is indicated on Fig. 9f.
We performed new analyses of nannofossils from the
Eraclea Minoa Section 1 to better characterize the major
environmental changes affecting the Lago Mare, Arenazzolo
and Trubi units. The calcareous nannoplankton identified
in the Lago Mare Unit of Section 1 includes, among
other taxa, Nicklithus amplificus, Amaurolithus primus, Coccolithus
pelagicus, Discoaster quinqueramus, Helicosphaera
carteri s.l., Helicosphaera intermedia, Pontosphaera multipora,
small-sized reticulofenestrids, Reticulofenestra pseudoumbilicus,
Sphenolithus group abies/moriformis,
Triquetrorhabulus striatus and Triquetrorhabulus rugosus
(Fig. 9e). Considering that the Sicilian Upper Evaporites
that end the Sicilian Messinian evaporitic series are significantly
younger than 5.96 Ma (the robust age of the
beginning of the MSC; Table 1), N. amplificus (highest
occurrence at 5.939 Ma: Raffi et al., 2006; Fig. 4) could
be reworked. This nannoflora, which includes D. quinqueramus
(highest occurrence at 5.54 Ma: Raffi et al.,
2006; Fig. 4), precedes Zone NN12 and hence might be
related to the Subzone NN11d (Fig. 4). Londeix et al.
(2007) studied dinoflagellate cysts from the successive
uppermost part of the Eraclea Minoa section (Lago Mare
and Arenazzolo units) and lowermost part of the classic
Capo Rossello section (Fig. 9b) (lowermost Trubi). The
dinoflagellate cyst assemblage of the Lago Mare Unit is
dominated (>60%) by Lingulodinium machaerophorum
and Homotryblium spp. (Fig. 10e) that indicate coastal to
lagoonal environments (Londeix et al., 2007). The presence
of Cretaceous reworked dinoflagellate cysts on top
of the Lago Mare Unit results from an increased terrestrial
input, and was considered to announce the major
erosional episode of the Mediterranean desiccation phase
(Londeix et al., 2007). The Arenazzolo Unit is characterized
by an increase in more marine dinoflagellate cysts
assemblages (occurrences of Impagidinium spp.) showing
fluctuations between dominant outer shelf conditions
and inner shelf to coastal conditions (everywhere