Page 8 - Martini_al_Facies_2007

396 Facies (2007) 53:389–400
solution-collapse of beds (e.g. evaporites) because even
though the evaporites were not directly observed in the
Weld, algal mats, evaporite pseudomorphs and cellular
structures provide evidence for evaporites (Eliassen and
Talbot 2005).
Finally, the clayey marls and marls (MF9) are inter-
preted as being deposited in restricted lagoonal areas (e.g.
in a back-ramp) under low-energy conditions. The reduced
diversity of shallow-water biota, which are only repre-
sented by non-disarticulated ostracods with high number of
individuals, conWrms this interpretation.
Facies types and assemblages of the Punta Bassano suc-
cession are closely comparable to those of other Alpine
Upper Triassic carbonate settings, pointing to similar peri-
tidal depositional conditions. Typical examples are the
Lofer sequences in the Northern Calcareous Alps (e.g.
Flügel 1981; Enos and Samankassou 1998), the Fatric Unit
in the West Carpathians, Slovakia (Tomasovych 2004), the
Kössen Formation in the Northern Calcareous Alps (Kuss
1983) and the Calcare di Zu Formation in the Southern Cal-
careous Alps (Lakew 1990). However, the Punta Bassano
facies indicate more restricted position of the intra-platform
environments from the open ocean, as demonstrated by the
complete absence of patch-reefs and derived skeletal
grains, as well as by the poor diversity of the microfaunal
assemblages.
Biostratigraphy
Biostratigraphically (foraminifers and palynomorphs) as
well as palaeoecologically (ostracods) signiWcant microfos-
sils, occur all along the Upper Triassic Punta Bassano suc-
cession. Foraminifers have been studied on thin sections
(SMA: 3, 5, 8, 9, 11 to 14, 16, 18, 19, 21, 23, 24, 26 and 27;
the signiWcant samples are: SMA: 3, 5, 8, 21, 23 and 26).
Samples for palynological slides (SMA: 2, 3/1, 5/1, 7/1,
8/1, 10, 11/1, 12, 13, 15, 17, 19/1, 22, 25, 27, 27/1, 27/2 and and Brugman 1981; Warrington 1996). This age assign-
28; the signiWcant samples for the palynomorphs are: SMA:
13, 19/1, 25, 27 and 28) and for ostracod extractions (SMA:
12, 16, 20 and 23; all samples are signiWcant) were collected
both in limestones and in clayey marls and marls (Fig. 5).
Foraminifers
The investigation of thin sections in the Punta Bassano sec-
tion evidenced monotonous associations of foraminifers,
represented by a low number of individuals. They are most
abundant in the peloidal wackestone/packstone (MF2)
where the foraminifers sometimes co-occur with abundant
ostracods as well as bivalve and echinoderm fragments.
Preservation of microfauna is quite poor due to strong
recrystallisation, which aVects the entire succession.
123
The biostratigraphically signiWcant species of benthic
foraminifers are Hoyenella inconstans (Fig. 6a, b) and
Endotriada cf. tyrrhenica (Fig. 6c). They have been found
in association with “Trochammina” (Fig. 6e), Endotriad-
ella (Fig. 6f, g) and Glomospira.
Hoyenella inconstans is a reliable marker for the Upper
Triassic Alpine Tethys (Kamoun et al. 1994 with synon-
ymy; Martini et al. 1998). It occurs at diVerent levels of the
sequence (Fig. 5), in the lower and in the middle part,
respectively (SMA: 3, 8 and 21), and allows us to attribute
this interval to Late Triassic (Carnian-Norian to Rhaetian).
We notice that the stratigraphic range of this species is
corroborated by its occurrence with the zone marker Tria-
sina hantkeni in many Upper Triassic successions, like in
the Raetavicula contorta beds in the Northern Apennines
(Ciarapica et al. 1987) and in the Briançonnais Domain in
the Western Alps and in the Préalpes Médianes (Zaninetti
et al. 1986).
Palynomorphs
The palynological study was carried out on both limestone
and clayey marls and marls intervals (Fig. 5). The palyno-
logical assemblage is not too much diVerentiated across the
Punta Bassano succession but the percentage of spo-
romorphs increase upwards, reaching its maximum at
around 30 m from the base of the succession (SMA13).
The most common and biostratigraphically signiWcant
species is Gliscopollis meyeriana (Fig. 6h, i), which occurs
at 30 m from the base of the section (SMA13) to its end
(SMA28). Other accessory elements are present, such as
Ovalipollis pseudoalatus (Fig. 6j), Concavisporites sp.,
Deltoidospora cf. toralis, Calamospora mesozoica, Cyc-
adopites sp. and Chordasporites sp. This assemblage can
be assigned to the Norian-Rhaetian (Schuurman 1977,
1979; Morbey 1975; Morbey and Dunay 1978; Visscher
ment is in agreement with the foraminifer’s distribution.
Ostracods
Ostracods are the most abundant and most common micro-
organisms in the whole Punta Bassano succession, as is
expected due to the restricted depositional environment of
the sequence. Combined with both the microfacies and the
micropalaeontological analyses, the study of the ostracods
helped to reWne the depositional environment of the Punta
Bassano succession.
The most representative genera and species, belonging
to Wve families are Laevicythere, Kerocythere cf. quatter-
valsi (Fig. 6k, l), Lutkevichinella lata (Fig. 6m, n), Cyther-
elloidea cf. praepulchella (Fig. 6o, p), Lutkevichinella
keuperea (Fig. 6q, r), and Coronocypris corunula.