UTRECHT MICROPALEONTOLOGICAL BUllETINS

A composite section of the Trubi is exposed along the beach of Capo
Rossello and in the cliffs around Lido Rossello (fig. 1). Its lower and upper
contacts are well exposed. Numerous normal faults trending NW-SE divide
the Trubi into separate compartments, on the average some 50 m wide.
The throw along these fractures seems to be small, not exceeding 10 to
15 m. Within each compartment reliable profiles can be sampled. Correlation
between one block and the other is often more difficult. For our study we
primarily sampled in detail the lower 40 m, exposed in an easily accessible
gully which ends at the beach (section 3, fig. 1) some 250 m NW of the
Miocene-pliocene boundary stratotype locality (section 2, fig. 1). In a
vertical sense the section is continuously exposed. The dip of the strata within
this tectonic block is negligible. Eight meters in the upper part of the section
was sampled in still greater detail for the "Accuracy in time" project
(Utrecht Micropal. Bull. 17). The upper 10 m of the Trubi were sampled at
two localities: Lido Rossello (section 5, fig. 1), and Punta Piccola, some 4
kilometers east of Lido Rossello (fig. 1). At both localities the marls of the
Monte Narbone formation follow in an upward direction. The Trubi sediments
in Capo Rossello, situated between the lower 40 m and the top, were
not sampled in comparable detail, for the tectonic reasons outlined above
(section 4, fig. 1). Sections 1 and 2 have been the subject of earlier publications
(Brolsma, 1975b).
The Trubi has a thickness of 100 to 120 m at Lido Rossello (Cita, 197 Sa,
fig. 10). It either starts from a disturbed contact at its base (section 2,
fig. 1, Miocene-pliocene boundary stratotype) or it has a transitional interval
(section 1) straddling the boundary with the underlying clastic Arenazzolo
(Brolsma, 1975b). The transitional interval shows plastic blue clay below,
which rapidly becomes marlier ,harder and more cream coloured in an upward
direction, and which in turn passes into the true biogenic limestones
of the Trubi type (fig. 7). Burrows filled with contrasting blue and cream
coloured sediment are present in this transitional interval but burrowing
is not held responsible for the gradual change in lithology.