UTRECHT MICROPALEONTOLOGICAL BUllETINS

98 and 99). The total thickness of this unit is 150 cm.
At the top of this 8 meters interval there is a sixth unit with laminated
sediments of some 50 cm thickness. The internal bedding is disturbed by
burrowing in its lower and upper parts. About half way, less intensive
organic activity allowed the preservation of discontinuous laminae. Sample
100 was collected from this middle part. In upward sense the sediment
changes rapidly into a relatively indurated, brown coloured and burrowed
limestone (sample 101).
Two meters of soft and marly limestones with intercalations of more
compact beds follow on top (samples 102-104). Higher up the marly
intercalations disappear, and the vaguely bedded and massive character
found in the basal few meters returns (thickness 6 to 7 m, samples 105-
107). At the boundary between two of the compact limestone beds, a
very thin clay seam was observed, which pinches out laterally to continue
as a red-brown coloured bedding plane. It could not be verified whether
similar bedding planes correspond to comparable clay seams in a horizontal
direction.
Some two meters below the top of the section a 50 cm clayey intercalation
is of special interest. The base of the clay is irregular. In a lateral sense
it shows a horizontal offshoot of 2 cm (sample 107 B) to zero under a wedge
of the underlying limestone and over a lateral distance of some 30 cm (fig.
11). The clay body is of dark green colour (samples 107 D-F). Larger, brown
coloured burrows (diameter 1 cm) usually follow horizontal paths. Smaller,
white coloured and bifurcating burrows form a system of branching tunnels
(fig. 12 and 13). Oriented samples show these tunnels to branch in a downward
direction. The tunnels are circular in cross-section and have a constant
diameter of about 1 mm. At some levels discontinuous lamination is still
preserved. The over- and underlying indurated limestones show no bioturbation,
but the contact between the clay and the overlying limestone is
burrowed (sample 107 G).
The top of section 3 shows gravels and soil in unconformable position.
Near Lido Rossello, to the west, the Trubi attains a greater thickness, of
more than 100 m. It passes upwards into marly sediments with intercalations
of brownish colour, which are unconformably covered by Quaternary
calcarenitic sands.
62 samples have been taken from section 3. The sampling was focussed
on the indurated/non-indurated sequences (20 samples) and the alternation
of laminated/non-laminated sediments (29 samples).