Page 241 - Carbonate Platforms Facies, Sequences, and Evolution

not
are
226
chains
region,
been
Barremian
Throughout
(Figs
observed
certain
the
21
proved,
above
&
Jura
(Valserina
but
it
the
and
22),
is
foraminifera
the
base of the Urgonian limestone.
basal
from
bronnimanni,
feasible
the
Inner-plat form facies (Urgonian platform)
since,
top
inner-platform
in
of
transgression
se­
lenticularis) are found just a few metres above the
this
the
northern Subalpine
Palorbitolina
facies
quence. These are white, exclusively carbonate facies
due
fera,
corals;
to
the
and
characterized
(2)
A. Arnaud-Vanneau and H. Arnaud
by
of algal oncolites.
activity
dasyclad algae,
the
of
oncolites (0); (D) Pseudotriloculina mudstone (restricted environment) . (Scale bar: 1 mm)
endolithic
micritization
packstone-wackestone
of
miliolidae and locally,
with
rounded bioclast-foraminiferal packstone with rudists (R); (C) micritized rounded bioclast-miliolid wackestone with
sequence: 4- 10 m. (B to D) Selected microfacies in thin sections from base B to top D of the sequence; (B) micritized
Fig. 21. Inner-platform shallowing-upward sequence (Urgonian platform). (A) General view of the Urgonian cliff. The
with large and small rudists, large benthic foramini­
Among the foraminifera, only miliolidae are abun­
rudists and oncolites which are locally very common.
bioclasts
a few
10 m thick. Always of the shallowing-upward type,
small
(Cyanophycae, bacteria, fungi) and by the presence
they display from the bottom upwards: (1) packstone
arrow marks the location of an inner-platform shallowing-upward sequence (S). Thickness of the cliff = 300 m, thickness 9f
dant. The sequence may end in two different ways.
micro-organisms
These sequences are from 4 to