Page 134 - Carbonate Platforms Facies, Sequences, and Evolution

1
in
are
(Fig.
rents).
the
underlain
12).
limestones
winnowing
gastropods
spicule-rich,
crowded
by
millimetre-scale.
Upper
or wackestone
Waves,
with
These
most
lagoonal m1cntes,
with
of
Longshore and swell
stages of tilting (S2).
is made of a ferruginous
mottled
Bajocian condensed bed,
storms
facies
phosphatic and ferruginous
the
oncolite. First generation of
brief increases of energy
crinoids,
open-marine
stromatolitic laminae (h) . Les
nucleus made of a ferruginous
are
Chiffraux near Aubenas. Early
stromatolitic crust (a) around a
and
textures with
ammonite
(g). The entire clast is coated by
oobiomicrite (c) with crinoids (d)
Fig. 13. Complex 'Snuff-box'-like
and bivalve (e) fragments, sponge
spicules (f) and scarce quartz grains
oobiomicrite (b). One other nucleus
protected
developed basinward
oomicrosparites
Sandy-Calcareous
shells.
sediments.
echinoids,
currents
limestones.
related to
condensed beds have been differentiated:
Two
Series
the
were
limestones
bivalves
or
(Fig.
kinds
abundant neritic bio­
(wave base, bottom cur­
to ostreid coquinas or to Favreina-bearing micrites
Towards the lagoon, the bioclastic limestones change
of the bioherms.
eustatic
Condensed beds and lenticular levels are common
2;
indicative of moderately shallow bottoms sustaining
initial transgression (Fig. 2; S1) and to the following
mottled limestones), and pelmicrites. At the end of
early Hettangian time, small reef-patches developed
and oosparites,
and by protected marine facies (heavily bioturbated,
by
limestones deposited in protected zones. Bioclastic
and
Thecosmilia
bioherms are surrounded by bedded Madreporaria
Toarcian to Bathonian). They have mainly packstone
Stromatolites,
Benthic communities and oxidizing conditions are
of
clasts and are commonly ferruginous. Locally, they
active,
13).
light.
grains
various
bation,
micritic
phosphatic.
These
Late Triassic and Jurassic platforms,
and
sized
Some
rocks
bioerosion
France
radial
are
bear
oncolites
oolites
(from
are
to decimetric oncolites or
commonly
desiccation
and desiccation have,
cracks.
millimetric
in
associated
ferruginous
Fig. 12. Biodolomicrosparite. Favreina pellets in cross­
cendres Formation (S2), early Hettangian. Soudournas
section. Top of the Lower Member, Calcaires noduleux
Biotur­
near Aubenas. Millimetre-scale. All thin sections, natural
or
123
(Fig.
coated
some
'snuff-boxes' and