Page 135 - Carbonate Platforms Facies, Sequences, and Evolution

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If
shales
erosion
shelves.
the
Deposits
steep
Aalenian
localities,
phatic or
Hettangian
vironments
by
swells
slopes
age
without
disrupted
are
currents
and
were
ferruginous
ferruginous
Overall thickness: 0.50m.
facies are indicative of
a
('schistes-carton',
in
thin
and
barriers
Proximal external, open shelf
lack
Fig.
features are related to steep
directly
breccias
or
of
deeper
beds
near Les Vans, where light-grey
Toarcian of the Privas Sub-basin.
a
16).
storms.
(Fig.
larger
overlain
water,
Distal shelf or sheltered areas of the shelf
shelf.
The
with current laminae and ripples (Fig. 15).
14).
by
Vicinity
oolites and oncolites.
the
facilitating
micrites of
They
to
Fig. 14. Sharp unconformity between Hettangian light­
grey micrite and Upper Aalenian ferruginous breccias,
peared when tilt blocks were well differentiated.
containing badly sorted Hettangian pebbles. Folcheran.
coasts and hinge en­
ap­
crinoidal packstones and grainstones. Iron and phos­
crinoids and sponge spicules associated with phos­
early
Upper
consist of skeletal limestones oolitic and
phate are common and iron ore occurs in the middle
Storm or gravity transported quartz grains or pebbles
shore or to the top of the swell is always noticeable.
These
facies
resulting
their
the
consist of biomicritic wackestones bearing abundant
'hinge sequences' bordered
perilittoral
In the Les Vans
Facies range from sponge-bearing micrites to black
area, lsocrinus grainstones form prograding bodies
unconformities can be very sharp as at Le Folcheran,
These
S. Elmi
early and middle Jurassic.
Escarpment or steep slopes
Callovian Triad (Gracilis Zone). Naves near Les Vans.
The Lower Bathonian beds are directly covered by the
spicules, Bositra-filaments, oncolites) (early Bathonian,
Fig. 15. Reduced Bajocian-Bathonian sequence (6m).
zones of the Bajocian. The Isocrinus limestones lie on a
thin lenticular Aalenian ferruginous limestone filling the
The lower part (B) consists of wavy laminated Isocrinus­
Zigzag Zone). Between the two: gap of the two topmost
irregularities of the Hettangian surface (see also Fig. 14).
part (A) is made of irregular beds of wackestones (sponge
grainstones (late Bajocian, Subfurcatum Zone). The upper
shelf but in a more uniform environment than during
and basin. Coarse clastics (quartz, metamorphic and
environment. In Upper Jurassic strata, well-bedded,
fine hemipelagic micrites can be related to the outer
the shelf or, without transition, between the swell
are abundant, making a transition to the succeeding
These were developed either between the swell and