Page 231 - Carbonate Platforms Facies, Sequences, and Evolution

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this region.
AND
in
sedimentation.
LITHOLOGY
been
facies
distinguished
Ai 1a
and by
Ai 1b
PARASEQUENCES
tems tract shows,
Highstand deposits
by
z
u
w
w
w
<f)
<f)
0
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once
the
If
fl·
observed.
inner-platform
a return to
(dominantly
again,
(3)
type
The
A.
-Kv
rudistid
disappearance
mfs
DLS
high
stand deposits is a fiat lithological surface.
of
1-
1-
1-
1-
(f)
I
(f)
(f)
I
facies)
environments
t
BA2 depositional sequence are composed of inner­
The lower boundary of these high­
was accompanied by the deposition of detrital ter­
In conclusion, the study of this transgressive sys­
ammonites in the marls clearly highlights the maxi­
that the rise in sea­
In terms of thickness, the highstand deposits make
exclusively carbonate
rich in coarse grains of detrital quartz. The rarity of
period, or even the beginning of the sea-level fall,
which is locally several meters thick and particularly
up most of the Urgonian limestone formation. The
mum deepening of this inner platform. No condensed
rigenous material even though the latter are usually
detrital
of
level preceded the maximum deepening period and
Bs3 and BsAi parasequences of the late Barremian
and
sea-level
Marine
of
the
end
J
I
I
I
Arnaud- Vanneau and H.
\
I
/
limestone
\ \ \
/
rather
I
I
\ \
very similar.
I
Characae
\
Emersion
\
I
appears to be
\
microstalactitic
I
Arnaud
\
I
in emergence
in the early Aptian.
middle-early Aptian
=
micrite
minor.
levels
unremarkable
distinct erosional surfaces.
cements).
It is
of
above
limestone).
or by a .very rarely
The
the
gullying
various
(Chartreuse) (Arnaud-Vanneau, 1980).
beds. Legend, see Fig.
of
deposits (upper Urgonian
transgressive systems tract
erosion
types
tract (marls and argillaceous
systems tract in the northern
emergence
to a clear lithologic boundary
limestones) and the highstand
(microstalactitic) cement. The
distinguished either
18. KV =
between the transgressive systems
Vercors (Ail parasequence). This
storm deposit level with vadose
Fig. 12. Early Aptian transgressive
hor­
The Ai2 parasequence,
Early Aptian emergence and the transgression of the
located very near the Barremian- Aptian boundary,
beach-level with keystone vugs; MC
depositional sequence (Al depositional sequence) is
The emergence at the top of the Ai2 parasequence,
corresponds to the lower Orbitolina
The emergence at the top of the BsAi parasequence,
grainstones, fenestral micrites, storm deposits with
izons appear to be localized and do not pass into
downlap surface (DLS) corresponds
by
its upper boundary, there is a major erosion surface
surface
first of all by diagenetic changes in the sediment at
(beach
on the other hand, is quite substantial. It is marked
making up the highstand deposit of the basal Aptian
highlighting the emergence of the Urgonian platform
preserved thin level
underlying
It does differ though in the fact that at