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Photo Album (I)
(by B. Granier)
This page displays photos of some common calcareous
Algae, mostly Dasycladales, found in the Lower Cretaceous carbonate
platforms.
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Barremian
- Jura
 
Diagnosis:
Thallus cylindrical, umbranched. Primary branches
numerous, in regular whorls, not mutually compressed, turgid,
perpendicular to the stipe at their proximal narrow ends, often
slightly inclined at their tips. These branches are assumed to be
sporangial chambers. Irregular occurrence of sterile hairs, located
within and/or between the whorls. Calcification is irregular: the
stipe is commonly coated with a thin membrane only, but the fertile
branches are strongly coated and joined together within a whorl. The
branches of two successive whorls are joined together near their
mid-points. The distal end of the branches is free. [CONRAD 1970]
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- Barremian
- Jura
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- Barremian
- Jura
 
Diagnosis:
The stipe is cylindrical, neither branched out or
segmented. The branches are simple, phloiophorous, strongly tilted
upwards, arranged in closely set alternating whorls. They communicate
with the stipe by means of a proximal narrowing. The calcareous sheath
covers a variable proximal portion of the branches and reaches the
stipe. Beyond the sheath the branches are enveloped by a rather thin
calcareous membrane which is very fragile since the space separating
the branches is no longer calcified. the branches converge again at
their tips, where they seeem to be a little less tilted. Most likely
the assimilatory cortex which characterized the phloiophorous type was
situated beyond that part. Where the branches are numerous they
squeeze one another and become polyhedral. The reproductive organs are
unknown but I think they were located in the branches (cladospory).
Both the calcareous sheath and membrane consist of a simple coat of
hyaline calcite. [CONRAD 1970]
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- Barremian
- Jura
 
Diagnosis:
Cylindrical thallus, neither branching, nor
segmented. Euspondylous, alternating, tighted and regularly spaced
whorls of a small number of branches. The branches are perpendicular
to the axis of the thallus, phloiophorous and compressed vertically.
The branches, or some of them at least, contain spores the imprint of
which is visible on the calcareous envelope. Calcification is strong
and reaches the stipe. No secondary branches. [BASSOULLET et alii
1978]
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- Barremian
- Jura
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- Barremian
- Jura
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- Barremian
- Jura
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- Barremian
- Jura
 
Photos by courtesy of A.
Arnaud-Vanneau
Diagnosis: Small
articuled Actinoporella species with a cylindrical main axis
bearing close-set whorls of branches. Branch consisting of a vestibule
followed by a vesicular to short club-shaped gametophore, by an open
pore on one side of the whorl, and by an "excrescence" on
the opposite side. Gametophore perpendicular to the main axis and
closed at its distal part. Calcareous sheath consisting of
microgranular calcite wall. [GRANIER 1995]
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