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Fig. 5.5
(
a
) Very small-sized
curved filaments (diameters
around 0.1-0.2
m) irregular
embedded in platelet-like
anhedral dolomite crystals
(possibly former EPS
substances). (
b
) Irregular
polygonal networks of
microcracks are omnipresent on
the dolomite as well on the
filaments. Sample MOU19,
Mouila old quarry, Gabon (photo
mou19-40/2007/ap). (
c
,
d
)
Dolomitic sphere (diameter of
1
μ
m) inside platelet-like
dolomicrospar with irregular
microcracks. The
sphere
is
composed of subrounded
microcrystals of dolomite (10 nm
in diameter, Fig.
5.5d
). Sample
MOU19, Mouila old quarry,
Gabon (photo mou19-36 and 33
respectively/2007/ap). SEM
photomicrographs. Bar scale: as
indicated
μ
Interestingly, some specific features of fossilized repro-
duction parts of fungi can be observed also. Figure
5.7a
shows the remains of sporangial forms connected to their
sporangiophores, and the black protrusions to the right sug-
gest a typical form of spore dispersion. A second smaller
sporangium lies next to the first structure. The first sporan-
gium reveals two concentric circles separated by about a
8-10
well-embedded in the mineral matrix of the dolomitic
substrate. This strongly suggests a pre-lithification
synsedimentary process and early diagenesis. Moreover,
these fungal structures are very similar to fungal parts
retrieved from the Late Riphean Neryuenskaya Formation
of southeastern Siberia (Hermann and Podkovyrov
2006
),
which represent the oldest reported fossil fungi.
Although the poor preservation caused by dolomitization
and per-mineralization of fungal relicts do not allow for
more detailed descriptions, and did not allow for extraction,
the well-contoured fungal features, substrate dissolution, pit
forms and colonization when compared with modern fungi
(e.g. Mucorales), and their patterns of colonization and
interaction with mineral surfaces, especially carbonates
(Kolo and Claeys
2005
; Kolo et al.
2007
), nonetheless
suggests strong similarities between modern and ancient
fungi.
m thick zone. The inner circle is visibly continuous
(diameter ~30
μ
m) and joins the sporangiophore. This struc-
ture and configuration actually reveal a fungal columella.
Furthermore, Fig.
5.7b
shows a richly colonized substrate
(not all traces shown) where an external black perimeter of
the sporangium suggests the sporiferous region of the spo-
rangium with a probable attached spore mass. The traces of
the ancient fungal parts are sometimes outlined by the disso-
lution figures, which relates the visible pitting on the
Neoproterozoic substrates, at least in these instances, to
fungal activity. Figure
5.7c
shows another fungal-related
shape and setting where possible sexual reproduction organs
involving the formation of a zygosporangium and
suspensors are observed. They display an anatomical mor-
phology comparable to modern fungal sexual reproductive
cycle and the production of zygosporangia, zygospores and
suspensors, e.g., in the Zygomycetes (Alexopoulos and
Mims
1979
; Moore-Landecker
1991
; Kendrick
2000
).
A negative and enhanced image (Fig.
5.7d
) of the above
reveals the well-defined and preserved morphology and
contours of these fungal structures that undoubtly appear
μ
5.4
Neoproterozoic and Modern Fungal
Diagenesis: Analogous Patterns
We have attempted to experimentally demonstrate (detailed
experimental procedure
in
Kolo and Claeys
2005
; Kolo et al.
2007
) that fungal interaction with dolomite crystals produce
characteristic colonization patterns, dissolution, pitting,
and neomineral formation
as observed in our
Neoproterozoic strata. For the experimental work,
“
nesting
”
thin
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