Geology Reference
In-Depth Information
Fig. 10. Photomicrographs of sediment of tablets in stepped waterfalls. (a) and (b): from thin sections of tablet 7.
The thickness of the cool and warm period sediment obtained with the MEM is indicated. Notice in (a) and (b) the
cyanobacterial-rich laminae (cy) in some warm perids and large crystals at the base of the cool period 1999 - 2000.
Notice in (b) filamentous algae (al). (c), (d), (e), (f) and (g): images from SEM. (c) and (d): Sediment from the cool
period 2002 - 2003. Notice in (c) calcite crystals on a moss leaf and clumps of filamentous microbes and diatoms.
(d): detail of one of the clumps. (e) and (f): Massive network of calcite microbial tubes, filaments and films from the
warm period of 2000. (g): Coalescent bush-like bodies of thin calcite microbial tubes from the warm period of 2001.
as they grow from subperpendicular to subparal-
lel to the accumulation surface depending on
water flow intensity. Associated filamentous algae
(macroscopic)
completely eliminate them. The microbial bush-like
body-bearing intervals are usually preserved at the
base of the warm intervals and are thicker than
those of the cool periods (Fig. 10a). However, no
clear textural differences between warm and cool
periods have been found. Neither the shape nor
size of calcite crystals present a clear pattern of sea-
sonal variation. Coatings around in situ flora appear
thicker
are
always
parallel
to
the
flow
direction.
Cyanobacterial mats consist of tube-like bodies,
20 - 80 mm in diameter (inner diameter: 6 - 20 mm;
coating thickness: 3 - 20 mm, rarely 60 mm) and
200 - 350 mm long (Fig. 10e, f). In some cases the
tubes are arranged as hemi-domic to bush-like
forms that may coalesce to form laminae (Fig. 10a,
b, g). Calcified microbial filaments are of several
sizes (Fig. 10d, e, f). Spar and less common
micrite calcite is present among these components.
In general, moss- and filamentous alga-bearing
layers
in
some
cool
intervals,
but
there
are
many exceptions.
(4) Steep banded deposits developed in vertical
waterfalls (subenvironment e), made of inclined
moss-rich layers, with similar characteristics to
facies 3, that include or alternate with curtains of
hanging herbaceous plants, which become rapidly
coated by calcite and constitute deposits with
steep accumulation surfaces. The plant coatings
are
thicker
in
the
sediment
from
warm
periods,
although
erosion
can
partially
or
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