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subperpendicular to the accumulation surface
forming bush-like groups that may coalesce later-
ally (Fig. 8d, e, g), or non oriented constituting a
massive network (Fig. 8f, h). Tube-like bodies are
15 - 60 mm in diameter (inner diameter: 4 - 20 mm;
coating thickness: 3 - 20 mm) and 200 - 250 mm
long, rarely up to 500 mm. Microbial filaments of
different
thick microbial tubes appear at the base of some
cool intervals (Fig. 10a, cool period 1999 - 2000).
(2) Dense to porous, commonly loose, massive
tufa (Figs 6 & 9), formed in slow flowing,
dammed and/or palustrine conditions (subenviron-
ment b). The sediment consists of lime mud,
coated phytoclasts and rare gastropods, unidentifi-
able tufa fragments, non-coated plant-remains and
rare, up to 10 cm long oncolites. Lime mud and
boundstones of plants are common in palustrine
conditions. Calcified microbial filaments of several
sizes, calcite microbial tube-like bodies and
diatoms appear in areas of faster flow. Cyanobacter-
ial filaments and diatoms are sometimes abundant
and commonly have no calcite coatings. Micrite
and spar calcite is present both coating the com-
ponents and among them (Fig. 9b, c).
The sediment of these tablets did not allow to
differenciate textural characteristics between warm
and cool periods, given the difficulty to identify
the corresponding intervals, due to poor preser-
vation and almost nule contrast between them.
(3) Porous, spongy tufa, crudely laminated or
without lamination (Figs 7 & 10), deposited in
stepped waterfalls, small falls and barrages, and in
spray and splash areas (subenvironments c and d).
This facies consists of mosses, filamentous green
algae, cianobacterial mats, diatoms and herbaceous
plants, which are impregnated and/or coated by
micrite and spar calcite, producing porous deposits
mostly made of moss and filamentous algae bound-
stones, and associated cyanobacterial mats. These
include trapped coated phytoclasts and other intra-
clasts (Fig. 10a) and hanging coated plants. In
spray areas, the thin deposits formed there are
mostly made of microbial mats.
Moss and alga intervals produce soft, generally
domed deposits, in which the plants are coated
sizes
are
among
the
tubes,
but
are
not abundant.
Intervals from the warm periods, as compared to
those of cool ones, are commonly thicker, and the
sediment is usually lighter in colour, more porous
and has more abundant micrite calcite, although
these features may change from site to site and
depending on the intervals (Fig. 8a, b, c). Porosity
is variable depending upon the type, relative pro-
portion and arrangement of the biological com-
ponents that are present. Empty cavities produced
from decayed fauna (e.g. crustacean and aquatic
insects) are more abundant in warm perids (e.g.
Fig. 8b, c). The cyanobacterial tube-like bodies con-
stitute either massive, open networks, or bush-like
groups that in places form laminae. The latter may
be more abundant and/or thicker in the warm than
in the cool periods (Fig. 8c, upper half of warm
period 2001) and, in some cases, present more
dense fabrics in the warm than in the cool period
cyanobacterial laminae (Fig. 8e, g). The thickness
of the microbial tubes commonly is thinner in the
warm (3 - 5, rarely up to 7 mm; Fig. 8g, h) than in
the cool intervals (3 to 20 mm) (Fig. 8e, f).
Intervals from the cool periods locally show
more dense fabrics and present thicker coatings of
the tubes (Fig. 8a, b, f); however, in particular
when these tubes form bush-like groups arranged
in laminae, the fabric can be less dense than that
of the warm period laminae (Fig. 8e). Ocassionally,
palisades of large blade calcite crystals associated to
Fig. 9. Photomicrographs of sediment of tablets in slow flowing water areas. (a): from a thin section (tablet 6). The
identification of the cool and warm period sediment is only clear at the top. The rest of the intervals are indicated as
approximate and cannot be dated. (b) and (c): images from SEM. Notice the massive appearance of calcite tubes (tu),
diatoms (di) and calcite crystals. Diatoms at the base of (a) are oriented with their long axes vertical.
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