Zemes un vides zinātnes Earth and Environment Sciences - Latvijas ...
Zemes un vides zinātnes Earth and Environment Sciences - Latvijas ...
Zemes un vides zinātnes Earth and Environment Sciences - Latvijas ...
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104 ADVANCES IN PALAEOICHTHYOLOGY<br />
enabled us to come to the conclusion that two oryctocoenoses most probably originated<br />
from the same palaeobiocoenosis, differing mainly in the character of transportation<br />
<strong>and</strong> burial conditions (Lukševičs 1992).<br />
No spores or conodonts have been fo<strong>un</strong>d in the Ketleri Formation, therefore the age<br />
of the formation (corresponding to the expansa conodont zone; Esin et al. 2000) could<br />
be judged only from its position above the Žagare Formation. Dolomite of the Žagare<br />
Formation yeilds conodonts providing the possibility to correlate it with the interval<br />
from marginifera to postera Zones (Esin et al. 2000). The <strong>un</strong>derlying Švete Formation<br />
(in Lithuania; corresponds to the Sniķere <strong>and</strong> Tērvete formations in Latvia) contains<br />
conodonts of the postera Zone (Middle – Lower styriacus Zone of the previous conodont<br />
zonation; Žeiba <strong>and</strong> Valiukevičius 1972).<br />
Results<br />
Sedimentology. The detailed studies of the outcrop of the Ketleri Formation on the left<br />
bank of Ciecere River, opposite the former Pavāri hamlet, show a s<strong>and</strong>stone body with<br />
a total thickness of more than 3 m, most of which is only visible after major excavation<br />
<strong>and</strong> cleaning of the wall-shaped outcrop. The lithology of the section is shown in Figure<br />
2. Very fine-grained to fine-grained white or light yellow almost <strong>un</strong>consolidated quartzose<br />
s<strong>and</strong>stone dominates the sequence. An erosional surface, interpreted here as a relatively<br />
shallow (about 0,5 m deep) <strong>and</strong> at least 8 m wide erosional channel, is traced in the<br />
lower part of the section (Fig. 3). Measurements of dip suggest that a stream flowing<br />
from NNE to SSW formed this erosional channel. The same direction is characteristic<br />
for the whole cross-stratified deposits of the Ketleri Formation (Savvaitova 1974). In<br />
accordance with the results from a grain-size analysis (Fig. 4), the erosional channel<br />
was filled by a well-sorted fine-grained s<strong>and</strong> in the lower part (Fig. 3, layer 6, sample<br />
6A) <strong>and</strong> more silty moderately sorted material in the upper part (sample 6), showing<br />
fining upward sequence which contains numerous vertebrate remains in the bottom<br />
part of infilling, but no admixture of dispersed clay particles. Vertebrate remains are<br />
<strong>un</strong>evenly spread in the rocks, mainly forming accumulations in the bottom part of the<br />
s<strong>and</strong>stone infilling of the erosional channel. Accumulations were fo<strong>un</strong>d also below a<br />
thin clay layer (number 5 in Fig. 3) <strong>un</strong>derlying the erosional surface.<br />
Large-scale cross-bedding is characteristic for the lower <strong>and</strong> middle part of the<br />
channel infilling. Small-scale current(?) ripples are also noticed above the cross-stratified<br />
s<strong>and</strong>stone. Cross-stratified beds are rather thick in the lower part <strong>and</strong> very thin in the<br />
middle part, usually bearing layers of mica on their surfaces. Measurements of crossstratified<br />
beds show their bipolar orientation (Fig. 5), <strong>and</strong> their dip azimuth is almost<br />
perpendicular to the axis of the erosional channel. Such orientation is usually explained<br />
by the influence of inter-tidal streams (Reineck <strong>and</strong> Singh 1980). Laminae of the crossbedded<br />
layers show variable angle of dip, in some places the high angle reaches 37 o .<br />
Deformations of s<strong>and</strong>stone bedding <strong>and</strong> intrabasinal conglomerate consisting of clay<br />
pebbles noticed mainly in the left side of the outcrop (along the right edge of the erosional<br />
channel) indicate the role of slump processes in the filling of sides of the channel.<br />
Another erosional surface (below the layer 7, Fig. 3) lies above the filling of the erosional<br />
channel, trapping animal remains. The azimuth <strong>and</strong> dip angle of the upper channel are