Zemes un vides zinātnes Earth and Environment Sciences - Latvijas ...

E. Lukševičs, I. Zupiņš. Sedimentology, fauna, and taphonomy of Pav āri
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separately for the whole set (n = 274). The analysis of azimuthal orientation shows that
convex bones are strongly oriented showing unidirectional distribution as exemplified
by orientation of the posteror ventro-lateral plates (Fig. 9 A). A dominant NNE-SSW
orientation is approximately parallel to the axis of the erosional channel, thus indicating
deposition in one-way stream. Long bones and flat almost isometric fossils do not show
obvious orientation (Fig. 9 B, C), which might indicate an insufficient strength of the
stream, failing to lift the bones lying chaotically on the bottom of channel. It also should
be mentioned that the comparison of a mean angle of azimuthal orientation of bones
demonstrates that elongated, as well as flat and almost isometric bones are differently
oriented in different parts of the channel, whereas convex bones lie almost parallel to
the axis of erosional channel along the whole outcrop.
Breakage, wearing and abrasion of skeletal elements. Broken bones are
comparatively rare, composing less than 2% of all specimens. On the other hand, only
four of 14 lower jaws of Ventastega curonica are complete. The other ten are only
partially articulated, or some skeletal elements are missing. It should be noted that the
number of broken plates and bones could be underestimated due to selection of better
preserved specimens for the collection, but it is not the case for material analysed in
1988. In most cases broken bones are still complete with detached portions separated
by narrow fissures or cracks (usually not wider than 5 mm). Possibly breakage of skeletal
elements might be explained mainly by diagenetic processes during compaction of
rocks or even much later.
Only a few of about 800 fossils show traces of wearing, for example, the central
dorsal plate 1 of the pectoral fin of Bothriolepis LDM 81/475 lacking ornamentation.
Almost total lack of wearing and the high degree of preservation indicates that the
remains were not transported for a long distance before burial.
Discussion
The sedimentation in the Baltic paleobasin during the Famennian took place mainly in
the Latvian-Lithuanian Depression. This basin was periodically connected with an open
sea in the west and southwest from Baltic area. During maximal transgressions in Kruoja
and Joniškis time (early Famennian) and in Žagare time (late Famennian) the basin
probably contacted also with the sea in Middle Russia through territory of Belarus
(Savvaitova 1977). During significant regressions this basin became more isolated,
smaller and more shallow, often turning into a semiclosed basin with changing water
salinity. The last Devonian transgression in the Baltic took place during the Piemare
time in the late Famennian, when sea waters flooded the Latvian-Lithuanian Depression
after partial or even total erosion of the Tērvete deposits (Savvaitova 1995; Lukševičs
et al. 1999). The widest transgression took place in the Žagare time when mainly
carbonates were deposited and rather diverse marine fauna existed, including articulated
brachiopods, crinoids, cephalopods, bivalves, gastropods, and fishes (Žeiba and
Savvaitova 1981). At the very end of the Famennian, when deposits of the Pavāri and
Varkaļi members, as well as Šķervelis Formation were formed, the basin was represented
by a shallow brakish water bay almost completely surrounded by land. Palaeocarst
phenomena in the middle part of the Šķervelis Formation and finds of dolocretes in the