The present article re-evaluates the record of Early Miocene plant megafossils in the upper part of the Most Formation (Libkovice and Lom Members) according to current taxonomy, and applies the results to phytostratigraphical correlation.The characteristics of the floras have been studied, and palaeovegetation has been reconstructed based on leaf, fruit, and seed assemblages for the sites studied within the basin. New methods based on foliar physiognomy (CLAMP) have been used for obtaining palaeoclimatic estimates, and are correlated with additional studies of CO₂ concentration. Climatic fluctuations are indicated by changing plant spectra during the deposition of the Libkovice Member. The position of the Miocene climatic optimum has been located in the upper part of the Libkovice Member, and is shown to be of late Early Miocene age. On that basis, this level has been correlated with adjacent regions (e.g., the Cypris Formation of the Cheb Basin, the Upper Coal Seam of the Hrádek part of the Žitava/Zittau Basin). • Key words: palaeoecology, palaeoclimatology, phytostratigraphy, Lower Miocene, leaves, fruits and seeds, Most Basin.

TEODORIDIS, V.& KVAÈEK, Z. 2006. Palaeobotanical research of the Early Miocene deposits overlying the main coal seam (Libkovice and Lom Members) in the Most Basin (Czech Republic). Bulletin of Geosciences 81(2), 93–113 (6 figures, 3 tables). Czech Geological Survey, Prague. ISSN 1214-1119. Manuscript received January 12, 2006; accepted in revised form April 10, 2006; issued June 30, 2006.

Vasilis Teodoridis, Charles University, Institute of Biology and Environmental Education, Faculty of Education, M.D. Rettigové 4, 116 39 Praha 1, Czech Republic; vasilis.teodoridis@pedf.cuni.cz • Zlatko Kvaèek, Charles University, Institute of Geology and Palaeontology, Albertov 6, 128 43 Praha 2, Czech Republic; kvacek@natur.cuni.cz

Diverse, well preserved benthic microbial assemblages are described from two stratigraphic levels of the Mìnín-1 bore-hole from southern Moravia. Abundant cyanobacterial sheets, acritarchs, prasinophytes, and acid-resistant tissues, together with the ichnological and petrological evidence, indicate a shallow marine environment with occasional terrestrial influence. A sheltered depositional environment enabled the preservation of algal coenobia and intracellular structures. A palynological assessment contributed to the more accurate biostratigraphy of the Early Cambrian sediments in southern Moravia and confirmed thel arge extent of thebasal Cambriandeposits. Some microfossils suggest the possible presence of undisturbed marine sediments of Ediacaran age. The tectonic position of the Brunovistulicum in pre-Variscan Europe is discussed. • Key words: Early Cambrian, acritarchs, biostratigraphy, Southern Moravia.

VAVRDOVÁ, M. 2006. Two benthic microbial assemblages from the Mìnín-1 borehole (Early Cambrian, Czech Republic). Bulletin of Geosciences 81(2), 115–122 (3 figures). Czech Geological Survey, Prague. ISSN 1214-1119. Manuscript received December 5, 2005; accepted in revised form March 28, 2006; issued June 30, 2006.

Milada Vavrdová, Academy of Sciences of the Czech Republic, Institute of Geology, Rozvojová 135, 165 02 Praha 6, Czech Republic; vavrdova@gli.cas.cz

The analysis of previous experimental work made on the simulation of stromatactis-like cavities in rapidly settling sus-pensions of particulate matter substantiates the continuation of experiments toward identifying the conditions of cavity formation. It has been suggested that the most promising directions in this experimental work involve the simplification of complex factors (e.g.,variables that derive from the properties of particles and media,as well as the sedimentation dynamics of slurries). Our new hydrodynamic concept of stromatactis formation addresses the traditional key arguments of previous authors on the origins of stromatactis systems. The direct production of stromatactis-type cavities during the sedimentation of fine particulate, polydisperse, multimodal aquatic suspended matter can be characterized in terms of competition between fluids escaping from compressed,diluted domains,and the dynamic effects of the dense packing of solid particles on their boundaries, the latter gradually overtaking from the former, until a middle layer of sediment is sufficiently stabilized and the first internal sedimentation from residual suspensions begins. With the earliest stabili-zation of the grain-supported, skeleton-like structures in the sediment, low domical but surprisingly stable vaults de-velop above the cavity zones. Underneath the coalescing arched structures, there often remain places in which grains can still be fluidized, and which consequently enable the further widening of these primary cavities. The specific grain size distribution is derived from natural counterparts, an attribute combined with the high internal friction angle, and increases the final sediment cohesion and stability. This process is particularly effective when highly polydisperse-multimodal sediment materials have highly angular, rugged, or potentially cohesive grains. When the rela-tively coarsest-and finest-grained fractions are present in increased amounts, the energy dissipation of the dense turbu-lent slurry is enhanced, and the stromatactis-producing mid-layer is gradually sealed by a relatively impermeable, non-stromatactis,very fine-grained cover in the upper part of the deposit.Two categories of experiments are discussed in this paper.The first is aimed at explaining how moderately large particles can interact with each other.In this category of experiments, moderately graded tridisperse mixtures of angular or highly textured particles tended to produce firmly packed clusters with ensuing domical vaulting above cavities. The second group of experiments is based on combina-tions of bidisperse mixtures of large grains with polydisperse nearly-unimodal matrices of small angular grains. These two components, if used separately, have close to zero capacity for producing any type of stromatactis-like cavities. However, once they were combined, even modest amounts of these large grains led to the growth of spacious cavity systems, particularly if artificial crinoid columnals were present. The comparison of our experimental results with natural examples suggest that crinoid columnals must be regarded as an important, although not indispensable accelerator of stromatactis cavity production. • Key words: sedimentation experiments, polydisperse suspensions, stromatactis cavi-ties, crinoid columnals, carbonate sediments.

HLADIL, J., RÙŽIÈKA,M.&KOPTÍKOVÁ, L. 2006. Stromatactis cavities in sediments and the role of coarse-grained accessories. BulletinofGeosciences81(2), 123–146 (7 figures). Czech Geological Survey, Prague. ISSN 1214-1119. Manuscript received January 31, 2006; accepted in revised form April 11, 2006; issued June 30, 2006.

Jindøich Hladil, Academy of Sciences of the Czech Republic, Institute of Geology, Rozvojová 269, 165 00 Prague 6, Czech Republic; hladil@gli.cas.cz • Marek Rùžièka, Academy of Sciences of the Czech Republic, Institute of Chemical Process Fundamentals, Rozvojová 135, 165 02 Prague 6, Czech Republic; ruzicka@icpf.cas.cz • Leona Koptíková, the same address as the first author and Charles University, Faculty of Science, Institute of Geology and Palaeontology, Albertov 6, 128 43 Prague 2, Czech Republic; koptikova@gli.cas.cz

The present article describes the following bivalves of the Bohemian type from the Carnic Alps of Austria: Slavinka plicata (Barrande, 1881) from the Silurian Cardiola Formation, Ludlow, lower Ludfordian, and Praeostrea bohemica Barrande, 1881 from the lowermost Devonian, Rauchkofel Limestone, Lochkovian, Cellon Section.The presence of these bivalves at the aforementioned localities further support the close palaeogeographic relations between the Carnic Alps (Austria) and Perunica (Bohemia, Prague Basin) region during the Ludfordian and early Lochkovian. • Key words: Bivalvia, Silurian, Devonian, Carnic Alps, Perunica, palaeogeographic relationships.

KØÍŽ, J. 2006. Bohemian type bivalves Praeostrea bohemica Barrande, 1881 and Slavinka plicata (Barrande, 1881) from the Silurian and earliest Devonian of the Carnic Alps (Austria). Bul-letin of Geosciences 81(2), 147–149 (1 figure). Manuscript received February 14, 2006; accepted in revised form May 29, 2006; issued June 30, 2006.

Jiøí Køíž, Czech Geological Survey, Klárov 3, 118 21 Praha 1, Czech Republic; kriz@cgu.cz