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Summary A stromatactis mud-mound has been found near Slavnické Podhorie in the Czorsztyn Unit of the Pieniny Klippen Belt (Western
Carpathians, Slovakia). Its stratigraphic range is Bathonian to Callovian and it is one of the youngest known true stromatactis
mud-mounds. The complete shape the mound is not visible since the klippe is a tectonic block encompassed by younger Cretaceous
marls. The matrix is micritic to pelmicritic mudstone, wackestone to packstone with pelecypods, brachiopods, ammonites, and
crinoids. An important component of the mound is stromatactis cavities that occur as low as the underlying Bajocian-Bathonian
crinoidal limestones. The stromatactis cavities are filled by radiaxial fibrous calcite (RFC) as well as in some places by
internal sediment and, finally, by clear blocky calcite. Some cavities remain open with empty voids in the centres. In some
stromatactis cavities, tests of cavedwelling ostracodsPokornyopsis sp. were found, surrounded by the latest stages of the RFC. This indicates that stromatactis cavities formed an open network
enabling migration of the ostracods and their larvae over a period of time.
Except in the case of the stromatactis cavities, there are numerous examples of seeming recrystallizationsensu Black (1952) and Ross et al. (1975) and Bathurst (1977). The radiaxial fibrous calcite encloses patches of matrix and isolated
allochems. The RFC crystals are oriented perpendicularly to the substrate whether it is a cavity wall or enclosed allochems.
This means that the RFC crystals could not grow from the centre of the cavity outward as postulated by Ross et al. (1975).
There are also numerous “floating” isolated allochems, which are much smaller than the surrounding RFC crystals. The explanation
involving three-dimensional interconnection of allochems seems to be unlikely. In the discussed mud-mound there is a conflict
between apparently empty cavities that had to exist in the sediment and seeming “recrystallization” related to the same RFC
that forms the initial void filling. The authors favor an alternative explanation of the “recrystallization”. We presume that
the allochems served as nucleation points on which the crystals started to grow. Obviously, the allochems and the micritic
patches were different from the surrounding material. RFC crystals (either short-or long-bladed) of the “recrystallization”
spar grew at the expense of decaying microbial mucillages. The mucus can enclose peloids, allochems, or whole micritic patches
that “floated” in the cavity and served as nucleation sites for the RFC crystals. The entire mud-mound represents a microbially
bound autochthonous micritic mass; the stromatactis and stromatactis-like cavities originated where purer mucillage patches
occurred, giving rise to open spaces. Such features as the morphological variety of stromatactis fabrics, the pervasive penetration
of the sparry calcite into matrix, and the enclosure of the “floated” allochems and mudstone patches by sparry calcite, seem
to provide support for the presence of mucus aggregates within the mound body. The mucus might be related to protozoans rather
than to sponges or other well organized metazoan organisms.
Occurrence of the stromatactis cavities in the underlying Bajocian-Bathonian crinoidal limestones support the inference on
biological origin of the stromatactis fabrics. The alternative inorganic models of stromatactis origin (e.g., internal erosion
or water-escape) are hardly applicable to the sediment formed by crinoidal skeletal detritus. 相似文献
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Dr. Jacek Matyszkiewicz 《Facies》1993,28(1):87-95
Summary The Middle Oxfordian strata in the southern part of the Cracow-Wielun Upland consist of platy and bedded limestones (‘normal
facies’), of massive limestones as well as locally of mass flow sediments. Massive limestones, prevailing in the Upper Oxfordian,
form commonly carbonate buildups, which are made up predominantly of cyanobacterial allochems and to a minor amount of siliceous
sponges.
Stromatactis can be best observed in the Mlynka quarry. They occurs in the uppermost part of slope sediments close to a cyanobacterial-sponge
buildup. The bedding-plane of the slope sediments is directly overlain by debris-flow and grain-flow sediments.
Fragments of a primary laminar framework rich in growth-cavities occur in the uppermost part of the slope sediments as precondition
for the formation of stromatactis. The stromatactis cavities were formed by internal reworking and erosion within these organic
growth cavities, caused by strong bottom currents due to mass transport from higher parts of the buildup. 相似文献
3.
The lower slope of the drowned Alpine Adnet Reef was recolonized in Hettangian time by sponge communities of hexactinellid (hexactinosid and lyssacinosid) taxa and a few demosponges. Special taphonomic processes caused an excellent preservation of these sponges. The preservation allows to define several growth forms and to study original spicule configurations of the mainly non-rigid skeletons. Sponge faunas of presumably similar associations are known from adjacent basins, but only by isolated spicules of completely collapsed specimens. In Adnet the sponges are embedded in biodetrital limestones of the Schnöll Formation. Orientation and distribution of the sponges reflect autochthonous faunas that have been mixed with dislocated individuals by local water currents. The predominance of erect sponge types indicates intermediate sedimentation rates and/or occasional high-energy events. Sponge types and community structures are comparable with those ones from Middle Paleozoic mud mounds. Several hiatuses, mostly characterized by ferromanganese crusts have been kept free of sponge settlement. Carbon stable isotopes of the sponge-rich sequence show a small negative δ13Ccarb excursion that covers the period from Lower Hettangian to Lower Sinemurian.This revised version was published online in May 2005 because several displayed passages had been inadvertently deleted in the original published version. 相似文献
4.
Prof. Dr. Gerd Flajs Dipl.-Geol. Manfred Vigener Prof. Dr. Helmut Keupp Prof. Dr. Dieter Meischner Dipl.-Geol. Fritz Neuweiler PD Dr. Josef Paul Prof. Dr. Joachim Reitner Dr. Klaus Warnke PD Dr. Helmut Weller Dipl.-Geol. Patrick Dingle Dipl.-Geol. Christian Hensen Prof. Dr. Priska Schäfer Dr. Pascale Gautret Prof. Dr. Reinhold R. Leinfelder PD Dr. Hansmartin Hüssner Dipl.-Geol. Bernd Kaufmann 《Facies》1995,32(1):1-69
Summary This research report contains nine case studies (part II to X) dealing with Palaeozoic and Mesozoic mud mounds, microbial
reefs, and modern zones of active micrite production, and two parts (I and XI) summarizing the major questions and results.
The formation of different types ofin situ formed micrites (automicrites) in close association with siliceous sponges is documented in Devonian, Carboniferous, Triassic,
Jurassic and Cretaceous mounds and suggests a common origin with a modern facies found within reef caves. Processes involved
in the formation of autochthonous micrites comprise: (i) calcifying mucus enriched in Asp and Glu, this type presumably is
linked to the formation of stromatolites, thrombolites and massive fabrics; (ii) protein-rich substances within confined spaces
(e.g. microcavities) result in peloidal pockets, peloidal coatings and peloidal stromatolites, and (iii) decay of sponge soft
tissues, presumably enriched with symbiotic bacteria, lead to the micropeloidal preservation of parts of former sponge bodies.
As a consequence, there is strong evidence that the primary production of micrite in place represents the initial cause for
buildup development. The mode of precipitation corresponds to biologically-induced, matrix-mediated mineralization which results
in high-Mg-calcites, isotopically balanced with inorganic cements or equilibrium skeletal carbonates, respectively. If distinct
automicritic fabrics are absent, the source or origin of micrite remains questionable. However, the co-occurring identifiable
components are inadequate, by quantity and physiology, to explain the enhanced accumulation of fine-grained calcium carbonate.
The stromatolite reefs from the Permian Zechstein Basin are regarded as reminiscent of ancestral (Precambrian) reef facies,
considered the precursor of automicrite/sponge buildups. Automicrite/sponge buildups represent the basic Phanerozoic reef
type. Analogous facies are still present within modern cryptic reef habitats, where the biocalcifying carbonate factory is
restricted in space. 相似文献
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