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1.
Pattern of conodont reworking in the Upper Devonian of the Alps: palaeoenvironmental and palaeotectonic implications 总被引:1,自引:0,他引:1
CLAUDIA SPALLETTA MARIA CRISTINA PERRI GIAN BATTISTA VAI 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1983,16(1):51-66
Transfer of sediments from shallow shelf to basin usually implies vertical (stratigraphic) reworking of fossils, but in a few instances produces only lateral reworking (actually within the time span of a subzone). An Upper Devonian (Frasnian) pelagic carbonate sequence with allodapic intercalations and thick intraclast parabreccias triggered by seismic shocks and related tsunami and turbidity currents has been studied. Here, the standard biozone sequence is undisturbed at the zonal as well as the subzonal level. However, distribution of conodonts is discontinuous, and ranges of some important species are altered; mature specimens are commonly broken, whereas complete specimens are mostly juvenile forms. Maxima and minima of element frequency and anomalous thickening or thinning of subzones are recognized. Such distribution patterns of conodonts are compared with the four main facies distinguished and related to the environmental interpretation (a platform-basin system, the original gentle slope of which was fragmenting in fault-controlled blocks). The mean frequency of shallow-water, proximal conodonts is 10% whereas transitional to distal deeper-water genera dominate throughout the entire section. In the dominant biofacies, conodonts settled vertically, in the subordinate one they were transported laterally. The 'intraclast parabreccia' is interpreted as a peculiar type of seismitc. The anomalous thickness variation of biozones is related to the step topography of the slope in a fault-controlled carbonate basin. 相似文献
2.
Dr. Andrei V. Dronov 《Facies》1993,28(1):169-180
Summary Several Waulsortian-type mud mounds nearly 500 m thick and about 5 km long occur in the Middle Paleozoic carbonate section
of the Aktur nappe in the mountains on the right bank of Isfara river. These buildups form a well developed barrier system
that stretches along the South Ferganian carbonate platform margin and divides the carbonate complex into a fore-reef and
a back-reef part. The time of the mounds' most active growth was from the Late Silurian (Ludlow) to the Middle Devonian (Eifel).
Three main facies types can be recognized in the mud mounds: 1. micritic core facies, 2. sparitic flank facies and 3. loferitic
capping facies. The central massive or crudely bedded part of the mounds consists of white or light grey clotted micrite.
Macrofossils are rare. The sparitic flank facies in contrast consists of coarse and densely packed crinoidal wackestone-floatstones
with some brachiopod shell debris. Solitary rugose corals, tabulate corals, stromato-poroids and fragments of mollusks are
also abundant. The tops of the mounds are usually covered with loferitic pelmicrites or oolitic grainstone caps. Stromatactis-like
structures are very rare and poorly developed in the South Ferganian mud mounds. However, almostin all such mounds horizons
of calcitic breccias can be found.
In order to explain all the features found in the Fergana mounds an ‘atoll-like’ model has been proposed which starts the
evolution of the mud mounds with a small nucleus bioherm. The main stage of the evolution corresponds to an atoll-like structure
developing on the surface of shallow water platforms. White clotted micrite of the mound core facies is interpreted as a accumulation
of fine-grained sediment in an inner lagoon flanked by crinoidal bar deposits. The mound flank facies represents the atoll
rim deposits from where the carbonate mud is derived. The capping loferitic facies is considered as tidal flat deposit that
developed on top of the buildups during the last stage of its evolution. The knoll shape of the mounds is explained by the
retreat of the atoll flanking crinoidal bars back into the inner lagoon during the rise in sea level. Stromatactis-like structures
of small cavities filled with sparry calcite owe their existence to burrowing organisms. Calcitic breccias are interpreted
as paleokarst collapse breccias. They indicate that the tops of the mud mound became subaerially exposed. Other evidence for
a subaerial exposure can be seen in the occurrence of Variscian ‘black and white’ limestone gravel on the tops of some mud
mounds. According toWard et al. (1970) these sediments were produced above the sea level at the edge of hypersaline lakes situated on islands. 相似文献
3.
Dipl. Geol. Jens Hefter Dipl. Geol. Volker Thiel Dr. Angela Jenisch Dr. Ursula Galling Dr. Stephan Kempe Dr. habil. Walter Michaelis 《Facies》1993,29(1):93-105
Summary Biomarker investigations were applied to the hydrocarbon fractions of three Recent (cyanobacterial mat, Lake Van microbialite
and Lake Satonda microbialite) and two Late Jurassic carbonate samples obtained from sponge bioherms. The relative concentrations
ofn-alkanes, monomethyl alkanes, acyclic isoprenoids, steroids and hopanoids in these samples are studied and their probable
biological precursors are discussed. Normal alkanes with carbon chain lengths ranging from C15 to C34 and monomethyl alkanes ranging from C17 to C21 with a varying methyl branching pattern are found. The major hydrocarbons are low molecular weight (LMW)n-alkanes (C15–C21) with a slight to strong predominance ofn-heptadecane (C17). High molecular weight (HMW)n-alkanes occur in low to moderate relative concentrations showing a preference of odd-carbon numbered compounds with a maximum
at C29. Within the acyclic isoprenoids, pristane, phytane/phytene, pentamethyl-eicosane, squalane and lycopane could be identified.
Polycyclic terpenoids of the sterane and/or hopane type are present in all carbonate samples. The carbon numbers of these
components range from 27 to 29 and 27 to 32, respectively. These organic compounds identified can be attributed to various
source organisms such as cyanobacteria, archaebacteria, algae and vascular plants. All hydrocarbon fractions of the samples
are characterized by moderate to high relative concentrations of compounds derived from cyanobacteria, signifying the role
of these organisms as contributors to the Recent as well as to the Late Jurassic carbonate deposits. 相似文献
4.
Dr. Jindrich Hladil 《Facies》1992,26(1):35-54
Summary A discussion arose in 1977 regarding the nature of the Silurian/Devonian boundary bed at Klonk, and the beds below and above
it. Present revision of the stratotype sequence found that most clayey limestones display a multiple and composed rhythmic
arrangement of laminae. Deposition of pelagic particles, effects of traction bottom currents, and turbidite inputs are distinguishable,
however, the latter are rare. Semilithified surfaces and hardgrounds were found. The boundary bed No. 20 consists of several
laminated rhythms. The Devonian base, marked by first occurrences ofMonograptus uniformis corresponds to a semilithified surface, a break in deposition for several tens to hundreds of years, and a change in direction
of bottom currents. A moderately rippled set at the Devonian base is only about 1 cm thick and passes again into the horizontal
laminated rhythms. The deposition of the boundary bed lasted about 1.2 to 2.0 Ka. It cannot be explained as a turbidite. 相似文献
5.
Riccardo A.A Muzzarelli Viviana Ramos Vesna Stanic Bruno Dubini Monica Mattioli-Belmonte Giorgio Tosi Roberto Giardino 《Carbohydrate polymers》1998,36(4):267-276
The effects of N,N-dicarboxymethyl chitosan (DCMC) on the precipitation of insoluble calcium salts, namely phosphate, sulfate, oxalate, carbonate, bicarbonate and fluoride, and magnesium salts, namely phosphate and carbonate, were studied. Results indicated that the chelating ability of DCMC interfered effectively with the well-known physico-chemical behaviour of magnesium and calcium salts. Dicarboxymethyl chitosan formed self-sustaining gels upon mixing with calcium acetate, as a consequence of calcium chelation. DCMC mixed with calcium acetate and with disodium hydrogen phosphate in appropriate ratios (molar ratio Ca/DCMC close to 2.4) yielded a clear solution, from which, after dialysis and freeze-drying, an amorphous material was isolated containing an inorganic component about one half its weight. This compound was used for the treatment of bone lesions in experimental surgery and in dentistry. Bone tissue regeneration was promoted in sheep, leading to complete healing of otherwise non-healing surgical defects. Radiographic evidence of bone regeneration was observed in human patients undergoing apicectomies and avulsions. The DCMC–CaP chelate favoured osteogenesis while promoting bone mineralization. 相似文献
6.
B. Delesalle R. Buscail J. Carbonne T. Courp V. Dufour S. Heussner A. Monaco M. Schrimm 《Coral reefs (Online)》1998,17(2):121-132
The export of carbon and carbonate from coral reefs was investigated through a multidisciplinary investigation of the hydrological,
geochemical, sedimentological and biological features of Tiahura reef on the northwestern coast of Moorea Island (French Polynesia).
The hydrology of the fore-reef is characterised by prevailing longshore western currents and a strong thermocline. As revealed
by turbidity structures (benthic and intermediate nepheloid layers) and by the amount of particles collected by near-bottom
sediment traps, horizontal and downslope advections of particles dominate over offshore vertical transport. The exported material
is rich in carbonate (ca. 80%) and poor in organic matter (ca. 4%). Sedimentation rates at 430 m depth, i.e. definitive export,
reached 209.6 mg m-2 d-1 (dry weight). Estimates of carbon and carbonates export for Tiahura reef also reported here represent respectively 47% and
21% of the organic and inorganic carbon produced within the reef. 相似文献
7.
The trace fossil Zoophycos has been described from the Middle Triassic carbonates of the German Basin for the first time. It occurs in a calcilutite bed at the top of a shallowing-upward cycle (parasequence) in the transgressive systems tract of the Middle to Upper Muschelkalk sequence of Thuringia (Germany). Based on sedimentological and palaeontological features, the studied interval is interpreted as deposited in a marine nearshore environment with proximal storm deposits (tempestites). Zoophycos occurs in a very simple planar form with lobate spreiten, which were most likely produced by a worm-like animal by strip mining. The upper tier of the ichnofabric consists of Zoophycos, whereas the lower tier is occupied by cylindrical trace fossils of unknown taxonomic affiliation and with decreasing size towards the bottom. Associated trace fossils such as Rhizocorallium, Balanoglossites and Trypanites indicate a partly firm to hard substrate. No mixed layer is developed at the top of the trace fossil bearing succession. The ichnofabric together with the sedimentological features (disseminated pyrite, blue-grey colour) and palaeontological circumstances (poor benthic fauna, meiofauna with a small body size) support an interpretation of a dysaerobic environment. In the view of evolutionary change, Palaeozoic Zoophycos occurs in both deep and shallow marine deposits, whereas Mesozoic and Cenozoic Zoophycos is only common in shelfal and deeper-marine deposits. The new finding from the shallow-marine Middle Triassic represents the first reliable occurrence of Zoophycos after the end-Permian mass extinction and shows close similarities to its Palaeozoic precursors. It demonstrates that the producer survived the end-Permian mass extinction, became re-established in the nearshore realm and progressively colonized deeper-marine environments during the Mesozoic and Cenozoic. 相似文献
8.
Summary Paleozoic carbonate ramp sedimentation has generally been described in terms of downlapping clinoforms composed of allochthonous
sediment derived from shallower environments. However, during transgressive episodes when carbonate sediment production is
low and down slope sediment transport by gravity becomes inactive, autochthonous carbonate sediment accumulates in vertical
stacks of essentially in situ sediment. Autochthonous outer ramp deposition is probably a part of many Paleozoic ramp strata,
but has heretofore not been recognized because of the general absence of adequate exposures.
Evidence of autochthonous, in situ deposition and preservation of sediments in a starved setting is well displayed in the
Alamogordo Member of the Lake Valley Formation in south central New Mexico. This evidence includes: 1) beds and bed sets that
are individually continuous and traceable along ramp slope for 32 km, 2) down-ramp sequential distributions of depth-sensitive
organisms and assemblages but patchy distribution of rock types, 3) lack of sedimentary structures indicative of transport,
4) well preserved, unabraded fossils, 5) the common occurrence of fossils in life position, 6) beds traceable into and through
mounds 7) bed thickness trends ascribed to biotic productivity, and 8) geopetal structures in original position.
Integrated paleontologic, sedimentologic, and stratigraphic data provide information about depositional processes and setting.
The depositional slope was approximately 0.5o based on the distribution of fossil algae; this is comparable to dips reported for other Mississippian homoclinal ramps.
An oxygen minimum zone may have impinged on the ramp during a major flooding event. Shifts in biotic gradients from bed to
bed reveal transgressive-regressive patterns that would not be resolvable without detailed paleontological evidence.
The Alamogordo Member formed as a result of transgressive and early highstand starved carbonate sedimentation along a narrow,
homoclinal outer ramp. The surface of maximum flooding and the boundary between the TST and HST are within the Alamogordo
Member. 相似文献
9.
Prof. Dr. Josip Tišljar M.Sc. Igor Vlahović Dr. Ivo Velić Dr. Dubravko Matičec Dr. Julie Robson 《Facies》1998,38(1):137-151
Summary During the Late Albian, Early and Middle Cenomanian in the NW part of the Adriatic Carbonate Platform (presentday Istria)
specific depositional systems characterised by frequent lateral and vertical facies variations were established within a formerly
homogeneous area, ranging from peritidal and barrier bars to the offshore-transition zone. In southern Istria this period
is represented by the following succession: thin-bedded peritidal peloidal and stromatolitic limestones (Upper Albian); well-bedded
foreshore to shoreface packstones/grainstones with synsedimentary dliding and slumping (Vraconian-lowermost Cenomanian); shoreface
to off-shore storm-generated limestones (Lower Cenomanian); massive off-shore to shoreface carbonate sand bodies (Lower Cenomanian);
prograding rudist bioclastic subaqueous dunes (Lower to Middle Cenomanian); rudist biostromes (Lower to Middle Cenomanian),
and high-energy rudist and ostreid coquina beds within skeletal wackestones/packstones (Middle Cenomanian).
Rapid changes of depositional systems near the Albian/Cenomanian transition in Istria are mainly the result of synsedimentary
tectonics and the establishment of extensive rudist colonies producing enormous quantities of bioclastic material rather than
the influence of eustatic changes. Tectonism is evidenced by the occurrence of sliding scars, slumps, small-scale synsedimentary
faults and conspicuous bathymetric changes in formerly corresponding environments. Consequently, during the Early Cenomanian
in the region of southern Istria, a deepening of the sedimentary environments occurred towards the SE, resulting in the establishment
of a carbonate ramp system. Deeper parts of the ramp were below fair-weather wave base (FWWB), while the shallower parts were
characterised by high-energy environments with extensive rudist colonies, and high organic production leading to the progradation
of bioclastic subaqueous dunes. This resulted in numerous shallowing- and coarsening-upwards clinostratified sequences completely
infilling formerly deeper environments, and the final re-establishment of the shallow-water environments over the entire area
during the Middle Cenomanian. 相似文献
10.
Summary A horizon with pot casts (potholes) is described from shallow-marine limestones of thespinosus-zone (‘Discitesschichten’, Upper Muschelkalk) near Weimar/Thuringia. The erosional structures are not developed as sole marks
but occur as isolated structures. They differe distinctly in size and composition from pot casts described from the Muschelkalk
of Southern Germany. Vertical sedimentary zonation and varying sediment infill in the structures suggest continuous erosion
and deposition contemporaneous with the background sedimentation. Deposition may have been caused by oscillatory and unidirectional
flows as well as a long period of micrite deposition. Early diagenetic deformations (e.g. dewatering, brecciation, pressure
solution) have controlled by a higher continuous water flux inside the pot casts and higher intergranular dispersal pressure. 相似文献