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1.
Fourteen sections in the Ammonitico Rosso Veronese (Callovian to Tithonian, Trento altipiano) disclose the presence of diverse facies ranging from pelagic to outer platform. In spite of this diversity, red limestones are present at different levels. Many microfacies are similar to those observed in other Paleozoic and Mesozoic red carbonates with an abundance of hematitic bioconstructions. We therefore postulate that the origin of the pigmentation is similar in all the studied cases and due to the activity of iron-oxidizing bacteria. Nevertheless, 2 notable differences are observed: the presence in the Ammonitico Rosso of manganese and the existence of in situ bacterial-fungal mats in the matrix. These “algal” mats can represent up to 20% of the sediment. Their excellent preservation (absence of packing down or crushing) is due to the slow sedimentation rate of the pelagic sediments or of the hardgrounds. 相似文献
2.
The fossil record of metriorhynchids and plesiosaurians from the Rosso Ammonitico Veronese Formation (RAVFm, Middle–Upper Jurassic, Italy) is represented by elements collected between the eighteenth and twentieth centuries. All the metriorhynchid material is referred to the genus Neptunidraco. The first RAVFm plesiosaurian material was collected in the nineteenth century and referred to Plesiosaurus: elements are here described and interpreted as a chimerical association of crocodylomorph and plesiosaurian bones, providing the first co-occurrence of these clades in the RAVFm. The second plesiosaurian is the associated skeleton that we refer to Anguanax zignoi gen. et sp. nov. Bayesian phylogenetic analysis confirms the basal geosaurine affinities of Neptunidraco resulted by parsimony analysis. Using both methods, Anguanax was recovered as a basal pliosaurid, sister group of the clade including Marmornectes and Thalassophonea. Bayesian inference methods indicate that both Italian lineages diverged from other known lineages between 176 and 171 Mya, also showing divergence rates significantly higher than any other representative of their respective clades. We suggest a phase of rapid evolutionary adaptation to deeper marine environments in the ancestors of the Rosso Ammonitico Veronese reptiles as a response to the latest Liassic regressive regime in Northern Tethys. 相似文献
3.
The Middle Bathonian to Middle Oxfordian interval in the Eastern External Subbetic (Betic Cordillera, SE Spain) is characterized by Ammonitico Rosso facies including various stratigraphic breaks. Five hardground-bounded units are recognized in relation to hiatuses in the ammonite record at the following stratigraphic boundaries: Hg1 (Lower–Middle Bathonian), Hg2 (Middle–Upper Bathonian), Hg3 (Lower–Middle Callovian), Hg4 (Middle–Upper Callovian), and Hg5 (Callovian–Oxfordian). Interesting features of these hardgrounds include their microfacies, ferruginous crusts and macro-oncoids, taphonomy of macroinvertebrates, trace fossils, neptunian dykes, and the hiatuses associated with each of them. The main hardgrounds (Hg1, Hg2, and Hg5) contain trace fossils of the Cruziana and Trypanites ichnofacies as well as abundant fossil macroinvertebrates with taphonomic features evidencing corrasion, early diagenesis, and reworking, indicating substrate evolution from softground to hardground. Neptunian dykes affected the trace fossils and ammonoid moulds, and their walls and the hardground surfaces were colonized by ferruginous microbial crusts. These features are characteristic of the External Subbetic pelagic swells, where the absence of sedimentation, sediment bypassing and erosion, and early diagenesis during relative sea-level falls produced hardgrounds. The neptunian dykes are indicative of tectonic activity in the areas of pelagic swells. Ferruginous crusts and macro-oncoids developed only on hardground surfaces and neptunian dykes walls prior to deposition of condensed bioclastic beds, which are interpreted as the first deposits after hardground development and are related to the onset of transgression. The varying ranges of the gaps as well as lateral facies changes are related to different local paleobathymetry controlled by the activity of listric faults. 相似文献
4.
Samples of Triassic pelagic limestones collected in several regions of the Central Mediterranean area were examined with the electron microscope. They show calcareous nannoplankton existing already from Middle Triassic time. The Middle Triassic nannofossils are contained in nodular limestones such as the “Ammonitico Rosso” of Epidaurus (Greece); the Upper Triassic ones are contained in nodular limestones like the Ammonitico Rosso of Hallstatt (Austria), as well as in Halobia cherty limestones of the Pindos basin in Italy, Yugoslavia and Greece. In the Halobia limestones it is possible, in spite of the recrystallization effects, to recognize such an abundance of organic forms — even if in fragments — that we can suppose the original sediment to be a kind of nannoplankton ooze.Because of the very low accumulation rate (few metres/m.y.) of the Middle Triassic Ammonitico Rosso limestones, the coccoliths cannot be considered a significant factor of carbonate pelagic sedimentation at this time; the very high accumulation rate (up to 25 metres/m.y.) of the Upper Triassic cherty limestones in the Pindos basin, on the contrary, allows the nannoplankton to be considered a very important agent of calcareous pelagic sedimentation. The authors hypothesize that the Dogger-Malm, mainly represented by radiolarites, was only a temporary interlude in the Mesozoic pelagic carbonate sedimentation. 相似文献
5.
A condensed Mid-Upper Devonian succession of the Tafilalt (Anti-Atlas) contains numerous red carbonate intervals. Bioclastic
tempestites form a transition between an outer shelf and a hemipelagic setting. The red pigmentation is not related to the
abundance of detrital iron oxides, but to the presence of iron bacteria and fungi. They form bioconstructions remarkably similar
to those previously described in the Jurassic Ammonitico Rosso from Italy and Spain. Thus, dysaerobic microenvironments are
proposed and not oxic conditions for these Fe-poor sediments. 相似文献
6.
In the Bou Rheddou mountain (Southern Tellian border), new biostratigraphic data based on Ammonites, allow precise and modify the age of the Arkell & Busson formations. The Oxfordian «Ammonitico rosso facies begin in the Transversarium zone and go into the Planula zone. This zone is characterized for the first time in this region. Lower Tithonian (Hybonotum zone) and Upper Tithonian (Microcanthum zone) are also recognized. Precisions on depositional environment and paleogeography are given. Facies and low sedimentation show a pelagic shoal (abundant planctonic organisms) slightly subsiding and lately recovered by the Jurassic transgression. During Oxfordian, episodic interruption of the «Ammonitico rosso deposits shows an unstable period with terrigenous deposits (intra-oxfordian tectonic movements). The facies of the Northern-Gondwanian carbonated platform begin earlier in the Bou Rheddou zone (Oxfordian-Kimmeridgian boundary) than in the Southern regions, where the same facies appears only in Upper Kimmeridgian. 相似文献
7.
Summary Compositional variations and grain-size properties of both carbonate constituents and conodonts as an alternative component
group were used for interpreting the processes governing the deposition of upper Famennian and middle Tournaisian calciturbidites
in Moravia, Czech Republic. Both the composition and grain-size properties of conodont element associations showed to be markedly
dependant on facies type of their host sediment. Upper Devonian calciturbidite successions deposited on flanks of wide, Moravian-Silesian
carbonate platform are composed mainly of echinoderm-and peloid-rich wacke/packstones and intraclastic float/rudstones (fine-grained
calciturbidites, “normal” calciturbidites with Tab Bouma sequences, debris-flow breccias) with abundance of shelf-and shelf
margin conodont taxa and epipelagic and “mesopelagic” conodonts. Upper Devonian calciturbidites deposited on slopes of volcanic
sea-mounts are composed of echinoderm-and peloid-rich wacke/packstones and float/rudstones with increased proportion of intraclasts
and volcanigenic lithoclasts (fine-grained calciturbidites, normal calciturbidites), yeilding abundant conodont associations
with higher proportion of “mesopelagic” taxa compared to the platform-flank examples. Middle Tournaisian calciturbidite succession
composed of crinoid-, peloid-, intraclast-and lithoclast-rich lime mudstones, wacke/packstones and float/rudstones (normal
calciturbidites and debris-flow breccias) yielded conodont element associations rich in shelt-and shelf-margin taxa, “mesopelagic”
conodonts and reworked Middle-and Upper Devonian conodonts.
In general, the ratio of shelf-and shelf margin conodont taxa to “mesopelagic” taxa is distinctly lower in finegrained calciturbidites
than it is in normal calciturbidites and debris-flow breccias. Grain-size properties (mean grain size and sorting) and percentage
of fragmented conodont elements, too, are markedly dependant on the facies type: in fine-grained calciturbidites the values
of mean grain-size and fragmentation are low and the sorting is good to very good whereas in normal calciturbidites and debris-flow
breccias the values of mean grain-size and fragmentation are distinctly higher and the sorting is poorer. The interdependence
of facies type and composition and grain-size properties of conodont element associations in gravity-flow deposits is explained
as resultant from hydrodynamic sorting during turbidity current flow and final deposition of the bed. Compositional variations
observed in our sections may thus be attributed to facies variability (coarsening-and thickening-upward trends) rather than
to sea-level fluctuations (highstand shedding of carbonate platforms). On the other hand, significant enrichment in reworked
conodont taxa in middle Tournaisian normal calciturbidites compared to scarcity and/or absence of such conodonts in essentially
identical facies of upper Famennian age indicate sea-level to be the major control governing such compositional variations,
with low relative sea-level stand in middle Tournaisian and high relative sea-level stand in upper Famennian. Thorough analysis
of conodont evolution, palaeoecology and taphonomy, with emphasis on understanding the processes of deposition of their host
rock, are recommended for any biostratigraphic and biofacies study to be done in carbonate sediments deposited under strong
hydrodynamic regimes, such as calciturbidites, temperstites, debris-flow deposits, shelf-edge oolitic sands, tidal-channel
facies etc. 相似文献
8.
Several mammal remains were recently discovered in the Cornillet gully deposits: Nyctereutes megamastoides, Pachycrocuta perrieri, Dicerorhinus etruscus, Gazella borbonica. Eucladoceros senezensis, Croizetoceros ramosus. This fauna is attributed to the middle Villafranchian.The most recent beds of the Riez-Valensole basin include several superimposed units with three type of facies: fluvio-eolian (i. e. a conglomeratesand-silt sequence), lacustrine and breccian. The Upper Pliocene represented in the Puimoisson-Ségriès region by fossiliferous lacustrine deposits is covered with coarse detrital material. The Cornillet deposits can be found at the lower part of the calcareous formation continuing this Plio-Pleistocene stratigraphy.The breccias of Balène, located at the top ofthese formations, constitute a thick spread of the detrital material of cryoclastic origin. This spread appeared later than the tectonical thrust of the surrounding calcareous mountains upon the Tertiary basin. 相似文献
9.
Summary Following a phase of predominantly siliciclastic sedimentation in the Early and Middle Jurassic, a large-scale, low-latitude
carbonate depositional system was established in the northern part of the Tabas Block, part of the central-east Iranian microplate,
during the Callovian and persisted until the latest Oxfordian/Early Kimmeridgian. Running parallel to the present eastern
block margin, a NNW/SSE-trending carbonate platform developed in an area characterized by reduced subsidence rates (Shotori
Swell). The growth of this rimmed, flat-topped barrier platform strongly influenced the Upper Jurassic facies pattern and
sedimentary history of the Tabas Block. The platform sediments, represented by the predominantly fine-grained carbonates of
the Esfandiar Limestone Formation, pass eastward into slope to basin sediments of the Qal'eh Dokhtar Limestone Formation (platform-derived
allochthonites, microbialites, and peri-platform muds). Towards the west, they interfinger with bedded limestones and marlstones
(Kamar-e-Mehdi Formation), which were deposited in an extensive shelf lagoon. In a N−S direction, the Esfandiar Platform can
be traced for about 170 km, in an E-W direction, the platform extended for at least 35–40 km. The width of the eastern slope
of the platform is estimated at 10–15 km, the width of the western shelf lagoon varied considerably (>20–80 km). During the
Late Callovian to Middle Oxfordian, the Esfandiar Platform flourished under arid climatic conditions and supplied the slope
and basinal areas with large amounts of carbonates (suspended peri-platform muds and gravitational sediments). Export pulses
of platform material, e.g. ooids and aggregate grains, into the slope and basinal system are interpreted as highstand shedding
related to relative sealevel variations. The high-productivity phase was terminated in the Late Oxfordian when the eastern
platform areas drowned and homogeneous deep water marls of the Upper Oxfordian to Kimmeridgian Korond Formation onlapped both
the Qal'eh Dokhtar Limestone Formation and the drowned Esfandiar Limestone Formation. Tectonic instability, probably caused
by faulting at the margins of the Tabas Block in connection with rotational movements of the east-central Iranian block assemblage,
was responsible for the partial drowning of the eastern platform areas. In some areas, relicts of the platform persisted to
produce shallow-water sediments into the Kimmeridgian. 相似文献
10.
A section at the top of Upper Callovian deposits at Louesme (district of Montigny-sur-Aube, Côte-d'Or, France) reveals an unbroken series of strata between the top of the Athleta zone and the base of the Lamberti zone (Upper Callovian). A few specimens of Aspidoceratinae, collected with primitive Quenstedtoceras, are refered to Euaspidoceras ferrugineum Jeannet (1951). The characters of this species, which was created for individuals collected from the Herznach Mine (Northern Switzerland), are poorly defined from the Swiss material and little is known for this stratigraphic extent. The new find provides information about the ontogeny and the stratigraphic extent of Euaspidoceras ferrugineum (base of the Henrici subzone) and helps refine the phylogenic scheme of the European Callovian Aspidoceratinae. It also casts new light of the faunal content of the Herznach C. level, which can be interpreted as a level of concentrated faunas. 相似文献
11.
A petrographic and biosedimentological study of the Rosso Ammonitico Veronese from the Trento Plateau (north-eastern Italy) shows that diagenetic (neomorphism, recrystallization) and biological processes (microbial content and pigmentation) influenced the formation and alteration of the carbonate matrix. The subject of this article is the interaction of early diagenetic processes and an attempt to explain the different colors of the matrix (red, pink, grey). Nearly 200 samples derived from 14 sections (Callovian to Tithonian) located in the Verona area have been studied by means of classical, cathodoluminescence and SEM microscopy. Calcite and ferruginous microfilaments of different shapes and sizes are present and tentatively attributed to fungi and iron bacteria. These micro-organisms precipitated iron oxy-hydroxides at poorly dysoxic-anoxic sediment–water interfaces. Further liberation of submicronic hydroxides (now hematite) was responsible for the red pigmentation of the carbonate matrices, originally composed of less than 1 μm-sized micrite. Controversial smaller nanograins (0.1–0.5 μm) attributed to nanobacteria or planktonic picoeukaryotes have been observed in the reddish samples. Recrystallization of the micrite leads to the formation of new micritic crystals, between 2 and 4 μm in size, then to microspar crystals. Micritic textures are linked to the different colours of the samples. The intensity of the red colour is correlated with the presence of hematite (former iron hydroxides) and the presence of planar subhedral micritic grains. In contrast, pink and greyish samples are linked to the increasingly coalescent structure of anhedral micritic and microsparitic crystals. 相似文献
12.
During the Late Miocene, the marginal areas of the Mediterranean Basin were characterized by the development of mixed siliciclastic-carbonate
ramps. This paper deals with a temperate siliciclastic-carbonate ramp (late Tortonian–early Messinian in age) which crops
out in the Capo Vaticano area, Southern Apennines (Italy). Carbonate components are mainly represented by calcitic skeletal
fragments of coralline red algae, bryozoans, bivalves, and larger foraminifera, whereas corals, brachiopods, echinoderms,
and planktonic foraminifera are subordinate. In the studied ramp, the depositional geometries of the main unit, the ‘Sabbie
gialle ad Heterostegina’, show a gradual steepening from low/middle (dip about 2–5°) to steep slope settings (up to 25°). The microfacies observations,
the quantitative analyses of the main biogenic components as well as the rhodolith shapes and growth forms allowed the differentiation
between the middle and the outer ramp depositional setting and the refining of the stratigraphic framework. The middle ramp
is characterized by coralline red algal debris packstone facies often associated with larger foraminiferal floatstone/packstone
facies, while the outer ramp is characterized by rhodolith floatstone/rudstone facies. These facies pass basinward into typical
open-marine deposits (planktonic foraminiferal facies). The taxonomic composition of the coralline red algal assemblage points
to a temperate paleoclimate and emphasizes the Miocene Mediterranean phytogeographic patterns. The absence of non-skeletal
grains (ooids and green algae), the paucity of Porites patch reefs, the rare occurrence of primary marine cementation, all confirm that the studied ramp was poorly lithified within
a warm–temperate setting. The flat depositional profile of the ramp can be related to the absence or paucity of primary marine
carbonate cements. 相似文献
13.
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 to Ward et al. (1970) these sediments were produced above the sea level at the edge of hypersaline lakes situated on islands. 相似文献
14.
Late Middle Jurassic dinoflagellate cyst assemblages are documented from a section in Kandern and in samples from additional localities in southern Germany. The changes in the composition of the marine microfloras through the Callovian sections are related to fluctuations in sea-levels and changes in depositional environments. The Lower Callovian claystones, which represent inner shelf, soft bottom deposits, contain rich, diverse and well preserved dinoflagellate cyst assemblages. In the Kandern section a marked transition from the Lower Callovian claystone facies to the Anceps-oolite occur within the Calloviense zone. This transition was caused by a regression, and coincides with the LZA−3.1/LAZ−3.2 boundary on the cycle chart of Haq et al. (1987). Diverse dinoflagellate cyst assemblages also occur in the Anceps-oolite, but they are not so abundant as the acritarchs which dominate the overall palynofloras. The Anceps-oolite is interpreted as representing an offshore, but shallow marine environment. The transition to the overlying Upper Callovian “Renggeri Clay” is more gradual, but accompanied by marked changes in the overall composition of the marine microfloras. The “Renggeri Clay”, which represent an outer shelf, soft bottom depositional environment, shows a higher species diversity and abundance of dinoflagellate cysts than the underlying sequences. The distribution pattern of selected species through the Kandern section indicates that some species were related to specific environments, i.e. open marine forms, and that others could have been opportunistic forms, tolerating more shallow marine environments. The distribution of the dinoflagellate cysts from southern Germany is related to the standard Northwest European ammonite zonation. The ranges of selected biostratigraphic key species are compared with ranges previously reported from the British and northwest European Jurassic. There are several discrepancies with respect to the earliest appearance and extinction datums, the only relevant Callovian palynostratigraphic “events” coinciding in southern Germany and Britain being: The extinction of Aldorfia aldorfensis at the top of the Calloviense zone, and the earliest incoming of Belodinium spp. and Liesbergia scarburghensis at the base of the Lamberti zone. 相似文献
16.
Summary The Upper Triassic carbonates of the area comprised between Maratea (Lucania) and Praia a Mare (Calabria) have been studied.
They have been grouped into six facies assemblages which, in turn, define two depositional systems.
1) |
a platform margin depositional system, comprising algae-bivalves-bearing dolomites (A1), Megalodontid-bearing limestones and
dolomites (A2), dololutites and stromatolitic/bioclastic dolomites. (A3);
|
2) |
a slope to basin depositional system comprising: buildup-facies, talus breccia and coarse to fine doloarenites (B1), coarse
to fine doloarenites and dark laminated dololutites (B2), dark laminated dololutites (B3).
|
The algal and bivalve dolomites represent typical peritidal platform sediments arranged in cyclical patterns formed as shoal
barrier and back-reef deposits periodically emerged and deformed in tepee structures.
The outer margin of the platform was colonised by peculiar bioconstructions dominated by microbialites and serpulids; little
sponges occur less frequently, whereas rare corals have been found only in some turbiditic beds.
Along the slope, in a distance that can be estimated in 5 or 6 km, the coarse breccias give way to coarse turbidites, then
finer turbidites and finally to dark, organic-rich micrites. Most of the floatstone and associated turbidites imply a fault-
controlled slope. The laminated texture and the high O.M. (Organic Matter) content of the latter facies quite obviously point
to a basin with poorly oxygenated bottom waters.
In the uppermost Triassic there is an indication of a regressive trend, evidenced by the progradation of the platform facies.
At that time a back-reef area was characterised by Megalodontid prairies alternated to areas of sandy bioclastic transport.
However, due to the poor biostratigraphic record and intense cataclasis, no definite evidence of a well-structured Rhaetian
platform margin with buildups and related basinal sediments exists.
These sedimentary and paleoecological features match well with those found in the intraplatform basins of the Dolomia Principale,
as well as with other coeval facies in Southern Apennines, Central Apennines, Southern Alps and in Southern Spain. Altogether,
this evidence suggests that in the Norian time both Southern Alps and Apennines experienced a very similar tectonic evolution
and comparable paleoceanographic conditions, characterised by the formation of numerous intraplatform throughs with restricted
circulation, the latter influencing the bottom conditions as well as the marginal communities. The margins of these restricted
basins, differently from the typical Dachstein reefs of the Upper Triassic Tethys, were dominated by microbial-serpulid communities. 相似文献
17.
Summary The Upper Triassic Dachsteinkalk of the Hochk?nig Massif, situated 50 km south of Salzburg in the Northern Calcareous Alps,
corresponds to a platform margin reef complex of exceptional thickness. The platform interior limestones form equally thick
sequences of the well known cyclic Lofer facies. Sedimentation in the reef complex was not so strongly controlled by low-amplitude
sea-level oscillations as was the Lofer facies. The westernmost of the 8 facies of the reef complex is an oncolite-dominated
lagoon, in which wave-resistant stromatolite mounds with a relief of a few metres were periodically developed. The transition
to the central reef area is accomplished across the back-reef facies. In the back-reef facies patch reefs and calcisponges
appear. The proportion of coarse bioclastic sediment increases rapidly over a few hundred metres before the central reef area
is encountered. The central reef area consists of relatively widely spaced small patch reefs that did not develop wave-resistant
reef framework structures. The bulk of the sediment in the central reef area is coarse bioclastic material, provided by the
dense growth of reef organisms and the wave-induced disintegration of patch reefs. Collapse of the reef margin is recorded
by the supply of large blocks of patch reef material to the upper reef slope. Additionally, coarse, loose bioclastic debris
was supplied to the upper reef slope and this was incorporated into debris flows on the reef slope and turbidites found at
the base of the slope and in the off-reef facies. Partially lithified packstones and wackestones of the lower to middle reef
slope were modified by mass movement to form breccia and rudstone sheets. The latter reach out hundreds of metres into the
off-reef facies environment. A reef profile is presented which was derived by the restoration of strike and dip information.
In conjunction with constraints imposed by sedimentary facies related to slope processes, the angle of slope in the reef margin
area ranged from 11° to 5°, forming a concave (dished downwards) slope. Water depth estimations require that the central reef
area did not develop in water of less than 10 metres depth. At the reef margin water depths were about 30 metres, at the base
of the reef slope 200 metres and deepening in the off-reef facies to 250 metres. While previous work on reef complexes from
this type of setting suggests growth in a heavily storm-dominated environment, the present author finds little evidence for
the storm generation of the fore reef breccias, although there is good evidence for storm-influenced sedimentation and reworking
in the central reef area.
Post-depositional processes were characterised by continued slope processes causing brecciation and hydraulic injection of
red internal sediments downwards into the reef slope and off-reef limestones. Hydrothermal circulation caused a number of
phases of post-depositional (diagenetic) brecciation. There appears not to have been an important period of emergence at the
Triassic/Jurassic boundary. 相似文献
18.
Summary Microbial organisms significantly contributed to the accumulation of shallow-marine carbonates in an open-ocean realm of the
Panthalassan Ocean during Late Carboniferous-Early Permian time. The Jigokudai plateau in the northern part of the Akiyoshidai
Plateau is the study area, where the limestone of the Upper Carboniferous Kasimovian Stage to the Lower Permian Artinskian
Stage is well exposed. The fusulinid biostratigraphy as well as top-bottom geopetal fabrics revealed that the rocks of the
study area are overturned. The thickness of this succession is approximated to 150 m.
The succession is lithologically divided into the Lower Jigokudai and Upper Jigokudai formations. The lime-stones of these
formations were deposited in a lagoonal setting. The Lower Jigokudai formation (95 m thick: Kasimovian to Asselian) is characterized
by sand shoal facies represented by crinoid- Tubiphytes-fusulinid peloidal pack/grainstones and oolitic grainstones. Phylloid algal grain/packstones and microbial boundstones subordinately
crop out.
The Upper Jigokudai Formation (55 m thick: Sakmarian to Artinskian) is characterized by shoal and tidal flat facies represented
by mollusk-fusulinid peloidal grain/rudstones, and peloidal grain/rudstones and peloidal lime-mudstones, respectively. Laterally
discontinuous microbial bound-stones occur intercalated in mollusk-fusulinid peloidal grain/rudstones. This formation contains
pendant and meniscus cements, and flat-pebble breccia indicative of an intertidal deposition and subaerial exposure.
Various types of boundstone and organosedimentary structures constructed mainly by filamentous cyanobacteria, Tubiphytes obscurus tubular microproblematicum A, and other microproblematica were recognized. Significant facies types are (1) filamentous cyanobacteria-microproblematicum
A bind/framestones, (2) Tubiphytes obscurus bindstones, (3) stromatolitic bindstones, (4) microbial laminites, (5) microbially linked structures, (6) oncoids, (7) microproblematica
B-C framestones. The calcimicrobes, combined with synsedimentary cementation, formed small-scale and low-relief mounds of
these facies, and greatly contributed to the deposition of the Kasimovian to Artinskian Panthalassan buildup. 相似文献
19.
Peltoceratoides athletoides (Lahusen) is currently used in the Tethyan domain (Submediterranean province) as an index-species for two separate biochronological units: one a horizon near the top of the Callovian, the other a zone at the base of the Oxfordian. Paleontological revision of the species, from specimens collected in situ in South East France and in Normandy shows that species is strictly localized in the lowermost Oxfordian. Consequently, the Callovian horizon, originally defined in Anjou, should be renamed the Schroederi horizon. The usefulness of Peltoceratoides athletoides as an indicator of the first Oxfordian zone in the Tethyan domain, the counterpart of the Mariae zone, is confirmed. In addition, strict localization of the species makes it is possible to define a subzone and a horizon for the base of the Oxfordian, which are the boreal equivalents of the Scarburgense subzone and Scarburgense horizon. These new data contribute to build a standard West Tethyan scale entirely independant of the boreal zonation for the Upper Callovian and Lower Oxfordian. 相似文献
20.
Summary Upper Jurassic (Malm δ to ζ1) massive limestones (‘algal-sponge-reefs, sponge-reefs, reef-complexes, reefs, algal-sponge-bioherms,
biolithites, Massenkalk, bioherms, Stillwasser-Mudmounds’) were analyzed in the Southern Swabian Alb, the Southern Franconian
Alb and in drilling wells in the Molasse basin (Southern Bavaria). This analysis was carried out within the frame of a multidisciplinary
DFG-study with the objective of decifering the controls on the development of Upper Jurassic spongiolites, their three-dimensional
distribution, their characteristic faunal composition, and the diagenetic trends of the different primary facies.
The data base consists of detailed facies mapping in the areas of the Eybtal and the Blautal (1300 samples) as well as comparative
studies in the Upper Donautal (Swabian Alb) and the Southern Franconian Alb (400 samples). All together about 500 thin sections
were studied. The distribution of the most important components (ooids, intraclasts, peloids, corals, sponges, sponge spicules,
cyanobacterial crusts, brachiopods, molluscs, echinoids, bryozoans, serpulids, Terebella, Tubiphytes), and diagenetic features (dolomite, dedolomite, silicification, stylolites, clay flasers, hematite patches) results in a
spatial distribution pattern of facies types.
The largest part (70 %) of the massive limestones consists of a peloid-lithoclast-ooid sand facies rich in completely or partly
micritized ooids. These ooids, especially in beds of the Malm δ to ε, might be the clue to a reinterpretation of the water
depth. True biogenic constructions occur (about 30 % of the volume; sponge-algalmudmounds, algal-sponge-boundstones, and brachiopod-algal-sponge-mounds)
within and at the margins of this facies and are interpreted as platform sands. The spatial distribution of the buildups in
relation to the sand facies was probably controlled by hydrodynamic conditions. In addition, zoned sponge-algal-mounds occur
in intraplatform channels and nodular sponge-algal-mudmounds in the marly basin sediments between platform sand areas.
Breccias and slumpings in beds older than the Malm ζ have to be reinterpreted. Most of the breccias found originated from
the flanks of the sand platforms, reflecting the faunal composition of the algal-sponge-boundstones which stabilized the flanks.
Breccias of this composition occur throughout the Malm δ-ζ1 and differ markedly in their composition from the sand facies.
The boundary breccia (Malm ε/ζ1) is interpreted as marking a regressive maximum. The increasing growth of buildups, rich in
brachiopods in the Malm ζ1, is ascribed to an increase of reef growth at the beginning of a transgression.
Detailed facies analyses necessary for the reconstruction of the spatial distribution of different facies types are in progress.
Most of the older data on faunal distributions cannot be used for detailed facies analysis because they differentiated only
between massive facies and bedded facies. Therefore Upper Jurassic limestones of Southern Germany should be restudied in order
to recognize the volumetric importance of sand facies and buildups within massive limestones. 相似文献
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