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Summary The Sikhor Formation (new) is a predominantly siliciclastic sediment package intercalated between the marly-silty Baghamshah
Formation (below) and the calcareous Esfandiar Limestone and Qal'eh Dokhtar Limestone formations (above). All stratigraphic
evidence points to an Early Callovian age of the formation. The Sikhor Formation is restricted to the southern and central
Shotori Mountains and consists of two members: The Kuh-e-Neygu Member (new) is composed of fluvialdeltaic conglomerates, sandstones,
and siltstones grading into marly silt of the Baghamshah Formation. The overlying Majd Member (new) is characterised by mixed
siliciclastic-carbonate sediments that record the interfingering of carbonate ramp sediments with fluvialdeltaic sands and
silts. Evidence of erosional truncation of the underlying Baghamshah Formation and confinement of the siliciclastic sediment
to a comparatively narrow, NNW-SSE elongated strip suggest that the formation had its origin in the asymmetric uplift of a
westdipping tilted fault block in the southern Shotori Mountains that shed its sediment predominantly in a northern and eastern
direction. After erosional levelling, the former uplifted areas were overgrown by the highly productive Esfandiar Carbonate
Platform. The Sikhor Formation thus is evidence of an extensional tectonic pulse in the early Callovian and underlines that
this area of the Tabas Block was a tectonically highly unstable area during most of the Jurassic. 相似文献
3.
Summary The high-plateau of the Jbel Bou Dahar, situated in the Central and Eastern High Atlas of Morocco, represents a Lower Jurassic
carbonate platform that drowned at the beginning of the Toarcian. Three phases of platform evolution can be distinguished:
During thepre-drowning phase (upper Sinemurian— upper Pliensbachian) the platform interior facies reflects a restricted-marine lagoonal environment, protected
by scattered buildups and cemented debris at the platform margin. Upper and mid-slope are dominated by coarse-grained, poorly
sorted limestones, deposited through debris flows during sea-level lowstands. Sea-level highstand deposits occur at the toe
of slope and are formed by an alternation of fine-grained litho- and bioclastic pack- to grainstones (turbidites), marls and
mud- to wackestones (hemipelagic oozes).
A condensed section, reflecting an abrupt and fundamental environmental change along the entire platform, characterises thedrowning phase (upper Pliensbachian— lower Toarcian). Within the platform interior densely packed biosparites represent the switch to high-energy
environments, causing erosion of the former pre-drowning lagoonal sediments. These erosional products were redeposited on
the platform slope, leading to the formation of coarse-grained non-skeletal sparites and micrites. Both platform interior
and slope successions show a series of cyclic variations in sediment composition that could have been triggered by small-scale
sea-level fluctuations.
In contrast to the abrupt facies change at the pre-drowning —drowning boundary, the transition to thepost-drowning phase (lower Toarcian—Aalenian) is gradual. During this phase, biopelmicrites and pure micrites were deposited in all platform
sections, followed by the deposition of calcistiltites. The facies point to quiet-water conditions below storm-wave base and
display a uniform deep-marine sedimentation.
This analysis shows that the drowning of the Jbel Bou Dahar carbonate platform was caused by abrupt and fundamental changes
in the shallow-water realm. After exposure of the platform, these changes prevented the carbonate factory from re-establishing
itself and made it impossible for the platform to keep up with the subsequent rise in sea level. These local changes were
probably triggered by high-frequency sealevel variations in combination with regional or even worldwide changes in ocean circulation
patterns. 相似文献
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Paleoenvironmental model for Eocene foraminiferal limestones of the Adriatic carbonate platform (Istrian Peninsula) 总被引:4,自引:3,他引:1
The foraminiferal limestones from the Middle Eocene Central Istrian region illustrate progressive deepening of depositional gradients. Shifting of Lower Cuisian to Upper Lutetian microfacies can be described in terms of a ramp model. The Orthophragminae-bearing parts of the foraminiferal limestones are interpreted in terms of larger foraminiferal faunal associations, planktonic foraminiferal relative abundance, limitations of algal endosymbionts, foraminiferal lamellar thickness and flattening of test shapes. Microfacies I contains the most diverse larger foraminiferal association with a predominance of large, thick nummulitids, assilinids, and asterocyclinids. Microfacies II is characterized by a gradual increase of Orthophragminae diversity and abundance. Nummulitids, equally abundant, are dominated by lenticular and subspherical specimens. The reduction in number of nummulitid specimens with characteristic biconical radiate morphologies, and relative abundance of flattened orthophragminids, characterizes Microfacies III. Scattered biodestructed orthophragminid tests and planktonic foraminifera constitute Microfacies IV, indicating the end of a long-lasting, shallow-marine Adriatic Carbonate Platform regime. 相似文献
7.
Upper jurassic to lower cretaceous carbonate facies of african affinities in a Peri-European area: Chalkidiki Peninsula, Greece 总被引:1,自引:0,他引:1
Summary The Epanomi-New Iraklia area (West coast of the Chalkidiki peninsula) is considered to belong to the Prepeonias subzone (or
Gevgeli unit), with a palaeogeographic position near the European margin, represented by the Serbo-Macedonian massif, and
at a considerable distance from the fragmented African plate, the marginal block of which is here the Pelagonian Domain. In
some boreholes in the area an Upper Jurassic to Lowei Cretaceous limestone sequence has been observed, ending with an unconformity
and followed by an Upper Middle-Lower Upper Eocene transgressive bioclastic limestone, an Upper Eocene to Lower Oligocene
clastic series and Neogene deposits.
This Upper Jurassic to Lower Cretaceous carbonate platform sequence and probably the Upper Jurassic limestones with bauxites
of the nearby Mt. Katsika, show African affinities, viz: the presence of the essentially Aptian algal speciesSalpingoporella dinarica, an African plate marker; the chlorozoan type association and the bauxite formation during the Late Jurassic indicating tropical
conditions; finally, the chloralgal type association and the sporadic presence of radial-fibrous ooids during the Early Cretaceous
indicating peritropical conditions. Lower Cretaceous limestones are apparently missing in the innermost Hellenides. In the
Pelagonian Domain s.l., on the other hand, Upper Jurassic to Lower Cretaceous limestones are found in some places, with same
characteristics as in the Epanomi-New Iraklia boreholes. On the contrary, the Upper Eocene to Lower Oligocene clastic series
of the boreholes can be correlated with the Axios (=Vardar) molassic basin, inline with its present situation.
During the Mesozoic, the Epanomi area therefore belonged to a micro-block, next to the NE margin of the Pelagonian Domain,
in contrast to earlier interpretations. Its present time position results from Early Cenozoic tectonic phases. 相似文献
8.
Kazem Seyed-Emami Franz T. Fürsich Markus Wilmsen Gerhard Schairer Mahmoud R. Majidifard 《Pal?ontologische Zeitschrift》2005,79(3):349-369
In the Jajarm area (eastern Alborz Mountains, NE Iran) the ?Upper Triassic — Lower Bajocian siliciclastic Shemshak Formation is up to 2000 m thick. Whereas the lower third of the formation is nearly exclusively non-marine, the upper two-thirds are fully marine. The middle part is characterized by several levels containing a relatively diverse and well preserved assemblage of ammonites of the Toarcian to Aalenian stages. Two sections of the ammonite-bearing strata, spaced 20 km, are presented and correlated by means of ammonite biostratigraphy. The ammonite fauna consists of 27 taxa, some of which are recorded for the first time from the Alborz Mountains. The ammonites are briefly described and their palaeobiogeographic context is reviewed. The ammonite fauna of the Shemshak Formation at Jajarm, as elsewhere in North and Central Iran, is exclusively Northwestern Tethyan in character and is closely related to the faunas of Northwestern and Central Europe. 相似文献
9.
The characterization and distribution of the microfacies and the microfossil assemblages of a Middle Oxfordian section from
Jura Mountains composed by thick oolitic–coral limestones is analyzed. Six microfacies types (mainly grainstones) are differentiated
mainly composed by ooids, intraclasts and bioclasts. Foraminiferal assemblages are dominated by agglutinated forms. Benthic
microbial communities and sessile foraminifera are the main components of the encrustations. The whole set of microfossil
assemblages is typical of shallow subtidal environments rich in “algae” (Cayeuxia, “Solenopora”, Thaumatoporella, Bacinella, Girvanella and Terquemella) and foraminifera such as Nautiloculina oolithica, Redmondoides lugeoni, Ammobaculites coprolitiformis, Troglotella incrustans and Rectocyclammina. The increasing upward record of debris of algae and Nautiloculina, and the decrease of serpulids, bryozoans, nodosariids and ophthalmidiids indicate a shallowing-upward trend. The stratigraphic
distribution of microfacies and microfossil assemblages lead to differentiate two main successive phases. The first is a deeper
subtidal environment in an open shelf, while the second is a shallow subtidal environment with evolution from winnowed to
more restricted conditions. Microfabrics of radial to concentric ooids upwards in the section correspond to higher energy
environments related to an oolitic shoal. This study shows how a very detailed analysis of microfacies, which integrates oolitic
features, microfossil assemblages and microtaphonomy is potentially a useful tool for interpreting hydrodynamism and sequence
evolution in marine carbonate shallow environments. 相似文献
10.
Ali Jalali Hamed Yarahmadzahi Daniel Vachard Mehran Arian Abdollah Saidi Mohsen Aleali 《Annales de Paléontologie》2021,107(2):102487
The Rectogordius (Foraminifera) abundance zone is described in the east of the Shishtu village in the Ozbak Kuh Mountain. The samples were collected in the Zaladou Formation., which is 60 m thick and composed of shales, sandstones, sandy limestones, microconglomerate, bioclastic limestones, coral limestone and fusulinid limestones. The Rectogordius abundance zone was found in sandy bioclastic limestone. It displays two species and three subspecies of this foraminifer, including Rectogordius iranicus, R. iranicus gadukensis, R. minimus and R. minimus shishtuensis n. subsp., R. iranicus ozbakensis n. subsp. The age of this abundance zone is considered to be Gzhelian, due to the distribution of Rectogordius in Central Iran (Ozbak Kuh; Zaladou Formation), central and eastern Alborz (Emarat Fm.), Sanandaj-Sirjan zone (Vazhnan Formation), as well as in the Donets, Arctic Canada, Afghanistan, and the Carnic Alps. The genus Rectogordius is possibly restricted to the northern Paleotethys margin, northern Cimmerian margin, shelf of the Uralian Ocean as far as the northernmost part of North America. Two new subspecies Rectogordius minimus shishtuensis n. subsp. and Rectogordius iranicus ozbakensis n. subsp. are described. 相似文献
11.
Summary A carbonate buildup near the top of the Upper Jurassic limestone sequence in the Cracow area with a rigid framework built
ofTubiphytes and thrombolites, and some fragments of encrusted siliceous sponges and serpules is described. The limestones form a dome-like
elevation at the eastern wall of a 15 m high quarry flanked on both sides by stratified limestones with cherts. Six microfacies
have been distinguished within the buildup: (1)Tubiphytes/thrombolite boundstone and (2) bioclasticTubiphytes/thrombolite wackestone dominate in the central and bottom part of the buildup. They gradually replace the cyanobacterial
crusts and siliceous sponges (3. sponge-algal boundstone), which are sporadically the rock-forming elements in the basal part
of the buildup as well as the top. Serpules randomly distributed within the buildup also form small cm-sized structures with
a rigid framework (4. serpula-peloid boundstone). (5) tuberoid-peloid wackestone/floatstone and (6) ooid intraclastic grainstone
exhibit no significant distributional pattern. Bioclastic-peloidal packstone comprising material derived from the destruction
of the buildup occurs in the highest part of the outcrop, overlying the buildup.
The sediments of the buildup were subject to rapid lithification, evidence by borings and neptunian microdykes filled with
internal sediments, as well as by fracturedTubiphytes. Numerous petrographic features indicate probable episodic emergence of the buildup during its growth; these include asymmetric
dissolution textures, asymmetric cements, vadose crystal silt and calcite pseudomorphs after gypsum.
Upper Oxfordian carbonate buildups in the Cracow area display various stages of evolution. The carbonate buildup in Mydlniki
most closely resembles classical Upper Jurassic reefs. 相似文献
12.
Summary East of Seefeld/Tyrol the Hauptdolomit facies (Triassic, Norian) is accompanied by an organic-rich intercalation, the Seefeld
facies. Three facies were distinguished, which developed within a separate basin within the Hauptdolomit carbonate platform.
These facies have been investigated in an environmental and palaeoecological context applying microfacies analysis, palynology,
organic petrology, organic geochemistry and stable isotope geochemistry. As the controlling factors of sedimentation, sea
level changes are suggested for large scale fluctuations, and climatic changes for variations on a smaller scale. Within the
basin facies a μm-scaled rhythm can be observed, which was obviously seasonally controlled. Amajor amount of organic material
of the deposit has been produced by microbial activity under anoxic conditions. Causes for the absence of pollen and spores
in many black shale deposits are discussed. 相似文献
13.
The rhodolithic slope deposits of a Burdigalian carbonate platform in Sardinia near Sedini were analyzed to reconstruct facies
and palaeobathymetry. There is a distinct red-algal growth zonation along the platform slope. The clinoform rollover area
consists of coralline-algal bindstones, which downslope change into a zone where rhodoliths are locally fused by progressive
encrustation. Mid-slope rhodoliths are moderately branched, and downslope rhodoliths have fruticose protuberances, resulting
in branching rhodolith growth patterns. There is a sharp change from the rhodolitic rudstones to the basinal, bivalve-dominated
rudstones at the clinoform bottomsets. Red-algal genera identified include Sporolithon, Lithophyllum, Spongites, Hydrolithon, Mesophyllum, Lithoporella, Neogoniolithon, and other mastophoroids and melobesioids. Genera and subfamilies show a zonation along the clinoforms, allowing palaeobathymetric
estimates. The clinoform rollovers formed at a water depth of around 40 m and the bottomsets around 60 m. Results from geometrical
reconstruction show that coral reefs in the inner platform formed at water depths of around 20 m. Therefore, the Sedini carbonate
platform is an example of a reef-bearing platform in which the edge or the platform-interior reefs do not build up to sea
level. 相似文献
14.
Bioclastic accumulations often occur on top of Tethysian carbonate platforms and crinoids are a common constituent of these
bioclastic deposits on Lower and Middle Liassic carbonate platforms. In contrast, the relevant literature contains few examples
in which the main constituent of the lumachels is thin-shelled bivalves (filaments). This paper presents a study of a filament
lumachelle cropping out on top of a Middle Jurassic carbonate platform. The carbonate platform is represented by the Jabalcuz
Formation, found in one of the northernmost Subbetic units (south of Jaén city). The lumachelle marks the demise of the carbonate
platform and has special features that characterize the drowning phase. This process has been related with the syn-rift extensional
tectonics associated to the opening of the Tethys westwards. Stratigraphically, the lumachelle occurs on top of shallow-water
oolite limestones (Middle Jurassic) and is overlain by radiolarian-rich pelagic and resedimented deposits (Latest Callovian–Oxfordian).
It occurs as a body (about 1.5 km wide and up to 8 m thick) made up entirely of densely packed thin bivalve shells. A remarkable
feature of the bivalve shell beds is stromatolite-like crumpled lamination at the outcrop. The observations made at the outcrop
scale, by microscope under transmitted light, and by cathodoluminiscence favor a diagenetic origin for this striking structure.
Other hypotheses, such as its possible relation with seismicity, cannot be confirmed. The filaments would have filled one
of the former basins that originated in relation with syn-rift fault-block tectonics leading to the demise of the carbonate
platform. Tectonics was one of the main factors setting in motion a carbonate productivity crisis and the inhibition of a
diverse benthic community. Once production failed in the carbonate factory, storms and probably hurricanes as well, swept
shell deposits from the shallowest areas of the shallow-water carbonate platform and accumulated them in a coevally formed
small half-graben basin. At least three main depositional stages can be differentiated in the fill of this half-graben basin,
which was a sediment trap for the accumulation and preservation of the tiny bivalve shells against ebb surges. The massive
accumulation of valves, the shortage of micrite around the filaments, outcrop morphology and facies relationships, along with
regional geology, are among the arguments supporting this interpretation. 相似文献
15.
Microfacies controls on weathering of carbonate building stones: Devonian (northern Sauerland,Germany) 总被引:1,自引:0,他引:1
Dr. Andreas May 《Facies》1994,30(1):193-208
Summary The Beisinghausen Limestone (Upper Givetian to Frasnian) in the Eslohe-Reiste area (northern Sauerland), used in the past
as building stone, corresponds to proximal carbonate turbidites which have been derived from the Attendom-Elspe ‘reef’ complex.
The particles of this allodapic limestone originated in different parts of the carbonate complex as shown by facies-diagnostic
microfossils (foraminifera, calcisphaeres, calcareous algae, microproblematica). The fossils as well as the other dominating
grain types (lumps, peloids) point to source areas located within lagoonal and slope environments. Reef-derived material is
rare.
The turbidites exhibit four microfacies types, differentiated by composition and size of the grains as well as by micrite
content and corresponding to the common vertical and lateral textural variation of limestone turbidites.
These MF types were recognized in outcrops as well as from building stones used in building the St. Pankratius church in Eslohe-Reiste
(northern Sauerland) in 1849 and in the renovation of the church in 1963/64.
The comparison of microfacies and the degree of the destruction of ‘old’ and ‘new” building stones by weathering (macroscopically
described by the ◂Fabric Index’: Product of the ‘Rock Destruction Risk’ and the ‘Rock Preparation Destruction Degree’) shows
that intrabioclastic rudstones (MF type 1) and bioclastic grainstones (MF type 2), both characterizing the basal parts of
the turbidite beds, are more resistant to weathering destruction originating from freezing and thawing than packstones (MF
type 4). Weathering of micritic facies types (e.g., MF 4) is more intensive due to the stronger development of joint systems
affecting not only the surface of the building stones but the entire dimension stone.
Porosity or the existence and amount of stylolites seem to have had no significant impact on the weathering of the building
stones studied. The stronger weathering of building stones used in the original construction of the church as compared with
the stones applied in this century is caused by the greater time interval available for mechanical weathering connected with
freezing and thawing.
The consideration of microfacies of limestone turbidites should facilitate the exploitation of weathering-resistant carbonate
building stones. 相似文献
16.
The Latemar is a mainly aggrading platform, but shows repeated backstepping during its entire development. The behaviour of the slope does not reflect accommodation changes and lateral consistencies of the lagoonal interior; the Latemar contemporaneously reveals different, even contrasting depositional characteristics. The slope of the late stage platform evolution corresponds at least partially to the base-of-slope apron model. Controlling factors on slope evolution are of tectonic (proximity of the Stava Line) and autocyclic (repeated oversteepening) nature. Other factors are insignificant and/or overprinted. The reef-facies at Latemar reveals a complex facies pattern; it varies along and across the margin and is rich in encrusting sponges, corals, biogenic crusts and Microproblematica. Some biota or fossil assemblages—e.g. foraminifers (Abriolina mediterranea, Turriglomina scandonei) or Tubiphytes multisiphonatus thrombolites—have not been described in the Dolomites before. Biostratigraphic evidence from the uppermost reef-facies confirms a mainly Anisian age of the outcropping platform interior. 相似文献
17.
A characteristic microfacies of the Late Jurassic to Early Cretaceous allodapic Barmstein Limestone of the Northern Calcareous
Alps are clasts of wackestones with numerous fragments of calcareous algae (“algal debris-facies”). According to dasycladale
palaeocoenoses, several subtypes comprising different associations can be distinguished. One association is characterized
by the debris of an unknown large dasycladalean alga reported as dasycladalean alga indet. sp. 1 from different localities
in the Northern Calcareous Alps, typically forming a monospecific assemblage. Another microfacies type contains star-like
calcitic bodies tentatively referred to the morphospecies Coptocampylodon pantici Ljubović-Obradović and Radoičić, originally described as being from the Turonian of NW-Serbia. Other Coptocampylodon-like bodies represent the calcified tufts of the laterals of Selliporella neocomiensis (Radoičić). The occurrence of Coptocampylodon pantici-like microfossils in the Late Tithonian to Early Berriasian, shows that obviously different species of dasycladaleans display
identical to similar shaped tufts of laterals in transverse sections when becoming fragmented. Coptocampylodon pantici Ljubović-Obradović and Radoičić was observed only from different occurrences of Barmstein Limestone, but not from the autochthonous
platform carbonates of the Plassen carbonate platform. The Coptocampylodon algal debris-facies is also reported from the Late Jurassic of Albania, Mirdita zone. Occurrences of different types of algal
debris-facies in components of mass-flow deposits can be used as a tool to reconstruct eroded carbonate platforms and tectonics,
as demonstrated in the Northern Calcareous Alps and the Albanides. Finally, the general occurrences of algal debris-facies
in both settings—intra-Tethyan mostly isolated platforms (Alps, Albanides) vs. extended epeiric platforms (Middle East)—are
compared and discussed. 相似文献
18.
Dr. Eric Fookes 《Facies》1995,33(1):129-149
Summary This study consists of a sedimentological and diagenetical analysis of reef facies from the Upper Kimmeridgian (sensu gallico). The investigated deposits are situated in eastern France, about fifty kilometres west of the city of Geneva (Switzerland).
The reef complex is a fine example of vertical development and facies differentiation. It is subdivided into two distinct
sequences by a perforated hardground horizon and sand shoals. The onset of the first reef sequence is characterized by a pioneer
growth stage followed by up to 20 m of reef-core and-flank facies. Corals forming the reef-core are typically the ramose variety
ofCalamophylliopsis flabellum. The second reef sequence has a reef-core with an average thickness of about 5 m. Corals, however, display much more varied
morphologies, and in some areas massive rudist (Heterodiceras) build-ups occur. Development of the second reef sequence was seriously weakened by a storm which produced a 2 m thick accumulation
of coral rubble. A shallowing-upwards trend gradually leads to the formation of beach deposits, followed by a newly detected
black-pebble horizon.
Diagenesis is an important aspect of the reef complex. Especially noteworthy is the dolomitization of certain horizons. At
the base of the reef formation, the passage of the phreatic mixing zone provoked invasive dolomitization in large irregular
patches (probably deposits richer in Mg-calcite). Some of the beds above the black-pebble horizon, in particular a deposit
of accumulated microbial mats, are also dolomitized. In this case, dolomitization is stratiform and is interpreted as having
precipitated under conditions of evaporative pumping.
The sedimentary record clearly shows the imprint of eustasy. The reef complex was initiated during a transgressive cycle and
the hardground found between the two reef sequences is interpreted as a maximum flooding surface (mfs). At the top of the
sequence, the horizon overlain by the black-pebble conglomerate is believed to represent the new sequence boundary SB140.
Other significant features identified from the St. Germain-de-Joux deposits include the discovery of a new foraminifera,Troglotella incrustans, which is only marginally covered here but is the topic of another paper (Wernli & Fookes, 1992); the subdivision of the first coralligenous level defined byPelletier (1953) into two reef sequences; and a proposition to redefine the ‘Calcaires de la Semine’ (Bernier, 1984).
The investigations carried out in the past on the Kimmeridgian deposits in the area of St. Germain-de-Joux were mostly based
on stratigraphy and palaeontology. These reefs are among the finest known in the Jura Mountains, but no thorough study had
been made on their sedimentological aspects. The aim of this study is to fill this void and also to clarify the more confusing
aspects of local stratigraphy (paper based onFookes, 1991). 相似文献
19.
Felix Schlagintweit 《Facies》2008,54(3):377-402
Examples of bioerosional processes (boring patterns) are described from shallow-water limestones of the Late Jurassic Plassen
Carbonate Platform (PCP) and the Late Cretaceous to Paleocene Gosau Group of the Northern Calcareous Alps, Austria. Some micro-/macro-borings
can be related to distinct ichnotaxa, others are classified in open nomenclature. In the Alpine Late Jurassic, bioerosional
structures recorded from clasts in mass-flows allow palaeogeographical conclusions concerning the source areas. In particular,
these are borings of the Trypanites-ichnofacies detected from clasts (Barmstein limestones) of the PCP or special type of bored ooids of unknown source areas
or restricted autochthonous occurrences. In the Lower Gosau Subgroup, Gastrochaenolites macroborings occur in mobile carbonate clast substrates of shore zone deposits (“Untersberg Marmor”). Different types of
borings are recorded from rudist shells and coral skeleton, some of which are referable to the ichnotaxon Entobia produced by endolithic sponges. In the present study, special attention is paid to the occurrences of the cryptobiotic foraminifera
Troglotella incrustans Wernli and Fookes in the Late Jurassic and Tauchella endolithica Cherchi and Schroeder in the Late Cretaceous. The latter is so far only known to be from the Early Cenomanian of France and
is reported here for the first time from the Late Turonian-Early Coniacian stratigraphic interval where it was found in turbulent
carbonate deposits within borings penetrating bivalve shells or coralline algae. The records of cryptobiotic foraminifera
from the Northern Calcareous Alps are supplemented by a single finding from the Middle Cenomanian of SE France. A palaeoenvironmental
interpretation of the occurrences of the cryptobiotic foraminifera is provided. 相似文献
20.
Dipl.-Geol. Fritz Neuweiler 《Facies》1993,29(1):231-249
The Middle Albian sequence from the western marginal area of the Vasco-Cantabrian Basin contains calcified microbialites in
different marine depositional environments, individually well defined by microstructure, lamina characteristics and mode of
formation. Microbialites may form the primary framework of reefs, which occur as composite stacks in mid to lower slope environments
or as isolated bodies in small intraplatform basins. In most areas microbialite reef growth was initiated below the photic
zone. Stratiform intercalations of microbialites and composite microbialite/foraminifer oncoids are restricted to well bedded
carbonate platform deposits (Urgonian). Three basis types of microbialites are recognized:
The results of geochemical analyses indicate a rock-buffered diagenetic system during early diagenetic and burial history
of microbialite reefs. Independent of microbialite type residual MgCO3-contents are in the range of 1.20 to 3.57 mole %, agreeing well with those from isopachous rim cements and indicating a high
Mg-calcite precursor of microbialite micrites. Stable isotope values (δ13C) are in the range of 3.13 to 3.80 (permil, vs PDB), close to the internal standard, the coralline spongeAcanthochaetetes (Albian species=2.93; Recent species=3.27) and comparable with inorganically precipitated Mg-calcite. 相似文献
(i) | Dense micritic/fenestral microbialites corresponding to laterally linked, stacked stromatolitic hemispheroids. The development and preservation of stromatolitic structure is a function of sediment supply and secondary obliteration by succesive boring activities. They were calcified in situ at the surface with irregularly curved linings of microcrystalline carbonate. Dense micritic/ fenestral microbialites, variously developed and preserved, are the main contributors to microbialite reefs. Microbialites form hard substrates bored by lithophagous pelecypods and boring sponges (Aka sp.). The main associated faunal elements include lithistid and coralline demosponges, hexactinellid sponges, encrusting foraminifera, brachiopods, polychaetes, and bryozoans. |
(ii) | Dense micritic/peloidal microbialites with subplanar, arhythmic lamination (binding habit). They were calcified in situ below the surface in conjunction with decaying organic matter. At large scale, they occur in shallow water, i.e. within the photic zone. They cover earlier microbialite reefs or occur on and in episodic deposits of coarse biodebris. At small scale they occur in protected microenvironments (e.g. intraparticle space, boring cavities). |
(iii) | Peloidal/in situ ooid microbialites with subplanar/ wavy lamination occur as small-scale stratiform intercalations in carbonate platform deposits, episodically revealing physical reworking. Other features are very similar to dense micritic/peloidal microbialites. |