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1.
Summary Coral-dominated communties are rare in Upper Permian reefs. The study of Murghabian rugose and tabulate corals from allochtonous
carbonates (‘Oman exotics’) of the Hawasina Complex and autochthonous carbonates of the Saih Hatat area/Arabian Platform (Oman)
provides evidence for a significant contribution of rugose corals to the formation of Late Permian reefs.
The corals are described with respect to taxonomy, microfacies and community structure. 8 genera and 7 species were recognized.Monothecalis minor n.sp.,Praewentzelella regulare n.sp. andWentzelella katoi magna n.ssp. are new. The corals represent three communities: (1)Praewentzelella community (Hawasina Complex), (2) cerioid coral community (Hawasina Complex), and (3)Waagenophyllum community (Hawasina Complex and Saih hatat). The corals from the Hawasina Complex and the Saih Hatat flourished in significantly
different environments: Rugosa from the Hawasina Complex are representatives of reefs, whereas their counterparts from the
Saih Hatat lived in level-bottom communities. Coral-bearing reefal boundstones are characterized by a diverse assemblage of
sphinctozoans, inozoans, chaetetids, bryozoans, crinoids,Tubiphytes, Archaeolithoporella and algae. These communities produced bafflestones or framestones and were part of a sponge reef complex. The level-bottom
community of the Saih Hatat is low-diverse only comprising rugose and tabulate corals. These of isolated colonies locally
acted as bafflers. 相似文献
2.
Anisian (middle triassic) buildups of the Northern Dolomites (Italy): The recovery of reef communities after the permian/triassic crisis 总被引:1,自引:0,他引:1
Dr. Baba Senowbari-Daryan Dipl. Geol. Rainer Zühlke Prof. Dr. Thilo Bechstädt Prof. Dr. Erik Flügel 《Facies》1993,28(1):181-256
Summary After the end-Permian crisis and a global ‘reef gap’ in the early Triassic, reefs appeared again during the early Middle Triassic.
Records of Anisian reefs are rare in the Tethys as well as in non-Tethyan regions. Most Anisian reefs are known from the western
part of the Tethys but there are only very few studies focused on biota, facies types and the paleogeographical situation
of these reefs. From the eastern part of the Tethys, Anisian reefs, reefal buildups or potential reef-building organisms have
been reported from different regions of southern China. Most of the Anisian reefs known from western and central Europe as
well as from southern China seem to be of middle and late Pelsonian age.
The study area is situated in the northern Dolomites (South Tyrol, Italy) southeast of Bruneck (Brunico). It comprises the
area between Olang (Valdaora) and Prags (Braies). The study is based on detailed investigations of the regional geology, stratigraphy
and lithofacies (R. Zühlke, T. Bechst?dt) as well as on a comprehensive inventory of Anisian reef organisms (B. Senowbari-Daryan,
E. Flügel). These data are used in the discussion of the controls on the recovery of reefs during the early Middle Triassic.
Most late Anisian reef carbonates studied are represented by allochthonous talus reef blocks of cubicmeter size. Small biostromal
autochthonous mounds are extremely rare (Piz da Peres). The reef mounds as well as most of the reef blocks occur within the
middle to late Pelsonian Recoaro Formation. They were formed on the middle reaches of carbonate ramps in subtidal depths,
slightly above the storm wave base with only moderate water energy. Most lithotypes observed in the reef blocks correspond
to sponge and/or algal bafflestones. Low-growing sessile organisms (Olangocoelia (sponge, alga?), sphinctozoan sponges, bryozoans, soleno-poracean algae, corals) and encrusting epibionts (sponges, porostromate
algae, cyanophycean crusts, foraminifera, worms, microproblematica) created low cm-sized biogenic structures (bioconstructions)
which baffled and bound sediment. Organic framework was only of minor importance; it is restricted to theOlangocoelia lithotype. Framework porosity was small in these reef mounds. Submarine carbonate cements, therefore, are only of minor importance
s compared with Permian or Ladinian reefs. The relatively high number of lithotypes encountered in the reef blocks indicates
a high biofacies diversity.
Regarding the relative frequency, the diverse biota consist in descending order ofOlangocoelia, sponges (sphinctozoans, inozoans, siliceous sponges), bryozoans, porostromate algae and worm tubes. The sphinctozoans are
characterized by small, mostly incrusting forms. The numerical diversity (species richness) is low compared with late Permian
or Ladinian and late Triassic sphinctozoan faunas occurring within reefs.
Following the sponges, monospecific bryozoans (Reptonoditrypa cautica
Sch?fer & Fois) are the most common organisms in the reef limestones. Porostromate algae were restricted to areas within the bioconstructions
not inhabited by sponges. The low-diverse corals had no importance in the construction of an organic framework.
Surprisingly, microbial crusts are rare or even lacking in the investigated Anisian bioconstructions. This is in contrast
to late Permian and Ladinian as well as Carnian reefs which are characterized by the abundance of specific organic crusts.
The same comes true for‘Tubiphytes’ which is a common constituent in Permian, Ladinian and Carnian reef carbonates but is very rare in the Anisian of the Olang
Dolomites. Instead of‘Tubiphytes’ different kinds of worm tubes (spirorbid tubes, Mg-calcitic tubes and agglutinated tubes) were of importance as epifaunal
elements. Macrobial encrustations consisting of characteristic successions of sponges, bryozoans, algae, worm tubes and microproblematica
seem to be of greater quantitative importance than in Ladinian reefs.
Destruction of organic skeletons (predominantly of bryozoans) by macroborers (cirripedia?) is a common feature.
The Anisian reef organisms are distinctly different from late Permian and from most Ladinian reef-builders. No Permian Lazarus
taxa have been found.
New taxa: Sphinctozoan sponges—Celyphia? minima n.sp.,Thaumastocoelia dolomitica n. sp.,Deningeria tenuireticulata n. sp.,Deningeria crassireticulata n. sp.,Anisothalamia minima n.g. n.sp., Inozoan sponges-Meandrostia triassica n.sp. Microproblematica-Anisocellula fecunda n.g. n.sp., Porostromate alga-Brandneria dolomitica n.g. n.sp.
Most of our data are in agreement with the model described byFois & Gaetani (1984) for the recovery of reef-building communities during the Ansian but the biotic diversity seems to be considerably
higher than previously assumed.
Anisian deposition and the formation of the reef mounds within the Pelsonian Recoaro Formation of the Dolomites were controlled
by the combined effects of synsedimentary tectonics and eustatic changes in sea-level. During several time intervals, especially
the early Anisian (northern and western Dolomites: tectonic uplift), the early Pelsonian (eastern Dolomites: drowning) and
the late Illyrian (wide parts of the Dolomites: uplift and drowning), the sedimentation was predominantly controlled by regionally
different tectonic subsidence rates. The amount of terrigenous clastic input associated with synsedimentary tectonics (tectonic
uplift of hinterlands) had a major influence on carbonate deposition and reef development. The re-appearance of reef environments
in the Olang Dolomites was controlled by a combination of regional and global factors (paleogeographic situation: development
of carbonate ramps; decreasing subsidence of horst blocks; reduced terrigenous input; moderate rise in sea-level). 相似文献
3.
Summary Anin situ Oxfordian patch reef from the Süntel hills (florigemma-Bank, Korallenoolith, NW-Germany) is described. It is composed of an autochthonous reef core overlain by a ‘parautochthonous’
biostrome. The exposed reefal area amounts to about 20 m in lateral and up to 4 m in vertical direction. Nearly all major
marine reefal fossil associations from the Tethyal realm are present.
In the reef core two facies can be distinguished: (1)Thamnasteria dendroidea thicket facies and (2) thrombolite facies.
The first facies is composed of a thin branched autochthonous coral thicket mainly constructed ofTh. dendroidea colonies with only a minor portion ofStylosmilia. Frequently, theTh. dendroidea branches laterally coalesce bridge-like forming a delicate initial framework which was subsequently reinforced by thick microbial
coatings, that make up approximately 80% of the rock volume. This facies is an excellent example for microbialite binding
in reefal architecture. Additionally, several generations of micromorphic and partly cryptic encrusting organisms settled
on theTh. dendroidea branches and microbialite crusts. They successively overgrow each other and fill the space between the coral branches in
the thicket forming a characteristic community replacement sequence.
Initial colonization of theThamnasteria dendroidea took place on an oncoidic/bioclastic hardground. During this early phase of reefal development, microbialites also played
an important role in stabilizing and binding the reef body.
The thrombolite facies (2) occupying nearly the same volume of the reef body as facies type (1) consists of a thrombolitic
microbialitic limestone which fills the interstice between the coral colonies. It shows a considerably lower faunal diversity
than theTh. dendroidea facies. Numerous cavities are interspersed in the thrombolithe and are almost completely filled with dolomitized allomicrite.
In contrast, microbialite and allomicrite adjacent to the reef core rarely reveal any dolomitized areas.
Above the reef core, mostly toppledSolenopora jurassica thalli occur together with a few massiveIsastrea colonies forming a parautochthnous biostrome. They are inhabited by a low diverse assemblage of encrusting organisms. Microbialites
are only rarely present in this biostromal unit.
The patch reef is developed within a lagoonal limemud facies both separated by a sharp interface. In contrast, continuous
facies transition exists between theSolenopora biostrome and adjacent deposits which are characterized by micritic to pelmicritic limestone sometimes with lenses of oncoids.
Debris derived from the patch reef is only sporadically intercalated in the reef surrounding lagoonal sediments. Gastropods,
bivalves, and dasycladalean algae dominate the lagoonal biota. Up-section following theSolenopora biostrome nerinean gastropods become the most abundant species amounting to a ‘Nerinea-bed’. This horizon moderately elevates above the patch reef indicating, that is arose above the surrounding sea floor forming
a relief.
The patch reef established on a secondary hardground probably released by a minor transgression and a nondepositional regime.
It grew up on a well-illuminated sea floor only a few meters below sea level. Only a low background sedimentation rate and
modest water circulation are assumed during reefal growth. These features characterize an open marine lagoon.
A subsequent shallowing upwards trend caused emergence of the early lithifiedflorigemma-Bank sediments. In the following erosional phase the reef core,Solenopora biostrome and ‘Nerinea-bed’ were sharply cut. Paleokarst phenomena (karst solution of the rocks, selective leaching of the aragonitic corals) truncate
the surface of theflorigemma-Bank. Released by a transgressive sea level, the paleokarst surface is densely inhabited by marine boring and encrusting
organisms (oysters, serpulids). Karst cavities are filled with an oncoid-bearing bioclastic limestone with a large portion
of siliciclastics. Theflorigemma-Bank is overlain by the reddish bioclastic sandstone of the ‘Zwischenfl?zregion’. 相似文献
4.
Dr. Oliver Weidlich 《Facies》1996,35(1):133-142
Summary Rugose corals are known from allochthonous Late Permian reefal blocks of the A1 Jil and Ba’id Formation (Hawasina Complex),
Oman Mountains. In contrast to many Late Permian Rugosa found elsewhere in the Tethys, they occurred in sponge reefs and contributed
to reef construction. The waagenophyllid warm water coral fauna is moderately diverse comprising cerioid, thamnasterioid,
and fasciculate taxa. In contrast to sponges, chaetetids, and low-growing reefbuilders, the corals secreted diagenetically
stable, most probably Mg-calcitic skeletons. Borings in coral skeletons are consequently well preserved providing important
data for the interpretation of reef destructive processes.
Thin-section analysis revealed three taxa of infaunal borers includingEntobia
Bronn 1837, uncertain thallophyte borings, and borings of unknown bioeroders. Macroborers were more important than microborers,
because of the dominance of clionid sponges. Good evidence exists also for the occurrence of two types of undetermined grazers
which destroyed the coral surfaces.
The amount and distribution of bioerosions is variable among different coral taxa. The fasciculate coralPraewentzelella regulare
Flügel 1995 was the favorate substrate. Up to 33% of the calices were bored. Dendroid and compound corals were bored subordinately.
Bioerosion of these colonies does not exceed 2%. There is good evidence for substrate preference amongst the borers. Major
controlling factors affecting borer distribution are believed to be variations of skeletal density and gross morphology. The
borer assemblage could not limit reef accretion significantly. Factors controlling boring activity might have been quality
of substrate, sedimentation rate, rapid incrustation of substrates, and competition for food with reef constructors including
sponges, chaetetids, and rugose corals. 相似文献
5.
Norian-Rhaetian reefs in Argolis Peninsula,Greece 总被引:2,自引:0,他引:2
PD Dr. Baba Senowbari-Daryan Dr. Dionissios Matarangas Dr. Myrsini Vartis-Matarangas 《Facies》1996,34(1):77-82
Summary Upper Triassic to Lower Jurassic shallow-water carbonate sequences of the ‘Pantokrator limestones’ are widely distributed
in the Argolis Peninsula, southern Greece. Within this sequence are some reef or reefal structures. In the Mavrovouni Mountains,
near Sarmeika, 6 km SE of the ancient theatre of Epidavros (Argolis Peninsula), a Norian-Rhaetian reef complex has been identified.
This is the first well-documented Norian-Rhaetian reef in Greece. The main reef builders are coralline sponges (‘sphinctozoans,’
‘inozoans’, and sclerosponges), followed by dendroid, cerioid, and solitary corals, and algae. The reef type corresponds to
a ‘sponge-coral reef’. 相似文献
6.
Dr. Karl Krainer 《Facies》1995,33(1):195-214
Summary A heretofore undocumented example of skeletal mounds formed by the dasycladacean algaAnthracoporella spectabilis is described from mixed carbonate-clastic cycles (Auernig cyclothems) of the Late Carboniferous (Gzhelian) Auernig Group
of the central Carnic Alps in southern Austria.
The massive mound facies forms biostromal reef mounds that are up to several m thick and extend laterally over more than 100
m. The mound facies is developed in the middle of bedded limestones, which are up to 16 m thick. These limestones formed during
relative sea-level highstands when clastic influx was near zero.
The mound facies is characterized by well developed baffler and binder guilds and does not show any horizontal or vertical
zonation. Within the massive mound faciesAnthracoporella is frequently found in growth position forming bafflestones and wackestones composed of abundantAnthracoporella skeletons which toppled in situ or drifted slightly.Anthracoporella grew in such profusion that it dominated the available sea bottom living space, forming ‘algal meadows’ which acted as efficient
sediment producers and bafflers. BecauseAnthracoporella could not provide a substantial reef framework, and could not withstand high water turbulence, the biostromal skeletal mounds
accumulated in shallow, quiet water below the active wave base in water depths less than 30 m.
The massive mound facies is under- and overlain by, and laterally grades into bedded, fossiliferous limestones of the intermound
facies, composed mainly of different types of wackestones and packstones. Individual beds containAnthracoporella andArchaeolithophyllum missouriense in growth position, forming “micromounds’.
Two stages of mound formation are recognized: (1) the stabilization stage when bioclastic wackestones accumulated, and (2)
the skeletal mound stage when the sea-bottom was colonized byAnthracoporella and other members of the baffler and binder guilds, formingAnthracoporella bafflestones and wackestones of the mound facies.
A slight drop in sea-level led to the termination of the mound growth and accumulation of organic debris, particularly calcareous
algae, fusulinids, crinoids and bryozoans, forming well bedded limestones, which overlie the mound facies 相似文献
7.
Summary During the Middle and early Late Triassic carbonate ramps and rimmed platforms developed at the northwestern margin of the
Tethys ocean. In the Northern Calcareous Alps, Anisian stacked homoclinal ramps evolved through a transitional stage with
distally steepened ramps to huge rimmed platforms of Late Ladinian to Early Carnian age. Middle Triassic to early Late Triassic
facies and biota of basin, slope and platform depositional systems are described. Special emphasis is given to foraminifers,
sponges, microproblematic organisms and algae.
The Ladinian to early Carnian reef associations are characterized by the abundance of segmented sponges, microproblematica,
biogenic crusts and synsedimentary cements. Among the foraminifers, recifal forms likeHydrania dulloi andCucurbita infundibuliformis (Carnian in age) are reported from the Northern Calcareous Alps for the first time. Some sphinctozoid sponges likeParavesicocaulis concentricus were known until now only from the Hungarian and Russian Triassic. 相似文献
8.
The distributions and population densities of large benthic foraminifers (LBFs) were investigated on reef flats of the Majuro
Atoll, Marshall Islands. Annual sediment production by foraminifers was estimated based on population density data. Predominant
LBFs were Calcarina and Amphistegina, and the population densities of these foraminifers varied with location and substratum type on reef flats. Both foraminifers
primarily attached to macrophytes, particularly turf-forming algae, and were most abundant on an ocean reef flat (ORF) and
in an inter-island channel near windward, sparsely populated islands. Calcarina density was higher on windward compared to leeward sides of ORFs, whereas Amphistegina density was similar on both sides of ORFs. These foraminifers were more common on the ocean side relative to the lagoon side
of reef flats around a windward reef island, and both were rare or absent in nearshore zones around reef islands and on an
ORF near windward, densely populated islands. Foraminiferal production rates varied with the degree to which habitats were
subject to water motion and human influences. Highly productive sites (>103 g CaCO3 m−2 year−1) included an ORF and an inter-island channel near windward, sparsely populated islands, and a seaward area of a reef flat
with no reef islands. Low-productivity sites (<10 g CaCO3 m−2 year−1) included generally nearshore zones of lagoonal reef flats, leeward ORFs, and a windward ORF near densely populated islands.
These results suggest that the distribution and production of LBFs were largely influenced by a combination of natural environmental
factors, including water motion, water depth, elevation relative to the lowest tidal level at spring tide, and the distribution
of suitable substratum. The presence of reef islands may limit the distribution and production of foraminifers by altering
water circulation in nearshore environments. Furthermore, increased anthropogenic factors (population and activities) may
adversely affect foraminiferal distribution and production. 相似文献
9.
Summary The late Triassic succession of the Asher-Atlit 1 borehole is over 1000 m thick, and is composed of reefal and associated
facies interbedded with volcanics of Norian age. Only borehole cuttings are available. Microfacies classification and cement
stratigraphy determined by optical and CL microscopy, allowed discrimination of six episodes of reef establishment, progradation,
shallowing, and termination. Organic buildups are constructed of reef-building biota (sponges, possible corals, encrusting
organisms) typical for the late Triassic of the Tethys. Reef-associated facies include fore-slope, central reef, ooid shoal,
lagoonal, and supratidal environments. Cement zoning patterns trace diagenetic signatures which range from early neomorphic
skeletal replacements and original marine cements, via characteristic burial sequences; depositional and diagenetic sequences
are terminated by marginal marine intra- or supratidal conditions, and subaerial exposure with pedogenic overprints. Volcanic
episodes tend to be associated with termination of carbonate sedimentation episodes, while volcanic quiescence and subsidence
permit vertical progradation of reefal and associated facies. The depositional and progradational environment, rapid rate
of sedimentation, periodicity, association with volcanics, and regional considerations, suggest a depositional setting on
the rifted shelf-margin of the nascent Neo-Tethys, with a possible eustatic overprint. 相似文献
10.
Summary In Southern Germany, two examples of travertines of different age and depositional morphology were examined in detail. Travertines
are laminated carbonate rocks formed by precipitation from mineral and/or thermal waters. They include characteristic facies
types, such as bushy layers (‘shrubs’) referred to calcification of branching microbes (‘Dichothrix’-morphotype), laminar microbial mats, peloidal layers, and gas bubble layers formed within the sediment. In travertines,
microbial activity is the most important factor for carbonate precipitation.
Tufas differ from travertines by their abundance of molds of higher plants (leaves, reed, moss, green algae). They may be
associated with travertines, but do not exhibit strict travertine facies types. Tufas are common in normal fresh water environments.
Contrary to travertines and tufas, calcareous sinters usually occur in restricted areas like spring fissures, caves, or in
pores, where microbial activity is not totally absent, but not of paramount importance for precipitation.
Pedogenetic processes, which can alter travertine deposits, are responsible for large-scale features such as tepee-structures,
and some intraclastic layers, and microscopic structures like endolithic borings andMicrocodium. Travertines may also grade into lacustrine limestones with Characeae, ostracods, and aquatic gastropods. 相似文献
11.
Pierre Moissette Jean-Jacques Cornée Beya Mannaï-Tayech Mohsen Rabhi Jean-Pierre André Efterpi Koskeridou Henriette Méon 《Palaeogeography, Palaeoclimatology, Palaeoecology》2010,285(1-2):85-103
The marine Messinian deposits of Tunisia cover a narrow littoral strip some 300 km long between the northern Bizerte and Cap Bon areas and the central–eastern Sahel region. Litho- and biofacies analysis of six stratigraphic sections reveals the distinctive features of these deposits.The lower Messinian deposits are characterized by ubiquitous siliciclastics and abundant oolitic/bioclastic limestones organized in an eastward facing ramp. Westward (landward), this ramp changes into coastal lagoons, sometimes containing evaporites. Eastward, the ramp passes to the reefal Pelagian Platform extending as far as Lampedusa.Two main sedimentary cycles are distinguished: 1) an early Messinian siliciclastic retrogradational then oolitic/bioclastic progradational cycle (Beni Khiar Formation and lower Oued bel Khedim Formation); 2) a late Messinian brackish to continental cycle that probably accumulated in rapidly subsiding lagoons (Oued el Bir Formation and upper Oued bel Khedim Formation). The Tunisian early Messinian cycle is partly eustatically controlled, but the late Messinian cycle cannot be confidently correlated to other well-known Messinian series because of tectonic movements.The lower Messinian deposits of Tunisia are also characterized by abundant suspension-feeding organisms (molluscs and bryozoans) and rare corals, calcareous algae, echinoids, and larger benthic foraminifers. The proposed palaeoenvironmental model shows that the lower Messinian ramp of Tunisia was located on a current-protected margin and subjected to continent-derived sediment and nutrient supply. Eastward, nutrient influx diminished and a shallow-water isolated carbonate platform with coralgal facies developed between the western and the eastern Mediterranean basins. The main hydrological connection between these two basins occurred through a narrow seaway situated to the northeast of the Pelagian Platform, south of Sicily and Malta. 相似文献
12.
Benoy K. Ghose 《Palaeogeography, Palaeoclimatology, Palaeoecology》1977,22(3):231-256
The paleoecology of reefal foraminifers and algae assumes a considerable importance in determining and delineating sub-environments of ancient reefs, especially those of non-coral origin.A review of the ecologic distribution of the Cenozoic larger foraminifers in different biofacies of the reef-complex environment has revealed the following: (1) a prolific growth of “Alveolina” was possible in the back-reef region near the reef core; (2) Orbitolites and Marginopora preferred sheltered waters on the reef-flat and in the back-reef zones; (3) nummulitids and Discocyclina thrived in both fore- and back-reef shoal areas, but the species living in the former are much stouter than those living in the latter; (4) Heterostegina is and, in the geologic past, was a form, preferring quieter waters of the back-reef lagoons and reef-flat pools; (5) Pellatispira was a typical fore-reef form.Smaller foraminifers, as a whole, are dominant in back-reef lagoons. An abundance of miliolids indicates a sheltered environment prevailing in the reef-flat pools and back-reef zones, whereas reef flats, in general, are characterized by a paucity of smaller foraminifers. An increase in the number of nodosariids and globigerinids points to a fore-reef environment, the depth of which is indicated by the relative abundance of the latter group. Encrusting foraminifers are characteristic of the reef core and are important constituents of for-algal (foraminiferal + algal) reef complexes.Of the algae, the calcarous chlorophyte Halimeda is relatively more abundant in the sheltered parts of a reef-complex, especially the lagoons, where water is moderately agitated and clear; its sudden abundance in the geologic record indicates the advent of a reefal environment. An abundance of the calcareous chlorophyte Dasycladaceae indicates the shallow back-reef areas adjacent to the reef core. Articulated coralline algae are associated with reef-complexes but are varied in their adaptability and, hence, are widely distributed in different parts of the complex. Abundant crustose coralline algae almost certainly indicate a reef-core sub-environment; their skeletons are among the chief constructional units of the core. They increase in abundance towards the outer edge of the reef core and decrease away from it. 相似文献
13.
Synopsis Research on eleven artificial reefs in Puget Sound, Washington examined the relative importance of reef-produced prey items
to recreationally important reef fish species assemblages. The colonization of potential prey items, and fish species assemblages
to ten artificial reefs were examined for the reefs first two to five years, and observations were conducted on an eleventh
reef during its forty-ninth productive year. Fish species became more abundant, or were seen more frequently on reef habitats
whose substrates had successionally developed from barnalces to algal mats. Fish species most affected by this successional
change foraged heavily on organisms which were associated with reef algae. Starfish and nudibranchs. who preyed on the barnacles,
were identified as the ‘keystone’ predators of these subtidal reef habitats. 相似文献
14.
Summary The Upper Rhaetian coral limestone of Adnet, southeast of Salzburg Austria has been repeatedly referred to as one of the most
spectacular examples of an ancient ‘autochthonous’ coral reef structure. The ‘Tropfbruch’ quarry is probably the best outcrop
for interpreting the distributional patterns of biotic successions and communities of a late Triassic patch reef. Our study
is based on the interpretation of a) outcrop photographs, b) reef maps resulting from quadrat transects, and c) the analysis
of quantitative data describing the distribution and frequency of reef organisms and sediment. A new methodological approach
(combination of reef mapping and photo-transects) is used to obtain quantitative field data which can be compared in greater
detail with data from modern coral reefs investigated by corresponding quantitative surveys.
Three unconformities and three well-defined ‘reef growth stages’ reflecting the vertical and lateral development of the reef
structure were differrentiated using transects:
Stage 1, representing the reef growth optimum, is characterized by laterally differentiated coral reef knobs with corals in
growth position. Criteria supporting this interpretation are the extraordinary size of the corals, their preservation in situ
and the great thickness of this interval. The massive coralPamiroseris grew under higher energy conditions at the rim of the reef knob, whereas branchingRetiophyllia colonies preferred less agitated water in the center. Vertical changes are reflected by an increase in frequency of the dasycladacean
algaDiplopora adnetensis and by the decreasing size ofRetiophyllia. These sedimentological and biological criteria together with the unconformity above indicate a fall in the sea level as
a major control mechanism.
Stage 2, separated from stage 1 by an unconformity caused by partial subaerial exposure and karstification, is characterized
by vertically stacked coral successions with diverse reef debris. Facies heterogeneity is reflected by differences in the
diversity, taphonomy and packing density of reef-building organisms as well as by differences in sediment input from the platform.
Water depths and accommodation space were lower, therefore minor sea level fluctuations had a stronger effect on the biotic
composition. The high percentage of coral debris and corals reworked by storms and the increase in the input of platform sediment
led to a reduction of reef growth.
Stage 3, again separated at the base by an unconformity associated with karstification, is characterized by bioclastic sediments
with isolated reefbuilders forming a level-bottom community. The distribution of different coral morphotypes suggests that
sea level fluctuations were not the only controlling factor. Variations in the substrate were caused by differences in the
input of platform sediment.
The three-step development seen in Adnet documents the response of low-diverse coral associations to variations caused by
small-scale sea level changes, storm activity and sedimentation. The vertical changes in reef community structures correspond
to a sequence of ‘allogenic replacements’.
The Adnet reef structure should not be regarded as a general model of Alpine Upper Rhaetian reefs, because of the particular
setting of the patch reef. Only the ‘capping beds’ of the Upper Rhaetian Reef Limestone of the Steinplatte exhibit criteria
similar to Adnet.
Potential modern analogues of features seen in the coral communities of Adnet are the internal structure of theRetiophyllia thickets, the key role of branching corals within the communities, the scattered distribution and low and even diversity
of corals subsequent to breaks in settlement, segration patterns of corals indicating ‘contact avoidance’, toppling of large
coral colonies by intensive boring, and decreasing coral coverage from deeper and sheltered settings to more shallower water
depths. 相似文献
15.
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
16.
Net pen fish farms generally enrich the surrounding waters and the underlying sediments with nutrients and organic matter, and these loadings can cause a variety of environmental problems, such as algal blooms and sediment anoxia. In this study we test the potential of biofiltration by artificial reefs for reducing the negative environmental impacts surrounding fish farms in the Gulf of Aqaba, Red Sea. Two triangular-shaped artificial reefs (reef volume 8.2 m3) constructed from porous durable polyethylene were deployed at 20 m; one below a commercial fish farm and the other 500 m west of this farm in order to monitor the colonization of these reefs by the local fauna and to determine whether the reef community can remove fish farm effluents from the water. Both reefs became rapidly colonized by a wide variety of organisms with potential for the removal of compounds released from the farms. Within the first year of this study fish abundances and the number of species reached 518–1185 individuals per reef and 25–42 species per reef. Moreover, numerous benthic algae; small sessile invertebrates (bryozoa, tunicates, bivalves, polychaetes, sponges, anemones) and large motile macrofauna (crustaceans, sea urchins, gastropods) settled on the reef surfaces. Depletion of chlorophyll a was measured in the water traversing the artificial reefs in order to assess the biofiltration capacity of the associated fauna. Chlorophyll a was significantly reduced to a level 15–35% lower than ambient concentrations. This reduction was greatest at intermediate current speeds (3–10 cm s–1), but was not influenced by current direction. The reef structures served as a successful base for colonization by natural fauna and flora, thereby boosting the local benthic biodiversity, and also served as effective biofilters of phytoplankton. 相似文献
17.
This study surveyed several locations at depths between 50 and 140 m within the Au’au Channel, Hawaii to characterize the
deep reef habitat and determine the depth distribution and relative abundance of the dominant, habitat forming megabenthic
taxa. In the Au’au Channel, the depth distribution of megabenthic taxa exhibited a pattern of vertical zonation with relatively
few taxa dominating each zone. Macroalgae particularly Halimeda spp. and to a lesser extent scleractinian corals Leptoseris spp. were dominant between 50 and 80 m; Leptoseris spp. were dominant between 80 and 90 m as macroalgae decreased in abundance; the invasive octocoral Carijoa riisei was dominant between 90 and 100 m primarily on rugose features; Antipathes spp. and Leptoseris spp. were dominant between 100 and 120 m on exposed fossil reef; and small wire corals were dominant between 120 and 140 m.
In general, the percentage of live benthic cover decreased with depth, particularly below 90 m where a large majority of the
area was uncolonized, soft substrata. The gradient of downwelling light intensity appears to play a major role in regulating
the depth distribution of photosynthetic organisms, skilophilous organisms, and other benthic fauna, which compete for space
with dominant photosynthetic species. The depth of the seasonal thermocline also appears to play an important role in limiting
the distribution of tropical benthic species. 相似文献
18.
Fringing reef development is limited around 22° S along the inner Great Barrier Reef, although there is substantial development
north and south of this latitude. This study examined the relationships among coral communities and the extent of reef development.
Reefs were examined to determine coral composition, colony abundance, colony size and growth form between the latitudes 20°S
and 23°S. Major reef framework builders (scler- actinian genus Acropora and families Faviidae and Poritidae) dominated reefs north and south of 22°S, but declined significantly at 22°S where foliose
and encrusting corals (Turbinaria and Montipora spp.) were most common. Porites spp. were present at 22° S but had encrusting morphologies. Consistently high turbidity at this latitude, caused by a 10
m tidal range and strong tidal flows, resuspends silts from the shallow shelf, and appears to have precluded reef development
throughout the Holocene, by limiting the abundance, stunting the growth, and shortening the life expectancies of reef framework
corals. The distinctions between ‘natural’ and ‘human-induced’ degradation may be interpreted on the basis of the relationship
between Holocene development and current benthic community longevity. A mismatch between substantial past reef building capacity (a broad and/or thick reef) and non-existent or limited present reef-building capacity could signify anything from a long-period, natural cycle to an unprecedented deterioration in ecosystem
function caused by human influence.
Accepted: 29 July 1996 相似文献
19.
Summary This study presents a microfacies analysis and palaco-environmental interpretations of Early Oligocene carbon ates from the
Lower Inn Valley Tertiary (“Unterinntal-Terti?r”) of Austria. The well preserved biogenic components allow detailed investigations
of component relationships and controlling ecological parameters. The carbonates are dominated by coralline algae, corals,
small and large benthic foraminifers, bryozoans and lithoclasts. Bivalves, gastropods, echinoderms, brachiopods and serpulids
are subordinate. The limestones are present as A) autochthonous carbonates transgressing directly above the Triassic basement
and B) allochthonous debris flows within deeper-water marls. These carbonates are found within the Paisslberg Formation. The
Werlberg Member within this formation, pertains to the autochthonous carbonates and larger debris flows.
Five facies types are separated following fabric analysis and statistical treatment (correlation, cluster analysis, principal
components analysis) of semi-quantitative data consisting of component frequencies of thin sections. Facies distribution patterns
are principally controlled by variations in substrate characteristics, turbulence and light along a depth gradient. Reconstruction
of facies pattern distribution reveal both lateral and proximal-distal facies trends: coral-coralline algal facies, coralline
algal facies as well as foraminiferal facies were situated in shallower environments, laterally adjacent to each other. These
grade distally into coralline algal-bryozoan facies, bryozoan facies and finally into mollusc rich marls. Debris flows consisting
of reworked material from all of the known facies (bioclastic packstone facies) is restricted to the debris flow and possible
represents transport induced differentiation of components and grain size within distal debris flows. 相似文献
20.
Scleractinian coral reefs, when coexistent with siliciclastic sediments, usually occur in association with deltaic or coastal
sands. Nevertheless, Pleistocene reef limestones in southwestern Taiwan are developed in association with thick claystones
that were deposited in a deeper-water environment. These reef limestones are characterized by: (1) rapid transition from underlying
claystones upward to reefal limestones, (2) lateral interfingering with open-shelf claystones, (3) being overlain by terrestrial
deposits or exposed with no covering strata, and (4) being located in close association with anticlines. The authors propose
that these reef limestones developed on anticlinal ridges raised above the adjacent sea floor by thrust-front migration in
a foreland setting.
Accepted: 21 April 1998 相似文献