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Taphonomy of modern deep, cold‐temperate watercoral reefsAndré Freiwald a & John B. Wilson ba Fachbereich Geowissenschaflen, Universität Bremen, Postfach 330 440, Bremen, D‐28334,Germanyb Geology Department, Royal Holloway College, University of London, Egham, Surrey, TW20OEX, United Kingdom

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To cite this article: André Freiwald & John B. Wilson (1998): Taphonomy of modern deep, cold‐temperate water coral reefs,Historical Biology, 13:1, 37-52

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TAPHONOMY OF MODERN DEEP, COLD-TEMPERATE WATER CORAL REEFS

ANDRÉ FREIWALD** and JOHN B. WILSON15

"Universität Bremen, Fachbereich Geowissenschaflen, Postfach 330 440, D-28334Bremen, Germany; bGeology Department, Royal Holloway College, University of

London, Egham, Surrey TW20 OEX, United Kingdom

Deep-water corals are widely distributed along the cold-temperate northeastern Atlanticcontinental margin. Despite the widespread occurrence of these aphotic coral construc-tions in deep shelf settings, the processes of framework formation and postmortemalterations which result in different preservational styles are still poorly known. Detailedmapping surveys on probably one of the largest Lophelia reef structures were carried outon the Sula Ridge, Mid-Norwegian Shelf in 270 to 300 m depth. Side scan sonar recordsand camera surveys yield information at various scales of resolution on the reef complexwhich is more than 9 km long and up to 45 m high. Living Lophelia colonies effectivelyprevent colonization by other organisms and are successful in the rejection of passingdetrital material from the soft tissue. In a healthy condition the coral is able to encrustrepetitively attached organisms by selectively secreted sclerenchyme layers, thus, thisdefensive reaction results in the thickening of the skeleton. Early postmortem alteration inLophelia colonies is introduced by the formation of a biofilm and Dodgella (fungi)infestation. The biofilm is associated with selective Fe-Mn precipitation on the coralskeleton. This is the zone of intense attachment of sessile invertebrates such as serpulids,brachiopods, foraminifers and encrusting bryozoans. More advanced taphonomic stagesshow an increasing dominance in sponges which reduce the interskeletal frameworkporosity significantly. In addition, boring sponges excavate the thickly calcified Lopheliaskeletons, thus leading to in situ collapsing structures on the sea floor. It is the intensityof sediment trapping biofilms and sponge colonization and the amount of imported detritalparticles predominantly from the pelagial zone that control the generation of a pure coralrubble facies or the preservation of collapsed but mud-rich detrital mounds.

Keywords: Lophelia, Deep-water reef taphonomy, Fungi, Boring sponge, Preservation,Cold-temperate carbonates

This paper is one of six contributions solicited by Richard Bromley and submitted toHistorical Biology in conjunction with the 1996 workshop on "Bioerosion" held inBornholm, Denmark.

*Corresponding author.

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INTRODUCTION

Azooxanthellate scleractinians show a belt-like distribution along the North-eastern Atlantic continental margin, preferentially living in water depths between270 and 450 m (Teichert, 1958; Wilson, 1979a). In Norwegian waters, however,most deep-water coral occurrences are located on the shelf (Henrich et al, 1995;Mortensen et al, 1995), and on deep-seated fjord sills where advection ofAtlantic water occurs (Dons, 1944; Freiwald et al, 1997). Despite theconsiderable water depth and the low temperature regime, no traces of large-scale carbonate undersaturation have affected the post-mortem alteration of thecoral framework (see Freiwald, this volume). A wide variety of developmentalstages in deep-water coral constructions exist on the NE-Atlantic shelves rangingfrom single colonies (Tudhope and Scoffin, 1995), patches measuring 10 to 50 min diameter and 1-1.5 m in height (Wilson, 1979b; Scoffin et al, 1980) andmature reef structures of more than 9 km in lateral extension and up to 45 m inthickness (Henrich et al, 1995, 1996; Mortensen et al, 1995; Freiwald et al,1997). The most important coral framework-builder in Norwegian waters isLophelia pertusa, while the second colonial coral, Madrepora oculata, onlycolonises dead and broken Lophelia colonies. Based on coral samples collectedfrom the Sula-Ridge, mid-Norwegian shelf during cruises, the following topics,will be addressed in this study: (1) the corals' response to epilithic and endolithicinfestations; (2) the complex taphonomic processes that alter the dead parts of thecoral colonies; and (3) an outline of observed preservational styles andanticipated geometries and fabrics of cold-temperate deep-water coral reefremains, which might result from the processes described under # (1) and #(2).

STUDY AREA AND METHODS

Physical Setting

The Sula Ridge is located about 80 km offshore at 64°N and 08°E betweenFr0yabank and Haltenbank (Figure I). As a morphological elongation of theFr0yabank, this ridge forms a NE-plunging spur at the southwestern end of theNE-SW-striking Haltendjup Basin. The Sula Ridge is bordered by morphologicaldepressions which are around 340 m in depth. Approximately 25 km further tothe west, a second apparent ridge structure, the Fr0yryggen, runs parallel to theSula Ridge. West of the Fr0yryggen, a broad depression, the Egga Basin, opensto the continental slope. The upper part of the shelf margin is accentuated by aslide scar which is part of the Storegga Slide area further to the south (Holtedahl,

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FIGURE 1 Location of Sula Ridge (circle) on the mid-Norwegian shelf (see inset map).

1993). The complex morphology between the Fr0yabank and Haltenbank areasresults from the different erosive resistance of the underlying bedrock to theabrasive forces of waning and waxing glaciers. While the depressions areunderlain by more easily erodible sedimentary rocks of Mesozoic and Cenozoicage, the two ridges consist of more competent Paleocene (Sula Ridge) andOligocene (Fr0yryggen) deposits (Bugge et al., 1984). Focusing on Sula Ridge,the western flank of the Paleocene bedrock structure is covered by morainicdeposits which were formed during the last ice advance on the shelf shortlybefore 12,000 y BP (Bugge, 1980).

Oceanographic Setting

The general current flow pattern of offshore Norway is characterized by twonorthward flowing water masses, the Norwegian Coastal Current (NCC) and theNorwegian Current (NC). The less saline NCC is the prominent water mass onthe shelf and forms a westward thinning wedge over the shelf margin (Eide,1978). The more saline and more dense NC water passes along the continentalslope but intrudes onto the shelf following the morphological depressions such asthe Egga Basin (Lj0en and Nakken, 1969). The temperature of the NC water nearthe reef site varies slightly, from 6° to 7°C, while the overlying NCC water variesfrom 5.5 to 13°C. It is this specific oceanographic configuration that providessuitable environmental conditions for Lophelia pertusa to exist on mid-shelf andin fjord locations.

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Shipboard Methods

Navigation on the surveys was carried out with a ship-based GPS (NavTrack XLusing NMEA 0183 standard). The positions were stored on a computer every 10seconds. Records of the coral mounds and the surrounding sea floor wereobtained with an 18 kHz sediment echosounder and a 30 kHz navigationechosounder. The equipment used for a side scan sonar survey was a Klein,Model 595. For high-resolution sonographs of the seafloor, the 500 kHzfrequency with a beamwidth of 0.2° was chosen. Visual transects along themounds and intermound areas were conducted with a towed underwater camerasystem. A colour CCD-video camera (Osprey OE 1364) was mounted on a pan/tilt-head within a bottom lander frame. Sampling of sediments was carried outusing a 35 kg Van Veen Grab while for the coral mounds a rectangular bottomdredge was used. For preservation of living organisms, a glutaraldehyde-Na-cacodylate-seawater solution was used. Fixation was done immediately after thesamples came on board. The fixing solution consists of 25% glutaraldehydesolution in water, to which a 0.4 mol Na-cacodylate solution and seawater wasadded. The fixed material was then dehydrated in 30, 50 and 70% ethanol-seawater.

Laboratory Methods

The fixed specimens were block stained either with basic fuchsine, methyleneblue or with the flourochromatic acridine orange before embedding in LR-Whiteresin and admixed propylene oxide (see Reitner, 1993). After polymerization ofthe resin the samples were cut with a Leitz hardpart microtome into 15-50 /mmthick sections.

THE DEEP-WATER LOPHELIA REEF STRUCTURE

Two major sites of deep-water reef growth can be defined (Henrich et al, 1995).The most impressive of these forms a wall of more or less coalesced coralmounds growing preferentially on the SE margin of Sula Ridge in 310 to 280 mof water (Figure 2). This reef complex shows a pronounced elongated geometry,with framework heights ranging from 10 to 30 m. Locally, the coral frameworkcan be as high as 45 m. The total length of the reef complex is more than 9 kmin extent. The deep-water reefs are 200 to 400 m wide at their base. A secondarea of deep-water reef formation is detectable west of the main reef chain alongthe northwestern flank of Sula Ridge. These frameworks, however, do not reachthe dimensions of the main reef-chain. At its southwestern end where Sula Ridge

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64°10N -i

64°00N

Occurrence ofCoral Mounds and Patches

on Sula Ridge

MainCoral Mound-Chain

FIGURE 2 Position of the Lophelia reef complex on Sula Ridge (above) and the position of thetransect A-B. A transect through the reef complex showing a cross-section through Sula Ridge, theasymmetrical geometry of the foundation and the position of the coral reef frameworks (below).

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merges into the Fr0yabank, the coherent coral reefs increasingly disintegrate intosingle pinnacle-type frameworks (Mortensen et al., 1995).

RESULTS

The Living Lophelia: Response to Fouling Organisms

The dendroid, growing colonies of Lophelia show wide variability with respectto the mode of branching, orientation of calices and morphology of the skeleton(Zibrowius, 1984). The formation of a sclerenchyme or stereome (Sorauf, 1972),which covers the calyx, is found to be a very variable characteristic in thecorallites studied so far. The sclerenchyme represents a massive and densearrangement of aragonitic bundles which grow perpendicular to the outer surfaceof the epitheca. Lophelia colonies lacking a massive sclerenchyme are rare atpresent, but did exist at the Stjernsund-Sill location (Freiwald et al., 1997). Inliving Lophelia colonies, the soft tissue of the polyp rarely exceeds the outer rimof the calyx. Moreover, living Lophelia colonies are not entirely covered byepithelial soft tissue (cf. Jensen and Frederiksen, 1992). As in zooxanthellateshallow-water corals, mucus production can be considerably increased inLophelia. On Lophelia colonies, mucus is very often produced in areas ofinfestation by other organisms. The presence of the polychaete Eunicenorvegicus in the living portions of a Lophelia colony largely influences theprecipitation of a sclerenchymatic tube beneath a mucus film that covers theprimary parchment-tube of the nestling polychaete (Figure 3A-B). Rapidcementation of small portions of living branches, perhaps broken off by passingscorpenid fish, that fall onto the living corallites, become rapidly cemented intothe colony (Wilson, 1979b). The rare shells of gastropods and bivalves thatperhaps were present accidently among the living corallites may also be rapidlycemented and become firmly attached to the living colony. Selective scler-enchyme precipitation is commonly found just beneath the polyp-protected area,where larval attachment of bryozoans, serpulids and the parasitic foraminifer,Hyrrokkin sarcophaga, is evident (Cedhagen, 1994; Freiwald and Schonfeld,1996; Freiwald et al, 1997). Frequently, the early colonizers of Lopheliaskeletons were repeatedly overcrusted by selective sclerenchyme secretion whichresults in extraordinary skeletal thickening of the outer corallite portion. Such aphenomenon has been observed in other azooxanthellate branched corals, such asHoplangia and Leptopsammia, from the Mediterranean Sea (Harmelin, 1990).The high and low density banding pattern observed in Lophelia pertusasclerenchymes (Freiwald et al., 1997) is then considered to document repeated,

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probably mucus- or soft tissue-controlled calcification events to defend thepolyps from colonization and competition by rapid skeletogenesis (Figure 3C).

Succession of Post-Mortem Alterations of the Lophelia Skeleton

On a broad scale, a tiering of communities that live on or within the dead (ortissue-barren) coral framework can be deduced. The first tier is always restrictedto the freshly dead parts of the colonies and is characterized by an association ofa microbial biofilm and endolithic fungal infestation. This is the zone whereintense settlement of planktonic larvae of sedentary polychaetes, brachiopods,encrusting bryozoans and bivalves is stimulated (Figure 4A).

In freshly sampled coral colonies a faint brownish coating is developedbeneath the soft tissue-protected areas of the corallites, thus, the boundary is verysharp (Figure 4A-B). EDX-SEM analysis proved that this brownish coat is a Fe-

FIGURE 3 Living Lophelia and sclerenchyme secretion. (A) The nestling carnivorous polychaete,Eunice norvegicus, is densely encrusted by secondarily precipitated aragonite. The arrows indicateformer apertures of the polychaete through the sclerenchymatic material and the succeeding growthadvance of both the coral.and the polychaete. Scale = 1 cm. (B) Cross-section through Lopheliacorallites. The thick sclerenchyme is precipitated around the epitheca and it encrusts Eunice (X). Thetree ring-like banding pattern in the sclerenchyme layers indicates a repetitive precipitation processwhich results in the formation of thick skeletons often observed in colonial azooxanthellate corals.Scale = 1 cm. (C) Microtome section of the outer surface of a sclerenchyme layer showing fungalinfestation (Dodgella type) beneath an opaque Fe-Mn coating. The arrows point to ah older layer offungal infestation with a faint Fe-Mn line which represents a former exposed surface of the coralskeleton. Scale = 100 /xm.

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Mn precipitate of less than 5 fim thickness. In detail, the Fe-Mn precipitates formring-like bodies each measuring 5-8 fim in diameter which strongly imply somemicrobial control. The complete coating may represent a more advanced stage ofthe metalliferous precipitation. Although no direct observations of the producerare available, this kind of selective metal accumulation strongly suggests abacterial involvement. Moreover, etching patterns are detectable on the coralskeleton especially beneath the area of Fe-Mn precipitation which indicatediscrete dissolution of the coral skeleton (see also Scoffin, 1981).

Globular spheroidal borings of 20 /^m-depth penetration and about 10 fim indiameter are arranged along all exposed surfaces of the coral skeleton (Figure4C). The long axis of these minute excavations is orientated perpendicular to theskeletal surface. The sac-like borings have 2 to 5 /mi-thick openings. Suchshallow-tier borings are characteristic for the endolithic chemoheterotrophchytridalid fungus Dodgella (Zeff and Perkins, 1979; Glaub, 1994).

FIGURE 4 Decaying Lophelia. (A) Underwater photograph from a decaying Lophelia colony fromStjernsund, 250 m water depth. While the few healthy corals show extruded polyp tentacles, beneaththe soft tissue-protected areas of the skeleton (white) a faint Fe-Mn coat is formed (arrow). Scale =4 cm. (B) Close-up of a Fe-Mn-stained Lophelia corallite which is the zone of intense settlement ofrapidly growing sessile invertebrates such as Filograna sp. and brachiopods (arrow). The whitecorallite (X) next to the stained one indicates protection by coral soft tissue which prevents theformation of a biofilm with Fe-Mn precipitating properties. Scale = 1 cm. (C) Microtome section ofa Lophelia skeleton showing examples of intense carbonate corrosion provided by Dodgella borings(circle) which occur abundantly beneath an opaque Fe-Mn coating. Detritus (X) is trapped on the Fe-Mn layer which indicates the presence of a biofilm. Scale =100 ^tm.

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In the zone of early microbial infestation by both the Fe-Mn precipitatingbiofilm and the endolithic fungi, intense attachment of sessile invertebratesoccurs. Most abundant are the sedentary attached polychaetes Hydroides sp.,Filograna sp., the brachiopods Crania anomala and Terebratulina retusa,bivalves (Delectopecten vitreus) and encrusting bryozoans (Figure 4B). Thinencrusting Hymedesmia-type sponges are also common.

The downward boundary of this first taphonomic zone is not well-defined andvaries from place to place within a Lophelia colony. The second taphonomictiering community is characterized by a dominance of sponges, octocorals(Paragorgia arborea, Paramuricea placomus, Primnoa resedaeformis), erect,rigid bryozoans and hydroids. The most obvious change in the more advancedstages of coral decay is the sudden appearence of the yellow demospongePlakortis cf. simplex and the greenish-brown Geodia sp. In addition, hyme-desmid sponge crusts also gain in dominance. The increased presence of thesponges tends to close the interskeletal porosity between the corallites effectively(Figure 5A). It is at this more advanced stage of coral decay where intensesponge boring occurs frequently (Figure 5B). Most abundant species is Akalabyrinthica while Alectona millaris is less common (Figure 5A). Skeletal loss of70-80% of the coral skeleton results in the weakening of the stability of the coralframeworks. Sponge bioerosion probably with an episodically increasedhydrodynamic regime results in the breakdown of Lophelia constructions (Figure5C). Owing to the position of the Lophelia reef below storm wave base, no widelateral transportation of coral debris occurs. Instead, the in situ collapsing of coralframework is the most dominant process observed on Sula Ridge. The collapsingof living coral colonies and portions of colonies onto the sediment floor owing tothe weakening of the skeletal structure as a result of the excavations of boringsponges, is responsible for the development of the coral patches on Rockall Bank(Wilson, 1979b).

The trapped sediment found in the Lophelia calices and in the internal parts ofthe decayed framework on Sula Ridge is a mixture of clayey to silty silici-clasticsand planktonic organisms such as foraminifers and coccoliths. In addition,clusters of characteristic sponge-produced chips are common (Figure 6). Thecarbonate content in the trapped sediments varies from 5 to 65%.

DISCUSSION

Lophelia—Fouling Organism Interactions

Lophelia interacts with other organisms during its lifetime and postmortalry.While alive, the healthy coral counteracts the settlement of sessile organisms by

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FIGURE 5 Late stage of Lophelia decay. (A) Microtome section of Aka labyrinthica (1) excavatedinto a Lophelia skeleton (2). The arrow indicates a spicule accumulation. Externally, the base of aPlakortis cf. simplex is attached (3). Scale = 1 mm. (B) Skeletal loss mediated by sponge bioerosionin Lophelia. The spicule meshwork (X) is partly preserved in situ. Scale = 1 cm. (C) Coral rubblepavement around a living Lophelia reef in 275 m depth from Stjernsund, northern Norway. Scale =5 cm.

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FIGURE 6 Mixed calcareous siliciclastic infill of a Lophelia gastral chamber. The double arrowmarks the position of septa while the single arrow points to a cluster of sponge chips. The test of aplanktonic foraminifer is shown in the encircled area. Scale = 30 fim.

increased mucus production which, in turn, can result in repeated overgrowth offouling organisms by selective precipitation of sclerenchymatic material.Increased mucus production certainly helps the coral to reject passing detritalmaterial from the living colonies. This is the reason why living Lophelia appearclean in comparison to decayed coral colonies. Selective calcification to suppressparasites, commensals or as a repair reaction to isolate extraneous particles isknown from shallow-water corals (Morse et al., 1977) and has been largelyignored in biomineralization studies (Le Campion-Alsumard et al., 1995). Indeep-water corals, comparable phenomena have been observed in the form ofgall formation after infestation by ascothoracid crustaceans (Grygier, 1990;Zibrowius and Gili, 1990) and callus formation after infestation of Hyrrokkinsarcophaga (Freiwald and Schonfeld, 1996). While these heterotypic coral-colonizer interactions result in a strengthening of the framework architecture ofhealthy coral colonies, the prolonged infestation, either by epibionts or byendoliths may cause the death of the polyps. Moreover, with the loss of theprotecting mechanisms, diversity of reef dwellers and nestlers increasesdramatically.

Lophelia colonies which exist in marginal environments can survive but showstrongly decreased growth rates yet relatively high budding rates. Such asituation was observed on the top of the Stjernsund Sill, West Finnmark,

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Norway, where Lophelia comes close to the thermocline (Freiwald et al., 1997).Above the thermocline, the fjord waters show wide seasonal fluctuations withrespect to temperature and salinity, while below the inflowing Atlantic water itremains stable throughout the year. The colonies from the upper Stjernsund Silldisplay a strong competition for space with octocorals, sponges and hydroids.The reduced growth advances and the high budding rates leads to a pronouncedlystout and crowded colony growth habit (Freiwald et al, 1997). Such a stout andcrowded' Lophelia ecotype has also been collected by Nordgaard (1912) from asill in the Trondheim Fjord.

Different Types of Preservation

The locally intense sponge excavation of the dead coral framework weakens thearchitectural stability of the living coral colony. Intensified bioerosion and lessstabilizing sponge encrustation will convert the coral framework into a coralrubble pavement (Figure 5C; Wilson, 1979b; Scoffin et al., 1980; Freiwald etal,1997). In an outcrop situation, a lens-like geometry of dislocated and highlybioeroded corallites and colonies embedded in a hemipelagic mud can beexpected. Lateral transportation of coral rubble and broken colonies is limitedbecause the position is far below the storm wave base.

Two processes have been recognized which prevent, or at least slow down,destruction of the deep-water coral reef framework:

1 Intensified sponge encrustation fosters the trapping of advected nannoplanktonooze from fertile surface waters. Contemporaneous accumulation of internallyproduced sponge chips converts the primarily coarse coral framework into acollapsed muddy biodetrital structure on the seafloor which still has a positiverelief. Such collapsed structures have been detected on the Sula Ridge coralreef complex. In more calcium carbonate saturated waters, automicriteformation could contribute to internal peloid sedimentation as a consequenceof organic decomposition (Wilber and Neumann, 1994; Reitner et al, 1995).In an outcrop situation such a preserved structure would show strikingsimilarities to a biodetrital mud mound (Bosence and Bridges, 1995).However, this type of "mud mound" has not grown upward because it resultsfrom collapsing through taphonomic degradation.

2 Submarine lithification. The preservational style of deep-water corals asexposed on the modern seafloor differs widely. The spectrum encompassesloose-lying coral rubble pavements admixed with degraded colonies as hasoften been documented from the Northeast Atlantic (Wilson, 1979b; Scoffin etal, 1980; Freiwald et al, 1997) and the Blake Plateau occurrences (Stetson et

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al, 1962), to surficially hardened mounds from the Straits of Florida, calledlithoherms (Neumann et al, 1977) and the embedding of corals in hardgrounds(Allouc, 1990). Florida Strait lithoherms represent up to 30 m thick and severalhundred meter long surficially hardened positive structures on the seafloor in600-700 m water depth (Neumann et al, 1977). In detail, these induratedlithoherms do not represent in situ deep-water coral frameworks. Theconstituents of lithoherms consist of pelagic foraminifers, pellets, pteropodsbut also ooids and Halimeda plates from the Bahama Bank which are alsoincorporated. Near the upcurrent portions of the lithoherms, broken azoox-anthellate corals gain in importance (Messing et al, 1990). The porosity of thecoarse bioclastic material is partly closed through trapped detrital lime mudand Mg-calcitic cements (Wilber and Neumann, 1994). In many Medi-terranean hardgrounds the incorporated azooxanthellate corals also often showevidence of fragmentation and intense bioerosion prior to lithification.Strikingly, the available radiocarbon dates of the lithoherms and Medi-terranean coral-bearing hardgrounds indicate submarine lithification duringcold climatic episodes (Mullins et al, 1981; Delibrias and Taviani, 1985;Newton et al, 1987; Allouc, 1990).

Perspectives

Deep-water coral reefs growing on deep (aphotic) cold-temperate shelf and fjordsettings are bathed in waters which are slightly carbonate supersaturated andshow increased values of dissolved organic matter (Levitus et al, 1993; Keckand Wassmann, 1996). Although carbonate supersaturation conditions prevail,the elevated PO4-concentration of cold-temperate seas is considered to inhibitany carbonate precipitation which is the result of physico-chemically-drivencrystallization (Morse, 1986; Allouc, 1990). The postmortem alteration of deep-water coral reefs on cold-temperate shelves is therefore controlled by the amountof laterally suspended material (nannoplankton ooze) and/or the rate and kind ofbiological activities of communities which utilize dead and decaying coralframework in various manners. Preliminary observations on the preservation ofdeep-water corals reveal two different styles which would also influence thegeometry in a potential outcrop situation. Probably the commonest type of coral-dominated sediment in cold-temperate seas is produced as coarse coral rubblepavements or veneers (Stetson et al, 1962; Wilson, 1979b; Scoffin et al, 1980;Freiwald et al, 1997). Fragmentation is forced predominantly by the activity ofexcavating sponges. The Sula Ridge example with its giant coral reef framework,however, indicates alternative processes of framework preservation. Whileinternal sponge excavation is presumably acting at the same magnitude, thick,

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encrusting sponge communities effectively contribute to closure of the open coralframework interspaces. This, in turn, might reduce current velocity in such away, that the lime mud, produced by the boring sponges, is kept within theframework and not exported by the current motion. Trapping of advected silt-sized and other particles certainly also increases the conversion of a coralframework texture into a mud-enriched biodetrital texture. A similarly actingmodel is proposed by Willumsen (1995) for the differentiated early diageneticevolution of the famous Danian azooxanthellate scleractinian lithoherms fromthe Faxe Quarries, Denmark. Future research on modern deep-water coralmounds is needed to understand the geological signals that document changingenvironmental conditions on the deep shelves.

Acknowledgements

This work was supported by the Deutsche Forschungsgemeinschaft as part of thePriority Programme "Regional and global controls on biogenic sedimentation—Evolution of reefs" (He 1671/1). Sincere thanks to the captains and crews ofthe research vessels "Johan Ruud", "Littorina" and "Victor Hensen". Themicrotome thin sections were provided by Joachim Reitner and his group fromGöttingen University. The study benefitted from fruitful discussions withRüdiger Henrich, Jenny Krutschinna, Mads Willumsen, Helmut Zibrowius,Joachim Reitner and Marco Taviani.

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