The reefal margin and slope of a Middle Triassic carbonate platform: the Latemar (Dolomites, Italy)
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- Emmerich, A., Zamparelli, V., Bechstädt, T. et al. Facies (2005) 50: 573. doi:10.1007/s10347-004-0033-6
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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.
KeywordsCarbonate slopeDepositional modelReefal zonationLate AnisianMiddle TriassicDolomites
Since von Richthofen discovered the organic origin of the Triassic carbonate masses (von Richthofen 1860), the carbonate reefs in the Dolomites have been a major study area for carbonate platforms and especially for the research on fossil reefal communities. Owing to the dolomitisation of most of the carbonate platforms in the Dolomites, many studies of reefal fossil assemblages focus on the so-called Cipit boulders. These are reef talus blocks transported to allochthonous positions on toe-of-slope and basin margin areas prior to platform-wide dolomitisation. Cipit boulders document the composition of Anisian to Carnian reefs in the Dolomites (e.g. Cuif 1974; Fürsich and Wendt 1977; Biddle 1981; Fois 1982; Brandner et al. 1991; Flügel 1991; Senowbari-Daryan et al. 1993; Russo et al. 1998). Only a few in-situ reefs in the Dolomites have been studied so far (Latemar: Harris 1993; Marmolada: Blendinger 1986; Mt. Cernera: Fois and Gaetani 1984; complete review on Triassic reefs with a compendium of references in Flügel 2002). As the reefal Cipit boulders are located at allochthonous, distal positions, studies of platforms in the Dolomites also focus on carbonate slopes and slope-basin relationships. Many research since von Richthofen (1860) has been carried out on facies patterns and geometries of platform-to-basin transitions (e.g. Mojsisovics 1879; Hummel 1928; Pia 1937; Leonardi 1967; Bosellini and Rossi 1974; Gaetani et al. 1981; Bosellini 1984; Blendinger 1986; Bosellini and Stefani 1991; Bosellini et al. 1996; Harris 1994; Maurer 2000).
Owing to its excellent outcrops, largely absent dolomitisation and early Middle Triassic (Anisian) setting, the Latemar is ideally suited for the study of an in-situ reefal community and carbonate platform after the faunal crisis at the Palaeozoic/Mesozoic boundary. The base for this study are new, detailed investigations on the lithofacies and geometries of the reef and slope as well as on the reef fossil assemblages. The aim of this study is (1) to identify the processes controlling slope and ultimately platform architecture development, (2) to investigate a possible evolution of fossil assemblages in time and their distribution within the reef and (3) to assess an Anisian/Ladinian age of the reefal fossil assemblages as inferred from the chronostratigraphic framework of the lagoon.
Few studies on reefs in the Dolomites (Fois and Gaetani 1984; Senowbari-Daryan et al. 1993) investigate the Anisian recovery of carbonate producing organisms from the mass extinction at the end of the Permian where 62% of marine invertebrate families (McKinney 1985) and up to 96% of species (Raup 1979) are extinguished. All previous studies observe a recovery during the Anisian when many reefal biota (calcisponges, calcareous algae, few “Microproblematica” and few scleractinians) occur for the first time in the Dolomites again since the Permian-Triassic crisis. This is confirmed by recent literature (Twitchett 1999) reporting a gradual reappearance of trace fossils throughout the Lower Triassic of the Dolomites (Werfen Fm) and a complete recovery already in the Uppermost Scythian (top of Werfen Fm). Furthermore, studies from other Triassic reefal locations of the world also indicate a recovery of calcimicrobial buildups during the Anisian (for complete discussion and references refer to Flügel 2002).
Evolution of most of the platforms like Rosengarten/Catinaccio, Schlern/Sciliar and Monte Agnello neighbouring the study area and probably also the evolution of the Latemar itself ended with the extrusion of the Longobardian Wengen Fm volcanics. Hence, the proximity of the volcanic centre of Predazzo/Monzoni as one of the possible sources of these volcano-clastic deposits plays a crucial role for the platform development in the SW Dolomites (Fig. 2(2)). This volcanic centre is controlling regional subsidence and accommodation development with deep reaching faults and magmatic updoming (Doglioni 1984) as well as terminating platform growth with phreatic eruptions (e.g. Viel 1979a, b).
The studies on the slope of the Latemar by Goldhammer and Harris (1989) and Harris (1994) are in accordance with the so-called “Ladinian model” of Bosellini (1984; Fig. 6(1)). In this model, the slope progrades over basinal sediments and the lagoonal interior aggrades simultaneously. Continuous and uniform subsidence takes place and coeval basins deepen because of their distinctly lower sedimentation rates (Bosellini 1984). This pattern of carbonate sedimentation is assumed to lead to net deposition on the entire platform-to-basin transition. Hence the slope of the “Ladinian model” should be depositional and correspond to the “slope-apron” facies model sensu Mullins (1983) and Mullins and Cook (1986). In this model, channeling and bypass sedimentation to the toe-of-slope is absent and the deposits on the slope consist of broad, sheet-like debris-flows (Fig. 6(2)). The crux of this interpretation however is that the original model of Mullins (1983) and Mullins and Cook (1986) requires gentle slopes with an inclination of less than 4°. Contrarily, almost all carbonate slopes in the Dolomites reveal steep slope angles with clinoforms dipping at 20 to 50° towards the basins. These clinoforms reflect primary angles of repose and/or tracts of mass transport (Bosellini 1984; Kenter 1990).
Retrogradation of the platform margin during times of early platform evolution (“Lower Edifice”, synonymous with Lower Platform Facies, LPF, in Fig. 5), aggradation during later times of platform development and eventual drowning of the platform is reported by De Zanche et al. (1995). This “anomalous” behaviour—with respect to other platforms in the Dolomites—of the Latemar is thought to be related to the vicinity of the volcanic centre at Predazzo/Monzoni (see Fig. 2(2)). According to these authors, the “Lower Edifice” platform growth ends in the Upper Fassanian (i.e. the Curionii zone) where the drowning platform is covered by a “pelagic drape” (De Zanche et al. 1995; p. 140). This feature/observation is not supported by any other study. We also consider this as an unlikely case, as (1) the “pelagic drape” is not present at the described locality and (2) volcanic deposits on the immediately neighbouring Mt. Agnello platform (Fig. 2(2)) directly overly its lagoonal interior without a “pelagic drape” at the contact.
The asymmetry of the platform and its respective margin with steep clinoforms and slump scars on the SW side and more gentle dipping strata on the NW side is attributed by Egenhoff et al. (1999) to windward-leeward effects and different nutrient influx. However, this is in contrast to the concept of a tectonically controlled platform (Doglioni 1984; Bosellini 1989; Emmerich 2001). Emmerich (2001) and Knopp (2002) propose a more differentiated concept of the slope, where aggradation, progradation and backstepping of the margin can occur simultaneously on the Latemar platform but at different exposures creating different, sometimes even contrasting sedimentological settings.
Lithofacies and palaeontology
Detailed facies, sedimentological and palaeontological analyses (logging, facies mapping, lateral tracing of physical surfaces, thin sections) of the margin facies zonation were carried out at five outcrops (Fig. 4), three vertical sections and one detailed, continuous platform margin transect. The respective margins were investigated and sampled every 2 to 5 m at the sections/transect. Quantitative microfacies analyses were carried out on polished slabs (up to several dm in size) and thin sections (4×6 cm). Overall, we collected and analysed 247 specimens and 154 thin sections.
Lithofacies types of the slope
List of lithofacies associations of the slope-facies
Abundance of megablocks (size up to several metres in diameter); grain- and/or mudsupported; neither grading nor bedding, homogeneous mixing
Lithoclastic rudstones; mud-free, owing to abundant cement between the clasts transition to microbreccia; angular to well-rounded clasts; origin of components: lagoon and reef, clasts of the slope are rare; size of components: few mm to a some cm
Lithoclastic rudstones with LF4 wackestones (fine-grained peloids and bioclastic material) filling inter-particle porosity; mostly grain-supported, sometimes transition towards floatstones; origin of components: lagoon and reef, clasts of the slope are rare; size of components: some mm to a few cm
Floatstones with bimodal grainsize distribution: fine-grained peloids in the matrix (LF4) together with litho- and/or bioclasts up several cm; lithoclasts of LF3a are of the same origin as those of LF2a/b; bioclasts are mainly fragments of “Tubiphytes” sp., others are: peloids, fragments of echinoids, filaments, annelids, fragments of calcareous algae and small cephalopods
Well-sorted grainstones, consisting of peloids solely; very fine-grained, grainsizes ranging from 0.2 to 0.7 mm; sometimes cross bedding; often fining-upward trends
Wacke-/packstones with components like small lithoclasts, grapestone/oncoid fragments, fragments of Olangocoelia sp., peloids, fragments of echinoids and shells; sedimentary characteristics are bioturbation and geopetals; LF4 is mainly the product of normal background sedimentation on the slope, but also filling interstices in LF1 and LF2a/b
Pure mudstones fractured through slumping before lithification; calcitic block and radiaxial-fibrous cements fill interstices; LF5 mudstones contain no components, merely some peloids <<0.5 mm
Deposits of open marine biota
Bioclastic rudstone; bioclastic components are Daonella sp. and small cephalopods solely; bivalve shells are closely packed and stacked one above the other; interstices are filled with cement and sometimes sediment (wackestones with red micrite and fragments of echinoids); geopetals
Red calcitic mudstones; restricted occurrence of cephalopods and open marine foraminifers, such as: nodosarids, Abriolina mediterranea and porcellaneous forams (Ophtalmidium sp.); other components are: lithoclasts of the same LF type, fine-grained peloids and coprolites (<0.5 mm), specialised dwarf fauna (ostracods, micro-filaments); closely packed layers of radiaxial-fibrous cements parallel the walls of the dykes and are often micritised
General biotic content of the reef-facies
List of biota encountered in the slope- and reef-facies of the Latemar
Celyphia n. sp.?
Celyphia? minima Senowbari-Daryan, Zühlke, Bechstädt and Flügel, 1993
Celyphia zoldana Ott, Pisa and Farabegoli, 1980
Colospongia catenulata catenulata Ott, 1967
Deningeria crassireticulata Senowbari-Daryan, Zühlke, Bechstädt and Flügel, 1993
Follicatena cautica Ott, 1967
Solenolmia manon manon (Münster, 1841)
Thaumastocoelia dolomitica Senowbari-Daryan, Zühlke, Bechstädt and Flügel, 1993
Vesicocaulis oenipontanus (Ott, 1967)
Meandrostia triassica Senowbari-Daryan, Zühlke, Bechstädt and Flügel, 1993
Olangocoelia otti Bechstädt and Brandner, 1970
Reptonoditrypa cautica Schäfer and Fois, 1987
Anisocellula fecunda Senowbari-Daryan, Zühlke, Bechstädt and Flügel, 1993
Baccanella floriformis Pantic, 1971
Bacinella ordinata Pantic, 1972
Ladinella porata Ott, 1968
Plexoramea cerebriformis Mello, 1977
Radiomura cautica Senowbari-Daryan and Schäfer, 1979
“Tubiphytes” n. sp.?
“Tubiphytes” gracilis Schäfer and Senowbari-Daryan, 1983
“Tubiphytes” multisiphonatus Schäfer and Senowbari-Daryan, 1983
“Tubiphytes” obscurus Maslov, 1956
Diplopora annulata Schafhäutl, 1863
Diplopora nodosa Schafhäutl, 1863
Zornia obscura Senowbari-Daryan and Di Stefano, 2001
Parachaetetes cf. triasinus Vinassa De Regny, 1915
Abriolina mediterranea Luperto, 1963
Arenovidalina chiangchiangensis Ho, 1959
Aulotortus? eotriasicus Zaninetti, Rettori and Martini, 1994
Diplotremina cf. astrophimbriata Kristan-Tollmann, 1964
Endoteba ex gr. obturata (Brönnimann and Zaninetti, 1972)
Endotriada cf. tyrrhenica Vachard, Martini, Rettori and Zaninetti, 1994
Endotriadella wirzi (Koehn-Zaninetti, 1968)
Flatschkofelia anisica Rettori, Senowbari-Daryan and Zühlke, 1996)
Krikoumbilica pileiformis He, 1984
Lamelliconus ex gr. ventroplanus Oberhauser, 1957
Palaeolituonella meridionalis (Luperto, 1965)
Reophax sp./Ammobaculites sp.
Turriglomina mesotriasica (Koehn-Zaninetti, 1968)
Turriglomina scandonei Zaninetti, Ciarapica, Martini, Salvini-Bonnard and Rettori, 1987
Algae incertae sedis
Thaumatoporella cf. parvovesiculifera Raineri, 1922
Fossil assemblages of primary reef-builders
The numbering of the fossil assemblages is in accordance with their occurrence from reef front (F1) to back reef (F6).
In this fossil assemblage, encrusting “sphinctozoan” sponges like Celyphia zoldana, Celyphia? minima (Figs. 9(1–13) and 10(1–3)) and isolated chambers of Deningeria sp. (Fig. 11(8,14)) are associated with hexacorals of varying abundance (Margarosmilia sp., Fig. 8(8)) and often display microboring. The corals are usually covered by biogenic crusts and are very recrystallised (Fig. 10(12–13)). Bryozoans—Reptonoditrypa cautica (Figs. 8(5–6) and 10(12)) exclusively—are similarly seldom. Bacinella ordinata (Figs. 12(1–2) and 16(29)), “Tubiphytes” obscurus (Fig. 12(3–5,10–11)) and other “Microproblematica” (e.g. Radiomura cautica, Fig. 12(8–9)) complete this fossil assemblage. Small foraminifers can be found in the trapped (baffled) sediment (duostominids, e.g. Diplotremina cf. astrophimbriata, Fig. 15(16–18), Duostomina sp., Fig. 15(19–20), and Endotriadidae, e.g. Endotriadella sp., Fig. 15(22), Endotriada cf. tyrrhenica, Fig. 15(23), and Endotriadella wirzi, Fig. 15(27–28)), whereas sessil foraminifers indicate intergrowth with biogenic crusts.
Generally, corals are primary framebuilders of the bioconstructions at Latemar. Later stages of reef development show the encrustation and overgrowth by secondary framebuilders like algae and/or microbial crusts. The scleractinians of F4 are mainly characterised by isolated, thick and tall corallites and are less commonly cerioid (branched). A patch-reef-like growth is typical, colonies are up to 3 m wide and 1 m high. These isolated coral knobs are laterally not continuous and their framestones are very often recrystallised. A low number of septa and a robust nature of the stems point to the identification as Retiophyllia sp. (Retiophyllia sp. 2 sensu Senowbari-Daryan et al. 1993). The biggest colonies are found in-situ at Kirchtagweide and in blocks on the slope at Cresta De Do Peniola. In-situ colonies at Cima Feudo and Erzlahn are smaller and the individuals are less robust (Fig. 8(11)).
The framework of this facies or fossil assemblage comprises different microbial crusts of cyanobacterial activity. The largest occurrence of F5 is at Erzlahn where the bioconstruction forms an elongated structure (microbial/algal ridge). Stromatolitic and clotted-thrombolitic fabrics are the vital part of this fossil assemblage (Fig. 14(7–9)). Both fabrics reveal a close intergrowth and an equal volumetric percentage. The biogenic crusts reveal different, alternating levels of growth (thrombolitic-stromatolitic) and contain intercalated fragments of cyanobacterial algae like Girvanella sp. and sessil foraminifers (nubecularids, Fig. 16(1)). Layers of the crusts are quite often replaced by Baccanella floriformis (Fig. 16(25,28)) on the inside and/or cements on the outside. In a few cases only, “Tubiphytes” group and Bacinella ordinata (Figs. 12(1-2) and 16(29)) are part of this symbiotic growth.
However, F5 is not very frequent at Latemar compared to its abundance in bioconstructions of other Middle and Upper Triassic reefs in the area of the western Tethys. Like in other palaeoenvironmental reconstructions (e.g. Flügel 2002 and references therein), this assemblage pertains to the reef crest area. Seldomly, F5 occurs together with “Tubiphytes” group associations also in the upper part of the slope.
F6—“Tubiphytes” multisiphonatus thrombolites
The space between the branches contains abundant cements of early marine (isopachous calcite crusts) and shallow burial diagenesis (block calcite). However, the cement filled “voids” between the “branches” are seemingly formed by diagenetic alterations. The bioclastic components incorporated by micritic filaments around the tubes of “Tubiphytes” multisiphonatus show abrupt terminations at the “branch”-cement-contact. The outer surfaces of the “branches” are very irregular—like attacked and destroyed by fringing cements. This leads to the assumption that the visible organisation of branches and cements might not reflect primary facies. Nevertheless, early syndepositional cements must play a crucial role during buildup of these thrombolites; at later stages, they might be replaced by secondary cements during fluid migration.
Ten to twenty centimetre thick lenses of small bivalves (1–2 cm in diameter; heavily dolomitised; possibly Daonella sp.) between the thrombolites are evidence for a regime of low wave energy. The proximity of the thrombolites to the lagoon-facies indicates a sheltered position at the back-reef margin. The strata on which the colonies are growing (pack-/grainstones of the lagoon), dip towards the centre of the Latemar lagoon. Therefore, a depression (back-reef lagoon) exists between the reef and the tepee belt which is the palaeobathymetrically most elevated part of the atoll.
Our facies and palaeontological investigations allow the deduction of a detailed growth development of the thrombolites (Fig. 13). Buildup starts with several subparallel tubes ramifying towards the end of the first growth stage forming a pillow-like nucleus on which new levels/layers of “Tubiphytes” multisiphonatus grow. The first, nucleus-like stage is rather small, with some dm in diameter, several cm in height. The next layers are up to a few tens of centimetres thick. These layers are easily distinguishable in outcrop, whereas in microfacies a separation of layers is not as obvious. Here, the bush-like ramification and radial growth of colonies prevails.
Aggtelek Reef Fm (Wetterstein Fm)
“Latemar Limestone”, reef-facies (Schlern Fm)
Esino Fm, reef-facies
Seeling et al. (2005) and this study
Anisian (Early Pelsonian-Upper Illyrian)
Anisian/Ladinian (Middle Illyrian-Earliest Fassanian)
Diameter of central tubes
Thickness of “branch”
200-400 μm (measured from Plate V, p.356)
500–1100 μm (measured from Plate 10, p.152)
Length of “branches”
0.3–0.7 cm (oblique section?, measured from Plate V, p.356)
“several cm” (Schäfer and Senowbari-Daryan 1983, p.129)
up to 3 cm
up to 5 cm
Height of bushlike “thalli”
Maximal dimensions of thrombolite
height: 70 cm; length: 300 cm
height: 70 cm; length: 300 cm
“protected parts of the central reef”, i.e. transition to back reef (cf. p.341)
back reef, transition to the lagoon
isopachous calcite around the branches and block calcite
isopachous calcite around the branches and block calcite
Thickness of micritic filaments surrounding central tubes
- (“Coenenchyma”, see p.345)
ca. 5 times smaller than central tube (i.e. ca. 10 μm)
ca. 5 times smaller than central tube (i.e. ca. 10 μm)
Fossil assemblages of secondary reef-builders
The “Tubiphytes” group at Latemar’s reef is characterised by different, heterogeneous microfabrics. Their common characteristics are circular tubes or central channels in the middle of micritic crusts with undulated laminae or reticular tissue. The smaller species of this fossil assemblage is referred to “Tubiphytes” gracilis, showing a dense network of small and very irregular branches. Sometimes “Tubiphytes” gracilis is associated with other encrusting organisms like sessil foraminifers or Ladinella porata (Fig. 16(27)). In some cases it is not possible to distinguish between individuals of Plexoramea cerebriformis and of the “Tubiphytes” group (Figs. 12(6–7) and 16(23–24); for intergrowth of both species see also Enos et al. 1997). Compared to other Anisian reefs in the Dolomites like in the Olang area (Fois and Gaetani 1984; Senowbari-Daryan et al. 1993), “Tubiphytes” group and “Microproblematica” are much more abundant at Latemar.
This fossil assemblage is not a major constructor of the reef-facies but is always assisting in the stabilisation of primary frameworks. Only in some cases, Bacinella-bindstones form primary fabrics where their framework is almost exclusively organised by this species. Bacinella sp. (Figs. 12(1–2) and 16(29)) is heavily encrusting sponges, corals and fragments of the “Tubiphytes” group. “Microproblematica” are generally of major importance for this fossil assemblage. Among the most abundant are the “Tubiphytes” group and Radiomura cautica (Fig. 12(8–9)). This faunal assemblage is also associated with bryozoans, bundles of Porostromata as well as some sponges, few dasycladaleans and encrusting sessil foraminifers (nubecularids, Fig. 16(1)). The isolated parts of the Bacinella ordinata-mesh have large, ordinate cells, whereas the dense, encrusting parts (Bacinella sp.) reveal closer spaced and less regular cells. The matrix of the boundstones are wacke-/packstones with peloids. Cavities are recrystallised and also covered with Bacinella sp. Duostominids (Fig. 15(16–20)), Endotebidae (Fig. 15(21,24–26)), fragments of sessil foraminifers and Palaeolituonella meridionalis (Fig. 16(5–14)) are the most abundant foraminifers within the intercalated sediment.
Fossil assemblages of the lagoon
The wacke-/pack-/grainstones of the lagoon-facies are part of the margin at the transition from back reef to tepee belt. They are full of fragments of dasycladaleans (Diplopora nodosa, Teutloporella sp. and Macroporella sp., Fig. 10(9–11)), Zornia obscura (Fig. 14(10), probably fragments of dasycladalean algae), benthic foraminifers (aulotortids, Fig. 15(12,14), Earlandinita sp., Fig. 15(29–31), Reophax/Ammobaculites sp., Fig. 16(2–3), and ?Textularia sp., Fig. 16(4)), gastropods, bivalves and worm tubes (Fig. 16(18–22)). The presence of lithoclasts indicates levels of higher energy. In some cases pelagic material (Daonella sp. and cephalopods) is washed into the lagoon by storms. For a detailed analysis and description of lagoonal facies at Latemar refer to Egenhoff et al. (1999).
The database for our study is provided by five outcrops of the reef- and slope-facies at different exposures of the buildup and at different times of platform evolution: (1) Cima Feudo, (2) Kirchtagweide, (3) Erzlahn, (4) Schenon and (5) Cresta De Do Peniola (see Figs. 4 and 5). At the first three outcrops, palaeontological investigations were carried out on in-situ reefs, at the latter two on reefal blocks within the slope-facies. The first four locations offer the possibility to study the platform-to-basin transition at approx. right angles to the margin. The last locality (Cresta De Do Peniola) provides a transect through the upper slope parallel to the margin. All of the locations can be tied into the bio-/chronostratigraphic framework of the cyclic lagoonal succession. The array of the studied outcrops covers the entire time of platform evolution (Fig. 5).
This location (Fig. 4) comprises the entire western flank of Cima Feudo until its summit—the highest point of the SW ridge of the Latemar. The studied interval of platform evolution ranges from lowermost LPF to middle LCF (Fig. 5).
Architecture and sedimentology of the slope
However, if the flat lying strata are traced from the lagoonal interior (NNW) towards the basin (SSE), they terminate against an antitethically tilted block of lagoon-facies in the centre of the picture (Fig. 17(1), large striped area; signature: megablock). The size of the block is considerable, it is approx. 400 m thick and 200 m wide. In the direction of the palaeo-basin (SSE), two additional areas of lagoon-facies are distinguishable by their different dip. The proximal one dips towards the basin (Fig. 17(1), small striped area; signature: megablock), the more distal one is horizontally stratified, conformably overlies Buchenstein Fm and seems to be in-situ (Fig. 17(1), signature: in-situ lagoon-facies). All three areas reveal an erosive top and are covered by slope deposits of LTF and LCF times. This facies boundary is relatively distinct and was mapped in the field (Fig. 17(1), signature: erosional surface). Reef-facies is—as mentioned above—absent in the lower part of the succession and reappears in the LTF underneath the summit of Cima Feudo.
The buildup phase of the LPF platform at this outcrop continues until a giant failure of the platform flank at the verge from LPF to LTF removes slope, margin and parts of the lagoon. The downward movement of the lagoonal megablock shows a throw of approx. 100 m alongside a listric fault plane (Fig. 17(1), signature: presumed slump scar). As the block moves downward, it crushes the footwall and pushes up another block at its front. Subsequently the platform margin backsteps and re-establishes itself at the former interior of the platform (Fig. 17(1), signature: reef-facies). The interval following this catastrophic event is characterised by the re-establishment of a depositional slope. The giant slump is subsequently buried underneath carbonate slope sediments. Drowning of the platform and development of a “pelagic drape” (De Zanche et al. 1995; p.140) cannot not be observed. The contrary is the case, the platform margin is successfully keeping up with relative sea-level rise and newly created accommodation space above the megablock is filled with slope deposits.
The sheer size of this slump implies that instability of the margin or slope is not the only reason for the collapse. It is most probably caused by a combination of synsedimentary tectonic movement and lithological weakness. Anisian faults are known from the Northern Dolomites (Bechstädt and Brandner 1970) and sinistral transpression with deep-reaching faults is ongoing near the study area until the Longobardian (Doglioni 1984). The resulting flower structures and domal uplifts are paving the way for the eruption of the Wengen Grp volcanics (Doglioni 1983). Evidence for regional volcano-tectonic activities in the surroundings of the Latemar is the proximity of the volcanic centre of Predazzo/Monzoni above the Stava Line-Cima Bocche Anticline (Doglioni 1984). The observation of a tectonically controlled and/or mutilated platform generally corresponds with Doglioni (1984), Bosellini (1989) and De Zanche et al. (1995), although differences exist with respect to mechanisms, size and timing of the backstepping of the LPF platform.
Sedimentology and general palaeontology of the reef
Microfacies mapping along a reef transect (length: 300 m; line A–B in Fig. 17(1)) at the stratigraphically highest point of Cima Feudo covers the transition from lagoonal interior across the in-situ margin to the upper foreslope. The transect runs in a single stratigraphic level and is time-equivalent with the uppermost LTF to lowermost LCF lagoonal strata (Fig. 5).
The transect begins in the lagoon with wacke-/pack-/grainstones (F10), characterised by the presence of bioclastic material (gastropods, pelecypods), dasycladalean algae (Fig. 10(9–11)), peloids and benthic foraminifers. Among the most abundant foraminifers are Duostominidae, Endotriadidae and Endotebidae (classification sensu Vachard et al. 1994). The proximity of the reef is indicated by typical detritus like fragments of worm tubes (Spirorbis sp., Fig. 16(18–22)), of sponges (e.g. Olangocoelia otti), of “Tubiphytes” group and of “Microproblematica” like Plexoramea cerebriformis, Bacinella ordinata and Baccanella floriformis. The abundance of these components increases towards to the reef where these biota are eventually found in-situ. “Tubiphytes”-rich wackestones are the main indicator of the reefal margin (F8). Foraminifers like Palaeolituonella meridionalis and small, micritic worm tubes are present in the central part of the reef-facies. Biogenic crusts together with “Tubiphytes” group (F5) intercalated with boundstones of Celyphia? minima, Deningeria sp., Celyphia zoldana and Thaumastocoelia dolomitica (F2) characterise the reef-facies above the foreslope.
An important feature of this reef is the overwhelming abundance of calcisponges (Solenolmia manon manon, Deningeria crassireticulata, Meandrostia triassica and Follicatena cautica) which are usually well preserved, as well as small blocks (or in-situ heads?) of large, robust scleractinian corals (Retiophyllia sp.) at the uppermost foreslope (F4). At Cima Feudo, “Microproblematica” like Anisocellula fecunda (Fig. 16(26)), Bacinella ordinata and Baccanella floriformis are less important and less frequent reef-builders than in other Anisian reefs (e.g. Olang area; Senowbari-Daryan et al. 1993). The occurrence of small foraminifers like Turriglomina mesotriasica (Fig. 15(8–9)) indicates the upper part of the slope. Abundant bioclasts (fragments of Olangocoelia otti, cephalopods, Porostromata and solenoporaceans; Fig. 10(14)) together with at least two generations of cement—isopachous and block cement—fill the cavities between the reef talus blocks.
In summary, the reef at Cima Feudo reveals a low initial topography and bears no signs of emersion. Our study confirms the model of Harris (1993) at this location although the diversity of biota is greater.
This outcrop is located at the northwestern termination of the Latemar and forms a prominent, protruding ridge (Fig. 4). The location Kirchtagweide provides a tectonically undisturbed transect from the lagoonal interior (summit of Kirchtagweide) through a slightly younger reef belt to the coeval toe-of-slope interfingering with basinal sediments of the Buchenstein Fm (summit of Bewaller Köpfl, to the NW of the pictured area in Fig. 17(2), for geographical position and geological context refer to Fig. 17(3)). The studied reef-facies correlates with the uppermost LPF to lower LCF.
Architecture and sedimentology of the slope
In this transect, slope evolution is recorded from the build-up of Schlern Fm upon Contrin Fm. Buchenstein Fm underneath the slope is represented by a very thin (<3 m) and proximal facies. The slope-facies at Kirchtagweide lacks erosional features—its clinoforms are more or less parallel and display a depositional-type slope. Hence, the slope at this NW exposure of the Latemar corresponds to the Ladinian model of Bosellini (1984) and with restrictions to the classification “slope-apron” sensu Mullins (1983) and Mullins and Cook (1986).
Sedimentology and general palaeontology of the reef
Architecture and sedimentology of the slope
The slope at Erzlahn corresponds to the upper LCF and lower MTF interval of the lagoonal succession (Fig. 5). The most striking feature of the southern side of the Erzlahn is the missing reef (Fig. 19(1), and for detailed geographic position refer to Fig. 19(3); legend of geological map Fig. 17(3)). The contact between lagoon- (SE) and slope-facies (NW) is of erosional nature. Horizontally bedded strata of the lagoon terminate to the NW against a slump scar (slump scar 1 in Fig. 19(1)) and steeply dipping slope-clinoforms (up to 60°, unit 1 in Fig. 19(1)). Slope unit 1 passes basinwards (NW) into significantly less steep clinoforms (unit 2 in Fig. 19(1)). Unit 1 and unit 2 are both erosionally truncated at their top by an unconformity (slump scar 2 in Fig. 19(1)). This slump scar 2 is conformably overlain by a slope unit with partly antitethic dip (unit 3 in Fig. 19(1)).
Before an erosional event creates slump scar 1, probably a normal platform-to-basin transition (i.e. with a reef) existed. After the event, newly created accommodation space is filled with deposits of slope unit 1, most likely too quickly for a stabilising reefal margin to establish. Much of the sediment bypasses the uppermost foreslope and accumulates further downslope (unit 2). Unit 2 is not as steeply stratified as unit 1 and is stabilising the clinoforms of unit 1. But the slope already reaches its maximum of stability, resulting in a second erosional event (slump scar 2) which removes a large quantity of upper slope sediments. Dip measurements in unit 3 above slump scar 2 reveal an inclination of clinoforms towards the lagoon. This antitethic dip is caused by the listric nature of slump scar 2. A couple of metres above it, slope clinoforms are already inclined towards the basin again and reveal dip values between 5° and 15° to the NW. This indicates the re-establishment of a depositional slope after these two erosional events.
Timewise, slump scar 1 corresponds to an onlap structure in the lagoonal-facies at the SE termination of the Latemar. The tilting of the entire platform to the SE might cause the oversteepening of the clinoforms and their subsequent failure in the NW of the platform (Erzlahn, location 3). Similar to the situation at Cima Feudo, the origin of the tilting can be seen in synsedimentary tectonic movements at the nearby Stava Line-Cima Bocche Anticline.
In summary, major backstepping by margin failure is not only restricted to the SW of the Latemar and LPF/LTF at Cima Feudo, it also occurs on the NW side of the platform during the LCF-MTF interval. A model of simple aggradation as main platform growth mode until the latest stages of platform evolution is not in line with our observations at these two locations.
Sedimentology and general palaeontology of the reef
The reef at this location is exposed at the northern flank of the Erzlahn gully (Fig. 19(2), and for detailed geographic position refer to Fig. 19(3); legend of geological map Fig. 19(3)) and its SW termination. The reef-facies is easily distinguishable from the adjacent lagoon-facies by the absence of stratification and its slight dolomitisation. The outcrops of reef-facies at Erzlahn are scattered and small; nevertheless, they display features very distinct from all other locations at Latemar.
The reef front is represented by some small patch-reef-like structures—up to two metres in diameter—made up of large, robust hexacorals (F4, Retiophyllia sp. with corallites of up to 15 mm in diameter). Usually, these framestones are heavily encrusted with “Tubiphytes” and other microbes (F8). The encrusted, small coral knobs (reef front) pass laterally—i.e. towards the main outcrop of reef-facies described below and pictured in Fig. 19(2)—into algae dominated boundstones (F5). The centre of the reef is a microbial/algal ridge formed by laminated microbialites (F5). At Erzlahn, this part of the reef-facies is documented by a 10–20 m wide outcrop.
If outcrop, microfacies and palaeoenvironmental observations are taken into account, it is obvious that the simple reef model of Harris (1993) cannot be applied to the situation at Erzlahn. Harris’ model is based on investigations at Cima Feudo where the topography is the same as at Erzlahn, but facies belts and biota differ strongly.
Architecture and sedimentology of the slope
At Schenon, an in-situ margin is almost absent. Contrary to Erzlahn, the contact between slope and lagoon is not synsedimentary erosional but of postsedimentary tectonic nature. Two faults dissect the platform at Schenon. They both can be traced for up to one kilometre on either side of the pictured area in Fig. 20(3). At this exposure, the preserved slope-facies proves a depositional characteristic of the platform-to-basin transition during UCF times. The clinoforms of the foreslope are subparallel, erosional structures of a larger scale are absent. The preserved slope corresponds to the depositional models proposed by Bosellini (1984) and Harris (1994).
General palaeontology of the reef
The reef-facies is found within talus blocks on the upper slope solely. However, the upright position of delicately branched corals (Margarosmilia sp.) at a few places suggests the possibility of localised in-situ growth. Some small scleractinian colonies (F3?) seem to be growing on talus blocks of a slope fan. This setting of a proximal talus fan with resedimented reef-facies is supported by the occurrence of biota from different reef palaeoenvironments in the same microfacies. The blocks contain mainly encrusting “sphinctozoan” sponges like Celyphia zoldana and Celyphia? minima as well as Colospongia catenulata catenulata and Follicatena cautica. These calcisponges are accompanied by fragments of the “Tubiphytes” group and “Microproblematica” (Plexoramea cerebriformis and Radiomura cautica). Fragments of cryptically growing sessil organisms like Olangocoelia otti (sponge, alga?) are associated with fragments of dasycladaleans (e.g. Diplopora nodosa). Foraminifers of the reef and back-reef facies are also abundant, e.g. Aulotortus? eotriasicus (Fig. 15(12)), Flatschkofelia anisica, duostominids, Palaeolituonella meridionalis and Endotebidae. A single occurrence of Gaudrinella sp. (Fig. 15(32)) is also observed. Less common components are echinoid fragments and worm tubes.
Cresta De Do Peniola
Sedimentological and palaeontological description of the sections
Sedimentological analyses on macro structures, detailed facies mapping and lateral correlation of physical surfaces showed that two units with different lithofacies and sedimentological characteristics are present in this slope transect. (1) The lower unit is more turbiditic and also contains stacked debris flow deposits with components from reef and lagoon (LF2a/b and LF3a/b). Accordingly, there is a broad variety in lithofacies and in the biotic spectrum. (2) The sediments of the upper unit are characterised by abundant megabreccia deposits (LF1) and contain plenty of resedimented material from the slope, but also reefal and lagoonal clasts. In order to define the boundary between these two units more accurately and to track a possible reefal development, three sections at Cresta De Do Peniola were established (Figs. 23 and 24(1–2)): two sections through the entire succession (P1 and P3) and another one through a megabreccia channel in the middle of the succession (P2).
Sections P1 and P2 reveal similar biota in the lower and middle part. With respect to the general content of the previously described locations, P1 and P2 are enriched in benthic foraminifers like Earlandinita sp., Reophax/Ammobaculites sp., ?Textularia sp. and Bacinella ordinata (F9). The uppermost part of these two sections contains “Tubiphytes” obscurus, other “Microproblematica”, sponges (Vesicocaulis oenipontanus), corals, Porostromata, Bacinella ordinata, Celyphia zoldana and eventually Ladinella porata for the first time.
The basal layer of the second unit is very rich in reefal biota. Huge boundstone clasts—up to 4 m in diameter—are made up of Celyphia zoldana and Celyphia? minima, Deningeria crassireticulata, “Tubiphytes” obscurus (F2), biogenic crusts, cerioid hexacorals like Margarosmilia sp. (F3), red algae (solenoporaceans), “Microproblematica” (Plexoramea cerebriformis) and foraminifers like duostominids and Endotriada cf. tyrrhenica (Fig. 15(23)). Some of the boundstone clasts are made up entirely of red algae (Parachaetetes cf. triasinus) associated with fragments of Bacinella ordinata and “Tubiphytes” obscurus. Foraminifers of the back reef and reef core (Aulotortus? eotriasicus, Flatschkofelia anisica) and large sponges (Solenolmia manon manon) continue upward until a lateral extension/sheet crack of the neptunian dyke with red micrite (Fig. 25(1)).
Architecture and sedimentology of the slope
The three sections at this location (Figs. 23 and 24(1–2)) reveal the presence of an erosional surface separating two different slope types. Whereas the lower part of the slope at Cresta De Do Peniola is characterised by stacked multiple debris flows and coarse-grained turbidites (LF2a/b and 3a/b; Table 1), the upper part contains abundant megabreccia (LF1 and 2a/b; Table 1).
The lower part of the slope corresponds to the depositional slope type where sedimentation takes place on the entire platform-to-basin transition. Thus, the slope can be classified as “slope-apron” sensu Mullins (1983) and Mullins and Cook (1986). The correlatable erosional surface (Figs. 23 and 24(1–2)) forms a timeline of an interval with net erosion on the slope, i.e. corresponds to a stage of an erosional slope. After this interlude, net deposition occurs again on the platform-to-basin transition. However, in contrast to the interval below the erosional unconformity, a large amount of sediment bypasses the upper slope through two minor and one major channel to the lower slope. Hence this slope—correlatable with middle UTF times—corresponds to the “base-of-slope apron” type sensu Mullins (1983) and Mullins and Cook (1986). Although the main characteristics of the slope at Cresta De Do Peniola are depositional, no indications of progradational patterns of the margin exist for the latest (UTF) stage of platform development. Contrarily, the platform is aggrading or even backstepping as evidenced by the timeline of an erosional slope.
The other striking feature of this location is a coeval neptunian dyke dissecting slope sediments (Fig. 23). At three levels, the neptunian dyke has thin (<1 m) horizontal, laterally correlatable continuations with sheet-like cement crusts on the walls and bioclastic material within the crack. The biotic content of the trapped mud-/wackestones (radiolarians, cephalopods and Daonella sp., Fig. 25(1–2)) point towards open marine conditions. The infill of the neptunian dyke furthermore contains small, rare foraminifers indicating an Anisian to Ladinian age and also open marine conditions. A significant relationship with reefal associations is evidenced by the important occurrence of Abriolina mediterranea (Zaninetti et al. 1992)—not previously described in the Dolomites. However, the characterising microfauna of the dyke is made up of filaments and small ostracods (photomicrograph in Fig. 25(1)). Palaeontological and sedimentological evidence—similar biotic content and lateral continuity—imply a common genetic history of the vertical and horizontal fractures. Mechanisms for the synsedimentary opening of the neptunian dyke and its lateral extensions are either extensional tectonics and/or dilatation of slope sediments due to downslope sliding (Winterer et al. 1991; Sarti et al. 2000; Mallarino 2002).
The majority of agglutinated foraminifers commonly found in the lagoonal facies is represented by Duostominidae, Endotriadidae and Endotebidae. The sessil agglutinated Flatschkofelia anisica is an equally important element of the epifauna (cf. Rettori et al. 1996) and is also typical for the reef facies in the Olang area (Fois and Gaetani 1984; Senowbari-Daryan et al. 1993). Among the most frequent benthonic foraminifers at Latemar are Palaeolituonella meridionalis and large Reophax/Ammobaculites occurring in the central reef as well as in the back reef. The small species Turriglomina mesotriasica appears in the fine-grained sediments of the slope-facies (cf. ecological distribution proposed by Zaninetti et al. 1990), whereas the larger species Turriglomina scandonei—found so far only in the Southern Apennines (Zaninetti et al. 1987)—is also present in boundstone clasts of the slope.
The neptunian dyke at Cresta De Do Peniola contains mudstones with fragments of small nodosarids, well-preserved samples of Abriolina mediterranea, together with a fine-grained association of Arenovidalina chianchiangensis, Paraophthalmidium sp. and ?Ophthalmidium sp. The occurrence of Abriolina mediterranea at Latemar is important for the correlation with other Tethydian reefs. Apart from the Anisian?-Ladinian reef facies from the Lagonegro area where it has firstly been described by Zaninetti et al. (1992), the genus of Abriolina has so far only been found in the Northern Calcareous Alps (Rüffer and Zamparelli 1997), probably in Turkey (Middle Triassic) and Southern China (Zaninetti et al. 1992).
Palaeoecology of the reef-facies at Latemar
In the reef front, three subzones are distinguished with the help of different fossil assemblages (Fig. 26). Those zones inhabiting sediment baffling organisms with a branching growth are situated beneath the mean wave base (F1 to F3). They have the least potential of preservation in the geological record due to their delicate forms. Clasts of these fossil assemblages are abundant in slope sediments. The base of the branching zone (sensu James 1983) is formed by stabilising algae and is followed by bryozoans, sphinctozoans and delicate branching corals. The wave resistant constructions of scleractinian framestones are located above the mean wave base and within the surf zone (F4; cf. Harris 1993). The reef crest—i.e. the backbone of the reef—is marked by a microbial/algal ridge withstanding wave energy and possibly tidal currents (F5; cf. Biddle 1981). The transition towards the lagoon is inhabited by patchy thrombolites of “Tubiphytes” multisiphonatus (F6) becoming less frequent towards the lagoon (cf. Scholz 1972; Schäfer and Senowbari-Daryan 1982, 1983).
The unique feature of the reef-facies at Latemar are lateral variations of its biotic content: (1) The reef at Cima Feudo is characterised by well-preserved sponges. (2) The main feature of the reef at Kirchtagweide is the abundant presence of scleractinian corals. (3) So far, Erzlahn is the only occurrence of “Tubiphytes” multisiphonatus in the reef-facies at Latemar and possibly also in the Dolomites. (4) Schenon, however, reveals a similar biotic content of the reef-facies in talus deposits like the in-situ margin at Cima Feudo. (5) Foraminifers of inter-reef sediment and especially “Microproblematica” are abundant at Cresta De Do Peniola; it is also the only “reefal” location with bryozoan heads.
The reasons for such lateral variations within the same reef belt remain unclear as—according to present knowledge—neither palaeo-current nor palaeo-wind directions at Latemar are the cause for such changes in fossil assemblages. Tying these micro-macroscale variations to differences in nutrient influx through synsedimentary volcanic dykes appears too speculative. Even at recent reefs where pronounced micro-macroscale biozonation can be directly observed, the causes for such lateral variations remain often obscure (e.g. James and Ginsburg 1979; Zacher 1980; Iryu et al. 1995).
Biostratigraphical position of the reef
The majority of fossil assemblages presented in our reef concept are of Anisian or Anisian/Ladinian age, only in a few cases Ladinian biota are observed (Table 2; 12 species are Anisian, 21 are Anisian/Ladinian and only 5 are Ladinian). Palaeontological evidence from the reef-facies points in many ways to a predominantly Anisian age of the entire Latemar platform (see also Table 2). Small encrusting “sphinctozoids” like Celyphia zoldana and Celyphia? minima are generally found in the Anisian and are very common throughout Latemar’s succession, even in the upper part of the sections at Cresta De Do Peniola. The occurrence of age-diagnostic foraminifers throughout the sections at Cresta De Do Peniola until the very top of Latemar also indicates a mainly Anisian age. Typical Ladinian associations are not present; only at the top of the sections at Cresta De Do Peniola there is a slight increase in abundance of rare sponges, foraminifers and “Microproblematica” which are generally more frequent in Ladinian reefs (like Colospongia catenulata, Solenolmia manon manon, Ladinella porata etc.).
A possible temporal trend in reefal evolution from Lower Platform Facies (LPF) to Upper Tepee Facies (UTF) has to be excluded as almost the same fossil assemblages can be found in the younger as in the older part of Latemar’s reef. Only a slight development of faunal associations is visible; e.g. bryozoans are present in the lower levels only, which is also the case for Olangocoelia otti. However, compared to other outcrops like Cima Feudo or Schenon, the reefal content of the uppermost levels at Cresta De Do Peniola reveal only insignificant deviations from their biotic content. According to the literature, the duration of reefal/platform growth is in the order of one biozone or only slightly more (Brack et al. 1996; Zühlke et al. 2000; Mundil et al 2003; Zühlke et al. 2003) and thus might be too short to establish any trends of faunal evolution. The lack of a distinct evolution of the reef within the timeframe of platform development—together with the general absence of biota truly indicative of Ladinian age—supports the observations of the above-mentioned authors. The topmost succession at Cresta De Do Peniola corresponds to the youngest strata of the lagoon and is consequently Latest Anisian/Earliest Ladinian (Fig. 22). Most of the typical Anisian “Tubiphytes” group boundstones still occur in this—Latest Anisian/Earliest Ladinian—interval of platform growth.
In summary, our palaeontological data from the Latemar reef is in accordance with the chrono-, cyclo- and biostratigraphical data of the lagoon presented by Zühlke et al. (2000), Zühlke et al. (2003) and Mundil et al. (2003). Additionally, the biotic content (dasycladaleans: Diplopora nodosa, Zornia obscura) of the lagoonal strata analysed at some localities further confirms the latest Anisian/earliest Ladinian age of the reef. Especially Zornia obscura—so far described only from Ticino (Ladinian: “Problematikum 1”; Zorn 1971, 1972), Sicily (Anisian?/Ladinian; Senowbari-Daryan and Di Stefano 2001) and Southern China (Upper Anisian: I. Bucur, pers. comm. 2003)—indicates the same biostratigraphical position.
Correlation with other Late Anisian/Early Ladinian reefs of the western Tethys
Compared to other—slightly older–Anisian reefs of the Dolomites as described by Fois and Gaetani (Olang and Mt. Cernera, 1984) and Senowbari-Daryan et al. (Olang, 1993), the Latemar reef reveals significant biotic relations to both areas concerning sponges (e.g. Celyphia zoldana and Olangocoelia otti), solenoporacean algae, “Microproblematica” (e.g. “Tubiphytes” obscurus and Radiomura cautica) and foraminifers (e.g. duostominids). At Latemar however, Olangocoelia otti is encrusting lithoclasts (F7), but it is remarkably rare and not a very important part of all fossil assemblages. F7 is generally present in the lower part of the Cresta De Do Peniola section but seems to become more rare upsection, i.e. towards the Anisian/Ladinian boundary. Differences exist with respect to the presence or absence of certain biota and our detailed microfacies investigations show, that the Latemar reef is considerably more diversified. This might partly be due to the fact that an in-situ reef at Latemar is compared with Cipit-like reefal blocks at Olang and Mt. Cernera. But the reef in the Olang and Mt. Cernera area certainly contains not as much “Tubiphytes” group biota as the studied locations at Latemar, especially as the Cresta De Do Peniola section.
Strong similarities—as far as the reefal margin and slope are concerned—exist with some Anisian platforms of the eastern Tethys (e.g. Guizhou/China; Enos et al. 1997). In this area, “Tubiphytes” and “Microproblematica” like Plexoramea cerebriformis are the main framework elements. In-situ reef-facies is characterised by sponges, various encrusters and cements. Like at Latemar, corals play a minor role and display a slender, digitate growth. Retreat of the platform margin is observed from the beginning of platform evolution on, although the scale is different (up to 2.7 km margin retreat; Enos et al. 1997).
With respect to the Foraminifera in Latemar’s reef, similar assemblages and biofacies are found in Late Anisian successions in North Bulgaria (Trifonova and Vaptsarova 1982) and Western Turkey (Palaeolituonella meridionalis; Isintek et al. 2000).
As mentioned earlier, the “Tubiphytes” multisiphonatus findings (originally: hydrozoans; refer to Table 3) in the Anisian to Ladinian Wetterstein reef complex in North Hungary by Scholz (1972) indicates a relationship with at least the situation at Erzlahn. The similarity is further amplified by the distinct zonation of the reef at Aggtelek despite its Anisian to Ladinian age as proven by age-diagnostic foraminifers, dasycladaleans and brachiopods. However, abundant brachiopods and echinoderms are not observed at Latemar.
The most important biotic affinities probably exist with the time equivalent reef described by Scheuber (1990) from the Vicentinian Alps of Northern Italy. The in-situ reef in the area of Recoaro is less diverse than the one described in this study. But the main characteristics are strikingly equal: with respect to the dominating, abundant “Tubiphytes” group encrustations, corals are of equally minor importance as reef-building organisms. Foraminiferal assemblages (including Palaeolituonella meridionalis) and calcisponge-fossil assemblages are similar as well. The observed biological zonations at the Monte Spitz reef seem to parallel the situation at Cima Feudo. The reefal organisation at Mt. Spitz–with sphinctozoan sponges like Solenolmia manon manon in the central reef area together with abundant encrusting “Microproblematica”—seems to be a copy of this location at Latemar. The presence of Olangocoelia otti at both reefal margins further underlines this impression.
The geographically closest reef is located at the Schlern/Rosengarten platform. But here dolomitisation and scarce in-situ reef-facies hamper an investigation of the primary reefal organisation. The reef as derived from the famous Cipit boulders (e.g. Biddle 1981; Brandner et al. 1991) is slightly younger (Early to Upper Ladinian) than at Latemar. But it displays significant similarities, e.g. concerning the abundance of low-growing sessile organisms as evidenced by microbial/biogenic crusts and calcareous algae (Ortonella sp., Parachaetetes sp., Solenopora sp. etc.). Hence, the biotic content is generally correlatable with the upper parts of Cresta De Do Peniola or the heavily encrusted microbial ridge at Erzlahn. According to Biddle (1981), these microbial constructs are wave-resistant. However, the occurrence of many species of corals (e.g. Margarophyllia sp., Proheterastraea sp. and Trochastraea sp.) is not paralleled by Latemar’s reef. Additionally, the foraminiferal assemblage at Schlern/Rosengarten differs completely from the one described in this study.
The Ladinian reef of the Marmolada platform in the western Dolomites—as studied by Blendinger (1986)—-is mainly made up of solenoporaceans and species of the “Tubiphytes” group. Porostromate algae, calcareous sponges and solitary corals play only a minor role. Nevertheless, enormous quantities of reefal debris in slope deposits suggest a considerable productivity of the reef belt. Similar to the location at Schenon, some coralline heads with upright stems (in-situ position) are resting directly upon talus deposits indicating a growth of reefal biota to water depths well below the mean wave base.
The Ladinian to Carnian Sass da Putia build-up as described by Fois (1982) provides insight into its reef-facies through basinal “Cipit” boulders like at Schlern/Rosengarten, but also offers the possibility to investigate an in-situ reefal margin. Its reef is in sedimentological and palaeontological terms comparable to the one at Latemar. The content of encrusters (“Tubiphytes” group and microbial crusts) and “Microproblematica” (Baccanella floriformis and Bacinella ordinata) is similar and scleractinians (Margarosmilia sp.) are equally rare.
In Anisian strata of the Northern Calcareous Alps (e.g. Rüffer and Zamparelli 1997), there are no equivalents of the reefs observed in the Dolomites and its surroundings. Ramps with a low topography prevail. However, Anisian successions (Steinalm Fm) reveal strikingly similar foraminifers, e.g. Palaeolituonella meridionalis, Arenovidalina chiangchiangensis, Abriolina mediterranea and Turriglomina mesotriasica. Ladinian reefs of the Northern Calcareous Alps are more diverse with respect to sponges and algae but show a similar abundance of encrusting “Tubiphytes” group (Rüffer and Zamparelli 1997; Henrich and Zankl 1986). The main difference between Wetterstein Fm-reefs of the Northern Calcareous Alps and the Latemar is the organisation of the margin and its geometries. Wetterstein Fm reefs typically prograde rapidly, show talus breccias with abundant early marine cementation and are characterised by a ramp-like topography (e.g. Henrich and Zankl 1986), all of these features cannot be observed at Latemar.
Controls on slope evolution at Latemar
In the case of the Latemar, variations in tectonic subsidence are the main allocyclic factors for slope evolution. Other parameters like wind and wave directions seem insignificant and/or are being overprinted by variations in tectonic subsidence. Hence, the deduction of a palaeo-wind and/or -wave direction as done by Egenhoff et al. (1999) is not possible. Even more so, as the presumed directions are derived from analyses of small restricted areas at the platform top only (Marmolada: Blendinger 1986; Latemar: Egenhoff et al. 1999). The pronounced asymmetry of many platforms in the Dolomites seems to be entirely related to responses to different tectonic settings (cf. Bosellini 1989).
Controlling factors for the development of the carbonate platforms differ strongly from lagoon to slope. Whereas the lagoon is chiefly controlled by non-orbital and orbitally forced small-scale sea-level oscillations, the slope is largely independent from these high-frequency accommodation changes of the platform top (cf. Bosellini 1989). The high frequency sea-level oscillations recorded by the platform top are not preserved or recorded by neither the platform slope nor the reef (cf. Harris 1994). In addition, the reef is submerged throughout the entire time of platform evolution. This fact rules out sea-level lowstands as causes for the repeated margin collapses.
The slope is a sedimentary environment of episodic and catastrophic events (Coniglio and Dix 1992) destroying any evidence of the accommodation changes as indicated by the lagoonal interior. Therefore, autocyclic processes are of even greater importance for the slope development than for the lagoonal evolution. Cycles of fast accommodation fill-oversteepening-collapse at a platform-wide scale play an important role during slope formation (cf. Crevello and Schlager 1980; Mullins et al. 1986). Autocyclic processes such as Blendinger’s (2001) interpretation of cementation driven self-fracturing of slope sediments at Marmolada are not observed. Fracturing of carbonate sediments at Latemar takes place through movements during re-sedimentation. All blocks from metre to millimetre scale at Latemar are the result of gravity driven brecciation.
Areas with volumetric importance of syndepositional cements are small and restricted to the “Tubiphytes” multisiphonatus thrombolites at Erzlahn, the talus fan at Schenon or the tepee belt. Hence, massive syndepositional cementation accompanied by the formation of cementstones sensu Wright (1992) as a key factor during the build-up of the margin as observed by Russo et al. (2000) at the Marmolada and Stefani et al. (2001) at the Latemar can be excluded. Early lithification/cementation, however, is a key factor at Latemar. Otherwise, it is difficult to explain the nearly vertical cliffs/escarpments created by abundant erosive events, the huge size of the boulders in debris-flow deposits (LF1) and the neptunian dykes. In addition, without extensive early lithification/cementation the Latemar would not build up such a distinct relief above the palaeo sea floor.
The occurrence of C. zoldana and C.? minima together with abundant species of the “Tubiphytes” group is a real novelty in the studies on reefs in the Dolomites. Celyphia zoldana is usually typical for the Anisian, whereas large species of the “Tubiphytes” group are typical for the Ladinian. As a consequence, this is taken as evidence for an Upper Anisian/lowermost Ladinian age of the youngest strata at Latemar. The correlation of slope outcrops with basinal deposits and the projection into nowadays eroded lagoonal strata further constrains the depositional ages of the youngest slope deposits at Latemar (Cresta De Do Peniola; lowermost Ladinian sensu Brack and Rieber 1993). Our studies on the microfacies of reefal clasts at this location indicate that a true boundstone facies with sponges, corals and “Tubiphytes” continues up into the Lower Ladinian. The presence of sponges like Colospongia catenulata catenulata, Solenolmia manon manon—generally very common in Ladinian communities—and of microproblematica like Ladinella porata together with encrusting “Tubiphytes” obscurus in the upper part of the slope facies at Cresta De Do Peniola supports a position near the Anisian-Ladinian boundary of Latemar’s upper level reef sections.
The concept of the reef-facies at Latemar consists of a very diversified biotic association generally correlatable with other localities of Anisian/Ladinian reefs in the Dolomite area (Fois 1982; Fois and Gaetani 1984; Brandner et al. 1991; Senowbari-Daryan et al. 1993). However, differences exist in the little abundance of Olangocelia sp., in the higher diversification proven by thrombolites of “Tubiphytes” multisiphonatus and the large abundance of “Microproblematica” like “Tubiphytes” obscurus.
The foraminiferal associations correspond with other Anisian/Ladinian reefs described in literature (e.g. Trifonova and Vaptsarova 1982; Isintek et al. 2000), in particular with the Olang area (Fois and Gaetani 1984; Senowbari-Daryan et al. 1993). Differences are witnessed by the presence of several genera, like Turriglomina mesotriasica, Turriglomina sp., Turriglomina scandonei, Lamelliconus ex gr. ventroplanus (Fig. 15(15)), Aulotortus? eotriasicus and Abriolina mediterranea, the latter one found only in the Lagonegro area in Southern Italy and a few other reef localities in the world (Zaninetti et al. 1992). Compared to all other reef assemblages in the Dolomites, foraminiferal associations in the Latemar reef are much more diversified. Additionally, many genera from Latemar’s reef facies have not been described in the Dolomites before.
The authors would like to acknowledge Baba Senowbari-Daryan (University of Erlangen, Germany) for palaeontological discussions. Axel Emmerich thanks the “Studienstiftung des deutschen Volkes” (German National Academic Foundation) and the International Postgraduate Programme (University of Heidelberg, Germany) for financial support during fieldwork and travel. To Ioan Bucur (Cluj-Napoca, Romania), André Freiwald (Erlangen, Germany) and Rüdiger Henrich (Bremen, Germany) we owe many valuable comments on the manuscript.