Triassic Reef Research Articles

MICROBIALITE FABRICS AND DIMINUTIVE SKELETAL BIOCONSTRUCTORS IN LOWER NORIAN SUMMIT POINT REEFS, OREGON, UNITED STATES

Abstract Microfacies analysis of five patch reefs from the Martin Bridge Formation (Upper Triassic/Norian, Summit Point, Oregon, United States) reveals that microbialite fabrics dominate reef construction versus corals or other large metazoans. Other reef bioconstructors include characteristic Late Triassic branching corals and diminutive calcifiers (solenoporacean red algae, foraminifera, and sponges). The patch reefs exhibit dense growth fabrics and had elevation above the seafloor, making them ecological reefs or true reefs. Robust binding and encrusting organisms inhabited higher-energy areas, whereas red algae, followed by phaceloid coral colonies, inhabited zones of decreasing water energy, defining a subtle zonation consistent with wave energy in the paleoenvironment. The dominance of microbial fabrics and diminutive bioconstructors make the Summit Point reefs distinct among Upper Triassic reefs from northeastern Panthalassa. Summit Point was originally identified as a Dachstein-type reef (e.g., hi...

Critical review of Pseudocucurbitidae (Miliolina, Foraminiferea) from the Late Triassic reef environments of the Tethyan area

Abstract. The Late Triassic foraminiferal genera Amphorella, Spiriamphorella, Urnulinella, Pseudocucurbita, Paratintinnina, Costifera and Siculocosta are considered junior synonyms of the genus Cucurbita. Consequently, the number of families of the Milioliporacea (Miliolina) is significantly reduced. The valid species of the genus Cucurbita are considered to be Cucurbita infundibuliforme Jablonský, 1973, C. subsphaerica (Borza & Samuel, 1977a) comb. nov., C. longicollum Senowbari-Daryan, 1983, C. battagliensis (Senowbari-Daryan, 1983) comb. nov., C. cylindrica (Senowbari-Daryan, 1983) comb. nov. and C. floriformis (Altiner et al., 1992) comb. nov..

Upper Triassic (Carnian) reef biota from the Sambosan Accretionary Complex, Kyushu, Japan

Calcified sponges, algae, and reef problematica are abundant yet poorly known from the Triassic of Japan. They are abundant in shallow-water carbonate, redeposited blocks of the Sambosan Accretionary Complex, Konose Group, and southern Kyushu. Based on study of thin-sections from reef limestone exposed along the Kuma River, some important organisms and reef microfacies are described, which seem typical of Upper Triassic reef complexes. The most abundant reef organisms are hypercalcified sponges, including sphinctozoans, inozoans and chaetetids, followed by cyanophycean algae (including “Tubiphytes”-like organisms), and solenoporacean red algae. Loose sponge spicules in one thin-section also indicate the occurrence of rare hexactinellid sponges. Chambered demosponges described from the Konose carbonate rocks include Solenolmia manon manon (Munster), Colospongia sp., Jablonskyia andrusovi (Jablonský), several unidentified chambered sponges as well as the inozoid Permocorynella sp. 1 and Permocorynella sp. 2. Also present are chaetetid sponges and solenoporacean red algae belonging to Parachaetetes cassianus (Flugel) and Parachaetetes? sp. or Solenopora? sp. Especially abundant in thin-sections are cyanophyceans and “Tubiphytes”-like organisms. Among the organisms is Cladogirvanella Ott and Hedstroemia sp. The composition of the biota and presence of typical problematic organisms increases our knowledge of shallow-water Upper Triassic carbonate rocks in a remote setting in western Panthalassa. The composition of the biota indicates a mostly Carnian age. Most comparable organisms are known from both the northeastern and southern Tethys.

Clay and shaly claystones in the Upper Triassic Siliceous sponge-microbe reef mounds and oolitic bank complex in NW Sichuan, China

The Upper Triassic Carnian siliceous sponge-microbe reef mounds and oolitic bank complex is located in the northwestern part of Sichuan province, China. The Carnian hexactinellid-thrombolite reef mound tract and its underlying oolitic bank were developed in a deeper marine gulf. The oolitic bank overlain by a bioclastic bank, corresponding to the Lower Carnian served as the foundation for growth of the reef mounds. The reef mounds, inter-mound strata and caprocks correspond to the Upper Carnian. There are some occurrences of clay and claystones in the reef mound–bank complex. The reef mounds contain a certain ratio of clay content. The clay content in reef mounds is originated from the turbid and muddy water in the Carnian gulf. It is conjectured that alive siliceous sponges preferred to grow in marine water with more silica content to be supplied to their skeletons, and that thrombolite preferentially dwelt in marine water containing a certain content of clayey mud with more organic matter, for cyanobacteria were heterotrophs in Mesozoic. The inter-mound and caprock facies consist mostly of claystones. There exist clay-filling neptunian dikes, karstic clay, and fault clay. Most of the clay is originated from claystone coating of the reef mounds, and fault clay is caused by earthquake.

DETRITAL RECORD OF UPPER TRIASSIC REEFS IN THE OLDS FERRY TERRANE, BLUE MOUNTAINS PROVINCE, NORTHEASTERN OREGON, UNITED STATES

We report a coral-sponge dominated reef lithofacies in detrital boulders of carbonate-clast conglomerate from the Olds Ferry terrane, Blue Mountains Province, Willow Spring locality, northeastern Oregon. This discovery constitutes the first report of Triassic reefal lithofacies from the Olds Ferry terrane. Corals at the site include a high-growing, dendroid-phaceloid species that acted as a framework or sediment baffle, and a low-growing, cerioid, encrusting coral and a sponge that acted as sediment binders. The co-occurrence of coral taxa in the Wallowa intraoceanic arc and Olds Ferry pericratonic arc terranes suggests that during the Late Triassic, these regions were in proximity to one another. With this report, Upper Triassic carbonate rocks are known from all of the major terranes of the Blue Mountains Province and a Tethyan affinity is established for the fauna of the Olds Ferry terrane. We suggest that the source of this Late Triassic coral-sponge reef fauna in the upper member of the Huntington Formation was intrabasinal and that the source rocks are no longer exposed in the region. Numerous possible regional source areas for these detrital limestone clasts rule out the need to call upon an exotic terrane source area.

Platy coral patch reefs from eastern Panthalassa (Nevada, USA): Unique reef construction in the Late Triassic

Upper Triassic (Lower Norian) reefal buildups near Mina, Nevada, represent some of the earliest scleractinian coral reefs from eastern Panthalassa. The small patch reefs (~ 20–40 m high and ~ 50–150 m wide, obvious metre-scale elevation above the surrounding sediments) are from the Luning Allochthon and grew on an inner to middle ramp or in a deep lagoon. The Mina patch reefs were constructed by several different coral ecomorphotypes (platy, tabular, domal/massive, and branching corals) interpreted to have had zooxanthellate symbionts, and record subtle coral zonation within the reefs. Based on modern coral ecomorphotypes, platy to tabular corals at Mina grew in the lower euphotic zone (stressed by low light conditions), and the massive or domal corals inhabited shallower water (possibly above fair weather wave base) and were stressed by wave energy. Unlike most other Late Triassic reef ecosystems where phaceloid branching corals or calcareous sponges constitute the principal bioconstructors, the platy to tabular corals were the primary builders in the Mina patch reefs. The Mina reefs are also unique because cryptic and cavernous internal environments, epibionts, cryptobionts, and thick microbial crusts are rare or absent. The combination of platy coral dominance with the lack of epibionts/cryptobionts/microbial crusts suggests that the Norian reefs from Mina, Nevada represent a unique form of scleractinian reef construction from the Late Triassic.

Sponges from the Middle Triassic reef limestone of the Aggtelek Karst (NE Hungary)

Sponges from the Middle Triassic reef limestone of the Aggtelek Karst (NE Hungary) The hypercalcified sponge fauna of the Middle Triassic (Anisian-Ladinian) reef limestone exposed between Aggtelek-Jósvafő-Égerszög (northern Hungary) is described. Almost all the identified species are chambered sponges ("sphinctozoa"). Only two fragments of a not determinable species of non-chambered species ("inozoa") were identified. Hexactinellid sponges are not found. The majority of the Middle Anisian "sphinctozoans" are absolutely different genera, not known from the Permian reefs. The sponge fauna of the Triassic pioneer reefs in the Aggtelek Karst are distinctly small-scaled occurring in "Tubiphytes"-dominated carbonates. The following taxa are described: Amblysiphonella sp., Celyphia zoldana Ott, Pisa & Farabegoli, Colospongia catenulata catenulata Ott, C. catenulata macrocatenulata Scholz, Follicatena cautica Ott, Kovacsia baloghi (Kovács), Solenolmia manon manon (Münster), S. radiata Senowbari-Daryan & Riedel, Olangocoelia otti Bechstädt & Brandner, Thaumastocoelia dolomitica Senowbari-Daryan, Zühlke, Bechstädt & Flügel, Thaumastocoelia cf., Th. cassiana Steinmann.

THE OLDEST TRIASSIC PLATFORM MARGIN REEF FROM THE ALPINE - CARPATHIAN REGION (AGGTELEK, NE HUNGARY): PLATFORM EVOLUTION, REEFAL BIOTA AND BIOSTRATIGRAPHIC FRAMEWORK

The 1:10,000 scale mapping of the southern part of the Aggtelek Plateau (Western Carpathians, Silica Nappe, NE Hungary) and the study of five sections revealed two Middle Triassic reef bodies. In the late Pelsonian the uniform Steinalm Platform was drowned and dissected due to the Reifling Event. A connection with the open sea was established, indicated by the appearance of gladigondolellid conodonts from the early Illyrian. Basins and highs were formed. In the NW part of the studied area lower - middle? Illyrian basinal carbonates were followed by a platform margin reef (early?-middle Illyrian; reef stage 1) developed on a morphological high. This is the oldest known Triassic platform margin reef within the Alpine-Carpathian region. The reef association is dominated by sphinctozoans and microproblematics. The fossils are characteristic of the Wetterstein-type reef communities. Differently from this in the SE part of the studied region a basin existed from the late Pelsonian until the early Ladinian. During the late Illyrian- early Ladinian, the reef prograded to the SE, and reef stage 2 was established. Meanwhile, on the NW part of the platform a lagoon was formed behind the reef. Based on our palaeontological study the stratigraphic range of Colospongia catenulata, Follicatena cautica, Solenolmia manon manon, Vesicocaulis oenipontanus must be extended down to the middle Illyrian. Synsedimentary tectonics were detected in the 1. Binodosus Subzone, 2. Trinodosus Zone - the most part of the Reitzi Zone, 3. Avisianum Subzone.

Hypercalcified segmented sponges (“sphinctozoans”) from the Upper Triassic (Norian) reef boulders of Taurus Mountains (southern Turkey)

Upper Triassic Norian reef boulders, exposed in a locality near the fountain “Tavuk Cesme” (“Chicken Fountain”) in Taurus Mountains, southern Turkey yielded a large number of hypercalcified sponges, including “sphinctozoans”, “inozoans”, “spongiomorphids”, and “chaetetids”. The sphinctozoans from this locality are described in this paper. Geologically, this locality belongs to the Anamas-Akseki autochthonous. The reef boulders of this locality are exposed near the “Tavuk Cesme” fountain, located at the road, leading from the town of Aksu to Yenisarbademli. The following taxa are described: Amblysiphonella taurica nov. sp., Anthalythalamia riedeli Senowbari-Daryan, Calabrisiphonella sphaerica nov. sp., Calabrisiphonellacuifi nov. sp., Cinnabaria minima Senowbari-Daryan, Colospongia recta nov. sp., Colospongia sp. 1, Colospongia sp. 2, Colospongia sp. 3, Cryptocoeliacompacta nov. sp., Cryptocoelia? sp., Deningeriacrassireticulata Senowbari-Daryan, Zuhlke, Bechstadt and Flugel, Discosiphonella minima Senowbari-Daryan and Link, Gigantothalamia ovoidalis Senowbari-Daryan, Hajarispongiadipoyrazensis nov. sp., Hajarispongia cortexifera nov. sp., Kashanella irregularis Senowbari-Daryan, Kashanella cylindrica nov. sp., Parauvanella ferdowsensis Senowbari-Daryan, Parastylothalamia cylindrica nov. gen., nov. sp., Asiphothalamia polyosculata nov. gen, nov. sp., Sollasia norica nov. sp., and Thaumastocoelia sphaeroida Senowbari-Daryan. The most abundant sponge is Amblysiphonella taurica nov. sp. followed by Hajarispongia dipoyrazensis nov. sp., Colospongia and Discosiphonellaminima Senowbari-Daryan and Link are also relatively abundant. The stylothalamid sponge Parastylothalamia nov. gen. is an abundant sponge genus in other Norian reefs of the Taurus Mountains, but is rare at the “Tavuk Cesme” locality.

Upper Triassic reef-limestone blocks of southwestern Japan: New data from a Panthalassan seamount

Norian–Rhaetian reef-limestone outcrops belonging to the Sambosan Accretionary Complex located near and within Inaba Cave, western Shikoku Island (Japan), are described in detail for the first time. This patch-reef complex is inferred to have formed within an atoll-type carbonate system accumulated over a mid-oceanic seamount surrounded by deep-water radiolarian cherts in the Panthalassic Ocean during the Late Triassic. Because most Upper Triassic reef studies are from the former Tethys Ocean, counterparts from the Panthalassic Ocean, such as this study, are fundamental in resolving sedimentological, palaeontological and palaeobiogeographical issues related to Late Triassic reefs. The microfacies, palaeontology and palaeoecology of the Inaba reef limestones were investigated. The reef-boundstone facies is characterised by abundant coralline sponges that, in association with microbial crusts, constitute the main framebuilders. Some phaceloid and/or dendroid corals occur, but these groups are poorly represented, as are algae. Microproblematica and foraminifers exhibit rich associations, acting as secondary reef builders and/or reef dwellers. The surrounding setting comprises biodetrital sponge–coral rudstone and well-preserved megalodont rudstone–floatstone. The sedimentary contact between reef and lagoon facies is observed for the first time within Inaba Cave. Important similarities with the coeval Upper Triassic reefs of the southern classic Peri-Tethys area and especially with the Omani seamounts are recognised, suggesting a more southern-Hemisphere origin for Upper Triassic Japanese reefs than predicted by previous reef studies.

Taxonomic affinities and paleogeography of Stromatomorpha californica Smith, a distinctive Upper Triassic reef-adapted demosponge

Stromatomorpha californica Smith is a massive, calcified, tropical to subtropical organism of the Late Triassic that produced small biostromes and contributed in building some reefs. It comes from the displaced terranes of Cordilleran North America (Eastern Klamath terrane, Alexander terrane, and Wrangellia). This shallow-water organism formed small laminar masses and sometimes patch reefs. It was first referred to the order Spongiomorphidae but was considered to be a coral. Other affinities that have been proposed include hydrozoan, stomatoporoid, sclerosponge, and chambered sponge. Part of the problem was diagenesis that resulted in dissolution of the siliceous spicules and/or replaced them with calcite. Well-preserved dendroclone spicules found during study of newly discovered specimens necessitate an assignment of Stromatomorpha californica to the demosponge order Orchocladina Rauff. Restudy of examples from the Northern Calcareous Alps extends the distribution of this species to the Tethys, where it was an important secondary framework builder in Upper Triassic (Norian-Rhaetian) reef complexes. Revisions of Stromatomorpha californica produce much wider pantropical distribution, mirroring paleogeographic patterns revealed for other tropical Triassic taxa. Review of Liassic material from the Jurassic of Morocco, previously assigned to Stromatomorpha californica Smith var. columnaris Le Maitre, cannot be sustained. Species previously included in Stromatomorpha are: S. stylifera Frech (type species, Rhaetian), S. actinostromoides Boiko (Norian), S. californica Smith (Norian), S. concescui Balters (Ladinian-Carnian), S. pamirica Boiko (Norian), S. rhaetica Kühn (Rhaetian), S. stromatoporoides Frech, and S. tenuiramosa Boiko (Norian). Stromatomorpha rhaetica Kühn described from the Rhaetian of Vorarlberg, Austria shows no major difference from S. californica. An example described as S. oncescui Balters from the Ladinian-Carnian of the Rarau Mountains, Romania, is very similar to S. californica in exhibiting similar spicule types. However, because of the greater distance between individual pillars, horizontal layers, and the older age, S. oncescui is retained as a separate species. The net-like and regular skeleton of Spongiomorpha sanpozanensis Yabe and Sugiyama, from the Upper Triassic of Sambosan (Tosa, Japan), suggests a closer alliance with Stromatomorpha, and this taxon possibly could be the same as S. californica.

Reef expansion during the Triassic: Spread of photosymbiosis balancing climatic cooling

The PaleoReefs Database indicates that reef abundance increased profoundly during the Triassic period, from a pronounced low in the Early Triassic to a major peak in the Norian. This expansion is also evident when standardizing for sampling. Corresponding to the reef expansion is a relative increase of scleractinian corals as reef builders, whereas the contribution of hypercalcifying sponges and microbes decreased during the Triassic. The numerical expansion of corals is paralleled by a proportional increase of morphological features that are suggestive of photosymbiosis, such that the Norian reef boom might be explained by the spread of photosymbiosis in corals. The geographical expansion of reefs was far less pronounced especially concerning palaeolatitude. Late Triassic reef growth was limited to more or less the same latitudinal range as modern reefs. As oxygen isotope data and new modeling results indicate declining temperatures and CO 2 concentrations during the Late Triassic, the lack of latitudinal expansion might be attributed to global cooling. Reef development during the Triassic can thus be explained by the evolutionary spread of photosymbiosis balancing the effects of climatic cooling.

Sedimentary facies from Upper Triassic reefal limestone of the Sambosan accretionary complex in Japan: mid-ocean patch reef development in the Panthalassa Ocean

Microfacies of the Early to Middle Norian reefal limestone of the Sambosan Accretionary Complex (SAC) at Kamase locality, southwest Japan, are classified into seven major facies types in stratigraphic order: peloidal grainstone-packstone, unfossiliferous lime-mudstone, tubular problematica-rich wackestone, sponge-coral floatstone, sponge bafflestone, coral rudstone, and peloidal-bioclastic packstone-grainstone. The SAC records patch reef development on a mid-oceanic seamount in the Panthalassa Ocean. Because most examples of Triassic reefs come from the former Tethys, counterparts such as those from the SAC are pivotal in resolving paleogeographic issues as well as clarifying the depositional patterns between the eastern Tethys and adjacent western Pacific (Panthalassa). We also reveal that the primary stratigraphy of the reefal limestone was disrupted by submarine landslides of the seamount in an open-ocean realm during the late Middle to Late Jurassic time.

The first Upper Triassic silicified hypercalcified sponges from the Alexander Terrane, Gravina island and Keku Strait, Southeast Alaska

This paper describes the first silicified Upper Triassic (Early Norian) hypercalcified sponges known from the Alexander terrane, southeast Alaska. Sponges consist of five taxa from the Cornwallis Limestone of Keku Strait, southeast Alaska:AmblysiphonellaSteinmann,ParauvanellaSenowbari-Daryan and Di Stefano,Nevadathalamia cylindrica(Seilacher),N. miniman. sp., andStellispongia(S.cf.subsphaericaDieci, Antonacci, and Zardini). The hypercalcified sponges of the Alexander terrane as described in this paper provide paleogeographic linkage with other far-flung terranes of western North America, namely the Western Great Basin of Nevada, Stikinia of the Yukon, as well as the Antimonio terrane of northwestern Mexico. In addition,Parauvanellacf.ferdowensisis known from the Upper Triassic Nayband Formation, Iran. FinallyStellispongiacf.subsphaericais known from the Upper Carnian Cassian Formation of the Dolomite Alps.Sponges (particularly hypercalcified inozoans, sphinctozoans, chaetetids, and sponge-like organisms) are known worldwide from many Upper Triassic reef and nonreef sites. Although Upper Triassic deposits within the Cordilleran terranes and cratonal North America do not typically contain reeflike buildups, hypercalcifying sponge-like organisms were noted as occurring as part of the intricate paleoecological structure within a biostrome along the western shoreline of Gravina Island, southeast Alaska (southern Alexander terrane). This is in contrast to Keku Strait, southeast Alaska (central Alexander terrane), where hypercalcified sponges were identified from limestone beds within nonreef deposits.

First hexactinellid sponge reported from the Upper Triassic Nayband formation of central Iran

Sponges, along with scleractinian corals, are among the main reef-building organisms in Triassic reefs. Hypercalcified groups, including the chambered sphinctozoans, and the unchambered inozoans, chaetetids, and spongiomorphids, represent the most abundant Triassic reef-building sponges. Earlier workers have described elements of the latter group as “hydrozoans.” Hexactinellid sponges, abundant in some Permian reefs (e.g., in Texas, Finks, 1960), are rarely known from similar Triassic deposits, in general (Tichy, 1975), and particularly from Upper Triassic stratigraphic units. Hexactinellid sponges have been sporadically reported from well-investigated Upper Triassic reefs in the western Tethyan region (e.g., Keupp et al., 1989). However, a variety of hexactinellid sponges have been reported from Upper Triassic deposits and reefal limestones of the northern and central Tethyan realm (Boiko, 1990; Wu, 1989; Wu and Xiao, 1989; Rigby et al., 1998).

Late Triassic reefs from the Northwest and South Tethys: distribution, setting, and biotic composition

The paleolatitudinal distribution patterns during Ladinian and Carnian time are characterized by an increasing expansion of reefs from the northern to the southern hemisphere. The optimum of reef diversity and frequency in the Norian is associated with the development of extended attached or isolated carbonate platforms. Norian-Rhaetian sponge and coral reefs of the Northern Calcareous Alps developed (1) as reef belt composed of patch reefs in platform-edge positions facing the open-marine northwestern Tethys basins and (2) as patch reefs in intraplatform basins as well as in ramp positions.

Filograna (colonial serpulid worm tubes) from Upper Triassic (Norian) reef boulders of Taurus Mts. (southern Turkey)

Two colonial serpulid worm tubes—Filograna taurica n. sp. and Filograna serialis n. sp.—from the Upper Triassic (Norian) reef boulders occurring in Taurus Mts. (south Turkey) are described. As bafflers, both species of Filograna build microbioherms reaching dimensions of up to 15 cm. Both species were not known either in Turkey or in any other Triassic localities of the Tethyan realm.

Tabasosphaera pustulosa nov. gen., nov. sp., a microproblematicum (foraminifer?) from the Upper Triassic (Norian-Rhaetian) reef limestone of Nayban Formation (NE Iran)

A microproblematicum with calcaerous test, Tabasosphaera pustulosa nov. gen., nov. sp., a hollow spherical microfossil with pustule-like elements on the outer surface, is described from Upper Triassic (Norian-Rhaetian) reef limestones exposed near the town of Ali-Abad, south of Tabas (northeast Iran). Tabasosphaera is an endobiotic organism living within the cavities of other organisms, such as brachiopods, worm tubes, or in sponge spongocoels. The systematic position of Tabasosphaera, its interspecific association and the fossil assemblage of which it makes part is discussed. Most probably Tabasosphaera represents a foraminifer belonging to the group Lagenina.

The role of modern and fossil cyanobacterial borings in bioerosion and bathymetry

Measurements on modern coral reefs at Lee Stocking Island (Bahamas) illustrate that boring cyanobacteria species make a major contribution to microboring bioerosion rates. Borings attributed to cyanobacteria also occur in fossil environments. Bioerosional studies on Permian and Triassic reefs show similar intensities to those observed on modern equivalents. The importance of borings assigned to cyanobacterial activity is even more apparent in paleobathymetry. Comparison of the bathymétrie ranges known from modern and fossil microborings demonstrates a preference of boring cyanobacteria for shallow marine environments. Furthermore, some traces are linked to distinct portions of the shallow euphotic zone. They significantly contribute to characterize typical microboring assemblages, which are used for paleodepth reconstructions. In contrast to these stenobathic species, one cyanobacterial species turned out to be eurybathic. It has been recorded as deep as the dysphotic zone but may even extend to the aphotic zone.

Upper Triassic reef facies in the Asher-Atlit-1 borehole, Northern Israel: Microfacies, cement stratigraphy and paleogeographic implications

The late Triassic succession of the Asher-Atlit 1 borehole is over 1000 m thick, and is composed of reefal and associated facies interbedded with volcanics of Norian age. Only borehole cuttings are available. Microfacies classification and cement stratigraphy determined by optical and CL microscopy, allowed discrimination of six episodes of reef establishment, progradation, shallowing, and termination. Organic buildups are constructed of reef-building biota (sponges, possible corals, encrusting organisms) typical for the late Triassic of the Tethys. Reef-associated facies include fore-slope, central reef, ooid shoal, lagoonal, and supratidal environments. Cement zoning patterns trace diagenetic signatures which range from early neomorphic skeletal replacements and original marine cements, via characteristic burial sequences; depositional and diagenetic sequences are terminated by marginal marine intra- or supratidal conditions, and subaerial exposure with pedogenic overprints. Volcanic episodes tend to be associated with termination of carbonate sedimentation episodes, while volcanic quiescence and subsidence permit vertical progradation of reefal and associated facies. The depositional and progradational environment, rapid rate of sedimentation, periodicity, association with volcanics, and regional considerations, suggest a depositional setting on the rifted shelf-margin of the nascent Neo-Tethys, with a possible eustatic overprint.