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Microfacies and Paleoenvironment of Donezella Accumulations across an Upper Carboniferous High-rising Carbonate Platform (Asturias, NW Spain) Giovanna Della Port& Jeroen A.M. Kenter, Amsterdamand Juan R. Bahamonde, Oviedo KEYWORDS: CARBONATEPLATFORM - MICROFA('II{S CALCARI-;OUSALGAl- (DO.VEZEI,LA) CARBONIFEROUS
Summary Donezella is a problematic organism that during the mid-Carboniferous (latest Serpukhovian to Moscovian) characterized carbonate depositional systems in Europe, North Africa, Russia, Kazakhstan, and North America. Though Donezella is generally included in the green calcareous algae, it has been attributed to different systematic groups and its classification and paleoecology still remain controversial. This work focuses on the distribution of Doner, ella across a carbonate platform (Sierra de Cuera) of Upper Carboniferous (lower Bashkirian-lower Moscovian) age located in the Cantabrian Mountains (Asturias, NW Spain). Sierra de Cuera exhibits a well-exposed crosssection from the horizontal platform through a steep slope (30 ~) to the basin floor. This unique feature allows reliable estimates of paleo-water depth and distance from the platform margin. Donezella specimens arc interpreted as in situ when they form a network supporting cement-filled primary cavities and the ramified skeletons are surrounded by micrite coatings, often with a peloidal fabric, or by early marine cement. In the platform interior, Donezella is associated with phylloid algae and occurs in mud-rich low-relief bioherms. Towards the platform margin, massive units of boundstone are characterized by clotted peloidal micritc and radial fibrous cement-filled primary cavities. They contain Donezella and a diverse fossil assemblage of calcareous algae, bryozoans, and foraminifers. Donezella's delicate network appears fortified by the in situ precipitation of peloidal micrite. On the upper slope in s'itu precipitated peloidal micrite, abundant radial fibrous cemcn|, and fenestellid bryozoans are the major COlnponents of the boundstone facies, along with Donezella and a skeletal community similar to the outer platform one. On the slope, in situ Donezella were observed down to paleowater depths up to 200 m. Sedimentologic, petrographic, and micro facies analysis of Donezella accumulations in the different Facies belts of Sierra de Cuera strongly suggest that this problematic organism was able to thrive over a large depth range, in
PAI,IDI'COI.OGY SPAIN
low-energy but also in moderately agitated environments or in settings with temporary increase in current action, and in organic, physical-chemical and oceanographic conditions that enhanced the precipitation of pcloidal micrite. The interval of water depth m ferred [rein the well-cxposed slope geometry of Sierra de Cuera suggests that either Donezella might not have belon,,ed~ to the green calcareous aleae~, or, alternatively, this depositional system was influenced by particular paleo-oceanographic conditions that extended the euphotic zone below the average depth. The morphology of Donezella's skeleton and its sedimentological occurrences are not exclusively indicative of an affinity with Chlorophyta. Therefore, it is suggested that Donezella should be considered as a microl)roblematicunl organism. The data presented in this study contribute to the interpretation of comparable Donezella accumulations in carbonate depositional systems where limited outcrop exposures do not allow COTTCCtevaluation of the geometry and facies distribution.
! INTRODUCTION
1.1 Carboniferous carbonate build-ups The Carboniferous is considered a time of crisis of reefbuilding organisms occurring betwccn the Late De,,onian reefs in Australia and Canada and the Lale Permian reef complex of West Texas (Wood, 1999). Due to the lack of large skeletal metazoans. Carboniferous carbonate buildups (used here as a general term to indicate any Iocali/.ed. organically-built carbonate deposit thai nol always contains an apparent bound fabric; Wood, 1999) did not exhibit a rigid skeletal framework. James (1983) defined these buildups as ree f mounds (flat lenses to slccp conical piles, consisting of poorly sorted bioclastic lime mud with minor amounts of organic boundstone) and as mud mounds according to the relative percentage of skeletal components and carbonate mud. During Tournaisian-lower Visdan time. common buildups are the Waulsortian-type mud mounds recorded in North America, British Isles, Belgium and North Africa (Prall, 1995). They commonly nucleated in deep-water ramp set-
Addresses: G. Della Porta, Dr. J.A.M. Kenter, Vrije Lniversitcit, Earth Sciences Department, De IBoelelaan 1085, 10811IV Amsterdam, The Netherlands; e-mail:
[email protected],
[email protected]. Dr. J.R. Bahamonde, Departamento de Geologia. Un iversidad de Oviedo. c/ Jesfs Arias de Velasco s/n., 33005 Oviedo, Spain; e-mail:
[email protected].
150
tings, though some developed into shallower depths. Waulsortian mounds are interpreted to be largely the result of precipitation of carbonate mud induced by microbial activity in association with a skeletal community dominated by fenestrate bryozoans and crinoids (Lees and Miller, 1995). Only a few shallow-water reef mounds have been reported for the Tournaisian (Pratt, 1995). In the late VisEan reef mounds developed in shallower settings on tectonically-controlled topographic highs, particularly in north-western Europe (Webb, 1994; Bridges et al., 1995; Somerville et al., 1996). These build-ups had rigid skeletal cementstone or microbialite frameworks (Bancroft et al., 1988, Mundy, 1994; Webb, 1994). Due to growth within the photic zone, these reef mounds contain a more diverse skeletal community than Waulsortian mounds, with locally abundant red and green calcareous algae, foraminifers and cyanobacteria (Somerville, 2000). In the Late Carboniferous, reef mounds are characterized by a more diverse assemblage of binding, baffling, and trapping forms, in agreement with the trend already manifested in the Visran (Wood, 1999). Associated with bryozoans, there is the occurrence of: phylloid algae, which dominate Upper Pennsylvanian algal banlcs (West, 1988), the supposed alga Donezella, the green paleosiphonocladales beresellid algae (Beresella and Dvinella), the red ungdarellid algae Ungdarella and Komia (Mamet, 1991), and the demosponge Chaetetes (West and Kershaw, 1991). The micrites within reef mounds and mud mounds display homogeneous to characteristic laminated, clotted and peloidal fabrics, with evidence of formation in place on the sea floor or within the sediment. These micrites, defined as polymuds by Lees and Miller (1985), are heterogeneous in terms of fabric, and often structured with successive geopetal relationships (Lees and Miller, 1995). Several authors relate their origin to microbially-induced precipitation (Riding, 2000 and references therein). Other authors, however, suggest that alternative mechanisms of crystal nucleation within non-living organic substrates (organomineralization; Trichet and DEfarge, 1995; DEfarge et al., 1996) play an important role in the in situ precipitation of carbonate muds (automicrite or organomicrite; Reitner et al., 1995). Although a diversification of the skeletal composition is observed within reef mounds from the Late Carboniferous, the in situ-precipitated carbonate mud remains a significant component of the build-ups (Pickard, 1996). 1.2 Upper Carboniferous Donezella accumulations in Asturias (Northern Spain)
Donezella is a problematic organism that emerged as an important element of reef mounds in the mid-Carboniferous (West, 1988). The present work analyzes Upper Carboniferous (Bashkirian-Moscovian) carbonate strata characterized by the remarkable occurrence of Donezella. This organism is associated with in situ-precipitated carbonate mud with heterogeneous microfabrics and a skel-
etal community of calcareous algae, bryozoans, foraminifers, brachiopods, and echinoderms. The studied Donezella accumulations developed on a high-rising flat-topped carbonate platform (Sierra de Cuera) located in the Cantabrian Mountains (Asturias, NW Spain). Sierra de Cuera outcrop exhibits a well-exposed and continuous crosssection from the platform interior to the toe-of-slope, across a sharp shelf break. The depositional slope dips from several degrees to more than 30 ~', and forms a relief with respect to the basin floor up to 800 m. This good exposure derives from nearly vertical orientation of the bedding planes after tectonic tilting. Donezella is recorded within in situ accumulations in different facies belts from the platform interior to the slope. The organically-built deposits of Sierra de Cuera platform are comparable with some Carboniferous reef and mud mounds in components and internal fabrics. This terminology, however, will not be used in the present study due to the lack of a mound geometry and evidence of topographic relief" on the sea floor, in particular at the platform margin and on the steep slope. This work aims: a) to describe the characteristics of Donezella accumulations occurring on an elevated steepfronted carbonate platform of Bashkirian-Moscovian age across a transect extending from the platform interior to the slope; b) to compare these findings with other case studies; c) to provide an additional sedimentological contribution to the understanding of the paleoecology and systematic affinity of the problematic organismDonezella. The present data set might provide contribution to the interpretation of depositional environments of outcrops lacking complete information about the geometry of the depositional system.
1.3 Previous studies of Donezella The genus Donezella was established by Maslov (1929) for calcareous algae with tubular cylindrical shape and segmented tubes that branch dichotomously. The wall of the tube is composed of two layers: an outer layer of calcite that forms regularly spaced segments extending inward at right angles, and an inner layer of micrite (Mamet, 1991). The type species is Donezella lutugini Maslov 1929. For several authors there is only one species (Rich, 1967; Mamet et al., 1987; Poncet, 1991) and Donezella lunaensis R~icz 1964 differs from Donezella lutugini Maslov 1929 exclusively in the larger size induced by changes in the environmental conditions. In contrast, new species have been established by Ivanova (1999). Moreover, in the Bashkirian stratotype i n the southern Urals, D. Iunaensis is reported to appear later than D. lutugini and to be numerically subordinate (Proust et al., 1996). Donezella was scarce from latest Vis6an-Serpukhovian, very abundant during Bashkirian-Moscovian, and very rare during late Carboniferous-early Permian (Mamet, 1991). Its paleogeographic distribution comprises two domains in the intertropical belts relative to the early Pennsylvanian Equator (Scotese and McKerrow, 1990),
151
Fig. 1.-A) Schematic geological map of the Cantabrian Zone showing the different tectonostratigraphic Provinces/LInits (modified after Julivert, 1971 ). B) Schematic tectonic map of the northeastern part of Ponga Nappe Unit (modified aflcr Bahamondc el al.. 1997).
152
Paleothethys in the southern hemisphere, and Laurentia in the northern hemisphere (Poncet, 1991 ). In fact, Donezella is recorded in: United States (Nevada, Utah, Idaho, Texas, Oklahoma, Arkansas; Groves, 1986; West, 1988), Spain (Rficz, 1964; Vachard and Beckary, 1991), Italy (Pasini, 1978), Algeria (Lemosquet and Poncet, 1974; Mamet and Roux, 1975), Turkey (Gfivenq, 1965), Iran (Poncet, 1991), Urals (Proust et al., 1996); Donetz basin and Russian Platform (Maslov, 1929; 1956), Kazakhstan (Cook et al., 1994), and in the Canadian Arctic (Mamet et al., 1979). The systematic classification of Donezella has been controversial owing to its limited occurrence and lack of resemblance with any extant form (Mamet, 1991). Maslov (1929) considered Donezella to be a red alga of uncertain affinity. Johnson (1963) indicated that Donezella might have been better placed in the Chlorophyta but classified it as alga incertae sedis (Rich, 1967). In successive studies Donezella was attributed to green algae Codiaceae (Rficz, 1964), Foraminifera (Riding and Jansa, 1974; Riding, 1977), calcareous sponges (Termier et al., 1977), microproblematica (Riding, 1979; Chuvashov and Riding, 1984), green algae Paleosiphonocladales (Shuysky, 1985), green algae of incertae familiae (Groves, 1986), green algae Dasycladales (1988), and pseudo-algae (Vachard et al., 1989). In the most recent classifications Donezella belongs to the green algae Paleosiphonocladales of the tribe Donezelleae (Ivanova, 1999), as emended by Shuysky (1985). There is, however, no univocal morphological evidence that Donezella was a green alga (Rgcz, 1964; Rich, 1967; Termier et al., 1977). In addition, the paleoecology and suitable water depth intervals for this organism are not univocally established. Interpretations have been driven by the assumption that Donezella was a green alga or are based on outcrops with limited exposures. Different environmental conditions, ranging from quiet to agitated settings, have been suggested forDonezella (Rficz, 1964; Bowman, 1979). As a consequence, the understanding of the paleoecology of Donezella can be improved only through the analysis of the sedimentary features and skeletal components of well-exposed and continuous outcrops.
stable areas (Picos de Europa and NE of Ponga Nappe provinces) extensive carbonate platforms nucleated (Colmenero et al., 1993). These carbonate successions comprise the Bashkirian Valdeteja Formation (850 m thick), predominantly progradational, and the Moscovian Picos de Europa Formation (800 m thick), mostly aggradational. They overly the Serpukhovian Barcaliente Formation that consists of 350 m-thick, dark finely laminated mudstone representative of an extensive and stable shelf that served as foundation for the Upper Carboniferous platforrz-s (Bahamonde et al., 1997). The Upper Carboniferous (lower Bashkirian-lower Moscovian; E. Villa pers. comm.) Sierra de Cuera outcrop corresponds to a south-verging thrust-sheet located in the NE sector of the Ponga Nappe province (Fig. I A,B) tilted in the early Kasimovian (Marqufnez, 1989). In Sierra de Cuera, no evident separation between the Valdeteja and the Picos de Europa Formations has been recorded (Bahamonde et al., 1997). During the lower Bashkirian, a low-angle ramp nucleated on the Barcaliente Formation. Initial vertical aggradation was followed by horizontal progradation. During the Bashkirian, dominant progradation alternating with several aggradational phases produced the steep clinoforms. At the transition between Bashkirian and Moscovian, the flat-topped shallow-water platform (1 km thick, 10 km wide) developed and accreted through alternation of mostly aggrading and prograding phases during the lower Moscovian. The following lithofacies-stratal pattern zones were distinguished (Fig. 2A): 1) inner platform (meter-scale cycles of sub-wave base open marine facies shallowing-upward into restricted lagoon); 2) outer platform (shallowing-upward cycles of massive boundstone overlain by ooid-skeletal shoals and crinoid-dominated bioclastic bars); 3) upper slope (massive boundstone rich in peloidal micrite, early marine radiaxial fibrous and botryoidal cement alternating with crinoid packstone, skeletal wackestone, and grainstonepackstone with reworked platform-derived grains); 4) lower slope (upper slope-derived breccias); 5) toe of slope (interfingering of basinal spiculitic limestone with breccias and turbidites beds).
2 REGIONAL AND GEOLOGIC SETTING 3 METHODS
The outcrop of Sierra de Cuera platform is located in the Cantabrian Mountains (NW Spain; Fig. 1A) that form the northeastern part of the Iberian Massif (SW sector of the late Paleozoic European Hercynian Orogen). The Cantabrian Zone constitutes one of the six zones in which the Iberian Massif was divided according to structural style and stratigraphy and it is characterized by a set of imbricated thrust sheets deformed by thin-skinned tectonism (Julivert, 1971). During Bashkirian-Moscovian time, the Cantabrian Zone was a marine foreland basin, where the subsiding proximal areas were occupied by thick silicielastic wedges of turbiditic and deltaic successions separated by calcareous units (Folds and Nappes, Central Asturian Coal Basin, and Pisuerga-Carri6n tectonostratigraphic provinces), whereas in the more distal and
Thirty-two stratigraphic sections were measured in the platform interior, in the outer platform, and across the slope (Fig. 2B). The sections are correlated laterally by marker horizons of layers of crinoid-rich packstone characterized by a red-stained micritic matrix. These beds are continuous for several hundreds of meters and allow lateral tracing and correlation among lithologic units both in the horizontally bedded platform and on the steep slope. Lithofacies boundaries were traced in the field and mapped on aerial photographs. Samples for petrographic analysis and polished slabs were collected along measured sections and from scattered locations. On the slope, bedding planes (Figs. 2 and 3) were traced, mapped on aerial photographs and sampled to obtain a time-equivalent distribution of
153
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litho- and microfacies. The tracing ol' bedding surfaces on the platform and slope and DGPS measurements of stratal patterns provided reliable estimates of slope clip (up to 30 ~ and paleo-water depths (Fig. 3). The petrographic analysis of nearly 400 thin sections revealed the distribution pattern of Donezella and the variations of textures and associated fossil assemblages in each facies belt. Donez.ella is considered in situ when: l ) the dichotomously ramified thalli form an open network departing in different directions; 2) the Donezella branches are generally embedded in micrite with clotted and p e l o f dal fabric, or are surrounded by micritic coatings and/or cement; together with the microcrystalline calcite they produce irregular digitate or rounded forms with sharp outlines, and enclose primary growth cavities filled by geopetal sediment and/or cement: 3) within the Donezella network almost no other skeletal element is observed besides a few encrusting foraminifers, which appear directly attached to the thalli. Donezella deposits occur as reworked clasts in shoal grainstone of the platform facies and in slope breccia and grain flow beds. In addition, this organism is considered reworked when: 11 it occurs as single tube fragments and the ramifications are not visible: 2) the fragments are generally closely packed in a homogeneous micritic matrix containing fine bioclastic debris in skeletal wackestone and packstone; 3) Donezella fragments are generally associated with a diverse fossil assemblage showing evidence of reworking and mechanical transport.
m) intraclast and coated grain-rich packstones and g,-ainstones represent a shoreface environment and are indicative of the renewed flooding of the platform top. These high-energy strata contain reworked Donezella facies in few mm-size, sub-rounded intraclasts. The increase of water depth, due to relative sea-level rise and consequent creation of accommodation space, enhances the development of massive, carbonate mud-rich accumulations in a low-energy setting. They consist of skeletal wackestone, rarely mudstone and fine-grained packstone with in situ Donezella (Fig. 3A: Pl. 26/1 ) and scattered phylloid algae (Fig. 3B; Pl. 26/2). This lithofacies (a few meters up to 20 m thick) shows a fiat-lens shape, and is adjacent to locally bioturbated, skeletal packstone with a diverse, open marine fossil assemblage. These low-reliefbioherms, besides Donezella and phylloid algae, contain bryozoans (P1.26/ 3), ostracodes, encrusting foraminifers (calcitornellids, PsetMoglomospira, Tuberitina, Tetrataxis), endothyrids, globivalvulinids, paleotextularids, rare fusulinids, brachiopods, echinoderms, polychaete worm tubes (PI. 26/4; referable to Thartarella or Terebella; Wahlman, 1988; Pratt, 1995), and rarely sponge spicules (Pl. 26/4) and trilobites (PI. 26/2). Chaetetes colonies and rare solitary rugose corals are observed towards the top of these lensshaped units. Donezella occurs both as fragments and in situ, concentrated in cln- to din-size lenses in which the thalli form an open network embedded in a microcrystalline calcite matrix, with homogeneous, clotted and peloidal fabric (Fig. 3A: P1.26/1,5, 6). The associated skeletal packstone are enriched in foraminifers (Profi~sulinella sp.,
4 DONEZELLA OCCURRENCES IN
E:~tsulina, Schubertella, EostqC.fella, Pseudosta,[.fella, O=awainella. Bradvina, Climacammina, and Endothyra)
SIERRA DE CUERA
The outcrop sites (Fig. 2B) selected to evaluate the characteristics of Donezella-bearing lithofacies are: a) lower Moscovian platform interior areas located more than 1 km behind the platform break; b) uppermost Bashkh'ian to lower Moscovian outer platform with lateral transition to the platform interior at a distance of 150-200 m inwards of the platform break; c) upper Bashkirian to lower Moscovian slope. 4.1
Inner Plattbrm
Platfl)rm interior deposits consist of subtidal limestones organized in shallowing-upward cycles ranging in thickness between 2.5 m and 15 m. At the base, thin (1-3
and echinoderms. The fossil assemblage also includes brachiopods, bivalves, bryozoans and calcareous algae such as Ungdarella, Komia (Pl. 26/7), and minor phylloid alga plates. In these bioclastic deposits Donezella is rarely present and only as scattered fragments. Following a decrease in relative sea level, the lowrelief algal bioherms are overlain by shallow lagoon facies. These strata (average thickness 3 m) contain beresellid algae (Beresella, Dvinella. Uraloporella: Pl. 26/8), Ungdarella, and small Chaetetes colonies. They grade fi'om an open marine to a restricted environment represented by peloidal packstone to wackestone with scarce fauna consisting of calcispheres and ostracodes. Done=ella specimens do not occur in these shallow lagoon deposits, except for some very rare fragments. >>>>
Fig. 3.- Aerial photograph (top) of a portion of Sierra de Cuera outcrop showing a transect from tile platfl)rm to the toe-of-slope. Line drawings indicate the stratal patterns measured with DGPS (continuous lines) and traced on the outcrop (dashed lines). Average dip of the slope is 30 ~ Done:.ella occurs in situ in the boundstone facies in sections SA4, G20, SC8B and at Q300 in paleo-water depths up to 200 m. A-B) Photomicrographs of the platform interior mud-rich algal banks: A) Done=ella specimens (arrow) floating in a homogeneous matrix wilh scanered poorly-defined peloids (sample W106/42.(1): B) wackestone to packstone with phylloid alga plates farrow: sample 253/60.01. C-D) Microfacies of boundstone facies occurring towards the platform margin: C) Donezella (arrow) surrounded by peloidal micrite (sample 253/40.4); D) bindstone with tubular entrusting calcitornellid fl)raminifers (arrow) and peloidal micrke (sample 0/27.3). In both boundstone facies there are primary irregular cavities filled by blocky sparite cement. E-F) Photomicrographs of boundstone facies occurring on the slope: E) abundant Donezella specimens (white arrow) in peloidal micrite (sample SC8/29.51: F) fenestellid bryozoan frond (white anow) encrusted by micrite with clotted and peloidal fabric (sample SC8/ 17.1). The primary cavity within the peloidal micrite is lined by isopachous rim of radial fibrous cement (black arrow).
155
156
4.2 Outer Platform From the platform interior towards the platform break there is a lateral facies change in the characteristics of the Done=ella-bearing deposits and in the vertical cyclic stacking pattern of depositional facies. This gradual change takes place approximately at a distance of 150-200 m from the platform break. The mud-rich bioherms of the inner platform grade laterally into massive units (few mete,s to nearly 20-25 in thick) of boundstone facies. These boundstones forin shallowing-upward cycles overlain by beds of crinoid packstone and ooid-coated grain-skeletal grainstone ((I.5 to 3.5 m thick). These high-energy shoal capping facies contain Donez.ella deposits in reworked clasts (PI. 27/I). The boundstone deposits are characterized by abundant micrite and microspar with peloidal fabric and by radial fibrous cenmnt-filled primary cavities. The peIoidal fabric consists of peloids (30-100 lain in diameter) lacking sharp outlines and floating in microsparite (Pl. 27/ 2, 3). Concentric irregular micritic crusts with accretionary growth form commonly surround skeletal conaponents and in sonle cases resemble the microproblematicum Archaeolithoporella (PI. 27/4). The in situ origin of the microcrystalline calcite and peloids is inferred by the presence within the boundslone of mud-supported primary cavities (PI. 27/2, 3) and by irregular and digitate micrite structures defying gravity and constituting the substrale for the nucleation of early mmine cement. Besides Done=ella, the diverse skeletal comnmnity that acted as baffler and binder comprises fenestellid and fistuliporid bryozoans, Terebella-like polychaete worm tubes (PI. 27/3), rare Shamovella, tubular encrusting calcitornellid foraminifers (Fig. 3D), calcareous algae (lberiaella R~icz 1984, Komia, and Archaeolithol)hylhml ), and biomolds of undetermined Plate Fig. 1.
Fig. 2. Fig. 3. Fig. 4. Fig. 5. Fig. 6.
Fig. 7. Fig. 8.
26
organisms (P1. 27/4, 5). Some biomolds might represent recrystallized specimens of the red ungdarellid alga Petschoria and others probably are sponges. Vachard et al. (1989) indicate, however, that recrystallized specimens addressed as Pelschoria in the Spanish outcrops by Rg.cz (1964) are actually calcifications of Archaeolithol~hylhml missouriense. Additional biota are crinoids, brachiopods, foraminifers (fusulinids, Bradyina, Climacammina, endothyrids, Tuberitina, Tetrataxis, Monotaxinoides. ttowchinia), and ostracodes. In this setting close to the platform margin, Donezella specimens form upstanding open networks in which they are surrounded by coatings of peloidal micrite (Fig. 3C; Pl. 27/6, 7, 8, 9). The encrusted thalli create primary cavities filled by ,'adial fibrous marine cement and/or blocky sparite (Fig. 3C: Pl. 27/8, 9). The skeletons can also be exclusively encased in isopachous rims of fibrous cement (P1.27/10, 11). The occurrence of Donezella rimmed by isopachous cement and associated with few Komia (P1.27/10) is not colnmon and recorded exclusively close to the platform break.
4.3 Slope The depositional slope of Sierra de Cuera (Figs. 2, 3) is divided into a boundstone-dominated upper slope and a breccia-dominated lower slope, extending respectively fi'om 0 to nearly 300 m, and 300 m to 600-700 m paleowater depth. The boundstones alternate with bedded layers of grainstone containing platform-derived grains, crinoidrich packstone, and skeletal wackestone with red-stained micritic matrix, sponge spicules and ostracodes. The bonndstone facies appears to form massive, several meter-thick units that do not exhibit a mound-shape and depositional relief on the sea floor. Therefore, they will be addressed as
Platform interior typical microfacies types from the lower Moscovian study window (Fig. 2B) and textural characteristics of Done=ella accumulations in the inner platfol'm (Northern Spain). Wackestone of the inner platform algal banks showing a kmgitudinal section of Done=ella specimen (centreleft) with the typical dichotomous ramification at nearly right angle and with the outer layer forming calcitic projections that extend inward at ,ight angles to the sides of the tube. The distal tips of the tubes are rounded. On the lower branch dark micritic, probably foraminifer encrustations can be observed (arrow). Several circular oblique sections of Donee.ella tubes are contained within the micrite matrix formed by poorly defined peloids. Sample W 106/45.7. Wackestone to packstone containing a phylloid alga with tubular foraminifer encrustations (arrows) and a trilobite f,'agment (upper right corner). Sample W106/41.5. Packed peloidal micrite containing a bryozoan fi'agment (centre) within a partially sheltered- and partly mudsupported cavity. Sample W 106/42.4. Photomicrograph showing micrile with peloidal fabric containing biomolds of monoaxon sponge spicules and a micrite tube attributed to Terebella or Thartarella polychaete worm (arrow). Sample W106/37.9. Done=ella specimens are randomly oriented and dispersed in micrite with poorly-defined peloids. Small in'egular cavities are filled by blocky sparite (awows). No other skeletal grain is present. Sample W 106/43.9. Photomicrograph showing a central area with tiny Donezella tubes (white arrow)and TerebelIa (black an'ow) embedded in micrite and enclosing some primary cavities filled by cement close to an area with peloidal micrite devoid of bioclastic debris (right). Sample W106/42.4. Skeletal packstone associated with the mud-rich Done=ella-bearing banks containing peloids, the red calcareous alga Komia (white an'ow), bryozoan (black arrow) and echinoderm fiagments. Sample 143/17.0. Algal-rich shallow lagoon facies overlying the Donezella and lnud-rich algal banks. This facies is devoid of Done~ella and dominated by Beresella (arrows). Sample 900/43.6.
Plate
26
I57
158
biostromes. This geometry might be the result of boundstone nucleation and growth on an inclined sea floor dipping at least 30 ~ Keim and Schlager (1999) reported similar observations of layer-like geometry of automicrite boundstone accreted on the planar steep depositional slope of the Triassic Sella platform in the Dolomites (southern Italy). In situ-fomled micrite with peloidal fabrics and micrite crusts with accretionary wavy growth form are thc principal components of the boundstone facies (Fig. 3E, 3F). The biostromes were stabilized by abundant early marine cementation represented by botryoidal aragonite (P1.28/1) and radial and radiaxial fibrous calcite. Mud- and skeletalsupported primary cavities filled by radial fibrous cement are a colnmon feature (Fig. 3F). The skeletal community consists mostly of fenestellid (Fig. 3F; PI. 28/1 ), fistuliporid and ramose bryozoans, Donezella (Fig. 3E), and red calcareous algae (A rchaeolithophylhml, Petschoria, lberiaella. Ungdarella, Komia). In minor amount the fossil assemblage includes: calcified cyanobacteria such as Renalcis and filaments referable to Girvanella, encrusting tubular calcitornellid foraminifers, scattered other fo,'aminifers ( Tuberitina, Tetrataxis, Palaeonubecularia, Turrisl~iroides, Monotaxinoides, archaeodiscids), probable Shamovella, Plate Fig. 1.
Fig. 2 Fig. 3. Fig. 4.
Fig. 5.
Fig. 6.
Fig. 7.
Fig. 8. Fig. 9. Fig. 10.
Fig. II.
27
Terebella worm tubes, remains of siliceous sponges (rarely monoaxon spicules are preserved as biomolds within the clotted peloidal micrite), brachiopods, crinoids, bivalves, and ostracodes. Donezella produces in situ accumulations with the branching skeletons surrounded by clotted and peloidal micrite followed by isopachous rims of radial fibrot, s cement (P1.28/2-5). Donezella and the associated micritic encrustations create primary growth cavities that occasionally are geopetally-filled by peloidal packstone and finally by rims of radial fibrous cement (PI. 28/7). In some cases Donezella is associated with the alga Iberiaella (as described by Rficz, 1984), in others with fenestellid bryozoans in deposits rich in radiaxial fibrous cement alternating with red-stained micrite wackestone (P1.28/8). Within the biostromes, biofacies distribution and textures vary at the cm- to din-scale. There are cases in which Donezella, Iberiaella, peloidal micrite, and fenestellid bryozoans are present together in the same sample. In other instances, Donezella and associated peloidal micrite and cement phases form cm to din-scale lenses, even up to 1 m in thickness. In the lower slope, breccia beds consist ofclasts mostly deriving from the upper slope boundstones, and contain reworked Donezella facies.
Outer platform typical inicrofacies types frona the uppermost Bashkirian-lower Moscovian study window (Fig. 2By and textural characteristics of Donezella accunmlations close to the platfoml break (Northern Spain). Ooid-coated grain grainstone deriving froln the shoal capping facies and containing sub-rounded intraclasts of Done=ella accumulations (arrow), echinoderms, coated Chaetetes fragment (centre left), fusulinids, Staffella (S), and Bradvina (By. Salnple 0/39.4. Boundstone facies formed by in situ precipitated carbonate mud with peloidal fabric with a central micritesupported primary cavity filled by blocky calcite. Sample 50/32.8. Boundstone facies dominated by peloidal micrite containing cement-filled primary growth cavities indicative of in situ precipitation and specimens of Terebella-like polychaete worm tubes (arrow). Salnple 0/28.0. Particular of the boundstone facies characterized by rounded unidentified biomolds coated by dark micritic encrustations and surrounded by thin unduhtted inicritic crusts resembling Archaeolithoporella (arrow) and isopachous rims of radial fibrous cement. Sample 0/8.5. Rounded and elongated recrystallized specilnens occurring in the boundstone facies which might belong to the red ungdarellid alga Petschoria; homogeneous and clotted peloidal micrite is present between the biomolds. Sample 0/33.3. Specimen of Donezella showing the two-layered structure of the wall with an outer calcitic layer and a dark micritic ilmer one. In some cases, where the partitions that produce the segmentation are presents, the tube is slightly constricted (white arrow). The uppermost end of the segmented tube is rounded (black arrow). Sample 50/35.5. Specimen of Donezella showing the ramification and the segmentation of the skeleton. Donezella skeleton is characterized by an outer layer of calcite that forms regularly-spaced segments extending inwards at right angles with the tube walls (arrow) and an inner dark micritic layer. The partitions separate rectangular cells and do not merge together producing a central open tubular su'ucture that is filled by fibrous cement. Sample 0/0.I. Donezella specimens creating a network associated with peloidal micrite with primary growth cavities filled with isopachous rims of radial fibrous celnent. Sample 0/0.1. Donezella branching skeletons display irregularly rami fled and sub-circular fomas (arrows) surrounded by clotted peloidal micrite encmstations, and isolating primary growth cavities filled by blocky' spar. Sample 253/40.0. Donezella with minor micrite coatings and isopachous rims of cement (arrow). In the upper right part, two specilnens of Komia (K) are present; they exhibit a thin micritic coating. The association with Komia in a cement-rich facies occurs only rarely in the outer platform setting and is indicative of a moderate agitated environment. Sample 50/13.0. Done=ella specimens forming an upstanding structure encased in cement without the interposition of the peloidal mic,ite coatings. This type of occurrence is rare and located towards the platform margin. Sample 50/13.0.
Plate
27
159
160
Stratal patterns of Sierra de Cuera platform can be raced on the outcrops and mapped on aerial photographs Fig. 3). Slope clinoforms are parallel to the crinoid-rich packstone bedding planes and have been tracked with DGPS. They represent paleo-sea floors on the slope and exhibit the lithofacies deposited laterally across a timeequivalent transect. Field evaluations and DGPS measurements of the depositional geometry indicate an average slope dip of at least 30 ~ At a distance of 300 m downslope (Q300; Fig. 3) of the platform break and in section SC8B, where Donezella was recorded in situ, paleo-water depth would range from 150 m to more than 200 m (assuming 1020 m water depth on the platform). Nevertheless, the amplitude of sea-level fluctuations and the height of water column on the flat-topped platform introduce uncertainty in the exact estimation of paleo-water depth.
5 INTERPRETATION AND DISCUSSION 5.1 Donezella and boundstone facies in Sierra de Cuera
From the platform to the slope an increase in micrite and microsparite with clotted and peloidal texture and early marine cement is recorded. In the upper slope botryoidal cement is associated with the radial and radiaxial fibrous calcite, while the fossil assemblage is enriched in fenestellid bryozoans. Bryozoans are more abundant in the slope than in the outer platform, where the skeletal material is more diverse as a consequence of the shallower setting. The textures observed in Sierra de Cuera suggest that in situ precipitation of micrite played a significant role in the
Plate Fig. 1.
Fig. 2.
Fig. 3. Fig. 4. Fig. 5.
Fig. 6.
Fig. 7.
Fig. 8.
28
development of bioherms and biostromes across all the depositional system. The fornlation of comparable peloidal fabrics has been attributed, alternatively, to abiotic precipitation (Macintyre, 1985), bacterially-induced precipitation (Chafetz, 1986; Folk and Chafetz, 2000; Riding, 2000), and precipitation related to nonliving organic substrates (Reitner et al., 1995; Trichet and D4farge, 1995). In some Lower Carboniferous studies, peloidal micrites are interpreted as the product of calcification of siliceous sponge bodies during decay processes, probably under the influence of microbial activity (Warnke, 1995; Madi et al., 1996; Labiaux, 1997). According to Reitner (1993), the end-product of calcified remains of decaying sponge tissue is a micropeloidal structure commonly present both in modern lnicrobialites and ancient sponge reefs. The rapid calcification of sponge tissue might be related to the presence of sulfate-reducing bacteria within the sponges: their activity in an anaerobic microenvironment would increase alkalinity, and consequently enhance the precipitation of microcrystalline and peloidal calcite (Reitner and Schumann-Kindel. 1997). The association between Donezella and clotted peloidal micrite suggests that peculiar environments likely existed during the encrustation of Donezella skeletons. It is not possible to determine the timing of peloidal micrite production, whether it was exclusively a post-mortem process, but it occurred relatively early, before the submarine cementation. The micrite precipitation required the presence of organic substrates and particular physicalchemical conditions such as high-alkalinity, a constant current system and warm waters (Reitner and Neuweiler, 1995). Organic matter could derive from siliceous sponges
Upper slope microfacies types from the stratigraphic sections within the transitional interval upper Bashkirianlower Moscovian (Fig. 2B) and textural characteristics of Donezella accumulations (Northern Spain). Horizontally oriented fenestellid bryozoan frond (F) surrounded by microsparite and constituting the substrate for the nucleation of fibrous cement with radial array of fibers forming semi-spheroids and botryoids alternating with microsparitic crusts (arrows). Sample SB17/2. hz situ Donezella accumulation in the upper slope forming an open network with micrite coatings. The irregular sharp outlines constitute the substrate for nucleation of inclusion-rich radiaxial fibrous cement (arrow). Sample SC8/3.3. Donezella branches are surrounded by thin micrite coatings and scattered peloids and formed the substrate for nucleation and growth of isopachous rims of radial fibrous cement. Sample SC8B/0.1. Detail of Figure 2 showing ramified longitudinal (arrow) and circular transverse cross-sections of Donezella specimens commonly surrounded by homogeneous to peloidal micrite. Sample SC8/3.3. Boundstone facies with a sub-rounded structure consisting of a network of Donezella skeletons (arrow), peloidal micrite and microspar and areas with exclusively peloidal micfite and microspar (right). In the lower left corner a brachiopod shell (B) shows micfite coatings. Sample G20/63.0. Boundstone facies with peloidal micrite areas with sharp outlines rimmed by submarine cement (left) and delicate upstanding Donezella (arrows) with minor micrite coatings followed by isopachous rims of fibrous cement. Sample SC8B/7.0. Geopetally-filled primm'y cavity within the Donezella-micrite accumulation. The cavity walls exhibit gravitydefying micritic encrustations (arrows); the internal sediment is a fine-grained peloidal packstone and it is followed by the precipitation of radiaxial fibrous marine cement. Sample SC8/45.1. Typical microfacies characterized by a fenestellid bryozoan frond (F) encased in thick rims of radiaxial fibrous cement associated with wackestone/packstone with red-stained micritic matrix. In this case redstained micrite contains abundant Donezella specimens (arrow). Sample SC8/8.1.
Plate
28
161
162
as several authors suggest, but also from Donezella itself. In fact, Mamet (1991 ) indicates that during life, the thallus may have been covered by a thin mucilagenous coating now preserved as clear cement. Within the bioherms and biostromes, Donezella is associated with different biota according to the facies belts. However, a common characteristic of most of Sierra de Cuera deposits, as well as of the case studies reported in Table 1, is that where there is high concentration of Donezella, other skeletal components are excluded from the network produced by the skeletons. Only small encrusting foraminifers such as Tuberitina and calcitornellids were adapted to live within the tight branching network. A similar explanation is suggested by Toomey et al. (1977) for Pennsylvanian (Virgilian) phylloid algal mounds in Texas and New Mexico. Alternatively, it might as well be that Donezella was an opportunistic organism, developing in microenvironments where other biota could not live.
5.2 Paleoeeology of Donezella 5.2.1 Environmental conditions inferred from Sierra de Cuera The information derived from Sierra de Cuera relative to the paleoecology of Donezella indicate that this organism could live from sub-wave base. shallow-water settings in the platform to deeper ones along the slope, where it is observed in situ down to water depths of at least 200 m. Water agitation was mostly of low energy in the inner platform, inferred from the mud content (homogeneous micrite with bioclastic debris), scarcity of marine cementation, and the association with biota generally considered of calm environment (phylloid algae). In the outer platform, when the environmental conditions were of low energy, Donezella was embedded in carbonate mud and associated with Petschoria (red alga commonly attributed to low-energy environments; Rficz 1964). In contrast, when Komia (red alga interpreted as indicative of model'ate water agitation; Rich, 1969), fenestellid bryozoans and early marine radial fibrous cement are abundant (both in the upper slope and at the platform margin), a certain cmTent action should be assumed. Fenestrate bryozoans show adaptation for food gathering in moderately moving currents below active wave base (Wilson, 1975). Abundant submarine cementation implies considerable porewater exchange and calcium carbonate replenishment by pumping (Pratt. 1995). Therefore, it is likely that Donezella preferred low-energy environments but could also live within moderate wave agitation. Persistent low-energy conditions dominated the plattbrm interior, whereas on the slope and outer platform mte,mittent water agitation should be assumed, as indicated by the presence of suspension feeding organisms (bryozoans, crinoids and brachiopods) and by the relatively abundant early marine cement. It could be that with the support of it, situ-precipitated micrite coatings, Donezella could preserve upstanding structures in environments in which at least periodic and moderate current action took place.
5.2.2
Depositional environment of Donezella in previous studies
The characteristics of Donezella deposits observed in Sierra de Cuera outcrop are compared with the literature case studies summarized in Table 1. Donezella is commonly interpreted to have inhabited rather shallow, lowenergy settings (Freeman, 1964; Rich, 1967, Bowman, 1979; Riding, 1979; Mazzullo, 1981; Wiggins, 1986; Lambert and Stanton, 1988; Dingle et al., 1993). Bowman (1979) suggests that mounds with Donezella developed in calm water because of its delicate skeletal structure, at a depth of 15 m (based on the association with dasycladacean algae). Mound-growth was atrested by increasing environmental energy due to shallowing up into wave base or during storm events. In contrast, according to Rficz (1964) Donezella preferred moderately agitated environments, in areas of rapid sedimentation and it is recorded also in oolitic limestones. In the Bashkirian of western Urals Donezella build-ups occur in low-energy areas of the middle ramp (Proust et al., 1996) where Donezella is associated with Cuneiphycus and Ungdarella (red algae indicative of quiet-water deposition; Wray, 1977). Donezella is recorded in lower-energy settings associated with Petschoria (Rficz, 1964; Eichmtiller, 1985), in moderate ones with Komia (Rich, 1969; Mazzullo, 1981) and in higher-energy oolitic limestones withArchaeolithophyllum (R~icz, 1964; Eichmtiller, 1985). Dingle et al. (1993)suggest that the association with Archaeolithophyllum is indicative of deeper and/or more turbid depositional environments with current movement. Donezella bioherms containing A rchaeolithophyllum and siliceous sponges are also recorded in the Ouachita Mountains (Oklahoma), where it is suggested that Donezella occupied a facies belt between the deep ramp open marine belt and the shoal area near the carbonate platform margin (Choh, 1998). The growth of the bioherms was located in quiet conditions, below storm wave-base in the open marine/slope environment seaward of the platform margin grainstone belt (Choh and Kirkland, 2000). The association with encrusting foraminifers and bryozoans is indicative of moderate water agitation in an open platform setting (Eichmtiller, 1985). In the island arc of Eastern Klamath Terrane (California), the lens-shaped Bashkirian build-ups were produced by the baffling and binding action of Donezella encrusted by Shamovella (Watkins, 1999). In Kazakhstan (Bolshoi Karatau, Cook et al., 2000), Donezella is indicated to form boundstone together with bryozoans, sponges and Shamovella in the upper slope of a high-rising platform. According to R~icz(1984), the association with lberiaella is indicative of low to moderate energy because micritic sediment tills the open space within the algal network. Iberiaella was able to develop both anastomosing networks and an encrusting habit and, therefore, provided the rigid framework of the mounds whereas Donezella, because not attached to a substrate, functioned as stabilizer. Rficz (1984) defines Donezella as a detached organism. In fact, also in Sierra de Cuera Donezella occurs with the
163
branches departing from each other but never growing on a substrate. Although Maslov (1956) describes Donezetla branches fixed to a substrate through the formation of a complex basal plate, Poncet ( 1991) stresses the fact that no other author has ever described a type of fixation to a substrate, therefore Maslov's observation has never been confirmed. Contrasting interpretations relative to the paleoeeology of Donezella originate from the fact that most of the listed case studies are based on isolated outcrops or on limited transects lacking a continuous geometry of the depositional system. The textural characteristics of the Donezella-bearing accumulations, i.e. mud-rich or ccmerit-rich deposits, are not sufficient to define univoeally the environmental range suitable for Donezella. In fact, the present study demonstrates that, when a laterally continuous outcrop is available, Donezella is recorded both in facies with abundant micrite and with marine cement, according to the distance and the position respect to the platform break. Moreover, carbonate mud with peloidal fabric showing evidences of in situ precipitation cannot be used as indicative of a low hydrodynamic regime. Clear water is assumed as necessary for Donezella to grow (Rich, 1967; Bowman, 1979). Rich (1967)indicates that the Donezella-Komia association occupied clear water or the algae acted to screen out clastic sediments. Donezella occurs generally in open marine environment of normal marine salinity and is frequently associated with stenohaline biota. However, it might be that this organism could also stand slightly higher salinity. In the Canadian Arctic, donezellid-beresellid algal build-ups alternate with evaporitic deposits in cyclic shallowing-upward successions (Davies and Nassichuck, 1989). The increase of salinity to metahaline levels (40-45 7~:c),due to relative sea-level falls, induced an increase in nutrient level and organic productivity that enhanced the proliferation of tubular algae.
to explain the quantity of carbonate mud within the mounds. Donezella is considered capablc of building small, oncoid type colonies as well as carbonate build-ups up to 30 m thick (Choh. 1998) but it is also suggested that siliceous sponges played a significant role in the growth of the bioherms (Choh and Kirkland. 2000). Despite the different interpretations, this overview integrated with the results fl'om Sierra dc Cuera, shows that Dcmezella is concentrated in randomly distributed areas and never represents the only skeletal component within the build-ups. Despite ils delicate structure, D(me~.ella might have been able to baffle but did not individually produce the growth of bioherms and bioslromes that accretcd independently from its local occurrence. On tile slope, biostromes are principally the product of m situ precipitation of micritc and stabilization by early marine cementation combined with the baffling and binding actions of bryozoans, calcareous algae, entrusting tubular foraminifers, and crinoids. Organically-mediated precipitation of microcrystalline calcite likely related to degradation of siliceous sponge bodies represented the fundamental proccss responsible of boundstonc formation. Other authors also propose either not-preserved organisms or sponges as key elements of buikl-ups growth and suggest an internal source of mud production (Riding. 1979; Hensen et al.. 1995: Choh and Kirkland, 2000). The coexislencc of in situ precipitated carbonate mud with Done~ella is a remarkable feature l'rom the platform interior to the slope of Sierra de Cuera. This precipitation was important for the stability and preservation of its delicate structure in moderate agitated environments and for the formation of cement-filled primary growth cavities that characterize the outer platform and slope boundstones. In the platform interior, where biogenic-mcdiatcd and abiotic mechanisms of precipitation are less abundant than at the platforn~ margin anti on the upper slope, hydrodynamic accumulation might have been also important.
5.3 The sedimentological role of Donezella
5.4 The affinity of Donezella
In most of the studies relative to Donezella (Table I), this organism is considered to be active in building lowrelief, lens-shaped algal banks and mounds (generally 515 m to 30-100 m thick and 30 m to few hundreds meters wide) through baffling of carbonate mud. In the build-ups described by Riding (1979) in the Cantabrian Mountains (northern Le6n), Donezella specimens constitute less than 5-10% of the rock volume. This low percentage induced Riding (1979) to conclude that Donezella was not able to baffle and was not responsible for the mound growth. Mound growth should be attributed to non-preserved softbody organisms or to hydrodynamic piling up of muddy substrates that were successively colonized by Donezella. In the Le6n area, Hensen et al. (1995) describe mounds that contain Donezella and Petschoria in a percentage of 5-20 % of rock volume. These mounds are considered to be the result of hydrodynamic accumulation and synsedimentary biogenetic stabilization and cementation. The authors also invoke a non-preserved, probably organic, mud producer
If I)onezella were a green alga. thc water-depth interval of iJz situ occurrences in Sierra de Cuera suggests particular palcoceanographic conditions with very clear water, which would extend the cuphotic zone to 200 m water depth. Altel-nativcly, l)o,m=ella might have belonged to a different taxonomic group. It might have becn a red alga. in agreement ~'ith Maslovs classification. In fact. Done~ella is comm~mly associated with red calcareous algae (Archaeolith(~phyllum, U~zgdarella. Komia, Petschoria, Cuneiphycus) and rarely with Chlorophyta (Bowman 1979). In the stt, dicd strala, Done,..ella can be associated with bcresellid algae but has not been recorded with Dasycladacean algae. The nlorphology of Drmezel/a skeleton can not be univocally attributed to the green o r red algae and it presents also features that resemble those of certain type of calcareous sponges. R~cz (1964) invoked the presence of branched tubes, segmentation, two-layered wall structure and pores perpendicular to the wall in the calcite portion as
164
Case Sludy I)el'lositional settin~ Texture Biota Age , , associated Marble I'all Fro.. NW edge Llano uplift D. tightly packed Komicl, genii F dipping NW in micrite matrix fusulinids central Texas (no good field control k'omia limestone Morrowail for geomet D ) are biosparitc Marble Fall Fro.. Platlbrm with steep central Texas seaward margin on lhe Morrowan I-; o f l tano uplili
[-ly I.ilneslonc (I.i Nevada. W Utah) MorrowanAiokan
Broad carbonate s b d f with undulaling bt)Uonl
Chaplnan l)ecp Shelf-slope depositJonal profile, Atoka Field, subsurlhce N hin~elille l)ela~are Perlnian B a s e I Basin ',3."Texas. S1! No',.','Mexico)l Atokan Magdalena Fro. Htleco MIs. (\:V Texas) AlokanI)eslnoinesian
Ixm M i c f acctlllltllalions ofl). with cocval slack4~alet skeletal wackestone and inlerbedded foraminiferal sands.
Snak.' Can)'olt S l_cmhi P,angc (Idaho) aorrowan-lo~cr Alokan Wapanucka Fnr Ouachita Mrs. (Oklahoma) Morrowalt
Altcnulal itUl of siliciclasiic and carbonate unils
Baird Fro. 1:! Klamatl~ Terralle (California) 13ashkirian
Island-arc area with carbonale deposition during period o[" qiiicscenl volcanism
Otto Fiord Fro. EIIcsmerc Island (Canadian Arctic Arclfipclago) lalc Serpukhovian earl); l~ashkirian
Cyclic anhydriie and marine liineslOllC sequeltces in the shallower parl o1"Sverdlllp Basin
()pen inarinc outer ralnp >?gentl)sloping to lhc 5;, (linlited oulcrop exposure)
i!).
tightly packed m clear spar Kont#a grainstone contain also I).
D. inOtlllds:~ acketo lighl packstone Micrile malrix I). grains!one: spar!re
I.o.'~-enero?, buildups at plalform Red alga? BaMing %II"IGGINS margin lamk~ard of higlt-ellerg) and (19861 oolitic-crinoidal deposits framework buik]ing
]x'omia, Dvmelhr
SMIIm~. low-energy, dear waler Alga Komta also lit more turbid and mcertae deeper ~.'ater. sedis from Johnson (1963)
lbranfini tots, ecbilloderlllS. bl),'ozoans. braehiopods. ostracodcs KOlllJd. phylloid algae, forammifcrs, crinoids. bl)O/Xlalls. ( "]?aclele.~
Ko#lio. Beresel&, t:ascmlla
Buildups ( 12-35m thick; 350m wide) bounds!one stabilized by illarine cement. {-)pen meshwork Lifalgal lubules wilh pelletal wackcslonc !matrix; i). lbrms Inlounds Isurroundcd by Icerncni or peloids.
I.ow-cncrg). protcclcd flank (if KOlllia lilnCslOne
S)'stemalic MOlilid Refereoce! attribution, b u i l d e r ? Alga I~REEMAN nln'rtae ,vc~.wh \\ Jill Canlabrian Mls. carbmmleiclaslic cycles c a r b o l l a i c nltld. (l.eon. NW Spain) Ioca]l) pcloidal Mosco~ian and ca\ ilic,, (inlernal scdJmcnl and , st l'Olnal~lCiOld
Bolshoi Karatau Kazakhstan SerpukhovianBashkirian Bechar Basra Algcria lalc SerlmkhovianM oscov iall
I-\~-cncr~\_.
t.}OuIldsi(lllC
Plaiform succession
Ba fllcslonc \~ ilh nlicrile and psciidosparilc. Iocall) pcloidal lexlllrc
Ct)IIIOIllMOIIC
aI!d >/4bi[I/c
huilJup>
J__
Aom~a. ,*,Vd Ilulldup~ on upper dupe )h\lloid algae. II i>x~cr I{a.hkilian
