Profil 5: 1-45; 19 Figs.; Stuttgart 1993

Upper reef types and controlling factors

A preliminary report

REINHOLD R. LEINFELDER, Stuttgart*

CONTENTS ABSTRACT 1 INTRODUCTION 2 OVERVIEW OF PLATFORM AND REEF TYPES 3 SPATIAL DISTRIBUTION OF REEF TYPES WITHIN PLATFORM SETTINGS 3.1 Reefs in ramp settings 3.2 Reefs in rimmed shelf settings and as isolated buildups 4 BASIC CONTROLLING FACTORS 4.1 Salinity 4.2 Sedimentation rate and substrate stability 4.3 Carbonate productivity and water energy 4.4 Bathymetry and illumination 4.5 The origin of thrombolitic reefs: the role of nutrient/oxygen fluctuations 4.6 The triple factor model: interplay of water depth, background sedimentation and oxygenation 5 SUPERIMPOSED CONTROLLING FACTORS 5.1 Evolutionary control 5.2 General setting: the role of shelf configuration, sea coverage and climate 5.3 A step towards palaeo-oceanographic reconstruction 6 SEA LEVEL FLUCTUATIONS AND THEIR EFFECTS ON UPPER JURASSIC REEFS 6.1 Data sets General succession: Terrigeneous vs. carbonate-rich intervals Marker beds Gravitational sediments and erosive structures Occurrence patterns of shallow water facies Platform and reef geometries 6.2 Evaluation: A modified sequence stratigraphic concept for 'greenhouse' scenarios Problems with sequence stratigraphy: The south German succession Deposition of marls: tectonics and sea-level driven climate The origin of condensed intervals Shallow-water oxygen depletion during sea level rise 6.3 Upper Jurassic sea level changes: Tectonic forcing, eustasy or climatic autocyclicity? 7 REEFS OF THE AND THE PRESENT: A BRIEF COMPARISON OF TYPES AND CONTROLLING FACTORS 8 CONCLUSIONS 9 ACKNOWLEDGEMENTS 10 REFERENCES

*Address of author: Reinhold R. Leinfelder, Institut für Geologie und Paläontologie der Universität, Herdweg 51, D-70174 Stuttgart. 2

Abstract shelf. Such oxygen-controlled reefs occurred even Reefs occurred widespread during the Late shallower when during times of intra-Upper Jurassic Jurassic, particularly along the northern Tethyan transgressions climate was aditionally buffered, shelf and the marginal basins of the young North leading to a rise of the dysaerobic zone. Atlantic Ocean. They thrived in a variety of settings Comparison of occurrence pattern of reefs, such as on intrabasinal tectonic and halokinetic condensed marker horizons and clay-rich intervals uplifts, within lagoons or within siliciclastic fan deltas. across the northern Tethyan shelf indicates that Most frequently they grew in homoclinal to modifications of sequence stratigraphic concepts steepened ramp settings, where they occupied a have to be made for ramp systems and 'greenhouse' wide bathymetric field from the innermost, partly times. The occurrence of microbial reefs and the even hypohaline, part down to outer ramp settings. lateral expanse of deeper water reef facies is Compositionally they comprise the end members considered to be of special significance for recogniz- 'coral facies', 'siliceous sponge facies' and 'microbial ing sea level rises, whereas due to climatic facies', but transitions and successions are frequent. feedbacks and tectonic effects clay-rich intervals are Microbial crusts are important not only in the not diagnostic for sequence stratigraphic inter- microbial facies where they build thrombolitic reefs pretation. A model is suggested where climatic and up to 30 metres thick but also within the siliceous oceanic feedback during sea level rise as well as sponge and coral facies where they occur at variable lowstand condensation is considered. The causes quantities and are largely responsible for for intra-Upper Jurassic sea level changes appear to constructing a positive relief. Reef facies without be mostly of tectonic origin, although, for higher crusts is mostly biostromal. Siliceous sponge facies order oscillations, the observed climatic feedbacks is frequently developed as sponge - microbial crust - point to an autocyclic component related to the mudmounds which occur in a belt from Romania carbon cycle. down to Portugal. Important factors determining the occurrence, composition and fabric of reefs are bathymetry, 1 INTRODUCTION background sedimentation rate and oxygen fluctu- ations. Bathymetric interpretation based on sequen- Upper Jurassic reefs occur widespread within the tial analysis of shallowing upward successions and epicontinental seas bordering the northern Tethyan on comparative semiquantitative palaeoecology ocean. They thrived in a continuous belt extending shows that coral facies, mixed coral - sponge facies from Romania to Poland, southern Germany, and siliceous sponge facies follow each other along Switzerland, France, eastern Spain, down to a deepening gradient, although the zones overlap southern Portugal (e.g. KEUPP et al. 1990) where broadly. Decrease and cessation of background this belt joined with another belt of isolated reef sedimentation increased diversity and favoured the occurrences situated in marginal basins on either growth of microbial crusts. An increasing rate of side of the immature North Atlantic (e.g. ELIUK 1978, oxygen/nutrient fluctuations excluded reef macro- JANSA et al. 1983, ELLIS et al. 1990, LEINFELDER fauna and eventually led to thrombolitic reefs. These 1989, in press). The reef belt then continued further were more frequent in deeper settings but occurred down to Florida, where reefs can be studied only in over a wide bathymetric range. the subsurface (BARIA et al. 1982, CREVELLO & The success and broad compositional range of HARRIS 1982). Upper Jurassic reefs and carbonate Upper Jurassic reefs is largely related to the high platforms also occur in the Ucraine (A.K. global sea level of this time. It provided wide KHUDOLEY; St. Petersburg, pers. commun.) and the epicontinental seas as well as the deeper shelf Asian part of the Tethys (e.g. MURATA 1962, settings suitable for the expanse of sponge reefs. BEAUVAIS 1986, 1989). In the southern part of the The much larger expansion of Upper Jurassic coral Tethys reefs grew in a more local fashion. Better and sponge reefs relative to their known occurrences are in Saudi Arabia (OKLA 1986, counterparts is largely due to the generally rising MITCHELL et al. 1988, EL-ASA´D 1991), Israel Jurassic sea and only to a small proportion to (PICARD & HIRSCH 1987), Greece (DECROUEZ et al. evolutionary diversification of reef biota. The high 1983), Yougoslavia (TURNSEK et al. 1981), Italy sea level of the Late Jurassic also resulted in (SARTORIO 1989), parts of the (dislocated) Northern climatic buffering, giving rise to a general Calcareous Alps (FENNINGER 1967, STEIGER & 'greenhouse'-type climate. This lowered atmospheric WURM 1980), Tunisia (GAUTRET & CUIF 1989) and and oceanic circulation and resulted in the Morocco (ADAMS 1979, AUZENDE et al. 1984, occurrence of dysaerobic bottom water in the deeper HÜSSNER 1985). Isolated reefal facies locally shelf, where thrombolitic reefs could thrive. occurred far to the North (northern Germany, Widespread occurrence of black shales and BERTLING 1993, southern England; ARKELL 1935, dysaerobic facies suggests that Upper Jurassic seas WILSON 1968, ALI 1983), even up to Greenland were widely stratified. The weak oceanic circulation (BEAUVAIS 1984). Another, to date less well known, was particularly driven by evaporization. It is high palaeolatitude area exhibiting Upper Jurassic suggested that weak but widespread upwelling along reef development is the Argentinian-Chilenian Basin the northern Tethyan shelf was responsible for the of Neuquén which was recently studied by occurrence of oxygen-controlled thrombolites on the LEGARETTA (1991) (Fig. 1). 3

Fig. 1: Global distribution of reefs during the Late Jurassic (modified after FLÜGEL & FLÜGEL-KAHLER 1992; palaeographic reconstruction from SMITH et al. 1982).

Upper Jurassic reefs comprise a wide variety of zoic reefs, to which the reader is referred for further structural, geometrical, fabric and compositional references. types. They range from small patches to huge buildups and occur in rather different environmental 2 OVERVIEW OF PLATFORM AND REEF settings. This paper gives an overview of Upper Jurassic reef types and discusses the controlling TYPES factors responsible for the occurrence and nature of Reefs are defined here in a broad, structural and the reefs. This is a preliminary report, summarizing compositional sense. Upper Jurassic reefs may be and bringing together ongoing comparative research buildups in a HECKEL (1974) sense, where formation from our own working group, part of which is of positive structures is governed by organisms. currently published in greater detail elsewhere (e.g. However, biostromes or meadows formed by reef EINFELDER 1992, in press, LEINFELDER et al. L biota, particularly corals and sponges, are also 1993a,b, WERNER et al. 1993). It should also serve understood as reefs in a biological sense (e.g. as a framework for future detailed studies on reef SCHUHMACHER 1982). facies, palaeontology and ecology. Reefs were studied in southern and central Portugal, eastern Platform types : Upper Jurassic reefs are Spain and the Swabian Alb of southwestern characteristic parts of carbonate or, more frequently, Germany; additional reconnaissance studies were mixed carbonate-siliciclastic ramp systems. The performed in eastern France, northern Switzerland entire northern shelf of the Tethyan ocean and Poland. Additionally, the evaluation of selected represents a large, sometimes steepened, ramp published data is also incorporated in this study. system (Fig. 2), which is expressed in the common Recently, FLÜGEL & FLÜGEL-KAHLER (1992) development of large-scale shallowing-up suc- published an exhaustive bibliography on Phanero- cessions without apparent bathymetric breaks (cf. 4

Fig. 2 (left): Strongly simplified sections through the Upper Jurassic northern Tethyan shelf and the Lusitanian Basin, with reefal settings. The Tethys shelf exhibits ramp characteristics, whereas the Lusitanian Basin is characterized by intense facies differentiation due to its tectonic activity. Bricks: limestone dominance; dashes: marl dominance; circles: coarse siliciclastics. Mostly based on data from FEZER (1988), GAILLARD (1983), GWINNER (1976), GYGI (1986), GYGI & PERSOZ (1986, 1987), LEINFELDER (in press), LEINFELDER et al. (1993a), MEYER & SCHMIDT-KALER (1989) and ROSENDAHL (1985).

The tectonically active Atlantic marginal basins also contain isolated reef buildups in various settings as well as reef-rimmed shelves with steep bypass margins (MEYER 1989, ELLIS et al. 1990, LEINFELDER 1989, in press). The latter type is frequent on the steeply bordered isolated platforms of the southern Tethyan sea (e.g. STEIGER & WURM 1980, STEIGER 1981).

Geometric types of platforms and reefs : Reef rimmed shelves with bypass margins always exhibit aggradational architecture in spite of sea level changes, whereas shelves with depositional margins commonly prograde as do most ramp systems (LEINFELDER 1989, in press). Isolated buildups such as the Barreiro or Monte Gordo buildups of central Portugal mostly show aggradational architecture accompanied by a mixture of catch-up, keep-up and give-up trends (ELLIS et al. 1990, LEINFELDER 1989, in press). Siliceous sponge - microbial crust buildups exhibit a wide variety of sizes as well as of overall and internal geometries. Such bioherms, of all sizes, GYGI 1986, GYGI & PERSOZ 1986, 1987, FEZER might aggrade, 'prograde' or 'retrograde' relative to 1988, CREVELLO & HARRIS 1984, LEINFELDER et the non-biohermal facies (ROLL 1934). However, al. 1993a, NOSE in prep.). Reef-containing ramps these progradational/retrogradational patterns are occur locally on the southern side of the Tethys (e.g. not unidirectional along a shelf profile, but are either Arabia, MITCHELL et al. 1988), in the marginal completely irregular or all-round. At a larger scale Atlantic basins (PRATT & JANSA 1988) as well as in the latter is often realized, i.e. sponge facies waxes western South America (LEGARETTA 1991). Ramps or wanes laterally in all directions on the cost or in may also grade upward into depositional rimmed favour of the non-reefal bedded facies (cf. Fig. 13). shelfs with reefs occurring in front of, within and Internally, sponge buildups may be homogeneous or behind the shoal rim as well as in lagoonal positions. exhibit facies differentiation (see below). 5

Fig. 3, top: Upper Jurassic reef types. Reef types can be plotted on a compositional triangle with the end members coral facies, siliceous sponge facies, and microbial facies. Bottom: Successions and facies transitions of Upper Jurassic reef types. 6

Compositional and fabric types of reefs : Calamophylliopsis) or ramose (e.g. Actinastrea) Compositionally, Upper Jurassic reefs can be associations, although massive coral meadows and subdivided into the end members coral facies, coral-coralline sponge associations occur as well siliceous sponge facies and microbial crust (LEINFELDER 1986, WERNER 1986, FÜRSICH & thrombolite facies (sensu AITKEN 1976, RIDING WERNER 1991). 1991)(Fig. 3, top). Coral facies occurs as low to high-diversity bafflestone biostromes and bioherms with or without microbial crusts, as debris piles Shallow carbonate ramps (sensu TUCKER & containing only minor amounts of framework, as WRIGHT 1990, = distal part of inner ramp after debris-rich coral-microbial bindstones and as true BURCHETTE & WRIGHT 1992) contain medium to coral or coral-stromatoporoid framestones. Siliceous high diversity coral bafflestones, coral framestones sponge-dominated facies occurs as sponge and, if constantly wave-agitated, debris pile reefs . meadows and biostromes, and as sponge-microbial Where sedimentation rate was very low, coral- crust mudmounds. Microbial crust facies forms reefal microbial reef patches developed in slightly deeper thrombolites ranging from a few centimetres to settings. Shallow ramp coral reefs are common in several tens of metres in height and may contain both Portuguese basins as well as in southeastern accessory siliceous sponges or corals, or both. Spain (FEZER 1988, NOSE in prep., LEINFELDER Thrombolites are particularly widespread in the 1989, in press, further unpubl. results), and are also Portuguese basins and, to a lesser extent, in eastern widespead in the ramp settings of Arabia, Florida Spain (cf. NOSE in prep.). Also, they represent the and Argentina (for references see above). Coral only reef type in the deeper part of the Subalpine reefs grew very extensively in a very large shallow Basin of southeastern France (DROMART 1989, ramp with almost negligible slope, extending from 1992). Transitions between the three reefal end the Paris Basin to the northern parts of the Swiss members are frequent. Common are mixed coral- Jura Ranges, where the ramp rapidly steepened (cf. siliceous sponge types which particularly occur in GEISTER & LATHUILLERE 1991, GYGI & PERSOZ southern Germany, Portugal, the subsurface of 1986, GYGI 1986, 1992). The coral reefs of the Paris Florida, offshore eastern North America (CREVELLO Basin are particularly well developed in its eastern & HARRIS 1982, PRATT & JANSA 1988), and part. They occur in a variety of settings within intra- Argentina (LEGARETTA 1991). Also frequent are ramp banks, such as the Burgundy, Armoricain and compositional reef type successions which occur Lorraine Platforms, chiefly of mid-Oxfordian age. along three basic lines (Fig. 3, bottom): 1) A line These banks were separated by zones of slightly poor in crusts is the transition from siliceous sponge deeper water (cf. HILLY & HAGUENAUER 1979). The meadows to mixed coral-siliceous sponge facies to margins of the banks were characterized by ooid coral facies (e.g. southern Portugal, Swabian Alb). 2) shoals containing coral reef patches rich in debris. An increase in crusts occurs along the transition Interior, lagoonal bank areas contain mud-rich low from siliceous sponge meadows to muddy siliceous energy reef knolls composed of branching and sponge-microbial crust facies which sometimes massive corals, as well as delicate to thick thickets culminates in thrombolitic facies (e.g. Swabian- of coral bafflestones. Also, crinoidal bars are Franconian Alb, see also BRACHERT 1992). 3) A widespread (GEISTER & LATHUILIERE 1991). These crust-rich line is the rapid transition from pure coral reef types also occur in the northern part of the thrombolites to siliceous sponge-containing throm- Swiss Jura Ranges. There, another coral-containing bolites to coral-rich thrombolites. Such reef zonation, buildup type was recenty discovered, which which can be repetitive, is realized in central apparently represents a coral-containing mud mound Portugal and southeastern Spain (LEINFELDER et al. (GEISTER, Bern, pers. comm., own inspection). 1993b). Coral debris reefs and coral meadows from northern Germany (BERTLING 1993) and southern England (WILSON 1968, ALI 1983) also grew in shallow ramp settings. In southern Germany, mixed coral-siliceous 3 SPATIAL DISTRIBUTION OF REEF sponge reef facies caps some of the major sponge- TYPES WITHIN THE PLATFORM microbial buildups growing upward from a mid-ramp SETTINGS position; see below). Debris-rich true coral facies occurs only rarely (e.g. GEYER 1953, 1954, MEYER & SCHMIDT-KALER 1989, 1990), due to the erosional 3.1 Reefs in ramp settings loss of most marginal shallow ramp deposits. The proximal, often siliciclastic parts of inner ramps may contain coral meadows and patch reefs besides bivalve meadows. The latter are not Mid-ramp settings , i.e. the parts between the fair discussed here (see e.g. FÜRSICH & WERNER weather wave base and the normal storm wave base 1986). This situation is widespread in the Lusitanian (BURCHETTE & WRIGHT 1992) are often Basin of Portugal. The coral meadows and patch characterized by mixed coral-siliceous sponge reefs reefs mostly exhibit bafflestone fabric and are at the transition to the shallow ramp and by siliceous composed of a low-diversity, rarely high-diversity sponge reefs as well as thrombolitic reefs occurring association dominated by phaceloid (mostly below. The Portuguese examples show that mixed 7

Fig. 4: Simplified ramp models from the central part of the Lusitanian Basin, the Eastern Algarve Basin and the Celtiberian Basin. Different reef types mostly occur at different water depths. Prograding ramps and position of reefs are reconstructed from shallowing upward successions according to WALTHER´S facies law. Partly after NOSE (in prep.). 8

coral-siliceous sponge reefs may be of the meadow provided the setting for the mixed reefs from the or of the debris-rich type, or are partly very rich in Smackover Formation and the Abenaki Formation microbial crusts. These types are commonly (subsurface from Florida and Baltimore through, associated with allochthonous slope sediments respectively; cf. CREVELLO & HARRIS 1982, 1984, (LEINFELDER et al. 1993a). They occcupied slope ELIUK 1978, 1988, ELLIS et al. 1990, MEYER 1989) steepenings which were due to tectonic accentuation and the Argentinian Neuquén Basin (LEGARRETA (Fig. 4). Similar steepened slopes presumably 1991).

Fig. 5: Sketches of two large siliceous sponge - microbial crust mudmound complexes from the Swabian Alb of Germany. Top: Massive complex composed of three stacked successions; Malm d, near Neidlingen, central Swabian Alb (after WOITKE 1992); Bottom: Large complex composed of a cluster of small bioherms, including bedded facies. Note maximum expansion of complex already close to the base, at the Malm a/b transition. Near Gosheim, western Swabian Alb. 9

In Portugal and, to a lesser extent in Spain, meadows and siliceous sponge-bearing thrombolites thrombolitic reefs are widespread in mid-ramp although mudmound facies occasionally occurs as settings and probably grew preferably where slopes well. However, pure siliceous sponge facies types steepened. However, they occur over a wide are less widespread in Portugal than the mixed bathymetric range according to the degree of coral-siliceous sponge reefs of the lower shallow oxygenation (see below). Both rapid and gradual ramp settings mentioned above (LEINFELDER et al. transitions of reef types are common in mid-ramp 1993a). Upper Jurassic bioherms characterized by settings, particularly in the Portuguese examples (cf. siliceous sponges are also known from Tunisia, LEINFELDER et al. 1993a). Subordinate thrombolite positioned at the southern margin of the Tethys facies also occurs within the siliceous sponge facies (GAUTRET & CUIF 1989). According to the author´s of southern Germany and elsewhere. present knowledge, pure Upper Jurassic siliceous Siliceous sponge reef facies is very widespread sponge facies (i.e. without containing hermatypic in the Swabian and Franconian Alb of southern corals) is not known from reefal areas other than Germany, where most outcrops of the Upper mentioned here. Jurassic represent mid-ramp settings. It is also well Outer ramp settings: It is not known for certain to developed in parts of the French and Swiss Jura chains as well as in Poland and Romania (for which depth siliceous sponge reef facies occurred. references see KEUPP et al. 1990). In the Swabian Widely accepted suggestions of water depths are Alb, for instance, siliceous sponge facies is mostly of down to hundred metres, or more (see below), which the sponge - microbial crust mudmound type, and would go well into the bathymetric zone of outer forms massive structures ranging from very small, ramps (sensu BURCHETTE & WRIGHT 1992). Other decimetre to metre-sized bioherms to buildups rising Upper Jurassic reefs of outer ramp settings are rare. up to 50 metres or more above the sea floor (cf. Small microbial buildups occur in the Subalpine GWINNER 1958, 1976, ZIEGLER 1967, WENDT Basin of southeastern France (DROMART 1989, 1980). Small bioherms sometimes exhibit internal 1992), which represents the distal part of the facies zonation. Large buildups may also show such northern Tethyan shelf, as well as in deeper settings internal zonation or are formed by the clustering and off eastern Canada (JANSA et al. 1988 ). In southern stacking of smaller biohermal lenses (Fig. 5). Portugal some of the thrombolitic buildups However, many larger buildups are completely apparently grew in the upper part of outer ramp altered by diagenetic dolomitization and settings (see below). Buildups with morphologies dedolomitization. At certain times siliceous sponge similar to sponge reefs also occur in the deeper meadow facies spread extensively both in the settings of the Subalpine French Basin. They differ Swabian and Franconian Alb (e.g. MEYER & in composition and isotopic characteristics from SCHMIDT-KALER 1989, 1990). Thrombolite facies organic reefs and represent pseudobioherms occurs as small structures in association with developed along cold seeps (GAILLARD et al. 1985). sponge meadow or mudmound facies or forms They occur where the ramp is fractured into en- patches and horizons within small and large echelon half-graben structures (GAILLARD et al. mudmound bioherms. Locally, transitions to mixed 1992). Since the formation of these pseudobioherms coral-siliceous sponge facies occur in the upper part is largely inorganic they are not considered here as of the south German succession, marking the organic reefs. transition to shallow ramp settings. Also, fine peloidal packstone to grainstone facies occurs 3.2 Reefs in rimmed shelf settings and widespread during the upper part of the Upper as isolated buildups Jurassic of southern Germany, possibly comprising Reefs in settings other than ramps were rare major parts of the massive siliceous sponge facies during the Late Jurassic. As mentioned above, (KOCH et al. in prep.). homoclinal ramps commonly pass vertically into Generally the south German siliceous sponge- ramps exhibiting a pronounced steepening at the dominated reefs grew on a very flat homoclinal ramp transition from the mid-ramp to the shallow ramp, in a mid-ramp setting, forming isolated mid-ramp and occasionally pass into rimmed shelfs exhibiting buildups (cf. Fig. 2). These locally caugth up to depositional margins. Reefs in such ramp - rimmed shallower waters which caused a change of reef shelf transitions are of the mixed coral-siliceous composition towards a mixed coral-siliceous sponge sponge type and, particularly, of the coral type. The association (cf. PAULSEN 1964). first type is rich in allochthonous debris and Widespread siliceous sponge facies is developed microbial crusts, and occurs in the upper slope, in the mid-ramp facies of the Jura ranges of whereas the coral reefs occur as debris-rich Switzerland (GYGI 1986) and France (GAILLARD varieties within the rimming shoal, or as bafflestone 1983) and occurs in Iberia as well. Contrasting the and framestone meadows or reef patches before south German occurrences, the Spanish examples and behind the shoal or within lagoonal settings. are dominated by sponge meadow facies rather than Well studied examples exist in the Lusitanian Basin crust-rich biohermal mud mound facies (DEUSCH et of west-central Portugal, where such transitions al. 1990, 1991, KRAUTTER 1991, KRAUTTER in occur also in connection with actively rising salt prep.). In the eastern Algarve of southern Portugal, pillows (ELLIS et al. 1990, LEINFELDER 1989, in pure siliceous sponge facies occurs mostly as press). Another known example is from Slovenia 10

(northern part of former Yugoslavia). There, a shoal- WURM 1980, STEIGER 1981, Italy: SARTORIO 1989). rimmed shelf contains marginal reefs rich in corals In most cases, bypass margins and escarpments are and stromatoporoids as well as bioclastic debris apparently not caused by rapid upward growth of the (TURNSEK et al. 1981, TURNSEK 1989, STROH- reef rim but are due to synsedimentary rift tectonics MENGER 1988). Shelves exhibiting by-pass margins (e.g. LEINFELDER & WILSON 1989). Contrasting, may contain high-energy coral reef framestones and ELIUK (1978) assumes that the formation of a steep bindstones which besides corals are rich in debris bypass margin in the Baltimore trough was due to and microbial crusts. A well studied example is the rapid lithification and submarine erosion. Isolated Ota reef from the Lusitanian Basin (LEINFELDER coraliferous reefal buildups situated on local tectonic 1989, 1992, in press). Similar reef-rimmed shelves uplifts, commonly within siliciclastic settings or within with by-pass escarpments apparently occur in other siliciclastic fans also occur in the tectonically active North Atlantic marginal basins (cf. ELIUK 1978). Atlantic type marginal basins such as the Lusitanian Also, they specifically occur along the steep-walled Basin of west-central Portugal (LEINFELDER 1987, relics of large carbonate platforms along the 1989, in press, ELLIS et al. 1990, LEINFELDER & southern Tethys margin (e.g. Morocco, STEIGER & WILSON 1989)(Fig. 6). JANSA 1984; Northern Calcarous Alps: STEIGER &

Fig. 6: The high-energy coral-microbial-debris Ota Reef from the Lusitanian Basin of Portugal grew at the margin of a tectonically uplifted block. Roughly coeval reefs grew closeby within a siliciclastic fan delta system. Modified after LEINFELDER et al. (1988).

4 BASIC CONTROLLING FACTORS faunal composition. Faunal diversities are commonly high, including a high percentage of stenohaline In this chapter, the classical autecologic organisms such as a variety of crinoids, echinoids, parameters of reef growth are briefly discussed articulate brachiopods and coralline sponges. In relative to their influence on the various reef types of siliceous sponge reefs, ammonoids are another, the Upper Jurassic. often very common, stenohaline element. Proximal, often siliciclastic, inner ramp settings of Portugal and Spain freqently exhibit bivalve and coral biostromes 4.1 Salinity of variable diversity. Monospecfic or oligospecific It is not surprising that most reefal associations bivalve biostromes mostly grew under oligohaline to from the Upper Jurassic clearly grew in a normal brachyhaline conditions (FÜRSICH 1981, FÜRSICH & salinity regime. This is obvious not only by their WERNER 1986), whereas high diversities of corals mostly open marine setting, but particularly by their and other fauna indicate stenohaline conditions for 11

most of the coral-dominated biostromes and exhibiting condensation characteristics such as meadows even in such settings (cf. ROSENDAHL ammonite shell beds, formation of authigenic 1985, FEZER 1988, LEINFELDER 1986, WERNER glauconite and hardground development 1986, WERNER et al. 1993). Oysters may be (LEINFELDER et al. 1993a,b, see below). common in coral facies, but in the Late Jurassic However, some reefal associations adapted to a represent euryhaline forms covering a broad range certain degree of sedimentation and correlatable of salinities and hence are not diagnostic of soft bottom settings existed during the Late Jurassic. restricted salinity conditions. However, in Portugal Since salinity fluctuations can be ruled out, low low-diversity coral meadows occur, which are mostly diversity associations of siliceous sponges may or entirely dominated by Amphiastrea piriformis. indicate higher sedimentation rates, particularly if These meadows grew in fresh-water influenced sponges are of the tube type. Eudea 'clavata', a proximal inner ramp settings of an estuarine delta, coralline sponge partly closes its lower inhalant as well as in a gulf-like estuarine to 'lagoonal' pores by a calcareous sheet in order to prevent succession of fluctuating salinity regimes penetration of sediments and can hence cope up (LEINFELDER 1986, 1989, WERNER 1986). Since with slightly elevated sedimentation rates other restricting factors, particularly high sedi- (KRAUTTER 1993). Morphologies of corals, mentation rate, can be largely ruled out by the lack particularly general growth form and calical types, to of functional adaptions in this respect and by a high some degree, reflect adaption towards encruser rate, this association obviously tolerated sedimentation (HUBBARD 1973, HUBBARD & oligohaline conditions. This interpretation is further POCOCK 1972). Using these parameters and substantiated by the occurrence in a gererally diversity patterns, some of the coral biostromes and restricted marine setting. However, such salinity small bioherms of Portugal seem to have been control on coral association was very exceptional. adapted to sedimentation in various degrees All other cases of low diversity patterns in reefal (LEINFELDER 1986, 1989, NOSE in prep.). Parti- associations have to be explained by other cularly many low-diversity coral bafflestones restricting factors. occurring in mixed or calcareous inner ramp lagoonal settings or within lagoons of rimmed 4.2 Sedimentation rate and substrate shelves apparently were adapted to a soft, instable stability substrate resulting from elevated background Most reefal associations occur in a regime of low sedimentation. One of the most widespread coral sedimentation rates leading to stable substrates. associations, thin-branched Calamophylliopsis- This is the expected case for reefal epibenthic dominated bafflestones (meadows and bioherms) associations. Direct evidence is the ubiquitous are particularly characteristic of soft substrate and attack of corals by bioeroders, particularly boring higher sedimentation rates. Some coral bushes are bivalves, and the frequent overgrowth by oysters, commonly toppled even within a general low-energy serpulids, bryozoans, encrusting coralline sponges setting, indicating substrate instability. Characteristically, coral branches are not bored or and microbial crusts (e.g. WERNER et al. 1993). Due to their slow growth capacity, microbial crusts are encrusted by microbial crusts. Low-diversity coral strongly dependant on very low sedimentation. bafflestones, particularly of the Calamophylliopsis- Hence, their frequent occurrence is of diagnostic type are not only widespread within marly to silty value for very low background sedimentation rates proximal ramps but also frequently occur in muddy lagoonal settings of Portugal (ROSENDAHL 1985, (LEINFELDER et al. 1993b; see below). On the other hand, microbial crusts rapidly spread once LEINFELDER 1986, 1989), Spain (FEZER 1988, ERRENST 1990a,b), Switzerland and France sedimentation has ceased and are able to stabilize (GEISTER & LATHUILIERE 1991; further person. soft and instable substrates. They hence help in the observations). However, particularly thick-branched rapid establishment of reefal associations once varieties of bushes may occur background sedimentation rate has fallen below a Calamophylliopsis together with other corals. Thick microbial critical value (op. cit.). In deeper settings, detection incrustations then often indicate low sedimentation of low sedimentation rates is sometimes more rates. difficult, since some biologic indicators, such as The assumption that the occurrence of reefal boring bivalves or encrusting coralline sponges are meadows within fine siliciclastics (clays, marls, silts) partly or entirely lacking. The ability of many modern automatically indicates the existence of background sponges to remove sediments is known (cf. sedimentation (e.g. BRACHERT 1992) is not KÜHLMANN 1984, WILKINSON 1984). Inasmuch Upper Jurassic siliceous sponges were adapted to substantiated. The common connection of marly elevated sedimentation rates is unclear. Generally sponge meadows with authigenic glauconite shows growing slowly and being epibenthic suspension that such meadows were related to pauses in fine feeders most of them were certainly also dependant siliciclastic sedimentation. on low sedimentation. Occurrences of microbial crusts are here of special interest to detect phases 4.3 Carbonate productivity and water of strongly suppressed sedimentation. Additionally, energy in Iberia, siliceous sponge facies and microbial Carbonate productivity must not be confused with thrombolitic reefs are restricted to horizons or units sedimentation rate (better: background sedi- 12

mentation rate). Commonly, Upper Jurassic reefal much less known than the well preserved, more settings were places of high carbonate productivity spectacular low-energy coral biostromes or which despite low background sedimentation led to bioherms occurring in protected or deeper settings a thick net accumulation of sediment. High of the same ramps. biohermal thicknesses, for instance in siliceous sponge - microbial crust mudmounds, can hence not The high production capacity of such reefal ramp be equated with high background sedimentation. On settings is at the same time the cause for the the other hand, a high carbonate productivity might demise of high-energy reef structures: corals will cause considerable problems particularly to corals if eventually suffocate in the skeletal sands created by the material accumulates between the coral bushes waves and, to a lesser extent, by bioeroders. Con- and cannot be stabilized or removed there. This sequently, reef patches are short-lived and have to problem besets many of the Upper Jurassic high- shift across the ramps at random (Fig. 7). Also, reef energy reefs. Actually, most of them can be patch framework will be frequently not preserved described as bioclastic piles containing only small due to the lack of efficient binding organisms. patches of coral framework (BARIA et al. 1992, Consequently, well preserved Upper Jurassic coral CREVELLO & HARRIS 1984, LEINFELDER 1992, bafflestones and larger coral framestones are typical NOSE in prep.). This is particularly true for reefs of for low-energy rather than high-energy settings. the high-energy part of shallow ramps which Even modern high-energy reefs commonly have possibly represent the majority of Upper Jurassic little framework preserved (e.g. GINSBURG 1992). coral reef settings (e.g. in the Corallian of southern However, during the Late Jurassic, framework England (ALI 1983) and northern Germany development and preservation in high-energy (BERTLING 1993), in the Paris Basin (own settings was even more difficult due to the following observations), in the northern Swiss Jura Chain facts (partly after LEINFELDER 1992): (1) Melo- (GYGI & PERSOZ 1986), in the Frías oolite and besioid