Project: Le “Vergleichende Palokologie und Faziesentwicklung oberjurassischer Riffstrukturen des westlichen Tethys-Nordrandes * und des Lusitanischen Beckens (Zentraiportugal)/E, Project Leader: R. Leinfelder (Stuttgart)

. Paleoecology, Growth Parameters and Dynamics of Coral, Sponge and Microbolite Reefs from the Late Jurassic

Reinhold R. Werner, Martin Nose, Dieter U. Schmid, Laternser, Martin Takacs & Dorothea

Area of Study: Portugal, Spain, Southern Germany, France, Poland Environment: Shallow to deep carbonate platforms Stratigraphy: Late Jurassic Organisms: Corals, siliceous sponges, microbes, microen- crusters Depositional Setting: Brackish-lagoonal to deep ramp set- tings Constructive Processes: Frame-building, baffling and binding (depending on reef type and type of reef- building organisms) Destructive Processes: Borings by bivalves and sponges; wave action Preservation: Mostly well preserved Research Topic: Comparative facies analysis and paleo- ecology of Upper Jurassic reefs, reef organisms and communities Spongiolitic facies Fig. I: Distribution of Upper Jurassic reefs studied in detail.

Abstract framework and pronounced relief whenever microbolite crusts provided stabilization. Reefs in steepened slope set- Reefs from the Late Jurassic comprise various types of tings are generally rich in microbolites because of bypass coral reefs, siliceous sponge reefs and microbolite reefs. possibilities for allochthonous sediment. Reef rimmed shal- Upper Jurassic corals had a higher ratio of heterotrophic low-water platforms did occur but only developed on pre- versus autotrophic energy uptake than modern ones, which existing uplifts. Upper Jurassic sponge-microbolite mud explains their frequent occurrence in terrigenous settings. mounds grew in subhorizontal mid to outer ramp settings Coral communities changed along a bathymetric gradient and reflect a delicate equilibrium of massive and peloidal but sedimentation exerted a stronger control on diversities microbolite precipitation and accumulation of allochthonous than bathymetry. One coral community was adapted to mud and fine allochems, determined by the distance to brackish waters. shallow-water carbonate factories. Disturbances in this Reefal siliceous sponge biostromes and sponge microbo- equilibrium lead to the development of sponge biostromes lite mud mounds generally occur below the coral facies, and or the disappearance of sponge facies. hexactinellid-dominated sponge communities generally oc- The growth of Upper Jurassic reefs was largely restricted cur below a zone of mixed “lithistid’‘-hexactinellid growth. to, or strongly facilitated by, rising global or regional This distribution mirrors differences in nutrient conditions, sealevel, reducing sediment influx occurring during 4th or !jth with coral facies related to stable, moderately oligotrophic to order transgressive pulses within the window of 3rd order mesotrophic conditions whereas siliceous sponges could sealevel rise. Consequently, transgressive/early highstand tolerate fluctuating levels and hence may range from ex- shallow-water reefs are rich in microbolite crusts and highly tremely oligotrophic to strongly mesotrophic settings. This is diverse, whereas the rare late highstand/lowstand coral due to the fact that hexactinellid sponges can largely live on reefs are of low diversity and have little framework pre- osmotrophy and “lithistid” sponges develop deposits of liv- served. In deeper waters, the frequency of sponge-micro- ing organic matter by hosting a huge mass of bacteria. bolite mounds is correlated with the sealevel development. Microbolite crusts demand strongly reduced sedimenta- Together with basin configuration climatic and oceano- tion and are important framework contributors in many coral graphic response to sealevel rise account for a predisposi- and sponge reefs. Eutrophication or oxygen depletion may tion for eutrophication and oxygen depletion particularly exclude reef fauna, giving rise to pure microbolite reefs. around the lberian Peninsula, giving rise to the occasional Most Upper Jurassic reefs developed in ramp settings. occurrence of pure microbolite reefs or repetitive succes- High-energy reefs contain little preserved framework, sions of coral-microbolite to pure microbolite reefs at fairly whereas low-energy reefs may have excellently preserved shallow water depths. The origin of Upper Jurassic reefs can only be unraveled by taking the paleogeographical, structural and sequence J., NEUWEILER, F. 8 GUNKEL, F. (eds., 1996): stratigraphic framework into account. On the other hand, Global and Regional Controls on Biogenic Sedimentation. the lateral and bathymetric distribution patterns of reef types I. Reef Evolution. Research Reports. - from the Late Jurassic provide valuable tools for the better Gcttinger Arb. Geol. Palaont., Sb2, 227-248, Gottingen Paleoecology of Late Jurassic reefs

dome shaped to conical growth bands

Fig. 2: The influence of sedimentation rate and water depth on the morphology MicrosoIenof a agariciformis (atier NOSE 1995) understanding of shelf dynamics and climate of this epoch more thorough discussion of selected aspects. Additional at a regional and even global scale. papers and monographs are in preparation.

1 Introduction 2 Paleobiology of Upper Jurassic Reef Organisms

Reefs grew widespread during the Late Jurassic. Most Paleobiology of organisms in general can be deduced were situated along the margins of the Tethys and its shelf from the fossilized remains, which are the product of ge- seas but also developed in some parts of the North Atlantic netically fixed constructional characteristics specific for a rifl systems and its adjacent epicontinental seas (central certain organism (intrinsic factors, such as given micro- Portugal, northern Germany, southern England) as well as structure and other general bauplan elements) and a flexi- in the Pacific realm (e.g. southern Argentina, Japan). Along ble reaction or adaptation to environmental conditions or the Tethys they were particularly frequent at its northern their change (extrinsic factors). The latter might be unrav- marginal seas. We analyzed, in a comparative approach, eled by well fixed or flexible morphology and growth rates, the belt-like reef region at the tectonically stable northern or isotopic signatures. margin of the Tethys (focusing on S-Germany, N-Switzer- land, NE-France, NE-Spain and S-Portugal) as well as the 2.1 Corals from the Late Jurassic reefs from the strongly differentiated and tectonically active Atlantic rift (Lusitanian Basin, west-central Portugal) and The ecological demands of hermatypic scleractinian cor- adjacent marginal seas (SW-France). Despite all differ- als from the Late Jurassic are similar to those of modern ences in the settings, a common feature of most regions is zooxanthellate scleractinians, although some significant the development of an Upper Jurassic, large-scale shal- differences exist. In the Upper Jurassic, the associated fa- lowing-upward succession, into which reefs are more or ties and fauna (e.g. oolites, green algae) as well as the less frequently intercalated at different positions. paleogeographical occurrence point to shallow, warm-water Reefs comprise very variable types and communi- environments in which hermatypic scleractinians grew and ties of coral reefs, siliceous sponge reefs and microbolite formed reefs. Nevertheless, the low latitude reef belt was reefs. These reefs were most widespread during the Ox- probably wider than today, since remarkable shallow-water fordian and, in some basins, during the Kimmeridgian, coral reefs were also described from the Neuqukn Basin in whereas they grew only locally during the Tithonian. Our Argentina (50“ paleolatitude) 1991), Northern main scope was to identify the factors responsible for the Germany (39’ paleolatitude) 1993a) and the Ox- occurrence and differences of Late Jurassic reefs, and to fordian of England (40’ paleolatitude) 1984). This indi- discuss their mutual interdependence and interaction in a cates a more equilibrated greenhouse-type climate during geological and paleogeographical framework. Our interpre- the Upper Jurassic (LEINFELDER 1993a, 1994a, LEINFELDER tation is based on qualitative and semi-quantitative paleo- et al. 1993a). ecological fauna1 analysis of reefal and non-reefal commu- In contrast to modern corals Upper Jurassic scleractini- nities (constructional morphology, taxonomy and population ans frequently occur in siliciclastic environments. Beside dynamics of reef organisms), on the sedimentology of reefs forms adapted to elevated sedimentation already by their (microfacies, petrography, geochemistry), as well as on phaceloid growth (e.g. Calamophylliopsis) highly morpho- their regional geological framework (biostratigraphy, se- variable taxa are able to cope quence stratigraphy, field mapping, incorporation of pre- with elevated sedimentation rates (Fig. 2). The latter exhibit existing data on paleogeography and basin tectonics). a change to “pseudobranching” morphotypes with non- This paper summarizes results of a six-year research enveloping growth bands indicative of elevated sediment project on reefs from the Late Jurassic which was per- input (cf. JAMES & BOURQUE 1992, NOSE 1995) and a strong formed by the Stuttgart reef group in the course of the Pri- increase in growth rate (up to 10 mm/yr). The growth rates ority Program “Global and Regional Controls on Biogenic of Upper Jurassic scleractinians from the investigated Sedimentation - Reef-Evolution” of the “Deutsche For- European localities (see above) range between 1 mm/yr schungsgemeinschaft”. We present an overview of our re- and a maximum of 10 mm/yr. search results at the current state of evaluation. We also The abilities and ecological demands of Upper Jurassic give pointers to other papers already published by us for a scleractinian corals are strongly related to the question Leinfelder, R.R., Werner, W., Nose, M., Schmid, D.U., Kraufter, M., Lafernser, R., Takacs, M. & Hartmann, D.

bacteria culture bacteria dissolved organic matter Fig. 3: a) Active filter feeding demosponge harboring bacteria cultures. b) Osmotrophic hexactinosan sponge. Dish shape favors collecting organic particles which may be harvested on the surface of the sponge. whether they possessed phototrophic symbionts or not. it rable environmental parameters (e.g. low turbidity, warm seems likely that this symbiotic relationship was initially de- and shallow water). Low density bands are considered to veloped in late Upper Triassic time, where the first large represent higher linear growth rates forming during epi- reef framework complexes, built by scleractinian corals, oc- sodes of high light availability (cf. WELLINGTON 8 GLYNN curred (STANLEY 1981, 1988). Some Upper Jurassic shal- 1983, ALLISON et al. 1996). Hence, scleractinians from the low-water scleractinian species may be azooxanthellate Upper Jurassic apparently could not use light as efficiently (e.g. Thamnastetia concinna, STANLEY 8 S~VAK~ 1995). as modern scleractinians for supporting skeletal growth. However, the symbiosis with zooxanthellae seems likely in many other highly integrated Upper Jurassic species, 2.2 Sponges from the Late Jurassic judged by the dominance of flattened and foliose morpho- types in deeper water (cf. BERTLING 1993a, b, LEINFELDER Sponges are widespread in many Upper Jurassic reefs 1993a, NOSE 1995) or turbid settings. Additionally, flattening but are difficult to use for paleoenvironmental reconstruc- might be an adaptation to impoverished availability of par- tions because little is known about the biology of modern ticulate organic matter. In this case, a flattened morphology representatives, let alone their Jurassic counterparts. Sili- facilitates to effectively collect the available organic ceous sponges belong to various taxonomic groups within particles (SCHLICHTER, pers. comm.). the demosponges (polyphyletic “lithistids”) or to the hexa- The relatively low growth rates, compared with modern ctinellids. As the two major groups differ remarkably in their scleractinians (with average growth rates of IO-15 mm/yr, physiology, their biological organization and their ecological up to 250 mm/yr) probably point to a lower efficiency of the demands, they must be carefully distinguished for paleoen- symbiotic relationship in Upper Jurassic scleractinians. vironmental interpretation. “Calcareous” and “coralline” Further evidence for this hypothesis derives from the fre- sponges belong to either demosponges or the Calcarea. quent occurrence of corals in shallow siliciclastic settings. Stromatoporoids and chaetetids are now also considered to Probably, scleractinians from the Late Jurassic were more belong to the demosponges. dependent on particulate organic matter, for influx of fine The “lithistid” demosponges are active filter feeding or- siliciclastics is generally coupled with an increase in nutri- ganisms. They feed on nutrition dominated by nannoplank- ents. Shallow siliciclastic settings were frequently colonized ton, mainly bacteria. Their retention rate is very high, nor- by genera of the family Microsolenidae (Comosetis, Micro- mally attaining 90-100 % (REISWIG 1990). Demosponges so/ens), corals exhibiting pennulae which probably sup- have a well developed mesohyl in which they can store ported a highly specialized gastro-vascular system like in large quantities of bacteria. These sponges can also con- the modern deeper water agariciid Lepfosetis fragik. This sume the metabolic products of bacterial activity, gaining a led to the improvement of suspension feeding and hence certain independence of external supply by storing the mi- heterotrophic energy supply in settings where the high crobes within their body (Fig. 3a). The bathymetric distribu- photosymbiotic activity of shallow-water corals was reduced tion of demosponges corresponds to a great extend with the due to great water depth (SCHLICHTER 1992, GILL 8 bathymetric distribution of bacteria. The reason why SANTANTONIO 1995). The existence of such features in Up- demosponges mostly occur from the very shallow to mod- per Jurassic shallow-water corals indicates that the effi- erately shallow water is that bacteria in the water column ciency of photosymbiosis was still lower than in modern diminish towards greater depth (RHEINHEIMER 1980). The shallow-water representatives, and that a considerable pro- fairly high preservation potential of rigid demosponges is portion of energy had to be gained by heterotrophic nutri- readily explained by a high amount of mesohyl-dwelling tion. bacteria, causing rapid calcification after death. Additionally, in Upper Jurassic reef building scleractinians Demosponges are able to close their inhalant pores the ratio of low to high density growth bands is much lower (ostia) under episodes of slightly increased sedimentation, than in modern zooxanthellate scleractinians under compa- preventing clogging of the filter pathways. Some of them Paleoecology of Lafe Jurassic reefs can even reverse the water flow by sudden contraction and Concluding, the observed bathymetric zonation of a eject material which is already drawn into the inhalant pores shallow coral-coralline sponge zone, followed towards (STORR 1976). This enables the animal to tolerate a certain deeper water by a mixed coral-“lithistid”, “lithistid”-hexa- amount of sedimentation, particularly if tube-like growth ctinellid and hexactinellid-dominated zone in Upper Jurassic shapes are realized. reef settings is largely a reflection of different nutrition Retention rates of only 20-30 % show that most hexa- strategies. Unlike modern coral reefs, Upper Jurassic coral ctinellid sponges are ineffective filter feeders. However, the and coral-coralline sponge communities were not restricted tissue organization of hexactinellids allows them to absorb to oligotrophic settings but were in demand of stable nutri- dissolved organic matter, making osmotrophy their pre- ent conditions. Siliceous sponges, on the other hand, could dominant feeding strategy 1990) (Fig. 3b). better handle unstable and more fluctuating nutrient condi- Whereas this kind of food is depleted in the shallow water tions reaching from predominantly oligotrophic to intermit- due to the consumption by living unicellular organisms in tently eutrophic situations. Both eutrophic and oligotrophic the photic zone (LEVINTON 1982), it is enriched in deeper- pulses could episodically cause predominance of siliceous water low-energy settings, causing the majority of the hexa- sponges in areas otherwise occupied by reef corals. ctineilids to dwell in such habitats. As the mesohyl of hexa- ctinellids is very thin, there is hardly any room to harbor 2.3 Selected other Reef Organisms from the Late bacteria (MACKIE & SINGS 1983). This easily explains why Jurassic microbially induced post-mortem calcification of the sponge animal by microbial automicrites occurs at a much lower Micro-Encrusters rate so that fossilization potential is much lower in compari- In nearly every Upper Jurassic reef micro-encrusting, of- son with rigid demosponges. ten problematic, organisms are present in great abundance. Strongly reduced to absent sedimentation is a prerequi- Many of these micro-encrusters have proven to represent site for the settlement of hexactinellid sponges. Unlike very valuable paleoecological marker fossils (LEINFELDER et demosponges, they are not able to close their ostia and al. 1993b, SCHMID 1996). These include cyanobacteria sediment particles would easily clog the circulation path- (GiwaneIa, Cayeuxia), polychaetes (serpulids and the ag- ways of the sponge. This sensitivity towards sedimentation glutinating Terebela), foraminifera (e.g. Virte//oidea), bryo- makes fossil hexactinellids good bioindicators for sediment zoans, thecideid brachiopods as well as the problematica starvation: dish- and bowl-shaped hexactinellids demand Bacinelia, Koskinobullina, Lifhocodium, and “Tubiphyfes” close-to-zero sedimentation whereas narrow cup and tube morronensis. The last two organisms were studied in detail. morphologies intensify the exhalant water stream, which, to Lifhocodium aggregafum, which has been regarded as an some degree, can shelter the animal from slow sedimenta- alga so far, could be shown by SCHMID & LEINFELDER (1995, tion (KRAUTTER 1995). Extremely low influx of sediment may 1996) to represent a loftusiid foraminifera, most probably cause severe nutrition problems for most other benthic or- possessing endosymbiotic algae. Diagnostic features are ganisms but the osmotic feeding strategy of hexactinellids the typical alveolar, micritic wall structure, the ability to ag- together with the development of dish morphologies allowed glutinate particles, and planispirally arranged chambers. the occupation of such hostile environments in the Late Ju- Frequently occurring within the chambers of Lithocodium is rassic by hexactinellid biostromes. Dish morphologies en- another foraminifera, Tmg/ofe//a incrusfans. Most probably, abled the collection of available organic particles, which this foraminiferal consortium represented a commensalic then were broken down by microbial activity into a form ap- relationship (op. cit.). It is clearly restricted to shallow-water propriate for the animal’s nutrition (see 3.2.2). settings with moderate water-energy. Environments characterized by low water energy, dis- “Tubiphytes” morronensis, having been very abundant in solved organic matter and very reduced sedimentation are Late Jurassic times, has been regarded as a community found mostly on the deeper shelf and in bathyal, abyssal consisting of a foraminifera and an overgrowth of some kind and even hadal depth. These are the regions where modern of algae or cyanobacteria (FLUGEL 1981). It is interpreted by hexactinellids are most frequent (TABACHNICK 1991, 1994). SCHMID (1995, 1996) as a miliolid foraminifera with a twofold Independent bathymetric calibration by other methods test, the more or less thick outer test wall being formed with shows that reefal communities of Upper Jurassic hexa- the help of endosymbiotic algae. Although occurring in a ctinellids occur in lower mid-ramp to outer ramp settings. wide variety of different facies, “Tubiphytes” morronensis Depth distribution is additionally dependent on the amount represents a valuable marker fossil for environmental con- of available nutrients at a given depth. The apparent restric- ditions. This is due to the ability of this foraminifera to adapt tion of extant hexactinellids to water temperatures colder to different conditions by developing different growth forms. than 15’C (LEYS, Victoria, pers. comm.) might be a result of For example, branching colonies are an adaptation to soti evolutionary adaptation. However, isotope measurements substrates (op. cit.). A specialty are trochospiral colonies, show that during the Late Jurassic deeper shelf waters were growing around the pores of different sponges (SCHMID noticeably cooler than the shallow water. 1996), clearly indicating syn-vivo encrustation (Fig. 4). An- Most Upper Jurassic species of “coralline” demosponges other important feature is the thickness of the outer test, and Calcarea are closely associated with coral reefs and apparently depending on the amount of light available for therefore many might have had more or less effective the algal symbionts. Shallow-water tests may show diame- cyanobacterial symbionts as have many modern counter- ters of more than 1 mm, whereas the diameters of the outer parts. However, some species did occur in deeper settings test of deeper water forms strongly tends towards zero. (LEINFELDER et al. 1993a, b, WERNER et al. 1994). Bandings, Thus, bathymetric trends may be measured indirectly, pro- if annual, show that growth rates of coralline demosponges vided that cryptic habitats such as reef caves, where test were slower than those of corals. Like corals, they occur in thickness is also strongly reduced, are not considered both, purely carbonate and terrigeneously influenced set- (Fig. 5). tings. They might also have demanded stable oligotrophic By comparing communities from shallowing-upward suc- to mesotrophic conditions. Branching species as C/ado- cessions of Portugal with those from Spain and southern coropsis mirabilis might form entire bafflestone biostromes Germany, the following standard micro-encruster communi- but only a few encrusting species are true contributors to ties we& obtained: - reef frameworks, which appears to be related to their slow Girvane//a-community, indicating very shallow settings growth rate. with fluctuating salinity; Bacinela-Lifhocodium community

230 Leinfelder, R.R., Werner, W., Nose, M., Schmid, D.U., Krauffer, M., Laternser, R., Takacs, M. & Hartmann, D.

Fig. 5: The diameter of the outer test of “Tubiphytes” morronensis depends mainly on the light.

based on general shape and thickness of tests and char- acteristics of mamillae and ambulacral pores shows that several species show perfect adaptations to high water en- ergy, soft bottoms, cavity dwelling or impoverished oxy- genation (LEINFELDER 1986, & LEINFELDER in press).

Fig. 4: Reconstruction of a “Tubiphytes” monvnensis colony exhib- 2.4 Origin, Types and Role of Reefal Microbolites from iting a chimney-like growth form, encircling a sponge ostium and thus indicating syn-viva-encrustation. the Late Jurassic Microbolites are organosedimentary deposits which have (slightly restricted, lagoonal to back-reef settings); high- formed due to the activity of microbes. The term diversity micro-encruster community (shallow water, “microbolite”, which is used here, has been introduced by “optimum” conditions); “Tu~iphytes’‘-~oskino~u//ina com- RIDING (1991) as a substitute for the incorrect term munity (occurring in middle ramp and moderately cryptic “microbialite” (BURNE 8 MOORE 1987). environments); and the ~ere~e//a-“~u~i~~y~es” community Microbolites are produced by a microbial community situ- in deeper water and/or dysaerobic environments. ated within a biofilm, generated by the activity of the mi- crobes. In general, the microbes are mainly cyanobacteria Bivalves and other bacteria (including heterotrophic bacteria), but Many of the bivalves frequent in Upper Jurassic reef set- other organisms such as algae or fungi may also contribute tings also occur in non-reefal settings (cf. FIIRSICH 8, to the biofilm. Under certain conditions, the microbes may WERNER 1986) and allow additional calibration of reef envi- induce carbonate precipitation (CHAFETZ 8 BUCZYNSKI ?992). ronments independent of the reef building organisms. Bur- Apparently, these conditions were frequently realized in the rowing bivalves occur occasionally in sponge-microbolite Late Jurassic, resulting in widespread microbolite deposi- mounds and, together with other burrowings, give evidence tions, which possibly hints to a slightly elevated seawater for the partial existence of soft mud within these structures. alkalinity, supporting carbonate precipitation (cf. KEMPE & At least some of the boring bivalves, attacking microbolite KA~MIERC~AK 1994). As the occurrence of Jurassic microbo- reefs from the underside, show a mushroom-like shape lite reefs far below the photic zone shows (DROMART et al. freely above the sea-floor (LEINFELDER et al. 1993b). En- 1994), microbolite formation is not necessarily light de- crusting bivalves show a substitution of several taxa along a pendent and can apparently take place without cyanobacte- bathymetric gradient (WERNER et al. 1994). The dysaerobic, ria. Considering the only partial organic character of this flat clam Au/acomye//a abadiensis, a common element of microbially induced carbonate precipitation, it is not sur- Upper Jurassic bituminous deposits, may also occur in mi- prising that stable isotopes yield carbon and oxygen isotope crobolite reefs, indicating pulses of oxygen depletion (see values close to seawater equilibrium (LEINFELDER et al. 4.2.4). A strong dominance of the oysters Praeexogyra 1993b, SCHMID 1996). pustulosa, Nanogyra nana and the bakevelliid lsognomon SCHMID (1996) proposed a refined classification and no- /usitanicum in Amphiastrea coral reefs gives further clues menclature of microbolites, based on a combination of both for the brackish character of these reefs (see below). The microstructure (e.g. peloidal crusts) and macrostructure latter bivalves may also form oyster reefs and Lsognomon (e.g. thrombolites) (Fig. 6). In macroscopical scale, three clusters without the participation of corals (F~RSICH 1981, types of microbolites can be distinguished: Thrombolites, LEINFELDER 1986, WERNER 1986). stromatolites and leiolites (BRAGA et al. 1995), the latter being characterized by a dense structure. In earlier litera- Echinoderms ture, some confusion was produced by mixing up structures Crinoids are a frequent element of most Upper Jurassic of different dimensions and using them both for classifica- reefs and occasionally even form crinoidal-microbolite reef tion, often also involving growth forms such as oncoids (e.g. patches (WERNER et al. 1994). In Lorraine, sand bars solely BURNE 8 MOORE 1987). composed of crinoid ossicles separate episodes of reef In mesoscopic scale, various growth forms do occur, growth which might be related to drowning events. Regular ranging from massive, columnar microbolites to dendroid or echinoids are frequent reef dwellers. Morphological analysis reticulate forms as well as spheroidal forms (=oncoids). The

231 Paleoecology of Lafe Jurassic reefs

variable conditions in a wide environmental window (Figs. 7, . 8). High-Diversity Coral Reefs pelotdat microstructure The fundamental pre-requisites for high-diversity coral reefs from the Late Jurassic are low sedimentation rate, normal salinity, warm waters and illumination. However, within this frame high diversity coral reefs may occur in dif- ferent environments according to the individual preferences and abilities of the reef organisms. One of the most important lberian reef types are debris- rich reefs dominated by corals, stromatoporoids and chae- tetids. Medium to high diversity communities formed low relief biostromes or elevated reef bodies with cumulative thicknesses up to 150 m mostly in moderate to high-energy shallow-water environments. The high diversity fauna is dominated by corals (Thamnasfetia, Fungiasfrea, Micro- solena, Acfinasfrea, Amphiasfrea) but stromatoporoids and chaetetids occur as well (stromatoporoids: /3urgundia, Dehornella, Acfinosfromaria; chaetetids: Chaefefes, Pfychochaefefes) (Algarve Basin, central Lusitanian Basin; NOSE 1995). Similar reefs grew also in the Oxfordian Swiss Jura chains on a huge carbonate platform system (St. Ursanne formation). Similar to modern high-energy coral reefs, massive to CLASSIFICATION OF JURASSIC MICROBOLKES hemisphaeroidal growth forms prevail. This widespread Up- ACCORDING TO THEIR FABRIC per Jurassic reef type is characterized by an imbalanced sediment budget (i.e. skeletal debris production exceeds Fig. 6: Classification of Jurassic microbolites accordingto their fab- ric (see teti for details). biogenic growth plus exporl of skeletal debris). The lack of effectively binding organisms such as algae or microbes growth forms depend mainly on sedimentation rate and prevented the formation or preservation of stable frame- water energy; for example, microbolites developed dendroid works. These reefs mostly exhibit an indistinct morphology forms as a reaction to slightly elevated sedimentation at having the aspect of debris piles. They are mostly situated low-energy conditions (SCHMID 1996). on ramps, but may also occur at the margins of intrabasinal Thus, characterizing a microbolite-rich reef by considering structural uplifts, contributing to the formation of rimmed microstructure, macrostructure, morphology and growth isolated platforms. In the latter case, physical debris is ef- form(s), some conclusions concerning the environmental fectively exported via the steep fore reef slope. Hence, such conditions can be drawn, whereas the occurrence of micro- reefs exhibit a equilibrated sediment balance which gives bolites alone is not very helpful in reconstructing environ- way to an intense development of binding microbolite ments. crusts, resulting in platform-rimming coral-microbolite-debris As discussed in Chapter 3.3, microbolites play a para- reefs (Ota reef, LEINFELDER 1992, 1994b). mount role in reef building. Whereas in the past microbo- Other reef types characterized by high-diversity commu- lites were mostly considered as secondary, merely binding nities are reefs with sporadical short-term input of fine silici- organisms within the reef guild (FAGERSTROM 1987), they elastics (marly coral-microbolite-reefs, NOSE 1994, 1995). are acknowledged by now also as genuine constructors High diversity in this case is in accordance with the as- which, especially in Late Jurassic reefs, frequently are re- sumption that Upper Jurassic scleractinian reef corals favor sponsible for large parts if not the entire primary reef higher nutrient levels than their modern counterparts since framework. the ratio of heterotrophic versus autotrophic nutrition is still higher than in modern reef corals (see 2.1). Provided illumination is available, differences in water depth did not have a strong impact on the diversity of coral 3 Reef Types, Reef Communities, and their reefs in the Late Jurassic. This is probably due to the higher Controlling Factors ratio of heterotrophic vs. autotrophic energy uptake of Ju- rassic scleractinians. On the other hand, the composition 3.1 Coral Reefs from the Late Jurassic does change along a bathymetric gradient and different lberian reefal coral facies can be subdivided into 16 reef coral communities substitute each other. This can be de- types which are grouped within 4 categories according to duced from shallowing upward profiles in the Lusitanian Ba- (Microsolena- similarities in fauna1 composition, structure, participation of sin where high diversity coral communities microbolite crusts and the content of carbonates and silici- Trocharea-community) occur even in deeper water settings elastics. The reef types are characterized by at least 15 (transition from mid to outer ramp, possibly about 40 m of water depth, Figs. 8, 9). These reefs represent coral micro- coral communities (NOSE 1995). Some of these and addi- tional coral communities are recognized on the Oxfordian bolites containing occasional siliceous sponges, developed Lorraine carbonate platform and in SW-Germany (e.g. as low relief biostromes or small patch reefs. In shallow Istein, Arnegg). The fauna1 composition and structure of the mid-ramp settings, coral microbolites are characterized by a communities, the morphotypes of the principal fauna1 ele- high-diversity coral-coralline sponge community developed ments, and the preservation of the reef fabric reflect the as larger patch reefs with a pronounced relief (PI. l/l). physical parameters of the former reef environments. Me- Stressed Coral Reefs dium to high-diversities are not restricted to a theoretical Upper Jurassic coral reefs also occurred in environments standard optimum but occur in several coral reef communi- with, at first glance, rather unfavorable conditions for coral ties from different environments. This shows that coral fau- growth. These coral communities and reefs are generally nas from the Late Jurassic could petfectly adapt to fairly

232 Leinfelder, R. R., Werner, W., Nose, M., Schmid, D.U., Krautter, M., Laternser, R., Takacs, M. & Hartmann, D. I characterized by their reduced diversity and by the occur- ronments, provided the latter are not smothered by sedi- rence of especially adapted corals which is partly reflected ment influx (Fig. 8). The pronounced vertical growth of the ” by specialized coral morphdlogies. phaceloid coral Calamophyliiopsis represented a good ad- aptation towards elevated sedimentation rates. Hence, the Salinity . coral frequently dominated communities in lagoons, Corals of the Upper Jurassic, just as those of the modern prodelta and mid-ramp positions (LEINFELDER 1986, WERNER world, only rarely lived in environments with reduced or 1986, NOSE 1995). Similar growth strategies were devel- fluctuating salinities. However, the distribution of the oped in some dendroid and ramose genera (e.g. Am@Gastrea pir#omGs patch reefs in Upper Oxfordian to Ova/a&ea, Convexasbea, ,Ena//he/ia) which dominate low Lower Tithonian brackish lagoons and bays of the Lusitan- to moderate diversity communities of protected mid and ian Basin shows that this community was adapted to gener- distal ramp environments (NOSE 1995). Another adapta- ally lowered salinity. The formation of small flat to knobby tional trend is realized by some highly morphovariable taxa patches up to 1 m in height by this eurytopic ceroid coral (Microsolena agaticifomis, Thamnasteria lobata) which de- was probably due to its ability to cope to some degree also veloped “pseudoramose” colonies with non-enveloping with fluctuations of other occasionally occurring adverse growth bands and elevated growth rates (see also 2.1). Epi- factors in these environments such as sediment influx, wa- sodic sedimentation stress could be tolerated even by platy ter turbidity and higher energy. Apart from the bivalve domi- to leaf-shaped corals provided the undulous “leaves” were nated fauna (oysters, kognomon shell banks) the low diver- oriented oblique to the substrate, so that sediment could be sity and sedimentologic as well as isotopic data of bivalve easier removed by gravitational support (Liesberg beds, shells suggest fluctuations within the brachyhaline to meso- Swiss Jura chains; TAKACS in prep.) haline range (YIN et al. 1995). Sediment-stressed reefs always grew as low relief mead- ows due to the almost lack of binding microbolites. The lat- Sedimentation ter only occurred under low sedimentation but then were Sedimentation was the paramount factor on determining capable of forming rigid reefal frameworks considerably fauna1 composition and structure of lberian coral communi- elevated above sea floor (cf. LEINFELDER et al. 1993b). ties. It obviously had a stronger impact on diversity than Beside stress by fine siliciclastics, strong input of carbon- bathymetry and related factors. This is clearly demonstrated ate mud may also have a negative impact on diversity and by the fact that sediment-stressed coral communities in may also shape coral morphology. Consequently, low diver- shallow water show stronger reduction in diversity than sity coral-coralline sponge-mud reefs occur in the central many coral communities from slightly deeper ramp envi-

(2) steepened ramps mafly coral meadow

mkrCbalwkh

(3) rimmed shelves with depositional margins

(4) rimmed shelves with bypass marglns

Fig. 7: Upper Jurassic reef types related to different shelf configurations. Pure siliceous sponge facies is restricted to subhorizontal mid to outer ramps (1). Mixed coral-siliceous sponge reefs may be diagnostic for the existence of steepened slopes (2, 3). Coral-debris sand piles, representing remains of high-energy reefs, are indicative of shallow ramp and shelf depositional margin situations(I-3), whereas microbo- lite-rich coral-debris reefs grew atop bypass margin situations (4). Rimmed shelves with steepened slopes were particularly characteristic of the southern Tethys and North Atlantic realm, whereas ramp configurations prevailed on the northern Tethys margin (from LEINFELDER 1994b).

233 Paleoecology of Late Jurassic reefs

Lusitanian Basin within protected inner ramp settings shapes. The Upper Jurassic counterparts are medium-di- (AIicfoso/ena-Convexastrea-community). Branching growth versity biostromal reefs dominated by microsolenids, forms predominate the reef btiilding fauna (LEINFELDER et al. Thamnasteda and kaskea. (e.g. Thamnastreen-marls and 1994, 1995). Liesberg-beds, French and Swiss Jura) (PI. 112). Water Depth Water Energy Coral communities changed along a bathymetric gradient, Although high-energy debris reefs often consist of mod- giving evidence of differentiated light demands of many Up- erate to high diversity communities, reefs exposed to ex- per Jurassic corals just as in modern ones. However, for treme wave action in inner ramp settings may also show most part of the photic zone, this had no major influence on low-diversity communities. The fauna in such wave-stressed diversities which can be explained by their higher uptake of environments is mainly composed of massive cerioid and heterotrophic energy relative to modern reef corals (see meandroid corals like AcCnaskea, Amphiaskea and 2.1). Only towards the lower boundary of the euphotic zone, Psammogyra (e.g. Acfinaskea-“Lithophaga’‘-community, many coral taxa disappear, and plates of microsolenid coral NOSE 1994, 1995). Boring bivalves occur abundantly, which colonies up to 1 m in diameter may dominate the commu- further increased an already high rate of debris production. nity, being accompanied by “lithistid” demosponges In sheltered gaps between the massive coral heads, deli- (LEINFELDER et al. 1993a). Similar to modern Leptosetis cate branching forms like Goniocora and Enallhelia could fragilis, horizontal platy shape not only helped catching the grow. Apart from their limited fauna1 composition, these available light but also digestible particles in order to sup- wave-stressed reefs largely resemble the coral-coralline port nutrition. Due to the supposed higher demand of het- sponge-debris-reefs (see 3.1 .I). erotrophic food of Jurassic microsolenids, this community lived shallower than modern Leptoseris communities. 3.2 Siliceous Sponge Reef Facies from the Late Depth-related stress was enhanced when waters were Jurassic turbid. Microsolenid-rich communities in terrigenous settings include bioindicators of fairly shallow water such as Siliceous Sponge Microbolite Mud Mounds Lithocodium and adaptations of regular sea-urchins to a Siliceous sponge microbolite mud mound facies devel- moderately, or occasionally elevated water energy oped extensively on the northern shelf seas of the Tethys, (BAUMEISTER 8 LEINFELDER in press). However, stress due to particularly in Romania, Poland, Southern Germany and the diminishing illumination was accompanied by sedimentation French Jura Range (LEINFELDER & KEUPP 1995). stress. This was solved by the development of flattened, but The mud mounds range from a few decimeters to more inclined and undulous “leaf morphology as a compromise than 70 m in size. Their shape varies from flat lenticular to solution between enlarging and flattening surfaces in order upward extended to very irregular buildups (PI. 1/3). Large to increase light uptake, and inclining them in order to fa- sponge mounds are sometimes formed by clustering of cilitate sediment removal, making these communities real much smaller buildups (LEINFELDER 1993a). sediment bafflers quite similar to some modern Agaticia In general, the siliceous sponge mud mounds consist of agaricites communities with strikingly similar growth frequent to rare calcified siliceous sponges, a light gray,

communities

Actinastrea -‘Lithophaga’-, I

Mkrosolena-Convexastrea- ,

Convexastrea- Dendrohelia-,

Ca/amophy//iopsis-Microsolena-,

Thamnasteda-Ovalastrea- (A)

~amnasteda-O~a/astrea- (B)

Ova/astrea-Ca/amophy//iopsis-,

Microso/ena-Ena//he/ia-,

Convexastrea Ca/amophy//iopsis-

Microsolena -,

Ova/astrea-Ena//he/ia- ,

Microsolena-Trocharea- (A) Microso/ena- Trocharea- (6)

ishallow deep1 low high1 low highlr 0 c a llow high $ % % 94 % 3 % % 3,

Fig. 8: Coral communities of the central Lusitanian Basin with some significant sedimentary features and their relation tobathymetry and water energy. Note that diversity shows no correlation withbathymetv but is apparently dependent on sedimentation rate. Sediment input can be deduced from the marl or carbonate mud content in combination with the intensity of encrustation (modified after NOSE 1995).

234 Leinfelder, R.R., Werner, W., Nose, M., Schmici, D.U., Krautter, M., Laternser, R., Takacs, M. 8 Hartmann, D.

often peloidal micritic matrix and variable proportions of the occasional occurrence of sponge spicules serving as darker, thrombolitic to leiolitic to rarely stromatolitic micro- nucleus for ooid-type coated grains, and the minute size bolites. Major areas are dominated by microbolite bound- and frequent irregular shape of these particles evidences stones which are characterized by a dominance of crustose that they represent the products of microbial activity. How- and non-crustose microbolites with irregular patches, lenses ever, some of the younger sponge-dominated buildups of or even layers of lighter, partly mottled mud interpreted as southwestern Germany may contain abundant particles, in- allomicrites (Fig. IOe). Both pure microbolite boundstone cluding true ooids, oncoids, cortoids and rounded peloids, buildups containing siliceous sponges (Fig. IOa) and occurring as layers within predominantly micritic mounds or mounds consisting of a rhythmical alternation of peloidal even dominating parts of some buildups (cf. SCHALLER & packstones, sponge-microbolite boundstones and peloidal KOCH 1996). Occasionally, these mounds grade upwards wackestones (Fig. lob) exist. Very frequently, mud mounds into coral and particle-rich buildups which in southern Ger- exhibit an indistinct spatial zonation of different micrite- many developed in selected localities at the end of the dominated microfacies types (Fig. 10~). Siliceous sponge- Kimmeridgian, whenever the underlying sponge mounds bearing microbolite boundstone is the most dominant fa- have developed a pronounced relief and a probable, short- ties. Allomicritic siliceous sponge floatstones can interdigi- term sealevel drop accounted for further shallowing. tate with microbolite boundstones but more frequently over- Frequencies of siliceous sponges within a sponge micro- lie the latter and form the top of mounds (Fig. IOd). Peloids bolite mud mound range from very rare to abundant. and minute coated grains are particularly frequent in the Sponges comprise both Hexactinellida (Hexactinosa, microbolites but also occur in the light micrite areas. They Lychniscosa and Lyssakinosa) and the polyphyletic are partially cemented by sparites, resulting in a packstone “lithistid” demosponges. The accompanying fauna is of to grainstone fabric, often occurring as patches. In-place fairly high diversity, consisting of different taxa of echino- relics of sponge skeletons within such patches, the domi- derms, gastropods, bivalves, brachiopods, ammonites and nance of peloidal fabric in microbolitic sponge mummies, belemnites. Encrusting organisms include polychaetes

M. do Cask4 S. Isabel Frias, Ados Comparative palaeoecology Now, Tavira Nlh3val Freires, Cobvio of Upper Jurassic reef facies -3Om

-60m

CORALS Fungiina: Microsolena Trocharea Tricyc/oseds Flhipidogyrina: Psammogyra Amphiastreina: AmMiasWea Caryophyllina: Trochocyathus Cafyopbyt/ia

significant coral communities: Actinastrea-‘Lithophaga’-

Microsolena-Trocharea- *

coral morphotypes: morphotype change within some species + Microso’e17a rates

!!I’ ’

SPONGES

lithistid - hexactinellid ‘Whistids’ -...... : ..i disVibution Hexackosa Lychniscosa ,.,.,. .,.

*&& BIVALVES species replacement in ;,,. -- cementing bivalves c_* PraeeXOgyra puStu/OSS 0 Atreta abundance of bivalve borings I% MICRO-ENCRUSTER f_%an&- COMMUNITIES t3acinella-Lithocodium - ” 4 high diversity micro-encruster - ‘Tubiphyfes’-Koskinobullina- Terebela-‘Tubiphytes‘- “’ ......

Fig. 9: Bathymetric distribution and comparative paleoecology of Upper Jurassic reef organisms from Iberia; modified and expanded from LEINFELDER et al. (1993a, 1993b) and WERNER et al. (1994).

235 Paieoecology of Late Jurassic reefs

(serpulids and Terebe//a), bryozoans and foraminifera in- also frequent on surfaces of microbolites evidencing the cluding “Tubiphyfes”. Among the encrusting fauna, bryozo- primary hard consistence of the latter. On the other hand, ans are entirely restricted to the surfaces of siliceous bivalves found in the dense, lighter micrites include some sponges whereas polychaetes (serpulids and Terebe//a) burrowing species, which together with the ichnofossil and particularly the encrusting foraminifera “Tubiphyfes” are Chordrifes and other indistinct burrowing traces is evidence

M!crobhl crust Boundstone 5;:. Pebid Wackestme Siliceous spmge Floatstone with siliceous sponges El

Marls with siliceous Tub-amid Wackestone Pddd P.xk&ne SpO”gSS

e

siliceous sponge bearing microbolite boundstone: mixture of microbolite crusts, non-crustose autmicrite, and pockets, lenses or layers of allomicrite

allomicrite with rare siliceous sponges, microboliteclasts (tuberoids) and poorly preserved, rare microbolite crusts. Frequently mottled by bioturbation, often marl layers or lenses.

Fig. 10: Sponge microbolite mud mound types, based on examples from Southwestern Germany. a-d) Small, microbolite-dominated mound structures. e) Growth history of a composite larger mound (compiled from various examples): 1) Mound initiation on a flooding sur- face. 2) Formation of mound by various episodes of dominance of automicritic microbolite precipitation and dominance of allomicrite accu- mulation. 3) Cessation of reef growth due to an increase in sedimentation of allomicrites. Further explanation see text.

236 Leinfekfer, R.R., Werner, W., Nose, M., Schmid, D.U., Krautter, M., Laternser, R., Takacs, M. & Hartmann, D.

of the soft original consistency of parts of the mounds. Most even allow enhanced growth of microbolites despite the fa- of the fauna of the mounds (hexactinosan sponges, en- vorable cessation of allochthonous sedimentation. Mud . crusters, epibenthic macrtiorganisms) indicates that sedi- mounds could not develop because together with the lack of mentation rates often must have been very low, but ar- pervasive microbolite growth the complete lack of alloch- borescent growth forms of some microbolites and the partial thonous mud did not allow building up such structures. lack of siliceous sponge fauna and distinct microbolites The regular echinoid Rhabdocidark aff. rhodani, occur- shows that they were variable, though never high. The ring rarely, shows adaptations towards impoverished oxy- combination of these features demands a combined model genation (BAUMEISER & LEINFELDER in press). Petiectly de- for mud mound growth where episodes of microbolitic veloped Chondrites horizons are evidence of episodical de- automicrite precipitation alternated with episodes of trap- pletion of oxygen in the bottom sediment due to the lack of ping allochthonous carbonate mud probably being exported water exchange and microbial activity. from shallow, more productive coral-dominated carbonate The Birmenstorf sponge biostromes from northern Swit- platforms (LEINFELDER 8 KEUPP 1995, see 4.1). zerland are similar in their richness of dish-shaped siliceous In southern Germany, “lithistid” sponges outnumbered the sponges but differ completely by their diversity and the hexactinellids towards the end of Kimmeridgian reflecting more equal distribution of sponge taxa (Hexactinosa, the general shallowing-upwards trend which, due to the Lychniscosa and “Lithistida”) and other accompanying strong submarine relief developed by the sponge mounds fauna. Rich epizoan fauna and the dominance of filter by this time (cf. GWINNER 1976), shows a very differentiated feeding organisms show that nutrition was improved relative spatial pattern: Coral facies developing on top of former to the above example. Position in the aphotic zone would mound apices was coeval with siliceous sponge facies con- not necessarily exclude microbolites, for they also occur in tinuing on earlier mounds with a less pronounced relief. Jurassic deep water facies (DROMART et al. 1994) and are thus facultatively aphotic. The scarcity of microbolites might Siliceous Sponge Biostromes be due to a, though very low but noticeable, influx of terri- In most regions, siliceous sponge biostromes occur sub- genous and carbonate mud apparently inhibiting growth of ordinate to sponge microbolite mud mounds with the ex- microbial mats and hence the development of mud mounds. ception of northern Switzerland and particularly eastern Additional increase in terrigenous sedimentation might Spain. result in sponge biostromes dominated by tube-shaped sili- In the Oxfordian of the lberian and Prebetic Basins ceous sponges. Such a situation was realized in southern (eastern Spain), sponge biostromes prevail and exhibit an Portugal: a set of very thin (0.1 m) marly siliceous sponge enormous lateral continuity (KRAUTTER 1995). The siliceous biostromes is intercalated within a 30 m thick pure microbo- sponges settled on a flat unstructured deeper shelf envi- lite mud mound. The biostromes could only develop over a ronment below storm wave base. The Oxfordian sponge very limited period of time because return to dysoxic condi- facies reaches a maximum thickness of 40-45 m with an tions (see below) terminated the growth of the sponge average of IO-15 m which might be reduced to less than population at a very early stage, leaving small juvenile two meters in many regions. Leiolitic, rarely thrombolitic mi- sponge individuals (LEINFELDER et al. 1993a). Tube shapes crobolites occur throughout the sponge biostromes but do in this case might also have had the advantage to elevate not dominate. The matrix is micritic and Chondrites which the animal rapidly above the sea floor which might still have occurs abundantly in some horizons is evidence of the been subject to oxygen depletion. originally soft character of at least parts of this matrix. lron- In general, both siliceous sponge biostromes and sili- hydroxide-stained, partly bored hardgrounds developed ceous sponge microbolite mud mounds developed in the very frequently and may be stacked, suggesting extremely same depth range. However, an unfavorable sedimentation low sedimentation rates. This is in accordance with the rate (too low or too high for mud mound growth) and factors great abundance of epibenthic and nektonic fauna, the first suppressing pervasive growth of microbolites (oligotrophy of which is strongly dominated by the sponge fauna. or continuous background sedimentation) favor biostrome Sponges are almost exclusively representatives of hexacti- over mound development. The development of mounds re- nosan siliceous sponges. Lychniscosa and “lithistid” flects a balanced equilibrium of intermittent allochthonous demosponges are extremely rare. Calcarea and coralline carbonate sedimentation providing material for accumula- sponges are absent. 80 % of all sponges regardless of their tion and episodes of zero sedimentation allowing the growth taxonomic position are developed in thin dish shape. Hexa- of stabilizing microbolites and automicrite formation ctinosa are always developed in dish morphologies. The (LEINFELDER 8 KEUPP 1995). The given water depth (below sponge fauna is of low diversity with only 25 species being the upper euphotic zone) and the given nutrient concentra- classified to date. The density of the sponge population was tion determine the composition of the sponge taxa and nevertheless high evidencing stable environmental condi- other organisms. tions for the represented taxa (PI. 1/4). There are some puzzling features of these biostromes: 3.3 Microbolite Reefs from the Late Jurassic Despite very low sedimentation rates hardly any epizoans such as serpulids or bryozoans occurred, and microbolite Microbolites play a key role for the majority of Late Juras- mounds did, apart from a very few exceptions, not develop. sic reefs, either building reefs together with metazoans or Other accompanying benthic fauna is scarce, of low diver- building reefs on their own (LEINFELDER et al. 1993b, SCHMID sity and dominated by brachiopods. 1996). This is due to the fact that microbolites account for The setting was a moderately deep, uniform low-energy the genuine reef framework, and reef metazoans are often ramp with extremely reduced carbonate and terrigenous merely accompanying organisms, contributing compara- background sedimentation. This is due to the lack of mar- tively little to the reef framework. Mud mounds, a mud-rich ginal shallow-water platforms and a rising sealevel, leading reef type in which microbolites often play a major role, are to the stacked, hardground terminated condensed succes- discussed in Chapter 3.2.1. sions. Obviously, the very reduced terrigenous influx re- Pure Microbolite Reefs sulted in an extremely low nutrient level, which is reflected by a strong reduction in filter-feeding organisms and the al- More or less pure microbolite reefs, with reef metazoans most exclusive occurrence of the osmotrophic hexactinellids never accounting for more than 10 %, occur in different (see 2.2). Probably, oligotrophy was too pronounced to growth forms. They include large bioherms up to 30 m thick as well as cup-shaped, conical patch-reefs (see PI. I/5 and

237 Paleoecology of Late Jurassic reefs . these reefs were able to rise distinctly above the sea-floor and thus to build bioherms. In coral-microbolite reefs, thrombolites are clearly prevailing: in siliceous sponge reefs, thrombolites are also abundant (PI. 1/6), but leiolites (= dense, poorly structured microbolites; see above) are a common feature as well. A special growth form, widespread in coral-microbolite reefs, is downward-facing hemispheroids (see LEINFELDER et al. 1993b, SCHMID 1996) being particularly abundant in some Spanish reefs and in the reefs of La Rochelle (Aquitanian Basin). At the reef base, microbolites seem to be the prevailing reef-builders, but closer examination shows that the hemispheroidal microbolites are mostly con- cealing large phaceloid corals inside the reef body. Be- tween some of these microbolite-rich reefs, reef caves could develop. Inside the caves, a special type of microbo- lites, so-called “pseudostalactites” (TAYLOR 8, PALMER 1994)

ca mm7 can be found. These reef-cave microbolites are associated I I with a cryptic micro-encruster fauna where thecideid Fig. 11: Reconstruction of a corai-microbolite reef occurring in mid- brachiopods, bryozoans and serpulids are clearly dominat- ramp settings. Several corals and stromatoporoids are being ing (unpublished results, see also op. cit.). encrusted by downward facing hemispheroid microbolites as well as some micro-encrusters (“Tubiphytes’I-Koskinobullina The dominating downward growth direction of the micro- community). Abundant reef-dwellers are echinoids; reef-destroyers bolites is due to the fact that the surface of the corals can are lithophagid bivalves and excavating sponges (from SCHMID only be encrusted after their death. Another limiting factor 1996). for microbolite growth is the grazing activity of cidarid echi- noids and rasping gastropods. By growing downwards and LEINFELDER et al. 1993b: PI. 38, Figs. 6-7). This special sidewards, thus building balcony-like structures, the micro- growth form developed due to the settling of microbes on bolites enable the reefs to extend laterally and vertically, isolated hard substrates and subsequent upward and side- rising above the sea-floor (Fig. 11). ward growth. Microbolite reefs consist mainly of layered In the mound-shaped and mostly mud-rich siliceous thrombolites, whose growth forms in mesoscopic scale sponge reefs, downward facing hemispheroids never occur. largely depend on sedimentation rate and water energy Instead, massive to columnar or dendroid growth forms (see 2.4). prevail, depending on the rate of sediment input. Pure microbolite reefs must have grown under conditions Metazoan reefs with a high amount of microbolites were that were unfavorable for reef metazoans, at least for most probably growing under conditions where a certain but not of the time. For quite some of these reefs, there are several too high amount of nutrients was favoring microbolite hints for dysoxic conditions during reef growth (LEINFELDER growth (LEINFELDER 1992). In metazoan reefs where levels et al. 1993b, 1994; see below), whereas others might have of nearly pure microbolites are intercalated, these levels been subject of extended periods of eutrophication. Both very probably grew during phases of oxygen depletion, processes inhibited settling of metazoans except for the which becomes quite evident if supported by other diagnos- episodes of better oxygenation, which resulted in sparsely tic features such as enrichment of pyrite, glauconite and distributed, mostly small-sized metazoans or, in other clusters of the “flat clam” Au/acomye//a (see 4.2.4). cases, intercalations of metazoan biostromes. Pure microbolites are characterized by a very low-diver- sity micro-encruster community, dominated by Terebela 4 Reefs of the Late Jurassic within their Regional and “Tubiphyfes” morronensis. This community also ap- and Global Geological Framework pears in well oxygenated and oligotrophic deeper water set- tings, but dysoxic conditions are at least quite probable The importance of allochthonous sedimentation, sub- whenever the community is shifted towards a strong domi- strate characteristics (consistency, inclination), bathymetry nance of Terebeila, and accessory encrusters such as (and related factors such as illumination, temperature and bryozoans are lacking. water energy), nutrients and oxygen was highlighted in the Microbolite Dominated Metazoan Reefs previous chapters (Fig. 12). Such strong dependence of reef occurrence and composition on abiogenic factors de- In the Upper Jurassic, microbolites often built up reefs mands an additional analysis of the geological framework together with corals or, in middle to outer ramp settings, which was responsible for the setting and switching of these with siliceous sponges. Only with the help of microbolites control parameters. This also emphasizes the importance of

Plate 1

Fig. 1: Coral-microbolite reef, approximately 10 m in height. Kimmeridgian; Jabaloyas (Celtiberian Basin, Spain). Fig. 2: Coral biostrome, predominantly consisting of platy microsolenid corals (Microso/ena /sasfrea and Fungiastrea). Height of figured section is 1 m. Middle Oxfordian; Euville (Paris Basin, France), Fig. 3: Siliceous sponge-microbolite mud mound, approximately 10 m in height. Oxfordian (Bimammatum zone); Podzamcze (Poland). Fig. 4: Siliceous sponge biostrome. The plate-shaped hexactinosan sponges are very densely spaced. Yctova Formation, Oxfordian; Pozo Cauada (Prebetic Basin, Spain). Fig. 5: Conical, cup-shaped microbolite in longitudinal section, exhibiting dendroid growth form. The base of the thrombolitic microbolite body is formed by a hexactinellid sponge (arrow). Lower Perai beds, Oxfordian; Cotovio (Algarve, Portugal). Polished slab. Fig. 6: Layered thrombolite exhibiting a columnar to flat growth form; densely structured leiolites are also appearing. The arrow points to the base of a dish-shaped siliceous sponge which has been attacked by numerous lithophagid bivalves. Yctova Formation, Oxford- ian; Calatorao (Celtiberian Basin, Spain). Polished slab; natural size.

238 Leinfeider, R.R., Werner, W., Nose, M., Schmid, D.U., Krautter, M., Laternser, R., Takacs, M. & Hartmann, D. . Paleoecology of Lafe Jurassic reefs

at: normal salinity normal water temperature low water energy (’ = high water energy)

coralframestones, debris reefs”

Fig. 12: The triple factor model of Upper Jurassic reefs. Differences in background sedimentation rate, nutrients and oxygen levels are the dominant factors determining the occurrence and character of Upper Jurassic reefs. Microbolite crusts onloccury when sedimentation is very low or ceases. The higher ratio of heterotrophic versus autotrophic energy uptake in Upper Jurassic corals indicates upper oligotrophic to mesotrophic settings. Siliceous sponge reefs might span lower oligotrophic to upper mesotrophisettingsc and are more tolerant towards nutrient fluctuations. Pulses of eutroohication and/or oxygen depletion may exclude calcifying reefal metazoans to give rise to pure microbolite facies (modified after LEINFELD~R 1993a). reefs as an excellent paleoindicator of regional and global, seaway narrowed considerably. Steep slopes may be occu- ecological and structural parameters and changes for the pied by coral-microbolite or pure microbolite reefs enabling Late Jurassic world. allochthonous sediment or reef debris being bypassed around these structures. Very reduced water convection in 4.1 Control by Basin Configuration these narrow seaways created a predisposition for eu- trophication and shallow-water oxygen depletion which was The strongest influence of basin configuration (cf. Fig. 7) established in the course of sealevel rise (see below). and related parameters on reef growth was detected in the Subhorizontal ramps existed in the Oxfordian of eastern Lusitanian Basin of West-Central Portugal. Syn-rift sedi- Spain and southwestern Germany, with little signs of syn- mentation during the Oxfordian and Kimmeridgian created sedimentary tectonic activity. These were the preferred sites many steep slopes, basement uplifts, rise of salt pillows, of sponge biostrome and mud mound formation provided strongly prograding siliciclastic slope settings, siliciclastic sufficient distance to sediment-exporting shallow-water estuarine and fan deltas as well as marginal embayments platforms was given. Pervasive growth of mud mounds all of which showed occasional reef and even platform could, in the course of time, change such a flat-bottom to- growth at various depths, slope angles and sedimentation pography to a rugged submarine relief, providing habitats rates (ELLIS et al. 1990, LEINFELDER 1986, 1992, 1994a, for shallow-water reefs similar to tectonic uplifts in active rift LEINFELDER & WILSON 1989, LEINFELDER et al. 1993a, b, basins. In the vicinity of large shallow-water platforms, as in NOSE 1995, SCHMID 1996, WERNER 1986, WERNER et al. the Swiss-French Jura Range reef growth was suppressed 1994). General morphology, fabric and particularly fauna1 on the slopes to be reestablished only in distal areas in the composition reflects the various abiogenic factors associ- form of sponge biostromes or sponge microbolite mud ated with these settings, and their changes in a very dy- mounds. Cumulative sediment thicknesses show that in- namic way. As to coral reefs, allochthonous sedimentation creased accommodation on the slope due to half-graben and episodes of oxygen depletion are the most important subsidence might have trapped major parts of shallow- moditiers of fauna1 diversities, whereas different bathy- water derived sediments there. metries are reflected by different fauna1 communities rather The vast, originally nearly horizontal shallow-water Ox- than drastic changes in diversity. Particularly in areas un- fordian carbonate platform of eastern France developed in dergoing a strong terrigenous influx reef growth was re- the course of reduction of terrigenous influx by the ability of stricted to optimum episodes characterized by a cessation nutrient-dependent and sediment tolerant microsolenid cor- of tectonic activity together with a regional or global als which created laterally extensive coral biostromes. Once sealevel rise (see below). A well developed type hardly re- the carbonate platform was established, these biostromes alized in other regions are high-energy coral-debris-micro- disappeared and other coral reefs occurred scattered bolite crust reefs which are restricted to shallow-water steep across the platform. However, many of these reefs are of slope breaks enabling export of the majority of reef debris moderate diversities with only minor percentage of microbo- (LEINFELDER 1992, 1994a, b). A similar tectonic control on lites and a considerable amount of carbonate mud or bio- slope accentuation occurs at the margin of the Aquitaine elastic particles. Many suffered from the incapacity of ex- Basin towards the North Atlantic rifts and at the shallow- porting mud and particles and apparently frequently suffo- deeper water break in the eastern Algat-ve where the Tethys cated by sediment accumulation. Some communities were

240 Leinfelder, R.R., Werner, W., Plose, M., Schmid, D.U., Krautter, M., Laternser, R., Takacs, M. & Hartmann, D. , steepened ramps, and distribution and composition of reefs is an important tool in basin analysis.

4.2 The Paramount Role of Sealevel Dynamics on Reef Growth in the Late Jurassic Regional or global sealevel fluctuations may change envi- ronmental parameters for reef growth considerably (Fig. 13). Our examples show that effects of actual changes in water depth are only important in very shallow reefs, trarL9gress/w whereas the effects of reduction of terrigenous material and the overall reduction of sedimentation rate during times of sealevel rise are the most important conditions for enabling reef growth. Climatic changes related to sealevel change as well as low-stand condensation in deeper settings may con- siderably complicate the picture. Geometries of carbonate platforms from the Late Jurassic are more dependent on synsedimentary tectonics than on sealevel development but analysis of keep-up vs. catch-up vs. give-up trends of ag- grading reefs can provide valuable clues as to the interplay of both (LEINFELDER 1994b). Frequencies of sealevel change are very variable. The first to second-order, nearly continuous Jurassic sealevel rise gradually improved the major transgressh’e peak: c/imatic equilibration microbial cfusf reefs I reefs overall conditions for reef growth particularly on the north- ern margin of the Tethys, but only third order floodings pro- vided a direct predisposition for reef growth. In some cases reef growth continued during major parts or even stacks of third order rises, whereas in other examples it were fourth and higher order floodings within the third-order rise which then actually opened the reef window to allow widespread growth of reefs along a broad bathymetric gradient. Cyclicity of fauna1 communities show that nutrient and oxygen fluc- Fig. 13: Simplified sequence stratigraphic model for reef occur- tuations were frequent during certain transgressive time in- rences in terrigeneously influenced settings. During high and falling tervals and probably were also associated with low- sealevel reefs could only grow in the constantly wave-washed zone. amplitude sealevel oscillations. Occasionally, there are Sealevel rises allowed reefs to develop over a wide bathymetric even hints for annual cyclicities of reef growth. range due to a general reduction in background sedimentation, Some rises caused an additional climatic equilibration, which may Sealevel Related Patterns of Reef Occurrence and have resulted in a slowdown of water circulation. This gave way to Composition in Siliciclastically Influenced Settings eutrophic or even oxygen-depleted settings in fairly shallow water, The major effect of sealevel rise on reef growth, particu- conditions to which only pure microbolites were adapted. larly in settings strongly influenced or dominated by silici- elastic sedimentation, such as during the Kimmeridgian of adapted to fairly high sedimentation rates, resulting in the the lberian Peninsula, was sediment trapping in landward development of several meters high bafflestones composed stepping coastal swamps or estuaries, resulting in the nec- of only one or a few species of thin branching corals. An essary reduction of allochthonous sedimentation in shallow- additional factor to explain the reduced occurrence of coral water and deep-water settings. reefs might be the assumption that the lack of terrigenous In terrigenous settings of the Late Jurassic, there are influx caused very oligotrophic waters on this vast carbon- many criteria other than the sudden occurrence of reefs, ate platform, a situation which the majority of Upper Juras- allowing for the interpretation of time-dependent, regional sic corals, and possibly also the microbial mats, were not sediment reduction. Such levels are frequently character- adapted to. Later differentiation of topography was probably ized by a short-term return to carbonate sedimentation, by due to a certain tectonic control as well as due to autocyclic higher concentrations of both benthic and nektonic fauna, platform dynamics. For instance, the development of sub- by telescoped transitions from soft bottom to firm-bottom marine, encrinite sand dunes provided topography more fauna1 communities (sedimentary condensation), including suitable for coral growth, and reefs developing on the crests the occasional development of bored and iron-stained or flanks of these dunes show slightly higher diversities, a hardgrounds which may be encrusted by microbolite crusts, higher percentage of microbolite and better preservation as well as by the enrichment of glauconite (LEINFELDER than many other ones (LATERNSER in prep.). 1993a, b, WERNER et al. 1994). In vast level-bottom ramp-type platforms unpredictable Transgressive and early highstand reefs: Most reefs con- minute differences in current and hence sediment accumu- sequently formed during sealevel rise. A special feature of lation patterns determined the points of reef initiation, which “transgressive” reefs is their richness in microbolite crusts. may either have rapidly ceased or developed further by Although microbial films and mats might possibly be toler- positive feedback mechanisms. Moreover, the distance to ant to sedimentation, extensive development of the typical the hinterland, climate and tectonic activity determines the thrombolitic to, rarely, stromatolitic crust fabric only oc- rate of terrigenous influx and hence strongly controls nutri- curred when no allochthonous sediment was trapped, ent levels. These controls both, were working on shallow making these crusts perfect indicators of zero or very low ramp-type platforms and determined the frequency, type sedimentation (LEINFELDER et al. 1993b; see 2.4). The and composition of coral and sponge reefs. Control of reef growth form of these crusts allows to decide whether sedi- growth by basin configuration and dynamics is naturally mentation was generally very low or was interrupted by more pronounced and direct in rift basins and tectonically sedimentation events, the latter case leading to digitate

241 Paleoecology of Lafe Jurassic reefs

diversity microbial edimentatiol CrlJS~S rate w moderate high 1y9 w moderate hi? 9 5? ,

Microsoiena- or Ac~i~asrrea-‘~i~bo~~aga’- Calarnophyii~opsis- Ovalastrea- Enallhelia

coral-debris-reef

outer ramk2 I mid ramp inner ramp I

foliose coral growth forms: massive solitary, Fig. 14: Distribution of Upper Jurassic coral communities from Iberia in relation tosealevel, water energy and sedimentation rate.Sealevel rise: Sealevel rise creates widespread shallow water shelf areas, which give way to an intensive reef development with various reef types. Rising sealevel holds back siliciclastic sedimentation in coastal regions, a major prerequisite for the vigorous development of microbial crusts and the settlement of hermatypic scleractinian corals. This sealevel state is characterized by moderate- to high-diversity coral com- munities both in shallow (Tbamnasferia-Ova/asfrea-community) and deeper (AJicroso/er?a-Trocbarea-community) water. Sealevel highstand, early lowstand: In the highstand and early lowstand siliciclasUcs are deposited across the entire ramp and bioclastic debris may be ex- ported from inner ramp settings to more distal areas. Reef development is hampered by elevated sedimentation rates and strong skeletal debris accumulation in areas exposed to strong wave action. Marly coral-meadows may grow both in sheltered inner ramp settings and deeper mid ramp environments, whereas coral-debris-reefs develop in strongly wave exposed areas. The fauna mostly represents moder- ate to low diversity coral communities. The elevated influx of siliciclastics is responsible for both low diversity and the meadow/biosVome geometry of coral communities. branching,crust growth (SCHMID 1996). Other good meas- pear already below or even within the coral zone, sup- uring sticks of the actual rate of reduced to zero sedimenta- pressing and substituting the sponge reef bathymetric zone. tion are morphological features of corals and diversity char- Repetitive changes of such conditions resulted in the devel- acteristics of coral communities (see 3.1.1) (Fig. 14). Con- opment of successions of pure microbolite reefs to coral sequently transgressive reefs in the shallow water are fre- reefs to pure microbolite reefs, and so on (see below). quently high-diversity coral reefs rich in microbolite crusts. Late highstand and lowstand reefs: Favorable conditions Their framework is often petiectly preserved which is due in terms of reduced sedimentation prevailed until early both to the enormous participation of microbolite crusts as highstand. The return of siliciclastic sedimentation killed well as to a very low fragmentation rate pointing to mostly most of these reefs during later highstand; consequently low-energy environments, which were maintained due to the late highstand and lowstand situations are mostly devoid of ongoing sealevel rise. High-energy reefs also occurred but reefs in such siliciclastically influenced basins. Only in the these are mostly preserved as piles of bioclastic debris with very shallow, high-energy zone, where constant wave agita- variable, mostly low proportion of original framework. Micro- tion prevented settlement of terrigenous mud and silt, reefs bolite crusts occur subordinately, probably due to their may have survived into the late highstand or even early suffocation within bioclastic debris. In very marginal set- lowstand. Such reefs are frequently not recognized as such tings, coral meadows even occur within fine siliciclastics, because they are mostly composed of bioclastic debris pointing out to the fact that sedimentation rate was suffi- without major areas of framework preservation and a very ciently reduced to allow growth of low-diversity communities low proportion or complete lack of microbolite crusts (see adapted to such settings. 3.1 .I) (Fig. 14). These features are due to the high-energy Towards the deeper water (several tens of meters), mixed character of these reefs and the lack of accommodation coral-siliceous sponge reefs, then pure siliceous sponge space caused by the falling sealevel. Termination of growth reefs occurred. Most of them were also thrombolitic, show- of such reefs was mostly caused by subaerial exposure and ing a high amount of microbolite crusts. Towards still karstification (LEINFELDER 1993a, LEINFELDER et al. 1993a, b, deeper waters, pure microbolite reefs could develop which NOSE 1995). show signs of adaptations towards elevated nutrient values In areas where sedimentation rate was generally low, and or even oxygen depletion (Fig. 13). During the transgressive terrigenous influence was more reduced than above, such by~~e/ocyc/um/divisu~ time episode such reefs may ap- as the Swabian Alb, reef development (in this case mostly

242 Leinfelder, R.R., Werner, W., Nose, M., Schmid, D.U., Krautter, M., Laternser, R., Takacs, M. & Hartmann, D. . sponge-microbolite mud mounds) could, at favorable sealevel rise the climate grades towards higher humidity. In places, persist during all phases of sealevel fluctuations such a scenario, terrigenous material is preferably intro- . (LEINFELDER 1993a). However, reefs expanded laterally duced into the marine realm and deposited during late rise during sealevel rise, enabling time-limited reef growth in ar- and early highstand, rather than during lowstands eas which were subject of non-tolerable allochthonous (LEINFELDER 1993a), contrasting the classical theory of se- sedimentation during times of falling sealevel. During the quence stratigraphy. The Zementmergel of the South Ger- Early Kimmeridgian reef growth was widely suppressed man Upper Jurassic seems to represent such an inverse even in southern Germany due to the strong influx of terri- situation. New biostratigraphic results show that the Ze- genous material across entire Europe. Only during the mentmergel of the Swabian Alb are topmost Kimmeridgian transgressive episode of the hypselocyclumldivisum zone in age (SCHWEIGERT 1996). This was a time of rapid specialized reefs (Lacunosa reefs) developed (see 4.2.4). sealevel rise as detectable in other parts of Europe (cf. LEINFELDER 1993a, PONSOT 8, VAIL 1991). Tongues of al- Reef Occurrence and Sealevel Change in Carbonate lochthonous sediments (Hattingen-Trtimmerkalk, Brenztal- Dominated Settings - Differences to the Classical Trtimmeroolith) were shed from nearby shallow-water, Sequence Stratigraphic Interpretation probably steeply confined isolated platforms developing on Whereas during the Kimmeridgian and Tithonian most top of earlier, major sponge-microbolite mounds, into the areas of Europe were subject to mixed carbonate-terrige- Zementmergel basins and may be interpreted as highstand nous sedimentation, the Oxfordian was largely dominated shedding. Whether deposition of the terrigenous clays of by carbonates. Among the differences to siliciclastically the Zementmergel was merely caused by stronger humidity dominated or mixed successions are: associated with rising and high sealevel or was additionally 1) Lowered nutrient values of carbonate systems: Since caused by a certain tectonic hinterland activity, is not yet it must be assumed that Jurassic corals not only tolerated fully solved, but the change from a kaolinite dominance to a but rather demanded higher nutrient values than modern illite/smectite dominance of the insoluble fraction in the up- reef corals due to their still imperfect photosymbiotic rela- per part of the middle Kimmeridgian (CHRISTMANN et al. tion with algae (see 2.1), minimum nutrition becomes an- 1994) might be indicative of a continuously more humid cli- other critical value for the establishment of Jurassic reefs. mate. Whereas in siliciclastic or mixed settings, sealevel rise may Geometries and Successional Trends of Carbonate lead to an overnutrition of reefs (causing reefs other than microbolite reefs to vanish), the same sealevel rise may be Platforms and Reefs: Expressions of Sealevel Change? of paramount importance in carbonate settings to create a As outlined above, most Upper Jurassic platforms owe minimum concentration of nutrients necessary for the their geometries to pre- and synsedimentary tectonic activ- growth of Jurassic reefs. This may be an additional reason ity rather than sealevel change. On the other hand, the dif- why we noted the expansion of south German sponge- ferentiation, within aggradational geometries, of catch-up, microbolite mud mound growth during sealevel rise keep-up or give-up trends is a tool for deciphering the vari- (LEINFELDER 1993a) as well as the restriction of sponge ous importance of tectonics and sealevel change. Particu- meadow development to transgressive episodes in eastern larly give-up trends of shallow-water platforms and coral Spain (see 3.2.2, cf. KRAUTTER 1995). reefs point to tectonic disturbances accompanied by 2) The various control of mud mound genesis was al- sealevel rise. Examples for this are the Barreiro-coral ready discussed in Chapter 3.2.1. In basins with elevated buildup from the eastern margin of the Lusitanian Basin, influx of micritic mud from proximal platforms, mud mounds which shows a pronounced deepening trend to be finally may occur only during sealevel rise, whereas in wider buried by fine sediments with a high proportion of siliciclas- ramps with a more moderate influx from distant shallow- tics (cf. ELLIS et al. 1990, LEINFELDER 1994b) or the Monte- water carbonate factories mound development may be gordo reef which exhibits a deepening-shallowing trend in- more persistent but frequently expands during sealevel dicative of very rapid subsidence along the strike-slip east- rises (LEINFELDER 1993a). ern margin of the Lusitanian Basin (LEINFELDER 1994b). On 3) Lowstand condensation: If slope and basinal carbonate the other hand, very rapid shallowing-up from siliceous settings are accompanied by a very shallow, level-bottom sponge facies to coral facies on isolated platforms is often carbonate shelf, sealevel fall might expose the entire shelf facilitated by falling sealevel, although changes in nutrient and shut off export of carbonate mud. This may lead to low- situation must not be neglected (see 2.2). For the Arnegg stand condensation in deeper settings which can compli- reef of southwestern Germany this is evident by the follow- cate dynamic analysis of reef growth. It may be difficult to ing observations: Preserved geometries show that autoch- distinguish this from transgressive condensation but deeper thonous coral communities grew on debris shed by the water hardgrounds with incorporated proximal allochthon- main coral reef. These coral meadows developed in the ous particles such as ooids, dasyclad algae and lignite litter same horizontal level than did the mixed coral-siliceous are good indicators for lowstand condensation. Signs of sponge reef earlier. Sealevel must consequently have bottom water oxygen depletion appear to not be compatible dropped. with lowstand condensation. An example for lowstand con- Purely aggradational platforms can be due to tectonic densation in association with sponge meadows stems from control (Ota Platform) or represent transgressive platform the Oxfordian of Southern Portugal (L EINFELDER et al. stacks developing on a prograding siliciclastic slope system 1993a, NOSE 1995). Due to the rarity of reef or shoal- (Amaral Platform, NOSE 1995). Final blanketing of such rimmed level-bottom carbonate shelfs and due to the avail- platforms by oolites during sealevel rise might have resulted ability of calcareous nannoplankton it is predicted that low- even in retrogradational architecture. stand condensation was rare during the Late Jurassic. Special Sealevel Related Reef Development 4) Climatic changes related to sealevel change: Re- During the Jurassic gional or global lowstand of sealevel might result in regional or global aridization so that terrigenous material, even if The generally rising and, during its late epoch, high available in the hinterland, will not, or only at a low rate, be sealevel of the Jurassic, together with the frequent sealevel transported towards the seas, maintaining the purity of car- fluctuations of various order caused some unique charac- bonate systems. This might change when as a response to teristics of Jurassic reef development.

243 Paleoecology of Late Jurassic reefs

Jurassic Reefs Through Time developed in the Celtiberian Basin, southern Portugal, cen- tral Portugal and southwestern France (cf. L EINFELDER Jurassic reefs became increasingly frequent in the course . of the Jurassic period. The rarity of Early Jurassic coral 1993a, 1994c, W ERNER et al. 1994). Deeper water reefs in reefs is still explainable by the rarity of scleractinian taxa. southern Germany also show signs of increase of nutrients However, the latest by the Mid-Jurassic, available coral taxa (the brachiopod-dominated Lacunosa reefs) and are asso- were sufficient to allow coral reef growth in various settings. ciated with poorly oxygenated sediments (Pseudomonotis- Siliceous sponges appear to have been available with many Bank). It is noteworthy that these peculiar reefs grew in a different taxa during the entire Jurassic. LEINFELDER (1994a) time-episode of siliciclastic dominance (caused by wide- gave arguments that the general increase of reef occupa- spread tectonic movements across Europe). The lack of tion through time was largely controlled by tectonics and carbonate platforms might have deprived the shallow ocean sealevel rise, with the first being the dominant factor for reef waters of an important carbon sink so that the shallow seas development on the southern margin of the Tethys and the became supersaturated by carbon which was expelled to latter playing the key role along the northern margin of the the atmosphere where it helped heating up the globe and Tethys. The continuing sealevel rise caused a nearly con- further diminished thermic convection of ocean waters stant retreat of the coastline, accompanied by the develop- (LEINFELDER 1993a, 1994a, LEINFELDER & SEYFRIED 1993). ment of transgressive sedimentary traps such as swamps Short-Term Sealevel Oscillations and estuaries. On the ramp-configured shelf of the northern Tethys and its adjacent shelf seas, this led to the nearly Orbital forcing of shallow-water peritidal cycles is well continuous decrease of terrigenous influx (at places earlier documented for Purbeckian sediments, that is for the latest than at others) and hence to the continuous improvement of pat-l of the Jurassic (STRASSER 1988, JOACHIMSKI 1991). conditions for reef growth. However, the lack of polar icecaps in the Late Jurassic world suggests that amplitudes were narrow, thus separa- Effects of Sealevel on Global Distribution of tion from short-term autocyclicity is very difficult. The coral- Upper Jurassic Coral Reefs reef rimmed peritidal cycles of the Ota Platform (central All evaluated Upper Jurassic coral reefs include many Portugal) are not laterally correlatable despite petfect out- taxa which obviously possessed photosymbionts (see 2.1) crop conditions even across short distances, and conse- and are associated with dasyclad algae and oolites, making quently were interpreted by LEINFELDER (1994b) as being them good indicators of warm surface waters. A look at the dominantly of autocyclic origin. Within shallow-water reefs global distribution of Upper Jurassic coral reefs shows, subaerial exposure horizons may frequently be developed however, that they also appeared in fairly high paleolati- and restriction of dissolution to aragonitic particles shows tudes (cf. compilation in LEINFELDER 1994a). Whereas reefs that this occurred synsedimentarily (LEINFELDER 1994b). ln- mentioned by BEAUVAIS (1984) from Sakhalin or Greenland ternal correlation of sediments of the coraliferous Amaral are poorly known and moreover might partly be situated on formation (central Portugal) as well as the nearly coeval exotic terranes (Sakhalin) of unknown position for the late Kimmeridgian shallow-water carbonate platform of eastern Jurassic, reefs from southern Argentina and Chile are Spain shows that fourth and even fifth order cycles may be somewhat better studied. These represent coral reefs ac- represented, but to date there are no means for an accurate companied by dasyclad algae and oolites. Diversities are time resolution of this complex pattern (NOSE 1995). low but in the light of the other features this is interpreted as Sequence stratigraphic interpretation shows that reef stress caused by sedimentation (LEGARRETA 1991, see growth is often associated with environmental ameliorations LEINFELDER 1994a for additional references). Consequently, (particularly with the push-back of siliciclastic influence) ac- these reefs should be indicative of fairly warm sutface wa- companying third order sealevel rise (see above). On the ters (at least 20°C?). This is contradictory to global circula- other hand, measurements and evaluations of growth ca- tion models provided by MOORE et al. (1992) or Ross et al. pacities of Upper Jurassic corals and microbolites show that (1992) (for discussion see LEINFELDER 1994a). It appears the growth of individual Upper Jurassic reefs must have that the high global sealevel of the Late Jurassic equili- been actually much more rapid, being in the range of thou- brated the climate much more than previously thought, sands to ten thousands, rarely hundred thousands of years highlighting the strong and to date insufficiently understood (SCHMID 1996). This shows that reef growth events occurred interaction of surface waters and global climate. within the window of third-order sealevel rise but are actu- ally often associated with other events, i.e. probably Eutrophication and Oxygen Depletion of Reef Settings sealevel rises of higher frequency. Short-term, partly repeti- Accompanying Sealevel Rise tive stacked successions of eutrophic/dysaerobic pure mi- In an equilibrated climate (as highlighted above), cold, crobolite reefs to mesotrophic sponge or coral reefs oxygen-rich sutface waters are not available and accumula- (LEINFELDER et al. 1993a, b, LEINFELDER 1994a) show that tion of organic matter possibly coupled with oxygen deple- environmental conditions can have changed rapidly, possi- tion will easily occur in the deeper waters which is not only bly in a fifth or higher order frequency. shown by widespread development of black shales and bi- Nearly pure microbolite reefs, even those interpreted as tuminous deposits of Late Jurassic age but also by our reef dysoxic due to their association with glauconite, pyrite fram- examples (deeper water microbolites). Our examples also boids, Chondrites levels and the dysaerobic bivalve show that in narrow seaways, such as the Tethys off the Aulacomyella, often contain scattered, small-sized, oxygen lberian Peninsula and the narrow Atlantic rift, pulses of dependent fauna such as siliceous sponges or, if shallower, strong nutrient accumulation which occasionally even reef corals. This shows that dysaerobic conditions were not &used strong bottom water oxygen depletion occurred stable across the entire time of development of the reef, during episodes of additional climate leveling provided by e.g. during a fourth or fifth order sealevel rise but must have intra-Late Jurassic sealevel rises. Such events happened oscillated at a higher frequency. Whether or not these os- particularly in a third-order transgressive episode at the end cillations were again correlated to sealevel fluctuations of of the Early Kimmeridgian (hypselocyclum-divisum chrons) high frequency or represent random oscillations of environ- where shallow-water, oxygen-depleted or eutrophic reefs mental factors is debatable.

Fig. 15: Comparison of general reef settingsin the Late Jurassic and the modern world. For explanation see text (redrawnatier LEINFELDER 1993a).

244 Leinfelder, R.R., Werner, W., Nose, M., Schmid, D.U., Krautter, M., Laternser, R., Takacs, M. & Hartmann, D. l

,

Modern reef settings

on forereef terrasses . ’

Upper Jurassic reef settings

thrombolite reefs

245 Paleoecology of Lafe Jurassic reefs . Even if no macrofauna is present in the above pure mi- and hexactinosan biostromes could handle even extremely crobolite reefs, an intimate association of the microbolite oligotrophic settings (KRAUTTER 1995). Upbuilding of micro- crusts with “Tuf$phytes” is obvious. Occasionally, minute bolite sponge mounds was due to a mutual, and ofien al- layers dominated by “Tubiphyfes” alternate with layers with- ternating, accumulation of dense to peloidal carbonate by out these although in most cases intergrowth is very inti- trapping of allochthonous sediment and by microbially in- mate probably due to the ragged and irregularly domed duced precipitation, both processes of which were related outer surfaces of the respective reefs. The Upper Jurassic to microbial activity. Sponges were no framebuilders but “Tubiphyfes” is interpreted by SCHMID (1995, 1996) as an rather seeked such settings for the following reasons: encrusting foraminifera associated with endosymbiotic al- 1) Filter feeding is optimized by a higher position, gae and also occurs in very shallow, obviously oxygenated 2) “lithistids” let themselves get intensely “infected” by coral reef environments (LEINFELDER 1992, LEINFELDER et al. bacteria which appears to help them through times of insuf- 1993b). It therefore must have been either a very euryoxic ficient food supply and or at least eurytrophic organism, or is indicative of high- 3) hexactinellids need an environment where indigestible frequency oxygen or nutrient fluctuations within the organic matter is broken to a useful form by microbial activ- dysaerobic or eutrophic microbolite reefs. Judging from its ity. photosymbiotic relation, the latter interpretation is more likely. Since foraminifera grow at the rate of days and Microbolites were an important constituent of both coral weeks, shifts from “Tubiphytes” to non-“Tubiphyfes” domi- and sponge microbolite reefs from the Late Jurassic. With- nance might even represent annual cycles. out their participation, no positive structures could have been produced. The dependence of microbolite formation on low sedimentation rates makes microbolite-rich reefs 5 Conclusions good indicators for generally reduced sedimentation and explains why such reefs are largely restricted to episodes of Upper Jurassic reefs are non-actualistic reefs although rising sealevel. Given low sedimentation microbolites can coral reefs share quite some features with their modern occur at any water depth, defining them as facultatively representatives (Fig. 15). Both modern and Upper Jurassic aphotic. They also can cope with deteriorated environ- coral reefs grew on preexisting shelf and intra-platform mental factors which exclude other organisms. Conse- margins but also might occur within siliciclastic fan deltas quently, pure microbolite reefs developed during episodes and turbid waters. However, the Upper Jurassic coral reefs of strong eutrophication or oxygen depletion. In hyper- occurred more frequently in terrigeneously influenced turbid saline, hyposaline, intertidal or freshwater settings, micro- waters of coastal settings, even entering brackish environ- bolites were also frequent during the Late Jurassic. ments. This is interpreted as a reflection of a higher propor- In general, reef communities from the Late Jurassic oc- tion of heterotrophic metabolism in Jurassic reef corals al- curred within a much wider range of environmental condi- though distinct bathymetric zonation, morphological adap- tions than their modern counterparts, but distinctly changed tations to decrease of illumination and distinct annual their composition and structure relating to environmental growth banding shows that photosymbiosis has already variations. Provided detailed paleoecological analysis is been developed in many taxa albeit of a lower efficiency. petformed, this variability allows to use them as perfect in- Another difference is the frequent position of Jurassic coral dicators for paleoenvironmental parameters, structural reefs in ramp settings, mostly forming low-relief structures situations, as well as for general paleogeographic, - in both low- and high-energy settings. Framework was only oceanographic and -climatic reconstructions. Analysis of preservable in settings of low to moderate energy where Upper Jurassic reefs suggests that the Late Jurassic was microbolites reflecting microbial activity largely accounted an epoch of equilibrated, warm climate, with a stable body for reef stabilization. They anticipated the tasks of the mod- of warm surface waters enabling coral reef growth up to ern reefs coralline red algae which only existed as precur- high paleolatitudes. These waters were superimposed to sor forms (LEINFELDER & WERNER 1993). Though being able slightly cooler waters occupied by siliceous sponge com- to tolerate elevated water energy, microbial mats were not munities, provided flat ramp-configured shelfs existed. Lack efficient enough to bind the high amount of debris produced of strong oceanic circulation resulted in occasional eu- in most of these settings, so that Upper Jurassic high- trophication or oxygen depletion even in shallow waters. energy coral reefs are largely preserved as originally unsta- This happened particularly in the narrow seaways sur- bilized debris deposits with only a minor fraction of frame- rounding Iberia, giving rise to extensive development of work preservation (LEINFELDER 1992, 1994b, NOSE 1995). pure microbolites at certain time-intervals. Besides microbial mats many other encrusting microorgan- isms, such as photoautotrophic foraminifera (SCHMID & LEINFELDER 1996, SCHMID 1996) contributed to sediment References fixation of Upper Jurassic coral reefs. Although modern communities dominated by siliceous ALI, O.E. (1984): Sclerochronology and carbonate production in sponges do exist (e.g. DAYTON 1978, VAN WAGONER et al. some Upper Jurassic reef corals. - Palaeontoiogy, 27, 537-548, 1989, CONWAY et al. 1991, HENRICH et al. 1992) they differ London greatly from their Jurassic counterparts in frequency of oc- ALLISON, N. TUDHOPE, A.W. & FALLICK, A.E. (1996): Factors influ- currence, lack of mound formation and environmental de- encing the stable carbon and oxygen isotopic composition of mands. Judging from independent sedimentological, se- fofites Mea coral skeletons from Phuket, South Thailand. - quential and paleoecological evidence, siliceous sponge Coral Reefs, 15, 43-57, Berlin (Springer) biostromes and mounds occurred on near-level bottom BAUMEISTER, J. & LEINFELDER, R.R. (in press): Constructional mor- phology and palaeoecological significance of three Upper Juras- ramps, in shallow to moderately deep, carbonate domi- sic regular echinoids. - Palaeontology, London nated shelf waters but below the zone of reef coral growth. BEAUVAIS, L. (1984): Evolution and diversification of Jurassic scler- The exact bathymetric position was strongly dependent on actinia. - Palaeontographica Americana, 54, 219-224, Cathaya nutrient characteristics and a fairly broad overlap zone with BERTLING, M. (1993a): Riffkorallen im norddeutschen Oberjura - coral growth existed. Upper Jurassic reef corals needed Taxonomie, okologie, Verteilung. - Palaeontographica (A), 226, stable upper oligotrophic to mesotrophic levels whereas si- 77-123, Stuttgart (Schweizerbart) liceous sponges were adapted to fluctuating nutrient levels, BERTLING, M. (1993b): Ecology and distribution of the Late Jurassic

246 Leinfelder, R.R., Werner, W., Nose, M., Schmid, D.U., Krautter, M., Laternser, R., Takacs, M. B Hartmann, D. C

Scleractinian Thamnasferia concinna (GOLDFUSS) in Europe. - LEINFELDER, R.R. (1992): A modern-type Kimmeridgian reef (Ota Palaeogeogr., Palaeoclimatol., Palaeoecol., 105, 31 I-335 Limestone, Portugal): Implications for Jurassic reef models. - * Amsterdam Facies, 26, 11-34, Erlangen BRAGA, J.C., MARTIN, J.M. & RIDING, R. (1995): Controls on micro- LEINFELDER, R.R. (1993a): Upper Jurassic reef types and control- bial dome fabric development along a carbonate-siliciclastic ling factors -A preliminary report. - Profil, 5, 1-45, Stuttgart shelf-basin transect, Miocene, SE Spain. - Palaios, IO, 347-361, LEINFELDER, R.R. (1993b): A sequence stratigraphic approach to Tulsa the Upper Jurassic mixed carbonate - siliciclastic succession of BURNE, R.V. & MOORE, LS. (1987): Microbialites: Organosedi- the central Lusitanian Basin, Portugal. - Profil, 5, 119-140, mentary deposits of benthic microbial communities. - Palaios, 2, Stuttgart 241-254, Tulsa LEINFELDER, R.R. (1994a): Distribution of Jurassic reef types: A CHAFETZ, H.S. 8. BUC~YNSKI, C. (1992): Bacterially induced lithifica- mirror of structural and environmental changes during breakup of tion of microbial mats. - Palaios, 7, 277-293, Tulsa Pangea. In: BEAUCHAMP, B., EMBRY, A.F. 8, GLASS, D. (eds.): CHRISTMANN, H., MENGES, G. 8, SCHWEIZER, V. (1994): Mineralo- Pangea: Global Environments and Resources. - Can. Sot. stratigraphy of well-bedded and spongiolitic massive carbonate Petrol. Geol., Mem., 17, 677-700, Calgary lithologies of the Swabian Alb. In: LEINFELDER, R.R. (ed. & LEINFELDER, R. R. (1994b): Karbonatplattformen und Korallenriffe coord.): The origin of Jurassic reefs: Current research develop- innerhalb siliziklastischer Sedimentationsbereiche (Oberjura, ments and results. - Facies, 31, 31-33, Erlangen Lusitanisches Becken, Portugal). - Profil, 6, 1-207, Stuttgart C ONWAY, K.W., BARRIE, J.V., AUSTIN, W.C. & LUTERNAUER, J.L. LEINFELDER, R.R. (1994c): A fossil example of environmental (1991): Holocene sponge bioherms on the western Canadian change related to sea-level rise: The Serra Isabel horizon (Upper continental shelf. - Continental Shelf Research, II, 771-790, Jurassic) of west-central Portugal and its equivalents. - London Abstracts, E 15, Internat. Geol. Congress (IAS), August 1994, DAYTON, P.K. (1978): Observations of growth, dispersal and popu- Recife lation dynamics of some sponges in McMurdo Sound, Antarctica. LEINFELDER, R.R. 8, KEUPP, H. (1995): Upper Jurassic Mud In: LEVI & BOURY-ESNAULT (eds.): Sponge Biology. - C.N.R.S., Mounds: Allochthonous Sedimentation versus autochthonous 291, 271-282, Paris Carbonate Production. In: REITNER & NEUWEILER (coord.): Mud DROMART, G., GAILLARD, C. & JANSA, L.F. (1994): Deep-marine mi- Mounds: A polygenetic Spectrum of fine-grained Carbonate crobial structures in the Upper Jurassic of Western Tethys. - In: Buildups. - Facies, 32, 17-26, Erlangen BERTRAND-SARFA-~I, J. & MONTY, C. (eds.): Phanerozoic stroma- LEINFELDER, R. & SEYFRIED, H. (1993): Sea level change - a philo- tolites II, 295-318, Dordrecht (Kluwer) sophical approach. - Geol. Rdsch., 82, 159-172, Berlin ELLIS,P.M., W ILSON, R.C.L. & LEINFELDER, R.R. (1990): Controls on LEINFELDER, R.R. 8, W ERNER, W. (1993): The systematic position Upper Jurassic carbonate build-up development in the Lusitanian and palaeoecology of the alga Marine//a hgeoni PFENDER. - Basin, Portugal. - lnt. Ass. Sediment., Spec. PubI., 9, 169-202, Zitteliana, 20, 105122, Munchen Tulsa LEINFELDER, R.R. 8, W ILSON, R.C.L. (1989): Seismic and sedimen- FAGERSTROM, J.A. (1987): The evolution of reef communities. - 600 tologic features of Oxfordian - Kimmeridgian syn-rift sediments pp., New York (Wiley) on the eastern margin of the Lusitanian Basin, Portugal. - Geol. FLUGEL, E. (1981): “Tubiphyten” aus dem frankischen Malm. - Rdsch., 78, 81-104, Stuttgati Geol. Bl. NO-Bayern, 31, 126-142, Erlangen LEINFELDER, R.R., KRAUTTER, M., NOSE, M., RAMALHO, M.M. & F~RSICH, F.-T. (1981): Salinity-controlled benthic associations from W ERNER, W. (1993a): Siliceous sponge facies from the Upper the Upper Jurassic of Portugal. - Lethaia, 14, 203-223, Oslo Jurassic of Portugal. - N. Jb. Geol. Pal3ont., Abh., 189, 199-254, F~RSICH, F.-T. & WERNER, W. (1986): Benthic associations and Stuttgart their environmental significance in the Lusitanian Basin (Upper LEINFELDER, R.R., NOSE, M., SCHMID, D.U. 8, WERNER, W. (1993b): Jurassic, Portugal). - N. Jb. Geol. Pal$iont. Abh., 172, 271-329, Microbial crusts of the Late Jurassic: Composition, palaeo- Stuttgart ecological significance and importance in reef construction. - GILL, G.A. & SAN-~ANTONIO, M. (1995): Ecological significance of Facies, 29, 195-230, Erlangen pennular coral assemblages in the Upper Jurassic pelagic de- LEINFELDER, R.R., KRAUTTER, M., LATERNSER, R., NOSE, M., posits of the Umbria-Marche-Sabina Apennines (Central Italy), - SCHMID, D.U., SCHWEIGERT, G., WERNER, W,, KEUPP, H., Abstracts, VII Intern. Symp. Fossil Cnidaria and Porifera, Madrid BRUGGER, H., HERRMANN, R., REHFELD-KIEFER, U., SCHROEDER, GWINNER, M.P. (1976): Origin of the Upper Jurassic limestones of J.H., REINHOLD, C., KOCH, R., ZEISS, A., SCHWEIZER, V., the Swabian Alb (Southwest Germany). - Contr. Sedimental., 5, CHRISTMANN, H., MENGES, G. & LUTERBACHER, H. (1994): The l-75g Stuttgart origin of Jurassic reefs: Current research developments and re- HENRICH, R., HARTMANN, M., REI-~NER, J., SCHAFER, P., FREIWALD, sults. - Facies, 31, 1-56, Erlangen A., STEINMETZ, S., DIETRICH, P. & THIEDE, J. (1992): Facies belts LEVINTON, J.S. (1982): Marine ecology (lst ed.). - VII-XV, 1-526, and communities of the Arctic Vesterisbanken Seamount London (Prentice-Hall) (Central Greenland Sea). - Facies, 27, 71-104, Erlangen MACKIE, G.O. & SINGLA, CL. (1983): Studies on Hexactinellid JAMES, N.P. & BOURQUE, P. (1992): Reefs and mounds. - In: Sponges. I. Histology of Rhabdoca/yptus dawsoni (LAMBE, 1873). WALKER, R.G. &JAMES, N.P. (eds.): Facies models. Response to - Phil. Trans. Royal Sot. London, B, Biological Sciences, 301, sea level change, 323-347, Geol. Assoc. Canada, Waterloo 365-400, London JOACHIMSKI, M.M. (1991): Stabile Isotope (C,O) und Geochemie der M OORE, G.T., HAYASHIDA, D.N., Ross, C.A. & JACOBSON, SR. Purbeck-Mikrite in Abh2ngigkeit von Fazies und Diagenese (1992): The Paleoclimate of the Kimmeridgian/Tithonian (Late (Berriasian/Schweizer und Franzusischer Jura, Stidengland). - Jurassic) world: I. Results using a general circulation model, - Erlanger geol. Abh., 119, 1-114, Erlangen Palaeogeogr., Palaeoclimatol., Palaeoecol., 93, 113-150, KEMPE, S. & ~ZMIERC~AK, J. (1994): The role of alkalinity in the Amsterdam evolution of ocean chemistry, organization of living systems, and N OSE, M. (1994): Upper Jurassic coral reefs from Iberia. - In: biocalcification processes. - Bull. Inst. oceanogr. Monaco, Num. LEINFELDER, R.R. (ed.): The origin of Jurassic reefs: Current re- spr?c., 13, 61-116, Monaco search developments and results. - Facies, 31, 22-23, Erlangen KRAUTTER, M, (1995): Kieselschwamme als potentielle lndikatoren N OSE, M. 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