Helmut Keupp

The origin of Jurassic reefs: Current research developments and results

SummaryIn order to elucidate the control of local, regional and global factors on occurrence, distribution and character of Jurassic reefs, reefal settings of Mid and Late Jurassic age from southwestern Germany, Iberia and Romania were compared in terms of their sedimentological (including diagenetic), palaeoecological, architectural, stratigraphic and sequential aspects. Upper Jurassic reefs of southern Germany are dominated by siliceous sponge—microbial crust automicritic to allomicritic mounds. During the Oxfordian these form small to large buildups, whereas during the Kimmeridgian they more frequently are but marginal parts of large grain-dominated massive buildups. Diagenesis of sponge facies is largely governed by the original composition and fabric of sediments. The latest Kimmeridgian and Tithonian spongiolite development is locally accompanied by coral facies, forming large reefs on spongiolitic topographic elevations or, more frequently, small meadows and patch reefs within bioclastic to oolitic shoal and apron sediments. New biostratigraphic results indicate a narrower time gap between Swabian and Franconian coral development than previously thought. Palynostratigraphy and mineralostratigraphy partly allow good stratigraphic resolution also in spongiolitic buildups, and even in dolomitised massive limestones.Spongiolite development of the Bajocian and Oxfordian of eastern Spain shares many similarities. They are both dominated by extensive biostromal development which is related to hardground formation during flooding events. The Upper Jurassic siliceous sponge facies from Portugal is more localised, though more differentiated, comprising biostromal, mudmound and sponge-thrombolite as well as frequent mixed coral-sponge facies. The Iberian Upper Jurassic coral facies includes a great variety of coral reef and platform types, a pattern which together with the analysis of coral associations reflects the great variability of reefal environments. Microbial reefs ranging from coralrich to siliceous sponge-bearing to pure thrombolites frequently developed at different water depths. Reef corals even thrived within terrigeneous settings.In eastern Romania, small coral reefs of various types as well as larger siliceous sponge-microbial crust mounds grew contemporaneously during the Oxfordian, occupying different bathymetric positions on a homoclinal ramp.Application of sequence stratigraphic concepts demonstrates that onset or, in other cases, maximum development of reef growth is related to sea level rise (transgressions and early highstand) which caused a reduction in allochthonous sedimentation. The connection of reef development with low background sedimentation is corroborated by the richness of reefs in encrusting organisms, borers and microbial crusts. Microbial crusts and other automicrites can largely contribute to the formation of reef rock during allosedimentary hiatuses. However, many reefs could cope with variable, though reduced, rates of background sedimentation. This is reflected by differences in faunal diversities and the partial dominance of morphologically adapted forms. Besides corals, some sponges and associated brachiopods show distinct morphologies reflecting sedimentation rate and substrate consistency. Bathymetry is another important factor in the determination of reefal composition. Not only a generally deeper position of siliceous sponge facies relative to coral facies, but also further bathymetric differentiation within both facies groups is reflected by changes in the composition, diversity and, partly, morphology of sponges, corals, cementing bivalves and microencrusters.Criteria such as authigenic glauconite, dysaerobic epibentic bivalves,Chondrites burrows or framboidal pyrite in the surrounding sediments of many Upper Jurassic thrombolitic buildups suggest that oxygen depletion excluded higher reefal metazoans in many of these reefs. Their position within shallowing-upwards successions and associated fauna from aerated settings show that thrombolitic reefs occurred over a broad bathymetric area, from moderately shallow to deep water. Increases in the alkalinity of sea water possibly enhanced calcification.Reefs were much more common during the Late Jurassic than during the older parts of this period. Particularly the differences between the Mid and Late Jurassic frequencies of reefs can be largely explained by a wider availability of suitable reef habitats provided by the general sea level rise, rather than by an evolutionary radiation of reef biota. The scarcity of siliceous sponge reefs on the tectonically more active southern Tethyan margin as well as in the Lusitanian Basin of west-central Portugal reflects the scarcity of suitable mid to outer ramp niches. Coral reefs occurred in a larger variety of structural settings.Upper Jurassic coral reefs partly grew in high latitudinal areas suggesting an equilibrated climate. This appears to be an effect of the buffering capacity of high sea level. These feedback effects of high sea level also may have reduced oceanic circulation particularly during flooding events of third and higher order, which gave rise to the development of black shales and dysaerobic thrombolite reefs. Hence, the interplay of local, regional and global factors caused Jurassic reefs to be more differentiated than modern ones, including near-actualistic coral reefs as well as non-actualistic sponge and microbial reefs.

Mud mounds-a polygenetic spectrum of fine-grained carbonate buildups

SummaryThis research report contains nine case studies (part II to X) dealing with Palaeozoic and Mesozoic mud mounds, microbial reefs, and modern zones of active micrite production, and two parts (I and XI) summarizing the major questions and results. The formation of different types ofin situ formed micrites (automicrites) in close association with siliceous sponges is documented in Devonian, Carboniferous, Triassic, Jurassic and Cretaceous mounds and suggests a common origin with a modern facies found within reef caves. Processes involved in the formation of autochthonous micrites comprise: (i) calcifying mucus enriched in Asp and Glu, this type presumably is linked to the formation of stromatolites, thrombolites and massive fabrics; (ii) protein-rich substances within confined spaces (e.g. microcavities) result in peloidal pockets, peloidal coatings and peloidal stromatolites, and (iii) decay of sponge soft tissues, presumably enriched with symbiotic bacteria, lead to the micropeloidal preservation of parts of former sponge bodies. As a consequence, there is strong evidence that the primary production of micrite in place represents the initial cause for buildup development. The mode of precipitation corresponds to biologically-induced, matrix-mediated mineralization which results in high-Mg-calcites, isotopically balanced with inorganic cements or equilibrium skeletal carbonates, respectively. If distinct automicritic fabrics are absent, the source or origin of micrite remains questionable. However, the co-occurring identifiable components are inadequate, by quantity and physiology, to explain the enhanced accumulation of fine-grained calcium carbonate. The stromatolite reefs from the Permian Zechstein Basin are regarded as reminiscent of ancestral (Precambrian) reef facies, considered the precursor of automicrite/sponge buildups. Automicrite/sponge buildups represent the basic Phanerozoic reef type. Analogous facies are still present within modern cryptic reef habitats, where the biocalcifying carbonate factory is restricted in space.

Die kalkigen Dinoflagellaten-Zysten der borealen Unter-Kreide (Unter-Hauterivium bis Unter-Albium)

ZusammenfassungAus überwiegend dunklen Tonsteinen der Unterkreide des Niedersächsischen Beckens (verschiedene Profile vom Unter-Hauterivium bis Unter-Albium) und dem Küstenprofil Speeton (Nordsee-Becken, E-England: Hauterivium-Barremium) werden anhand rasterelektronenmikroskopischer Methoden die kalkigen Dinoflagellaten-Zysten beschrieben. Alle gefundenen Morphotypen stellen eine monophyletische Einheit dar. So lassen äußerlich paratabulierte Zysten (Calcigonellum, Echinodinella, Pithonella guetafeoni, Bicarinellum, Carinellum, Alasphaera, Heptasphaera) eine Homologisierung mit einem peridinialen Plattenschema zu. Eine vollständige Paratabulation auf der Innenseite des organischen Periphragmas weist auch die typischen Calcisphaerulidae BONET 1956, die BOLLI 1974 unter der GattungPithonella zusammenfaßt, als gesicherte Peridiniaceen-Zysten aus. Das Plattenschema vermittelt zwischen den beiden rezenten Unterfamilien Peridinioideae WALL & DALE und Calciodinelloideae DEFLANDRE, die die Fähigkeit haben, Kalkzysten zu bilden.Die radiale bzw. schräge Orientierung der Außenwandkristallite ermöglicht eine Aufspaltung der unterkretazischen Kalkdinoflagellaten-Zysten in zwei Großgruppen. Die Mineralisierung besonders der Zysten mit schräg orientierten Wandkristallen wird als primär kalzitische, extracelluläre Fällung ohne nennenswerte genetische Steuerung erkannt. Für die Anzahl mineralisierter Wandschichten (1–3), die jeweils von organischen Membranen begrenzt sind, die strukturelle und texturelle Ausbildung der Innenwände, absolute Größe und Habitus der Oberflächenkristalle wird mit Hilfe morphologischer Trendreihen mit z.T. deutlicher Faziesbezogenheit eine starke ökologische Kontrollfunktion wahrscheinlich gemacht. In Analogie zu Zysten rezenter Dinoflagellaten kann auch gezeigt werden, daß die Dicke einzelner Wandschichten durch die individuell variablen Abstände der organischen Phragmen modifiziert sein kann. Ebenso variiert die Intensität einer thekalen Plattenreflexion von sehr deutlich bis fehlend. Die phänotypische Variabilität aller an den Kalkzysten erkennbaren Merkmale, mit Ausnahme der Kristall-Orientierung der Außenwand, stellt die bisher nach diesen morphologischen Kriterien vorgenommene Aufspaltung in Arten in Frage.In dieser Monographie werden charakteristische Phänotypen im Hinblick auf ihren regional-stratigraphischen und palökologischen Aussagewert mit Artnamen im Sinne einer Parataxonomie belegt. Voneinander ableitbare Morphotypen werden in “Arten-Gruppen” zusammengefaßt, deren Umfang wohl eher dem biologischen Art-Begriff nahekommt. Darüberhinaus erfolgt aus Gründen der besseren Überschaubarkeit bei den Zysten mit schräger Orientierung der Außenwandkristalle die Aufspaltung in diePithonella patriciacreeleyae/multistrata-Gruppe mit ihren äußerlich paratabulierten DerivatenBicarinellum undCarinellum und diePithonella loeblichi-Gruppe künstlich.Innerhalb des untersuchten Profilabschnitts ermöglicht die paläogeographische Entwicklung im Unter-Hauterivium, im Ober-Barremium/Unter-Aptium und im Unter-Albium jeweils einen Faunen- und Florenaustausch mit der Tethys. Die Verteilung der kalkigen Dinoflagellaten-Zysten zeichnet die Wechsel zwischen mehr mediterran bzw. boreal beeinflußten Zeiten deutlich nach. So erscheinen die morphotypischen GattungenCalcigonellum undBicarinellum als stenotherme Kaltformen,Alasphaera und stark pirumellidePithonella als stenotherme Warmformen.Im Zuge der monographischen Beschreibung der unterkretazischen Kalkdinoflagellaten-Zysten werden folgende morphologischen Taxa neu beschrieben:Echinodinella levata n.sp.,Carinellum monocarinatum n.g., n.sp.,Carinellum conulum n.sp.,Nephrodinella reniformis n.g., n.sp..SummaryThe calcareous dinoflagellate cysts are described from different sections of the Lower Cretaceous of the Lower Saxonian Basin (Lower Hauterivian-Lower Albian) and from the East coast of England (Speeton, North Sea Basin: Lower Hauterivian-upper Barremian). Diagenetic alterations of carbonate particles are mostly lacking within the dark marly claystones. Therefore SEM study is possible for isolated individuals washed out of the matrix. All the morphotypes belong to the same monophyletic group. Cysts with an outside paratabulation (Calcigonellum, Echinodinella, Pithonella gustafsoni, Bicarinellum, Carinellum, Alasphaera, Heptasphaera) show a peridinioid plate pattern. A complete peridinioid paratabulation inside the organic periphragm ofPithonella patriciacreeleyae BOLLI 1974 and an outside epithecal paratabulation ofPithonella gustafsoni BOLLI 1974 proves the dinoflagellate nature of the Mesozoic incertae sedis family Calcisphaerulidae BONET 1956. Their plate pattern shows a position intermediate between both Recent subfamilies Peridinioideae WALL & DALE and Calciodinelloideae DEFLANDRE, having calcareous cysts.Due to the normal respectively oblique orientation of the crystallographic c-axis of the calcite crystals forming the outer wall, two groups of the Lower Cretaceous dinoflagellate cysts can be distinguished. The mineralization of the cyst wall especially of the cysts with oblique orientation of crystals, seems to occur with low Mg-calcite as a precipitation controlled slightly by the algal cell within an extracellular mucus. The number of single wall-layers (1–3) each separated by an organic membrane, the texture and structure of the inner layers, size and form of the crystals forming the cysts surface are all controlled by palecological factors. These can be shown by morphological sequences with intermediate transitional stages. In some cases the immediate connection between morphological alterations of the dinoflagellate cysts and the change of palecological conditions is visible. Analogous to Recent dinoflagellate cysts, the thickness of single wall layers varies due to the individual variability of the interspaces between the organic phragms. FOTTERER 1976 could show a significant variation of outside paratabulation ofCaldiodinellum operosum. In the same way the sculptures on the surface of Lower Cretaceous calcareous dinoflagellate cysts based on a paratabulation vary from well developed to absent.The phenotypic variability of all characteristics, except the orientation of outer wall crystals, poses questions on the validity of splitting the cysts into single taxa used up to day according to these morphological criterias. In this monograph single morphotypes useful for local stratigraphical and for palecological purposes, are treated like real species in the sense of parataxonomy. Morphotypes derived from each other are understood to be species groups. This corresponds more with the biological species. Beyond this, the separation of thePithonella patriciacreeleyae/multistrata-group with its outside paratabulated derivatesBicarinellum andCarinellum, and of thePithonella loeblichi-group is artificial.In the studied sections the vertical distribution of calcareous dinoflagellate cysts is dependant on repeated alterations of Boreal versus Mediterranean flora ingressions. Due to the paleogeographic situation an exchange of fauna and flora was possible between the boreal environments and the Tethys realm during Lower Hauterivian, Upper Barremian/Lower Aptian, and Lower Albian. The morphotypical generaCalcigonellum andBicarinellum seem to be stenothermic cold forms,Alasphaera and strongly pirumellide cysts ofPithonella seem to be stenothermic warm forms.In connection with the monographic description of the Lower Cretaceous calcareous dinoflagellate cysts the following new taxa are dexcribed:Echinodinella levata n.sp.,Carinellum monocarinatum n.g., n.sp.,Carinellum conulum n.sp.,Nephrodinella reniformis n.g., n.sp..

Microbial carbonate crusts-a key to the environmental analysis of fossil spongiolites?

SummaryMorphological and geochemical comparisons between modern cryptic microbialites from Lizard Island/Great Barrier Reef and fossil counterparts in the Upper Jurassic (Southern Germany, Dobrogea/Romania) and late Lower Cretaceous (Aptian/Albian from Cantabria/Spain) spongiolitic environments show that there are common factors controlling the crust formations mostly independent of light despite of diverging (paleo-) oceanographic positions as well as relationships of competitors. Factors such as increased alkalinity, oligotrophy, and reduced allochthonous deposition are of major importance. Thrombolitic microbialites are interpreted as biologically induced and therefore calcified in isotopic equilibrium with the surrounding sea water. Corresponding with shallowing upward cycles, microbial mats which produce stromatolitic peloidal crusts become more important. Different biomarkers are introduced for the first time extracted and analyzed from spongiolitic limestones of Lower Kimmeridgian age from Southern Germany.

Die kalkigen Dinoflagellatenzysten des Mittelalb bis Untercenoman von Escalles/Boulonnais (N-Frankreich)

ZusammenfassungAus dem ungefähr 14 m mächtigen Strandprofil werden erstmalig für den Abschnitt Mittel-Alb bis Cenoman-Basis die kalkigen Dinoflagellaten-Zysten systematisch erfaßt. Es werden 4 Gattungen und 11 Arten neu beschrieben. Die Familie der Calciodinellaceae DEFLANDRE 1947 emend. BUJAK & DAVIES 1983 wird in drei neue Subfamilien untergliedert: Orthopithonelloideae, Obliquipithonelloideae und Pithonelloideae. Für die bisher in ihrer systematischen Stellung umstrittenen Calcisphaeruliden derPithonella sphaerica-Gruppe kann unter anderem aufgrund rudimentärer Paratabulationen ebenfalls die Dinoflagellatennatur wahrscheinlich gemacht werden,Die Assoziation der Kalkdinoflagellaten wird im Mittel- und Oberalb durch Vertreter der Obliquipithonelloideae dominiert. Eine Zuweisung der einzelnen Texte zu einem bevorzugten Lebensraum (Boreal bzw. Tethys) kann derzeit noch nicht erfolgen, da der Ablagerungsraum im Überschneidungsbereich beider Einflußsphären gelegen war, und Vergleichsfloren aus dem Boreal bzw. dem mediterranen Raum noch fehlen. Dennoch scheinen die Arten vonCalcigonellum undBicarinellum ähnlich wie in der tieferen Unterkreide eher ein boreales Element zu sein, während die meisten Formtypen derObliquipithonella multistrata- undO. loeblichi-Gruppe als Kosmopoliten anzusehen sind. Mit der Cenoman-Transgression und dem damit verbundenen Wechsel in der Lithologie zu tethyalen Schelfkarbonaten werden Assoziationen kalkiger Dinoflagellaten-Zysten unvermittelt durch die Pithonelloideae dominiert.SummaryThe flora of calcareous dinoflagellate cysts of Middle Albian to Early Cenomanian age were studied in an approximately 14 m thick coastal section of Escalles/-Boulonnais, France. Four new genera and 11 new species are described. The systematics of the family Calciodinellaceae DEFLANDRE 1947 emend. BUJAK & DAVIES 1983 is modified by the introduction of three new subfamilies: Orthopithonelloideae, Obliquipithonelloideae, Pithonelloideae. The incertae sedis calcisphaerulidae of thePithonella sphaerica-group are calcareous cysts of peridinian dinoflagellates indicated especially by relicts of outside paratabulations.During the Middle and Late Albian the association of calcareous cysts was strongly dominated by Obliquipithonelloideae. But in most cases it was not yet possible to correlate certain species with certain realms, because*the sedimentation area studied was situated between both realms during this time and was therefore influenced by the Boreal as well as the Tethyan.*up to now no studies have been made of synchroneous flora extracted from typical Mediterranean sections such as those from typical Boreal sections. Nevertheless, the rare specimens ofCalcigonellum andBicarinellum seem rather to be elements of the Boreal Realm, according to the floral analysis of the lowermost Lower Cretaceous. The morphotypes of theObliquipithonella multistrata and of theO. loeblichi group seem to be cosmopolitan. The association of calcareous dinoflagellate cysts is dominated by Pithonelloideae as a result of the Cenomanian transgression and the lithological change to Mediterranean influenced shelf carbonates.

A molecular phylogeny of Scrippsiella sensu lato (Calciodinellaceae, Dinophyta) with interpretations on morphology and distribution

The phylogenetic relationships of Scrippsiella sensu lato (including cyst taxa such as Calcigonellum, Calciodinellum, and Pernambugia) were investigated based on sequences from the ribosomal 5.8S rRNA and the Internal Transcribed Spacers ITS1 and ITS2, including interpretations on morphology and distribution. To attach importance to the cyst diversity present in calcareous dinoflagellates, a segregation of Scrippsiella sensu lato into four well-recognizable and monophyletic groups is proposed, corresponding to more- or less-established taxonomic units: (i) Calciodinellum (including Calcigonellum and a few species assigned to Scrippsiella), (ii) Pernambugia (presumptively including Lebessphaera), (iii) S. precaria and S. ramonii, and (iv) Scrippsiella sensu stricto comprising largely the S. trochoidea species complex. The phylogenetic relationships among these four groups are not sufficiently resolved. Molecular data suggest the existence of numerous cryptic taxa showing molecular, but not morphological, variation (especially in Scrippsiella sensu stricto). Closely related strains have a wide range of distribution and occur (at least partly) sympatrically in cold through to tropical seas of the world.

Steuerungsprozesse der Entwicklung von Oberjura-Spongiolithen Süddeutschlands: Kenntnisstand, Probleme und Perspektiven

ZusammenfassungDie jurassischen Spongiolithe der epi- bis perikontinentalen Randentwicklung der Tehys erreichen im Malm ihre maximale Entfaltung. Sie können in der Evolution von Riffassoziationen während der Erdgeschichte als ein historisch einmaliges Phänomen gesehen werden. Der Beitrag diskutiert den derzeitigen, zum Teil kontrovers beurteilten Kenntinisstand über Genese und Rahmenbedingen dieser autochthonen Kieselschwamm-Gesteine Süddeutschlands und seiner Nachbargebiete. Im Hinblick auf das Teilprojekt ‘Riffevolution’ des DFG-Schwerpunktprogrammes ‘Biogene Sedimentation’ beleuchtet er insbesondere folgende genetischen und prozeßorientierten Aspekte: 1.Stratigraphische Rahmenbedingungen (Bio-, Litho- und Mineralostratigraphie).2.Die geotektonischen und paläogeographischen Rahmenbedingungen auf dem breiten passiven nördlichen Tethys-Schelf werden anhand der Faktoren Schelfbreite, Schelfstabilität, Landferne und terrigener Sedimenteintrag sowie Meeresspiegel erörtert.3.Für die aus der Sedimentologie ableitbaren klimatischen Fluktuationen liegt noch keine widerspruchsfreie Bestätigung durch die Organismenverteilung vor.4.Die klassische Deutung der sich in der stratigraphischen Abfolge verändernden Wuchsformen biostromaler und biohermaler Spongiolithe als Stillwasserbildungen des tieferen Schelfs, die sich unter anderem auf die (wechselnden) Mikrofazies-Merkmale stützt, wirdneben paläogeographischen und sedimentologischen Argumenten auch durch die sedimentbindende Bedeutung biogener Karbonatkrusten in Frage gestellt.5.Aspekte sedimentologischer Rahmenbedingungen der oberjurassichen Spongiolithe konzentrieren sich im wesentlichen auf die Fragen nach gesicherten bathymetrischen Hinweisen, sedimentären Zyklen, dem möglichen Zusammenhang mit re- und transgressiven Entwicklungen und auf biogene Interaktionen als mutmaßliche Initiatoren der Kieselschwamm-Fossilisation einerseits und der Boundstone-Bildung andererseits.6.Biologische Rahmenbedingungen lassen sich aus den in der Zeit wechselnden benthonischen Organismen-Assoziationen und aus der wechselnden Substratbindung der Organismen ableiten. Neue phylogenetische Errungenschaften innerhalb der dominanten Kieselschwämme sind als Auslöser der Buildups derzeit nicht erkennbar.7.Für die Analyse der steuernden Parameter der Schwammfazies (Paläogeographie, Bathymetrie, Sedimentationsraten, Nährstoffangebot) ist der Vergleich der mit der Schwammfazies vertikal und lateral assoziierten Korallenfazies von grundsätzlicher Bedeutung.8.Die Bedeutung diagenetischer Prozesse für die Interpretation der Spongiolithe wird anhand von früher Lithifizierung, Lösung und epigenetischer Dolomitisierung bzw. Dedolomitisierung diskutiert.SummaryThe sponigolitic facies reaches its widest distribution along the epicontinental to pericontinental margin of the Northern Tethys during the Upper Jurassic. These buildups formed by siliceous sponges represent a singular event within the evolution of reef communities during earth’s history. In this paper the present knowledge of causal and environmental aspects of the spongiolithic limestones in Southern Germany and adjacent areas is discussed. With regard to the research project ‘Evolution of Reefs’ (a major part of the Schwerpunktprogramm ‘Biogenic Sediments’ established by the Deutsche Froschungsgemeinschaft in 1990) the following genetically and process orientated aspects are of interest: 1)The stratigraphic classification using biostratigraphic, lithostratigraphic and mineralostratigraphic methods.2)The paleogeography, oceanography and geotectonics along the broad passive northern shelf of the Tethys are discussed with regard to width and stability of the shelf, distance to the land mass and terrigenous influence and sea level fluctuations.3)Certain sedimentological features seem to be indicative of climatic fluctuations, but this is not always proved by the distribution patterns of organisms.4)The classical interpretation that spongiolites formed below the wave base gets oppositon by the significance of biogenic carbonate crusts as well as sedimentological and paleogeographic arguments.5)Important sedimentological factors of the Upper Jurassic spongiolites are paleobathymetry, sedimentary cycles, possible control of spongiolite growth by sea level fluctuations, as well as biogenic interactions which probably initiated the fossilization of siliceous sponges as well as the formation of spongiolitic buildups.6)Paleoecological conditions can be reconstructed by the community patterns of benthonic organisms and substrate control patterns, both changing through time. Phylogenetic innovations of related sponge groups (hexactinellids, lithistide demospongeans) most probably are not responsible for the initial growth of buildups.7)Comparison of the spongiolites with the laterally and vertically associated coral facies is of major importance for the interpretation of controlling parameters (bathymetry, sedimentation rates, nutrient and nutrient availability) of the sponge facies.8)The genetic significance of diagenetic processes in spongiolites is discussed with regard to early lithification, dissolution, epigenetic dolomitization and dedolomitization.

The Fossil Record of the Haplosclerid Excavating Sponge Aka de Laubenfels

Only few publications deal with Recent species of the genus Aka or Siphonodictyon, a younger synonym of Aka (Johnson 1899; de Laubenfels 1936; Bergquist 1965; Rutzler 1971; Thomas 1972; Pang 1973). In the literature, only two publications figure and describe fossil Aka spicule arrangements — Muller (1978) and Reitner (1987a). Aka spicules are commonly found within burrows in Jurassic and Cretaceous shallow marine carbonates.

Fossil Calcareous Dinoflagellate Cysts

Present knowledge of fossil calcareous dinoflagellate cysts is summarized briefly. All genera of the cyst family Calciodinellaceae Deflandre 1947, including most of the Mesozoic “Calcisphaerulidae” Bonet 1956, known from the fossil record since the late Triassic, are listed here and subdivided into three subfamilies.

Organismenverteilung in den D-Beds von Speeton (Unterkreide, England) unter besonderer Berücksichtigung der kalkigen Dinoflagellaten-Zysten

ZusammenfassungErstmals wird eine kleine, formenarme Flora isolierter Zysten kalkiger Dinoflagellaten aus dem Ober-Berrias vorgestellt. Ihre vertikale Assoziationsabfolge in den D-Beds von Speeton, die im Zusammenhang mit lithologischen Aspekten und den übrigen Floren- und Faunenelementen gesehen wird, läßt erkennen, daß die phänotypische Variabilität nicht nur von Temperaturunterschieden (Keupp 1982), sondern auch von Salinitätsschwankungen im Zuge von Regressionen und Transgressionen gesteuert wird. Die Unter-Hauterive-Transgression läßt ab Horizont D2D nach einem nahezu Calcisphären-freien Valang in eine durch mediterrane Elemente geprägte Kalkdinoflagellaten-Flora einwandern. Die systematische Beschreibung der Calcisphären führt zur Aufspaltung der SammelgattungPithonella Lorenz 1901 sensu Bolli 1974. Für die gesicherten Dinoflagellaten-Zysten werden die beiden GattungenOrthopithonella Keup n.g. undObliquipithonella Keupp n.g. eingeführt, die der durchPithonella ovalis (Kaufmann 1865) charakterisierten GattungPithonella (Lorenz 1901) sensu Villain 1977 gegenüberstehen. Die Belemniten zeigen in den D-Beds eine vertikale Abfolge von 5 Assoziationen, deren Verbreitung die ± kongruent verlaufenden Profilabfolgen der übrigen Organismengruppen teilweise durchbricht. Ihr frühes Auftreten im brackisch beeinflußten Schichtglied D8 und das Durchhalten der Belemniten in der regressiven Phase D5 wird als Umlagerung gedeutet.SummaryA small low diversity flora of calcareous dinoflagellate cysts is described for the first time from the Upper Berriasian. The vertical association sequence in the Speeton D-Beds, seen in connection with lithological aspects as well as the remaining floral and faunal elements, shows that the phenotype variability is governed not only by differences in temperature (Keupp 1982) but also by salinity changes due to regressions and transgressions.After the Valanginian, which was almost completely lacking in calcispheres, the Lower Hauterivian transgression permitted a calcereous dinoflagellate flora characterized by Mediterranean elements to invade the area beginning with the D2D horizon. The systematic description of the calcispheres leads to a splitting up of the collective genusPithonella Lorenz 1901, sensu Bolli 1974. For the positive dinoflagellate cysts two new genera, i.e.Orthopithonella Keupp n.g. andObliquipithonella Keupp n.g., are being introduced in addition to the genusPithonella (Lorenz, sensu Villain 1977 which is characterized byPithonella ovalis (Kaufmann 1865). Five associations of Belemnites exist within the D-Beds in the Vertical sequence; their distribution differs from the more or less congruent pattern of the remaining groups of organisms in the profile. Their early appearance in the brackish bed D8 and persistence in the regressive phase D5 is interpreted as redeposition.