Some more abstracts from the Leinfelder-group and Leinfelder-cooperations:
LEINFELDER, R.R. (1997): Coral reefs and carbonate platforms within a siliciclastic setting: General aspects and examples from the Late Jurassic of Portugal.- Proc. 8th Int. Coral Reef Symp., 2, 1737-1742, Panama City.- Proc. 8th Int. Coral Reef Symp., , 2, 1737-1742, Panama City.
Abstract
Both in the Modern and Ancient examples coral reefs and carbonate platforms occur frequently very close to or even directly within areas of siliciclastic sedimentation. Particularly fine grained, often suspended terrigeneous influx is mostly problematic for the reef fauna due to lowering of illumination and oxygenation, increasing nutrient values or directly settling on the organims. The modern examples show that reef growth in such settings is only possible by the existence of sheltering mechanisms such as arid climate, structural and sedimentary traps or longshore currents. If not completely effective, reefs may still prosper under reduced but noticeable siliciclastic sedimentation, but both composition and diversity of the reefs changes drastically. The Ancient examples show that temporal relations are important as well: Autocyclic switches in depositional systems and especially allocyclic events such as tectonic activation/deactivation or sea level change may open and close reef windows through time. Positive effects of siliciclastic sedimentations on reef growth include the availability of suitable substrate morphologies and, in some cases, favourable increases in nutrient concentration, an aspect which appeared to be im-portant particularly for Mesozoic coral reef growth. The Upper Jurassic coral reefs of the siliciclastically dominated Lusitanian Basin of Portugal are a perfect example for the the intimate cooperation and juxtaposition of all these controlling factors.
NOSE, M. & LEINFELDER, R.R. (1997): Upper Jurassic coral communities within siliciclastic settings (Lusitanian Basin, Portugal): Implications for symbiotic and nutrient strategies.- Proc. 8th Int. Coral Reef Symp., 2, 1755-1760, Panama City.
Abstract
Upper Jurassic coral reefs of Portugal (Lusitanian Basin) grew despite high siliciclastic influx. Small, reef-rimmed carbonate platforms existed on basement uplifts over an extended period of time. Other reefs grew whenever episodes of tectonic quiescense and/or rising sea level reduced siliciclastic influx. Reefs grew within a coarse siliciclastic fan delta and on a fine-grained, silici-clastic slope system. The latter is de-veloped as a distally steepened mixed carbonate-siliciclastic ramp system, which provided excellent examples for constantly or periodically sediment-stressed reefs. Sedimentation rather than water depth was the major modifier of diversity of coral communities and coral growth forms. For example, massive to foliose Microsolena agariciformis changed to a 'pseudobranched' morphology composed of thinly stacked encrusting layers during eleva-ted sedimentation. Depth distribution patterns and morphologic changes clearly show that Jurassic hermatypic corals had photosymbionts. However, their frequent occurrence with-in, or very close to, siliciclastic settings indicates that they could tolerate higher nutrient rates than modern reef corals, probably be-cause a still imperfect symbiotic relation. Consistent with this interpretation are the slower growth rates and the lower low to high density band ratios of Upper Jurassic reef corals even in very shallow non sediment-stressed reef settings.
Baumeister, J.G. & Leinfelder, R.R. (1998): Constructional Morphology of three Upper Jurassic Echinoids. Palaeontology, 41(2), 203-219.
Abstract
General shape of test, spine and tubercle morphologies, and ambulacral pore characteristics of three regular echinoid species from the Upper Jurassic are interpreted in functional terms. Results are compared with independent sedimentological and palaeoecological analyses of the host sediments. In Acrocidaris nobilis the existence of a basal P3/4 isopore phyllode suggests the development of a strong sucker disc which enabled firm attachment in a high energy hardground setting. This interpretation is corroborated by tubercle characteristics indicating firmly attached but largely immotile spines, forming a 'secondary test'. Morphological interpretation of Rhabdocidaris rhodani suggests a low energy, possibly partly dysaerobic, firmground setting as evidenced by (1) the exclusive occurrence of slit-like C isopores and (2) oblique tubercles with a broad muscle attachment area indicating strong, motile stalking spines. Flattened general shape, lack of aboral spines and a fairly strong sucker disc enabled Glypticus hieroglyphicus to crawl across very irregular topography and even browse on the undersides of corals or within an open coral framework. On the other hand, the fairly massive test suggests that elevated water energy occurred at least occasionally, so that the host oligospecific sish-shaped coral association was probably positioned at shallower depths than previously thought. It is suggested that the adaptations of some Late Jurassic regular echinoids to variable niches independently accompanied and mirrored similar adaptive strategies developed in irregular echinoids, such as the evolution of respiratory flattened tuve feet or adaptations towards sedimentation.
Leinfelder, R.R. & Nose, M. (1999): Increasing complexity - decreasing flexibility. A different perspective of reef evolution through time.- Profil, 17, 135-147, Stuttgart
The evolution of reef systems is dependent on a great variety of factors. Evolution, adaptive radiation, and extinction of reef organisms provide the reef building potential whereas plate tectonics, sea-level changes and oceanographic conditions define where and when reefs actually develop. However, two additional important trends superimpose this pattern. These are (1) the evolution of reef building blocks and (2) the variable width of the global reef window.
In terms of ecological structure and carbonate productivity, reefs are composed of different reef building blocks which define the modular complexity of a reef. Such basic building blocks include microbial, parazoan, metazoan, photosymbiontic and red algal modules. These building blocks successively developed throughout the evolution of the System Earth, and are still all available in modern reef systems (REITNER 1997). The unidirectional increase in modular complexity is partly modified, partly paralleled by the variable environmental sets of physicochemical conditions which reef organisms demanded and were adapted to. Until the base of the Cenozoic, such global 'reef windows' mostly widened, due to new adaptational strategies of reef organisms (e.g., photoautotrophy, baffling, aphotosymbiotic and photosymbiotic reef building). The reef windows of the Late Jurassic to Cretaceous were possibly the widest ever. Subsequently, the modular complexity of reefs and the interdependence of reef biota increased with the improvement of the photosymbiotic relation, the appearence of fast growing corals, new synecologic strategies, and the radiation of encrusting coralline algae. This resulted in a distinct narrowing of the tropical reef window and, consequently, the separation of a new, distinct, deep-water coral mound window.
Reef systems existed nearly throughout the entire Earth history. However, reef evolution was punctuated by global reef crises. Extinction events were rapid, but recovery times were very slow. In the light of possible extinction of modern coral reefs by human impact, Earth history provides two major lessons: The high modular complexity of modern reefs which includes Archaean, Proterozoic, Phanerozoic, Mesozoic, and Cenozoic building blocks makes it likely that some robust reef types such as microbial reefs, Halimeda-mounds or low-diversity coral meadows might survive. However, lag time for the reestablishment of complex systems, thus for modern coral reefs, are extremely large, often spanning millions of years and hence extending far beyond human time scales.
LEINFELDER, R.R. & SCHMID, D.U. (2000): Mesozoic Reefal Thrombolites and other Microbolites.- In: RIDING, R.E. & AWRAMIK, S.M. (eds.): Microbial Sediments.- Berlin (Springer).- 289-294, Berlin (Springer).
Abstract
Calcareous microbolites are widespread in the Mesozoic. They play a paramount role in reefbuilding and are often contributing to the reef framework. In the Early Triassic, stromatolites took over the vacant reef habitats. During Middle Triassic and Late Jurassic times, microbolites reached their peak development in the Mesozoic, often forming reefs together with different groups of metazoans. No major break in microbolite development appeared from the Late Jurassic to the Early Cretaceous. In the course of the Cretaceous, microbolites in shallow water reefs were for the most part replaced by encrusting corallinaceans.
SCHMID, D.U., LEINFELDER, R.R. & NOSE, M. (2001): Growth dynamics and ecology of Upper Jurassic mounds, with comparisons to Mid-Palaeozoic mounds.- In: HAYWICK, D.W. & KOPASKA-MERKEL, D.C. (eds.): Carbonate Mounds: sedimentation, organismal response, and diagenesis.- Sedimentary Geology, 145, 343-376, Amsterdam.
Abstract
The Mid-Palaeozoic, including the Late Jurassic, was a time of both widespread coral reef growth and pronounced mound formation. A comparison of mound features and their general setting highlights, despite all differences, general similarities in overall growth dynamics. Mound formation was frequently driven by discontinuous patterns, particularly by background sedimentation. In many examples, episodes of mound stabilisation by early lithification, growth of microbolite crusts and winnowing of fines was followed by growth episodes of benthic fauna under reduced to negligible background sedimentation. This pattern of variable sedimentation and organic buildups may have occurred in different orders and magnitudes, inducing a fractal pattern in some mound complexes. A composite approach in estimating growth rates of mounds demonstrates that high-frequency oscillations necessary for growth of most mounds might have ranged from a few thousand years to 4th and 5th order Milankovich cycles that were superimposed by autocyclic factors.
Henßel, K., Schmid, D.U. & Leinfelder, R.R. (2002): Computergestützte 3D-Rekonstruktionen in der Paläontologie anhand von Serienschnitten.- Mathematische Geologie, 6, 1-18, Dresden.
Abstract
Dreidimensionale Rekonstruktionen aus Serienschnitten stellen im Prinzip eine gängige Methode in der Paläontologie dar. Computergestützte Rekonstruktionen sind jedoch noch nicht sehr weit verbreitet. Die vorliegende Arbeit gibt einen Überblick über die Funktionsprinzipien dieser Methode und über geeignete Softwarelösungen für die verschiedenen PC-Plattformen (Windows, Macintosh, Linux). Anhand eines Anwendungsbeispiels aus dem Oberjura wird eine relativ einfache und schnelle Methode vorgestellt, mittels der computer-gestützte Rekonstruktionen im Makro- und Mikrobereich durchgeführt werden können.
LEINFELDER, R.R., SCHMID, D.U., NOSE, M. & WERNER, W. (2002): Jurassic reef patterns - The expression of a changing globe.- In Flügel, E., Kiessling W. & Golonka, J. (eds), Phanerozoic Reef Patterns.- SEPM Spec. Publ., 72, 465-520, Tulsa.
Abstract
Jurassic reef patterns reflect the fulminant global and regional changes initiated by the breakup of northern Pangea. The pattern of reef distribution across the Jurassic reflects a complex mix of (1) different and changing tectonic styles along the continental margins and adjacent shelf seas; (2) sea-level rise and its modulating influence on extrinsic sedimentation; (3) oceanographic and climatic reorganizations related to general sea-level rise and the new plate-tectonic configurations; and (4) evolutionary changes in the ecological demands and abilities of reef biota, which, in part, appear to have been triggered by the extrinsic changes during the breakup of northern Pangea. Rifting and onset of drift in the central Atlantic as well as in the western Tethys resulted in a distinct sea-level rise, which transformed Jurassic shelf seas along the northern Tethys margin from dominantly siliciclastic to dominantly carbonate settings. The opening of the ocean passageway from the Tethys to the Caribbean and Pacific completely reorganized global oceanic circulation patterns. During the Late Jurassic, shelf seas were considerably deep, increasing the areas of settings suitable for development of siliceous sponge mounds on the northern Tethys margin. In contrast, many parts of the southern Tethys margin underwent strong morphological changes due to rift tectonics within the Triassic carbonate platforms, which resulted in a completely different pattern in Jurassic reef distribution relative to the northern Tethys. After the end-Triassic extinction event, Jurassic reefs recuperated gradually during the Early Jurassic, with a first major reef domain developing in Morocco. Their temporal distribution through the Middle Jurassic was more balanced, but reefs occurred in scattered domains often distant from each other (e.g., Portugal, France, Madagascar, Iran). Late Jurassic reefs expanded rapidly in the course of the ongoing sea-level rise and the oceanographic reorganization, resulting in mostly interconnected domains. A pattern of waxing and waning of reef abundance and spatial reef distribution through time is superimposed on this trend. It is again, at least to a large extent, correlatable with sea-level fluctuations of greater magnitude. Jurassic reef growth had peaks during the transgressive episodes of the Sinemurian–Pliensbachian, Bajocian–Bathonian, and Oxfordian–Kimmeridgian, with superimposed higher-frequency peaks. The Jurassic represents the peak not only of development of Mesozoic coral reefs but equally of development of sponge mounds. Sponge mounds represent siliceous sponge–microbolite mud mounds, which expanded enormously during the Oxfordian along the European part of the northern Tethys. A peculiar type of bivalve reefs, the Lithiothis reefs, were widespread particularly during the Sinemurian and Pliensbachian, and they might have partially filled a potential reef-growth habitat not occupied by corals, owing to the reduced availability of coral taxa at that time. Bivalve reefs, in particular oyster reefs, also occurred scattered in Middle and Late Jurassic times, mostly representing marginal marine environments. Sea-level rise and tectonic opening of new seaways had a pronounced influence on climate and marine circulation patterns, which were the principal factors in Jurassic reef development. Particularly in the Late Jurassic, coral and stromatoporoid reefs occurred in high paleolatitudinal settings (e.g., Argentina, Patagonia, Japan) evidencing strong climatic equilibration of marine and coastal areas, despite the fact that strong seasonal contrasts should have prevailed in the Gondwana interiors. There are only a few records of low-latitude reef sites, despite the availability of carbonate platforms, which might reflect overheated waters in this area. Humidity was probably higher than previously thought. Siliciclastic influx was partially high during the Kimmeridgian, owing to fluvial runoff and renewed tectonic activity, and reduced the number of reef sites and domains considerably, despite ongoing global sea-level rise. Jurassic, chiefly Upper Jurassic, reefs not only grew within the expanding carbonate settings but also thrived in terrigeneously influenced environments. This is particularly obvious in the North Atlantic rift basins, such as the Lusitanian Basin of west-central Portugal, but it is also discernible in many other Jurassic reef domains.
Occurrence of coral associations in fine siliciclastics, ratios of skeletal low-density vs. high-density banding, morphological adaptations towards sedimentation, high proportions of bioerosion, and overlap of many coral domains with proposed upwelling areas suggests that there was a considerable stock of Jurassic zooxanthellate corals with a distinct heterotrophic proportion of feeding, thus living in mesotrophic settings. In contrast, reefs on the isolated, oceanic shallow-water Apulia–Adria platforms differ considerably, being dominated by stromatoporoids, chaetetids, and corals. We propose the theory that these oceanic faunas might have already had a more advanced photosymbiotic relationship than the other forms and thus could thrive in presumably strongly oligotrophic settings. Such associations, which might have occurred similarly on oceanic platforms in the Pacific, are thought to have been the stock for Cenozoic development of coral reefs into superoligotrophic settings, whereas the more nutrient-tolerant reefs along the continental margins vanished in the course of latest Jurassic and Berriasian sea-level drop. Sediment-stressed, nutrient-rich shallow-water settings might then have been reconquered by rudist bivalves in the course of the Cretaceous.
Jurassic reefs not only constitute widespread and important hydrocarbon reservoir rocks; their manifold characteristics and related dependence on basin tectonics, sea-level change, and ecological parameters makes them valuable basin-analysis tools for potential hydrocarbon plays.
Olivier, N., Hantzpergue, P., Gaillard, C., Pittet, B., Leinfelder, R.R., Schmid, D.U. & Werner, W. (2003):
Microbialite morphology, structure and growth: a model of the Upper Jurassic reefs of the Chay Peninsula (Western France).- Palaeogeography, Palaeoclimatology, Palaeoecology, 193, 383-404.
Abstract
During the Early Kimmeridgian, the northern margin of the Aquitaine Basin (Western France) is characterised by a significant development of coral reefs. The reef formation of the Chay Peninsula comprises two main reefal units, in which the microbial structures can contribute up to 70% of framework. The microbial crusts, which played an important role in the stabilisation and growth of the reef body, show the characteristic clotted aspect of thrombolitic microbialites. Corals are the main skeletal components of the build-ups. The bioconstructions of the Chay area are thus classified as coral-thrombolite reefs. Four main morpho-structural types of microbial crusts are distinguished: (1) pseudostalactitic microbialites on the roof of intra-reef palaeocaves; (2) mamillated microbialites, found either on the undersides or on the flanks of the bioherms; (3) reticular microbialites in marginal parts of the reefs and between adjacent bioconstructed units; and (4) interstitial microbialites in voids of bioclastic deposits. Thrombolitic crusts developed on various substrates such as corals, bivalves, or bioclasts. The thrombolites formed a dense, clotted and/or micropeloidal microbial framework, in which macro- and micro-encrusters also occur. Variations in accumulation rate strongly influenced the reef morphology, in particular its relief above the sediment surface. The coalescence of the coral-microbialite patches created numerous intra-reef cavities of metre-scale dimensions. The direction of microbial growth, which defined the macroscopic microbialite forms, strongly depended on the position within the reef framework but was also controlled by water energy, accumulation rate and light availability.
Zühlke, R., Bouaouda, M.-S., Ouajhain, B, Bechstädt, T., & Leinfelder, R.R. (2003): Quantitative Meso-/Cenozoic development of the eastern Central Atlantic continental shelf, western High Atlas, Morocco.- Marine and Petroleum Geology 21 (2004) 225–276, Elsevier.
Abstract
The well exposed Late Paleozoic to Cenozoic succession in the western High Atlas (Morocco) documents the early rift to mature drift development of the eastern Central Atlantic continental shelf basin. Vertical sections, depositional geometries and unconformities have been used to reconstruct the basin architecture prior to Atlasian inversion. Two-dimensional reverse basin modeling has been performed to quantitatively analyze the development of the continental shelf between the latest Paleozoic to Early Cenozoic. Basin evolution stages include (i) early rift, Late Permian to Anisian; (ii) rift climax, Ladinian to Carnian; (iii) sag, Norian to Early Pliensbachian; (iv) early drift, Late Pliensbachian to Tithonian; (v) mature drift, Berriasian to Cenomanian; (vi) mature drift with initial Atlasian deformation, Turonian to Late Eocene; (vii) Atlasian deformation; Late Eocene to Early Miocene; (viii) Atlasian uplift and basin inversion, Early Miocene to Recent.
The Late Permian to Late Cretaceous basin development comprises eight subsidence trends of 10–35 Myr duration. Trends were initiated by changes in thermo-tectonic subsidence, which in turn triggered positive and negative feedback processes between sediment flux, flexural and compaction-induced subsidence. Plate-tectonic reconfigurations in the Atlantic domain controlled the thermo-tectonic subsidence history and the basin development of the Agadir segment of the northwest African passive continental margin: (1) major shifts in the sea-floor spreading axis; (2) significant decreases in sea-floor spreading rates; (3) the stepwise migration of crustal separation and sea-floor spreading in and beyond the Central Atlantic; (4) African–Eurasian relative plate motions and convergence rates. During the Early Pliensbachian/Toarcian to Cenomanian the first three plate-tectonic reconfigurations triggered changes in ridge-push forces and modulated the extensional stress field of Central Atlantic plate drifting. Since the Turonian, African–Eurasian relative plate motions and convergence rates represented the dominant control on the thermo-tectonic subsidence history in the Agadir Basin. Major variations in sediment flux and total subsidence characterize the development of the northwest African passive continental margin. The explanation of typical stratigraphic sequences as caused predominantly by sea-level fluctuations, and rough assumptions on sediment input/production and subsidence, is not necessarily applicable to passive continental margins. The methodology applied in this study, including the newly developed tool of ‘Compositional Accommodation Analysis’, allows to develop more rigorous genetic models for the development of continental shelf basins.
Keywords: Continental margin; Basin modeling; Central Atlantic; Morocco; Agadir Basin; Ridge push; Intra-plate compression; Subsidence trends; Compositional accommodation analysis; Mesozoic; Cenozoic
Mancini, E.A., Llinás, J.C., Parcell, W.C., Aurell, A., Bádenas, B., Leinfelder, R.R. & Benson, D.J. (2004): Upper Jurassic thrombolite reservoir play, northeastern Gulf of Mexico.- AAPG Bulletin, v. 88, no. 11 (November 2004), pp. 1573–1602.
Abstract
In the northeastern Gulf of Mexico, Upper Jurassic Smackover inner ramp, shallow-water thrombolite buildups developed on paleotopographic features in the eastern part of the Mississippi Interior Salt basin and in the Manila and Conecuh subbasins. These thrombolites attained a thickness of 58m(190 ft) and were present in an area of as much as 6.2 km2 (2.4 mi2). Although these buildups have been exploration targets for some 30 yr, new field discoveries continue to be made in this region. Thrombolites were best developed on a hard substrate during a rise in sea level under initial zero to low background sedimentation rates in low-energy and eurytopic paleoenvironments. Extensive microbial growth occurred in response to available accommodation space. The demise of the thrombolites corresponded to changes in the paleoenvironmental conditions associated with an overall regression of the sea. The keys to drilling successful wildcat wells in the thrombolite reservoir play are to (1) use three-dimensional seismic reflection technology to find paleohighs and to determine whether potential thrombolite reservoir facies occur on the crest and/or flanks of these features and are above the oil-water contact; (2) use the characteristics of thrombolite bioherms and reefs as observed in outcrop to develop a three-dimensional geologic model to reconstruct the growth of thrombolite buildups on paleohighs for improved targeting of the preferred dendroidal and chaotic thrombolite reservoir facies; and (3) use the evaporative pumping mechanism instead of the seepage reflux ormixing zonemodels as ameans for assessing potential dolomitization of the thrombolite boundstone.
Last changes Nov. 2004 by R. Leinfelder