German Triassic Research Articles

Trace fossils and ichnofabrics on the Lower Muschelkalk carbonate ramp (Triassic) of Germany: tool for high-resolution sequence stratigraphy

In the German Triassic of Thuringia, the Lower Muschelkalk sequence can be subdivided by application of ichnological methods. Three ichnofacies with five ichnofabrics are described. In accordance with the lithological features, trace fossils are found to defining parasequences on the basis of a regular change of bioturbation. Furthermore, it is possible to establish deepening-upward cycles. The reconstruction of parasequences allows the establishment of a high-resolution sequence stratigraphy. The position of the maximum flooding surface can be identified in the Terebratula Member and is developed in a condensed interval. The most significant of the additional major marine flooding surfaces is found at the top of the Upper Oolith Bed, characterized by lithostratigraphy, ichnology, biostratigraphy and parasequence thickness trends.

Fossil reptiles from the Spanish Muschelkalk (mont‐ral and alcover, province Tarragona)

The marine tetrapods from the late Ladinian Spanish Muschelkalk deposits located between the towns of Mont‐ral and Alcover (province Tarragona) are reviewed. The fauna comprises an undetermined thalattosaur, a small cyamodontoid placodont probably referrable to Psephoderma, a possible pachypleurosaur with (if any) affinities to the Serpianosaurus‐Neusticosaurus clade, lariosaur specimens currently referred to Lariosaurus balsami, an incomplete specimen of Lariosaurus calcagnii, an endemic nothosaur (Nothosaurus cymatosauroides), and a possible pistosaur. Collectively, the faunal mix comprises endemic taxa as well as elements with affinities to the fauna of the Alpine and/or Germanic Triassic. The fauna suggests faunal interchange through the Burgundy Gate linking the southern branch of the developing Neotethys to the Germanic Basin.

Outcrop gamma-ray logging and its applications: examples from the German Triassic

Gamma-ray logging of outcrops is a quick and simple, yet powerful technique to better correlate well data with surface geology. It is particularly useful for integrated sequence stratigraphic analysis and for reservoir and aquifer characterisation using outcrop analogues. Three examples from the Triassic of the cratonic German Basin are discussed: (1) shallowing-upward cycles in the Upper Muschelkalk carbonate ramp with retrogradational and progradational stacking patterns; (2) evaporite-to-red bed cycles of the Gipskeuper; (3) fluvial architecture across the terminal alluvial plain system of the Stubensandstein. Such outcrop analog studies help: (1) to calibrate subsurface well log data; (2) to evaluate the heterogeneity of subsurface reservoirs (and aquifers); and (3) to provide improved data for quantitative reservoir modelling.

Palaeoecology and evolution of Mesozoic salinity‐controlled benthic macroinvertebrate associations

Salinity-controlled benthic macroinvertebrate associations are typical of many Mesozoic marginally marine environments. They can be recognized by abiotic criteria (e.g., environmental setting, specific autigenic minerals), by biotic criteria (faunal composition, diversity, shell morphology, size-frequency histograms, taphonomic features, associated micro fauna and microflora), and by isotope geochemistry of shells. Although salinity-controlled associations must have been widespread in the European German Triassic, very little is known about their ecology. They appear to have been dominated by the bivalve Unionites and the brachiopod Lingula. In the Jurassic, brackish-water associations are characterized by bivalves, in particular neomiodontids, corbulids, mytilids, bakevelliids, isognomonids, and oysters. In the Cretaceous, in addition, corbiculid bivalves and gastropods become increasingly abundant. Salinity-controlled benthic macroinvertebrate associations can be used to reconstruct salinity regimes of ancient environments, but emphasis should be placed on an integrated sedimentological and ecological approach, as salinity is rarely the only parameter influencing faunal composition and diversity. Although the species composition of salinity-controlled benthic associations changes distinctly through time, the composition of morphotypes remains surprisingly constant throughout the Mesozoic and up to the Recent, evidence of a conservative evolution of benthic faunas within marginal marine high-stress environments. □Salinity, benthic associations, palaeoecology, Mesozoic.

Sequence stratigraphy and micropaleontology of the Triassic series from the southern part of Tunisia

The Triassic series in the southern part of Tunisia, only known from the oil exploration wells in the Kirchaou area (sandy series from Early Scythian to Ladinian) and in its Djeffara/Dahar-North outcrops (alternating series from Ladinian to Rhaetian) is now subdivided into 10 Depositional Sequences (DS) sensu Vail et al. (1987), T 1 to T 10 corresponding approximately to most of the 3 rd order eustatic cycle from the Haq et al. curve (1987). Within the DS succession, 3 basal discontinuities (or sequence boundaries) appear to be important in Tunisia: the base of T 2, correlated to the “H Discordanz” from the “Germanic Triassic” (intrascythian); the base of T 6 (intracarnian), well-marked by the Sidi Stout angular discordance from Dahar North; the base of T 8 (intranoirian additional DS, previously recognized in Germany) pointed by the cartographic discordance of Low Stand conglomerates. The shallow-water facies from the carbonate Transgressive Systems Tracts of 7 Tunisian DS contain macrofauna, such as Myophoria, and particularly 6 successive benthonic Foraminifera assemblages, F 1 to F 6 giving chronostratigraphic informations as complement of Palynomorphs and Conodonts. Belonging to the genus Meandrospira, Triadodiscus, Aulotortus, Lamelliconus, Endothyranella, Pilamminella, Agathammina, Gandinella etc.…, most of them, commonly used as zone-indices in Europe, are new in Tunisia.

Sequence-stratigraphic framework of the German Triassic

The sequence stratigraphic methodology can be readily applied to the cratonic basin-fill of the classic German Triassic, consisting of shallow-marine to terrestrial mixed carbonate/siliclastic rocks. The whole Triassic succession represents a second-order transgression/regression cycle, built by third-order depositional sequences, systems tracts, and parasequences. Many bounding surfaces represent widely used marker beds, long used in classical lithostratigraphy. Using a synthesis of outcrop, well-log and literature data on stratal geometry, facies, cycle stacking patterns and paleogeography, a regional chart of coastal onlap was constructed. Within the limitations of the presently available biostratigraphic data, the observed cycles appear to correlate fairly well with those in other areas, but include a number of additional sequences not included in the Haq et al. (1988) chart. Comparative analysis of regional onlap curves from different, globally spread Triassic basins, together with an improved biostratigraphy will be necessary to relate the accommodation changes to eustatic versus tectonic and climatic controls and to produce a refined eustatic chart. The German Basin could provide a favourable reference point for such an analysis.

Las mineralizaciones de Pb-Zn-Ba en el Muschelkalk inferior de los Catalánides

The Catalan Triassic is divided into the three characteristie facies of the Germanic Triassic: Buntsandstein, Muschelkalk (Loxver, Middle and Upper Muschelkalk) and Keuper. The base fractures condition the Mesozoic sedimentation, whereby the Catalanid are divided into sedimentary domains, which are separated by transversal faults to the mountain range (ANADON et aL, 1979) (fig. 1). The carbonatic facies from the Catalanid Lower Muschelkalk, Anisien Age, corresponds itself with a ramp depositional environment, in which the paleokarstic levels are frequent, the importance of which development, number of Ihe afected paleokarstic surfaces and materials vanes in accordance with the location of the different domains (MARZO et al., 1983). In this context you can find numerous traces of Pb-Zn-Ba stratabound mineralizations (SAGRISTA et al., 1980, and MATA, 1982) associated with paleokarstic surfaces or algal-mats leveIs (fig. 2). me associated karst mineralizations are singenetic with the karstic filling, Anisiense age. Ihe algal-mats, rich in organic matter, present a high level of Pb-Zn-Ba, Uds elements themselves accumulated into the algal facies while this build up. As fon the origin of this deposits a model named supergen singenetic by AMSTUTZ (1962) is proposed, in `which Ihe minerals themselves deposited at selisame time which the sediments and the mineralizants elements are supergen source. The main contribution of the elements comes from the continent lixiviation (strong anomalies in Pb, Zn, Ba, Cu in the Paleozoic Age) (CASAS, 1979 and FONT, 1983).

Stratégie adaptative de la croissance de Placunopsis ostracina Schlotheim, épizoaire du Muschelkalk supérieur (Trias germanique, Est de la France)

Stratégie adaptative de la croissance de Placunopsis ostracina Schlotheim, épizoaire du Muschelkalk supérieur (Trias germanique, Est de la France)

Palaeoenvironmental interpretation of fluvial red beds by statistical analysis of palaeocurrent data: Examples from the buntsandstein (lower triassic) of the eifel and bavaria in the German basin (middle Europe)

Palaeocurrent data from parts of the Upper Buntsandstein (Lower Triassic) of both the western (Eifel: Kyllburg-Schichten) and eastern (Bavaria: Plattensandstein) margin of the German Triassic Basin (Middle Europe) have been interpreted by circular directional statistics, eigenvalue and eigenvector analysis, autocorrelation analysis and vector trend analysis. Examination of current roses, histograms of normalized vector magnitudes and plots, of circular skewness of the distribution vs. circular kurtosis, together with the palaeocurrent plots indicate bimodal palaeocurrent distributions with bipolar orientations within long, short and very short sedimentary sequences. Subset I of the directional data is interpreted to represent larger, more continuous flows in a high-energy regime of probably perennial type, whereas subset II may represent smaller, partially episodic flows of probably ephemeral type with larger variability in direction and flow regime; transport and sedimentation rates being significantly smaller than during deposition of subset I. A part of the bimodal palaeocurrent distributions within short sedimentary sequences fits rather well into the general transport pattern. Other bipolarities are primarily interpreted as effects of superimposition of channels of different orientations as well as of main channels and crevasse-splay channels, and condensation of deposition from discontinuous or episodic flows. The main mechanism creating the vertical succession of various directions is stacking of different substratum members to multistorey complexes by primary-depositional restriction of formation and/or secondary-erosional removal of topstratum sediments. The occasional occurrence of herring-bone cross-stratification representing bipolarities within very short depositional sequences, testifies to probably episodic and random changes in water surface slopes allowing currents to reverse locally. Examination of long sedimentary sequences by autocorrelation analysis reveals changes of transport directions with time in a sinusoidal manner, indicating a conformable environmental development of the alluvial watercourses which reflects a time-cyclic trend of sedimentation by spatially continuous and time-concordant shifting of the channel system. The results of the statistical analysis enable an enhanced palaeoenvironmental reconstruction of the alluvial network which fits best to a transitional meandering-thalweg-braided channel pattern. Comparison of the statistical results, especially in the light of vector trend surface analysis, clearly reflects the different palaeogeographic positions of both investigated areas, but rules out only minor influences of regionally different palaeoslopes on the alluvial depositional environment, with the basic principles of fluvial style at the western margin (Eifel) generally matching those at the eastern margin (Bavaria) of the German Basin.

Triassic stratigraphy of the southern North Sea Basin

Intensive drilling activity, particularly in the United Kingdom part of the North Sea, has greatly increased our knowledge of the subsurface geology of north-west Europe. The Triassic, perhaps more than any other system, has provided results of a special interest. In this paper a stratigraphical study of the Triassic System of the southern North Sea basin has been undertaken by lithological and palynological analysis. The type Germanic Triassic and the dated Alpine Triassic are briefly reviewed. The facies development of the Germanic Triassic is traced by means of subsurface data from north-west Germany and the northern Netherlands into the North Sea. Further studies of the onshore Triassic of England from subsurface well data and surface outcrop sections are discussed. The results, particularly those from wells in the North Sea, provide a lead to the understanding of the position of the English Triassic of Keuper and Bunter within the framework of the Germanic Triassic.

The stratigraphic classification of the German Triassic and Lower Jurassic by means of spores

The microflora of the Zechstein in Germany is essentially different from that of the Lower Triassic. Palynologically, the Triassic can be subdivided into eleven subunits, the Liassic into four subunits. In the Middle Bunter, part of the Middle Keuper and the Lower Rhaetic thusfar, no palynomorphs have been found. Generally, in the Triassic there are no distinct boundaries between the distinguishable microbotanical subunits.

Elevation and Subsidence; or, the Permanence of Oceans and Continents

IT has been observed, and with increasing frequency within the last few years, that wherever considerable weight is added on any part of the earth's surface, a corresponding subsidence of its crust almost invariably follows. It is generally admitted that nearly the whole of the sedimentary rocks, enormous as their known thickness is, were deposited in shallow water, and therefore in slowly subsiding areas. The Palaeozoic rocks consist mainly of sandy and muddy sediment, with occasional intercalated zones of limestone. They everywhere bear witness to comparatively shallow water and the proximity of land. Their frequent alternations of sandstone, shale, conglomerate, and other detrital materials, their abundant rippled and sun-cracked surfaces, marked often with burrows and trails of worms, as well as the prevalent character of their organic remains, show that they must have been deposited in areas of slow subsidence, bordering continental or insular masses of land.1 Vast thicknesses of strata have been continuously deposited at or near the sea-level. The coal-measures present a series of alternating layers of vegetable matter and brackish water sediments, reaching in the South Wales district a thickness of upwards of 10,000 feet, whose accumulation must have been accompanied almost foot by foot by a corresponding subsidence. The Cambrian sediments accumulated in the British area to a thickness of 23,000 feet apparently without any gieat change in the depth of the sea in which they were formed; and throughout the deposition of the whole of the Silurians, subsidence seems to have kept pace with sedimentation. The Permian again furnishes many instances of sedimentation at or near the sea level sustained throughout great thicknesses, and of frequent alternation of marine and freshwater deposits. Among Mesozoic rocks, the New Red Sandstone furnishes an example of isolated basins of deposit to which the sea found repeated access, though a thickness in places of 3000 feet had accumulated in them. The German Triassic basin is for the greater part of its thickness a succession of terrestrial deposits containing plant-remains. The Jurassic and Cretaceous systems were deposited during interrupted depression of the sea bottom, while the Tertiaries abound with local instances in which subsidence has kept pace with sedimentation.