Raimund Feist

Rare earth elements in old biogenic apatites

Abstract The REE distributions in individual Upper Devonian conodonts have been measured by ion probe. The patterns of all analyzed conodonts are enriched in middle REE (Eu-Gd) and have a weak or no Ce anomaly. Concentrations and La Yb or La Sm ratios vary very little within or among individuals from the same zone, which suggests that uptake of labile REE from sediments was essentially quantitative. Therefore, the REE signature of the primary carriers, probably organic and oxyhydroxides particulates from marine suspensions, was efficiently transferred to biogenic apatites and survived late diagenetic processes. REE patterns of conodonts do not resemble those of present-day seawater and post-Cretaceous biogenic phosphates, which are typically depleted in Nd and Sm with a negative Ce anomaly. Since REE distributions in the modern water column mimic those of nutrients, we assume that, in pre-Cretaceous seawater, they were not controlled by surface biological activity. We assume instead that REE in pre-Cretaceous seawater can be explained by mechanism of desorption-adsorption on particle surfaces. Progressive extraction of LREE from river water by oxyhydroxides leads to precipitates enriched in middle REE. A simple quantitative model was calculated in order to illustrate the proposed mechanism.

Magnetostratigraphy susceptibility of the Frasnian/Famennian boundary

Magnetosusceptibility event and cyclostratigraphy (MSEC) is used to establish a non-polarity-based magnetostratigraphy susceptibility (MSS) between the stratotype region for the Frasnian/Famennian (F/F) boundary sequence in the Montagne Noire of southern France, the eastern Rheinisches Schiefergebirge of Germany, Belgium, the eastern Anti-Atlas of Morocco, and the Arbuckle Mountains of southern Oklahoma (USA). Despite differences of depositional environment, the MSS is remarkably consistent and can be described in the context of a hierarchy of magnetozones that allow the extension of correlation away from the Montagne Noire reference section. The nature of the controls on the influx of iron into the marine system produces a natural hierarchy of at least seven orders or magnetozones designated MSZ1, MSZ2, MSZ3, MSZ4, MSZ5, MSZ6, and MSZ7. These are characterized in terms of the magnitude of their duration. The MSS reference section of choice for the F/F boundary is the well-known Trench C at La Serre (LSC) in the northeastern Montagne Noire of southern France. The F/F boundary is located at the lower boundary of magnetozone La Serre Iα3b at La Serre as well as in all other sections studied. MSZ4 and MSZ5 magnetozones are used to establish intra- and inter-regional correlation between the reference sequence and the other regions. The base of the Upper Kellwasser event is as variable within the MSS zonation as it is within the biostratigraphic zonation, as is the position of the Lower Kellwasser event.

Chitinozoan bio-event in the Frasnian-Famennian boundary beds at La Serre (Montagne Noire, Southern France)

Abstract Chitinozoans and other palynomorphs have been investigated in Frasnian-Famennian boundary beds from trench C at La Serre (Montagne Noire, Southern France). This section is located some 30 km from the Coumiac quarry containing the Global Stratotype Section and Point (GSSP) for the base of the Famennian. At La Serre, the Frasnian-Famennian (F-F) boundary falls within interbedded anoxic dark shales and limestones. This lithology proves to be more suitable for palynological investigations than the reddish nodular limestones of the F-F stratotype in the Coumiac section, which are virtually devoid of organic matter. At La Serre, the uppermost meter of Frasnian deposits, corresponding to the Upper Kellwasser Event level, contains only a few chitinozoans but other palynomorphs, especially tasmanaceans ( Maranhites ) proliferate in some horizons. Conversely, the most basal Famennian bed yields an exceptional number of chitinozoans (up to 19,000 specimens per gram of rock), a few tracheids, but virtually no tasmanaceans. The absence—or the extremely low numbers—of miospores and acritarchs in these F-F boundary beds seems related to the distal position of the deposition site. We have compared the fluctuation of the chitinozoan abundance both with the abundance of the other palynomorphs, and with that of the conodonts present in the same samples. These data, collated with sedimentological and palaeoecological information document the relationships between the anomalous abundance of the chitinozoans and the latest Frasnian-earliest Famennian mass extinction. It is concluded that the exceptional chitinozoan concentration in the most basal Famennian bed at La Serre is not related to a sorting process generated by turbidity currents or by a temporary increase in the hydrodynamic energy at the water-sediment interface. It corresponds to the conjunction of a high production of chitinozoans, a very low rate of destruction of the vesicles and minimal dilution of the deposit by terrestrial mineral input. The environmental factors leading to such an exceptionally high record of chitinozoans are discussed with a particular attention to consequences of the late Frasnian mass extinction.

Chapter 7Subdivision of the terminal Frasnian linguiformis conodont Zone, revision of the correlative interval of Montagne Noire Zone 13, and discussion of stratigraphically significant associated trilobites

Abstract The terminal zone of the Frasnian standard conodont zonation, the linguiformis Zone has been subdivided into alower part defined by the total range of Palmatolepis linguiformis and an upper part defined by the absence of the nominal species together with the rare occurrences of Pa. ultima (= Pa. praetriangularis) and Ancyrognathus (= Ancyroides) ubiquitus . This subdivision has proved to be effective in sections on different continental blocks. Furthermore, the two subdivisions correlate exactly with subdivisions formally recognized herein of Montagne Noire Zone 13 (13b and 13c). The lower boundary of the linguiformis Zone lies closely below the base of the Upper Kellwasser event bed, the top of which coincides with the end-Frasnian extinction. Nonetheless, prominent gaps in the geographic distribution of Pa. linguiformis have led to some difficulty in the identification of the zone. These gaps have been partially closed by discoveries of the species in areas where it was unknown until now, notably the central Moroccan Meseta and especially the Frasnian/Famennian boundary-stratotype section at Coumiac Upper Quarry in the Montagne Noire, southern France. Nevertheless, anomalous areas of absence, such as the Anti-Atlas Mts. of southern Morocco and western Canada still exist. The trilobite Palpebralia brecciae is widespread in Europe, North Africa, and Australia, providing evidence for correlation of the lower part of the linguiformis Zone in sections where the nominal conodont species has not been found. Analysis of variation in the relative abundance of the principal conodont genera leads to the conclusion that no substantial difference exists in the conodont associations among representative sections in four of the continental blocks.

Larval morphology and ontogeny of a Late Devonian phacopid with reduced sight from Thuringia, Germany

Exceptionally rich and well-preserved silicified exuviae comprising numerous immature growth stages allow the tracing of detailed morphological and morphogenetical features of the reduced-eyed phacopid species Cryphops ? ensae (Richter and Richter, 1926) from the latest Famennian of Thuringia (Central Germany). Ontogenetic features of this species are more similar to those of Phacops than to Trimerocephalus.

FIRST CARBONIFEROUS PROTASPID LARVAE (TRILOBITA)

Abstract The recovery of well-preserved silicified larvae from the early Tournaisian of Montagne Noire, southern France, allows the first description of the early ontogeny of proetoid trilobites, survivors of the end-Devonian Hangenberg extinction event. The fauna comprises various taxa that can only partly and tentatively be assigned to the genera Liobolina, Diacoryphe, and Pedinocoryphe without specific attribution. The close resemblance of these larvae to previously described proetoid larvae from the Ordovician and Devonian emphasizes the ontogenetic homogeneity of this superfamily. Moreover, it supports the view that the Proetida is composed of two clades: the Aulacopleuroidea/Bathyuroidea group and the Proetoidea. The Carboniferous anaprotaspides exhibit an unusually wide size-range that may provide evidence of the acquisition of an extended planktonic period in the early ontogeny of at least some Carboniferous proetoids. This change in the ontogenetic strategy may have enabled proetoid trilobites to survive during the end-Devonian biocrises.

Variation in the eye of Acuticryphops (Phacopina, Trilobita) and its evolutionary significance: a biometric and morphometric approach

Abstract Distributional patterns of eye lens variation in different morphs of the phacopine trilobite Acuticryphops acuticeps (Kayser 1889) are investigated. The specimens were collected from the latest Frasnian preceding the Upper Kellwasser (UKW) global extinction event in the Frasnian– Famennian (Late Devonian) stratotype section at Coumiac, southern France. In six successive populations a gradual reduction in the mean number of lenses occurs within the short time span of a single conodont Zone. This morphological change cannot be imputed either to the size of individual specimens or to variation in cephalic morphology. Thus morphs with different numbers of eye lenses are considered intraspecific. However, the intrapopulational percentage relation between morphs does not remain constant, as the coefficient of variation in lens number continuously increases from one population to the next. Cases of individuals with asymmetric eyes appear in the two latest assemblages prior to the UKW level. The fact that the total variation of the shape of the cephalon is not affected in these assemblages suggests that the morphological changes observed in the visual complex may account for the relaxation of selective pressures on this trait. Such a change in the regime of selection would have been accompanied by a lessening of the processes that control the development of this trait. As the phenomenon of eye reduction is not restrained by local conditions at Coumiac (Montagne Noire) but occurs contemporaneously to various extents in other crustal blocks such as Rhenish Slate Mountains (Avalonia), Thuringia (Armorica), and Morocco (Northern Gondwana), it is considered as constituting an adaptation to global eustatic deepening that occurred in the terminal Frasnian just before the global extinction event.

THE DEVONIAN STYGINID TRILOBITE PARALEJURUS, WITH NEW DATA FROM SPAIN AND MOROCCO

Abstract A review of all known species of the scutelluine trilobite Paralejurus corroborates its distinction from contemporaneous representatives of the subfamily. The overall morphology together with observed habitat conditions favor the view of its having had a semiendobenthic life habit analogous to that of many earlier illaenids. Particular features that are shared with the Silurian Rhaxeros, such as the pronounced convexity of the exoskeleton and the wide axis, are considered as homeomorphies related to a burrowing lifestyle rather than the expression of phyletic relationships. The data set based on conodont biostratigraphy reveals earliest occurrences of Paralejurus in the Pragian and the disappearance of last representatives at the base of the Middle Devonian. In the lower Early Devonian Paralejurus was restricted to the North Gondwana margin and related microplates. Later and in consequence of geodynamic plate movements that led to the reduction of oceanic barriers, the Paralejurus dormitzeri group succeeded in spreading to the epicontinental margin of Laurussia in Late Emsian times. New material from Southern Morocco, including Paralejurus spatuliformis n. sp. and Paralejurus tenuistriatus n. sp., and the first representative of the genus from Spain, Paralejurus carlsi n. sp., are described. Paralejurus dormitzeri rehamnanus Alberti, 1970 is considered an independent species emphasized by the discovery of complete exoskeletons.

Search for impact remains at the Frasnian–Famennian boundary in the stratotype area, southern France

In order to detect whether the end-Frasnian worldwide biotic crisis is related to an extraterrestrial impact, the global stratotype section of the Frasnian-Famennian boundary and auxiliary sections within the stratotype area have been examined for impact indicators: iridium. Ni-rich spinel bearing spherules and glassy microtektites. This area is particularly well suited to the search for discrete events because it exhibits biostratigraphically continuous sections of sedimentologically homogenous off-shore deposits. Different environmental settings on oxygenated deep-water seamounts, such as the stratotype section at Coumiac, and in oxygen-depleted depressions (La Serre section) are available. The latter is investigated in more detail because it is the least condensed across the boundary, which is determined by the first occurrence of the typical morphotype of Palmatolepis triangularis, the indicator of the first Famennian conodont biozone. Samples from the biostratigraphically defined boundary and adjacent levels failed to provide significantly high Ir values and no Ni-rich spinel or microtektite has been recovered. This is in contradiction with the results of earlier investigations carried out by H. Geldsetzer on the same section. In contrast, the values of Ir concentrations that we measured are always very low or not detectable. The small overabundances observed in some samples, which are about two orders of magnitude lower than what is currently observed at the Cretaceous-Tertiary boundary, are probably due to the accumulation of the normal flux of cosmic dust during periods of relatively low depositional rates or to a terrestrial origin. At present, we have no evidence that an extraterrestrial impact occurred at the F-F transition.

Discovery of Famennian trilobites in Australia (Late Devonian, Canning Basin, NW Australia)

Abstract For the first time a Famennian (Late Devonian) trilobite fauna is described from Australia. It has been recovered from sandy cephalopod and crinoid limestones of the Virgin Hills Formation in the Canning Basin (NW Australia). Small assemblages dated as latest crepida to rhomboidea Zone include two new Phacopinae (Babinops planiventer nov. gen. nov. sp. and Trimerocephalus tardispinosus nov. sp.) and a proetid: Cyrtosymbole (Crytosymbole) playfordi nov. sp. These forms are closely related to contemporaneous European and North African forms. Particular features such as the absence of vincular furrows and the retarded presence of genal spines are discussed. The occurrence of mainly large-eyed forms accords with euphotic level bottom conditions in the distal reef slope environments of the Canning Basin. Steps in post-event recovery after the end-Frasnian trilobite crisis are reviewed; the possible origin of oculated crytosymbolines from shallow-water ancestors is briefly discussed.