Jean Broutin

Isotope reconstruction of plant palaeoecology. Case study of Cenomanian floras from Bohemia

Palaeoenvironments inferred from stable carbon isotope ratios of fossil plants collected from various environments of the Cenomanian of Bohemia were compared with palaeobotanical and sedimentological data to test the use of isotope ratios as a record of local palaeoenvironments and fossil-plant ecology. A number of isotope and biogeochemical patterns suggested that stable carbon isotope ratios in the Cenomanian plants from Bohemia have not been significantly affected by diagenesis. Stable carbon isotope ratios of the palaeoflora from one of the sections studied were used as a reference for a non-stressed habitat since both sedimentological and palaeobotanical evidence suggested that the fossil flora underwent no environmental stresses that could have influenced its δ13C values. Comparisons of δ13C values of the other palaeofloras with that of the reference section, allowed inference of the palaeoenvironmental stresses undergone by fossil plants. These palaeoenvironmental patterns deduced from 13C/12C ratios are in agreement with the palaeoenvironments previously reconstructed by sedimentological and palaeobotanical studies. Combining evidence from those studies with isotope data provided detailed insights into the palaeoecology of the plants studied. Finally, stable carbon isotope ratios allowed precise characterisation of the ecology of the best-represented species of the deposits studied, the ginkgoalean plant Eretmophyllum obtusum and the conifer Frenelopsis alata, which were quite common in the salt-marsh environments in Europe during the Cenomanian. Hence, stable carbon isotope ratios can help in evaluating the environmental stresses undergone by fossil plants and the combination of these results with palaeobotanical and sedimentological data can provide detailed insights into fossil-plant ecology.

Permian freshwater stromatolites associated with the conifer shoots Cassinisia orobica Kerp et al. — a very peculiar type of fossilization

Foliated shoots of Cassinisia orobica Kerp et al., 1996 are fossilized by a combination of two processes, i.e. by tufaceous/stromatolitic encrustation, preserving their external morphology, and the formation of sparite crystal which include leaf tissues and vascular bundles. Encrustation took place in two phases, interrupted by a period of emersion. The arrangement of the stromatolitic laminations and the aspect of the crystals and their inclusions allow a comparison with some specific recent forms of Schizothrix. On the lake bottom, cavities in the axes and leaves were finally filled with internal sediment, gypsum and diagenetic sparite.

Discovery of Latest Carboniferous-Early Permian radially symmetrical peltaspermaceous megasporophylls from Europe and North Africa

Abstract In recent years several types of peltaspermaceous ovuliferous organs were described from the Permian of the Northern Hemisphere. The earliest peltasperms had fan-shaped bilaterally symmetrical megasporophylls. In this note, we describe radially symmetrical ovuliferous discs discovered for the first time in the Lower Rotliegend of the Saar–Nahe Basin, Germany (Latest Carboniferous), and the uppermost Lower Permian of Central Morocco. The implications of such discoveries in terms of early peltasperm radiation and geographic distribution are discussed.

Pedological nodules with cone in cone structure in the Permian of Sierra Morena (Spain) and Central Morocco

The occurrence of (1) calcite aureoled quartz, and (2) vertical cylindrical features (“rhizocretions” in literature), and subspherical or unevenly shaped nodules resulting from the coalescence of smaller elements (“nodular calcrete”) is reported in various Permian continental series from Western Europe (Sierra Morena, Spain) and North Africa (Central Meseta of Morocco). These features are developed in flood plain pelites (mudstones) interbedded with gravelly channel material and debris flow deposits. These nodules are interpreted as pedological concretions formed in hydromorphic soils under tropical climatic conditions with contrasting seasons and not under desertic environments.These nodules show the close association of a classical micritic/microsparitic internal sediment with areas where cone in cone structures prevail. The distribution of facies suggests an early pedogenic origin. At this early stage, vegetal roots were alive (probably Cordaitales) and were encrusted by the redistribution of calcitic components in the soil profile resulting from oscillations of the water table. The cone-in-cone structure probably resulted from bacterial activity.

Aspects of Permian palaeobotany and palynology. XIV. A new form-genus of broad-leaved late carboniferous and early Permian Northern hemisphere conifers

Abstract This paper deals with two conifer species with a leafy axis of penultimate order with distichous ultimate branches and broad, non- or hardly decurrent leaves from the Lower Permian of Europe and North Africa. These species are accomodated in the new form-genus Feysia and they are described as F. minutifolia sp. nov and F. puntii sp. nov. Feysia is compared with other Late Palaeozoic conifer taxa and the form-genus Hermitia Kerp et Clement-Westerhof is emended.

Early Permian silicified floras from the Perdasdefogu Basin (SE Sardinia): comparison and bio-chronostratigraphic correlation with the floras of the Autun Basin (Massif central, France)

ABSTRACT In the Perdasdefogu Basin (Ogliastra, Sardinia) plants occurring in angular cherts are preserved as siliceous permineralizations. The plant assemblage consists of the genera Sphenophyllum, Arthropitys, Astromyelon, Palaeostachya, Pecopteris, Scolecopteris, Stewartiopteris, Psaronius, Ankyropteris, Anachoropteris; furthermore, probable medullosan wood and ovules, cordaitean stems, leaves and ovules, and Dadoxylon wood have been recorded. Arborescent marratialean ferns are the dominant elements with Pecopteris and Scolecopteris leaves being the most common; the calamiteans are the second in abundance. Generally the chert blocks contain a large number of plant fragments — roots and leaves are being almost equally represented — suggestive of a coal ball-like plant accumulation. More rarely a chert block may consist of a single plant part, for example a piece of wood. The preservation and accumulation of the plants are closely comparable to the silicified plant assemblages described from the Lower Permian of Autun and the upper Pennsylvanian of Grand-Croix (Massif central, France) and from the Early Permian Döhlen Basin (Germany). It is certainly significant that the assemblage from the Perdasdefogu Basin is dominated by tree ferns and calamites like the coeval silicified vegetation from Autun. However, like in Autun, the permineralized flora contrasts with the underlying compression floras dominated by conifers and peltasperms. The Perdasdefogu macroflora record suggest a middle-upper Autunian age which corresponds to the Surmoulin and Millery formations of the Autun Basin. This is in agreement with the Asselian-Sakmarian transition as pointed out by the amphibian species found in the same formation, and perfectly correlatable with the same association found in Gottlob-lake (Thuringian Forest Basin). Because of its rich fossil content, the Perdasdefogu Basin represents a reference succession for the Autunian of the entire westernmost palaeo-Tethyan domain and its macrofloral record.

Palaeoecology of non marine algae and stromatolites: Permian of France and adjacent countries

Abstract Some Permian, continental basins from Algeria, Morocco, France, Italy, Germany and Poland reveal algal remains and stromatolites, mainly during Lower Permian, but also during Middle and Upper Permian. The algae belong to 8 morphogenera and 12 morphospecies. Two species are new. The taxonomic attributions are difficult, even if some species resemble living species. The algae make unorganized masses, or laminated builtups (stromatolites, oncolites, oolites). Algal masses and stromatolites are contained in fluviatile sediments (active or abandoned channels) and lacustrine deposits (playas, ephemeral lakes shorelines, lakes several meters or decameters deep). Considering the sedimentological context, the water salinity could range from karstic springs (hard water) to evaporic ephemeral lakes (playas).