Pierre Breuer

Stratigraphic palynology of Devonian boreholes from northern Saudi Arabia

This extended abstract describes well-preserved palynomorph assemblages recovered from Devonian strata in five shallow boreholes in the northern part of Saudi Arabia. These fully cored holes overlap stratigraphically to form a 1,640 ft composite section spanning the upper Tawil, Jauf and lower Jubah formations. Only the Jauf and lower Jubah, represented by 188 samples taken over a 1,300 ft stratigraphic interval, are addressed here as the sandy Tawil lithologies are unsuitable for palynological analysis. The 900 feet of alternating of siliciclastic and carbonate units, that together comprise the five members of the Jauf Formation, were sampled comprehensively. However, the Jubah Formation, like the Tawil Formation, is mostly sandstone and is productive palynologically at only two levels separated by a 300 ft barren interval. The age of the sampled succession is assessed using index species from the established Euramerican Devonian palynozonations of Richardson & McGregor (1986) and Streel et alii (1987), and is shown to span the late Early and Middle Devonian.

Morphometric analysis of proposed evolutionary lineages of Early Devonian land plant spores

Early Devonian miospore assemblages from ‘La Gileppe’ (Eastern Belgium) include five varieties of trilete spore belonging to the genus Emphanisporites. These five varieties show a continuous variation of their morphological characteristics. The variation in morphological characteristics can be related to the evolution of morphological features and allows us to define the Emphanisporites micrornatus Morphon. A statistical evaluation of this population highlights the interdependence of almost all morphological parameters. This study proves the increase in size of ornamental and structural parameters over several million years. The biometric changes and the progressive replacement of older morphotypes by younger ones indicate that a temporal link exists between these different varieties. Two phylogenetic hypotheses for the E. micrornatus Morphon are proposed. This morphological evolution is so far observed only on the Eastern Old Red Sandstone Continent and defines a palaeophytogeographic sinuosus–zavallatus Province.

Palaeozoic Innovations in the Micro- and Megafossil Plant Record: From the Earliest Plant Spores to the Earliest Seeds

Recently, major advances have been made in understanding terrestrialization processes and the development of early vegetation. This chapter reviews the major steps in the evolution of early land plants, with focii on cryptospores, trilete spores and on the meso- and megafossil remains of Silurian and Devonian plants. The major morphological innovations of plants and their spores are described. Cryptospores are the earliest fossil record of a terrestrial vegetation cover; the oldest indisputable specimens are observed from Darriwilian (mid-Ordovician) strata in Saudi Arabia and the Czech Republic. The biological affinities of cryptospores are discussed. It is generally agreed that cryptospores were derived mainly from ‘bryophytes’, but some cryptospores may have arisen from early tracheophytes or their immediate ancestors. The earliest trilete spores are Ordovician in age. Most trilete spores are considered to have tracheophyte affinities; we discuss possible relationships between trilete spores and several cryptospores in dyads or monads. The earliest record of plant mesofossils comes from Middle Silurian strata. The evolution and affinities of the major groups of Late Silurian and Devonian land plants are presented within a phylogenetic and a stratigraphic framework.

DESCRIPTION AND MICROSCALE ANALYSIS OF SOME ENIGMATIC PALYNOMORPHS FROM THE MIDDLE DEVONIAN (GIVETIAN) OF LIBYA

Abstract Large acritarchs were recovered from the Awaynat Wanin II Formation in the A1-69 borehole, western Libya at 394.4 m. This sample has been dated by acritarchs and spores as Givetian (Middle Devonian). Two species of acanthomorph acritarchs were recovered that are unusually large for the Paleozoic. The first type, represented by a single specimen, is a new occurrence of a previously described but unnamed form from the Middle Devonian of the Sahara. The second type, which is more abundant, is named as Vanguestainidium cucurbitulum gen. et sp. nov. Biogeochemical analysis using infrared microspectroscopy shows that the wall composition of this new taxon is close to algaenans isolated from the green alga Botryococcus braunii Kützing 1849 although these forms are not morphologically similar. The presence of well-preserved fragile palynomorphs, abundant terrestrially-derived palynomorphs including large megaspores, and rare marine palynomorphs suggests deposition in a low-energy nearshore environment such as a coastal swamp.

Pragian–Emsian palynomorphs from the Cordobés Formation, Norte Basin, Uruguay: stratigraphically restricted and regionally correlative palynological events in the cool-water Malvinokaffric Realm

ABSTRACT Palynological analyses of core samples from Achar E1 well (Norte Basin, Uruguay), yield abundant well-preserved Lower Devonian assemblages. Four new acritarch species (Bimerga acharii, Bimerga nuda, Polyplanifer turbatum and Veryachium woodii) are described. Two of them belong to the Devonian bipolar genus Bimerga Wood 1995, being the oldest representatives of this lineage. Generic diagnosis of Bimerga is emended to fully document species variation. The Devonian recurrence of bipolar symmetry among acritarchs is discussed. New Bimerga species were recorded in the Cordobés Formation, the principal potential hydrocarbon source rock in the basin. These species have biostratigraphic value, confirmed by studies from Argentina, Brazil and Bolivia. All stratigraphic records are from the Gondwanan Malvinokaffric Realm. Associated to Bimerga appear other acritarchs, prasinophycean algae, chitinozoans, and miospores. Miospore assemblage is comparable to those previously described in part of the Ponta Grossa Formation (Paraná Basin, Brazil), confirming a late Pragian–early Emsian age span.

Imaging of Vanadium in Microfossils: A New Potential Biosignature

The inability to unambiguously distinguish the biogenicity of microfossil-like structures in the ancient rock record is a fundamental predicament facing Archean paleobiologists and astrobiologists. Therefore, novel methods for discriminating biological from nonbiological chemistries of microfossil-like structures are of the utmost importance in the search for evidence of early life on Earth. This, too, is important for the search for life on Mars by in situ analyses via rovers or sample return missions for future analysis here on Earth. Here, we report the application of synchrotron X-ray fluorescence imaging of vanadium, within thermally altered organic-walled microfossils of bona fide biological origin. From our data, we demonstrate that vanadium is present within microfossils of undisputable biological origin. It is well known in the organic geochemistry literature that elements such as vanadium are enriched and contained within crude oils, asphalts, and black shales that have been formed by diagenesis of biological organic material. It has been demonstrated that the origin of vanadium is due to the diagenetic alteration of precursor chlorophyll and heme porphyrin pigment compounds from living organisms. We propose that, taken together, microfossil-like morphology, carbonaceous composition, and the presence of vanadium could be used in tandem as a biosignature to ascertain the biogenicity of putative microfossil-like structures. Key Words: Microfossils-Synchrotron micro-X-ray fluorescence-Vanadium-Tetrapyrrole-Biosignature. Astrobiology 17, 1069-1076.