Description and Microscale Analysis of Some Enigmatic Palynomorphs From the Middle Devonian (Givetian) of Libya

Abstract

International audienceLarge 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

A Givetian tintinnid-like palynomorph from Libya

“…In order to prevent the destruction of the large palynomorphs, samples have been submitted to a specific laboratory treatment, "softer" than the usual technique used for miospores. The technical process of the sample has been described by Steemans et al(2009). The specimens observed here are exceptionally well preserved.…”

“…While selecting megaspores under a dissecting microscope, two kinds of enigmatic large palynomorphs have been observed. The first one has been identified as a very large acritarch: Vanguestainidium cucurbitulum Steemans et al 2009. The second kind, a vase-shaped palynomorph, is described here.…”

“…Samples have been collected from cores of the A1-69 borehole drilled by SHELL in 1959 through the Ghadamis Basin (see Text- Figure 1 in Steemans et al 2009) and provided during the eighties to the palynological laboratory of the Liège University thanks to the courtesy of D. Massa. Previous palynological results on this borehole have been published (Loboziak et al, 1992;Loboziak and Streel, 1989;Steemans et al, 2009;Streel et al, 1990). Some new levels have been investigated for a PhD research work on miospores (PB) and for a master degree on megaspores (FDVDG).…”

“…In order to chemically establish the biological affinity of the enigmatic specimens studied here, we undertook FTIR microspectroscopic analysis on one specimen of N. reticulata (for technical aspect see in Steemans et al, 2009). Unfortunately, no more palynological material from the Lybian sample is available, and additional analyses are impossible.…”

Morphology of the megaspore Lagenoisporites magnus (Chi and Hills 1976) Candilier et al. (1982), from the Carboniferous (lower Mississippian: mid-upper Tournaisian) of Bolivia

“…It is considered that these deposits have been influenced by marineglacial and deltaic sedimentation (Isaacson and Díaz Martínez 1995). Palynological assemblages that contained the studied megaspores were similar in their composition and preservation in both boreholes (di In order to prevent megaspores destruction, samples were exposed to a 'gentler' laboratory treatment (see Steemans et al 2009). For each sample, 20-30 g of sediment were crushed in sizes greater than 5 mm and macerated using 30% hCl for 8 hours followed by 45% hF for 48 hours.…”