Three-dimensional Preservation Research Articles

Ultrastructural and chemical studies on Oligocene fossil wood from Bovey Tracey, Devon, UK

A specimen of Oligocene fossil wood from Bovey Tracey, Devon, UK, was examined using microscopical and chemical techniques. Although macroscopic examination clearly established that it was fossil wood, as opposed to fossil charcoal, both transmission electron microscopy and scanning electron microscopy of its fine structure revealed that the previously stratified cell walls were apparently homogenized; a characteristic previously taken to be diagnostic of fossil charcoal. This fossil thus represents the only known example so far of fossil wood which was definitely not exposed to charring or charcoalification, yet possesses homogenized cell walls. Examination of the fossil wood using solid state 13C nuclear magnetic resonance suggests that the specimen was depleted in carbohydrate carbon and enriched in aromatic carbon and carbon from non-carbohydrate wood components when compared with NMR spectra of native ligno-cellulose. It is suggested that conditions in the unusual deposition environment of a highly acidic freshwater lake, could have directly or indirectly resulted in the cell wall homogenization. The existence of this unusually preserved specimen suggests that the differentiation between fossil wood and fossil charcoal requires the use of a number of characteristics; fossil charcoal being recognised as possessing homogenized cell walls, three-dimensional anatomical preservation, high reflectance under reflected light microscopy, and macroscopical resemblance to modern charcoal. It is not suggested here that this material represents a transition stage between wood and non-pyrolysis fusain (e.g. degradofusinite), but rather that caution needs to be exercised when identifying the mode of preservation/fossilization of plant material based on a limited number of physicochemical characteristics.

Three‐dimensional preservation of arthropod integument from the Middle Cambrian of Australia

Three-dimensional preservation of arthropod soft integument occurs in Middle Cambrian sediments of the Georgina Basin, western Queensland, Australia. The beds are referred to the Monastery Creek Phosphorite Formation, Gowers Formation, Inca Shale Formation and Devon-court Limestone Formation. The finds include arthropod type-A larvae previously described by Muller & Walossek and several complete appendages, possibly of early Palaeozoic ‘ostracodes’, as well as indeterminable cuticular remains. The Australian sediments were in part deposited under high water-energy conditions, whereas previously known occurrences of three-dimensional soft-integument preservation have been from environments of lower water energy. Such preservation may thus be more widespread in the Early Paleozoic than hitherto known. □Phosphatization, arthropods, type-A larvae, appendages, Middle Cambrian, Geogina Basin, Australia, three-dimensional preservation.

Cambrocaris baltica n. gen. n. sp., a possible stem‐lineage crustacean from the Upper Cambrian of Poland

Bodily preserved, secondarily phosphatized arthropods discovered in drill cores on He***l Peninsula, northern Poland, and in its vicinity date from the Upper Cambrian. Comparisons between a group of arthropods of the Upper Cambrian of Sweden recognized as stem-lineage crustaceans indicate that one of these new forms, Cambrocaris baltica n. gen. n. sp., also represents a derivative of the early phase of crustacean evolution prior to the crown-group level. The material also yielded a specimen identified as Skara minuta Muller & Walossek, 1985, hitherto known only from Vastergotland, Sweden, and two limb fragments which cannot be assigned to species. □Crustacea, stem-lineage derivatives. Phosphatization, three-dimensional preservation, Upper Cambrian, Alum shales, ‘Orsten’, northern Poland.

Uric acid salts of magnesium: crystal and molecular structures and thermal analysis of two phases of Mg(C 5H 3N 4O 3) 2 · 8H 2O

Two structurally different phases of a uric acid salt of magnesium, Mg(hydrogenurate) 2 · 8H 2O, have been prepared by crystallization from solution at pH = 7.5–8.0 and were investigated by x-ray crystallography, thermal analysis, and ir spectroscopy. Both phases are monoclinic, space group P2 1/c with a = 9.573(2), b = 14.627(3), c = 7.170(1) Å, β = 101.91(1)° (phase I) and a = 10.397(2), b = 14.306(3), c = 6.732(1) Å, β = 104.64(2)° (phase II). The crystal structures of both phases (R = 0.053 and 0.051, respectively) contain isolated octahedral [Mg(H 2O) 6] 2+ cations, hydrogenurate monoanions, and two molecules of water of crystallization per formula unit. The structural formula representing these facts is [Mg(H 2O) 6] (hydrogenura-te) 2·2H 2O. The tautomeric form of the hydrogenurate molecule corresponds to the tri-keto form of uric acid deprotonated at N(3). Differences in bond length between uric acid and the hydrogenurate molecule may be described in terms of three additional resonance structures distributing the formal negative charge at N(3) within the pyrimidine (but not the imidazole) ring. Deprotonation at N(3) significantly decreases the internal C-N-C angle at N(3). Alternating pairs of medium-strong intermolecular N-HO hydrogen bonds lead to infinite chains of hydrogenurate molecules extending along the b axis of the unit cells in both phases. The main difference between the two phases lies in their stacking pattern of the hydrogenurate molecules. Infrared data confirm the hydrogen bonding characteristics resulting from the crystal structure analysis. Thermogravimetric measurements and differential scanning calorimetry data show that the dehydration of both phases occurs in two distinct steps with Mg(hydrogenurate) 2.6H 2O as an intermediate phase. The first dehydration step (−2H 2O) is a topotactic reaction with three-dimensional preservation of the main structure elements of the octahydrate in the structure of the hexahydrate.

Palaeobotany and petrology of a Middle Jurassic ironstone bed at Wrack Hills, North Yorkshire

SUMMARY The palaeobotany and petrology are outlined of a recently discovered Middle Jurassic (Saltwick Formation) ironstone bed at Wrack Hills, a locality near Runswick Bay, North Yorkshire. The plant fossils are remarkable for their excellent preservation in three dimensions. Similar material was much collected in the last century, including specimens from Runswick Bay, but after 1910 the localities were thought to have been entirely lost. The species diversity at the new or perhaps newly available old locality considerably exceeds that obtained by the old collectors, including about five new species out of the total of 31 collected. Androstrobus cones preserved in three dimensions and with well-preserved pollen in situ are reported; new material of Williamsonia gigas is discussed and a revised reconstruction of its mature ‘flower’ proposed; and three-dimensionally preserved leaves of Solenites are recorded. These prove to be circular in transverse sectional outline rather than elliptical as previously reconstructed. There is an intimate association of clay minerals with the plant remains in such siderite-rich ironstone beds. The clays (kaolinite and dickite) were evidently deposited within voids in the organic material during diagenesis and the temperatures required for their recrystallisation indicate former burial of the sediments to a depth of some 2 km. The three-dimensional preservation of the plant organs despite this burial indicates that the ironstone became lithified early in diagenesis.