Preservation of phosphatic wood remains in marine deposits of the Brentskardhaugen Bed (Middle Jurassic) from Svalbard (Boreal Realm)

Abstract

International audienceThe exceptional record of well-preserved wood remains from the Middle Jurassic of Svalbard is studied from the taphonomic point of view. These remains were recovered from the Brentskardhaugen Bed, a conglomerate with phosphatic nodules, which constitutes the record of the eroded deposits corresponding to the Toarcian-Early Bathonian gap. The wood remains occur in the cores of these nodules. These wood fragments are preserved as phosphate (francolite) and as charcoals. The well preservation allows us to identify xenoxyloid cross-field pits and xenoxylean pitting on the radial wall of tracheid, characterizing the species Xenoxylon phyllocladoides. Phosphatic nodules originated as the result of early phosphate precipitation filling the inter-particle pore space of the sandy quartz sediment around the wood fragments (and other organic-rich nucleation centers) below the sediment-water interface. This phosphatization involved a sudden burial of the wood remains in the sea-bottom, the subsequent decay of the lignin, and a fast growth of carbonate fluorapatite forming phosphatic inner moulds. Fossil microbial biofilms induced the phosphatization. The dissolution/decay of the lignin is not possible in charcoal, and phosphatic casts did not develop in charcoalified parts. Some remains were not totally charred, with the lignin preserved only in reduced relicts that were later replaced by phosphate. The phosphate precipitation occurred in recurrent episodes during the Toarcian-Callovian as a result of distinct sea-level rises and the associated nutrification of the shelf. The phosphatic nodules were developed and reworked during the transgressive-regressive cycle of the Toarcian-Early Bathonian, as well as during the final transgression of the Late Bathonian-Earliest Callovian, which resulted in the Brentskardhaugen Be

Origin and paleoecology of Middle Jurassic hiatus concretions from Poland

“…Although most hiatus concretions described from the fossil record (see above) are calcitic, some have a different mineralogy. Phosphatic hiatus concretions are known from, for example, the Middle Jurassic of Svalbard (Bäckström and Nagy 1985;Reolid et al 2010b), the Upper Cretaceous of Ireland (Marshall-Neill and Ruffell 2004) and Kazakhstan (see Olszewska-Nejbert 2007), and the Neogene of California (Garrison et al 1988). Hiatus concretions may even form in Recent times.…”

Fluid flow properties of the Wilhelmøya Subgroup, a potential unconventional CO2 storage unit in central Spitsbergen

“…The Norian to Bathonian Wilhelmøya Subgroup was deposited as a highly condensed unit (now approximately 25 m thick) in an open marine-dominated inner-shelf to shore-face environment (Bjaerke & Dypvik, 1977;Wierzbowski et al, 1981;Mørk et al, 1982Mørk et al, , 1999Bäckström & Nagy, 1985;Maher et al, 1989;Krajewski, 1990;Krajewski, 2000aKrajewski, , 2000bNagy & Berge, 2008;Reolid et al, 2010;Mørk, 2013;Rismyhr et al, in press). This inferred depositional environment has the potential to introduce stratigraphic closures and pinchouts, i.e., sand bodies may be lenticular in shape up dip and/or along strike of the depositional slope.…”

Mineralogy of Non-Silicified Fossil Wood

“…Availability of phosphorus as a nutrient is commonly a limit for growth in biotic communities; low concentrations of this element in most ground and surface waters explain the scarcity of phosphatized petrified wood. High levels of dissolved phosphorus in some marine environments explain occurrences of phosphatized wood, e.g., Middle Jurassic wood from Svalbard (Boreal Realm) [21,22] and the Pacific sea floor [23]. Plant remains preserved in freshwater phosphatic nodules near Queensland, Australia have been inferred to result for phosphate dissolved from abundant insect remains and local guano deposits [24].…”

“…These components are common in marine environments, sometimes producing extensive phosphorite deposits [87]. Reports of phosphatized wood commonly describe occurrences in marine sediments [10,[21][22][23]. Phosphatized wood is also known from terrestrial and lacustrine environments [2,20,[26][27][28][29][30], where the source of phosphorus is more difficult to interpret.…”