title: Geochemical Evidence of the Seasonality, Affinity and Pigmenation of Solenopora jurassica.
abstract: Solenopora jurassica is a fossil calcareous alga that functioned as an important reef-building organism during the Palaeozoic. It is of significant palaeobiological interest due to its distinctive but poorly understood pink and white banding. Though widely accepted as an alga there is still debate over its taxonomic affinity, with recent work arguing that it should be reclassified as a chaetetid sponge. The banding is thought to be seasonal, but there is no conclusive evidence for this. Other recent work has, however demonstrated the presence of a unique organic boron-containing pink/red pigment in the pink bands of S. jurassica. We present new geochemical evidence concerning the seasonality and pigmentation of S. jurassica. Seasonal growth cycles are demonstrated by X-ray radiography, which shows differences in calcite density, and by varying δ13C composition of the bands. Temperature variation in the bands is difficult to constrain accurately due to conflicting patterns arising from Mg/Ca molar ratios and δ18O data. Fluctuating chlorine levels indicate increased salinity in the white bands, when combined with the isotope data this suggests more suggestive of marine conditions during formation of the white band and a greater freshwater component (lower chlorinity) during pink band precipitation (δ18O). Increased photosynthesis is inferred within the pink bands in comparison to the white, based on δ13C. Pyrolysis Gas Chromatography Mass Spectrometry (Py-GCMS) and Fourier Transform Infrared Spectroscopy (FTIR) show the presence of tetramethyl pyrrole, protein moieties and carboxylic acid groups, suggestive of the presence of the red algal pigment phycoerythrin. This is consistent with the pink colour of S. jurassica. As phycoerythrin is only known to occur in algae and cyanobacteria, and no biomarker evidence of bacteria or sponges was detected we conclude S. jurassica is most likely an alga. Pigment analysis may be a reliable classification method for fossil algae.
authors.affiliation: Williamson Research Centre for Molecular Environmental Science, School of Earth Atmospheric and Environmental Sciences, University of Manchester, M13 9PL, Manchester, United Kingdom.
authors.forename: Holly E
authors.initials: HE
authors.lastname: Barden
authors.affiliation: School of Materials Science, University of Manchester, M13 9PL, Manchester, United Kingdom.
authors.forename: Julia
authors.initials: J
authors.lastname: Behnsen
authors.affiliation: SLAC National Accelerator Laboratory, Menlo Park, CA 94025, United States of America.
authors.forename: Uwe
authors.initials: U
authors.lastname: Bergmann
authors.affiliation: NERC Isotope Geosciences Facilities, British Geological Survey, Keyworth, Nottingham NG12 5GG, United Kingdom; Centre for Environmental Geochemistry, School of Geography, University of Nottingham, Nottingham, NG7 2RD, United Kingdom.
authors.forename: Melanie J
authors.initials: MJ
authors.lastname: Leng
authors.affiliation: Williamson Research Centre for Molecular Environmental Science, School of Earth Atmospheric and Environmental Sciences, University of Manchester, M13 9PL, Manchester, United Kingdom.
authors.forename: Phillip L
authors.initials: PL
authors.lastname: Manning
authors.affiliation: School of Materials Science, University of Manchester, M13 9PL, Manchester, United Kingdom.
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Withers
authors.affiliation: Williamson Research Centre for Molecular Environmental Science, School of Earth Atmospheric and Environmental Sciences, University of Manchester, M13 9PL, Manchester, United Kingdom.
authors.forename: Roy A
authors.initials: RA
authors.lastname: Wogelius
authors.affiliation: Williamson Research Centre for Molecular Environmental Science, School of Earth Atmospheric and Environmental Sciences, University of Manchester, M13 9PL, Manchester, United Kingdom.
authors.forename: Bart E
authors.initials: BE
authors.lastname: van Dongen
mesh_terms: D005580:Fossils; D013058:Mass Spectrometry / Q000379:methods; D010799:Phycoerythrin / Q000032:analysis*; D000461:Rhodophyta / Q000737:chemistry* / Q000145:classification*; D012621:Seasons
chemical_list: D010799:Phycoerythrin