PALEOSALINITY OF EDIACARAN DICKINSONIA AND OTHER FOSSILS INFERRED FROM BORON CONTENT

Boron content is a novel index of paleosalinity for Ediacaran Dickinsonia in South Australia and northwestern Russia. In both places Dickinsonia fossils were concave hyporeliefs in mineralogically similar, covering silty sandstone. Russian sandstones differ in grey color, little-altered illite-smectite and siderite, but South Australian sandstones have illite and chlorite from deep burial, and authigenic hematite. These and other fossils and paleosols from the same regions have tight covariance of B (ppm) and K₂O (wt %), as evidence that B in both regions is carried largely by illlite-smectite clays. Nearby marine Cambrian and Ediacaran rocks of Russia and South Australia have more than 20 ppm B, but Dickinsonia ovata from South Australia (<10 ppm) and D. menneri from Russia (10 ppm) fall within freshwater values. Additional exploratory assays of Cryogenian to Devonian vendobionts (Dickinsonia, Arumberia, Rangea, Pteridinium, Ernietta, Aspidella, Rutgersella, Protonympha) and discoids (Beltanelliformis, Cyclomedusa, Nemiana) are indistinguishable from Devonian to Triassic plants in low to negligible B/K molar ratios, and both are significantly different (p<0.01) from 0.002 mole fraction or higher B/K for trilobites, brachiopods, ammonites and other securely marine fossils.