IT'S NOT RIDICOLOUS TO BE TUBICOLOUS: AN ANABARITES AND CAMBROTUBULUS-BEARING SHELL-HASH ASSEMBLAGE FROM THE EDIACARAN-CAMBRIAN TRANSITION, SOLTANIEH FORMATION, NORTHERN IRAN

The fossil record of the latest Ediacaran is characterized by the proliferation of mineralized and unmineralized vermiform organisms, several of which cross the Ediacaran-Cambrian boundary and make up part of the early Cambrian small shelly fauna. Due to their simple morphology, these fossils have historically been both difficult to interpret and to distinguish from one another. This study investigates a community of likely mineralized but poorly preserved tubicolous organisms from two fossiliferous slabs from the Soltanieh Formation of northern Iran. Analysis of the taphonomy of this fossil assemblage using thin-section petrography, scanning electron microscopy, and energy dispersive x-ray spectroscopy, suggests a two-part preservational pathway involving phosphatic recrystallization of the shell wall and separate, diagenetically later infillings of void space with either phosphatic or calcium carbonate cements. In parallel with the taphonomic study, morphometrics of the shelly organisms were also explored. Biometric measurements were collected from high-resolution photomosaic images of the surface fossils, as well as from a three-dimensional volume of the interior of one of the slabs generated via x-ray tomographic microscopy. Statistical analysis of these measurements revealed a separation of the fossils into two morphologically distinct groups of conical and tubular forms, which we characterize respectively as ‘conomorphs’ and ‘tubomorphs’. Based on previous studies of fossils from the Soltanieh Fm. and on the tri-radial symmetry observed herein, limited assignment to the genera Anabarites and Cambrotubulus is possible.