REFINED SIBERIAN PLATFORM EARLY CAMBRIAN SMALL SHELLY FOSSIL FIRST APPEARANCES BASED ON DYNAMIC TIME WARPING ALIGNMENTS OF δ13CCARB SEQUENCES

While many invertebrate phyla evolved during the Cambrian "explosion", the first appearance age for many of these fossils is not precisely known. Strata of the Cambrian Terreneuvian Series (~539–521 Ma) from the Anti Atlas Mountains, Morocco, contain dated ash beds, but the region does not contain pre-trilobitic small shelly fossils; Terreneuvian Series strata in Siberia contain an abundance of small shelly fossils, but no absolute dates. Yet the two regions share a similar stable carbon isotope record from carbonate stratigraphy (δ¹³C_carb) which can facilitate the extrapolation of the Moroccan age model to the Siberian Platform fossils.

Here we apply dynamic time warping to create different alignment possibilities between pairs of δ¹³C_carb curves for the Kotuj River region, Lena-Alden region, Sukharikha section, Selinde section, and the Bol-Shaya section, measured across the Siberian Platform. We selected the relatively temporally complete Sukharikha section as the target against which to align the remaining candidate sections. From a library of 60 target–candidate alignment possibilities, we select different alignments based on three criteria. A lithostratigraphic alignment is chosen based on the δ¹³C_carb alignment that best correlates with a formation boundary between the target and candidate section. This selection can be optimized for multiple boundaries. A biostratigraphic alignment minimizes diachroneity of select fossil first appearances between the target and candidate section. Finally, a chemostratigraphic alignment selects the highest correlation coefficient "r" value between the target and the candidate records. By building distinct Siberian Platform δ¹³C_carb composite curves, we explore and debate different relative ages for small shelly fossil appearances on the Siberian Platform; by aligning Siberia's regional composites to the Morocco age model we establish absolute ages for Siberian fossil appearances, meaning that evolutionary rates can be calculated.