REFINED ZAVKAHN TERRANE, MONGOLIA EARLY CAMBRIAN SMALL SHELLY FOSSIL FIRST APPEARANCES BASED ON DYNAMIC TIME WARPING ALIGNMENTS OF δ13CCARB SEQUENCES

The dearth of radiometrically datable material in fossiliferous sections creates difficulties in assigning absolute ages to early Cambrian Period Terreneuvian Series (~539 – 521 Ma) fossil first appearances. Through the use of dynamic time warping, we hope to assign ages to fossil first appearances by using 𝛅¹³C_carb data processed from particularly fossil rich paleo-sedimentary basins in Australia, China, Mongolia, and Siberia. Each of these paleo-basins has a varying amount of information on the lithostratigraphy and biostratigraphy that can guide chemostratigraphic correlation but do not have any absolute ages within the stratigraphy. In contrast, the Anti Atlas region in Morocco has a high-resolution 𝛅¹³C_carb record with four radiometrically dated ash beds, though the region contains no pre-trilobitic small shelly fossils (Maloof et al., 2010). Here we use dynamic time warping to create 𝛅¹³C_carb alignments between stratigraphic sections within each fossiliferous region. Once completed, 𝛅¹³C_carb alignments are stacked into regional composites that can be compared to the Morocco age model to produce a global 𝛅¹³C_carb isotope composite that will be used to assign ages to fossil first appearances on a global scale.

Here I use lithologic, biostratigraphic, and chemostratigraphic data from the Zavkahn Terrane, Mongolia (Smith et al., 2016), to create plausible Mongolia regional 𝛅¹³C_carb composites. To compose the entire regional composite for Mongolia, we first generated sub-composites of alignments for each of the three local formations, from oldest to youngest, the Zuun-Arts, Bayangol, and the Salaagol formations. The alignments chosen meet three different criteria. The first sub-composite is based on the alignments with the highest correlation coefficient (r² value), which is the most mathematically ideal. The second is based on the lithology, in which an alignment is chosen that has the least diachroneity by aligning formation boundaries. Lastly, an alignment is chosen based on biostratigraphic data that aligns fossil horizons within each locality. We compare these three separate regional composites with the Moroccan age model to assign ages to Mongolian fossil first appearances.