T113 EARTHTIMEs and EarthRates: Exploring the Tempo and Mode of Earth-System Processes and Evolution (Posters)

Monday, 5 November 2018
9:00 AM - 6:30 PM
Halls J-K

REVISED FIRST AND LAST APPEARANCES OF EARLY CAMBRIAN ANIMALS FROM DYNAMIC PROGRAMMING-DETERMINED δ13CCARB CORRELATIONS

Paper number: T113-3
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

Assessments of the tempo of Cambrian animal evolution arise from the use of δ13Ccarb chemostratigraphic correlation in exporting the Cambrian Series 1–2 radiometrically calibrated age-model from the Anti-Altas, Morocco, to fossil first and last appearances from temporally unconstrained marine stratigraphic sections located elsewhere (Maloof et al., 2010; Smith et al., 2016). To date, these correlations rely on visual alignment of δ13Ccarb excursions. Here we employ dynamic programming (DP), an optimization algorithm utilizing least squares fitting and variable penalty functions, to align δ13C records from Morocco (Adoudounian, Lie de Vin, and Igoudine fms.) to fossil-bearing, time-uncertain sections from Mongolia (Bayangol––Zuun-Arts fms.), Siberia (Sukharika Fm.), China (Dengying, Yanjiahe, and Shuijingtuo fms.), and Nevada (Deep Spring Fm.). We demonstrate that DP can successfully align each record to the Moroccan reference curve, reproducing previously proposed correlations while also revealing overlooked, statistically significant alignment solutions. This result demonstrates the need to assemble correlation libraries, not single solutions, when comparing interbasinal geochemical records. In turn, each alignment solution assigns a unique age to fossil first and last appearances at Mongolia, Siberia, China and Nevada. This outcome allows us to (a) determine an age range for each taxon appearance/disappearance in a single location and (b) quantify the diachroneity of the appearance/disappearance of a single taxon between all study locations. As an example of the former, alignment solutions between Morocco and Siberia predict the local first appearance datum (FAD) of T. pedum between 540.2 and 538.4 Ma. Numerical results indicate that the local FAD of T. pedum varies between localities by ~20 Myr (540.2 Ma in Siberia versus 520.8 Ma in Mongolia). Since all fossil FADs display some diachroneity due, in part, to underlying patterns of biological dispersal, local sedimentation, and taphonomy, quantifying the temporal bounds on local and global FADs will have implications for conclusions about Cambrian evolutionary pulses.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-324058

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