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GSA Connects 2023 Meeting in Pittsburgh, Pennsylvania

Paper No. 134-5
Presentation Time: 2:45 PM

NEW GEOCHRONOLOGICAL, GEOCHEMICAL, AND PALEOENVIRONMENTAL CONSTRAINTS ON THE TONIAN EUKARYOTIC MICROFOSSIL ASSEMBLAGE IN THE CHICHKAN FORMATION IN THE MALYI (LESSER) KARATAU, KAZAKHSTAN


SMITH, Emily F.1, LONSDALE, Mary C.1, NELSON, Lyle L.2, SZYMANOWSKI, Dawid3, MUSTAPAYEVA, Sezim4, BOLD, Uyanga5, MOORE, Kelsey1, SANDERS, Cecilia1 and SCHOENE, Blair6, (1)Department of Earth and Planetary Sciences, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218, (2)Earth and Planetary Sciences, Carleton University, 2201 Herzberg Laboratories, Ottawa, ON K1S 5B6, Canada, (3)Department of Geosciences, Princeton University, Guyot Hall, Princeton, NJ 08544; Institute of Geochemistry and Petrology, ETH, 8092 Zurich, Switzerland, (4)Kazakh National Technical University, Satpaev St. 22, Almaty, Almaty 050013, Kazakhstan, (5)School of Geology and Petroleum Engineering, Mongolian University of Science and Technology, Ulaanbaatar, 210349, Mongolia, (6)Princeton University Geosciences, 208 Guyot Hall, Princeton, NJ 08544-0001

Major diversification within the eukaryotic clade is observed from the Tonian fossil record, but the drivers behind it remain unresolved, in part due to ambiguity surrounding the temporal and paleoenvironmental contexts of many Tonian microfossil assemblages. Here, we present new geochronological, geochemical, and sedimentological data from a vase-shaped microfossil (VSM)-bearing fossil assemblage preserved within the Malokaroy Series of the Malyi (Lesser) Karatau in Kazakhstan. We present U-Pb zircon geochronology and geochemistry of a volcanic unit within the Kurgan Formation, which overlies the Chichkan microfossil assemblage. T/REE data from the Tonian magmatic zircons suggest crystallization from magmas of rift or intraplate affinity. Based on these T/REE data, occurrences of pervasive fabric-retentive diagenetic chert within the strata, and abundant intercalated volcanic and volcaniclastic horizons, we suggest that early silicification contributing to microfossil preservation within these units resulted from localized syn-depositional to early-diagenetic sourcing of volcanogenic and/or hydrothermal silica. This model, in addition to the broader stratigraphic architecture of the basin, suggest that this Tonian ecosystem existed within a restricted basin rather than on an open, shallow marine shelf. Geochronology results indicate that the Chichkan Formation preserves one of the oldest VSM communities globally.

Session No. 134

T131. New Advances in Geobiology
Monday, 16 October 2023: 1:30 PM-5:30 PM
325 (David L Lawrence Convention Center)
Geological Society of America Abstracts with Programs. Vol. 55, No. 6
doi: 10.1130/abs/2023AM-391753
© Copyright 2023 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.
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