Silurian carbonate high-energy deposits of potential tsunami origin: distinguishing lateral redeposition and time averaging using carbon isotope chemostratigraphy

This is a Preprint and has not been peer reviewed. The published version of this Preprint is available: https://doi.org/10.1016/j.sedgeo.2014.10.012. This is version 1 of this Preprint.

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Authors

Emilia Jarochowska, Axel Munnecke

Abstract

Stable carbon isotope curves are used as a precise stratigraphic tool in the Paleozoic, even though they are commonly based on shallow-water carbonate record, characterized by low stratigraphic completeness. Identification of episodes of large-scale redeposition and erosion may improve δ13Ccarb-based correlations. Here, a series of at least three episodes of high-energy onshore redeposition are described from the Makarivka Member (new unit) of the Ustya Formation from the Homerian (middle Silurian) of Podolia, Ukraine. The Makarivka Member is emplaced within a tidal flat succession. Its most prominent part is divided into a lower polymictic conglomerate of sand- to boulder-sized clasts representing a range of subtidal facies, and an upper heterolithic unit composed of grainstone and mudstone laminae. The aim of the study is to identify the mechanism of deposition of the allochthonous conglomeratic material in this Member. Based on analogies with Recent tsunami deposits, the conglomerate is interpreted to reflect the strongest landward-directed current in the tsunami run-up phase, and the heterolith – alternating high-density landward currents, stagnant intervals allowing mud and land-derived debris to settle, and backwash flows. The tsunamite was deposited during an interval of decreasing isotopic values of the Mulde Excursion, a global δ13C excursion reaching +5.2‰ in the studied sections. Clast redeposition in an interval characterized by rapidly changing δ13Ccarb offers the opportunity to evaluate the degree of temporal and spatial averaging caused by the tsunami. The clasts in the polymictic conglomerate show scattered δ13Ccarb values (-0.3‰ to +2.1‰) compared to homogenous (1.3‰ to 1.6‰) values in the matrix. The presence of clasts characterized by low δ13Ccarb values is explained by their decrease with bathymetry rather than erosion of pre-excursion strata, whereas high values characterize material entrained from the sea-floor and strata directly underlying the tsunamite. Close (1.3‰ and 1.5‰) average δ13Ccarb values suggest that the matrix of the conglomerate is potentially a product of clast grinding.

DOI

https://doi.org/10.31223/X5JP55

Subjects

Earth Sciences, Geochemistry, Geology, Sedimentology, Stratigraphy

Keywords

sequence stratigraphy, Ukraine, carbonates, carbon isotopes, sequence stratigraphy, Wenlock, Homerian, positive carbon isotope excursion, temporal mixing, Baltic Basin, transgressive lag, Homerian, positive carbon isotope excursion, Silurian, temporal mixing, Baltic Basin, transgressive lag, time averaging

Dates

Published: 2021-03-17 23:37

License

CC BY Attribution 4.0 International

Additional Metadata

Conflict of interest statement:
None

Data Availability (Reason not available):
Supporting data is available under 10.17605/OSF.IO/MU9AQ

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