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.
| Original language | English |
|---|---|
| Pages (from-to) | 14-28 |
| Number of pages | 15 |
| Journal | Sedimentary Geology |
| Volume | 315 |
| DOIs | |
| Publication status | Published - 1 Jan 2015 |
Bibliographical note
Funding Information:This work was supported by the Deutsche Forschungsgemeinschaft (project no. Mu 2352/3 ). We thank C. E. Brett, L. Ainsaar, P. I. McLaughlin, and A. Immenhauser for suggestions which helped us to improve an earlier version of this manuscript. K. Frisch is acknowledged for the help in field and laboratory work, R. Nawrot for the assistance in fieldwork and the finding of P. decipiens , B. Leipner-Mata for the help in producing thin sections, M. Joachimski and D. Lutz for carbon and oxygen isotope analyses, and O. Lehnert, R. Nawrot, W. Kozłowski, and M. López Correa for discussions. This paper is a contribution to the International Geoscience Programme (IGCP) Project 591 — The Early to Middle Palaeozoic Revolution.
Publisher Copyright:
© 2014 Elsevier B.V.
Funding
This work was supported by the Deutsche Forschungsgemeinschaft (project no. Mu 2352/3 ). We thank C. E. Brett, L. Ainsaar, P. I. McLaughlin, and A. Immenhauser for suggestions which helped us to improve an earlier version of this manuscript. K. Frisch is acknowledged for the help in field and laboratory work, R. Nawrot for the assistance in fieldwork and the finding of P. decipiens , B. Leipner-Mata for the help in producing thin sections, M. Joachimski and D. Lutz for carbon and oxygen isotope analyses, and O. Lehnert, R. Nawrot, W. Kozłowski, and M. López Correa for discussions. This paper is a contribution to the International Geoscience Programme (IGCP) Project 591 — The Early to Middle Palaeozoic Revolution.
Keywords
- Homerian
- Positive carbon isotope excursion
- Sequence stratigraphy
- Temporal mixing
- Transgressive lag
- Wenlock