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- Title
Decoding Deep‐Time Rhythms: Probing the Limit of Stratigraphic Correlation in the Time‐Specific Facies of the Late Devonian Usseln Limestone (Rhenish Massif, Germany).
- Authors
Wichern, N. M. A.; Bialik, O. M.; Nohl, T.; Becker, R. T.; De Vleeschouwer, D.
- Abstract
The iso‐ or diachronous character of a geologic unit is scale‐dependent, especially for time‐specific facies. The Usseln Limestone is a Late Devonian time‐specific facies from Germany, occurring immediately below the Lower Kellwasser black shale. Here, we investigate whether cm‐scale rhythmical bands within the Usseln Limestone are correlatable across its depositional basin. Its facies were studied at three locations ca. 50 km apart, representing different depositional settings. Its cm‐scale alternations in lithological facies and elemental content (μXRF) form an excellent target for correlations on millennial timescales. Correlation attempts failed to converge to a solution at the cm‐scale of individual rhythmites. Dynamic Time Warping, however, provided convincing correlations at the dm‐scale, supporting its use as a high‐resolution correlation tool. The Usseln Limestone base may be diachronous, but the top is likely isochronous. This finding is in agreement with sudden basin‐wide black shale deposition at the onset of the Kellwasser Crisis. Plain Language Summary: A time‐specific facies is a rock unit that can be recognized in different places and always represents the same specific moment in Earth history. Here, we study the Usseln Limestone from the Rhenish Massif in Germany. This time‐specific facies is intruiging, as it is characterized by internal cm‐ and dm‐scale rhythmites. We sampled the Usseln Limestone at three different locations and assessed how consistently individual rhythmites occur across the basin, with approximately 50 km between sites. To do this, we first obtained mm‐resolution geochemical elemental data from all samples. Subsequently, the mathemathical method "Dynamic Time Warping" was applied to attempt correlation. At the cm‐level, our correlation attempt failed. Depositional differences between the three sites were too substantial for precise correlations at the scale of individual rhythmites. However, we successfully made stratigraphic correlations at the decimeter‐scale of the rhythmite bundles. These correlations suggest that while the base of the Usseln Limestone might have formed at different times in different places, the top of this time‐specific facies likely is synchronous throughout the basin. This is important, because the top of the Usseln Limestone aligns with the sudden appearance of a widespread black shale layer, marking the start of a major biotic crisis in Earth history. Key Points: This case study illustrates how the isochronony of a time‐specific facies breaks down at smaller thickness scalesDynamic Time Warping applied to an ensemble of proxies is demonstrated to be a useful high‐resolution correlation toolThe inferred isochronous top of the Usseln Limestone is in line with a rapid onset of Lower Kellwasser black shale deposition
- Subjects
GERMANY; STRATIGRAPHIC correlation; FACIES; LIMESTONE; BLACK shales; DEVONIAN Period; RHYTHM
- Publication
Geophysical Research Letters, 2024, Vol 51, Issue 10, p1
- ISSN
0094-8276
- Publication type
Article
- DOI
10.1029/2024GL109392