Abstract
High resolution δ 13C calb data are presented for two composite sections in England covering much of the Homerian Stage. Micrite samples collected at ~0.5 m intervals from outcrop and core in the Dudley area, West Midlands, span the upper-most Coalbrookdale, Much Wenlock Limestone and basal Lower Elton formations. Deposition there occurred in a mid-shelf setting. A similar suite of samples from the Wenlock type area, Wenlock Edge, Shropshire, represents a coeval sequence deposited closer to the shelf-basin margin. The successions concerned extend from the upper lundgreni to nilssoni graptolite biozones and provide a detailed record of variation in stable carbon isotope ratios across the well-known double-peaked Homerian positive excursion (Mulde Excursion), a time of significant global biological and chemical perturbation. In the West Midlands, this excursion occurs in the Much Wenlock Limestone Formation. The lower peak (Lower Quarried Limestone Member) has δ 13C calb values rising to +5.5%o VPDB. Values fall to +0.8%c VPDB higher in the section before rising again to +4.1%o VPDB (Nodular Beds Member). Analysis of lithofacies varia-tion in this interval indicates two transgressive-regressive cycles, the two positive peaks of the excursion correlating with relative sea-level lows and the intervening dip with a relative sea-level high, the local expression of Johnson's (2006) Highstand 5A. The double-peaked nature of the excursion at Dudley resembles that previously recorded for the area; however, our δ 13C carb values are consistently 2%c higher, and accord more closely with values published for sec-tions elsewhere. The lower of the two peaks found in the West Midlands cannot be identified on Wenlock Edge, where 813Ccarb values fluctuate somewhat around +2%c VPDB. The upper peak, though less distinct, can be identified on Wenlock Edge with values rising to +3.8%c VPDB. Correlations based on biostratigraphy, sequence stratigraphy and bentonite geochemistry suggest that not all changes in δ 13C calb occurred synchronously in the two areas studied, de-spite their close proximity.
Original language | English |
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Pages (from-to) | 669-679 |
Number of pages | 11 |
Journal | Bulletin of Geosciences |
Volume | 87 |
Issue number | 4 |
DOIs | |
Publication status | Published - 2012 |
Keywords
- δ C stratigraphy
- English Midlands
- Homerian
- Mulde Excursion
- Silurian
- Wenlock
ASJC Scopus subject areas
- Environmental Science(all)
- Earth and Planetary Sciences(all)