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Early Mississippian evaporites of coastal tropical wetlands

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posted on 06.04.2018, 12:40 by D Millward, Sarah. J Davies, F Williamson, Rachel Curtis, T. I Kearsey, Carys. E Bennett, J. E. A Marshall, M. A. E Browne
Extensive evaporites in Lower Mississippian successions from palaeoequatorial regions are commonly used as evidence for an arid to semi‐arid palaeoclimate. However, in this study, detailed studies of evaporites and their context refute this interpretation. Detailed sedimentological and petrographical analysis of the Lower Mississippian of northern Britain, is combined with archived log data from more than 40 boreholes across southern Scotland, northern England and Northern Ireland, and published literature from Canada. Two key cores from the Tweed Basin and the northern margin of the Northumberland – Solway Basin contain 178 evaporite intervals and reveal twelve distinct forms of gypsum and anhydrite across seven facies that are associated with planar laminated siltstone and intercalated thin beds of ferroan dolostone. Nodular gypsum and anhydrite, typically in intervals less than 1 to 2 m thick, are integral components of the succession. Nodular evaporite occurs within about 1 m of a palaeosurface, but most evaporite deposits represent ephemeral brine pans to semi‐permanent hypersaline lakes or salinas on a floodplain that was subjected periodically to storm surges introducing marine waters. Formation of evaporites under a strongly seasonal climate in a coastal wetland is supported by palaeosol types and geochemical proxies, and from palaeobotanical evidence published previously. Although 65% of modern equatorial areas experience a strongly seasonal climatic regime, salinas and sabkhas are a minor component today in comparison with the evidence from these Lower Mississippian successions. This implies that the earliest terrestrial environments were complex and dynamic providing a diverse range of habitats in which the early tetrapods became terrestrialized and represent a setting that is rarely preserved in the geological record.

History

Citation

Sedimentology, 2018

Author affiliation

/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/School of Geography, Geology and the Environment

Version

AM (Accepted Manuscript)

Published in

Sedimentology

Publisher

Wiley

issn

0037-0746

eissn

1365-3091

Copyright date

2018

Available date

17/02/2019

Publisher version

https://onlinelibrary.wiley.com/doi/abs/10.1111/sed.12465

Notes

The file associated with this record is under embargo until 12 months after publication, in accordance with the publisher's self-archiving policy. The full text may be available through the publisher links provided above.

Language

en

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