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Early Mississippian evaporites of coastal tropical wetlands

Early Mississippian evaporites of coastal tropical wetlands
Early Mississippian evaporites of coastal tropical wetlands
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.
0037-0746
2278-2311
Millward, David
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Davies, Sarah J.
9c08e102-7013-4ee4-9076-565ad12235cc
Williamson, Fiona
8496b5dd-f498-4bb6-ac19-5e00cedd5a82
Curtis, Rachel
d158ddd9-89fc-442f-b24a-328d60f06dcc
Kearsey, Timothy I.
d81e2518-1290-4c61-87ed-e6f0d4b8e7c1
Bennett, Carys E.
e1684f72-df39-4d08-8321-f5d512f66727
Marshall, John E.A.
cba178e3-91aa-49a2-b2ce-4b8d9d870b06
Browne, Michael A.E.
478437e6-837f-498d-876c-3566192b39a6
Millward, David
c438e99d-66d1-46c9-8caa-00967348c49a
Davies, Sarah J.
9c08e102-7013-4ee4-9076-565ad12235cc
Williamson, Fiona
8496b5dd-f498-4bb6-ac19-5e00cedd5a82
Curtis, Rachel
d158ddd9-89fc-442f-b24a-328d60f06dcc
Kearsey, Timothy I.
d81e2518-1290-4c61-87ed-e6f0d4b8e7c1
Bennett, Carys E.
e1684f72-df39-4d08-8321-f5d512f66727
Marshall, John E.A.
cba178e3-91aa-49a2-b2ce-4b8d9d870b06
Browne, Michael A.E.
478437e6-837f-498d-876c-3566192b39a6

Millward, David, Davies, Sarah J., Williamson, Fiona, Curtis, Rachel, Kearsey, Timothy I., Bennett, Carys E., Marshall, John E.A. and Browne, Michael A.E. (2018) Early Mississippian evaporites of coastal tropical wetlands. Sedimentology, 65 (7), 2278-2311. (doi:10.1111/sed.12465).

Record type: Article

Abstract

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.

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Millward_et_al-2018-Sedimentology - Accepted Manuscript
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Accepted/In Press date: 13 February 2018
e-pub ahead of print date: 17 February 2018
Published date: December 2018

Identifiers

Local EPrints ID: 418232
URI: http://eprints.soton.ac.uk/id/eprint/418232
ISSN: 0037-0746
PURE UUID: 39c64e6b-ffe2-4772-b8cf-b8c866775111
ORCID for John E.A. Marshall: ORCID iD orcid.org/0000-0002-9242-3646

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Date deposited: 26 Feb 2018 17:30
Last modified: 11 Mar 2022 05:03

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Contributors

Author: David Millward
Author: Sarah J. Davies
Author: Fiona Williamson
Author: Rachel Curtis
Author: Timothy I. Kearsey
Author: Carys E. Bennett
Author: Michael A.E. Browne

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