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Constraints on palaeoenvironments in the Lower Cretaceous Wealden of southern England, from the geochemistry of sphaerosiderites

Stuart A. Robinson, James I. Scotchman, Timothy S. White and Tim C. Atkinson
Constraints on palaeoenvironments in the Lower Cretaceous Wealden of southern England, from the geochemistry of sphaerosiderites
Journal of the Geological Society of London (March 2010) 167 (2): 303-311

Abstract

Sphaerosiderites are millimetre-scale concretions of FeCO (sub 3) that form predominantly in waterlogged environments and are of use in palaeoenvironmental and palaeohydrological studies. We present petrographic, elemental and stable-isotopic (delta (super 13) C, delta (super 18) O) data from sphaerosiderites collected from the Lower Cretaceous Wealden sediments of southern England. The sphaerosiderites are composed of very pure FeCO (sub 3) , with only small amounts of Ca, Mg and Mn present, suggesting that they are well preserved and were precipitated from fresh groundwater. delta (super 13) C values display a relatively large range from about -5 to -30 per mil (VPDB). In contrast, delta (super 18) O values are relatively invariant (1sigma =0.83 per mil), with an average of -3.01 per mil (VPDB). The relationship between carbon and oxygen suggests that the sphaerosiderites faithfully record palaeo-groundwater delta (super 18) O. Likely delta (super 18) O values for groundwater were calculated using a published, experimentally derived siderite-water fractionation equation and plausible assumed values for palaeotemperature. The average estimate was -4.9 per mil (SMOW). The Wealden sphaerosiderite oxygen-isotope values are comparable with other early Cretaceous data from similar palaeolatitudes but lower than estimated Holocene values for equivalent latitudes. This observation may indicate greater rainfall at 30 degrees N during the Cretaceous relative to the Holocene and also suggests relative stability of palaeoclimatic conditions during the early Cretaceous at this palaeolatitude.


ISSN: 0016-7649
EISSN: 2041-479X
Coden: JGSLAS
Serial Title: Journal of the Geological Society of London
Serial Volume: 167
Serial Issue: 2
Title: Constraints on palaeoenvironments in the Lower Cretaceous Wealden of southern England, from the geochemistry of sphaerosiderites
Affiliation: University College London, Department of Earth Sciences, London, United Kingdom
Pages: 303-311
Published: 201003
Text Language: English
Publisher: Geological Society of London, London, United Kingdom
References: 56
Accession Number: 2010-030914
Categories: Geochemistry of rocks, soils, and sedimentsStratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table, geol. sketch map
N50°52'60" - N50°52'60", E00°40'60" - E00°40'60"
Secondary Affiliation: Pennsylvania State University, USA, United States
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data from The Geological Society, London, London, United Kingdom
Update Code: 201018
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