Soil-zone microfabrics in calcrete and in desiccation cracks from the Upper Jurassic Purbeck Formation of Dorset
Soil-zone microfabrics, alveolar-septal structure, needle-fibre calcite, and calcans are described from horizontal calcrete layers, stringers, and infillings in vertical desiccation cracks from an Upper Jurassic limestone in the Lower Purbeck Formation of Dorset. These calcrete palaeosols occur in a...
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1988
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Online Access: | https://ueaeprints.uea.ac.uk/id/eprint/25616/ https://doi.org/10.1002/gj.3350230306 |
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ftuniveastangl:oai:ueaeprints.uea.ac.uk:25616 2023-05-15T15:52:46+02:00 Soil-zone microfabrics in calcrete and in desiccation cracks from the Upper Jurassic Purbeck Formation of Dorset Andrews, Julian E. 1988 https://ueaeprints.uea.ac.uk/id/eprint/25616/ https://doi.org/10.1002/gj.3350230306 unknown Andrews, Julian E. (1988) Soil-zone microfabrics in calcrete and in desiccation cracks from the Upper Jurassic Purbeck Formation of Dorset. Geological Journal (23). pp. 261-270. ISSN 0072-1050 doi:10.1002/gj.3350230306 Article PeerReviewed 1988 ftuniveastangl https://doi.org/10.1002/gj.3350230306 2023-01-30T21:26:53Z Soil-zone microfabrics, alveolar-septal structure, needle-fibre calcite, and calcans are described from horizontal calcrete layers, stringers, and infillings in vertical desiccation cracks from an Upper Jurassic limestone in the Lower Purbeck Formation of Dorset. These calcrete palaeosols occur in an oolitic limestone (the Hard Cap) which represents former evaporitic lagoonal to carbonate mudflat environments. The calcretes occur 6-10 cm below the Great Dirt Bed, a former rendzina soil with rooted tree remains. Desiccation cracks and vugs formed in the oolitic sediment before Great Dirt Bed times. After formation of the Great Dirt Bed, soil-water rich in dissolved CaCO3 preferentially flowed through natural conduits in the underlying sediment, namely the desiccation cracks and vugs. Calcrete precipitated in these cracks and vugs around decaying plant roots, and probably, during more arid (evaporative) climatic periods. These palaeosol microfabrics are among the first to be described from the British Jurassic and were probably preserved due to the semiarid Lower Purbeck climate where rapid oxidation of organic matter limited the amount and strength of carbonic acid generation, thereby limiting extensive dissolution of early formed soil-zone carbonate. Early diagenetic cementation of the sediment also aided microfabric preservation by sealing off soil-zone structures from subsequent diagenetic fluids. Article in Journal/Newspaper Carbonic acid University of East Anglia: UEA Digital Repository Geological Journal 23 3 261 270 |
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University of East Anglia: UEA Digital Repository |
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ftuniveastangl |
language |
unknown |
description |
Soil-zone microfabrics, alveolar-septal structure, needle-fibre calcite, and calcans are described from horizontal calcrete layers, stringers, and infillings in vertical desiccation cracks from an Upper Jurassic limestone in the Lower Purbeck Formation of Dorset. These calcrete palaeosols occur in an oolitic limestone (the Hard Cap) which represents former evaporitic lagoonal to carbonate mudflat environments. The calcretes occur 6-10 cm below the Great Dirt Bed, a former rendzina soil with rooted tree remains. Desiccation cracks and vugs formed in the oolitic sediment before Great Dirt Bed times. After formation of the Great Dirt Bed, soil-water rich in dissolved CaCO3 preferentially flowed through natural conduits in the underlying sediment, namely the desiccation cracks and vugs. Calcrete precipitated in these cracks and vugs around decaying plant roots, and probably, during more arid (evaporative) climatic periods. These palaeosol microfabrics are among the first to be described from the British Jurassic and were probably preserved due to the semiarid Lower Purbeck climate where rapid oxidation of organic matter limited the amount and strength of carbonic acid generation, thereby limiting extensive dissolution of early formed soil-zone carbonate. Early diagenetic cementation of the sediment also aided microfabric preservation by sealing off soil-zone structures from subsequent diagenetic fluids. |
format |
Article in Journal/Newspaper |
author |
Andrews, Julian E. |
spellingShingle |
Andrews, Julian E. Soil-zone microfabrics in calcrete and in desiccation cracks from the Upper Jurassic Purbeck Formation of Dorset |
author_facet |
Andrews, Julian E. |
author_sort |
Andrews, Julian E. |
title |
Soil-zone microfabrics in calcrete and in desiccation cracks from the Upper Jurassic Purbeck Formation of Dorset |
title_short |
Soil-zone microfabrics in calcrete and in desiccation cracks from the Upper Jurassic Purbeck Formation of Dorset |
title_full |
Soil-zone microfabrics in calcrete and in desiccation cracks from the Upper Jurassic Purbeck Formation of Dorset |
title_fullStr |
Soil-zone microfabrics in calcrete and in desiccation cracks from the Upper Jurassic Purbeck Formation of Dorset |
title_full_unstemmed |
Soil-zone microfabrics in calcrete and in desiccation cracks from the Upper Jurassic Purbeck Formation of Dorset |
title_sort |
soil-zone microfabrics in calcrete and in desiccation cracks from the upper jurassic purbeck formation of dorset |
publishDate |
1988 |
url |
https://ueaeprints.uea.ac.uk/id/eprint/25616/ https://doi.org/10.1002/gj.3350230306 |
genre |
Carbonic acid |
genre_facet |
Carbonic acid |
op_relation |
Andrews, Julian E. (1988) Soil-zone microfabrics in calcrete and in desiccation cracks from the Upper Jurassic Purbeck Formation of Dorset. Geological Journal (23). pp. 261-270. ISSN 0072-1050 doi:10.1002/gj.3350230306 |
op_doi |
https://doi.org/10.1002/gj.3350230306 |
container_title |
Geological Journal |
container_volume |
23 |
container_issue |
3 |
container_start_page |
261 |
op_container_end_page |
270 |
_version_ |
1766387864652742656 |