Late Precambrian glacial climate and the Earth's obliquity
Summary Late Precambrian (∼ 750±200 Ma) glaciogenic sequences exhibit substantial evidence for marked climatic inequability of seasonal and longer periodicity (10° to ∼ 10 6 yrs): (1) tillites are closely associated with dolomites, limestones and evaporites apparently of warm-water origin; (2) tilli...
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1975
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Online Access: | http://dx.doi.org/10.1017/s0016756800046185 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0016756800046185 |
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crcambridgeupr:10.1017/s0016756800046185 2024-09-15T18:11:38+00:00 Late Precambrian glacial climate and the Earth's obliquity Williams, G. E. 1975 http://dx.doi.org/10.1017/s0016756800046185 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0016756800046185 en eng Cambridge University Press (CUP) https://www.cambridge.org/core/terms Geological Magazine volume 112, issue 5, page 441-465 ISSN 0016-7568 1469-5081 journal-article 1975 crcambridgeupr https://doi.org/10.1017/s0016756800046185 2024-07-31T04:04:38Z Summary Late Precambrian (∼ 750±200 Ma) glaciogenic sequences exhibit substantial evidence for marked climatic inequability of seasonal and longer periodicity (10° to ∼ 10 6 yrs): (1) tillites are closely associated with dolomites, limestones and evaporites apparently of warm-water origin; (2) tillites occur with red beds and iron-formations whose iron probably was derived ultimately from lateritic weathering; (3) glacial dropstones occur locally within carbonates and iron-formations; (4) laminae, interpreted as varves by many workers, are common in argillites, carbonates and iron-formations; and (5) permafrost structures attributable to repeated seasonal changes of temperature are locally abundant. Such climatic, particularly seasonal inequability apparently conflicts however with the probable low (≲30°) palaeolatitudes of deposition of numerous late Precambrian glaciogenic sequences. The contradictions presented by such sequences may be resolved by postulating a considerably increased obliquity of the ecliptic (ε) in late Precambrian time. Substantial increase in e would: (1) greatly amplify global seasonality; (2) weaken climatic zonation, thus allowing warm-water sedimentation and lateritic weathering over wide latitudes; and (3) increase the ratio of radiation received annually at either pole to that received at the equator, so when 54° < ε < 126° low and middle latitudes (≤ 43°) would be glaciated in preference to the poles. Ice sheets and permafrost thus can be envisaged principally in low and middle latitudes with contiguous warm-water and iron-rich facies under a markedly seasonal climate. The concept of secular change of e is supported by other geological evidence. Article in Journal/Newspaper Ice permafrost Cambridge University Press Geological Magazine 112 5 441 465 |
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Open Polar |
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Cambridge University Press |
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crcambridgeupr |
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English |
description |
Summary Late Precambrian (∼ 750±200 Ma) glaciogenic sequences exhibit substantial evidence for marked climatic inequability of seasonal and longer periodicity (10° to ∼ 10 6 yrs): (1) tillites are closely associated with dolomites, limestones and evaporites apparently of warm-water origin; (2) tillites occur with red beds and iron-formations whose iron probably was derived ultimately from lateritic weathering; (3) glacial dropstones occur locally within carbonates and iron-formations; (4) laminae, interpreted as varves by many workers, are common in argillites, carbonates and iron-formations; and (5) permafrost structures attributable to repeated seasonal changes of temperature are locally abundant. Such climatic, particularly seasonal inequability apparently conflicts however with the probable low (≲30°) palaeolatitudes of deposition of numerous late Precambrian glaciogenic sequences. The contradictions presented by such sequences may be resolved by postulating a considerably increased obliquity of the ecliptic (ε) in late Precambrian time. Substantial increase in e would: (1) greatly amplify global seasonality; (2) weaken climatic zonation, thus allowing warm-water sedimentation and lateritic weathering over wide latitudes; and (3) increase the ratio of radiation received annually at either pole to that received at the equator, so when 54° < ε < 126° low and middle latitudes (≤ 43°) would be glaciated in preference to the poles. Ice sheets and permafrost thus can be envisaged principally in low and middle latitudes with contiguous warm-water and iron-rich facies under a markedly seasonal climate. The concept of secular change of e is supported by other geological evidence. |
format |
Article in Journal/Newspaper |
author |
Williams, G. E. |
spellingShingle |
Williams, G. E. Late Precambrian glacial climate and the Earth's obliquity |
author_facet |
Williams, G. E. |
author_sort |
Williams, G. E. |
title |
Late Precambrian glacial climate and the Earth's obliquity |
title_short |
Late Precambrian glacial climate and the Earth's obliquity |
title_full |
Late Precambrian glacial climate and the Earth's obliquity |
title_fullStr |
Late Precambrian glacial climate and the Earth's obliquity |
title_full_unstemmed |
Late Precambrian glacial climate and the Earth's obliquity |
title_sort |
late precambrian glacial climate and the earth's obliquity |
publisher |
Cambridge University Press (CUP) |
publishDate |
1975 |
url |
http://dx.doi.org/10.1017/s0016756800046185 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0016756800046185 |
genre |
Ice permafrost |
genre_facet |
Ice permafrost |
op_source |
Geological Magazine volume 112, issue 5, page 441-465 ISSN 0016-7568 1469-5081 |
op_rights |
https://www.cambridge.org/core/terms |
op_doi |
https://doi.org/10.1017/s0016756800046185 |
container_title |
Geological Magazine |
container_volume |
112 |
container_issue |
5 |
container_start_page |
441 |
op_container_end_page |
465 |
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1810449228681445376 |