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Title: Effects of paleogeology, chemical weathering, and climate on the global geochemical cycle of carbon dioxide

Abstract

A new method of geologic reconstruction has been developed that determines areas of exposure for each epoch of the Phanerozoic. The paleogeologic maps reveal that the relative proportions of exposed rock types show few abrupt changes through Phanerozoic time, compared to the secular changes in areal extent of rock deposition. Chemical weathering of silicate minerals acts as a long-term transfer of CO{sub 2} from the atmosphere to carbonate sediments via river runoff. Thus, the roles of silicate and non-silicate rocks must be differentiated. Chemical records of streams draining monolithologic basins confirm that the relative weathering susceptibility of lithologies clearly favors carbonate over silicate rocks; surprisingly, among the silicates (clastic and igneous) there is no significant distinction. A survey of basalt catchments shows no correlation between temperature and weathering. Although a warm, wet climate promotes mineral weathering, this may be countered over time by soil shielding of bedrock-groundwater interactions. Mean annual runoff rates are 60% higher at {minus}100 my (using 4x current CO{sub 2}) from CCM simulations but, since Cretaceous land area is 30% smaller, total runoff changes very little. However, in a spatially distributed model of the Earth the annual bicarbonate flux of the Cretaceous (4x CO{sub 2}) is 59more » {times} 10{sup 12}eq, compared to 39 {times} 10{sup 12}eq for the present-day. Net HCO{sub 3}{sup {minus}} flux from silicate weathering is 25% higher in the Cretaceous, because the distribution of silicate exposures coincides with regions of intense runoff. Thus, by adding spatial dimensions of runoff and geology to preexisting models, the balance of CO{sub 2} levels by silicate dissolution can be achieved without severe changes in either atmospheric chemistry or rock proportions.« less

Authors:
Publication Date:
Research Org.:
Pennsylvania State Univ., University Park, PA (United States)
OSTI Identifier:
6099322
Resource Type:
Miscellaneous
Resource Relation:
Other Information: Thesis (Ph.D)
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; 58 GEOSCIENCES; CARBON DIOXIDE; GEOCHEMISTRY; SILICATE MINERALS; WEATHERING; AMBIENT TEMPERATURE; ATMOSPHERIC CHEMISTRY; BASALT; CARBON CYCLE; CARBONATE ROCKS; CENOZOIC ERA; CLIMATES; CORRELATIONS; CRETACEOUS PERIOD; DISSOLUTION; GEOLOGIC HISTORY; GEOLOGIC MODELS; GEOLOGY; GLOBAL ASPECTS; GROUND WATER; MESOZOIC ERA; PALEOZOIC ERA; RESERVOIR ROCK; RUNOFF; CARBON COMPOUNDS; CARBON OXIDES; CHALCOGENIDES; CHEMISTRY; ENVIRONMENTAL TRANSPORT; GEOLOGIC AGES; HYDROGEN COMPOUNDS; IGNEOUS ROCKS; MASS TRANSFER; MINERALS; OXIDES; OXYGEN COMPOUNDS; ROCKS; SEDIMENTARY ROCKS; VOLCANIC ROCKS; WATER; 540110*; 580000 - Geosciences

Citation Formats

Bluth, G J.S.. Effects of paleogeology, chemical weathering, and climate on the global geochemical cycle of carbon dioxide. United States: N. p., 1990. Web.
Bluth, G J.S.. Effects of paleogeology, chemical weathering, and climate on the global geochemical cycle of carbon dioxide. United States.
Bluth, G J.S.. Mon . "Effects of paleogeology, chemical weathering, and climate on the global geochemical cycle of carbon dioxide". United States.
@article{osti_6099322,
title = {Effects of paleogeology, chemical weathering, and climate on the global geochemical cycle of carbon dioxide},
author = {Bluth, G J.S.},
abstractNote = {A new method of geologic reconstruction has been developed that determines areas of exposure for each epoch of the Phanerozoic. The paleogeologic maps reveal that the relative proportions of exposed rock types show few abrupt changes through Phanerozoic time, compared to the secular changes in areal extent of rock deposition. Chemical weathering of silicate minerals acts as a long-term transfer of CO{sub 2} from the atmosphere to carbonate sediments via river runoff. Thus, the roles of silicate and non-silicate rocks must be differentiated. Chemical records of streams draining monolithologic basins confirm that the relative weathering susceptibility of lithologies clearly favors carbonate over silicate rocks; surprisingly, among the silicates (clastic and igneous) there is no significant distinction. A survey of basalt catchments shows no correlation between temperature and weathering. Although a warm, wet climate promotes mineral weathering, this may be countered over time by soil shielding of bedrock-groundwater interactions. Mean annual runoff rates are 60% higher at {minus}100 my (using 4x current CO{sub 2}) from CCM simulations but, since Cretaceous land area is 30% smaller, total runoff changes very little. However, in a spatially distributed model of the Earth the annual bicarbonate flux of the Cretaceous (4x CO{sub 2}) is 59 {times} 10{sup 12}eq, compared to 39 {times} 10{sup 12}eq for the present-day. Net HCO{sub 3}{sup {minus}} flux from silicate weathering is 25% higher in the Cretaceous, because the distribution of silicate exposures coincides with regions of intense runoff. Thus, by adding spatial dimensions of runoff and geology to preexisting models, the balance of CO{sub 2} levels by silicate dissolution can be achieved without severe changes in either atmospheric chemistry or rock proportions.},
doi = {},
url = {https://www.osti.gov/biblio/6099322}, journal = {},
number = ,
volume = ,
place = {United States},
year = {1990},
month = {1}
}

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