Skip to Main Content
Skip Nav Destination
GEOREF RECORD

Vesicle paleobarometry in the Pongola Supergroup; a cautionary note and guidelines for future studies

E. A. Goosmann, R. Buick, D. C. Catling, C. Luskin and N. Nhleko
Vesicle paleobarometry in the Pongola Supergroup; a cautionary note and guidelines for future studies
South African Journal of Geology (February 2020) Pre-Issue Publication: 95-104

Abstract

Earth's global barometric pressure, currently 1 bar at sea level, may have changed over its 4.5-billion-year history. Proxy measurements, including N (sub 2) / (super 36) Ar ratios in nearly equal 3.5 to 3.0 Ga hydrothermal quartz, nearly equal 2.7 Ga raindrop imprints, and nearly equal 2.7 Ga vesicle sizes in subaerial basalt lava flows indicate Archean air pressure could have been between 0.1 and 1.2 bar. However, some models argue air pressure in the Archean should have been much higher than now and could allow pressure broadening of greenhouse gas absorption lines to counteract the "Faint Young Sun". Thus, additional paleobarometric measurements would be useful to further constrain Earth's atmospheric evolution. We attempted to use vesicle sizes in lavas erupted near sea-level from the nearly equal 2.9 Ga Pongola Supergroup from Mahlangatsha and Mooihoek, eSwatini (formerly Swaziland) and the White Mfolozi River gorge of KwaZulu-Natal, South Africa to provide further Archean paleobarometric data. However, reliable results were unobtainable due to small and scarce amygdales, irregular vesicle morphologies and metamorphic mineralogical homogenization preventing the use of X-ray Computed Tomography for accurate vesicle size determination. Researchers attempting paleobarometric analysis using lava vesicle sizes should henceforth avoid these areas of the Pongola Supergroup and instead look at other subaerially emplaced lava flows. With this being only the second time this method has been used on Precambrian rocks, we provide a list of guidelines informed by this study to aid future attempts at vesicular paleobarometry.


ISSN: 1012-0750
EISSN: 1996-8590
Serial Title: South African Journal of Geology
Serial Volume: Pre-Issue Publication
Title: Vesicle paleobarometry in the Pongola Supergroup; a cautionary note and guidelines for future studies
Affiliation: University of Washington, Department of Earth and Space Sciences and Astrobiology Program, Seattle, WA, United States
Pages: 95-104
Published: 20200219
Text Language: English
Publisher: Bureau for Scientific Publications, Pretoria, South Africa
References: 36
Accession Number: 2020-041593
Categories: General geophysicsStratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. strat. cols., geol. sketch maps
S27°00'00" - S27°00'00", E31°00'00" - E31°00'00"
Secondary Affiliation: University of Johannesburg, ZAF, South AfricaGeological Survey and Mines Department, SWZ, Swaziland
Country of Publication: South Africa
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Abstract, Copyright, Geological Society of South Africa. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 2020
Close Modal

or Create an Account

Close Modal
Close Modal