Early archean spherule beds in the Barberton mountain land, South Africa: Impact or terrestrial origin?

Reimold, W. U.; Koeberl, Christian; Johnson, S. H.; McDonald, Iain

doi:10.1007/bfb0027759

Cited by 31 publications

(72 citation statements)

References 75 publications

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“…15B) (Lowe and Byerly, 1986), and in many rocks, spherule shapes have been locally modified by pressure solution and stylolite development. In the Sheba Mine spherules in S3 are typically flattened (Reimer, 1983), as are many from the area of the Agnes Mine (Reimold et al, 2000).…”

Section: Spherulesmentioning

confidence: 98%

“…A number of recent investigators have questioned the impact interpretation of the BGB spherule beds (Koeberl et al, 1993;Koeberl and Reimold, 1995;French, 1998;Ryder et al, 2000;Reimold et al, 2000). Koeberl et al (1993), Koeberl and Reimold (1995), and Reimold et al (2000) noted that samples of spherule beds collected in the vicinity of gold mines in the northern BGB show non-chondritic ratios among siderophile elements and a correlation between PGE and chalcophile element abundances.…”

Section: Introductionmentioning

confidence: 95%

“…Koeberl et al (1993), Koeberl and Reimold (1995), and Reimold et al (2000) noted that samples of spherule beds collected in the vicinity of gold mines in the northern BGB show non-chondritic ratios among siderophile elements and a correlation between PGE and chalcophile element abundances. They suggested that elevated PGE levels in the spherule beds are the result of postdepositional mineralization and hydrothermal alteration and that the spherule beds formed through unspecified volcanic processes.…”

Section: Introductionmentioning

confidence: 96%

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Spherule Beds 3.47–3.24 Billion Years Old in the Barberton Greenstone Belt, South Africa: A Record of Large Meteorite Impacts and Their Influence on Early Crustal and Biological Evolution

et al. 2003

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Four layers, S1-S4, containing sand-sized spherical particles formed as a result of large meteorite impacts, occur in 3.47-3.24 Ga rocks of the Barberton Greenstone Belt, South Africa. Ir levels in S3 and S4 locally equal or exceed chondritic values but in other sections are at or only slightly above background. Most spherules are inferred to have formed by condensation of impact-produced rock vapor clouds, although some may represent ballistically ejected liquid droplets. Extreme Ir abundances and heterogeneity may reflect element fractionation during spherule formation, hydraulic fractionation during deposition, and/or diagenetic and metasomatic processes. Deposition of S1, S2, and S3 was widely influenced by waves and/or currents interpreted to represent impact-generated tsunamis, and S1 and S2 show multiple graded layers indicating the passage of two or more wave trains. These tsunamis may have promoted mixing within a globally stratified ocean, enriching surface waters in nutrients for biological communities. S2 and S3 mark the transition from the 300-million-year-long Onverwacht stage of predominantly basaltic and komatiitic volcanism to the late orogenic stage of greenstone belt evolution, suggesting that regional and possibly global tectonic reorganization resulted from these large impacts. These beds provide the oldest known direct record of terrestrial impacts and an opportunity to explore their influence on early life, crust, ocean, and atmosphere. The apparent presence of impact clusters at 3.26-3.24 Ga and approximately 2.65-2.5 Ga suggests either spikes in impact rates during the Archean or that the entire Archean was characterized by terrestrial impact rates above those currently estimated from the lunar cratering record.

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Section: Spherulesmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 96%

See 1 more Smart Citation

Spherule Beds 3.47–3.24 Billion Years Old in the Barberton Greenstone Belt, South Africa: A Record of Large Meteorite Impacts and Their Influence on Early Crustal and Biological Evolution

et al. 2003

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“…The meteoritic signature can also be modified by fractionation, alteration and post-impact remobilization, as observed at a number of terrestrial impact structures (e.g. Evans et al, 1993;Colodner et al, 1992;McDonald et al, 2001), the Archaean spherule layers in Western Australia and South Africa (Simonson et al, 1998(Simonson et al, ,2009Reimold et al, 2000), the ∼590 Ma Acraman impact ejecta and host shales (Wallace et al, 1990) and the 65 Ma K-Pg boundary clay (Evans et al, 1995). However, these processes are unlikely to account for the complete absence of a meteoritic contribution.…”

Section: Os Isotope Systemmentioning

confidence: 99%

Projectile Identification in Terrestrial Impact Structures and Ejecta Material

Goderis¹,

Paquay²,

Claeys³

2012

Impact Cratering

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“…The interpretation of these layers is complicated by their alteration and recrystallization and by the apparent absence of shocked quartz associated with the spherules. As a result, the impact origin of these layers is still debated, especially for some of the South African ones (Koeberl and Reimold 1995;Reimold et al 2000;Shukolyukov et al 2000). The evidence for impact appears stronger for: 1) several Australian spherule layers ~2.5 Ga old, at least 1 of which is a clearly exotic unit in fine-grained dolomite (Simonson and Hassler 1997) and several of which display small but definite iridium anomalies (Simonson et al 1998(Simonson et al , 2000McDonald and Simonson 2002); and 2) the so called "Monteville layer" in South Africa (Simonson et al 2000).…”

Section: Distal Ejecta: Records Of Young and Old Impact Eventsmentioning

confidence: 99%

The importance of being cratered: The new role of meteorite impact as a normal geological process

French

2004

Meteorit & Planetary Scien

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Abstract-This paper is a personal (and, in many ways, incomplete) view of the past development of impact geology and of the newly recognized importance of impact events in terrestrial geological history. It also identifies some exciting scientific challenges for future investigators: to determine the full range of impact effects preserved on the Earth, to apply the knowledge obtained from impact phenomena to more general geological problems, and to continue the merger of the once exotic field of impact geology with mainstream geosciences. Since the recognition of an impact event at the Cretaceous-Tertiary (K-T) boundary, much current activity in impact geology has been promoted by traditionally trained geoscientists who have unexpectedly encountered impact effects in the course of their work. Their studies have involved: 1)

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Early archean spherule beds in the Barberton mountain land, South Africa: Impact or terrestrial origin?

Cited by 31 publications

References 75 publications

Spherule Beds 3.47–3.24 Billion Years Old in the Barberton Greenstone Belt, South Africa: A Record of Large Meteorite Impacts and Their Influence on Early Crustal and Biological Evolution

Spherule Beds 3.47–3.24 Billion Years Old in the Barberton Greenstone Belt, South Africa: A Record of Large Meteorite Impacts and Their Influence on Early Crustal and Biological Evolution

Projectile Identification in Terrestrial Impact Structures and Ejecta Material

The importance of being cratered: The new role of meteorite impact as a normal geological process

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