Chemostratigraphy of the paleoproterozoic Duitschland Formation, South Africa: Implications for coupled climate change and carbon cycling

Citation
A. Bekker et al., Chemostratigraphy of the paleoproterozoic Duitschland Formation, South Africa: Implications for coupled climate change and carbon cycling, AM J SCI, 301(3), 2001, pp. 261-285
Citations number
131
Language
INGLESE
art.tipo
Review
Categorie Soggetti
Earth Sciences
Journal title
AMERICAN JOURNAL OF SCIENCE
ISSN journal
0002-9599 → ACNP
Volume
301
Issue
3
Year of publication
2001
Pages
261 - 285
Database
ISI
SICI code
0002-9599(200103)301:3<261:COTPDF>2.0.ZU;2-H
Abstract
The Paleoproterozoic Duitschland Formation lies stratigraphically beneath t he Timeball Hill Formation, which contains the only unequivocal glacial uni t of this era in the Transvaal Basin, South Africa. Lithologic evidence in Paleoproterozoic successions of North America, however, indicates the exist ence of three discrete and potentially global ice ages within this 300 my i nterval. Carbonates of the Duitschland Formation are significantly enriched in C-13 UP to +10.1 permil in the upper part of the succession above a not able sequence boundary, In contrast, the lower part of this unit contains c arbonates with consistently negative delta C-13 values. Trace and major ele ment compositions of these carbonates as well as carbon-isotopic compositio ns of coexisting organic matter support a primary origin for the markedly p ositive carbon isotope anomaly. The stratigraphic constraints indicate that C-13-enriched carbonates were deposited prior to Paleoproterozoic glaciati on in southern Africa, similar to carbonates stratigraphically beneath Neop roterozoic glacial diamictites worldwide. Also mirroring the Neoproterozoic record are strongly negative delta C-13 values in cap carbonates atop glac ial diamictites in Paleoproterozoic strata of Wyoming and Ontario. The lith o- and chemostratigraphic constraints indicate that the interval of negativ e carbon isotope values in well-preserved carbonates of the lower Duitschla nd Formation may reflect a second Paleoproterozoic ice age in the Transvaal succession. This interpretation is further supported by recently discovere d bullet-shaped clasts with striations in diamictite from the basal part of the succession. Thus, the emerging temporal pattern of carbon isotope vari ations and glaciation in the Paleoproterozoic has a close analogue to Neopr oterozoic events, suggesting a coupling of climatic and biogeochemical chan ges at both ends of the eon.