The sequence stratigraphic concept and the Precambrian rock record: an example from the 2.7–2.1 Ga Transvaal Supergroup, Kaapvaal craton

1999 ◽  
Vol 97 (3-4) ◽  
pp. 215-251 ◽  
Author(s):  
Octavian Catuneanu ◽  
Patrick G. Eriksson
Keyword(s):  
Kaapvaal Craton ◽  
Precambrian Rock ◽  
Sequence Stratigraphic ◽  
Rock Record ◽  
Transvaal Supergroup

Revised definition/outline of the Kheis Terrane along the western margin of the Kaapvaal Craton and lithostratigraphy of the newly proposed Keis Supergroup

2019 ◽  
Vol 122 (2) ◽  
pp. 187-220 ◽  
Author(s):  
H.S. van Niekerk ◽  
N.J. Beukes
Keyword(s):  
South Africa ◽  
Satellite Imagery ◽  
Aerial Photography ◽  
Kaapvaal Craton ◽  
Thrust Belt ◽  
Western Margin ◽  
Fold And Thrust Belt ◽  
Stratigraphic Subdivision ◽  
Northern Cape ◽  
Transvaal Supergroup

Abstract The Kheis Province is situated between the Namaqua-Natal Province and the western margin of the Kaapvaal Craton in the Northern Cape Province of South Africa. It has been described as a thin-skinned fold and thrust belt formed between 1800 and 1700 Ma. The lithostratigraphic subdivision of the rock units comprising the Kheis Province has been a source of much controversy. From detailed study of aerial photography and satellite imagery, as well as field-based studies, the outcrop patterns in the Kheis Province and Kaaien Terrane were reinterpreted and a new stratigraphic subdivision is outlined here. It is proposed that the structural Kaaien Terrane and Kheis Province should be combined into the Kheis Terrane and that the rocks occurring in the Kheis Terrane should be grouped together to form the new Keis supergroup, with the basal metaconglomerate of the Mapedi/Gamagara Formation recognised as the regional unconformity between the Keis supergroup and the underlying rocks of the Transvaal Supergroup in the Griqualand West area. The Keis supergroup is subdivided from the base upwards into the Elim-, Olifantshoek-, Groblershoop- and Wilgenhoutsdrif groups. The basal Elim group is composed of the Mapedi/Gamagara- and Lucknow formations. It is overlain with a regional erosional unconformity by the Olifantshoek group, which is made up of the Neylan-, Hartley-, Volop- and Top Dog formations. The Olifantshoek group is conformably overlain by the Groblershoop group which is comprised of three upward coarsening successions:the Faanshoek- and Faansgeluk formations,the Maraisdraai- and Vuilnek formations andthe Opwag- and Skurweberg formations. The Groblershoop group is in turn erosively overlain by the rocks of the Wilgenhoutsdrif Group, which include the basal erosive Groot Drink formation which is overlain by the Zonderhuis- and Leerkrans formations. The lithologies of the Keis supergroup are in faulted contact with the rocks of the younger Areachap Group of the ~1200 Ma Namaqua-Natal Metamorphic Province.

A southern African perspective on the co-evolution of early life and environments

2021 ◽  
Vol 124 (1) ◽  
pp. 225-252
Author(s):  
K. Hickman-Lewis ◽  
F. Westall
Keyword(s):  
Southern Africa ◽  
Early Life ◽  
Current Knowledge ◽  
Limited Attention ◽  
Deep Time ◽  
Sulphur Cycle ◽  
Rock Record ◽  
Transvaal Supergroup ◽  
African Perspective ◽  
Pilbara Craton

Abstract The Kaapvaal and Zimbabwe cratons host some of the earliest evidence for life. When compared to the contemporaneous East Pilbara craton, cherts and other metasedimentary horizons in southern Africa preserve traces of life with far greater morphological and geochemical fidelity. In spite of this, most fossiliferous horizons of southern Africa have received relatively limited attention. This review summarises current knowledge regarding the nature of early life and its distribution with respect to environments and ecosystems in the Archaean (>2.5 Ga) of the region, correlating stratigraphic, sedimentological, geochemical and palaeontological understanding. There is abundant and compelling evidence for both anoxygenic photosynthetic and chemosynthetic biomes dominating Palaeoarchaean-Mesoarchaean strata dating back to around 3.5 Ga, and the prevalence of each is tied to palaeoenvironmental parameters deducible from the rock record. Well-developed, large stromatolites characteristic of younger Mesoarchaean-Neoarchaean sequences were probably constructed by oxygenic photosynthesisers. Isotopic evidence from the Belingwe greenstone belt and the Transvaal Supergroup indicates that both a full sulphur cycle and complex nitrogen cycling were in operation by the Mesoarchaean-Neoarchaean. The Archaean geological record of southern Africa is thus a rich repository of information regarding the co-evolving geosphere and biosphere in deep time.

Evidence for widespread oil migration in the 1.88 Ga Gunflint Formation, Ontario, Canada

Geology ◽  
2019 ◽  
Vol 47 (10) ◽  
pp. 899-903
Author(s):  
Birger Rasmussen ◽  
Janet R. Muhling
Keyword(s):  
Oil And Gas ◽  
Iron Formation ◽  
Precambrian Rock ◽  
Oil Migration ◽  
The Core ◽  
Fold And Thrust Belt ◽  
Rock Record ◽  
Petroleum Generation ◽  
Two Phases ◽  
Later Phase

Abstract The abundance of Precambrian organic-rich shales, heated beyond the oil and gas window, requires that enormous volumes of hydrocarbons were generated and transported through the ancient crust. However, the former passage of fluid hydrocarbons rarely leaves a trace, so evidence for this process in the early Precambrian rock record is sparse. Here, we report the widespread presence of solidified oil (pyrobitumen) in the iron formation of the 1.88 Ga Gunflint Formation, Ontario, Canada. Petrographic textures indicate at least two phases of oil migration, an early phase marked by pyrobitumen in granules and intergranular pores, synchronous with synsedimentary silica cementation, and a later phase restricted to crosscutting fractures. The paragenetic relationships between the pyrobitumen and iron oxides indicate that oil migration commenced before hematite and some magnetite growth. Our evidence for early oil migration can be explained by petroleum generation during the 1.86–1.80 Ga Penokean orogeny, expelling hydrocarbons generated in the core of the fold-and-thrust belt outwards and updip through the sediments of the Gunflint Formation.

scholarly journals A template for an improved rock-based subdivision of the pre-Cryogenian time scale

2021 ◽  
pp. jgs2020-222
Author(s):  
Graham A. Shields ◽  
Robin A. Strachan ◽  
Susannah M. Porter ◽  
Galen P. Halverson ◽  
Francis A. Macdonald ◽  
...  
Keyword(s):  
Detailed Analysis ◽  
Future Development ◽  
Time Scale ◽  
Precambrian Rock ◽  
Geological Time ◽  
Geological Time Scale ◽  
Current Time ◽  
Rock Record ◽  
Event Based ◽  
Wide Community

The geological time scale before 720 Ma uses rounded absolute ages rather than specific events recorded in rocks to subdivide time. This has led increasingly to mismatches between subdivisions and the features for which they were named. Here we review the formal processes that led to the current time scale, outline rock-based concepts that could be used to subdivide pre-Cryogenian time and propose revisions. An appraisal of the Precambrian rock record confirms that purely chronostratigraphic subdivision would require only modest deviation from current chronometric boundaries, removal of which could be expedited by establishing event-based concepts and provisional, approximate ages for eon-, era- and period-level subdivisions. Our review leads to the following conclusions: 1) the current informal four-fold Archean subdivision should be simplified to a tripartite scheme, pending more detailed analysis, and 2) an improved rock-based Proterozoic Eon might comprise a Paleoproterozoic Era with three periods (early Paleoproterozoic or Skourian, Rhyacian, Orosirian), Mesoproterozoic Era with four periods (Statherian, Calymmian, Ectasian, Stenian) and a Neoproterozoic Era with four periods (pre-Tonian or Kleisian, Tonian, Cryogenian and Ediacaran). These proposals stem from a wide community and could be used to guide future development of the pre-Cryogenian timescale by international bodies.

scholarly journals Organic biomorphs may be better preserved than microorganisms in early Earth sediments

Geology ◽  
2021 ◽  
Author(s):  
Christine Nims ◽  
Julia Lafond ◽  
Julien Alleon ◽  
Alexis S. Templeton ◽  
Julie Cosmidis
Keyword(s):  
Early Life ◽  
Colloidal Silica ◽  
Early Earth ◽  
Correct Identification ◽  
Precambrian Rock ◽  
Geochemical Conditions ◽  
Organic Composition ◽  
Siliceous Rocks ◽  
Rock Record ◽  
Life On Earth

The Precambrian rock record contains numerous examples of microscopic organic filaments and spheres, commonly interpreted as fossil microorganisms. Microfossils are among the oldest traces of life on Earth, making their correct identification crucial to our understanding of early evolution. Yet, spherical and filamentous microscopic objects composed of organic carbon and sulfur can form in the abiogenic reaction of sulfide with organic compounds. Termed organic biomorphs, these objects form under geochemical conditions relevant to the sulfidic environments of early Earth. Furthermore, they adopt a diversity of morphologies that closely mimic a number of microfossil examples from the Precambrian record. Here, we tested the potential for organic biomorphs to be preserved in cherts; i.e., siliceous rocks hosting abundant microbial fossils. We performed experimental silicification of the biomorphs along with the sulfur bacterium Thiothrix. We show that the original morphologies of the biomorphs are well preserved through encrustation by nano-colloidal silica, while the shapes of Thiothrix cells degrade. Sulfur diffuses from the interior of both biomorphs and Thiothrix during silicification, leaving behind empty organic envelopes. Although the organic composition of the biomorphs differs from that of Thiothrix cells, both types of objects present similar nitrogen/carbon ratios after silicification. During silicification, sulfur accumulates along the organic envelopes of the biomorphs, which may promote sulfurization and preservation through diagenesis. Organic biomorphs possessing morphological and chemical characteristics of microfossils may thus be an important component in Precambrian cherts, challenging our understanding of the early life record.

A new lithostratigraphic framework for portions of the Pongola Supergroup within the Nkandla sub-basin, southern Kaapvaal Craton, South Africa; insights into Mozaan Group stratigraphy

2021 ◽  
Author(s):  
N. Hicks ◽  
D.J.C. Gold ◽  
M. Ncume ◽  
L. Hoyer
Keyword(s):  
Passive Margin ◽  
Kaapvaal Craton ◽  
Coarse Grained ◽  
Iron Formation ◽  
Genetic Sequence ◽  
Sequence Stratigraphic ◽  
Tectonic Model ◽  
Quartz Arenite ◽  
Southeastern Margin ◽  
Main Basin

Abstract A revised lithostratigraphic framework for Mozaan Group-equivalent strata within the Nkandla sub-basin is presented based on new field data, remote sensing and genetic sequence stratigraphic interpretations. Although previous literature has suggested that no Mozaan Group lithologies were deposited within the sub-basin, reinterpretations presented here indicate that 90% of the lithostratigraphy developed within the main basin occurs within the Nkandla and Mhlatuze inliers. Mozaan Group units previously defined as the Vutshini and Ekombe formations are correlated with stratigraphy from the lowermost Sinqeni Formation to the Gabela Formation. Although thinner than units within the type area in the main basin, thicknesses of the Sinqeni Formation are comparable to those observed within the White Mfolozi Inlier. A ~1 000 m composite reference profile is measured within the Mdlelanga Syncline of the Nkandla Inlier. Further profiles were measured for sequences in the Gem-Vuleka Syncline of the Nkandla Inlier, as well as within the Mhlatuze Inlier. These latter profiles, however, host only lower Mozaan Group strata. In all sections the basal portion of the sequence comprises two quartz arenite units, separated by a ferruginous shale, which hosts minor iron formation interbeds. This predominantly coarse-grained lower sequence is overlain by a shale-dominated succession with multiple sandstone interbeds. A prominent coarse-grained quartz arenite unit forms a distinct marker in the middle portion of the sequence. This is overlain by a sequence of shales and sandstones with two prominent igneous units present. Genetic sequence stratigraphic interpretations indicate cyclical deposition of dominantly shallow marine sediments with condensed sections, marked by iron formations or ferruginous shales, denoting periods of marine highstand along the southeastern margin of the Kaapvaal Craton. The evidence of Mozaan Group stratigraphy within the Nkandla sub-basin supports a passive margin tectonic model whereby deposition occurred in an arcuate shallow continental margin which opened to the southeast. The extension of Mozaan Group strata into the Nkandla sub-basin suggests that the Mozaan Basin likely formed a single depository rather than separate sub-basins as previously proposed.

Isotopic constraints on the Late Archean carbon cycle from the Transvaal Supergroup along the western margin of the Kaapvaal Craton, South Africa

2009 ◽  
Vol 169 (1-4) ◽  
pp. 15-27 ◽  
Author(s):  
W.W. Fischer ◽  
S. Schroeder ◽  
J.P. Lacassie ◽  
N.J. Beukes ◽  
T. Goldberg ◽  
...  
Keyword(s):  
South Africa ◽  
Carbon Cycle ◽  
Kaapvaal Craton ◽  
Western Margin ◽  
Transvaal Supergroup ◽  
Isotopic Constraints
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