The Witputs diamictite in southern Namibia and associated rocks: constraints for a global glaciation?

Abstract The long-conceived idea of the glacial origin of Blaini diamictite of Lesser Himalayan Neoproterozoic succession reached its maxima when the diamictites and capping pink limestone were attributed to the Neoproterozoic Snowball Earth event and its aftermath, respectively. Occurrences of diamictite-limestone association in two different levels have also been correlated with the Sturtian and Marinoan glaciations. Critical review, however, reveals that the interpretations of the glacial origin of diamictites are not well founded. The diamictite-limestone association, which occurs at the lower part of a thick, light brown shale unit and laterally grades into light brown shale, primarily indicates episodic surge events in an otherwise tranquil condition favorable for hemipelagic sedimentation. The lithology, bed geometry, internal organization, and disposition of the diamictite bodies suggest deposition of debris flow fan lobes along fault scarps in a rift setting. Emplacement of subaqueous debris flows is indicated by the associated deposits of entrained turbidity currents. The limestone also bears the signature of claciturbidites. The appearance of diamictite bodies and associated limestone in two distinct levels is not a stratigraphic disposition; on the contrary, the deposits were dislocated and repeated by two successive regional thrust faults. The Chemical Index of Alteration (CIA) values of the light brown shale and the matrix of the diamictites indicate that these sediments formed through prolonged subaerial weathering. The events leading up to development of the rift system and evidence of prolonged weathering within the basin-fill sediments are consistent with supercontinental break up, the prologue of Snowball Earth.

Diamictite

Snowball Earth

Dalradian

Subaerial

Mudflow

Debris flow

Chemostratigraphy

10.1130/b35483.1

Cite

Citations (13)

dummyHistory of sedimentological research on clastic sediments with remarks on history of Russian sedimentology

Journal of the Sedimentological Society of Japan (1500)

authorGalina dummyKirillova

sedimentologists are chronologized from Steno ( ) to Vail ( ) who greatly contributed to the development The book of an internationally famous Japanese Pro-of sedimentology.The major events, among which are fessor of sedimentology Hakuyu Okada "The Evolution the Challenger expedition ( ) ; the Journal Seof Clastic

10.4096/jjssj.63.17

Cite

Citations (0)

Microbial Mats in Terrigenous Clastics: The Challenge of Identification in the Rock Record

Palaios (1999)

Jürgen Schieber

Increasingly, microbial communities are recognized for playing a potentially important role in defining and modifying surface sediment characteristics in various settings, ranging from terrestrial, through marginal marine, to continental margins. Whereas, the presence of microbial mats can be established with comparative ease in modern terrigenous clastics, their recognition in sedimentary rocks poses a big challenge. Terrigenous clastics of the Belt Supergroup (Mid-Proterozoic) show a number of features that can serve as microbial mat indicators: (A) domal buildups; (B) cohesive behavior; (C) wavy-crinkly character of laminae; (D) irregular wrinkled bed surfaces; (E) ripple patches; (F) laminae with mica enrichment; (G) irregular, curved-wrinkled impressions on bedding planes; and (H) lamina-specific distribution of early diagenetic minerals (dolomite, ferroan carbonate, pyrite). Positive identification of a fossil microbial mat requires one to find microbial filaments in life position. This is a difficult task even in the case of very favorable preservation of organic matter, and impossible to accomplish in many instances where fossil microbial mats are suspected. Nonetheless, the above features (especially when found in combination) are highly suggestive of microbial mats, and can serve as guides to sediments that may have accumulated under the influence of microbial mats. Whereas the Belt Basin examples are all from shallow-water environments, microbial mats may also have played an important role in deeper-water oxygen-deprived settings-the realm of black shale formation. In areas of modern oxygen-minimum zones, microbial mats have been found to thrive at the seafloor, profoundly influencing the chemistry of the sediment/water interface and sediment stability. Possible ancient analogs occur in a variety of black shale deposits (e.g. Jet Rock, Monterey Formation, Green River Formation), with wavy to crinkly kerogen-rich laminae being the main indication of possible microbial mat origins. Although microbial mats clearly have the ability to thrive in black shale environments, it will require more research to firmly establish whether, and how extensively, they occupied this niche in the geologic past.

Terrigenous sediment

Identification

10.2307/3515357

Cite

Citations (228)

Index to Volume 25, 1986

Journal of the American Academy of Child Psychiatry (1986)

Diamictite

Snowball Earth

Chemostratigraphy

10.1016/s0002-7138(09)60216-8

Cite