Tillite


Also found in: Dictionary, Thesaurus, Medical, Legal, Financial, Wikipedia.
Related to Tillite: Mid oceanic ridge

tillite

[′ti‚līt]
(petrology)
A sedimentary rock formed by lithification of till, especially pre-Pleistocene till.

Tillite

 

any one of the ancient moraines occurring as rudaceous, unsorted formations that have undergone consolidation and, sometimes, even metamorphism. Tillites are formed from a silty unstratified mass known as glacier milk; they also contain boulders bearing glacial striations.

A distinction is made between marine tillites, formed as a result of glacial transport and deposition in the sea, and continental tillites, the composition of which often provides information on the type of rock underlying the glacier and, by extension, on the ablation area and direction of the glacier. Tillites are often confused with similar rocks of nonglacial origin, for example, the deposits of mud-laden torrents and the sedimentary rock formed underwater from the deposits of turbidity currents. Tillites are testaments to periods of glaciation; they are known to have existed since the early Proterozoic era and are very widely distributed in late Proterozoic deposits on nearly all continents. Their horizons are encountered among the Upper Riphean strata of the Eastern European Platform, the Upper Ordovician regions of Africa, and the Upper Carboniferous and Permian regions of the southern continents. The thickness of tillites reaches tens and hundreds of meters.

Tillites are widely used in solving problems of stratification and paleogeography (paleoclimatology), as well as in prospecting for sedimentary minerals (iron ores). A comparison of tillites with anthropogenic moraines makes it possible to obtain a general picture of glacial sedimentation.

REFERENCE

Gretskaia, T. A: “Tillity i ikh znachenie dlia resheniia geologiche-skikh zadach.” In Itogi nauki: Seriia “Geologiia.” Moscow, 1966.

T. A. GRETSKAIA

References in periodicals archive ?
Alfred Wegener saw the global scattering of tillites in a very different light; here was clear evidence that continents were previously clustered together and had since been moved apart (Wegener, 1912, 1924).
The work of Mawson (1949) on the Sturtian Tillites of South Australia ('the greatest thing of the kind recorded anywhere in the world; Mawson, 1958) is a good example of the classical approach to interpretation of sedimentary strata containing poorly sorted, laminated and banded rocks.
It was soon appreciated that not all poorly sorted rocks are glacial tillites deposited below glaciers on elevated continental surfaces; many are non-glacial deep-marine mass-flow deposits interbedded with turbidites (Fig.
Harland and Bidgood (1959) reported magnetic data purporting to record equatorial paleolatitudes for Neoproterozoic glacials, and invoked a huge 'infracambrian glaciation' of global extent involving 'near synchronous worldwide tillites' (Harland, 1964, Harland and Herod, 1975, p.
Building on the work of Crowell (1957) and others, he argued that many supposed Neoproterozoic 'tillites' are non-glacial debris flows of unknown climatic significance, deposited in tectonically active marine basins marginal to uplifted source areas.
The Harvard team showed that if the global warming proposed by Kirschvink occurred after the Neoproterozoic glaciation, then carbonates atop the Neoproterozoic tillites are precisely what would be expected.
But the fact that they found carbon 13 eventually springing back to normal levels above the tillites suggested that life must have gradually increased in the warm equatorial waters.
They questioned the hypothesis that the cap carbonates deposited over the tillites resulted from the reaction of atmospheric carbon dioxide released from volcanoes with calcium and magnesium washed into the seas by weathering of the continents.