Interaction between turbidity currents and a contour current – A rare example from the Ordovician of Shaanxi province, China
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Date
2019-04
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Wydawnictwo Naukowe UAM
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Abstract
The silty top parts of graded turbidites of the Late Ordovician Pingliang Formation, which accumulated along the
southern margin of the Ordos Basin (central China), have been reworked by contour currents. The reworking of the
turbidites can be proven on the basis of paleocurrent directions in individual layers: the ripple-cross-bedded sandy
divisions of some turbidites show transport directions consistently into the downslope direction (consistent with the di-
rection of other gravity flows), but in the upper, silty fine-grained division they show another direction, viz. alongslope
(consistent with the direction that a contour current must have taken at the same time). Both directions are roughly
perpendicular to each other. Moreover, the sediment of the reworked turbidites is better sorted and has better rounded
grains than the non-reworked turbidites.
Although such type of reworking is well known from modern deep-sea environments, this has rarely been found before
in ancient deep-sea deposits. The reworking could take place because the upper divisions of the turbidites involved are
silty and consequently relatively easily erodible, while the contour current had locally a relatively high velocity – and
consequently a relatively large erosional capability – because of confinement within a relatively narrow trough.
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Keywords
contourites, turbidites, reworking, Ordos Basin, Pingliang Formation
Citation
Geologos, 2019, 25, 1, s.15-30.
ISBN
978-83-232187-4-6