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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 63 (1979)

Issue: 3. (March)

First Page: 456

Last Page: 456

Title: Provenance Studies in Tunisia by U-Pb Ages of Detrital Zircons: ABSTRACT

Author(s): Henri E. Gaudette, Patrick M. Hurley, T. Lajmi

Article Type: Meeting abstract

Abstract:

In recent years, with increasing availability of radiometric age determinations, age provinces in continental areas have become more clearly defined. Thus the possibility of establishing source areas for extensive sedimentary sequences by means of radiometric age determination of included detrital minerals is enhanced. With this objective, samples in northern and central Tunisia of detritus in river channels draining Oligocene-early Miocene sandstones, and rock samples of the Oligocene-early Miocene Numidian flysch, and Chercheri-Fortuna sandstones were obtained. Permian and Triassic sandstone outcrops and Ordovician sandstone cores from exploratory wells in southern Tunisia were also sampled. Zircons were separated from the detritus and the sandstones, and U-Pb isotopic ompositions of the zircons were determined. Analytic results are interpreted on Concordia plots.

The results of zircon analyses of detrital sands in drainages from northern and central Tunisia indicate a primary intercept age of 1,750 ± 100 m.y. Analyses of the zircons from the Oligocene-Miocene sandstones cropping out in the drainage areas yield an age of 1,706 ± 50 m.y., strongly suggesting that the zircons in the drainage channel sands represent the population of zircons in the rocks themselves, and that the detrital zircon may provide a useful indicator of provenance. F. C. Wezel has shown a predominant transport direction of south to north for the Oligocene-Miocene sedimentary units of Tunisia. A southern source for the sedimentary sequences in northern Tunisia was sought in the Permian-Triassic and Ordovician sandstones of the Medenine area. Zircons from the Permi n and Triassic sandstones give an intercept age of 1,650 ± 60 m.y. The U-Pb age of zircons from the Ordovician sandstone core samples is 1,871 ± 26 m.y. Thus, we find a coherence, within analytical error, of all the zircon separates from rocks of widely differing stratigraphic ages and geographic locations. This does not preclude the possibility of mixed populations; however, on the basis of our analytical methods, it is strongly suggested that the zircon populations appear homogeneous, and that their U-Pb isotopic ages do represent the primary age (i.e., the source age) of the zircons regardless of stratigraphic setting.

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