--> Abstract: The Effectiveness of Heavy Mineral Composition as Useful Indicators of Individual Turbidite Bodies and its Application to the Analysis of their Sedimentary Process: A Case Study on Neogene Turbidite Bodies in the Niigata Backarc Oil Basin, Central Japan

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by S. Tokuhashi and C. M. Agyingi; #90933 (1998).

Abstract: The Effectiveness of Heavy Mineral Composition as Useful Indicators of Individual Turbidite Bodies and its Application to the Analysis of their Sedimentary Process: A Case Study on Neogene Turbidite Bodies in the Niigata Backarc Oil Basin, Central Japan

Tokuhashi, Shuichi - Geological Survey of Japan; Christopher M. Agyingi - University of Buea, Cameroon

Many turbidite sandstone bodies, deposited during the Middle Miocene to Pliocene, are distributed and form one of major reservoirs in the Neogene Niigata backarc oil basin, the most productive oil basin around the Japanese Islands. We practiced detailed and systematic heavy mineral analysis of these turbidite sandstone bodies for the following purposes.

Firstly, we verify the effectiveness of heavy mineral composition as useful indicators to characterize the individual turbidite bodies which occupy the specific spaces with specific formation names or member names. Main results are as follows: 1) The turbidite sandstones in the study area can be classified into at least six types based on the combination of the quantitatively major heavy minerals such as opaque minerals, hornblende, hypersthene, and augite. 2) The turbidite sandstones of one formation or one member are represented by one type or closely related two types. 3) The different formations or members in the study area are often composed of the different heavy mineral composition. The different provenance or the different geologic event (e.g. the beginning of volcanic activities) at the same provenance may be suggested as a cause of the difference.

Secondly, we show a typical case study that the positive combination of heavy mineral analysis with sedimentological analysis leads to a completely different idea on the sedimentary process. Detailed vertical and lateral heavy mineral analysis of the early Pliocene turbidite sandstone body, located at the eastern margin of the basin, disclosed that heavy mineral composition of the turbidite sandstones in the eastern half of the body are completely different from that in the western half of the body. The results of heavy mineral and sedimentological analysis convince that two kinds of turbidite sandstones, shallow-marine shelf turbidite sandstones in the eastern half and deep-marine submarine-fan turbidite sandstones in the western half, were juxtaposed in the area during the early Pliocene age.

As a conclusion, we stress that the heavy mineral analysis is valuable not only as a conventional tool to estimate the provenance, but also as a strong measure to estimate the original relationship of several sandstone bodies neighboring each other, to disclose their sedimentary process in combination with other sedimentary data, and to predict the three-dimensional extents of turbidite sandstone bodies both on the surface and subsurface.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil