岡山大学 地球科学研究報告
Published by Okayama University Earth Science Reports Editorial Committee

Provenance of Lower Cretaceous sediments in the Nariwa and Hokubo areas, Okayama Prefecture, deduced from detrital modes and geochemistry of sandstones

Daniel K. Asiedu
Thumnail ESR_3_1.pdf 753 KB
Abstract
Petrographic and geochemical study of sandstones from the Kenseki Formation have shown that the sandstones are compositionally immature. The immaturity is reflected geochemically by their low SiO2 contents (52-66 wt%) and petrographically by low modal percents of quartz and K-feldspar, and high modal percents of plagioclase and volcanic lithic fragmants. The Kensaki sandstones are, however, poor in Na2O (up to 2.1 wt%). Both petrography and geochemistry suggest a heterogeneous source lithologies of acidic and basic volcanics, sedimentary, and ultramafic rocks. Petrographic evidence is supplied by quartz and plagioclase of volcanic origin, acidic volcanic fragments, basic volcanic fragments, volcanic glass, serpentinite fragments and detrital spinel grains. Geochemical evidence is provided by high FeO* (total iron as FeO), MgO, TiO2, CaO and K2O contents. Petrographic and geochemical study of the Kenseki sandstones indicate calc-alkaline oceanic island are provenance. The sediments were locally derived, with Alpine-type ultramafic rocks exposed in the north and volcanic materials of the Akiyoshi Belt supplying the bulk of the detritus.
Keywords
Kenseki Formation
modal analyses
provenance
ISSN
1340-7414
NCID
AN10506284