Provenance analysis of sand-matrices of chert breccias in the Kamiaso unit, Mino terrane, was carried out on the basis of the chemical composition of detrital garnets and chromian spinels.
Chert breccia is a clast-supported breccia composed mainly of radiolarian chert clasts, and includes clasts of siliceous shale, claystone and sandstone. The matrix of chert breccia is quartzo-feldsparthic sandstone and contains mica minerals, garnet, zircon, tourmaline, chromian spinel and opaque minerals.
Detrital garnets, which commonly occur in the sand-matrices, consist mainly of almandine with a higher pyrope component, and these Mg-rich garnets are likely to have been derived from the upper amphibolite to granulite facies metamorphic rocks. Detrital chromian spinels are characterized by lower TiO₂ content, lower Cr/(Cr+Al) atomic ratio, and a negative correlation of Cr/(Cr+Al) and Mg/(Mg+Fe²⁺) atomic ratios, and were probably derived from mantle peridotites.
The heavy mineral analysis suggests that the provenance of the sand-matrices of chert breccias was composed mainly of a continental basement comprising high-grade metamorphic rocks. The absence of clasts derived from continental basements in chert breccias suggests that the clasts of chert breccias had fallen from the surface of the accretionary prism to the trench and been mixed with trench-fill sandy sediments derived from continental basements.

View full abstract

High possibility of liquefied and fluidized flow from reworked volcaniclastics is clarified by grain-size distribution combined with settling velocity. Samples are obtained from “mudflow” deposits of the Pliocene Ohta and Souri tephra beds. Grain size of autofluidization in these samples can be calculated based on the comparison between superficial fluid velocity at minimum fluidization and superficial fluid escape velocity. Autofluidization can occur when particle diameter is finer than 0.4mm in the Ohta tephra, and finer than 0.7mm in the Souri tephra. However, particles finer than 0.001mm in diameter have low possibility of autofluidization because of their cohesion. Mean particle diameters of all samples are satisfy the size range of autofluidization, suggesting the particles in those deposits must be supported by fluidization.

View full abstract

Channel fills in the Iwaki Formation of the Paleogene Shiramizu Group in the Joban Coalfield are deviled into two types, which are simple fills and complex fills. Their vertical distribution, steady paleocurrent direction and decreasing grain size imply upward change in fluvial environment.

View full abstract

Two-dimensional computer simulation of depositional sequences based on the regime concept is applied to evaluate changes in their stacking patterns in response to geometry of basement, trajectories of relative sea-level changes and trend of subsidence. The simulation results that (1) stacking patterns of the sequences are different between which accumulated on the gentle coastal plain and that on the steep rocky coast, (2) differences in paths of relative sea-level changes, i. e. sinuous or zigzag-shaped, are reflected in stacking patterns from the transgressive to high-stand systems tract in the sequences, and (3) trajectories of isofathoms in progradational high-stand successions differ by the rates of subsidence increasing basinward and being constant. Then this model is also applied to reconstruct the thickness of the parasequences in a depositional sequence of the Plio-Pleistocene Kakegawa Group.

View full abstract

The arid, shallow marine, carbonate/evaporite succession of the Arab-Hith Formations (Upper Jurassic) is the reservoir interval for the GA Field, offshore Abu Dhabi, UAE. It consists of multiple sequences bounded by second-fourth order marine flooding surfaces, which are powerful tools for detailed regional stratigraphic correlation. Using these key bounding surfaces, the chronostratigraphic framework between the GA Field and WMB-1 well, which is located 50km westward of the field, can be constructed to describe the facies changes within this sedimentary package.
The second order transgressive systems tract (TST) is composed of an aggradational/retrogradational parasequence set that was deposited in a barrier shoal-sabkha complex. The highstand system tract (HST) comprises a thickening upward parasequence set that is characterized by a sabkha depositional system.
The evolution of flood tidal delta deposits of Upper Jurassic age in this region is controlled by the second and third order sea level changes. The flood tidal delta deposits were well-developed in the second order TST deposits, especially at the third order highstand sea level phase. However, the flood tidal delta deposits are not found in the second order HST deposits. This can be interpreted by the fact that accommodation space in the lagoon had already been filled by the prograding sabkha deposits in the second order highstand phase.

View full abstract