Biogeochemical signatures preserved in ancient siliceous sediments; new perspectives to Triassic radiolarian bedded chert compositions

Abstract

Major and minor elements of successively collected 70 Middle Triassic radiolarian bedded cherts from the Mino Belt in central Japan were studied. In order to reveal pre-diagenetic, primary geochemical signatures related to marine biogeochemical cycles, composite data of chert-shale couplets in addition to raw data were examined. The results show that Mn, Cu, Sr, Ba and P were supplied significantly by non-lithogenic excess fractions. Positive correlation with SiO 2 / TiO 2 suggests that accumulations of Ba, Sr, Mn and Cu were closely related to sedimentation of biogenic silica; Mn and Cu were probably incorporated into oxides, whereas Ba into barite. Relationship between SiO 2 /TiO 2 and excess-Ba, proxy for surface productivity implies that regeneration of silica from sinking radiolarian tests was not significant. This may have been caused by an expected relatively short travel time of radiolarian tests from the ocean surface to the bottom, reflecting their large size compared with diatoms. Positive correlations between CaO and P 2 O 5 imply that apatite species are host phases for P and Ca. Although conodont composed of apatite is abundant in both chert and shale, their CaO/P 2 O 5 ratio differs markedly from those of cherts and shales. Other apatite species, possibly carbonate apatite of diagenetic origin, are present in the bedded cherts and contribute to excess-P accumulation. Early diagenesis is believed to have modified only slightly primary geochemical features of the studied bedded cherts. This suggests relatively oxic depositional environment for the bedded cherts, under which regeneration of redox sensitive elements were not active.

Sediment pollution impacts sensory ability and performance of settling coral-reef fish

“…Behavioural avoidance of acid sulfate soils has been shown in juveniles of various fishes when pH levels were well within the range exhibited in natural systems (Kroon 2005). Red soil in Okinawa is acidic, with a pH of ~5 (Mkadam et al 2006), and analysis of the rearing conditions used here showed that the pH decreased with both increasing concentration of red soil and time. Reductions in pH of a similar magnitude (0.07) were shown to elicit similar behavioural changes in juvenile coral trout (Plectropomus leopardus) (Munday et al 2013).…”

Paleoenvironmental reconstruction for termination stage of Superanoxia in Middle Triassic (Anisian) sedimentary sequence of the Mino belt, central Japan

“…Most of these oxides had positive correlations among them. In particular, the correlation coefficient between P 2 O 5 and CaO was the highest and positive (r = 0.90), which indicates that the two oxides are mainly derived from apatite (Takiguchi, Sugitani, Yamamoto, & Suzuki, ). After correcting contribution from apatite, the correlation coefficients of CaO* with Al 2 O 3 and K 2 O (r = 0.33 and 0.56) became higher than those of CaO (r = 0.18 and 0.50) except for that with Na 2 O, whereas that with P 2 O 5 (r = 0.64) became lower than that of CaO.…”

Composition and accretion rate of fossil micrometeorites recovered in Middle Triassic deep-sea deposits

“…The accretion rate of spherules is controlled by the sediment accumulation rate for shale and chert beds. Sedimentological and geochemical studies have suggested that the present alternations of chert and shale beds refl ect original cyclic sedimentation of siliceous and relatively clay-rich materials (Hori et al, 1993;Takiguchi et al, 2006), though probably biased and exaggerated by later diagenetic redistribution of Si (Tada, 1991). Although there is no direct estimation of accumulation rates on individual shale and chert beds, Hori et al (1993) suggested that the shale bed has a much slower accumulation rate than the chert bed, based on the 10-100 times higher abundance of magnetic microspherules of probable extraterrestrial origin in shale than in chert.…”