Distribution Of Phytoliths Research Articles

Interet de l'etude du cycle biogeochimique du silicium pour interpreter la dynamique des sols tropicaux

Abstract Recent studies on the biogeochemical cycle of silica put new constraints into models of genesis and evolution of silica in tropical environments. The role of plants in weathering mass balances are illustrated by phytolith studies. In Dimonika (Congo) latosols, dissolved silica originates mainly from the dissolution of phytoliths rather than from the dissolution of non-biogenic silicates. In andosols from La Reunion island (Indian Ocean), a 15 cm thick, biogenic silica accumulation formed within 4000 years from bamboo forests fires. The turn-over of silica by plants must therefore be taken into account in studies of weathering rates. Weathering rates of trachytic ash layers in La Reunion island show that all the primary minerals are destroyed and that 50% of amorphous secondary Al/Si products are transformed into halloysite. Theses rates, which are faster than the ones obtained in the Hawaii islands, may strongly influence the turn-over of carbon in soils. Besides, phytoliths preserved from dissolution may help to decipher the records of environmental changes in soils. In Salitre (Brazil), the phytolith distribution has been calibrated with charcoal and pollens. The age of phytoliths, which increases with depth, allow to trace the savanna/forest changes.

Paleoenvironmental history of post-Toya Ash tephric deposits and paleosols at Iwate Volcano, Japan, using aeolian dust content and phytolith composition

Abstract Physicochemical, mineralogical, and geochemical analyses of post-Toya Ash (90–130 ka) tephric and aeolian deposits at the foot of Iwate volcano, northeastern Japan, revealed the accumulation of deposits of long-range aeolian dust transported from the Asian continent and interstratified with the tephric deposits. Oxygen isotopic ratios of quartz in the 1–10μm fractions from two paleosols formed in the aeolian units (Shibutami cracked layers) are +16.2 and +17.0‰, consistent with this fine-grained quartz being of an aeolian origin. The accumulation of Asian aeolian dust onto tephric deposits in northeastern Japan was dominant in the cold stages of the Last Glacial period (20–34 ka and 50–70 ka). We determined the changes in vegetation and climate by using opal phytolith distribution in the tephra and aeolian deposits and associated paleosols. Similarly, we interpreted the paleoenvironmental history of the tephric deposits by relating the vegetation history to the dust flux and fossil periglacial phenomena (i.e. involution) observed on tephra beds. The paleoclimate sequence obtained coincides closely with the marine oxygen isotope curves, indicating that opal phytolith analysis is useful in determining the Interglacial/Glacial-cycle recorded in aeolian and tephric deposits.

Phytolith Size Characteristics Between Udolls and Ustolls

AbstractTo test a phytolith size‐annual rainfall relationship hypothesis, the sizes of opaline phytoliths from four Oklahoma soils were compared. Opaline phytoliths form in intimate association with plant cells and the variation of plant cell size with moisture stress forms the theoretical basis for the hypothesis. The soils sampled were St. Paul, a Typic Argiustoll; Zaneis and Vanoss, Udic Argiustolls; and Fitzhugh, a Typic Argiudoll. Opaline phytoliths were isolated from the 5–20µ, 20–35µ, and 35–50µ soil fractions. The relative amounts of phytoliths in these size fractions in the upper 10 cm of each soil was used to measure their size variation among soils. Phytoliths were further characterized by shape in each soil. Distribution of phytoliths with depth was also noted.There was a higher incidence of the 5–20µ phytoliths in the Ustoll than in the Udoll (66.9% vs. 53.2%) and a correspondingly higher percentage of 35–50µ phytoliths in the Udoll compared to the Ustoll (14.8% vs. 4.4%). The Udoll‐Ustoll intergrades contained intermediate quantities of the 35–50µ phytoliths but not of the 5–20µ and 20–35µ phytoliths. It was concluded that the hypothesized relationship seemed to exist with further work required to understand the relationships in the intermediate areas. Such a relationship would be a very useful tool in paleosol and paleoclimate studies.