The problems of soils in limestone area ot the Nansei Shoto, southwest Japan

[cat] En les terrasses formades a Nansei Shoto (SW del Japó) a causa de l’aixecament de l’escull coral.li, els sols més antics tenen les següents característiques: tonalitat rojenca, quantitats més altes d’òxids de ferro lliures (Fez03 %) així com una major intensitat del pic corresponent a l’hematita. En les terrasses més recents els sòls són groguencs, però els òxids de ferro lliures (Fe203 %) són encara elevats amb una intensitat mes alta del pic de la goethita. Les àrees cobertes per sols rojos (anomenats Shimajiri-mãji) en els esculls coral·lins aixecats, es veuen sovint afectades per la sequedat en les zones de conreu de canya de sucre. Per evitar els danys causats per l'aridesa s'ha mesclat Jagar (originat a partir de roques argiloses terciàries) amb els sols rojos de les àrees de Shimajiri-mãji. No obstant això, la introducció de maquinària agrícola, les millores del sòl a gran escala i l’augment de la superfície conreada, han tengut per resultat una erosió accentuada del sòl en aquests camps. Endemés, els sols arrossegats pels rius resulten perjudicials per a la pesca costanera i ocasionen l’extinció dels corals.[eng] Soils on the terraces formed from uplifted coral reef in the Nansei Shoto, SW Japan, have characters that hue of soils is more reddish, amounts of free iron oxides (Fez03 %) are higher, and peak intensity of hematite is higher on the older terraces. On the younger terraces, soils become yellowish hue, but free iron oxides (Fe203 %) are still higher with higher peak intensity of goethite. The areas covered by red soils, called Shimajiri-mãji, on the uplifted coral reef suffer frequently from drought on the sugar cane cultivation. For avoid the damages by drought, Jagar, originated from Tertiary muddy rock, has been mixed into the red soils in the Shimajiri-mãji areas. However, introduction of machines for cultivation, soil amelioration in a large scale, and enlarging unit area of each fields have resulted in a large amount of soil erosion at the fields. Soils flowed from the rivers hinder coastal fishery and corals become extinct

Lithology, Rock Relief and Karstification of Minamidaito Island (Japan)

Minamidaito Island is a karstified coral island located on the Philippine plate. Karstification periods occurred during the end of the Pliocene, in major part of the Pleistocene, and in the Holocene. The first period of karstification can be observed in the lower Daito dolomitized limestone (5 Ma and 4 Ma); the karstification seems to have occurred as a result of sea level change caused by the cooler conditions of the paleoclimatic environment. Geological studies were performed to study reef carbonates in detail. Among them, biointrasparite limestone of framestone and bafflestone types with transitions to grainstone and dolomitized biointrasparry limestone of framestone and bafflestone types dominate. Calcimetric analyses established that in certain locations the distribution of limestone and dolomite differs from the distribution previously described. Rock relief reveals the unique formation of coastal karren, the development of the surface in the interior of the island, and the most characteristic periods of cave development.Key words: Minamidaito Island, lithlogy, coral dolomitized limestone, rock relief, coastal karren, karstification, vegetation