139736eo.pdf (20MB) - Japan Oceanographic Data Center

GEOLOGICAL-GEOPHYSICAL MAPPING OF THE INDIAN OCEANN.N. TURKO, G.B. UDINTSEV AND D.I. ZHIVInstitute of Earth Physics of USSRAcademy of Sciences, P. Grusinakaya 10113810 Moscow, USSRHISTORICAL PERSPECTIVEThe history of the geological-geophysical mapping of the Indian Ocean bottom hasencompassed several stages. The first stage started in the middle of the 19* century, when the layingof the first telegraph cables necessitated some knowledge of the sea floor. Early scientific expeditions,such as the “Challenger” “Askold”, “Gazel”, “Valdivia”, “Enterprise”, “Sealark”, “Planet”, “Snellius”,“Investigator”, also resulted in bathymetric soundings and the collecting of bottom sediments. Thefirst bathymetric maps were compiled on the basis of these data (RYKACHEV, 1881; KRUMMEL,1881; SCHOTT, 1902; MURRAY and HJORT, 1912; GROLL, 1912). Three editions of the GeneralBathymetric Chart of the Oceans (GEBCO) also were published, the first in 1903 and the third in1938-1942. The first gravity measurements were taken in the 1920’~-1930’s (VENING-MEINESZ,1948).The end of the World War I1 was the starting point of the second stage, which manifesteditself by the use of new techniques, particularly the use of both high frequency and low frequencyecho-sounding, seismic profiling, magnetics and gravity studies and increasingly accurate navigation.Large expeditions were undertaken by the research vessels “Albatros”, “Galathea”, “Challenger”, “Ob”and “Lena”. As in earlier cruises, however, the measurements were made along single profiles, andthe resulting maps often merely supplemented the third edition of GEBCO (e.g. ATLAS OF THEWORLD, 1959; STOCKS, 1944). The maps were still very schematic.INTERNATIONAL INDIAN OCEAN EXPEDITIONAn important step in the study of the ocean was the organization of the International IndianOcean Expedition (IIOE) in 1960-1965, with the encouragement of the Scientific Committee onOceanic Research (SCOR) and UNESCO. The work of research vessels from more than 20 countriesproduced a great volume of new data on the topography, geophysics and geology of the ocean, andfew major discoveries were made: the Ninetyeast Ridge, the Lanka Ridge, the Chagos Trench, andnumerous seamounts. The results of IIOE research were published in the International Geological-Geophysical (IGG) Atlas of the Indian Ocean (1975). Because this enormous task took so much time,other maps based on IIOE results were published and later incorporated into the Atlas. Among themwere the physiographical map of the ocean (HEEZEN and THARP, 1964), the Red Sea(LAUGHTON, 1970b) and the Gulf of Aden (LAUGHTON, 1966, 1970a), maps of the Somali andMascarene basins and of the Karlsberg Ridge (FISHER, 1968; SCLATER and FISHER, 1974),maps of the Sunda Arc (MAROVA, 1966), the Andaman Sea (RODOLFO, 1969) and the Gulf ofOman (SEIBOLD and ULRICH, 1970), and many maps of individual canyons and seamounts. TheIGG Atlas also contained the results of international projects which were conducted in the IndianOcean after the end of IIOE: the Upper Mantle Project (UMP) and the Deep Sea Drilling Project(D S DP) .In discussing the maps in the IGG Atlas of the Indian Ocean, several points should beemphasized: 1) the topographic and of geophysical maps, both ocean-wide and local, are presented ata single scale, thus enabling easy comparison; 2) the tracks plotted on the maps make it possible todistinguish interpretation from real data. In this way the maps also serve to point out areas requiringfurther research. In the course of future studies it should be sufficient to enter new data on the mapsand to reinterpret these parts without re-evaluating the previous data. Data interpretation, however,differs from author to author, as does the manner of cartographic representation. For example, in thebathymetric maps from the Indian Ocean in the IGG Atlas and the 5th edition of GEBCO chart, the