Magnetic properties of black mud turbidites from ODP Leg 116, distal Bengal Fan

Conference · Thu Feb 28 23:00:00 EST 1991 · AAPG Bulletin (American Association of Petroleum Geologists); (United States)

OSTI ID:7013082

Sager, W W ^[1]; Hall, S A ^[2]

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1. Texas A and M Univ., College Station (United States)
2. Univ. of Houston, TX (United States)

Turbidites from the distal Bengal Fan cored on ODP Leg 116 showed large magnetic susceptibility (MS) variations. MS peaks were traced to individual turbidites, the most magnetic being dark gray mud turbidites. In addition to large MS values, the turbidites stand out from surrounding layers because of high NRMs, ARMs, SIRMs, and ratios of ARM and SIRM to susceptibility. Alternating field and thermal demagnetization properties and IRM acquisition curves suggest titanomagnetite grains as the primary magnetic mineral with some amount of hematite present. These properties are similar to those of Deccan flood basalts and suggest this formation as a source of magnetic grains. Magnetic granulometry tests implied that the magnetic particles behave as single-domain and pseudo single-domain grains. They also indicate that the large susceptibility peaks result from a tenfold increase in the concentration of titanomagnetite grains. Electron microscope, EDX, and SIRM analyses revealed detrital titanomagnetites with typical sizes around 8-10 {mu}m, but as large as 20-25 {mu}. These are probably the dominant magnetic grains in the black mud turbidites; however, ARM and susceptibility frequency-dependence suggested that there may also be a submicrometer fraction present. Most of the observed titanomagnetite grains are tabular and some display exsolution lamellae, accounting for the pseudo single-domain behavior despite their moderate sizes. Variations in individual MS peak shapes may reflect sedimentological factors such as current velocity changes. Moreover, downhole variations in the amplitudes of turbidite MS peaks suggest a tectonic or environmental influence.

• OSTI ID: 7013082
• Report Number(s): CONF-910403--
• Journal Information: AAPG Bulletin (American Association of Petroleum Geologists); (United States), Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (United States) Vol. 75:3; ISSN AABUD; ISSN 0149-1423
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ASIA
BASALT
BLACK SHALES
CRYSTAL STRUCTURE
DEVELOPING COUNTRIES
HEMATITE
IGNEOUS ROCKS
INDIA
INDIAN OCEAN
IRON ORES
MAGNETIC PROPERTIES
MAGNETIC SUSCEPTIBILITY
MAGNETITE
MINERALOGY
MINERALS
OFFSHORE SITES
ORES
OXIDE MINERALS
PHYSICAL PROPERTIES
ROCKS
SEAS
SEDIMENTARY ROCKS
SEDIMENTS
SHALES
SURFACE WATERS
TITANIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
VOLCANIC ROCKS