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A laboratory electromagnetic model study of the Juan de Fuca Plate region
OLR 0986) 33 (12)
D. SubmarineGeologyand Geophysics
circulation. Palaeogeogr. Palaeoclimatol. Palaeoecol., 55(1):55-64. Eolian dust grains extracted from SE Pacific pelagic sediments provide a Neogene record of Southern Hemisphere atmospheric processes. The mass accumulation rate of dust has been low and generally constant since the Late Oligocene. Eolian grainsize data show an increase from 8.2q, (3.40 /0 in older sediments to 7.2q~ (6.80 #) in younger material. This shift occurred about 10.5 mya and reflects a significant increase in the intensity of atmospheric circulation. Comparison with existing information from the Northern Hemisphere suggests that the Southern Hemisphere has had more intense atmospheric circulation throughout the Neogene and that this asymmetry reached its greatest extent between 10.5 and 2.5 Ma. Oceanogr. Prog., Univ. of Michigan, Ann Arbor, MI 48109, USA. 86:6932 Williams, G.E., 1986. The Acraman impact structure: source of ejecta in Late Precambrian shales, South Australia. Science, 233(4760):200-203. A major probable impact structure occurs in middle Proterozoic dacitic volcanics in the Gawler Ranges. The structure has an inner depressed area about 30 km in diameter that contains the Lake Acraman salina, an intermediate depression or ring about 90 km in diameter, and a possible outer ring approximately 160 km in diameter. The Acraman structure is the largest probable impact structure known in Australia and is the likely source of dacitic ejecta found in Late Precambrian marine shales some 300 km to the east. ©1986 by AAAS. Dept. of Planet. Sci., Univ. of Arizona, Tucson, AZ 85721, USA.
DI80. Paleontology (see also
E-BIOLOGICAL
OCEANOGRAPHY) 86:6933 Hartmann, Gerd and Hans Petersen, 1985. Homonyms of recent and fossil Ostracoda (Crustacea) and the introduction of three new names. Mitt. Hamb. Zool. Mus. Inst., 82:263-267. Zool. Inst., Martin-Luther-King-Platz 3, 2000 Hamburg 13, FRG. 86:6934 Martini, Erlend and Carla MUller, 1986. Current Tertiary and Quaternary calcareous nannoplankton stratigraphy and correlations. Newsl. Stratig., 16(2):99-112. The nannoplankton zonation is updated on the basis of new information, mainly from DSDP. Because
1015
certain species used as datum indicators are restricted by paleoclimatic or paleodepth conditions, additional species for identifying the NP- and NN-zones are mentioned as substitutes. Range charts for most of the important species in the Tertiary and Quaternary are given. Geol.-Palaontol. Inst. der Univ., Senckenberg-Anlage 32-34, D-6000 Frankfurt am Main, FRG. 86:6935 McMillan, I.K., 1986. Cainozoic planktonic and larger Foraminifera distributions around southern Africa and their implications for past changes of oceanic water temperatures. [Extended abstract.] S. Aft. J. Sei., 82(2):66-69. Southern Oil Explor. Corp. Ltd., P.O. Box 3087, Johannesburg 2000, South Africa.
D200. Gravity, geodesy, magnetism 86:6936 Dosso, H.W. and W. Nienaber, 1986. A laboratory electromagnetic model study of the Juan de Fuca Plate region. Phys. Earth planet. Interiors, 43(!): 34-46. The scaled laboratory model includes a simulation of the complex Juan de Fuca Plate subducting beneath the Vancouver Island region. Magnetic field calculations for over Vancouver Island, over the Olympic Peninsula, and over a linear portion of the U.S. coastline are examined in detail. The general conclusion is that the dipping, subducting plates significantly attenuate, at short periods, maxima in the anomalies at the overlying coastlines, while leading to anomalous vertical and horizontal fields over ranges as large as 500 km inland over a wide period range. Dept. of Phys., Univ. of Victoria, B.C., Canada. 86:6937 Hildebrand, J.A. and H. Staudigel, 1986. Seamount magnetic polarity and Cretaceous volcanism of the Pacific Basin. Geology, geol. Soc. Am., 14(6):456-458. Analysis of the magnetic polarity of Pacific seamounts excluding the Hawaiian Ridge shows a predominance of seamounts with normal polarity on crust older than 65 Ma, whereas normal, reversed, and mixed polarity characterize seamounts younger than 65 Ma. It is suggested that the predominantly normal seamounts formed 110-70 Ma during a time of extensive magmatic activity; this time frame 'overlaps the long Cretaceous normal period (118-84 Ma) and corresponds to 85% normal polarity for
D. SubmarineGeologyand Geophysics
circulation. Palaeogeogr. Palaeoclimatol. Palaeoecol., 55(1):55-64. Eolian dust grains extracted from SE Pacific pelagic sediments provide a Neogene record of Southern Hemisphere atmospheric processes. The mass accumulation rate of dust has been low and generally constant since the Late Oligocene. Eolian grainsize data show an increase from 8.2q, (3.40 /0 in older sediments to 7.2q~ (6.80 #) in younger material. This shift occurred about 10.5 mya and reflects a significant increase in the intensity of atmospheric circulation. Comparison with existing information from the Northern Hemisphere suggests that the Southern Hemisphere has had more intense atmospheric circulation throughout the Neogene and that this asymmetry reached its greatest extent between 10.5 and 2.5 Ma. Oceanogr. Prog., Univ. of Michigan, Ann Arbor, MI 48109, USA. 86:6932 Williams, G.E., 1986. The Acraman impact structure: source of ejecta in Late Precambrian shales, South Australia. Science, 233(4760):200-203. A major probable impact structure occurs in middle Proterozoic dacitic volcanics in the Gawler Ranges. The structure has an inner depressed area about 30 km in diameter that contains the Lake Acraman salina, an intermediate depression or ring about 90 km in diameter, and a possible outer ring approximately 160 km in diameter. The Acraman structure is the largest probable impact structure known in Australia and is the likely source of dacitic ejecta found in Late Precambrian marine shales some 300 km to the east. ©1986 by AAAS. Dept. of Planet. Sci., Univ. of Arizona, Tucson, AZ 85721, USA.
DI80. Paleontology (see also
E-BIOLOGICAL
OCEANOGRAPHY) 86:6933 Hartmann, Gerd and Hans Petersen, 1985. Homonyms of recent and fossil Ostracoda (Crustacea) and the introduction of three new names. Mitt. Hamb. Zool. Mus. Inst., 82:263-267. Zool. Inst., Martin-Luther-King-Platz 3, 2000 Hamburg 13, FRG. 86:6934 Martini, Erlend and Carla MUller, 1986. Current Tertiary and Quaternary calcareous nannoplankton stratigraphy and correlations. Newsl. Stratig., 16(2):99-112. The nannoplankton zonation is updated on the basis of new information, mainly from DSDP. Because
1015
certain species used as datum indicators are restricted by paleoclimatic or paleodepth conditions, additional species for identifying the NP- and NN-zones are mentioned as substitutes. Range charts for most of the important species in the Tertiary and Quaternary are given. Geol.-Palaontol. Inst. der Univ., Senckenberg-Anlage 32-34, D-6000 Frankfurt am Main, FRG. 86:6935 McMillan, I.K., 1986. Cainozoic planktonic and larger Foraminifera distributions around southern Africa and their implications for past changes of oceanic water temperatures. [Extended abstract.] S. Aft. J. Sei., 82(2):66-69. Southern Oil Explor. Corp. Ltd., P.O. Box 3087, Johannesburg 2000, South Africa.
D200. Gravity, geodesy, magnetism 86:6936 Dosso, H.W. and W. Nienaber, 1986. A laboratory electromagnetic model study of the Juan de Fuca Plate region. Phys. Earth planet. Interiors, 43(!): 34-46. The scaled laboratory model includes a simulation of the complex Juan de Fuca Plate subducting beneath the Vancouver Island region. Magnetic field calculations for over Vancouver Island, over the Olympic Peninsula, and over a linear portion of the U.S. coastline are examined in detail. The general conclusion is that the dipping, subducting plates significantly attenuate, at short periods, maxima in the anomalies at the overlying coastlines, while leading to anomalous vertical and horizontal fields over ranges as large as 500 km inland over a wide period range. Dept. of Phys., Univ. of Victoria, B.C., Canada. 86:6937 Hildebrand, J.A. and H. Staudigel, 1986. Seamount magnetic polarity and Cretaceous volcanism of the Pacific Basin. Geology, geol. Soc. Am., 14(6):456-458. Analysis of the magnetic polarity of Pacific seamounts excluding the Hawaiian Ridge shows a predominance of seamounts with normal polarity on crust older than 65 Ma, whereas normal, reversed, and mixed polarity characterize seamounts younger than 65 Ma. It is suggested that the predominantly normal seamounts formed 110-70 Ma during a time of extensive magmatic activity; this time frame 'overlaps the long Cretaceous normal period (118-84 Ma) and corresponds to 85% normal polarity for