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A nonmarine pelecypod assemblage in the Pennsylvanian of Arizona and its correlation with a horizon in Pennsylvania
- R. M. C. Eagar, H. W. Peirce
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- Journal:
- Journal of Paleontology / Volume 67 / Issue 1 / January 1993
- Published online by Cambridge University Press:
- 20 May 2016, pp. 61-70
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A nonmarine pelecypod occurrence was reported in 1977 within a zone of gray shaly mudstones yielding carbonized plants at Promontory Butte, Mogollon Rim, east-central Arizona. On paleobotanical evidence, the zone appeared then to be either of Late Carboniferous or Early Permian age. Work on 50 measurable shells indicates that the fauna is of Anthraconaia protracta Eagar and has wide variation. Standard dimensions of the Arizona fauna are identical to those of the type assemblage of A. protracta, which forms a thin band immediately above the Benwood Limestone of the Monongahela Group near Pittsburgh, Pennsylvania, 2,700 km to the east. The Arizona shell varieties match 50–60 percent of those from the band in Pennsylvania. Matching falls off rapidly to nil 70 m below this horizon and 100 m above it. Small differences in the trends of variation of the shells from Promontory Butte and Pennsylvania are accompanied by small differences in their respective host sediments, as reflected in their organic carbon and carbonate contents. When these results are compared with earlier conclusions on recurrent, apparently ecophenotypic, changes in the shape of Anthraconaia from other horizons in the Carboniferous and Lower Permian, they provide further evidence that the Arizona and Pennsylvania faunas were approximately contemporary. When the two bands are correlated, the Promontory Butte band is placed in the upper Pennsylvanian and in the upper Virgilian as traditionally accepted.
Theileria parva: Comparative infection rates of adult and nymphal Rhipicephalus appendiculatus
- R. E. Purnell, C. D. H. Boarer, M. A. Peirce
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- Journal:
- Parasitology / Volume 62 / Issue 2 / April 1971
- Published online by Cambridge University Press:
- 06 April 2009, pp. 349-353
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Sections of salivary glands from adult R. appendiculatus ticks and sections of the whole bodies of nymphal R. appendiculatus ticks were studied to obtain data on the incidence and development of T. parva during feeding. Since, in their previous instars, all the ticks had dropped engorged from a parasitaemic calf on the same day, it was possible to compare the resultant infection rates in nymphs and adults.
In the adult ticks, the highest percentage infection (45%) and the greatest number of infected acini (45 from 20 ticks) were observed after 3 days feeding. Mature parasites were first seen after 4 days. In the nymphs, the highest percentage infection (35%) was observed after 3 days feeding. Equal numbers of infected acini (14 from 20 ticks) were observed in unfed nymphs and in those which had fed for 2 or 3 days. Mature parasites were first seen after 2 days, and all were mature after 3 days.
It was concluded that a batch of nymphs would contain more parasites per gramme than a corresponding batch of adult ticks. This fact, together with the observed uniformity of maturation of the parasites in nymphs, may make nymphs a more suitable choice than adults for the preparation of ground tick stabilates.
We are most grateful to Mr M. P. Cunningham, who inoculated the calf on which the ticks fed, and to Mr A. Musoke who observed the subsequent clinical reaction of the calf.
This work was carried out as part of the programme of the Immunological Research on Tick-borne Cattle Diseases and Tick Control Project which is supported by the United Nations Development Programme/Special Fund, with F.A.O. as the Executing Agency, in collaboration with the East African Community. The assistance of our colleagues on the Project is gratefully acknowledged. This paper is published by kind permission of Mr A. Rashid, the Director of the East African Veterinary Research Organization.
Evidence for accumulated melt beneath the slow-spreading Mid-Atlantic Ridge
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- By M. C. Sinha, Bullard Laboratories, Department of Earth Sciences, University of Cambridge, Cambridge CBS OEZ, UK, D. A. Navin, Department of Geological Sciences, University of Durham, Durham DH1 SLE, UK, L. M. MacGregor, Bullard Laboratories, Department of Earth Sciences, University of Cambridge, Cambridge CBS OEZ, UK, S. Constable, Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093, US, C. Peirce, Department of Geological Sciences, University of Durham, Durham DH1 SLE, UK, A. White, School of Earth Sciences, Flinders University of South Australia, Adelaide 5001, Australia, G. Heinson, School of Earth Sciences, Flinders University of South Australia, Adelaide 5001, Australia, M. A. Inglis, Department of Geological Sciences, University of Durham, Durham DH1 SLE, UK
- Edited by J. R. Cann, University of Leeds, H. Elderfield, University of Cambridge, A. S. Laughton, Southampton Oceanography Centre
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- Book:
- Mid-Ocean Ridges
- Published online:
- 04 August 2010
- Print publication:
- 22 July 1999, pp 17-38
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Summary
The analysis of data from a multi-component geophysical experiment conducted on a segment of the slow-spreading (20 mm yr−1) Mid-Atlantic Ridge shows compelling evidence for a significant crustal magma body beneath the ridge axis. The role played by a crustal magma chamber beneath the axis in determining both the chemical and physical architecture of the newly formed crust is fundamental to our understanding of the accretion of oceanic lithosphere at spreading ridges, and over the last decade subsurface geophysical techniques have successfully imaged such magma chambers beneath a number of intermediate and fast spreading (60–140 mm yr−1 full rate) ridges. However, many similar geophysical studies of slow-spreading ridges have, to date, found little or no evidence for such a magma chamber beneath them.
The experiment described here was carefully targeted on a magmatically active, axial volcanic ridge (AVR) segment of the Reykjanes Ridge, centred on 57° 43′ N. It consisted of four major components: wide-angle seismic profiles using ocean bottom seismometers; seismic reflection profiles; controlled source electromagnetic sounding; and magneto-telluric sounding. Interpretation and modelling of the first three of these datasets shows that an anomalous body lies at a depth of between 2 and 3 km below the seafloor beneath the axis of the AVR. This body is characterized by anomalously low seismic P-wave velocity and electrical resistivity, and is associated with a seismic reflector. The geometry and extent of this melt body shows a number of similarities with the axial magma chambers observed beneath ridges spreading at much higher spreading rates.