Depth distribution of calcareous sediments in the Mesozoic and Cenozoic North Atlantic Ocean

The upper Mesozoic and Cenozoic distribution of calcareous, biogenic particles which are produced by planktonic foraminifers and nannoplankton and which are the most important components of pelagic sediments since mid-Mesozoic times, has been reconstructed using data from North Atlantic deep-sea drill sites. Two phases of sedimentation of carbonate-rich sediments are separated by an interval from 100 to 80 m.y. B.P. when CaCO₃ particles were diluted by chiefly terrigenous material. Prior to 100 m.y. B.P. the highest concentrations of calcareous matter were confined to the deepest part of the then 4–4.5 km deep North Atlantic. After 80 m.y. B.P. sediments with high concentrations of calcareous matter have been deposited above 3 km paleodepth, but during the last 25 m.y. also between 4 and 5.5 km paleo-water depth. The latter occurrence is associated with indications of downslope displacement of calcareous material into the abyssal plains of the deepest parts of the North Atlantic.     

SEA and SDA measurements at panská VES — peculiar Events

Summary The results of the twelve-year (1962–1973)SEA (27 kHz) andSDA (5 kHz) measurements at the Panská Ves Observatory are presented with an emphasis on peculiar events. About half of allSIDs are observed asSEA events and about 10% asSDAs. NoSID has been observed only as anSDA. A fewSIDs have been observed asSEA only, most of them being probably of non-solar origin. A few events observed asSEA andSDA only, or as anSID withSDA, but withoutSEA, are briefly discussed, too.     

Ionospheric effects of the December 16–18, 1971 geomagnetic storm

Summary The post-storm effect (PSE) of the December 16–18, 1971 geomagnetic storm is studied with the use of the ionospheric radio wave absorption measurements and f _min data from a network of the GDR, USSR and Czechoslovak observatories. Only a high latitude effect of the storm was found. We found more significant absorption effects associated with later weaker enhancements of geomagnetic activity. The part played by the interplanetary magnetic field is demonstrated. A magnetospheric explanation of the observed variability of PSE based on the time-development of filling up the slot region is suggested.