Studying the dynamics of cosmic dust flux on the earth’s surface from peat deposits

Peat cores sampled from different climatic zones are studied. The petromagnetic and microprobe methods are used to find peat layers enriched with cosmic dust. It is established that the behavior of saturation isothermal remanent magnetization (SIRM) of peat deposits from the zones where the aeolian transfer of terrigenous particles is negligible can be used for studying the dynamics of the fall of cosmic matter on the Earth’s surface. The cosmic dust flux can be conditionally divided into the background and burst components. Here, the background flux of cosmic dust varies cyclically. The characteristic times of these cycles are about 100 years. The cyclicity in the background flux of cosmic material most clearly manifested itself in the interval of 1200 to 500 years ago. The most significant burst in the influx of cosmic material (by an order of magnitude above the background) is revealed in the layer that was formed about 5000 years ago. The microprobe studies established that the mineralogical content of cosmic dust differs between the background and burst fluxes.

Late Holocene Changes in Precipitation and Hydrography Recorded in Marine Sediments from the Northeastern Caribbean Sea

We present a record of climate variability spanning the last 2000 years obtained from sediment cores retrieved south and west of Puerto Rico in the northeastern Caribbean Sea. The records include lithological and mineral magnetic parameters as well as planktonic foraminifer data. For chronostratigraphic control, AMS 14C and 210Pb/137Cs measurements were made. Harmonic analysis of the values of the mineral magnetic parameters “saturation isothermal remanent magnetization” (SIRM), “anhysteric remanent magnetization divided by magnetic susceptibility” (ARM/χ), and “saturation isothermal remanent magnetization divided by magnetic susceptibility” (SIRM/χ) indicate the existence of a ∼200-year-long climate cycle in the northeastern Caribbean during the last 2000 years. The detected cycle may reflect changes in precipitation patterns over the low-latitude North Atlantic Ocean and surrounding continental areas. Higher organic carbon contents appear in the sediments both off southern and western Puerto Rico before and at the onset of the Little Ice Age around A.D. 1300 to 1500. This is indicative of increased run off and/or enhanced surface productivity possibly associated with more intense wind-induced upwelling. Major changes in the geochemical and mineral magnetic records around A.D. 850–1000 concur with changes in other records from the Caribbean and North African regions indicating a shift toward a more humid climate over the low-latitude North Atlantic.

Paleomagnetism of the Eocene Kamloops Group and the cratonization of Terrane I of the Canadian Cordillera

The lower Middle Eocene (49.4 ± 2.4 Ma) Kamloops Group is exposed in the middle of the Quesnellia subterrane of Terrane I. The group consists of the siliciclastic Tranquille Beds and the overlying Dewdrop Flats plateau basalts and andesites. Detailed alternating field (AF) and thermal step demagnetization was carried out on 282 specimens from 26 flow sites and one conglomerate site, and saturation isothermal remanent magnetization (SIRM) tests were performed to examine the remanence carriers. The petrology of the gently dipping flows, the presence of antiparallel normal and reverse remanence, the conglomerate test, and the fold test all indicate that a primary remanence has been isolated. It resides in both magnetite and hematite over a broad range of AF coercivities, blocking temperatures, and domain sizes. Its mean direction of 355.0°, 73.4 °(α95 = 6.9°) gives a pole position of 138.4°W, 81.4°N (dp = 11.0°, dm = 12.3°) that is statistically indistinguishable from the 50 Ma reference pole for the North American craton. This indicates that the cratonization of Terrane I was complete by the Middle Eocene after it had undergone ~1300 km of northward translation and ~45 °of clockwise rotation since the mid-Cretaceous.

The Effect of Microtopography and Vegetation on the Catchment of Airborne Particles Measured by Remanent Magnetism

Measurements of saturation isothermal remanent magnetization (SIRM) for recent ombrotrophic peats show that the rate of deposition of magnetic particulates from the atmosphere varies strongly in response to the persistent, small-scale, spatial changes in vegetation and microtopography characteristic of many raised bogs. Hummock environments may trap over an order of magnitude more magnetic particulates than do Sphagnum lawns and pools. These results, thought to reflect the interception of subhorizontally moving particles by the hummock forming plants, have potentially important implications for studies of pollen deposition (“influx”) rates in peat.