[en] Complete text of publication follows. Paleomagnetic results obtained from rocks of Ediacaran age in several localities in Laurentia and Baltica persistently display co-existence of two magnetization components, one shallowly and the other steeply inclined. Both components pass criteria for a primary magnetization while geological considerations and radiometric age dating indicate that these magnetizations are surprisingly close in age. A straightforward interpretation of these results would imply that rocks acquired magnetizations in positions switching back and force between equatorial and near-polar latitudes. In a geographic reference frame, such large-scale and fast (up to 70 cm/year) migrations of a continent have long been rejected as dynamically implausible. Alternative explanations involve either a very rapid migration of bulk lithosphere with respect to the rotation axis (TPW = True Polar Wander) or an unusual behavior of the geomagnetic field, e.g., an alternation of the geomagnetic dipole axis between a co-axial and an equatorial alignment. Theoretical arguments suggest that such switching from an axial to an equatorial dipole mode is possible at not unreasonable conditions of outer core thickness and Rayleigh numbers (Aubert, J. and Wicht, J., EPSL, v. 221, p. 409-419, 2004). These two hypotheses entail different geodynamic conditions and have different climatic implications. The TPW velocities are dependent on mantle viscosity structure; at presently accepted viscosity values projected maximum velocities fall short from the required to explain the Ediacaran data (Tsai and Stevenson, JGR, v. 112, issue B5, B05415). Conversely, the lower mantle viscosity is not well constrained by any current observations; the accepted value for the average mantle viscosity might be incorrect. In contrast, the change in geomagnetic field configuration is not speed-limited. The likelihood of the equatorial dipole configuration, however, is contingent on specific outer core conditions. Whether these conditions are met in the Earth's core is unknown; the present - and even more so the past - core conditions are much less understood than those of the mantle. Discrimination between the TPW and equatorial dipole hypotheses, possible with further studies, will provide the key to understanding the thermal evolution of the Earth's interior.

[en] Complete text of publication follows. Studies of modern tropical soils have demonstrated that the relative abundance of pedogenic goethite and hematite is controlled by moisture availability. To evaluate the utility of a G/H ratio as a paleo-precipitation proxy, we conducted a rock-magnetic study of paleosol samples from a known paleo-environmental context. Goethite and hematite content of the studied samples has been estimated based on saturation IRM values of the corresponding magnetization components as identified by a statistical analysis of IRM acquisition curves. Independently, goethite contribution to the high coercivity fraction has been determined by the low-temperature cycling of the IRM. Both methods give identical estimates for the goethite content. The Neogene Siwalik strata of Pakistan are composed of several thousand meters of stacked fluvial floodplain and channel deposits representing deposition by ancient river systems that drained the Himalaya Mountains and foothills. The Middle Miocene Chinji Formation, which is dominantly fine-grained, provides particularly good exposures of successive floodplain paleosols. G/H ratios of samples collected over 100's of meters along a lateral transect in a single Chinji Fm. paleosol show a good correlation (R² =0.88) with δ¹⁸O of soil carbonate, indicating that the ratio can be effectively used as an indicator of moisture availability during pedogenesis. Based on lateral fluvial architecture and varying thickness of this paleosol, we can test the prediction that G/H ratios are lower on topographic highs compared with G/H ratios from topographic lows. Siwalik paleosols affected by fire show a significant change in the high coercivity fraction. In contrast to unbaked samples, burned paleosols lack the goethite component, while the hematite component shows a ∼ 350 mT increase in the mean coercivity value. Evidence for paleo-fires as well as the G/H ratios and their correlation with soil carbonate δ¹⁸O provide new insights on varying environmental conditions that characterized the Miocene sub-Himalayan alluvial plains.