ABSTRACT The mid-Pleistocene transition is a time interval between ca. 1.2 and 0.7 Ma during which a shift occurred from ~41 k.y. glacial-interglacial cycles to ~100 k.y. cycles. Although the mid-Pleistocene transition has been well documented in global marine records, its effects in continental environments, including North America, are incompletely understood owing to the paucity of terrestrial sediment records spanning the entire Quaternary. A notable exception is the ca. 1.4 Ma and younger Blackwater Draw Formation, an extensive eolian sequence on the Southern High Plains of the United States. Intervals of the Blackwater Draw Formation section that are inferred to span the mid-Pleistocene transition can be divided into pre–, syn–, and post–mid-Pleistocene transition parts. Weathering profiles in the pre–mid-Pleistocene transition section are dominated by weakly developed soils formed in arid environments, as evidenced by well-expressed pedogenic carbonate horizons, lack of clay formation during hydrolysis, and magnetically soft, coarse-grained magnetite/maghemite populations. Conversely, the syn– and post–mid-Pleistocene transition intervals demonstrate an increase in weathering intensity by an abrupt increase in clay content formed in part by hydrolysis of feldspars, soil profiles that demonstrate leaching and illuviation, and a fining-upward grain size of the magnetite/maghemite population. Sedimentologic, geochemical, and rock-magnetic data are consistent with a southern and coarser sediment source derived from the Pecos River drainage prior to the mid-Pleistocene transition, followed by a mixture of northern and southern sources during and after the mid-Pleistocene transition. Overall, our results indicate that pre–mid-Pleistocene transition conditions on the Southern High Plains were arid with wind energy sufficient to mobilize sand sheets out of the Pecos River and deposit them on the plateau. The syn– and post–mid-Pleistocene transition environments reflect somewhat wetter conditions and potentially an influx of silt from the north, in addition to continued sand derived from the Pecos River valley. The wetter conditions and silt influx may have resulted from longer-lived and more robust glacial activity in the Northern Hemisphere that characterized the post–mid-Pleistocene transition Earth system.

Abstract A marine sediment core from the western Mediterranean provides a new high-resolution 4500 year record of palaeomagnetic secular variation and relative palaeointensity. In 2013, the 7.1 m C5 core was recovered from the Tyrrhenian Sea as part of the NextData climate data project. The coring site, 15 km offshore from the Volturno river mouth, is well located to record combined marine and terrestrial palaeoclimatic influences, and the fine-grained, rapidly deposited sediments are effective palaeomagnetic recorders. We investigate the palaeomagnetic field direction and strength recorded in the core, which provide a valuable high-resolution record of Holocene geomagnetic variation in the area. Using rock magnetic techniques, we constrain the magnetic mineralogy of the studied sediments and confirm their suitability for palaeomagnetic analysis. Palaeomagnetic declination and inclination records were determined by stepwise alternating-field demagnetization, and relative palaeointensity estimates were obtained based on normalization to anhysterestic and isothermal remanent magnetization and to magnetic susceptibility. The age of the core is well constrained with a tephra and biostratigraphic age model, and its magnetic records are compared with relevant core and model data for the region, demonstrating that our record is compatible with previous results from the area. An automated curve matching approach is applied to assess the compatibility of our data with the existing secular variation path for the Mediterranean area.

ABSTRACT We conducted a detailed rock magnetic and mineralogical study of bole beds from the Deccan magmatic province, India. Magnetic susceptibility of 15 bole beds showed two contrasting patterns, with susceptibility values either increasing or decreasing up the profile. We then focused on two representatives red boles located in the Western Ghats, the RBB and RBAN profiles, to unravel the nature and origin of these contrasting magnetic susceptibility patterns. The presence of smectite argues against significant secondary thermal alterations. Major-elemental compositions obtained by X-ray fluorescence spectrometry of RBB and RBAN red boles are comparable to the parent basalt and show significant and typical depletion of mobile elements such as sodium and calcium compared to the parent basalt. The Ti/Al ratio of both the red boles and their overlying clay layers is close to the typical value of Deccan basalt (0.2), suggesting that the material of the red boles has been derived from weathering of the parent basalt. The chemical index of alteration varies from 40–50 in the parent basalt to 80–90 at the top of the bole beds, consistent with moderate to intense weathering of the bole beds. However, similar to other Deccan bole beds, indices of lateritization below 50 suggest that the state of lateritization has not been reached. Although the RBB and RBAN profiles share similar mineralogical signatures, their magnetic mineral assemblages are distinctly different. In the RBB profile, magnetic susceptibility decreases up-profile as a result of oxidation/dissolution of primary titanomagnetite inherited from the parent basalt, with subsequent formation of pedogenic hematite and superparamagnetic particles. In contrast, magnetic susceptibility in the RBAN profile, which contains magnetite, some hematite, and goethite, increases up-profile. The increase in the magnetic signal is mainly due to the increasing amounts of phyllosilicate and goethite, while the content of magnetite and hematite remains constant along the profile. We attribute the variation in the magnetic mineral assemblage to contrasting humid and dry environments during weathering, leading to the preferential formation of goethite or hematite, respectively. The combined mineralogical and rock magnetic data suggest the existence of a single weathering profile involving soil formation in the two studied red boles, with few or no contributions from an external source.