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Summary Chemical extraction techniques are being introduced into environmental magnetism studies to aid in the interpretation of magnetic climate proxies. Previous studies have shown that the acid‐ammonium‐oxalate/ferrous‐iron (AAO–Fe2+) extraction technique can be used to selectively dissolve very fine‐grained magnetite and maghemite from synthetic samples. Here, we present the results of a study of this extraction technique to serve as a tool for selective dissolution of pedogenic magnetic minerals from a loess–palaeosol transect. Before and after extraction, the samples were subjected to classic mineral–magnetic methods (measurement of low‐field susceptibility and hysteresis parameters), as well as first‐order reversal‐curve analysis. In addition, acquisition curves of the isothermal remnant magnetization (IRM) were fitted with logarithmic distributions. These analyses showed the magnetic dominance of low‐coercivity magnetic minerals. By subtracting the IRM remaining after extraction from that before extraction, the magnetic fraction that was dissolved could be characterized as well, supplying extra information concerning the performance of the extraction technique. The AAO–Fe2+ method successfully dissolved the superparamagnetic and part of the single‐domain material from the palaeosol samples in one extraction step, repeating the extraction resulted in hardly any further changes to the magnetic content of the samples. The magnetic characteristics of the loess samples remained stable throughout the extraction experiment. The combination of the AAO–Fe2+ extraction with mineral–magnetic analysis has successfully identified the pedogenic contribution in our samples. Therefore, variations in the lithogenic fraction potentially present in pedogenically enhanced intervals can be assessed, improving the merit of mineral–magnetic climate proxy parameters.

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The oldest rocks of the Miramar sheet are represented by sediments of the Punta Carballo Formation (Miocene), which are exposed at the SW corner. However, volcanic rocks of the older Aguacate Group (Miocene-Pliocene) and overlying Monteverde Formation (Lower Pleistocene) dominate the area. The Pliocene to Pleistocene silicic ignimbrites and Quaternary sediments are subordinate. New K-Ar ages yielded 4,41±0,15 to 4,99±0,36 Ma for the Aguacate Group and 1,71±0,22 to 1,77±0,11 Ma for the Monteverde Formation. Gabrodioritic stock was newly mapped in the Aguacate Group accompanying numerous other intrusive bodies of variable composition. New K-Ar ages were obtained for the rhyodacitic domes: 1,71±0,14 Ma for the cerro La Cruz Dome and 1,59±0,12 Ma for the cerro San Miguel Dome. Definition of volcanic units is based on detailed petrography, XRD, microprobe and 33 new bulk-rock chemical analyses.

A giant rockslide occurred on the southern side of an Upper Tertiary shield volcano in central Nicaragua in the Holocene. The failure caused tectonic-like deformation of rock masses and changed the local stress regime. The lower, compressional part of the rockslide produced a stress field with the axis of maximum stress (σ1) parallel to the displacement vector of the main body. The upper part of the rockslide was gravity-driven with σ1 vertical and σ3 horizontal, and oriented SE–NW. The mass tended to move SE. In the crown, the stress field had a subvertical σ1 steeply dipping towards the west. Data at the base of the Santa Lucia Depression, where east- and west-dipping reverse and thrust faults developed, showed that the compressional stress, σ1, was nearly horizontal and east–west oriented, the horizontal σ2 was north–south oriented, and the σ3 was subvertical. These compressional conditions resulted from the collapse of the crown after the main slope failure phase. Simultaneously, along with the gravity relaxation of the main displaced mass, the slopes and mountain slopes along the main scarp depression underwent deep-seated sliding, sagging and flowing.