Sistema Regional de Información
en línea para Revistas Científicas de América Latina,
el Caribe, España y Portugal

The Ruma loess section, located in the central part of the south slope of Fruška Gora Mountain, exposes a 20 m thick series of loess and paleosols in the local brickyard. Results of amino acid racemization geochronology confirmed middle- and late-Pleistocene ages of Ruma’s loess-paleosol sequences, and correlates with aminostratigraphic subdivisions at other Central European sites. Paleopedological analyses describe morphology, mineralogy, grain-size distribution and carbonate content of the sediments and paleosols. Five paleosol levels represent the environmental transition from humid forest environments to relatively dry steppe interglacial landscapes during the last about 350 ka. Especially interesting are thick pedogenic layers formed in distinct paleo-depressions, which were created during the last glacial cycle. These horizons provide proxy data useful in the detailed reconstruction of environmental conditions during marine oxygen-isotope stages 5 and 3.

A late Quaternary loess-paleosol sequence at Schattenhausen (SW Germany) was studied by isotopic methods (δ13C, δ18O, 14C age). The stable isotopic composition of organic carbon indicates that C3 vegetation dominated the site during most of the time of formation of the loess-paleosol sequence (δ13C = -26 to -20 ‰). However, there was a short period in the Late Pleniglacial with a pronounced C4 excursion of the δ13C values (-16 to -19 ‰) of organic matter. Calcified root cells (δ13C = -8 to -11 ‰ and δ18O = ca. -6.5‰) are isotopically different from diffuse carbonate in the loess and soil matrix (δ13C = -1 to -2.5 ‰; δ18O = -6 to -7.5 ‰). The stable isotopic composition of carbon and oxygen of the calcified root cells in combination with their 14C ages suggest that they formed, at least partially, in the Holocene.

The upper Pleistocene loess-paleosol sequence of Val Sorda (northeastern Italy) is investigated with paleopedological, micromorphological, and mineralogical methods. Special emphasis is placed on magnetic parameters and analysis of clay minerals. The base of the sequence is an Eemian paleosol, which consists of a rubefied Bt-horizon formed in till. This Bt-horizon is covered by loess, three interstadial paleosols and colluvial deposits. The three interstadial paleosols have a Chernozem morphology and characteristics, reflecting a dry and continental paleoclimate. The top of the sequence is covered by till deposited during the Solferino Stage glacial advance.

The morphologic-analytical features of the Bryansk fossil soil classified as Umbric Gley Soil formed in moraine loams and overlain by Upper Pleistocene moraine of the Valday (Würmian) glaciation are described. This paleosol, formed during the Dunaevo Interstadial of the upper Pleistocene and corresponding to the marine isotope stage 3, is confined to the extraglacial zone of the Valday glaciation. The paleosol marks the northernmost area of existence of the Bryansk soil cover in Europe. It is shown that the Bryansk fossil soil can serve as a direct indicator of landscape and soil forming processes in the center of the Russian Plain.

Several dark-colored buried paleosols are studied in balkas (valley) in the south of Russia (Kalmykia Republic). The paleosols differ from modern soils by chemical and physical properties that indicate differences in the character of soil-forming processes in the past and in the present. The paleosols are buried under colluvial and eolian deposits, whose intensive accumulation followed the late Holocene climatic optimum (about 1,000 years ago). We hypothesize burial was caused by landscape erosion associated with social developments within this territory. One reason for simultaneous burial of soils within the large study area probably was catastrophic landscape erosion caused by immense flocks of sheep kept by tribes that occupied the territory of the collapsed Khazar state.

Investigations concerning the pedological linkages between modern soils and paleosequences, as well as the research regarding their spatial distribution and variability dynamics along the landscape are unfortunately very scarce. Both studies can provide, in a geochronological scale, a very useful paradigm to decipher the present and past biotic and abiotic environmental conditions that prevailed in many regions of the world. The aim of this paper is: (1) to characterize the environment as well as the soil groups and paleosequences located in landscapes of the Transmexican Volcanic Belt, Morelos state, and (2) to explain, relate, and visualize in two dimensions and at a reconnaissance scale, the spatial distribution of soil groups within these landscapes. Such knowledge can provide the basis to establish a unique paleopedological record of late Pleistocene to Holocene environmental conditions in the Transmexican Volcanic Belt. In our study, the interpretation of thematic cartography and the application of sophisticated methods like remote sensing and laboratory automated image analyses combined with field transects, provided a unique set of tools for generating and synthesizing data. These data were invaluable in order to obtain the spatial predictions about soil and paleosequence distribution. Our research results reveal that: (a) in the study area there are seven different soil groups, 19 subgroups, one group of relict paleosols, and two genetic types of alterites; (b) the phenomenon of topography-induced environmental differences, and the slope-profile position commonly have a notable influence on the spatial distribution and variability of soil groups; (c) all studied paleosols meet many of the taxonomic requirements for Luvisols, while some alterites satisfy the diagnostic characteristics of Fragipans or Duripans; (d) the pattern of paleosequence spatial distribution in the Morelos landscapes is closely parallel to the distribution of late Pleistocene–Holocene volcanic geomorphic elements. In addition, many of the studied soils and paleosequences show distinctive spectral properties that allow their accurate identification by means of automated image analyses. These results suggest that the spatial distribution of these soils and paleosequences in Morelos state are geographically predictable.

The Peña Colorada iron deposit is made up by three different mineralized bodies: (1) an upper massive magnetite body, up to 20 meters thick, sub-concordant with the regional stratification, that contains decimetric to metric fragments of a granatite rock completely replaced by K-feldspar; (2) a lower disseminated magnetite body, also subconcordant with the regional stratification, with a maximum thickness of 150 meters and made up by pyrite–magnetite–pyroxene rhythmic alternances with poiquilitic K-feldspar masses (episienite “sensu lato”); and (3) a mineralized polymictic breccia, with evidences of hydraulic fracturing, with a diatrema-like morphology, cutting the whole stratigraphical serie at Peña Colorada. The latter includes xenoliths of “low-Ti nelsonites” (in the sense of Fooses and Grauch), found exclusiverly at the lower breccia outcrops. In this paper we report the first two K–Ar absolute ages obtained from the main magnetite bodies at Peña Colorada. A fresh K-feldspar from one episienite mass of the lower disseminated body gave an older age of 65.3±1.5 Ma, whereas a K-feldspar sample from the pseudomorfosed granatites gave a younger age of 57.3±2.1 Ma. These ages place the age of this deposit between the upper Cretaceous– Paleocene transit and the middle Paleocene. As the dated bodies represent the second and third genetic events (of five) in the origin of the Peña Colorada deposit, it is possible to assert that the mechanisms that gave origin to Peña Colorada acted, at least, during a 4.4 Ma period. The disposition of the different mineralized bodies, their textural characteristis and the difference in ages among them suggest that the Peña Colorada iron deposit formed due to recurrent mineralizing events in a discrete cortical volume and within a relatively wide time lapse (>4 Ma). All these facts are against a skarn origin caused by the intrusion of a magmatic rock. Morevoer, we propose that the Peña Colorada deposit has strong affinities with the IOCG (Iron–Oxide–Copper–Gold deposits of Phanerozoic age, similarly to the Fe deposit of Cerro de Mercado in Durango.

We present a detailed study of the geology of the San Pedro–Ceboruco graben (SPC) supported by extensive field work, subsurface information of eight exploratory wells drilled by the Comisión Federal de Electricidad, as well as the review of 74 published K–Ar and 40Ar/39Ar ages and seven new K–Ar unspiked age determinations. The SPC is the northwesternmost tectonic structure of the Tepic–Zacoalco rift, which has developed since the late Miocene in the western Trans-Mexican Volcanic Belt (TMVB). The SPC has a broad WNW–ESE orientation and is located at the boundary between two different basement blocks: the Cretaceous to Paleocene batholith of the Jalisco block to the south, and the Oligocene to early Miocene Sierra Madre Occidental silicic volcanic province to the north. Calcalkaline, transitional and Na-alkaline volcanic products of the TMVB cover the tectonic contact between the two blocks. The oldest volcanism related to the TMVB consists of a thick succession of mafic lava flows only found in a deep drilling beneath Ceboruco volcano. These lava flows have a late Miocene age and are the early fill of a paleo-graben that possibly formed in response to the opening of the Gulf of California. In the early Pliocene, a large amount of rhyolitic lavas and silicic pyroclastic flows shortly followed by mafic lavas were emplaced mainly to the north of the study area. A second phase of faulting occurred between the emplacement of the silicic rocks (~5–4.2 Ma) and the mafic ones (~3.8 Ma). Volcanism resumed at the end of Pliocene along a NW–SE alignment of cinder cones and domes that bounds the southern part of the SPC. Most activity occurred in the last 1 my. It first produced several dacitic to andesitic domes and a small calc-alkaline stratovolcano (Tepetiltic); then, after the formation of a small caldera (San Pedro) a mildly Na-alkaline succession of lava flows made up a small volcano (Amado Nervo). The recentmost volcanism is represented by intracaldera silicic domes, a northern WNW–ESE alignment of monogenetic volcanoes, and the active Ceboruco stratovolcano. Late Miocene to present cumulative extension in the area accounts for a modest 10%. A period of very low volcanic activity in late Pliocene coincides with a low convergence rate between the Rivera and North America plates, confirming a strong relation between subduction regime and upper plate volcanism.

A chronosequence consisting of paleosols buried under kurgans of the Savromatian (2,500–2,600 yr BP) and the Late Sarmatian Time (1,700–1,800 yr BP), along with the modern Dark Kastanozems was studied in a dry steppe area of the southern Pre-Ural region, Russia. We focus on morphological features of carbonate accumulations, that occur as white soft spots (WSSs) at different scales of soil mass organization, to understand their role in paleoenvironmental reconstruction. The carbonate accumulations in Bk horizons of paleosols buried within the Savromatian period and of the modern Dark Kastanozems are similar in quantity but differ slightly in their diameter. Calcic features in the Savromatian paleosols are diverse and have signs of both dissolution (calcite crystals in voids) and segregation. Only in the Savromatian paleosols, desiccation cracks have broken the WSSs into pieces. We consider highly probable that the Savromatian paleosols formed under slightly drier and more continental climate than present. The Late Sarmatian paleosols are characterized by WSSs in Bk horizons with the largest size and greatest quantity, and their diversity is great enough to divide the Late Sarmatian paleosols into two morphological groups, ‘upper’ and ‘lower’, based on signs of dissolution. The ‘lower’ group shows no signs of dissolution, so we conclude that the WSSs formed in stable dry climatic conditions. Establishment of a more humid climate at the beginning of the Late Sarmatian period produced signs of dissolution preserved in the ‘upper’ group that was buried late in this chronointerval. The WSSs in the modern soils have the clearest signs of dissolution compared with other soils in the chronosequence, which we interpret to indicate that the modern climate is likely the most humid interval of the late Holocene. Detailed investigation of morphological peculiarities of carbonate accumulations on the different scales of soil mass organization in the chronosequences of steppe soils is a valuable source of information on the paleoecological situation of Holocene climate intervals and can be successfully used for that aim.

In the Uruguay River basin (South America; 365,000 km²), an episode of pedogenesis occurred during the Climatic Optimum of the Holocene, approximately between 8,500 and 3,500 yr BP. This period of 5,000 years was characterized by a humid and warm climate. In terms of factors of soil formation, an interesting pattern appears. The climate was relatively homogeneous over the whole basin. The age is the same in all cases and the influence of relief and vegetation was modest. Therefore those factors can be considered as basically uniform. On the contrary, the parent materials form a complex mosaic. The granulometric and mineralogical characteristics of the parent materials dominate the nature of the hypsithermal pedogenesis even at the higher level of the soil classification. Several cases of this regional pattern can be cited. Moderately to well developed B-horizons of five buried soils have been registered in the region. Each of them covers a significant area. A conspicuous Vertisol covers the southwestern of the river basin (in Entre Ríos province, Argentina). The parent material of this buried soil is a clayey playa unit (the Hernandarias Formation, lower Pleistocene in age). A buried soil belonging to the Ultisol order was developed on the Oberá Formation (the late Pleistocene tropical loess) in the north of the region (in Misiones province, Argentina and Rio Grande do Sul state, Brazil). On a late Pleistocene–lower Holocene paludal unit (the Tapebicuá Formation, in eastern Corrientes province) a distinct buried soil with a plinthic yellowish brown horizon was developed. A moderately developed Alfisol formed on the lower fluvial terrace of the Uruguay River (the Holocene Concordia Formation). On the late Pleistocene loess, at the southern end of the basin (in southeastern Entre Ríos province and western Uruguay), a well developed Alfisol occurs, which is similar to the typical soil of the Pampa region. Some profiles are pedocomplexes with clear evidence of soil formation interruption by the accumulation of Andean volcanic ashes. The hypsithermal soil was truncated by eolian erosion in most of the region. Later, it was covered by a thin loess layer (the San Guillermo Formation, deposited during the Upper Holocene). Both, the remaining B and C horizons and the loess layer are affected by the current incipient pedogenesis under a humid subtropical/tropical climate which began 200 years ago. The only exception to this influence is represented by the Ultisol and the Alfisol (in the fluvial terrace), which are covered by 2–4 m of upper Holocene sediments, and consequently isolated from the present dynamic.