Palaeoenvironmental record of the last 70 000 yr in San Felipe Basin, Sonora desert, Mexico: preliminary results (original) (raw)
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Pleistocene paleosols associated with megafauna in Northwestern Mexico: Paleoecological inferences
Spanish Journal of Soil Sciences, 2018
The pedological cover of the state of Sonora, in northern Mexico, is predominantly composed of moderately developed red soils that evidence processes of weathering, humification, rubification, neoformation of clay, and carbonation, classified as Cambisols according to the WRB. These soils constitute a pedological unit denominated the San Rafael Paleosol (SRP). In contrast, gray soils are recorded in some sites located in semi-closed basins and are characterized by processes of weathering, neoformation of clay, reductomorphism and carbonation. These soils developed during the late Pleistocene under a semi-arid and cold climate, slightly more humid than the present one, with winter dominant rains, and marked seasonal changes. These paleosols are associated with remnants of Pleistocene Rancholabrean fauna of diverse composition, associated with arid and humid climates, demonstrating local climatic variations much more complex than at present. This paper evaluates the physical, chemical and micromorphological attributes of paleosols located in the San Francisco and El Arenoso ranches in the north of Sonora. The analyses are undertaken in order to identify the main pedogenetic processes and to establish the predominant environmental conditions during their formation, specifically the particular characteristics associated with semi-enclosed basins that allowed the accumulation of water and the formation of ponds. At both sites remains of Pleistocene megafauna have been found associated with paleosols. These results are contrasted with previous paleopedological studies and the paleontological record, permitting a broader discussion of regional paleoclimatic trends. RESUMEN La cubierta edáfica del estado de Sonora, en el norte de México, está formada predominantemente por suelos rojos de desarrollo moderado, con procesos de intemperismo, humificación, rubificación, neoformación de arcillas y carbonatación, clasificados como Cambisoles según la WRB, que constituyen una unidad edáfica denominada Paleosuelo San Rafael (SRP). Sin embargo, en algunos sitios se han registrado suelos grises formados en cuencas semicerradas, con procesos de intemperismo, neoformación de arcillas, reductomorfía y carbonatación. Estos suelos se desarrollaron durante el Pleistoceno Superior bajo un clima semiárido y frío, un poco más húmedo que el actual, favorecido por las lluvias invernales y cambios estacionales marcados. Estos paleosuelos se encuentran asociados a restos de fauna pleistocénica rancholabreana de composición diversa, asociada a climas tanto áridos como húmedos, lo que muestra variaciones climáticas locales mucho más complejas que en la actualidad. Con la intención de establecer las características particulares de los paleosuelos formados en cuencas semicerradas que pudieron permitir la acumulación de agua y la formación de estanques, se evaluaron las características físicas, químicas y micromorfológicas de los
We present elemental concentrations and magnetic susceptibility data from a new 270-cm-long sediment core collected from the western part of palaeolake Babicora and infer millennial-scale hydrological variations over the last 27 cal. ka in the western Chihuahua Desert. Variations in the available water content at the sediment-air interface of the watershed, lake salinity and lake productivity are inferred from values of the chemical index of alteration (CIA), CaCO3 and Corg, respectively. An abrupt increase in runoff at c. 24 cal. ka BP appears correlative with the Heinrich 2 (H2) event. Except for this event, diminished runoff between c. 27 and 19 cal. ka BP indicates lower annual precipitation (weak summer rainfall) during the Last Glacial Maximum. The deposition of chemically altered sediments between c. 25 and 22 cal. ka BP results from the higher sediment-water interaction in the watershed owing to lower evaporation, cooler conditions and higher precipitation during the H2 event. Since 19 cal. ka BP the runoff has been characterized by high-amplitude fluctuations with intervals of reduced precipitation identified at
European Journal of Soil Science, July 2014, 65, 455–469, 2014
Red palaeosols of the late Pleistocene-early Holocene, both buried and non-buried, were studied recently in Sonora (NW Mexico) to reconstruct their pedogenesis as well as the palaeoenvironmental conditions. The alluvial palaeosol-sedimentary sequence of the La Playa archaeological site is a key locality for the buried San Rafael palaeosol, which exhibits a 2Ah-2Bw-2BCk-3Bgk profile and was defined as a Chromic Cambisol. Radiocarbon dates from pedogenic carbonates and charcoal set the soil formation interval between >18 000 and 4300 calibrated years before present (cal. year BP). Micro-morphological observations together with profile distribution of clay, carbonates, organic carbon, pedogenic iron oxides and rock magnetic properties indicated a strong eluvial-illuvial redistribution of carbonates, moderate silicate weathering and gleying in the lower horizon. Although this soil was much more developed than the overlying syn-sedimentary late Holocene Fluvisols, clay mineral composition and stable carbon isotope signatures of humus and carbonates were similar in both soils. We suggest that pedogenesis of the San Rafael palaeosol took place under a slightly more humid climate and relative geomorphic stability. This agrees with the regional palaeoclimate reconstruction, which indicates a moister climate during the Late Wisconsin glaciation (MIS 2). An abrupt termination of the San Rafael pedogenesis marked by disturbance and aridization features in the Ap horizon of the palaeosol could be linked to a global drought around 4200 years cal. year BP. Surface Chromic Cambisols in northern Sonora show similar pedogenetic characteristics to the buried red palaeosols of La Playa. They appear to be a relict component of the present day soil mantle.
Palynological and magnetic susceptibility records of Lake Chalco, central Mexico
Palaeogeography, Palaeoclimatology, Palaeoecology, 1994
Pollen and magnetic susceptibility data from a 11.27-m-long core drilled in the central part of Lake Chalco (99°00'W, 19°15'N), located at the southeastern part of the Basin of Mexico, are interpreted in terms of paleoenvironmental changes. The record of this subtropical highland lake, dated by radiocarbon methods, spans approximately 24,000 yr B.P. and documents changes in climate, vegetation, lake level and volcanic activity. Seven palynozones were established by using the method of cluster analysis for correlation purposes. Zones 7, 6 and 5, between 20,600 and 18,300 yr B.P., indicate reduced forests with extensive grasslands, relatively high input of sediments by water discharge of surface streams and high lake level. The evidences obtained in zone 4, between 18,300 and 17,500 yr B.P., suggest a dry and warm climate with xerophytic vegetation, lower lake level and erosion rates. Zone 3, between 17,500 and 10,000 yr B.P., shows a trend to increasing moisture and cooler temperatures. Volcanic activity during this period is intense, and strongly influences the natural environments. At around 12,000 yr B.P., a clear expansion of forests and fulfillment of the lake are recorded. At the beginning of the Holocene, an oak forest expansion and a lowering of lake levels are initiated, and by the mid-Holocene (Zone 2) subhumid-temperate conditions are detected, although lake level continues to be low. The human impact is recorded in the last 4000 yr.
Rock-magnetic and sedimentological studies of the Quaternary sequence of lake Babícora (29.4°N, 107.7°W; 2,100 m a.s.l.) from Late Wisconsin to Holocene are reported. Two vertical profiles have been studied. Magnetic susceptibilities and natural remanence (NRM) and isothermal remanence (IRM) intensities correlate with sand, silt and clay contents in the sediments, suggesting that magnetic minerals are allogenic. IRM acquisition curves and alternating field coercivity spectra document the occurrence of Ti-poor titanomagnetites, hematites and iron-hydroxides. The fluctuations in the input of sediment correlate with changes in erosional processes, climate and tectonics in the catchment basin. Five radiocarbon dates ranging from 4,346 to 16,343 yr B.P. were obtained. The southern profile covers a longer time span than the western profile, which spans from 11,000 to 6,000 yr B.P., when the lake extended over a larger area. Two major periods of increased rainfall and high lake levels in Late Pleistocene and Early Holocene are recognized. The Late Wisconsin wet period was followed by gradual drying up to around 6,000 yr B.P. Between 11,000 and 8,000 yr B.P. there was another wet period, related to increased summer rainfall. The dry period between 3,000 and 2,000 yr B.P. was followed by widespread erosion.
https://www.sciencedirect.com/science/journal/08959811, 2020
Northern Mexico is predominantly composed of moderately developed red soils that provide evidence of weathering, rubification, neoformation of clay, and pedogenic carbonate accumulation. These soils constitute a pedological unit named San Rafael Paleosol (SRP) which were developed during the late Pleistocene (MIS 2) to the middle Holocene (15,000-4500 cal years BP). These paleosols can use as a chronologic marker at a regional scale. In this paper, we present a pedogenic interpretation of the paleosol-sedimentary processes during the late Quaternary, which contributes to the reconstruction of regional paleoenvironment. The development of SRP takes place over more than 15,000 years, and this pedogenesis is interrupted by stages of strong climatic instability, causing erosion of the SRP and sedimentation, presumably during the Altithermal. The records of La Playa show that SRP is buried by fluvial sediments, which include different facies. These sedimentation events are associated with the end of the Altithermal period and evidence more active geomorphic processes. These conditions are also observed at El Gramal, where dune sediments overly the SRP. This discontinuity evidence an intense erosional/sedimentation phase. In the particular case of El Fin del Mundo site, it is observed more mesic conditions as the water table rose, creating a wetland. Much of the synchronous variation in the morphology of the paleosols (pedofacies) can be explained by differences in local geomorphological conditions. These palaoesols developed under a semi-arid climate, slightly more humid than the present one with winter dominant rains and marked seasonal changes. These assumptions are supported by soil micromorphology, physical characteristics (color, grain size distribution) and composition of total organic and inorganic carbon. Additional paleoenvir-onmental information is also extracted from microbiomorphic analyses and diatoms assemblages from the one profile at El Fin del Mundo site.
Red palaeosols of the late Pleistocene-early Holocene, both buried and non-buried, were studied recently in Sonora (NW Mexico) to reconstruct their pedogenesis as well as the palaeoenvironmental conditions. The alluvial palaeosol-sedimentary sequence of the La Playa archaeological site is a key locality for the buried San Rafael palaeosol, which exhibits a 2Ah-2Bw-2BCk-3Bgk profile and was defined as a Chromic Cambisol. Radiocarbon dates from pedogenic carbonates and charcoal set the soil formation interval between > 18 000 and 4300 calibrated years before present (cal. year BP). Micro-morphological observations together with profile distribution of clay, carbonates, organic carbon, pedogenic iron oxides and rock magnetic properties indicated a strong eluvial-illuvial redistribution of carbonates, moderate silicate weathering and gleying in the lower horizon. Although this soil was much more developed than the overlying syn-sedimentary late Holocene Fluvisols, clay mineral composition and stable carbon isotope signatures of humus and carbonates were similar in both soils. We suggest that pedogenesis of the San Rafael palaeosol took place under a slightly more humid climate and relative geomorphic stability. This agrees with the regional palaeoclimate reconstruction, which indicates a moister climate during the Late Wisconsin glaciation (MIS 2). An abrupt termination of the San Rafael pedogenesis marked by disturbance and aridization features in the Ap horizon of the palaeosol could be linked to a global drought around 4200 years cal. year BP. Surface Chromic Cambisols in northern Sonora show similar pedogenetic characteristics to the buried red palaeosols of La Playa. They appear to be a relict component of the present day soil mantle.
Journal of Arid Environments, 2012
Rare earth element, major and trace element and mineralogy in the sediments representing last 50 cal kyr BP from the summer precipitation fed paleolake San Felipe identify the different association of minerals and selective transportation of different grain size fractions and relate them to the variation in pluvial discharge into the basin as well as aeolian activities in the western Sonora Desert. Period of lower pluvial discharge during 14e48 cal kyr BP is contemporary to the regime of dominant winter storms in the region. Transportation of coarser quartz and plagioclase during 40e48 cal kyr BP and dominant finer fractions during 14e40 cal kyr BP possibly mirror the variation in the frequency of winter storms. During 3e14 cal kyr BP, higher catchment erosion (sedimentation increased 4e12 times) and transportation of REE bearing heavy minerals into the basin indicate higher pluvial discharge. We relate this period to a regime of dominant summer precipitation associated with the North American Monsoon and tropical cyclones. Geochemical and mineralogical signatures of the sediments deposited during ca. 8, 12e13 and >48 cal kyr BP suggest selective mobilization of quartz and plagioclase from the surrounding sand dunes by the aeolian processes.