Present-day Arid Research Articles

Clarification of the Lopingian palaeoclimatic conditions of the northwestern coastal regions of Palaeotethys based on the Transdanubian geological record

The Lopingian sedimentary rocks of South and South-Central Europe play an important role in reconstructing the same-age equatorial climate of the Pangea. However, geological evidence suggests a mismatch between the previously supposed equatorial monsoonal, tropical summer wet climate and the more arid Lopingian climatic conditions. To clarify the Lopingian climate of the northwest coastal region of the Palaeotethys, palynofloral assemblages and the climatic background behind the occurrence of soil, aridity, biome, and vegetation patterns of present-day arid and semi-arid territories were studied. In contrast to the similar lithological characters and the proposed Lopingian geographical proximity of the Southern Alpine and Transdanubian sequences, notable differences exist between the palynofloras of these regions. While the conifer-dominated, low-diversity Transdanubian flora belonged to the tropical, the more diverse Southern Alpine flora was part of the Permian Euramerican floral kingdom. Based on the occurrence of modern conifers, it is not plausible that Permian ones occupied arid regions. However, the current distribution of juvenile anhydrite, gypsisols and calcisols shows that the similar palaeosoils of the South Alpine and Transdanubian formations were formed in a tropical desert biome. By synthesizing the evidence exhibited above, it can be concluded that arid and semi-arid environments existed along the northwestern margin of the Palaeotethys and the humid, monsoonal regions were restricted to the Hercynian ranges. Local hydrological conditions plausibly had a notable impact on the occurrence of plant taxa in semi-arid regions which can explain the differences in the palynoflora despite the similar palaeoclimates.

Palaeoenvironments and landscape diversity in Egypt during the Last Interglacial and its implications on the dispersal of Homo sapiens

ABSTRACT The Last Interglacial period is important for the spread of humans from Africa to Eurasia. Significant wetter climatic conditions allowed humans to live in the present-day arid landscape in Northeastern Africa. However, not only the environment but also other parameters, such as the topography and the availability of good raw material sources, impact past human behaviour. Our mapping with the integration of archaeological sites and environmental archives clarifies regional differences and similarities across Egypt. The Eastern Desert is characterized by a small structured landscape with an above-average occurrence of eligible raw material and it differs from the more homogeneous landscape of the Western Desert with its large palaeo-lakes. The given map allows a more distinct evaluation of regional variabilities for Out-of-Africa’s northern migration route as a complex intermediate scale between a global and local approach to human-environment relations.

Climatic history from early Weichselian (MIS 5D-C) valley-fill deposits and associated factors for basin sedimentation, mainland Kachchh, western India

Ephemeral fluvial systems in the dryland region of Kachchh are susceptible to climatic fluctuations. An increase in Indian Summer Monsoon Intensity (ISM) is responsible for the aggradation of sediments as valley-fill deposits in the river basins. In the present study sedimentological, chronometric, and geochemical analysis on the fluvial terrace sequences of Nirona and Bhukhi river basins are being used to interpret southwest summer monsoon variability from MIS 5D-5C along with the fluvial response to local tectonics. The sediment record indicates increased ISM precipitation from ∼110ka to ∼90ka, which corresponds to the MIS 5D to MIS 5C (Interstadial stage). The ISM became progressively weaker during the MIS-5B (stadial stage), leading to present-day arid conditions. The climatic factors weakened along with an interplay of local tectonics, leading to present-day conditions of bedrock incision.

Fjord network in Namibia: A snapshot into the dynamics of the late Paleozoic glaciation

AbstractFjords are glacially carved estuaries that profoundly influence ice-sheet stability by draining and ablating ice. Although abundant on modern high-latitude continental shelves, fjord-network morphologies have never been identified in Earth's pre-Cenozoic glacial epochs, hindering our ability to constrain ancient ice-sheet dynamics. We show that U-shaped valleys in northwestern Namibia cut during the late Paleozoic ice age (LPIA, ca. 300 Ma), Earth's penultimate icehouse, represent intact fjord-network morphologies. This preserved glacial morphology and its sedimentary fill permit a reconstruction of paleo-ice thicknesses, glacial dynamics, and resulting glacio-isostatic adjustment. Glaciation in this region was initially characterized by an acme phase, which saw an extensive ice sheet (1.7 km thick) covering the region, followed by a waning phase characterized by 100-m-thick, topographically constrained outlet glaciers that shrank, leading to glacial demise. Our findings demonstrate that both a large ice sheet and highland glaciers existed over northwestern Namibia at different times during the LPIA. The fjords likely played a pivotal role in glacier dynamics and climate regulation, serving as hotspots for organic carbon sequestration. Aside from the present-day arid climate, northwestern Namibia exhibits a geomorphology virtually unchanged since the LPIA, permitting unique insight into this icehouse.

The potential future change of the suitability patterns of six leishmaniasis vectors in Iran.

Visceral and cutaneous leishmaniasis are endemic in Iran. The aim of this study was to model the changing suitability patterns of five confirmed and one suspected leishmaniasis vector Phlebotomus species resident in the country. The potential present and future suitability patterns of the sandfly species in Iran were modelled using climate envelope forecasting method for the reference period 1970-2000 and the future period 2041-2060. The reference period climate of Iran seemed to be the most suitable for Phlebotomus perfiliewi and Phlebotomus tobbi and less suitable for Phlebotomus simili, while Phlebotomus neglectus, Phlebotomus papatasi and Phlebotomus sergenti showed intermediate values among the studied sandfly species. The modelled changes in the suitability values show a similar pattern in the case of the six species, even the exact magnitude of the modelled values varied. The model results indicate that climate change could decrease the sandfly habitability in the present-day arid regions in Central Iran. The Iranian sandfly populations will move to higher elevation regions, and the suitability values of the sandfly species are predicted to increase in the foothills of the mountainous regions in the northern and the western part of the country. The increase of the maximally suitable areas in Iran was found which was predicted to be accompanied by the parallel shrinkage of the sandfly-inhabited areas in the arid regions of the country. Topographical conditions could strongly influence the suitability patterns of the vectors in Iran.

Enhanced zoogeomorphological processes in North Africa in thehuman-impacted landscapes of the Anthropocene

New zoogeomorphological features discovered in dryland landscapes of Northern Africa reflect human-animal agency since prehistory, and attest to complex, networked activities over great distances. We discuss the role of zoogeomorphology in shaping Earth's surface since the beginning of the Anthropocene, the timeframe when natural processes shifted and landscape evolution became more human-dominated. We focus on contexts in arid and semiarid lands of Northern Africa, which are metastable, sensitive ecosystems that are prone to modifications triggered by climatic and anthropogenically forced factors. Studying the geoarchaeological record in context of landscape impact and animal procurement by people throughout Antiquity is important for reconstructing domestication and husbandry of cattle, sheep, and goats in this region. Among the features we recognize in association with transhumance, pastoralism, and herding are trails, trackways, footholds, animal daybeds, stables, animal dwellings, rockshelters, game blinds, and monuments, to name a few. Related activities with landscape-scale impacts include herding, transport, corralling and browsing of cattle (Bos sp.), goats, and sheep (ovicaprines) as well as pasturage activities like cropping, fire-setting, and manuring. These activities were disturbances that affected surface processes like erosion and dust mobilization, as well as reduced vegetation and ecosystems productivity. In dryland Africa, and especially in the Sahara, intensive herding led to the alteration of the pristine aspects of bare rock surfaces and of the stone desert pavement (i.e., the hamada); many regions preserved evidence of middle-late Holocene animal daybeds, trampled areas, and barren tracks and trails. We suggest that human and herd animal activities affected geomorphic surfaces that affected slope stability, intensified erosion and dust mobilization, and enhanced dust export from the African continent offshore. We reinterpret the increased dust emission from North Africa during the mid-Holocene at the end of the African Humid Period, as has been interpreted from ocean cores; aridification of the Green Sahara followed the insolation-forced monsoonal maximum, and was exacerbated by human-animal activities across the Sahara and the Sahel. We argue that the spread of human activities and intensive husbandry of cattle, and caprines (goat and sheep) in this region significantly influenced the geomorphic stability, ecosystem and landscape sustainability in a comparable manner of overuse observed in present-day arid and marginal environments, where pastoral overgrazing pressure increases erosion processes and enhances dust mobilization. We suggest that human-animal activities have amplified dust generation from the North African continental interior since ~7 ka BP. This evidence of prehistoric human impacts on surface processes in North Africa supports arguments for an early beginning of the Anthropocene.

Management thresholds stemming from altered fire dynamics in present-day arid and semi-arid environments

Changes in fire frequency, size, and severity are driving ecological transformations in many systems. In arid and semi-arid regions that are adapted to fire, long-term fire exclusion by managers leads to declines in fire frequency, altered fire size distribution, and increased proportion of high severity fires. In arid and semi-arid systems where fire was historically rare, factors such as invasion by highly combustible non-native plants elevate fire frequency and size, elevating mortality of native species. Altered temperature and precipitation regimes may exacerbate these changes by increasing biomass and flammability. Current transformation in fire dynamics carry social as well as ecological consequences. Human cultures, livelihoods, values, and management behaviors are attuned to fire dynamics. Changes can make it costly or impossible to maintain traditional landscape use and economic activities. We review the ecological and social science literature to examine drivers of altered fire dynamics in arid and semi-arid systems worldwide and the conditions representing fire dynamics thresholds—points at which altered conditions may make it difficult or impossible to achieve management objectives, even via traditional adaptive management focusing on alternative management activities to achieve objectives. Such thresholds could force a wholesale shift in management objectives and practices and a new approach to adaptive management that redefines objectives when no viable adaptive action can be undertaken.

Dolomitization of supratidal to shallow-marine carbonates in the Pennsylvanian successions of the Wyoming Shelf

Laterally extensive beds of dolomitized carbonate are found interbedded with eolian to peritidal sandstones in the hydrocarbon-producing Pennsylvanian to earliest Permian successions of the Wyoming Shelf, USA. Subsurface and surface correlations often rely on these dolomite intervals yet their origin is poorly constrained. To characterize the nature of dolomitization, we integrate petrography, carbon and oxygen isotope data, and sedimentological characteristics of pervasively dolomitized shallow-marine, supratidal, and pedogenic facies in the Amsden and Tensleep Formations of the Bighorn Basin (early to middle Pennsylvanian, northern Wyoming). Stable isotopic compositions are compared with the documented isotopic signature of protodolomite forming on present-day arid coastlines. The composition of fine- to medium-grained dolomitized matrix differs from that of late-stage calcite spars, suggesting that dolomites preserve a primary or early diagenetic signal. The δ18O values of dolomites (-1.2 to 7.6‰ VPDB) display a similar range to that of modern protodolomite forming in the tidal flats of the coast of Abu Dhabi. The δ13C values, however, are consistently lower than expected if dolomite had precipitated from sea-water. These relationships suggest that dolomite incorporated a considerable amount of isotopically light carbon during primary formation or later during overgrowth and/or recrystallization of the initial protodolomite. Pennsylvanian and earliest Permian successions in Wyoming, Montana, and northeastern Utah display very similar diagenetic modifications (i.e., pervasive dolomitization, evaporite replacement, silicification), suggesting that the models discussed here may be applicable to these contemporaneous formations.

Where were the monsoon regions and arid zones in Asia prior to the Tibetan Plateau uplift?

Abstract The impact of the Tibetan Plateau uplift on the Asian monsoons and inland arid climates is an important but also controversial question in studies of paleoenvironmental change during the Cenozoic. In order to achieve a good understanding of the background for the formation of the Asian monsoons and arid environments, it is necessary to know the characteristics of the distribution of monsoon regions and arid zones in Asia before the plateau uplift. In this study, we discuss in detail the patterns of distribution of the Asian monsoon and arid regions before the plateau uplift on the basis of modeling results without topography from a global coupled atmosphere–ocean general circulation model, compare our results with previous simulation studies and available biogeological data, and review the uncertainties in the current knowledge. Based on what we know at the moment, tropical monsoon climates existed south of 20°N in South and Southeast Asia before the plateau uplift, while the East Asian monsoon was entirely absent in the extratropics. These tropical monsoons mainly resulted from the seasonal shifts of the Inter-Tropical Convergence Zone. There may have been a quasi-monsoon region in central-southern Siberia. Most of the arid regions in the Asian continent were limited to the latitudes of 20–40°N, corresponding to the range of the subtropical high pressure year-around. In the meantime, the present-day arid regions located in the relatively high latitudes in Central Asia were most likely absent before the plateau uplift. The main results from the above modeling analyses are qualitatively consistent with the available biogeological data. These results highlight the importance of the uplift of the Tibetan Plateau in the Cenozoic evolution of the Asian climate pattern of dry–wet conditions. Future studies should be focused on effects of the changes in land–sea distribution and atmospheric CO2 concentrations before and after the plateau uplift, and also on cross-comparisons between numerical simulations and geological evidence, so that a comprehensive understanding of the evolution of the Cenozoic paleoenvironments in Asia can be achieved.

Stable isotope analysis of the tooth enamel of Chaingzauk mammalian fauna (late Neogene, Myanmar) and its implication to paleoenvironment and paleogeography

The tooth enamel of a mammalian fauna from the uppermost Miocene/lower Pliocene Irrawaddy sediments at Chaingzauk, west-central Myanmar were analyzed using stable carbon and oxygen isotopes. The δ13C values of porcupines, tragulids, rhinocerotids, suids and proboscideans show that these mammals preferentially consumed C3 plants in a wooded environment, whereas the δ13C values of bovids and hippopotamids indicate that they were grassland-adapted grazers to mixed feeders. In contrast to the thorn scrub, grassland and shrubland vegetation of present-day central Myanmar, stable carbon isotope results of the Chaingzauk fauna suggest a presence of wooded environment in the Chaingzauk area at that time. Present-day arid conditions are likely to have been caused by the uplift of the Indo-Burman Ranges due to the Himalayan Orogeny during the late Miocene to Pliocene, resulting in a rainshadow effect in central Myanmar. Furthermore, southward marine regression due to the rapid influx of sediments from the Indo-Burman Ranges, Eastern Himalayan Ranges and Sino-Burman Ranges into the Central Myanmar Basin in the Miocene to Pliocene might have played an important role in the aridification of this region since the lower Pliocene.

Astrobiology through the Ages of Mars: The Study of Terrestrial Analogues to Understand the Habitability of Mars

Mars has undergone three main climatic stages throughout its geological history, beginning with a water-rich epoch, followed by a cold and semi-arid era, and transitioning into present-day arid and very cold desert conditions. These global climatic eras also represent three different stages of planetary habitability: an early, potentially habitable stage when the basic requisites for life as we know it were present (liquid water and energy); an intermediate extreme stage, when liquid solutions became scarce or very challenging for life; and the most recent stage during which conditions on the surface have been largely uninhabitable, except perhaps in some isolated niches. Our understanding of the evolution of Mars is now sufficient to assign specific terrestrial environments to each of these periods. Through the study of Mars terrestrial analogues, we have assessed and constrained the habitability conditions for each of these stages, the geochemistry of the surface, and the likelihood for the preservation of organic and inorganic biosignatures. The study of these analog environments provides important information to better understand past and current mission results as well as to support the design and selection of instruments and the planning for future exploratory missions to Mars.

The paleoclimate of the eastern desert of Jordan during marine isotope stage 9

Two Cardium horizons from the topmost Azraq Formation in the eastern desert of Jordan were investigated and dated by U/Th at 330 ka; MIS 9. Fossil diversity and abundance, especially for Charophytes and gastropods with the absence of palygorskite, dolomite and evaporites, suggest the presence of a fresh water lake changing to a brackish environment at certain time intervals. A lake or possibly several smaller and shallower lakes occupied an area of about 50 km wide within the Azraq Basin. The present-day arid climate cannot support the presence of lakes in the eastern desert of Jordan, and thus MIS 9 in Jordan must have been much wetter. The source of humidity was most probably more intense Mediterranean cyclones associated with warmer than present MIS 9. However, the possibility of summer monsoon rain from the south cannot be fully excluded.

Late Quaternary sedimentation within a submarine channel–levee system offshore Cap Timiris, Mauritania

Aeolian and fluvial sediment transport to the Atlantic Ocean offshore Mauritania were reconstructed based on grain-size distributions of the carbonate-free silt fraction of three marine sediment records of Cap Timiris Canyon to monitor the climatic evolution of present-day arid north-western Africa. During the late Pleistocene, predominantly coarse-grained particles, which are interpreted as windborne dust, characterise glacial dry climate conditions with a low sea level and extended sand seas that reach onto the exposed continental shelf off Mauritania. Subsequent particle fining and the abrupt decrease in terrigenous supply are attributed to humid climate conditions and dune stabilisation on the adjacent African continent with the onset of the Holocene humid period. Indications for an ancient drainage system, which was discharging fluvial mud offshore via Cap Timiris Canyon, are provided by the finest end member for early to mid Holocene times. However, in comparison to the Senegal and Niger River further south, the river system connecting Cap Timiris Canyon with the Mauritanian hinterland was starved during the late Holocene and is non-discharging under present-day arid climate conditions.

A large landslide on the urban fringe of metropolitan Phoenix, Arizona

A granitic rock avalanche, one of the largest Quaternary landslides in Arizona outside the Grand Canyon with a volume of approximately 5.25 M m 3 and a width a little under 0.5 km, ran ∼1 km from the eastern McDowell Mountains. With lateral levees and pressure ridges, the rock avalanche deposit displays many features found on classic sturzstroms. Failure occurred along a major joint plane paralleling the slope with a dip of 44°, when a major base level lowering event in the Salt River system would have undermined the base of the failed slope, and probably during a period of more moisture than normally available in the present-day arid climate. Failure at the subsurface weathering front highlights the importance of the dramatic permeability change between grussified regolith and relatively fresh bedrock. Rock varnish microlaminations (VMLs) dating, in concert with other geomorphic evidence, suggests that the rock avalanche deposit is slightly older than ∼500 ka. The rock vanish results also have important implications for sampling strategies designed to use cosmogenic nuclide to date Quaternary landslide deposits. Discovery of a large landslide in close proximity to the extending urban fringe of metropolitan Phoenix argues for a more careful analysis of landslide hazards in the region, especially where rapid development excavates bedrock at the base of steep mountain slopes and where the subsurface weathering front is near the surface.

Pleistocene meteoric pore water in dated marine sediment cores off Callao, Peru

During cruise SO 147 of the German research vessel SONNE, a large decrease in salinity with depth was found in the pore water at a site about 10 sea miles off Callao, Lima, Peru. The origin of this freshening was investigated in a multidisciplinary approach using geochemical, geochronological and isotope hydrological methods. The methodology applied is a possible strategy to deal with anomalous pore water freshenings and if necessary to put them into the general framework of submarine groundwater discharge. Concentrations of the major and conservative elements (e.g., Na, K, Cl, B, Br) decrease at the same ratios. Deuterium ( δD) and oxygen-18 ( δ 18O) data reveal the meteoric origin of the fresh water end member, indicating a mixture of 30% seawater and 70% fresh water at a depth in sediment of about 10 m. 210Pb and 137Cs sedimentation rates determined by gamma spectrometry range between 2 and 4.5 mm/y for the last century whereas values derived from AMS 14C for the last millennia give mean rates smaller than 1 mm/y. This indicates strongly varying sedimentation conditions. Nevertheless, from the geochronological data it can be concluded that the origin of the fresh water end member is situated in sediments of Pleistocene age. Literature data of the isotope signature of modern water in the nearby Lima aquifer are clearly different from the calculated values for the fresh water end member in the pore waters. On the basis of the isotopic altitude effect described in the literature, the isotopic signature of the fresh pore water end member can be explained as rain water directly infiltrated into the Lima aquifer. In contrast, this infiltration is negligible there under present-day arid climatic conditions. Theoretical considerations on pore water advective and diffusive transport give further indications that the fresh pore water end member is entrapped paleowater of Pleistocene origin. The observed pore water freshening and the geochemical and geochronological data can be conclusively explained by diffusive mixing of seawater with meteoric water, which infiltrated during the last sea level low stand and stayed entrapped during transgression and sedimentation.

Holocene non-orbital climatic events in present-day arid areas of northern Africa and China

A preliminary comparison between the climatic evolution of the arid regions in northern Africa and northern China showed that the variations in continental aridity, on time scales of 10 4 years, were roughly synchronous over the last 140 ka. Whether this relationship can be established for the Holocene drought events on a century-scale, as reported for tropical and equatorial Africa, is still not known. The comparison of 560 radiocarbon dates on surface fresh water indicators from the Sahara with 158 dates on palaeosols and lake sediments from the arid regions in northern China demonstrates that the Holocene humid phase has been affected in both regions by several drier events, inlaid in the slow trend attributable to orbital forcing. The variations of the southern margins of the deserts, associated with the northern monsoon front, are documented by the latitudinal distribution of these indicators through time. The most startling aspects are a prolonged somewhat drier interval between 7000 and 5600 years BP and the onset of severe aridity at c. 4000 years BP similar to glacial conditions.

Holocene climatic changes over northwest India: An appraisal

Multidisciplinary studies of the climatic conditions of the present-day arid regions of the northwest Indian region indicate phases of distinct change during the recent post-glacial period. In view of the topical importance of the subject, and the sources of information being scattered throughout multidiscipli-nary research journals, an attempt has been made to summarize and present a coherent picture of the climate of the present-day desert regions of northwest India for the Holocene period. The present-day climatology and physiography of the region is presented as introductory material. The important studies which throw some light on the glacial arid phase, the wet phase, coinciding with the Harappan civilization, and the present-day arid phase are reviewed.

A basis for geochemical exploration models for tropical terrains

the principles and mechanisms of geochemical dispersion and the formation of anomalies govern the effective use of exploration geochemistry. In any terrain, the dispersion characteristics can be summarized in the form of geochemical exploration models that illustrate the nature of the surface expression of mineralization and that in turn should aid the planning, execution and interpretation of future surveys. In much of the tropics and sub-tropics, and in some areas in higher latitudes, evidence of weathering under former seasonal tropical conditions is preserved. These regions have similarities in landforms, deeply weathered regoliths and hence geochemical dispersion patterns relating to such weathering conditions. Geochemical models can be based on these common features and their subsequent modification under different climatic regimes. Two model systems are described, one in which the deeply weathered profile is preserved and the other in which the profile has been partially truncated. These models can be used to compare and contrast the surface expression of mineralization under present-day arid, savanna and equatorial rainforest environments, thereby, in effect, extending the data base for exploration of such areas.

Some fossil woods from the Tertiary of Kachchh, Western India

Fossil woods resembling the modern genera Dipterocarpus Gaertn. L, Sterculia Linn., Terminalia Linn. and a species of Palmoxylon Schenk are described from the probable Pliocene (Kankawati Series) beds of district Kachchh, Gujarat. They represent the families Dipterocarpaceae, Sterculiaceae, Combretaceae and Palmae respectively. The modern comparable forms of the fossil species indicate a more humid climate at the time of deposition contrary to the present-day arid conditions in Kachchh.

PEDIMENT CONCEPT APPLIED TO SHINARUMP AND SIMILAR CONGLOMERATES

The Shinarump and Buckhorn conglomerates and the Dakota sandstone are widespread deposits of Mesozoic age in the western interior. The physical characters indicate a fluvial origin, but the wide areal extent, scarcity of fossils, and exceptional thinness are difficult to explain by current concepts. It is suggested that these and similar continental formations are extensive pediment deposits which originated by processes observable in present-day arid and semiarid regions. These ancient deposits are compared with known pediment deposits, and the implications with regard to stratigraphic terminology and age assignments are briefly discussed.