Spring Mound Research Articles

Spring mounds of the Nefzaoua oases in Tunisia: Irreversible degradation of exceptional geomorphic structures

The oases in the arid the Nefzaoua region in central-western Tunisia are associated with spring mounds. Spring mounds result from an exceptional succession of geomorphological, hydrogeological and climatic conditions and processes that follow each other in a specific order. They look like small volcanoes that range from 200 m to more than 2000 m in diameter and 3–30 m in height, which centres were once occupied by a pond fed by an artesian spring. They are at the origin of each oasis's irrigation system, which radiates from the mound's foot. Due to intense irrigation of intensive date palm plantations (Phoenix dactylifera) in recent decades, all artesian springs dried out. We established a complete inventory and typology (i.e. location, dimension, and types of degradation) of all spring mounds in the Nefzaoua region. Overall, in an area of 3000 km2, 126 spring mounds of 7 types were identified, of which 112 (89%) were degraded. Due to the low salt content in spring mound sediments, they are excavated and used as a soil amendment to expand new palm plantations. Only 14 mounds (11%) are presently preserved. Their qualification as a geomorphosite could preserve them from complete destruction.

Late Cretaceous volcanism and fluid circulation in the South Atlantic: Insights from continental carbonates in the onshore Namibe Basin (Angola)

The Namibe Basin developed in the Early Cretaceous as part of the South Atlantic rift system between Africa and South America. Magmatic activity occurred during the syn-rift (Valanginian-Hauterivian) and post-rift (Coniacian-Early Campanian) phases, with the latter triggering fluid circulation events that had significant impacts on reservoir quality and hydrocarbon prospectivity. The continental carbonates of the Mariquita Member (Mb.) developed during the Late Cretaceous magmatic pulse and record the associated fluid circulation. Thus, study of these carbonates provides insights into paleo-fluid sources and circulation pathways, which can ultimately help to constrain diagenetic phases, their effects on reservoir quality, and hydrocarbon re-mobilisation.This study analyses the tectonostratigraphic setting, facies and diagenesis of the Mariquita Mb. carbonates by integrating field, petrographic and geochemical data. The carbonates are stratigraphically bound by Upper Cretaceous magmatic rocks, and constitute a series of fault-associated spring mound systems that pass laterally into lacustrine sediments. The main diagenetic events include pervasive dolomitisation, silicification and multi-stage fracturing. Fluid temperatures during dolomitisation were between ∼32 and 56 °C, while silicification occurred between ∼70 and > 260 °C. Fluids likely followed fault-controlled convective circulation pathways. The fluid compositions comprised infiltrated/modified meteoric and marine waters, as suggested by negative carbon isotopes, enriched oxygen and strontium isotopes, and REE data. Fluid modification occurred via interaction with subsurface rock units, such as basement, volcanic/siliciclastic aquifers and evaporites. However, higher temperatures during silicification could suggest late contributions from magmatic fluids too. Bitumen within porosity possibly reflects regional hydrocarbon mobilisation processes driven by magmatic fluids.

Crystallization pathways in the Great Artesian Basin (Australia) spring mound carbonates: Implications for life signatures on Earth and beyond

AbstractRecent studies of continental carbonates revealed that carbonates with similar fabrics can be formed either by biotic, biologically‐induced, biologically‐influenced or purely abiotic processes, or a combination of all. The aim of this research is to advance knowledge on the formation of carbonates precipitated (or diagenetically altered) in extreme, continental environments by studying biotic versus abiotic mechanisms of crystallization, and to contribute to the astrobiology debate around terrestrial analogues of Martian extreme environments. Both fossil (upper Pleistocene to Holocene) and active carbonate spring mounds from the Great Artesian Basin (South Australia) have been investigated. These carbonates consist of low‐Mg to high‐Mg calcite tufa. Four facies have been described: (i) carbonate mudstone/wackestone; (ii) phytohermal framestone/boundstone; (iii) micrite boundstone; and (iv) coarsely crystalline boundstone. The presence of filaments encrusted by micrite, rich in organic compounds, including ultraviolet‐protectants, in phytohermal framestone/boundstone and micrite boundstone is clear evidence of the existence of microbial mats at the time of deposition. In contrast, peloidal micrite, despite commonly being considered a microbial precipitate, is not directly associated with filaments in the Great Artesian Basin mounds. It has probably formed from nanocrystal aggregation on colloid particulate. Thus, where biofilms have been documented, it is likely that bacteria catalyzed the development of fabrics. It is less certain that microbes induced calcium carbonate precipitation elsewhere. Trace elements, including rare earth element distribution from laminated facies, highlight strongly evaporative settings (for example, high Li contents). Carbon dioxide degassing and evaporation are two of the main drivers for an increase in fluid alkalinity, resulting in precipitation of carbonates. Hence, although the growth of certain fabrics is fostered by the presence of microbial mats, the formation of carbonate crystals might be independent from it and mainly driven by extrinsic factors. More generally, biological processes may be responsible for fabric and facies development in micritic boundstone whilst micrite nucleation and growth are driven by abiotic factors. Non‐classical crystallization pathways (aggregation and fusion of nanoparticles from nucleation clusters) may be more common than previously thought in spring carbonate and this should be carefully considered to avoid misinterpretation of certain fabrics as by‐products of life. It is proposed here that the term ‘organic‐compound catalyzed mineralization’ should be used for crystal growth in the presence of organic compounds when dealing with astrobiological problems. This term would account for the possibility of multiple crystallization pathways (including non‐classical crystallization) that occurred directly from an aqueous solution without the direct influence of microbial mats.

Palynology of Middle Stone Age spring deposits in grassland at the Florisbad hominin site, South Africa

New pollen evidence and a review of past palynological research at the Pleistocene Florisbad thermal spring mound, which produced faunal, hominin and archaeological remains, allow a reconstruction of past conditions in the central Free State grassland, South Africa. Pollen sequences at the spring consist of alternating pollen-rich organic peaty horizons interrupted by hiatuses or pollen-poor layers of sandy and clayey deposits. The paleoclimatic interpretation of pollen sequences in springs like Florisbad, which contain a mixture of local and regional pollen and are influenced by spring mound cycles and changes in swamp configuration, requires consideration of taphonomy and site geomorphology to separate local from regional influences. By correlating the pollen stratigraphy in different parts of the site we suggest that the lower layers containing the Florisbad hominin (dated to 259 ka) and its associated Middle Pleistocene fauna, experienced cool moist and grassy conditions. Dating of some of the overlying Middle Stone Age layers suggest that they encompass the Last Interglacial period (MIS 5e; ca. 124–119 ka). In these levels the pollen evidence of upland fynbos shrubs unexpectedly suggests that cool conditions prevailed. This raises questions about the taphonomy, precision of the age estimate of occupation or the way we interpret pollen spectra.

Vegetation and environmental changes at the Middle Stone Age site of Wonderkrater, Limpopo, South Africa

AbstractWonderkrater, a Middle Stone Age site in the interior of South Africa, is a spring and peat mound featuring both paleoclimatic and archaeological records. The site preserves three small MSA lithic assemblages with age estimates of 30 ka, >45 ka and 138.01±7.7 ka. Here we present results of the pollen analysis of a core retrieved from the middle of the peat mound, which covers, with hiatuses, the timespan between ca. 70±10 ka and 30 ka. Pollen percentages of terrestrial, local aquatic, and semi-aquatic plants reveal changes in the regional climate and in the water table of the spring. Results identify regional wet conditions at ca. 70±10 ka, followed by a dry and a wet period between 60 ka and 30 ka. Superimposed on these three phases, recurring changes in the size and depth of the water table are observed between >45 ka and 30 ka. Wet conditions at 70 ka and 30 ka are tentatively correlated here with Marine Isotope Stage 4 and Heinrich Stadial 3, respectively. A warm and dry savanna landscape was present during human occupation older than 45 ka, and a wet phase was contemporaneous with the final occupation, dated at ~30 ka.

Helobdella blinni sp. n. (Hirudinida, Glossiphoniidae) a new species inhabiting Montezuma Well, Arizona, USA.

A new leech species Helobdella blinni sp. n., is described from Montezuma Well, an isolated travertine spring mound located in central Arizona, USA. In its native habitat, Helobdella blinni had been previously identified as Helobdella stagnalis (Linnaeus, 1758), which was later reclassified to Helobdella modesta (Verrill, 1872). Similar to the European Helobdella stagnalis and North American Helobdella modesta, Helobdella blinni has six pairs of testisacs, five pairs of smooth crop caecae, one lobed pair of posteriorly-directed crop caecae, one pair of eyes, a nuchal scute, and diffuse salivary glands. However, the pigmentation of this new species ranges from light to dark brown, unlike Helobdella modesta which tends to be light grey in color. Also, Helobdella modesta produces a clutch of 12-–35 pink eggs, whereas Helobdella blinni produces smaller clutches of white eggs (7–14, 0.5 ± 0.15 mm, N = 7) and consequently broods fewer young (1–14, 7 ± 3.3 mm, N = 97). Helobdella blinni are also able to breed year-round due to the constant warm water conditions in Montezuma Well. Their breeding season is not restricted by seasonal temperatures. These species are morphologically similar, however, comparing the COI mtDNA sequences of Helobdella blinni with sequences from nearby populations of Helobdella modesta and other Helobdella species from GenBank indicate that Helobdella blinni is genetically distinct from these other Helobdella populations.

Late Holocene hydroclimatic change at Cienega Amarilla, west-central New Mexico, USA

AbstractA late Holocene carbonate spring mound and associated wetland deposits at Cienega Amarilla, New Mexico, contain a 4000-yr record of geomorphic, paleoenvironmental, and hydroclimatic change on the southern Colorado Plateau. Forty-four14C dates support a century-scale chronostratigraphic framework. Pollen, plant macrofossil, mollusk, ostracode, and soil analyses indicate rapid spring mound growth and wetland expansion beginning ~2300 cal yr BP, followed by a pronounced decline in groundwater discharge (GWD) between ~1500 and 1000 cal yr BP. The isotopic composition of Cienega Amarilla springwater suggests GWD is driven primarily by winter precipitation. Historical climate data indicate that El Niño and warm Pacific Decadal Oscillation (PDO) conditions foster wetter-than-average winters in the Cienega Amarilla area, whereas dry winters are associated with La Niña conditions regardless of PDO phase. The ~2300–1500 cal yr BP Cienega Amarilla pluvial appears to represent an interval of peak, late Holocene cool-season precipitation that implies unusually strong or persistent El Niño–like and warm PDO–like conditions in the Pacific. Other southwestern paleoenvironmental records corroborate atypically wet conditions during this interval, and pluvial conditions related to increased winter precipitation likely fostered significant prehistoric cultural changes throughout the region, including increased sedentism, population, and dependence on agriculture.

Construction and deflation of irrigation soils from the Pharaonic to the Roman period at Amheida (Trimithis), Da

Most of the environmental studies performed in the Western Desert of Egypt have dealt with climate change since the Late Pleistocene, notably with the humid Holocene (10000 to 4500 cal. BC) and following desertification. In the last dry period of the Holocene, human societies had to cope with changing environments and they selected refuges where water was permanently available. Some of the archaeological investigations in the Western Desert have studied the available water resources and the role of irrigation in the building of soils. In some cases, they have explained the abandonment of sites by the progressive depletion of water resources. This paper focuses on the site of Amheida (the Roman Trimithis) located in the Dakhla depression in the Western Desert of Egypt. It is an elongated area located south of a limestone plateau, where spring mounds provided abundant water during the period of occupation, which lasted from the Old Kingdom (2700 cal. BC) to the Late Roman period (end of the 4th century AD). Trimithis was abandoned after a long period of prosperity. The reasons for its abandonment, as well as that of other settlements in the oasis in the same period, have not been clarified yet. Geoarchaeological surveys carried out in 2011 and 2013 point to several phases including 1) the use of a spring mound during part of the Pharaonic period (2700 to 1069 cal. BC) and the formation of irrigation soils in the vicinity of spring mounds from the Late Pharaonic times (712 to 332 BC) to the beginning of the Roman period (30 BC); 2) the degradation of these soils by wind deflation in the irrigated perimeter during the early Roman period; 3) a recovery until the 3rd century AD, made possible by the digging of wells, before 4) a severe phase of deflation and sand drifting which destroyed the irrigation soils and forced farmers to till the poorly irrigated bedrock. The Trimithis case exemplifies the way former societies could cope with harsh constraints (aridity, drifting sand and wind erosion) as long as water was plentiful. Water scarcity due to the progressive depletion of groundwater resources was probably compensated by an increase in human labour until thresholds were crossed, recovery being impossible due to water scarcity. A model summarizes the main findings of this study.

Prehistoric Sites in the Sabine River Valley in Northeastern Smith County, Texas Timothy K. Perttula and Mark Walters

In the winter of 2003, the junior author completed archaeological survey investigations of a small area of the Sabine River valley in northeastern Smith County in the East Texas Pineywoods. The work consisted of limited surface collections and shovel tests, and four archaeological sites were found during the work. The sites are about 2.4-3.0 km south-southwest of the Early Caddo period Boxed Spring mound site (41UR30) on the north side of the Sabine River. Two of the archaeological sites (41SM307 and 41SM308) are situated on alluvial landforms in the Sabine River valley at elevations of ca. 280-290 ft. amsl. The other two (41SM309 and 41SM310) are on upland landforms at elevations of 310 ft. amsl and 350 ft. amsl, respectively.

Pan floor ‘barchan’ mounds, Ntwetwe Pan, Makgadikgadi, Botswana: Their origin and palaeoclimatic implications

The variety of forms, assumed to be dunes, and palaeolakes of northern Botswana have long been perceived as geoproxies for the elucidation of Quaternary palaeoclimates. Mounds on the floor of Ntwetwe pan have been regarded as modified barchans, pertaining to a time in the past when conditions were drier than at present. The morphology, hydrogeology, and biology of these, placed in the wider context of the palaeolacustrine hinterland, indicate that they are not dunes but subaqueous features, spring mounds. The morphology is inconsistent with barchans. Conspicuous features are the elevated ‘eyes’ within the enclosing arms of the crescentic forms that occur furthest from the pan edge. Seepages discharge from their flanks, commonly about 7 m higher than the dry, saline pan floor. On the top of forms nearer the pan margins, permanent pools of potable water occur, similarly elevated above the floor. Hydraulic pressure to sustain the upward discharge of groundwater is provided by the excellent recharge through silicate karst depressions in the hinterland, particularly those of the 936 m palaeolake floor. Groundwater discharge, still operating today, was formerly much stronger and associated with lacustrine conditions. A chronological framework is provided by archaeological remains on the palaeolake floors of the hinterland. These indicate that the oldest palaeolake floor pertaining to the Quaternary is the 920 m level. Periods of spring mound formation are associated with both this and the 912 m palaeolake. The implications for future luminescence dating targeting palaeoenvironmental reconstruction are discussed in the light of this new model of mound formation.

Models of formation and activity of spring mounds in the mechertate-chrita-sidi el hani system, eastern Tunisia: implications for the habitability of Mars.

Spring mounds on Earth and on Mars could represent optimal niches of life development. If life ever occurred on Mars, ancient spring deposits would be excellent localities to search for morphological or chemical remnants of an ancient biosphere. In this work, we investigate models of formation and activity of well-exposed spring mounds in the Mechertate-Chrita-Sidi El Hani (MCSH) system, eastern Tunisia. We then use these models to explore possible spring mound formation on Mars. In the MCSH system, the genesis of the spring mounds is a direct consequence of groundwater upwelling, triggered by tectonics and/or hydraulics. As they are oriented preferentially along faults, they can be considered as fault spring mounds, implying a tectonic influence in their formation process. However, the hydraulic pressure generated by the convergence of aquifers towards the surface of the system also allows consideration of an origin as artesian spring mounds. In the case of the MCSH system, our geologic data presented here show that both models are valid, and we propose a combined hydro-tectonic model as the likely formation mechanism of artesian-fault spring mounds. During their evolution from the embryonic (early) to the islet (“island”) stages, spring mounds are also shaped by eolian accumulations and induration processes. Similarly, spring mounds have been suggested to be relatively common in certain provinces on the Martian surface, but their mode of formation is still a matter of debate. We propose that the tectonic, hydraulic, and combined hydro-tectonic models describing the spring mounds at MCSH could be relevant as Martian analogs because: (i) the Martian subsurface may be over pressured, potentially expelling mineral-enriched waters as spring mounds on the surface; (ii) the Martian subsurface may be fractured, causing alignment of the spring mounds in preferential orientations; and (iii) indurated eolian sedimentation and erosional remnants are common features on Mars. The spring mounds further bear diagnostic mineralogic and magnetic properties, in comparison with their immediate surroundings. Consequently, remote sensing techniques can be very useful to identify similar spring mounds on Mars. The mechanisms (tectonic and/or hydraulic) of formation and evolution of spring mounds at the MCSH system are suitable for the proliferation and protection of life respectively. Similarly, life or its resulting biomarkers on Mars may have been protected or preserved under the spring mounds.

The persistence of a chlorophyll spectral biosignature from Martian evaporite and spring analogues under Mars-like conditions

AbstractSpring and evaporite deposits are considered two of the most promising environments for past habitability on Mars and preservation of biosignatures. Manitoba, Canada hosts the East German Creek (EGC) hypersaline spring complex, and the post impact evaporite gypsum beds of the Lake St. Martin (LSM) impact. The EGC complex has microbial mats, sediments, algae and biofabrics, while endolithic communities are ubiquitous in the LSM gypsum beds. These communities are spectrally detectable based largely on the presence of a chlorophyll absorption band at 670 nm; however, the robustness of this feature under Martian surface conditions was unclear. Biological and biology-bearing samples from EGC and LSM were exposed to conditions similar to the surface of present day Mars (high UV flux, 100 mbar, anoxic, CO2 rich) for up to 44 days, and preservation of the 670 nm chlorophyll feature and chlorophyll red-edge was observed. A decrease in band depth of the 670 nm band ranging from ∼16 to 80% resulted, with correlations seen in the degree of preservation and the spatial proximity of samples to the spring mound and mineral shielding effects. The spectra were deconvolved to Mars Exploration Rover (MER) Pancam and Mars Science Laboratory (MSL) Mastcam science filter bandpasses to investigate the detectability of the 670 nm feature and to compare with common mineral features. The red-edge and 670 nm feature associated with chlorophyll can be distinguished from the spectra of minerals with features below ∼1000 nm, such as hematite and jarosite. However, distinguishing goethite from samples with the chlorophyll feature is more problematic, and quantitative interpretation using band depth data makes little distinction between iron oxyhydroxides and the 670 nm chlorophyll feature. The chlorophyll spectral feature is observable in both Pancam and Mastcam, and we propose that of the proposed EXOMARS Pancam filters, the PHYLL filter is best suited for its detection.

New evidence for persistent impact‐generated hydrothermal activity in the Miocene Ries impact structure, Germany

AbstractThe extent of impact‐generated hydrothermal activity in the 24 km sized Ries impact structure has been controversially discussed. To date, mineralogical and isotopic investigations point to a restriction of hydrothermal activity to the impact‐melt bearing breccias, specifically the crater‐fill suevite. Here, we present new petrographic, geochemical, and isotopic data of postimpact carbonate deposits, which indicate a hydrothermal activity more extended than previously assumed. Specifically, carbonates of the Erbisberg, a spring mound located upon the inner crystalline ring of the crater, show travertine facies types not seen in any of the previously investigated sublacustrine soda lake spring mounds of the Ries basin. In particular, the streamer carbonates, which result from the encrustation of microbial filaments in subaerial spring effluents between 60 and 70 °C, are characteristic of a hydrothermal origin. While much of the primary geochemical and isotopic signatures in the mound carbonates have been obliterated by diagenesis, a postimpact calcite vein from brecciated gneiss of the subsurface crater floor revealed a flat rare earth element pattern with a clear positive Eu anomaly, indicating a hydrothermal fluid convection in the crater basement. Finally, the strontium isotope stratigraphic correlation of the travertine mound with the crater basin succession suggests a hydrothermal activity for about 250,000 yr after the impact, which would be much longer than previously assumed.

Quantification of climate change for the last 20,000 years from Wonderkrater, South Africa: Implications for the long-term dynamics of the Intertropical Convergence Zone

In southeast Africa – a region for which few palaeoenvironmental records are available – the fossil pollen record from the Wonderkrater spring mound has contributed substantially to our understanding of past vegetation change since the Last Glacial Maximum (LGM; 21ka). Multivariate analysis of the pollen data by Scott and Thackeray (1987) provided environmental reconstructions suggesting relatively mesic LGM conditions, with warm and dry conditions during the early Holocene (11–6calkBP). This conforms to predicted patterns of precipitation change in the southern African tropics in response to Northern Hemisphere cooling and orbital forcing. Subsequent data from the Cold Air Cave speleothems and a sea-surface temperature record from the Mozambique Channel, however, indicate that conditions during the early to mid-Holocene may have been wetter than present in the Wonderkrater region. To explore this question further, we have created a series of botanical–climatological transfer functions based on a combination of modern climate and plant distribution data from southern Africa. Applying these to the Wonderkrater fossil pollen sequence, we have derived quantitative estimates for temperatures during the cold and warm quarters, as well as precipitation during the wet and dry quarters. In addition, a species-selection method based on Bayesian statistics is outlined, which provided a parsimonious choice of likely plant species from what are otherwise taxonomically broad pollen-types.We do not propose that our findings invalidate the previous principal component analyses, but they do have the advantage of being based more clearly on the relationship between modern plant distributions and individual climatic variables. Results indicate that temperatures during both the warm and cold seasons were 6±2°C colder during the LGM and Younger Dryas, and that rainy season precipitation during the Last Glacial Maximum was ~50% of that during the mid-Holocene. Our results also imply that changes in precipitation at Wonderkrater generally track changes in Mozambique Channel sea-surface temperatures, with a steady increase following the Younger Dryas to a period of maximum water availability at Wonderkrater ~3–7ka. These findings argue against a dominant role of a shifting Intertropical Convergence Zone in determining long-term environmental trends, and indicate that the northern and southern tropics experienced similar climatic trends during the last 20kyr.

Depositional environments of the Florisbad Spring site and surrounds: a revised synthesis

The Florisbad Spring site displays lithological and stratigraphical complexity within a unique geomorphological setting. Various hypotheses have been proposed to explain this complex depositional environment, and the origins of the spring site and mound are an ongoing topic of debate. To provide a context within which better to understand the depositional environment of Florisbad, the site and its surroundings were investigated. To this end, aerial photographs and Google Earth imagery, combined with field mapping and an analysis of sediments from and around the spring mound, were used to assist in a broad palaeoenvironmental reconstruction. Particular attention was paid to the depositional environment on and around the spring mound. The results did not reveal obvious differences with respect to the sedimentology of lunette dunes in the vicinity, and the spring mound itself. However, there were minor, but potentially significant differences in structure and chemical composition. Evidence suggests that the sediments are primarily of aeolian origin, while geochemical differences suggest that the south-western lunette could predate the spring mound. Optically stimulated luminescence ages confirm reworking of sediment for one of the lunettes. The morphology of the lunettes suggests that this technique would not necessarily yield primary ages for lunette formation due to sediment reworking. The meso-scale geomorphology suggests a shallow depression in which structural control and both fluvial and aeolian processes have worked together to create a unique landscape that promoted the formation and preservation of dune deposits and the unique archaeological site that is Florisbad.

Paleolandscape and paleoenvironmental interpretation of spring-deposited sediments in Dakhleh Oasis, Western Desert of Egypt

Abstract Iron-rich sediments in Dakhleh Oasis, Western Desert of Egypt, have been recognized as spring mounds and as archaeological sites where Paleolithic materials have been recovered. Detailed sedimentologic investigation and mapping of these features reveal that spring mound sediments were deposited in a shallow vegetated wetland formed by the discharge of iron-rich Nubian Aquifer waters along the southern margin of the oasis, controlled largely by localized faulting and the variable paleotopography of the basin floor. The spring sediments represent peri-lacustrine or lake independent features and can be differentiated from fully lacustrine deposits on the basis of their sedimentary characteristics as well as the presence of goethite and jarosite in a region where authigenic deposition during Pleistocene pluvial activity principally resulted in tufas and lacustrine marls. Spring mound formation incorporated sediment through the ponding of surface water, aeolian entrapment by local vegetation, and the formation of iron precipitates in a low-energy, oxidative and acidic environment that was not dependent upon surface water inputs into the Dakhleh basin. The potentially interpluvial nature of this water resource makes it an important sedimentary archive for archaeological investigations in the basin. The Dakhleh spring mounds record a unique groundwater controlled paleoenvironment, providing the first evidence of a bog iron in Egypt and one of the few occurrences of iron-rich wetland remnants in the modern Sahara.

Descriptions and palaeoecological implications of bird remains from the Middle Pleistocene of Florisbad, South Africa

The spring mound deposit Florisbad (Free State, South Africa) yielded several bird remains dating to the late Middle Pleistocene. These specimens derive from spring vent structures and are the product of natural taphonomic processes relating to the spring as primary sampling agent. The bird fossils can be assigned to Ostrich, Struthio camelus; Greater Flamingo, Phoenicopterus ruber roseus; Wattled Crane, Bugeranus carunculatus; an anatine dabbling duck; and a francolin with strong resemblance to Shelley’s Francolin, Scleroptila shelleyi. As in the case of the large mammal record, the bird remains from the Florisbad spring reflect two components in the palaeoenvironment. Evidence for Greater Flamingo, Wattled Crane, and a dabbling duck strongly supports previous hypotheses regarding the presence of a palaeolake system, while records for Ostrich and a francolin, but also Wattled Crane accord with the presence of open landscapes, such as grasslands.

The character, origin and palaeoenvironmental significance of the Wonderkrater spring mound, South Africa

Wonderkrater is a spring mound consisting entirely of peat in excess of 8 m thick. It has yielded a pollen record extending back over 35,000 years, which has provided one of the very few proxy climatic records for the interior of southern Africa in the Late Pleistocene and Holocene. The current investigation of the morphology and sedimentology of the site has revealed that the peat mound formed due to artesian conditions at the spring, but that accumulation of the thick peat succession was made possible because of clastic sedimentation on the surrounding piedmont which in turn was brought about by aggradation on the adjacent Nyl River floodplain. The peat mound has remained elevated relative to the surrounding piedmont for most of the 35,000 year period. Aggradation of the mound was slower during the Late Pleistocene than the Holocene (0.06–0.1 m/1000 year and 0.2–0.38 m/1000 year, respectively). Controlled archaeological excavations yielded a diverse late Pleistocene fauna preserved in peat and sand in the mound. A 1 m thick, coarse sand horizon at the base of the peat deposit contained a rich Middle Stone Age (>30 k year) lithic assemblage. The MSA sand layer likely represents an arid phase, suggesting the site’s antiquity as a place of refuge for Quaternary animals and the people that hunted them.

Endolithic microorganisms from spring mound evaporite deposits (southern Tunisia)

This paper investigates endolithic microorganisms in modern gypsum crusts located in arid and saline areas of southern Tunisia. In arid regions, the endolithic mode of life facilitates the survival of the microorganisms and protects them from extreme environmental conditions. The gypsum crusts are the product of evaporite precipitation atop spring mounds developed at the margins of the Chott el Jerid, a saline lake close to the Algerian border. The early mineral precipitation has prevented the complete degradation of these microorganisms and their metabolic products because of the rapid sealing provided by the gypsum crusts. The spring mound structures of the Chott el Jerid offer an opportunity to study the endolithic communities in evaporite and arid environments. An understanding of where and how life survives in such extreme conditions, and how life signal prints in the rocks may help in search for life in the geological record and for astrobiological purposes.

Luminescence dating of spring mound deposits in the southwestern Great Artesian Basin, northern South Australia

Artesian spring mound deposits in the southwestern part of the Great Artesian Basin arise from groundwater discharge from flowing springs in the southern and western margins which reaches the surface through faults and weaknesses in thin confining beds overlying the Mesozoic artesian aquifers. Carbonate in solution in the artesian groundwater is deposited by many springs as tufa, building ‘spring mounds.’ Active flowing and dry inactive spring mounds occur in a variety of sizes and shapes. The ages of a representative selection of spring mound deposits have been found by luminescence dating of quartz sand grains that have been incorporated in the mound deposits. The spring deposits of the active flowing springs, Big Bubbler, Blanche Cup and Beresford Spring have ages of 15.1 ± 2.2, 10.9 ± 1.5 and 13.9 ± 1.0 ka, respectively. Spring complexes with both active flowing and dry extinct mounds, Strangways and Beresford Springs, have ages of 60 ± 8 and 219 ± 35 ka, respectively. Spring deposits of springs which ceased flowing and are overlying pedestals of Cretaceous Bulldog Shale and of substantial height (up to >45 m above the surrounding plain) of Beresford Hill and Kewson Hill gave ages of 128 ± 33 ka and 400 ± 100 ka, respectively. Elizabeth Springs is a large spring mound, and parts contain active flowing springs; a sample from a dry inactive part gave an age of 740 ± 120 ka. The analyses for radioactive content, necessary for the estimation of dose rates for luminescence dating, were unusual because the uranium radioactive decay chain is in disequilibrium, with the parent uranium patently unable to support the lower part of the chain. We interpret this as being due to radium being carried up with the spring water from the confined Mesozoic aquifer, which overlies Proterozoic basement rocks. Calculations of dose rates take account of detailed measurements on individual nuclides and differ from site to site.