Salty Matters

The Blog is written by me, John Warren. Once every three or four weeks or so I will post an article or two on an evaporite topic that has piqued my interest. On the Saltwork Publications webpage (under "the Works") there is a growing library of pdfs and epubs based on these blogs. These articles on the website have much higher resolution extractable graphics in than in the blog. There is also a link to this set of pdfs and epubs on the home page (www.saltworkconsultants.com).

Aeolian Gypsum and Saline Pans - an indicator of climate change

John Warren - Friday, June 30, 2017

Introduction

Evaporites deposited as aeolian dunes are not commonplace in Quaternary successions and not yet documented in any pre-Quaternary succession (Table 1). These eolian deposits are deposited above the water table in a vadose setting, generally in a degrading playa or salt lake hydrology. Consequently, there is an inherent low preservation potential for this style of evaporite; most documented examples are less than a few tens of thousands of years old.

 

Even though relatively rare as an evaporite type, the presence of eolian evaporites, usually as gypsum dunes or lunettes with associated soils and saline mudflats, does indicate particular climatic and hydrological conditions. Eolian gypsum deposits may have possible counterparts in the Martian landscape (Szynkiewicz et el., 2010).

Over the Quaternary and across the Australian continental interior, increased aridity is expressed by episodes of dune reactivation, lake basin deflation with eroded sediment accumulating downwind in transverse dunes or lunettes (Bowler, 1973; Fitzsimmons et al., 2007), Deposition is tied to increased dust mobility (Hesse and McTainsh, 2003) and reduced river discharge and channel size (Nanson et al., 1995). Such responses to increasing landscape aridity in saline groundwater sumps are seen in most arid to semi-arid regions of the world where water tables are falling, usually driven by increasing aridity.

This article focuses on eroded subaerial evaporites as a response to increasing aridity, especially the formation of gypsum dunes and lunettes (Table 1; Figure 1).


Gypsum dune styles and saline pans

Figure 1 and Table 1 plot documented occurrences of eolian gypsum across the world, overlain on a Koeppen climate base (Figure 1a). Figure 1b plots the latitudinal occurrences of documented gypsum dunes versus elevation and Koppen climate type. Figures 1c and 1d plot the detail of these same occurrences for the USA and Australia, where individual deposits are better documented. At the worldscale, there is an obvious tie to the world's desert belts with occurrences consistently situated in regions of the cool dry descending cells of northern and southern hemisphere Hadley cells (positions indicated by light blue rectangles in Figure 1b - See also Salty Matters article from Jan. 31, 2017). Many occurrences are also situated in Late Pleistocene to Holocene climate transition zones, marked by aridification at the transition from Late Pleistocene to Holocene climates, and in many case tied to transitions from perennial saline lakes and mega-lakes to continental saltflats to dunes and interdunal pans, An example of a quartz sand erg association (downwind of a gypsiferous strandzone) is seen in the transition area into the southern Kallakoopah Pans from the northern margin of Lake Eyre, Australia and its megalake precursor (Figure 2).


At the local scale, gypsum dunes generally occur downwind or atop a saline pan or playa that is, or was, recently subject to a lowering of its lacustrine watertable. In many situations the elongation of individual pan shapes line up in an orthogonal direction to the dominant wind and so also show an eolian control, like the associated gypsum dune position and alignment (Figure 3). Wind-aligned lakes and sumps and oriented-pans are much more numerous with a broader climatic range than gypsum dunes (Goudie and Wells, 1995; Goudie et al., 2016). When present, eolian bedforms associated with oriented pans lacking evaporites are dominated by clay pellets or quartz sand.


Many of the pan edge dunes show crescent shapes and so are termed lunettes. (Figure 3; Bowler, 1973). Lunette sediments range in composition from quartz-rich to sandy clay, gypsiferous clay to nearly pure gypsum. Pure quartz dune lunettes likely formed under lake-full conditions, and so show a distinct hydrology from that of the clay pellet or gypsum-rich varieties, which form by deflation of subaerially-exposed adjacent lake floors. The flocculation of suspended clays into pellets requires some degree of salinity but is less than that required to precipitate gypsum.

Lunette sediments range in composition from quartz-rich, sandy clay, through gypseous clay to nearly pure gypsum. Pure quartz dunes formed under lake-full conditions and are distinct from that of the clay and gypsum-rich varieties, which formed by flocculation and deflation from adjacent subaerially exposed lake floors. (Bowler, 1986). Gypsum and pelleted clay dunes (lunettes) line the edges of many salt lakes and playas in southeastern, southern and southwestern Australia; Prungle Lakes and Lake Fowler (gypsum lunettes), Lake Tyrell (clay lunette with occassional gypsum enrichment) and Lake Mungo (quartz sand lunette). All these lunettes are lake or pan-edge relicts from the Late Pleistocene deflationary period, when the lacustrine hydrology changed from perennial water-filled lakes to desiccated mudflats. Likewise, there are gypsum dunes in deflationary depressions in Salt Flat Playa and the Bonneville/Great Salt Lake region of Utah (Figure 4; Table 1).


Internal sedimentary structures in many of these lake-edge gypsum dunes or lunettes show tabular cross beds with consistent bedform orientation. Many lack abundant trough or festoon cross beds, suggesting consistent wind directions (Jones 1953; Bowler, 1973, 1983). Grain constituents clearly indicate deflation of former lake sediments, which were mostly vadose prior to deflation and passage into the dunes (Figure 4).

Gypsum dunes are part of a much broader lake-edge eolian sandflat association with the lakes often supplying large volumes of quartzose eolian sediment into adjacent sand seas or ergs (Figure 2; Warren, 2016). As mentioned pan-edge dunes described as ‘lunettes’ have a characteristic crescentic shape, other lake edge dunes may show more linear or longitudinal outlines, sometimes with parts of large sand seas or ergs being fed by the deflation of the salt lake or pan as at the southern edge of the Simpson Desert in Australia where it is in contact with the expanding and contracting edge of (Lake Eyre Figure 2).

Hydrological transitions from downwind evaporite dunes and lunettes

The role of salts, groundwater oscillations and the associated lake water levels/watertables are critical in creating eolian evaporites. Typically, once seasonal drying of an increasing arid lake floor sump begins, remaining surface waters with suspended clay become saline enough for the clay to flocculate and sink to the bottom of the desiccating water mass. If surface water concentration continues and the water surface sinks into the sediments to become a saline water table, then secondary gypsum prisms and nodules grow within the capillary zone of already-deposited sediment. In waters that are increasingly saline but not saturated with gypsum or halite, pelletization can continue to occur in the capillary fringe of clayey surface sediment (Figure 5).


Ongoing seasonal aridity further lowers the watertable in a saline mudflat, so the upper part of the vadose sediment column leaves the top of the capillary zone. It then deflates, leading to an accumulation of sand-sized sediment in adjacent eolian lunettes. If there is a prevailing wind direction, this builds significant volumes of dune sediment in a particular wind-aligned quadrant of the saline pan edge. Whether clay pellets or gypsum crystals are the dominant lunette component depends on the humidity inherent to the pan climate. In hyperarid situations, halite can be an eolian component in the lake hydrology (Salar de Uyuni; Svendsen, 2003).

In some lunettes, the mineralogy changes according to climate-driven changes in the hydrogeochemistry of the lake waters sourcing the lunette. For example in the Lake Tyrell lunette in semi-arid southwest Australia, the sediments in a layer range from clay pellets (75%) and dolomite (25%) in somewhat humid times of deflation to layers, with gypsum making up >90%, indicative of a more arid hydrochemistry. Lunettes associated with the shrinkage and deflation of Late Pleistocene Estancia megalake (New Mexico, USA) show similar variations in the proportions of clay pellet and gypsum sands in lake margin deposits around the edges of up to 120 blowout depressions. These blowouts define the former extent of the shrinking megalake and encompass both shoreline and lunette sands (Allen and Anderson, 2000)

Thus, the presence of an active gypsum lunette-field at a saline pan or playa edge is tied to landscape instability and a change from more humid to more arid conditions. To form a lunette requires a change in climate and an associated change in pan or playa hydrology and it hydrological base level and lake edge water table level, over time frames typically measured in hundreds to thousands of years.

 

Not just sand and dust-sized particles

Coarser than sand-sized gypsum crystals are transported in in lake margin mounds under hyperarid windy conditions that typify ephemeral pans and saline mudflats in parts of the Andean Altiplano and even higher elevations in the alpine tundra climatic zones. Salar Gorbea is a type example for this type of coarse-grained eolian transport (Figure 6; Benison, 2017). Whirlwinds, dry convective helical vortices, can move large gypsum crystals in their passage over the saline muflat. The transported gravel-sized crystals are entrained on the saline pan surface, after they first grew subaqueously in shallow surface brine pools. Once the pools dry up the crystal clusters disaggrate and then are transported as much as 5 km to be deposited in large dune-like mounds.

The dune gravel is cemented relatively quickly by gypsum cement precipitating from near-surface saline groundwater, resulting in a gypsum breccia. This documentation marks the first occurrence of gravel-sized evaporite grains being moved efficiently in air by suspension and provides a new possible interpretation for some ancient breccias and conglomerates, and improves understanding of limits of extremity of Earth surface environments.

 

References

Allen, B. D., and R. Y. Anderson, 2000, A continuous, high-resolution record of late Pleistocene climate variability from the Estancia basin, New Mexico: Geological Society of America Bulletin, v. 112, p. 1444-1458.

Arakel, A. V., 1980, Genesis and diagenesis of Holocene evaporitic sediments in Hutt and Leeman lagoons, Western Australia: Journal of Sedimentary Petrology, v. 50, p. 1305-1326.

Benison, K. C., 2017, Gypsum gravel devils in Chile: Movement of largest natural grains by wind?: Geology, v. 45, p. 423-426.

Bowler, J. M., 1973, Clay dunes: their occurrence, formation and environmental significance: Earth-Science Reviews, v. 9, p. 315-338.

Bowler, J. M., 1983, Lunettes as indices of hydrologic change; a review of Australian evidence: Proceedings of the Royal Society of Victoria, v. 95, p. 147-168.

Bowler, J. M., 1986, Spatial variability and hydrologic evolution of Australian lake basins; analogue for Pleistocene hydrologic change and evaporite formation: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 54, p. 21-41.

Chavdarian, G. V., and D. Y. Sumner, 2011, Origin and evolution of polygonal cracks in hydrous sulphate sands, White Sands National Monument, New Mexico: Sedimentology, v. 58, p. 407-423.

Chen, X. Y., J. M. Bowler, and J. W. Magee, 1991, Aeolian landscapes in central Australia; gypsiferous and quartz dune environments from Lake Amadeus: Sedimentology, v. 38, p. 519-538.

Chen, X. Y., J. R. Prescott, and J. T. Hutton, 1990, Thermoluminescence dating on gypseous dunes of Lake Amadeus, central Australia: Australian Journal of Earth Sciences, v. 37, p. 93-101.

Dutkiewicz, A., C. C. Von der Borch, and J. R. Prescott, 2002, Geomorphology of the Lake Malata-Lake Greenly complex, South Australia, and its implications for Late Quaternary Palaeoclimate: Transactions of the Royal Society of South Australia, v. 126, p. 103-115.

Eardley, A. J., 1962, Gypsum dunes and evaporite history of the Great Salt Lake Desert: Utah Geol. and Mineralog. Survey Spec. Studies vol. 2, 27 p.

Fitzsimmons, K. E., 2007, Morphological variability in the linear dunefields of the Strzelecki and Tirari Deserts, Australia: Geomorphology, v. 91, p. 146-160.

Forti, P., E. Galli, and A. Rossi, 2004 Los mecanismos minerogenéticos activos en las Pozas, in G. Badino, T. Bernabei, A. de Vivo, I. Giulivo, and G. Savino, eds., Bajo el desierto, el misterio de las aguas de Cuatro Cíenegas, La Venta Esplorazioni Geografiche, Instituto Coahuilense de Ecología, Gobierno del Estado de Coahuila & Tintoretto Edizioni, p. 122–125.

Goudie, A., P. Kent, and H. Viles, 2016, Pan morphology, Distribution and formation in Kazakhstan and Neighbouring areas of the Russian federation: Desert, v. 21, p. 1-13.

Goudie, A. S., and G. L. Wells, 1995, The nature, distribution and formation of pans in arid zones: Earth Science Reviews, v. 38, p. 1-69.

Hesse, P. P., and G. H. McTainsh, 2003, Australian dust deposits: modern processes and the Quaternary record: Quaternary Science Reviews, v. 22, p. 2007-2035.

Holser, W. T., B. J. Javor, and C. Pierre, 1981, Geochemistry and Geology of Salt Pans at Guerrero Negro, Baja California: Field trip Guide No 1. Prepared for the Geological Society of America, Cordilleran Section, Annual Meeting, March 22-24, 1981.

Hussain, M., and J. K. Warren, 1989, Nodular and enterolithic gypsum; the ''sabkha-tization'' of Salt Flat Playa, West Texas: Sedimentary Geology, v. 64, p. 13-24.

Jones, D. J., 1953, Gypsum-Oolite Dunes, Great Salt Lake Desert, Utah: Bulletin American Association Petroleum Geologists, v. 37, p. 2530-2538.

Kinsman, D. J. J., 1969, Modes of formation, sedimentary associations, and diagnostic features of shallow-water and supratidal evaporites: Bulletin American Association of Petroleum Geologists, v. 53, p. 830-840.

Kottek, M., J. Grieser, C. Beck, B. Rudolf, and F. Rubel, 2006, World Map of the Köppen-Geiger climate classification updated: Meteorologische Zeitschrift, v. 15, p. 259-263.

Langford, R. P., 2003, The Holocene history of the White Sands dune field and influences on eolian deflation and playa lakes: Quaternary International, v. 104, p. 31-39.

Magee, J. W., 1991, Late Quaternary lacustrine, groundwater, aeolian and pedogenic gypsum in the Prungle Lakes, southeastern Australia: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 84, p. 229-257.

Mainguet, M., and C. Jacqueminet, 1984, Le Grand Erg Occidental et le Grand Erg Oriental. Classification des dunes, balance sédimentaire et dynamique d'ensemble. (Grand Erg Occidental and Grand Erg Oriental. Classification of the dunes, sediment balances and overall dynamics): Travaux de l'Institut de Géographie de Reims, 59-60:29-48. (in French).

Minckley, W. L., 1969, Environments of the Bolsón of Cuatro Ciénegas, Coahuila, México: Texas Western Press, The University of Texas at El Paso, Science Series, Number 2, 65 pages.

Minckley, W. L., 1992, Three Decades near Cuatro Cienegas, Mexico: Photographic Documentation and a Plea for Area Conservation: Journal of the Arizona-Nevada Academy of Science, v. 26, p. 89-118.

Minckley, W. L., and G. A. Cole, 1968, Preliminary Limnologic Information on Waters of the Cuatro Cienegas Basin, Coahuila, Mexico: The Southwestern Naturalist, v. 13, p. 421-431.

Nanson, G. C., X. Y. Chen, and D. M. Price, 1995, Aeolian and fluvial evidence of changing climate and wind patterns during the past 100 ka in the western Simpson Desert, Australia: Palaeogeography Palaeoclimatology Palaeoecology, v. 113, p. 87-102.

Svendsen, J. B., 2003, Parabolic halite dunes on the Salar de Uyuni, Bolivia: Sedimentary Geology, v. 155, p. 147-156.

Szynkiewicz, A., R. C. Ewing, C. H. Moore, M. Glamoclija, D. Bustos, and L. M. Pratt, 2010, Origin of terrestrial gypsum dunes--Implications for Martian gypsum-rich dunes of Olympia Undae: Geomorphology, v. 121, p. 69-83.

Warren, J. K., 1982, Hydrologic setting, occurrence, and significance of gypsum in late Quaternary salt lakes, South Australia: Sedimentology, v. 29, p. 609-637.

Warren, J. K., 2016, Evaporites: A compendium (ISBN 978-3-319-13511-3): Berlin, Springer, 1854 p.

White, K., and N. Drake, 1993, Mapping the distribution and abundance of gypsum in south-central Tunisia from Landsat Thematic Mapper data: Zeitschrift fur Geomorphologie, v. 37, p. 309-325.

Wilkins, D. E., and D. R. Currey, 1999, Radiocarbon chronology and δ13C analysis of mid- to late-Holocene aeolian environments, Guadalupe Mountains National Park, Texas, USA: Holocene, v. 9, p. 363-372.

Zheng, H. B., C. M. A. Powell, and H. Zhao, 2002, Eolian and lacustrine evidence of late Quaternary palaeoenvironmental changes in southwestern Australia: Global and Planetary Change, v. 35, p. 75-92.


 

 


Recent Posts


Tags

sinjarite North Pole Archean methanogenesis chert hydrological indicator evaporite-metal association CO2 Danakhil Depression, Afar bedded potash jadarite 18O Karabogazgol Koppen climate K2O from Gamma Log meta-evaporite lazurite lot's wife Stebnik Potash hydrothermal potash Paleoproterozoic Oxygenation Event venice brine lake edge capillary zone cauliflower chert brine evolution Salar de Atacama Evaporite-source rock association York (Whitehall) Mine Lomagundi Event ancient climate sulfate dihedral angle Atlantis II Deep Mega-monsoon mirabilite Belle Isle salt mine silicified anhydrite nodules 13C enrichment anomalous salt zones salt leakage, dihedral angle, halite, halokinesis, salt flow, lithium carbonate perchlorate Realmonte potash Warrawoona Group McArthur River Pb-Zn saline clay Neoproterozoic gas in salt Deep seafloor hypersaline anoxic lake magadiite Lake Magadi dark salt crocodile skin chert intersalt Pangaea MOP gem Gamma log stevensite dissolution collapse doline anthropogenic potash source rock auto-suture salt trade stable isotope Neoproterozoic Oxygenation Event Messinian causes of glaciation carnallitite African rift valley lakes zeolite mine stability collapse doline NPHI log marine brine doline Quaternary climate Dead Sea caves waste storage in salt cavity HYC Pb-Zn gypsum dune gassy salt Deep flowing salt water in modern-day Mars mummifiction tachyhydrite astrakanite salt ablation breccia vadose zone supercontinent organic matter potash ore deep meteoric potash anthropogenically enhanced salt dissolution evaporite-hydrocarbon association Red Sea mass die-back DHAB methane salt periphery Turkmenistan Calyptogena ponderosa GR log evaporite dissolution CaCl2 brine Seepiophila jonesi eolian transport cryogenic salt basinwide evaporite Pilbara Mesoproterozoic solikamsk 2 Dead Sea karst collapse Zabuye Lake sulphur sedimentary copper well blowout hydrothermal karst Ingebright Lake sulphate well logs in evaporites Muriate of potash lapis lazuli Proterozoic alkaline lake Thiotrphic symbionts kainitite gas outburst Zaragoza Clayton Valley playa: sinkhole Kalush Potash water on Mars Hell Kettle vanished evaporite salt mine deep seafloor hypersaline anoxic basin sulfur halokinetic Schoenite potash ore price epsomite silica solubility evaporite NaSO4 salts halotolerant H2S hectorite Bathymodiolus childressi halite-hosted cave High Magadi beds 18O enrichment Sulphate of potash Jefferson Island salt mine nuclear waste storage intrasalt Hadley cell: Boulby Mine sepiolite allo-suture Neutron Log Crescent potash blowout Lamellibrachia luymesi Hyperarid salt suture Catalayud MVT deposit authigenic silica Weeks Island salt mine SedEx Badenian natural geohazard evaporite karst black salt Stebnyk potash lunette subsidence basin lithium battery carbon cycle sodium silicate Ripon Lake Peigneur Five Island salt dome trend brine pan geohazard Musley potash vestimentiferan siboglinids circum-Atlantic Salt Basins palygorskite salt seal Corocoro copper RHOB base metal trona carbon oxygen isotope cross plots Dallol saltpan recurring slope lines (RSL) rockburst knistersalz bischofite Dead Sea saltworks Ure Terrace Precambrian evaporites nitrogen CO2: albedo Ethiopia hydrohalite freefight lake endosymbiosis nacholite lithium brine Density log well log interpretation wireline log interpretation 13C halite Lop Nur Kara bogaz gol halophile hydrogen oil gusher potash Lop Nor Magdalen's Road SOP climate control on salt Koeppen Climate salt tectonics snake-skin chert namakier DHAL extrasalt seal capacity salt karst methanotrophic symbionts solar concentrator pans Sumo antarcticite Great Salt Lake Platform evaporite

Archive