Holocene evolution of Arabian coastal sabkhas: a re‐evaluation based on stable‐isotope analysis, forty years after Shearman's first view of the sabkha

Abstract

The location of Arabian Gulf sabkhas at the interface between seawaters, continental groundwaters and meteoric waters results in characteristic geochemical signatures that have been acquired over a single transgressive-regressive cycle of $10,000 years duration. The stable-isotope compositions (especially those of deuterium, sulphur and oxygen) of diagenetic evaporite minerals and coexisting sabkha groundwaters, when interpreted with respect to coastal geomorphological controls, give perhaps the best description of the hydrology and evolution of sabkhas with time. The hydrological framework of marine sabkhas in the southern Arabian Gulf (UAE) is controlled mainly by marine flood-recharge and reflux with a dominant marine isotopic signature in the sulphate evaporites. By contrast, in the northern Arabian Gulf (Kuwait) the marine sabkha sulphates show dominantly continental water-derived isotopic signatures. In the latter region, continental groundwaters have virtually reached the coast, displacing the marine waters in the sabkhas. As the coastline progrades, a given marine sabkha can have sulphate minerals with both isotopic signatures, but formed at different times. Similarly, the volumes of dolomite formed in sabkhas are dependent on their respective hydrological and geomorphological (i.e. open vs barriered coasts) frameworks. Low dissolved sulphate contents and organic matter availability in the environment are associated with dolomite precipitation. The current (late Quaternary) 100,000-year orbitally driven climatic cycle with its glacial-interglacial contrasts and resulting sea/base-level changes, and accompanying groundwater-table fluctuations in the sabkhas, indicate that their preservation potential is extremely poor. This accounts for the general absence of Pleistocene sabkha deposits. The Arabian Gulf and Peninsula region, which earlier was under the influence of the Indian Ocean Monsoon rainfall belt, went into a climatically hyper-arid phase just over 6000 years ago, more than a thousand years before sabkhas started forming ($4800 BP), thus priming the sabkhas for diagenetic evaporite mineral precipitation, which requires high groundwater salinities. Anhydrite, an index evaporite mineral, is limited to latitudes of 23 to 28 N in the Gulf. Climate and hydrology in conjunction with palaeogeography have important implications when discussing ancient sabkha analogues, which are known since the early Archaean, and were of a different order of magnitude from those forming today (e.g. the giant sabkhas of the Arabian Jurassic).

New data on the sedimentary processes and timing of the initial inundation of Lower Khuzestan (SW Iran) by the Persian Gulf

“…The data from southern Kuwait presented by Gunatilaka (2011) are interesting with respect to the southern Mesopotamian plain as a whole. There, the change from a braidplain environment to a shallow marine environment started at 8540 ± 70 yr BP in the most seaward area and progressed landwards until ca.…”

“…Considering the time delay of the landward transgressive migration along the estuaries in the Lower Khuzestan plain, it may have been the case that both sides of the northern part of the Persian Gulf experienced most probably a coeval evolution. In Kuwait, progradation began in the landward area at 4730–4530 ± 60 yr BP (Gunatilaka, 2011). Our results show that this period corresponds with the approximate age (prior to 4292 ± 33 yr BP or 4820–4970 yr cal.…”

“…However, this view is based on very limited data, and there is almost no precise information on the chronology of the marine inundation nor of any regional variations in the timing of marine flooding. Gunatilaka (2011) dates the start of the transgression in southern Kuwait between 8540 and 7650 ± 70 yr BP (not calibrated). According to Aqrawi (2001), brackish–marine conditions were present in the vicinity of Fao–Abadan around 9000 yr BP and reached Basra at ca.…”

The moldic pore evolution of the Middle Ordovician sabkha dolostone in Ordos Basin, China: A study based on the petrographic and geochemical characteristics of pore fillings

“…The REE concentration and the REE pattern of C2 can exclude the hydrothermal origin for the high 87 Sr/ 86 Sr values of C2b. Research studies about modern sabkha in the Arabian Gulf (Kuwait) show that the groundwater in the sabkha environment is derived from the uplift area with silicon‐rich aluminate strata (Gunatilaka, 2011). Based on the strontium isotopes composition and the research studies about modern sabkha, we suggest that the diagenetic fluids of C2 mainly consisted of the groundwater, which flowed through the ancient aluminosilicate rocks in the Central Palaeo‐uplift and held high 87 Sr/ 86 Sr values (Grobe et al, 2000; Pu et al, 2012).…”

The onset of the Messinian Salinity Crisis in the central Mediterranean recorded by pre‐salt carbonate/evaporite deposition

“…8D). The influx of freshwater floods of fluvial origin to sabkhas is not rare; in fact, it is documented in both modern and ancient environments (Goodall, 1995;C ß iner et al, 2002;Evans, 2011;Gunatilaka, 2011). Moreover, well-known is the presence of cyclic humid climate episodes during CdB formation that can explain the presence of such deposits Perri et al, 2015).…”