Organoclastic sulfate reduction and bacterial sulfide oxidation have been suggested to explain the formation of authigenic carbonate and native sulfur replacing gypsum in the Lorca Basin, Spain. To gain more insight into the nature of this replacement, two types of sulfur-bearing carbonate (laminated and brecciated) from the late Miocene Lorca Basin were studied. Petrographic observations revealed that a sulfur-bearing laminated carbonate consists of clay-rich and dolomite-rich laminae with carbonate and native sulfur pseudomorphs after gypsum. Positive δ18Ocarbonate values in the laminae (δ18O = 2.6‰) and lipid biomarkers of halophilic archaea (e.g., extended archaeol) suggest formation under hypersaline conditions. Bacterial sulfate reduction, evidenced by biomarkers such as iso-C15, iso-C16, and iso-C17 fatty acids, produced hydrogen sulfide inducing the abiotic formation of organic sulfur compounds. Gypsum in the laminated carbonate likely dissolved due to undersaturation as evidenced by a low content of carbonate-associated sulfate (3,668 ppm) and 34S-enriched native sulfur (δ34S = 22.4‰), reflecting sulfate limitation. Such 34S-enrichment implies limited fluid flow, which probably restricted the supply of molecular oxygen required for native sulfur formation through oxidation of hydrogen sulfide. Alternatively, sulfate-reducing bacteria may have mediated native sulfur formation directly as a stress response to environmental conditions. The formation of sulfur-bearing calcite in brecciated carbonates is due to post-depositional alteration. Negative δ18O values of the calcite (δ18O = −1.5‰) and a tenfold decrease in carbonate-associated sulfate content (752 ppm) suggest gypsum dissolution and subsequent calcite precipitation from meteoric water. Relatively 34S-depleted native sulfur (δ34S = 13.1‰) leaves it ambiguous whether meteoric water influx could have supplied sufficient molecular oxygen for oxidation of hydrogen sulfide. In case of the brecciated carbonate, methanogenesis, anaerobic oxidation of methane, and bacterial sulfate reduction apparently mediated the formation of secondary minerals as indicated by 13C-depleted lipid biomarkers representative for the respective metabolisms. This study reveals that the conditions and timing of gypsum replacement are variable–taking place 1) during or shortly after gypsum deposition or 2) significantly after sedimentation–and suggests that methanogens in addition to anaerobic methanotrophic archaea and sulfate-reducing bacteria may be involved in the mineral-forming processes in the sedimentary subsurface.

The Messinian microbialites of the Terminal Carbonate Complex (TCC) from the Neogene basins of southeastern Spain show both diversified morphologies and an excellent preservation of primary microbial microstructures. Their stratigraphic architecture, fabric (micro-, meso-, and macro-fabric), and mineralogical composition were investigated in eight localities from three sedimentary basins of southeastern Spain: The Sorbas and Bajo Segura basins and the Agua Amarga depression. Two recurrent microbialite associations were distinguished. Laterally linked low relief stromatolites predominated in Microbialite Association 1 (MA1), which probably formed in low energy lagoons or lakes with fluctuating normal marine to hypersaline water. The microfabrics of MA1 reflected the predominance of microbially induced/influenced precipitation of carbonates and locally (Ca)-Mg-Al silicates. Microbialite Association 2 (MA2) developed in high energy wave and tidal influenced foreshore to shoreface, in normal marine to hypersaline water. High-relief buildups surrounded by mobile sediment (e.g., ooids or pellets) dominated in this environment. MA2 microbialites showed a significant proportion of thrombolitic mesofabric. Grain-rich microfabrics indicated that trapping and binding played a significant role in their accretion, together with microbially induced/influenced carbonate precipitation. The stratigraphic distribution of MA1 and MA2 was strongly influenced by water level changes, the morphology and nature of the substratum, and exposure to waves. MA1 favorably developed in protected areas during third to fourth order early transgression and regression phases. MA2 mostly formed during the late transgressions and early regressions in high energy coastal areas, often corresponding to fossil coral reefs. Platform scale syn-sedimentary gypsum deformation and dissolution enhanced microbial carbonate production, microbialites being thicker and more extended in zones of maximum deformation/dissolution. Microbial microstructures (e.g., microbial peloids) and microfossils were preserved in the microbialites. Dolomite microspheres and filaments showed many morphological similarities with some of the cyanobacteria observed in modern open marine and hypersaline microbialites. Dolomite potentially replaced a metastable carbonate phase during early diagenesis, possibly in close relationship with extracellular polymeric substances (EPS) degradation. Double-layered microspheres locally showed an inner coating made of (Ca)-Mg-Al silicates and carbonates. This mineral coating could have formed around coccoid cyanobacteria and indicated an elevated pH in the upper part of the microbial mats and a potential dissolution of diatoms as a source of silica. Massive primary dolomite production in TCC microbialites may have resulted from enhanced sulfate reduction possibly linked to the dissolving gypsum that would have provided large amounts of sulfate-rich brines to microbial mats. Our results open new perspectives for the interpretation of ancient microbialites associated with major evaporite deposits, from microbe to carbonate platform scales.

The late Neogene marls from the Lorca, Murcia and Vera basins in S-E. Spain contain abundant dolomite nodules that were formed due to intense methane-rich fluid migration. The pathways for these fluids are evidenced by dense networks of fractures that are crossing the sedimentary layers and eventually the dolomite nodules. The fractures are generally filled by secondary fibrous gypsum that form veins of a few cm thick. The oxygen and sulfur isotopic compositions of the gypsum veins exhibit wide ranges (-2.2 < delta O-18 parts per thousand VSMOW < 6.7;-22.3 < delta S-34 parts per thousand VCDT < 10.5) that are far away from the average d values of Tortonian-Messinian gypsum from the basins of Lorca, Fortuna and Sorbas (delta O-18 = 13.8 +/- 2.3 parts per thousand; delta S-34 = 21.3 +/- 1.0%) precipitated from the late Neogene seawater sulfate. These low delta values of the gypsum veins clearly indicate their diagenetic origin that would have resulted from sulfide oxidation with O-18-depleted water. The isotopic compositions of the diagenetic dolomite nodules close to the gypsum veins (-0.7 < delta O-18 parts per thousand VPDB< 3.7; -11.9 < delta C-13 parts per thousand VPDB< 7.3) are indicative of their formation in methane-rich fluids. In this context, the formation of sulfide is related to the bacterial sulfate reduction that is associated with the anaerobic oxidation of methane. During this process, pyrite coprecipitated with dolomite, either within the dolomite framework or within conduits where the fluids were seeping. The pyrite oxidation occurred later during diagenesis when more or less oxygenated groundwaters circulated within the fractures during the sealevel drawdown of the Messinian Salinity Crisis and after the regional uplift of the sedimentary deposits in relation with the Betic cordillera tectonics.

Unlike most Neogene basins of the Betic Cordillera where the Salinity Crisis is dated to the Messinian, a contradictory Tortonian dating was proposed for evaporites of the Lorca Basin. As a consequence, complex structural models have been proposed in the literature to explain this discrepancy in the timing of evaporites. In order to integrate the Lorca Basin into the geological context of the western Mediterranean domain during the Late Miocene, new sedimentological and stratigraphical studies coupled with new dating were performed, which allow us to propose a Messinian age for both diatomite-bearing deposits and evaporites of the Lorca Basin. These new ages challenge the idea of a Tortonian salinity crisis in the Lorca Basin. Three main events of base-level drop were evidenced during the Messinian. Each event is correlated with successive steps of basin restriction. Shallow salina evaporites were deposited after a base-level fall during the Messinian before a final base-level drop, which led to the entire exposure of the basin. This last exposure is interpreted as coeval with the deposition of first evaporites and halite in the deep Mediterranean basins. The reflooding which allowed the deposition of brackish deposits and a short-lived marine incursion occurred at the end of the Messinian. Base-level drops occurred during eustatic falls amplified by the gradual uplift of the Betic Cordillera. The exhumation of the Tercia ridge along the strike-slip Alhama de Murcia fault system during the Messinian probably favoured the gradual restriction of the basin. A discussion on correlations of main unconformities between several Neogene basins of the Betics is proposed, suggesting a similar structural evolution at the regional scale.

A detailed biostratigraphical and cyclostratigraphical study provided the opportunity of cycle-bycycle correlations between sections from the marginal and deep areas of the Caltanissetta Basin (Sicily), and the northern Calabrian Rossano Basin. All the sections were compared with the Falconara-Gibliscemi composite section. We present new mineralogical and geochemical data on the transition from Tripoli to Calcare di Base (CdB), based on the study of several field sections. The outcrops display good record of the paleoceanographical changes that affected the Mediterranean Sea during the transition from slightly restricted conditions to the onset of the Mediterranean Salinity Crisis (MSC). This approach permitted to better constrain depositional conditions and highlighted a new palaeogeographical pattern characterized by separated subbasins. The sedimentological and geochemical parameters of these basins introduced a different and diachronous response to the global constraints of the MSC. Our preliminary results display already evidences of paleoenvironmental changes: (1) a lithological transition passing from the Tripoli’s triplet (grey marls, reddish laminites and diatomites) to the complex carbonates of CdB; (2) the appearance of evaporite pseudomorphs implying early stage diagenesis; (3) the presence of sulphur-rich deposits involving process of bacterial sulphate reduction. The local transition from the uppermost part of the Tripoli cycles to the CdB reflects the worsening of the marine connections, leading to the individualisation of semi-closed settings where the marine inputs were not great enough to balance the effects of the climate fluctuations and especially of the evaporation/precipitation budget.

The return to normal marine conditions in the Mediterranean Sea after the end of the Messinian Salinity Crisis (MSC), that led to the deposition of thick evaporitic succession followed by settlement of brackish to freshwater conditions of the “Lago-Mare”, is still subject to extensive debate between two opposite scenarios. One scenario implies an abrupt reflooding through the Gibraltar gateway of the Mediterranean Sea previously disconnected from the world ocean and partly desiccated. The second scenario postulates that the Mediterranean Sea kept a high-water level throughout the Messinian Salinity Crisis and was connected continuously to the Atlantic Ocean and to the Paratethys. The stratigraphic record of the classical Cuevas del Almanzora section (Vera Basin) is of a crucial importance as the Vera Basin is located on the eastern margin of the Alboran Sea close to the Gibraltar gateway where Atlantic waters reflooded the Mediterranean Sea after the MSC. The present new study completes previous investigations (Pierre et al., 2006) and is mostly focused on detailed sedimentological observations, analysis of ostracod and foraminifer assemblages and on stable isotopes study of three species of planktonic foraminifers (Globigerina bulloides, Globigerinoides obliquus s.l. and Sphaeroidinellopsis spp.) from the lower Pliocene deposits. Biostratigraphical correlations with the reference deep-sea section from ODP Site 975 (Balearic Basin) and the onshore succession of Eraclea Minoa (Sicily) provide an accurate chronostratigraphy and paleoclimatic reconstruction during the Zanclean. During the late Messinian, the Vera Basin was characterized by very unstable lacustrine to brackish environments with significant water depth variations and the deposits display evidences of subaerial exposure. The ostracod content is dominated by Loxocorniculina djafarovi and Cyprideis gr. agrigentina associated to reworked planktonic foraminifera from older sediments. The Messinian/Zanclean contact is well marked by a clear erosional surface that grades laterally into a megabreccia with reworked gypsum blocks and to the large incision of the Palomares canyon in the offshore domain. The marine reflooding occurred abruptly with a sea level rise by more than 250m, an important value for a marginal basin. In this western part of the Mediterranean Sea, the marine invasion began with the onset of the lowermost biozone MPl 1 at the base of the Zanclean. The fluctuations of the planktonic foraminifer assemblages and of their stable isotopes allowed to identify five lithological cycles forced by Milankovitch’ precession periodicity, as well as paleoclimatic variations through the lower part of the Zanclean. Thus, these new data allow us to reaffirm that the Messinian/Zanclean boundary corresponds to a major change, characterized by an “instantaneous” restoration of marine conditions at the onset of the Pliocene, related to the abrupt re-flooding of the Mediterranean Sea from the Atlantic Ocean.

Manzi et al. (in press) took the opportunity offered by our paper to repeat again all the set of ideas supporting an interpretative model of the Messinian Salinity Crisis (MSC), a model they assert to be valid for the whole Mediterranean basin. What emerges from reading this long comment may be summarized in one criticism of our article: we have not systematically applied their interpretative model to our data! The aim of our paper was not to promote their ideas, but to submit the results of more than 20years of field studies and petrographical and geochemical analyses on Sicilian and Calabrian sequences of the Messinian “Calcare di Base”. It is out of our purpose to enumerate again in this reply the data and interpretations we have developed in our paper, which disagree with their model and rule out most of their propositions. Thus, we will not reply in detail to this repetitive stream of ideas supporting their model. But we want to respond to some general and unfair comments, which are often far away from objectivity, and rectify some inaccurate assertions about the description of some sections.

Dolomite nodules are widespread within the Tortonian marls of Fortuna and Lorca basins in southern Spain. They occur as large bodies of various forms (round, ovoid, tabular) that are parallel or secant relative to the stratification. They are massive and present sometimes internal conduits that are considered as drains used for the migration of fluids.

The depositional and diagenetic processes involved in the formation of carbonates in the evaporitic environment of the Messinian Salinity Crisis are investigated in Southern Italy (Sicily and Calabria). Strong differences are observed between the studied sections that reflect specific depositional and diagenetic evolution in the interconnected sub-basins resulting from the syn-sedimentary tectonic fragmentation of the Central Sicilian and Calabrian domains. These carbonates formed diachronously in restricted perched sub-basins between the Tripoli Formation and the hypersaline settings of the MSC. The Calcare di Base (CdB) that can be interbedded with gypsum layers occurs rhythmically at the transition between the upper part of the Tripoli Formation and the massive gypsum, and at places synchronously with the deposition of the Lower Gypsum unit. It deposited initially as primary peloidal and microbial limestones, but their original structure and mineral composition were modified by the superimposition of early to late diagenetic processes. The first diagenetic step was the development of interstitially grown gypsum and halite crystals from trapped saturated brines that locally led to the formation of salt beds. The Sulphur Limestone (SL) resulted from the activity of sulphate reducing bacteria that occurred locally in the deeper parts of the various basins where anoxic bottom waters favoured microbial processes fuelled by biogenic methane and crude oil, and caused the carbonate replacement of gypsum and the formation of native sulphur. The migration of hydrocarbon and H2S-rich fluids caused the epigenetic dissemination of sulphur and a late diagenetic carbonate replacement of the gypsum. Later influxes of continental fresh waters were responsible for the dissolution of the halite crystals and their replacement by sparry calcite. The vugs, formed during both the gypsum/calcite conversion and the halite dissolution, either remained empty or were filled with calcite, celestine, fibrous silica, anhydrite, secondary gypsum, and native sulphur. The initial accumulation of fine-grained carbonate and gypsum sediments was strongly destabilised by volumetric changes resulting from mineral replacements and fluidisation processes. Their superimposition explains the vuggy and boxwork-like textures, in situ brecciation and lateral displacement, which are responsible for the chaotic organisation without necessarily involving basin-scale re-sedimentation in the form of debris flows.

Methane-rich fluids that are generated at depth in organic-rich deposits migrate within the sediments to the seafloor where they are expelled to form mud volcanoes or pockmarks. These migrating fluids are generally involved in diagenetic processes as authigenic carbonate formation that is mediated by microbial activity and they may participate to gas hydrate formation. These features are well-known in the present-day continental margins but their fossil records are relatively scarce. In the Huercal Overa basin (South East Spain), there are chaotic to roughly layered structures intruding the Tortonian-Messinian marls that are interpreted as due to mud volcanism. Moreover, the surrounding marls contain abundant authigenic dolomite nodules. The oxygen and carbon isotopic compositions of these dolomites exhibit wide ranges (-1.4 < δ18O <+3.9 ; -35.5 < δ13C <+5.1). They indicate that authigenic carbonate precipitation occurred within the marly sediments due to circulation of deep fluids that might be relatively warm as shown by the low δ18O values and where anaerobic oxidation of methane (low δ13C values) and methanogenesis (high δ13C values) were active. These two features, methane derived authigenic dolomites and mud volcanism, are testifying of the intense methane-rich fluid migration in the marly deposits of the western Mediterranean basins during the late Neogene, which was the time of major paleoenvironmental changes in the Mediterranean sea climaxing during the Messinian salinity crisis.

The Afar area provides a good representation of the facies distribution, the associated geometries, the relations of carbonate travertines with the basaltic/lacustrine basement and a chemical characterization of fluids responsible for the creation of such carbonated objects.

Evaporite successions may undergo significant lithostratigraphic changes laterally and vertically in tectonically-active basins. The Las Minas Gypsum, a lacustrine unit of Late Tortonian age and up to 160m thick in the Las Minas-Camarillas basin (SE Spain), consists of a number of shallowing-upward cycles. Each cycle is made up of a lower interval with marl and carbonate, and an upper interval with gypsum. In the upper interval, the base displays carbonate-gypsum laminites (couplets, yearly microcycles) showing a large variability of textures and fabrics; gypsum textures are cumulates and bottom-grown crystals. Laminites are overlain by selenitic gypsum. The carbonate is a primary dolomite induced by sulphate-reducing bacterial activity. Native sulphur was formed in early diagenesis and during exhumation was partly transformed into late diagenetic gypsum. The isotopic compositions of gypsum suggest that the sulphate mainly derived from chemical recycling of Triassic evaporites; however, marine sulphate was probably supplied by episodic marine incursions. A perennial saline lake characterized by irregular bottom topography and depositional settings with variable subsidence ratios is interpreted. In addition to climate, saline diapirism, Neogene volcanism, synsedimentary faulting and seismicity influenced the evaporitic deposition. Las Minas-Camarillas basin is an example of how in tectonically active zones different factors interplay to produce significant variability of the evaporitic sedimentation and cyclicity.

Along the western coast of the Gulf of Suez large amounts of evaporitic gypsum of Miocene age have been microbially transformed into carbonates and elemental sulfur in the presence of petroleum. Similar diagenetic transformations have been described from numerous sites worldwide but the role of petroleum, specifically as a carbon source for the sulfate-reducing microbial community, remains elusive. We carried out a geochemical investigation of microbial carbonates from the Gulf of Suez that suggests the presence of a community of sulfate-reducing bacteria thriving on carbon substrates contained in petroleum. Specifically, a set of non-isoprenoidal macrocyclic glycerol diethers (McGDs), that we tentatively ascribe to sulfate-reducing bacteria, have a stable carbon isotope composition close to that of petroleum n-alkanes associated with the carbonates. The presence of archaeol that is 13C-enriched relative to bacterial lipids suggests that Archaea are present but either indirectly involved or not involved in the transformation of petroleum-derived carbon. The lipid biomarker pattern we observe is distinct from those observed in settings where sulfate reduction is coupled to the anaerobic oxidation of methane. Our results suggest that petroleum migration has triggered the microbial transformation of gypsum into carbonates in the Gulf of Suez. By extension, the involvement of petroleum in the microbial transformation of gypsum into carbonates in other settings, which was suggested by more indirect, geological and inorganic geochemical evidence, seems very likely.

The ∼5.3-6.0 million-year-old evaporitic gypsum deposits of Cyprus and Crete contain a variety of stromatolites that formed during the Messinian salinity crisis. We recognize four stromatolite morphotypes, including domical, conical, columnar, and flat-laminated structures. Observations of morphological and textural variations among the different morphotypes reveal significant diversity and complexity in the nature of interactions between microorganisms, gypsum deposition, and gypsum crystal growth. Nonbiological processes (detrital gypsum deposition, in situ crust precipitation, syntaxial crystal growth, subsurface crystal growth, and recrystallization) interacted with inferred microbial processes (including localized growth of biofilms, trapping and binding of grains in mats, nucleation of gypsum on cells) to produce distinct morphological-textural assemblages. Evidence for biological origins is clear in some stromatolite morphotypes and can come from the presence of microfossils, the spatial distribution of organic matter, and stromatolite morphology. In one stromatolite morphotype, the presence of the stromatolite, or the biota associated with it, may have determined the morphology of gypsum crystals. In some stromatolite morphotypes, definitive evidence of a microbial influence is not as clear. There are broad similarities between the Messinian gypsum stromatolites and carbonate stromatolites elsewhere in the geologic record, such as the formation of precipitated and granular layers; the development of domed, columnar, and conical morphotypes; the potential for microbes to influence mineral precipitation; and the recrystallization of deposits during burial. However, in detail the array of microbial-sedimentary-diagenetic process interactions is quite distinct in gypsiferous systems due to differences in the way gypsum typically forms and evolves in the paleoenvironment compared to carbonate. Unique aspects of the taphonomy of gypsum compared to carbonate chemical sediments, generally speaking, include the following: the potential for growth of individual crystals to determine the shape of a stromatolite (and possibly vice versa), a more diverse set of outcomes relating to preservation versus destruction of textures through crystal growth and recrystallization, and a greater likelihood of preserving microfossils through encapsulation in large crystals. These insights gained from the study of terrestrial gypsum sedimentary rocks provide valuable guidance for the search for clues to past life in sulfate chemical sediments on Mars.

During mid Eocene times, the northwestern margin of the Gosiute Lake (Wyoming) has been characterised by the extensive development of a microbialite dominated carbonate sequence corresponding to the Laney Member of the Green River Formation, thus providing a potential analogue for petroleum carbonate reservoirs developed in similar marginal lacustrine settings. A detailed sedimentological study carried out on the Little Mesa plateau near LaBarge (SW Wyoming) allows the reconstruction of: 1) lateral and vertical facies variations of the carbonate sequence across the margin, 2) development patterns of complex microbial bioconstructions, and 3) the evolution of the margin through time. The carbonate sequence, up to 18m-thick, starts with the deposition of sandy limestones which fill channels in the underlying siliciclastic unit of the Cathedral Bluff Formation. The increasing microbial contribution in the upper part of the sequence results in the development of large insect-microbial build-ups which represent up to 80% of the total volume of the carbonate deposits and which aggregated to form reef-like geometries up to several tens of metres in diameter, including bioherms, spur and groove alignments and reef-flat structures. The initiation and development of the lacustrine carbonate platform was controlled both by the general lake expansion associated to the Eocene Climatic Optimum and by local drainage diversions responsible for a new water inflow in the basin from the northern volcanic provinces. Short-term lake level changes driven by high-frequency climate fluctuations which are superimposed to this general transgressive trend may explain the discontinuous and polygenic growth of the individual insect-microbial build-ups. The basin infilling by prograding alluvial volcaniclastic deposits originated from the northwestern volcanic province caused the rapid turn off of the marginal lacustrine carbonate factory during mid Eocene time.

Abstract Recent discoveries offshore Brazil have induced a renewal of interest in the study of recent and ancient continental carbonate systems which developed in a wide range of depositional settings, reflecting aerial to subaqueous environments. Recent and ancient continental carbonate analogs provide some keys to depict the sedimentologic/sequential pattern observed at the core scale and help in the understanding of the impact of climate change, fluid flow and water chemistry on the carbonate factory. It is noteworthy that the widespread microbial development in continental carbonate systems occurs in stratigraphic intervals typified by specific climatic and geodynamic conditions, and sometimes coincides with similar development in the marine realm. Stromatolites are more developped in high water level condition. But comparative studies between intracratonic (Recent Great Salt Lake; Eocene Green River lacustrine systems) and rift lacustrine systems demonstrates that they are more extensive on a flat substrate. The control exerted by the topography may increase during abrupt alternations of arid and humid periods, influencing the water chemistry and, accordingly, leading to the development of anoxic and/or evaporitic conditions. The key issue is therefore to understand the development of carbonate in lacustrine condition, how the sedimentary bodies and features can be preserved, and how their good reservoir properties can be maintained. High subsidence rate will influence the preservation potential of the relevant carbonate bodies, while the geothermal gradient, water chemistry or volcanic activity will impact the reservoir properties. In addition, meteoric or thermogenic travertine deposits, are an additional carbonate product that must be considered in the evaluation of continental carbonate reservoir systems.

Here, we interpret the evolution of Maryut lagoon (Egypt) during the past ∼2000 years. Chronostratigraphy and laboratory analyses have enabled us to identify four main phases since the 3rd century AD: (1) a fluvial-dominated lagoon between the 2nd–3rd and the 8–9th centuries cal. AD; (2) a gradual desiccation of the lagoon toward a sebkha-like environment from the 9–10th to the 13th centuries cal. AD; (3) a fluvial-dominated lagoon from the 13th century cal. AD; and (4) a second gradual desiccation between the 17th and the 18th centuries cal. AD. The general aridification trend described throughout the study period may be linked to the gradual decline of the Canopic branch, which supplied the Maryut lagoon with freshwater. Nonetheless, at shorter timescales, the different phases of lagoon aridification and flooding coincide with land abandonment and irrigation works in the region. It is suggested that the history of the Alexandria countryside has been a key driver in shaping the environmental history of the Maryut during the past ∼2000 years.