Elat Area Research Articles

Cadomian (ca. 550 Ma) magmatic and thermal imprint on the North Arabian-Nubian Shield (south and central Israel): New age and isotopic constraints

The Arabian-Nubian Shield (ANS) is a province of mostly juvenile Neoproterozoic continental crust in NE Africa and Arabia, forming the northern extension of the East-African orogen. Subsequent to widespread, mostly late- to post-orogenic early-Ediacaran calc-alkaline granitoid emplacement, the latest magmatic phase in the ANS saw the intrusion of alkaline shallow plutons alongside volcanic massifs and dikes of variable compositions. While some of these intrusions were dated to 550–530 Ma by Rb-Sr and Ar-Ar, U-Pb zircon data has mostly limited ANS magmatism to no younger than ca. 580 Ma. Here we report new age and isotopic data from latest Neoproterozoic intrusions along a N-S transect within the northern ANS and its periphery, substantiating the record of a ca. 550 Ma igneous-thermal event in the area. In the northern Negev of Israel, mafic igneous rocks intruded into the subsurface late Neoproterozoic clastic wedge of the Zenifim Formation produced apatite U-Pb isochron ages between 557 and 545 Ma. In the Amram alkaline massif, 150 km to the south, an alkali-granite was dated to 605 ± 2.5 Ma by zircon U-Pb, but apatite U-Pb ages from all rocks of the massif concentrate at ca. 550 Ma indicating thermal resetting. Apatites from the zircon dated 611 ± 5 Ma Roded quartz diorite in the Elat area, south of Amram, produced a 600 ± 4 Ma U-Pb age, demonstrating that southern segments were not thermally reset at ca. 550 Ma. Nd isotopes in apatite and whole rock show the ca. 550 Ma igneous rocks to be variable in their isotopic composition, ranging between εNd(t)=(-4) – (+2), far less juvenile than typical ANS magmas. The ca. 550 Ma intrusions resemble in their age and isotopic properties Cadomian granites and volcanic rocks that are known from southern Turkey, Iran and Europe. We interpret the ca. 550 Ma igneous overprint and thermal resetting documented in the northernmost ANS as related to the superposition of Cadomian orogeny on the ANS periphery. This can be related to the late Ediacaran subduction of proto-Tethys accompanying the accretion of the Cadomian basement of the Tauride block to NE Africa and Arabia, before the area was overstepped by Cambrian platform sedimentation.

The geology of the northern tip of the Arabian–Nubian Shield

Recently, a detailed (1:50,000) geological map of the Elat area, southern Israel was published. Attached to this map is a stratigraphic table of the Neoproterozoic metamorphic–magmatic complex of the study area. The Neoproterozoic basement in the Elat area encapsulates the Arabian Nubian Shield (ANS) geologic evolution. Uranium–Lead and Lead–Lead zircon ages, included in previous studies and referred to in this paper, reveal that these rocks were formed during more than 300 million years of Neoproterozoic time. The major process controlling the formation of the ANS as part of the East African Orogen is the closure of the Mozambique Ocean. The first orogenic phase in the Elat area, represented by the metamorphic rocks, includes the development of an island arc, erosion of the islands and deposition, and metamorphism. This event took place between ∼950Ma and 780–790Ma. Elat Schist, the oldest metamorphic rock in the area, was deformed and then intruded by quartz dioritic and granitic plutons that were later deformed and metamorphosed. The amphibolite metamorphic rock facies indicate metamorphic conditions of up to 650°C and between 4 and 5kbar. The peak of the metamorphic event was most probably before 750Ma. A gradual change from compressional to extensional stress regime is evidenced by emplacement andesitic magnesium-rich dykes dated to 705Ma that were later metamorphosed to schistose dykes at a greenschist metamorphic facies. The second orogenic phase (terrane amalgamation, main shaping of crust) was associated with the emplacement of large volumes (>50% of area) of calc-alkaline intrusions in a post-collision setting. These very last stages of metamorphism and deformation are characterized by intrusion of ∼630Ma granitoids exhibiting some foliation. Pluton emplacement continued also after the end of deformation. Exhumation and transition to an extensional regime is recorded by the intrusion of shallow alkaline granites in ∼608Ma which were accompanied in ∼609Ma by rhyolite, andesite and composite dykes. The last magmatic event in the Elat area is represented by the volcano-conglomeratic series comprising rhyolites, basalts, andesites, hypabyssal intrusions of monzonite and syenite and conglomerates. The conglomerates, dated to about 590Ma, are the products of a major erosion phase in which about 12,000m of the section were removed. These conglomerates were intruded by 585Ma rhyolite, andesite and composite dykes. The Neoproterozoic basement is truncated by a peneplain whose age, post 532Ma, is constrained by the age of the youngest eroded dolerite dykes. This Early Cambrian peneplain was associated with erosion of 2000m of the section and by chemical weathering. Three major breaks in Neoproterozoic magmatic activity are recognized: the first, occurred in Cryogenian time, lasted ∼60 million years after the amphibolite facies metamorphism and before emplacement of the calc alkaline plutons, separating the first and the second orogenic phases; the second break between the orogenic and the extensional phases occurred in early Ediacaran time, encompassed ∼20 million years between the emplacement of the calc-alkaline and alkaline plutonic rocks and rhyolite, andesite and the composite dykes; and the third, ∼50Ma break, occurred between the emplacement of the last felsic intrusions at ∼585Ma and intrusion of the dolerite dykes in 532Ma, before the Early Cambrian peneplain developed.The great lateral extension of the Cambrian to Eocene sedimentary rocks and their slow facies and thickness changes suggest a stable flat platform area at the northern tip of the ANS. Early Cambrian sedimentation began with fluviatile subarkoses of the Amudei Shlomo Formation. It was overlain by an Early to Middle Cambrian transgressive–regressive lagoonal cycle of dolostones, sandstones, and siltstones of the Timna Formation. Then Middle Cambrian subarkoses and siltstones of the Shehoret Formation and the quartz arenite of the Netafim Formation were deposited in a coastal, intertidal environment representing the southern transgression of a Cambrian ocean.

U–Pb detrital zircon provenance of the Saramuj Conglomerate, Jordan, and implications for the Neoproterozoic evolution of the Red Sea region

The latest stage in the evolution of the northernmost Arabian-Nubian Shield is characterized by the development of volcano-sedimentary successions. In Jordan the Saramuj Conglomerate Formation is considered to be one of these post-tectonic basins. It is polymict and poorly sorted with wide range of clast compositions, roundness and size. We present the first SIMS U–Pb dating of detrital zircons from two sandstone samples representative for the conglomerate matrix and of four clasts from the Saramuj Conglomerate for provenance and age determinations. The relative probability curve for the matrix samples indicates a major contribution (85%) from c. 600 to 650Ma, subclusters at 624 and 640Ma, a minor source from 700 to 750Ma, and a clear gap between 650 and 700Ma. These ages are consistent with those obtained from andesitic, rhyodacitic, granitic and gneiss clasts (624, 642, 650 and 734Ma respectively). In contrast to the adjacent volcano-sedimentary successions in the Elat area, Sinai and the Eastern Desert, no ages older than 750Ma were found. The good match between the known ages of the nearby exposed basement with the matrix ages and the immature nature of the sediments implies that the principal input was locally derived erosional detritus. The age of the youngest 10 detrital zircons at c. 615Ma represents the maximum age of deposition, which is consistent with the stratigraphic position of the Saramuj Conglomerate. Clast ages of 642Ma and 650Ma are interpreted as evidence for a magmatic source that has not been recognized in SW Jordan. This study implies that the volcano-sedimentary successions in the northernmost Arabian-Nubian shield may be broadly coeval but have distinct provenance and therefore evolved as isolated basins. Furthermore, U–Pb zircon provenance analysis allows us to recognize igneous products that are no longer preserved and/or exposed in the region.

Three successive Proterozoic island arcs in the Northern Arabian–Nubian Shield: Evidence from SIMS U–Pb dating of zircon

Four isolated metamorphic complexes located within post-collisional granitoids occupying up to 70% of the total area, were distinguished in Sinai (Egypt) and Elat area (southern Israel), the northernmost part of the Arabian–Nubian Shield. The metamorphic rocks include metasediments, felsic and mafic metavolcanic rocks intruded by granitic, dioritic, and gabbroic plutons, all subjected to penetrative deformation.We present new SIMS U–Pb dating of zircons from 13 rock units comprising metasediments, volcanic rocks, gneisses and plutons from three metamorphic complexes (Sa'al, Feiran–Solaf, and Kid). In addition we present a SIMS U–Pb titanite age of a granitic gneiss previously dated using zircon. On the basis of the new and published U–Pb data, three successive Meso- to Neoproterozoic island arcs formed during a period of ca. 500My are recognized. The Sa'al arc (represented by the oldest arc rocks in the ANS) evolved from 1.03 to 0.93Ga (100My); the Feiran–Elat arc developed from ca. 870 to 740Ma (130My), and the Kid arc formed from ca. 640 to 620Ma (20My). Evidence for an older, ca. 1.1Ga, pre-Sa'al island arc was established from the zircon xenocryst population, though no exposures of rocks of this age were found. In the Sa'al and Kid arcs both volcanic and sedimentary rocks are preserved, whereas in the Elat–Feiran arc volcanic rocks are missing. We suggest that at ~700Ma the Elat−Feiran arc was subjected to rifting that resulted in separating of the Qenaia block and its movement to the SE.

1000–580 Ma crustal evolution in the northern Arabian-Nubian Shield revealed by U–Pb–Hf of detrital zircons from late Neoproterozoic sediments (Elat area, Israel)

The final stages in the evolution of the Arabian-Nubian Shield (ANS) during the late Neoproterozoic include the deposition of sub-aerial volcano-sedimentary sequence above exhumed deep-seated plutonic-metamorphic rocks. In southern Israel the sediments in this sequence, known collectively as the Elat conglomerate unit, consist primarily of immature polymictic conglomerates whose composition closely reflects their underlying basement. U–Pb dating and Hf isotopic analysis of single zircons from two samples of the Elat conglomerate is used here to gain a complementary perspective on crustal evolution processes in the northern ANS. The U–Pb age spectra of the detrital zircons bear evidence for two major magmatic cycles separated by a lull; early island-arc magmatism occurred at 880–760Ma and peaked at ∼800Ma, whereas post-collisional granitoids and volcanics invaded the amalgamated arc crust between 660 and 580Ma and peaked at 610–630Ma. Integration with previously published data from Sinai suggests the aforementioned igneous cycles and the intervening lull are of regional significance. Although island-arc igneous activity in the ANS ranged mostly between 880 and 760Ma, the occurrence of detrital zircons with strongly positive ɛHf(t) values and U–Pb ages of up to 1.0Ga in the Elat conglomerate suggests that island-arc magmatism in the northern ANS started in the early Tonian, earlier than previously recognized.The youngest zircons in the Elat conglomerate constrain its deposition age to ∼580Ma. No younger U–Pb zircon ages were obtained for crystalline rocks in this region, our data thus indicates that 580Ma marks the cessation of igneous activity in the northern ANS.The great majority of detrital zircons in the Elat conglomerate display positive ɛHf(t) values, in line with the overall juvenile character of the Shield. Nonetheless, the relatively wide range of ɛHf(t) values in zircons representing island-arc magmatism (between +3.6 and +11.6), and the presence of zircons with pre-Neoproterozoic ages and/or negative ɛHf(t) values, suggest some contamination of the arc magmas by an older crustal component. The ɛHf(t) values in zircons representing the younger, post-collisional magmas are all positive (between +4.9 and 9.2) and resemble those in the preceding arc-derived zircons. This feature is consistent with both reworking of mafic island-arc crust and contribution from mantle-derived melts during the post-collisional stage. Thus, it cannot be deciphered whether the 1000–580Ma igneous activity in the northern ANS represents continuous juvenile crustal addition from the mantle, or subsequent recycling of early-formed arc crust during a later post-collisional phase.

Radon variability at the Elat granite, Israel: Heteroscedasticity and nonlinearity

The basic statistical features of radon time series from continuous radon monitoring at the Elat granite, Israel are analysed. A similar analysis is carried out for ancillary and possibly related geophysical parameters for the Elat area. The results show that air temperature, precipitable water and long‐wave radiation time series exhibit constant variance over the analyzed period, while radon time series, atmospheric pressure, short‐wave radiation and total electron content exhibit heteroscedasticity. Furthermore, for radon and short‐wave radiation the variability is associated with the overall mean level, while for atmospheric pressure such an association is not present. The analyzed radon time series not only are non‐stationary but also nonlinear, reflecting the complex dynamics of radon emanation and transport in natural subsurface systems.

Geochemical and K–Ar age constraints on the Late Neoproterozoic (?) gneisses at Um Tenassib area, north Eastern Desert, Egypt

Wadi Um Tenassib metamorphic rocks consist mainly of biotite gneiss and biotite-hornblende gneiss with subordinate intercalations of amphibolite, migmatitic gneiss, and aplitic granite. Biotite-hornblende gneiss, biotite gneiss, and aplitic granite are geochemically characterized and their cooling ages are determined by using the K–Ar method on biotite. The Um Tenassib gneisses (UTG) range in composition from quartz diorite/monzodiorite to granodiorite. They were derived from igneous rocks that pertain to calc alkaline and metaluminous to weakly peraluminous affinities and were generated in continental volcanic arc setting. REE patterns of the UTG are moderately fractionated (La N/Lu N = 5.9–7.5) relative to those of the aplitic granite (La N/Lu N = 33). The similarity in the geochemical characteristics and REE patterns of both gneiss types indicate their magmatic consanguinity. Amphiboles of the UTG biotite-hornblende gneisses are mainly hornblende, together with few paragasitic hornblende and edenite. Plagioclase composition is oligoclase to andesine (An 21–46) in the biotite-hornblende gneiss, and oligoclase (An 11–26) in the biotite gneiss. Mineral chemistry of amphibole and plagioclase indicate that the gneisses were metamorphosed under low- to medium-pressure of 2.6–6.4 kbar and at medium to high temperatures of 660–755 °C. The K–Ar biotite cooling ages (seven samples) range from 585 ± 12 Ma to 598 ± 12 Ma for the UTG, except one biotite-hornblende gneiss sample gives age of 577 ± 11 Ma. These ages suggest a latest metamorphic cooling event at ca. 585–600 Ma time span, which is consistent with the proposed cooling ages of ∼600 Ma for the Elat metamorphic rocks [Cosca, M.A., Shimron, A., Caby, R., 1999. Late Precambrian metamorphism and cooling in the Arabian–Nubian Shield: petrology and 40Ar/ 39Ar geochronology of metamorphic rocks of the Elat area (southern Israel). Precamb. Res. 98, 107–127]. It may indicate that the metamorphism of the UTG might have been contemporaneous with the suggested regional metamorphism at 620 ± 10 Ma for Sinai metamorphic rocks (Cosca et al., 1999) and/or the emplacement age at 614 Ma for the granodiorite in the study area [Stern, R.J., Hedge, C.E., 1985. Geochronological and isotopic constraints on the Late Precambrian crustal evolution in the Eastern Desert of Egypt. Am. J. Sci. 285, 97–127]. These ages also lie within the range of magmatic activity of the Younger Granites in the North Eastern Desert (575–600 Ma).

Interrelations between coeval mafic and A-type silicic magmas from composite dykes in a bimodal suite of southern Israel, northernmost Arabian–Nubian Shield: Geochemical and isotope constraints

Late Neoproterozoic bimodal dyke suites are abundant in the Arabian–Nubian Shield. In southern Israel this suite includes dominant alkaline quartz porphyry dykes, rare mafic dykes, and numerous composite dykes with felsic interiors and mafic margins. The quartz porphyry chemically corresponds to A-type granite. Composite dykes with either abrupt or gradational contacts between the felsic and mafic rocks bear field, petrographic and chemical evidence for coexistence and mixing of basaltic and rhyolitic magmas. Mixing and formation of hybrid intermediate magmas commenced at depth and continued during emplacement of the dykes. Oxygen isotope ratios of alkali feldspar in quartz porphyry (13 to 15‰) and of plagioclase in trachydolerite (10–11‰) are much higher than their initial magmatic ratios predicted by equilibrium with unaltered quartz (8 to 9‰) and clinopyroxene (5.8‰). The elevation of δ 18O in alkali feldspar and plagioclase, and extensive turbidization and sericitization call for post-magmatic low-temperature (≤ 100 °C) water–rock interaction. Hydrous alteration of alkali feldspar, the major carrier of Rb and Sr in the quartz–porphyry, also accounts for the highly variable and unusually high I(Sr) of 0.71253 to 0.73648. The initial 143Nd/ 144Nd ratios, expressed by ε Nd( T) values, are probably unaltered and show small variation in mafic and felsic rocks within a narrow range from + 1.4 to + 3.3. The Nd isotope signature suggests either a common mantle source for the mafic and silicic magmas or a juvenile crustal source for the felsic rocks (metamorphic rocks from the Elat area). However, oxygen isotope ratios of zircon in quartz porphyry [ δ 18O(Zrn) = 6.5 to 7.2‰] reveal significant crustal contribution to the rhyolite magma, suggesting that mafic and A-type silicic magmas are not co-genetic, although coeval. Comparison of 18O/ 16O ratios in zircon allows to distinguish two groups of A-type granites in the region: those with mantle-derived source, δ 18O(Zrn) ranging from 5.5 to 5.8‰ (Timna and Katharina granitoids) and those with major contribution of the modified juvenile crustal component, δ 18O(Zrn) varying from 6.5 to 7.2‰ (Elat quartz porphyry dykes and the Yehoshafat alkaline granite). This suggests that A-type silicic magmas in the northern ANS originated by alternative processes almost coevally.

Four successive episodes of Late Pan-African dikes in the central Elat area, southern Israel

Four successive episodes of Late Pan-African dikes in the central Elat area, southern Israel

Four successive episodes of Late Pan-African dikes in the central Elat area, southern Israel

Katzir, Y., Litvinovsky, B., Eyal, M., Zanvilevich, A., and Vapnik, Y. 2006. Four successive episodes of Late Pan-African dikes in the central Elat area, southern Israel.lsr. J. Earth Sci. 55: 69-93. Four successive Late Pan-African dike suites are recognized in the central Elat area: (I) microdiorite and lamprophyre; (2) dacite porphyry with subordinate andesite and fcldspathic (Fsp) rhyolite porphyry; (3) quartz porphyry and Fsp-rhyolite porphyry with minor trachydolerite and trachyandesite; (4) trachydolerite, mostly high-Ti. Dike swarms formed over the period of -600 Ma to 530 Ma. The dike episodes alter­ nated with plutonic. volcanic. and sedimentary events. Microdiorite and lamprophyre from suite I correspond to calc-alkaline, medium- to high-K trachyandesite. Dacite porphyry is prevalent in suite 2 and forms together with augite-bearing andesite and rhyolite a high-K calc-alkaline series. In suite 3 silicic rocks are dominant; they are alkaline (NK/A >D.9) and have chemical characteristics of A-type granites. Among the trachydolerites from suites 3 and 4, high-Ti varieties are abundant (2.8-2.9 wt% and 3.3-4.5 wt% TiO:!, respectively). Trachydolerites are enriched in REE, Zr, Y, Ti, and P. Although Late Pan-African dikes are postorogenic, magmas of the first two suites were derived from mantle sources that are characteristic of a subduction-related environment of active continental margins. Trachydolerites-3 and -4 were produced, however, from sources enriched in asthenospheric components. Late Pan-African dike swarms similar to those described in southern Israel are extremely abundant through­ out the Sinai Peninsula and Eastern Desert of Egypt. Significant overlap of composi­ tions in mafic dike rocks from southern Israel and the same rock types from southern Sinai suggest similar sequence and sources of dikes over a large region.

Origin of northern Gondwana Cambrian sandstone revealed by detrital zircon SHRIMP dating

Voluminous Paleozoic sandstone sequences were deposited in northern Africa and Arabia following an extended Neoproterozoic orogenic cycle that culminated in the assembly of Gondwana. We measured sensitive high-resolution ion microprobe (SHRIMP) U-Pb ages of detrital zircons separated from several Cambrian units in the Elat area of southern Israel in order to unravel their provenance. This sandstone forms the base of the widespread siliciclastic section now exposed on the periphery of the Arabian-Nubian shield in northeastern Africa and Arabia. Most of the detrital zircons we analyzed yielded Neoproterozoic concordant ages with a marked concentration at 0.55‐0.65 Ga. The most likely provenance of the Neoproterozoic detritus is the Arabian-Nubian shield; 0.55‐0.65 Ga was a time of posttectonic igneous activity, rift-related volcanism, and strike-slip faulting there. Of the zircons, 30% yielded pre-Neoproterozoic ages grouped at 0.9‐1.1 Ga (Kibaran), 1.65‐1.85 Ga, and 2.45‐2.7 Ga. The majority of the pre-Neoproterozoic zircons underwent Pb loss, possibly as a consequence of the Pan-African orogeny resetting their provenance. Rocks of the Saharan metacraton and the southern Afif terrane in Saudi Arabia (;1000 km south of Elat) are plausible sources of these zircons. Kibaran basement rocks are currently exposed more than 3000 km south of Elat (flanking the Mozambique belt), but the shape of the detrital zircons of that age and the presence of feldspar in the host sandstone are not fully consistent with such a long-distance transport. Reworking of Neoproteorozoic glacial detritus may explain the presence of Kibaran detrital zircons in the Cambrian of Elat, but the possibility that the Arabian-Nubian shield contains Kibaran rocks (hitherto not recognized) should also be explored.

Late Precambrian metamorphism and cooling in the Arabian–Nubian Shield: Petrology and 40Ar/ 39Ar geochronology of metamorphic rocks of the Elat area (southern Israel)

Representative samples of metamorphic rocks and one sample of undeformed granite from the Elat area of southern Israel have been analyzed by microprobe and conventional 40Ar/ 39Ar geochronological methods. The highest-grade metamorphic assemblages, formed during the collision of greater east and west Gondwanaland, give equilibrium P–T conditions of 7±1 kbar and 650–700°C. The timing of regional metamorphism in Elat has been estimated at 620±10 Ma on the basis of published single zircon evaporation ages, correlations with geochronological data from rocks that adjoined the Elat area prior to later faulting and 40Ar/ 39Ar age spectra from amphibole and phlogopite of the Shahmon metabasite complex. Samples of muscovite and biotite from the Elat schists, Taba gneiss, Elat granitic gneiss and Elat granite yield remarkably uniform ages ∼600 Ma, interpreted to record the potentially rapid cooling and unroofing of the metamorphic basement. Unroofing of the Elat metamorphic basement was synchronous with widespread igneous activity in the Sinai Peninsula and elsewhere in the Arabian–Nubian Shield, reflecting its transition from orogenic to post-orogenic tectonics. The P–T and 40Ar/ 39Ar data agree well with field, geochemical, geochronological and structural data consistent with a single metamorphic event at 620±10 Ma followed by large-scale extension and tectonic escape in the northern Arabian–Nubian Shield during the late stages of the Pan-African orogenic cycle. The lack of any evidence of a Devonian thermal event in the Elat area, previously inferred from complex 40Ar/ 39Ar age spectra from altered dikes, indicates that any such event was very localized.

Morphogenesis and facies relationships of thrombolites and siliciclastic stromatolites in a Cambrian tidal sequence (Elat area, southern Israel)

Thrombolites and siliciclastic stromatolites occur within the Lower Cambrian marine Timna Formation in the Elat area, southern Israel. This rock succession consists of four consecutive stratal suites which together represent a transgressive-regressive cycle within a peritidal depositional system. The thrombolites are associated with the sea-ingression stage and occur as a series of massive-bedded strata with laminoid fenestral layers and with a microclotted-peloidal fabric of the micritic material. SEM-EDS study of the clotted and peloidal micrite reveals a calcitic framework of pitted polygonally shaped units, 2 μm wide, together with a few groups of compressed, large hollow structures. These forms are interpreted as the possible remnants of bacterial decomposers and of coccoid-dominated mat-forming unicells, respectively. The intimate structural connection between the carbonate fraction and the microbe structures suggest in situ carbonate production through bacterial decay of the cyanobacterial material during its self-burial, with carbonate precipitating as solid phases on vacant extracellular envelopes. The siliciclastic stromatolites developed during seashore progradation and now occur as rare, laterally linked columnar forms within channelled cross-stratified sandstones at the top of the Timna succession. They are finely laminated with a low to moderate degree of inheritance of the laminae and are partly burrowed by Skolithos . Textures and the geometry of the siliciclastic stromatolites suggest that they were formed through binding of transported quartz sand-sized particles by bottom-dwelling filamentous microorganisms. Sediment production and the growth-pattern of the two structures within the Timna sequence seem to have been regulated by different microbial assemblages which shifted in response to changes in environmental factors through time and space. The differential distribution of the two buildups in the sedimentary sequence reflects the difference in balance between the biological attributes of the two biotas and the physical environment. Pitted architectures, such as those displayed by the Timna thrombolites, could be an ontogenetic fingerprint of microbially constructed rocks, which might help to recognize them in the fossil record when other evidence is lacking.

Significance of Gold Exploitation in the Early Islamic Period, Israel

An archaeological site in southern Israel contains the remains of industrial settlements and implements. The comminuted product of millstones is a powdery material consisting mainly of quartz, and containing up to 20 ppm gold. It appears that the gold was mined within proximity of the site, and that the ore contained microscopic gold. This is the first indication of gold operations in the ancient or modern Levant and it sheds new light on the importance of the Elat area during the Early Islamic period.