Paleoclimate reconstruction based on the timing of speleothem growth and oxygen and carbon isotope composition in a cave located in the rain shadow in Israel     

Anton VaksMiryam Bar-Matthews  Avner AyalonBettina Schilman  Mabs GilmourChris J Hawkesworth  Amos FrumkinAaron Kaufman  Alan Matthews 《Quaternary Research》2003,59(2):182-193

High-resolution ²³⁰Th/²³⁴U ages and δ¹⁸O and δ¹³C compositions of speleothems in Ma’ale Efrayim Cave located to the east of the central mountain ridge of Israel enable us to examine the nature of the rain shadow aridity during glacial and interglacial intervals. Speleothem growth occurred during marine glacial isotopic periods, with no growth during the two last marine isotope interglacial intervals and during the peak of the Last Glacial Maximum. This contrasts with speleothem growth in caves located on the western flank of the central mountain ridge, in the Eastern Mediterranean semiarid climatic zone, which continued throughout the last 240,000 yr. Thus, during glacial periods water reached both sides of the central mountain ridge. A comparison of the present-day rain and cave water isotopic compositions and amounts at the Ma’ale Efrayim Cave site with those on the western flank shows that evaporation and higher temperatures on the eastern flank are major influences on isotopic composition and the lack of rainfall. The δ¹⁸O and δ¹³C profiles of the speleothems deposited between 67,000 and 25,000 yr B.P. match the general trends of the isotopic profiles of Soreq Cave speleothems, suggesting a similar source (eastern Mediterranean Sea) and similar climatic conditions. Thus, during glacial periods the desert boundary effectively migrated further south or east from its present-day location on the eastern flank, whereas interglacial periods appear to have been similar to the present, with the desert boundary at the same position. The decrease in overall temperature and a consequent reduction in the evaporation to precipitation ratios on the eastern flank are viewed as the major factors controlling the decay of the rain shadow effect during glacial periods.  相似文献   

Refractory inclusions in the Murchison meteorite     

Glenn J. MacPherson  Miryam Bar-Matthews  Tsuyoshi Tanaka  Edward Olsen 《Geochimica et cosmochimica acta》1983,47(4):823-839

Mineralogical and petrographic studies of a wide variety of refractory objects from the Murchison C2 chondrite have revealed for the first time melilite-rich and feldspathoid-bearing inclusions in this meteorite, but none of these is identical to any inclusion yet found in Allende. Blue spinel-hibonite spherules have textures indicating that they were once molten, and thus their SiO₂-poor bulk composition requires that they were exposed to higher temperatures (>1550°C) than those deduced so far from any Allende inclusion. Melilite-rich inclusions are similar to Allende compact Type A's, but are more Al-, Ti-rich. One inclusion (MUCH-1) consists of a delicate radial aggregate of hibonite crystals surrounded by alteration products, and probably originated by direct condensation of hibonite from the solar nebular vapor. The sinuous, nodular and layered structures of another group of inclusions, spinel-pyroxene aggregates, suggest that these also originated by direct condensation from the solar nebular gas. Each type of inclusion is characterized by a different suite of alteration products and/or rim layers from all the other types, indicating modification of the inclusions in a wide range of different physico-chemical environments after their primary crystallization. All of these inclusions contain some iron-free rim phases. These could not have formed by reaction of the inclusions with fluids in the Murchison parent body because the latter would presumably have been very rich in oxidized iron. Other rim phases and alteration products could have formed at relatively low temperatures in the parent body, but some inclusions were not in the locations in which they were discovered when this took place. Some of these inclusions are too fragile to have been transported from one region to another in the parent body, indicating that low temperature alteration of these may have occurred in the solar nebula.  相似文献   

Lower palaeozoic and precambrian petroleum source rocks and the coalification path of alginite     

Miryam Glikson  Dennis Taylor  Douglas Morris 《Organic Geochemistry》1992,18(6)

Organic-rich samples derived from a Middle Cambrian Formation in the Georgina Basin, and from the Middle Proterozoic of the McArthur Basin in northern and central Australia, yielded alginite ranging from immature oil shale material to overmature residue. A maturation scale has been developed based on the thermal evolution of alginite as determined from reflectance and fluorescence. The coalification path of alginite is marked by jumps in contrast to the linear path of wood-derived vitrinite. Six zones have been recognised, ranging from undermature (zone I), through the mature (zones II/III), followed by a stable stage of no change (zone IV) to the overmature (zones V and VI). The onset of oil generation in alginite as evident from the present study is at 0.3% R_{o Alg.} and is expressed in a change of fluorescence from yellow to brown, and a coalification jump from 0.3 to 0.6% R_o of Alg. In many boreholes zone III can be distinguished between 0.6 and 0.8% R_o of Alg. where subsequent oil generation occurs. Zones II and III represent the oil window.A zone of little or no change designated zone IV, at of alginite follows zones II/III. A marked coalification jump characterises zone V, where a pronounced change in reflectance occurs to >1.0% R_{o Alg.}, signifying peak gas generation. The border of oil preservation lies at the transition of zone V and VI, at 1.6% R_{o Alg.} In zone VI gas generation only occurs.Comparison of reflectance results with experimental and geochemical pyrolysis data supports high activation energies for hydrocarbon generation from alginite, and therefore a later onset of oil generation than other liptinite macerals (i.e. cutinite, exinite, resinite) as well as a narrow oil window.Transmission electron microscopy (TEM) confirms that alginite does not go through a distinct intermediate stage but that the percentage of unreacted organic matter decreases as maturation proceeds. A clear distinction can be made in TEM between immature alginite, alginite after oil generation, and alginite residue following gas generation. Alginite beyond 1.6% R_o acquires very high densities and the appearance of inertinite in TEM.Bitumens/pyrobitumens make a pronounced contribution to the organic matter throughout the basins and have been shown to effect pyrolysis results by suppressing T_max. The bitumens/pyrobitumens have been divided into four groups, based on their reflectance and morphology, which in turn appears to be an expression of their genetic history. Their significance is in aiding the understanding of the basins' thermal history, and the timing of oil and gas generation.  相似文献   

The chronology of the late Lower Paleolithic in the Levant based on U–Th ages of speleothems from Qesem Cave,Israel     

A. Gopher  A. Ayalon  M. Bar-Matthews  R. Barkai  A. Frumkin  P. Karkanas  R. Shahack-Gross 《Quaternary Geochronology》2010,5(6):644-656

We present here the results of a U–Th dating project at Qesem Cave, a Middle Pleistocene, late Lower Paleolithic site in Israel. It provides 54 new MC-ICP-MS U–Th ages for speleothems from the cave. The results indicate that human occupation started sometime between ～420 and 320 ka and ended between 220 and 194 ka. A survey of dates from culturally similar sites in the Levant indicates that the general range of ca. 400–ca. 200 ka is an appropriate estimate for the life span of the Acheulo-Yabrudian Cultural Complex (AYCC).  相似文献   

Microbial remains in some earliest Earth rocks: Comparison with a potential modern analogue   总被引：1，自引：1，他引：0  

Miryam Glikson  Lawrence J. Duck  Suzanne D. Golding  Axel Hofmann  Robert Bolhar  Robyn Webb  Justice C.F. Baiano  Lindsay I. Sly 《Precambrian Research》2008,164(3-4):187-200

Carbonaceous matter (CM) from ca. 3.5 Ga hydrothermal black cherts of the Pilbara Craton of Western Australia and the Barberton Greenstone Belt of South Africa yielded transmission electron microscopy (TEM) images that are suggestive of microbial remains and possible remnants of microbial cell walls. These are compared to a potential modern analogue, the hyperthermophilic Methanocaldococcus jannaschii, derived from an active seafloor hydrothermal environment and cultured under similar conditions. A striking resemblance to the early Archaean forms was evident in wall structure and thermal degradation mode. Cell disintegration of the cultures occurred at 100 °C marking the limits of life. Complete disintegration, deformation and shrinkage occurred at 132 °C. A multidisciplinary approach to the characterisation of the CM was undertaken using organic petrology, TEM coupled with electron dispersive spectral analysis (EDS), high resolution TEM (HRTEM) to determine molecular ordering, and elemental and carbon isotope geochemistry. Reflectance measurements of the CM to determine thermal stress yielded a range of values corresponding to several populations, and pointing to different sources and processes. The δ¹³C values of Dresser Formation CM (−36.5 to −32.1‰) are negatively correlated with TOC (0.13–0.75%) and positively correlated with C/N ratio (134–569), which is interpreted to reflect the relative abundance of high R_o/oxidised/recycled CM and preferential loss of ¹²C and N during thermal maturation. TEM observations, inferred carbon isotopic heterogeneity and isotope fractionations of −27 to −32‰ are consistent with the activity of chemosynthetic microbes in a seafloor hydrothermal system where rapid silicification at relatively low temperature preserved the CM.  相似文献   

Diagenetic effects on the distribution of uranium in live and Holocene corals from the Gulf of Aqaba     

Boaz Lazar  Rivka Enmar  Miriam Bar-Matthews  Mordechai Stein 《Geochimica et cosmochimica acta》2004,68(22):4583-4593

We investigated the effects of diagenetic alteration (dissolution, secondary aragonite precipitation and pore filling) on the distribution of U in live and Holocene coral skeletons. For this, we drilled into large Porites lutea coral-heads growing in the Nature Reserve Reef (NRR), northern Gulf of Aqaba, a site close to the Marine Biology Laboratory, Elat, Israel, and sampled the core material and porewater from the drill-hole. In addition, we sampled Holocene corals and beachrock aragonite cements from a pit opened in a reef buried under the laboratory grounds. We measured the concentration and isotopic composition of U in the coral skeletal aragonite, aragonite cements, coral porewater and open NRR and Gulf of Aqaba waters.Uranium concentration in secondary aragonite filling the skeletal pores is significantly higher than in primary biogenic aragonite (17.3 ± 0.6 compared to 11.9 ± 0.3 nmol · g⁻¹, respectively). This concentration difference reflects the closed system incorporation of uranyl tri-carbonate into biogenic aragonite with a U/Ca bulk distribution coefficient (K_D) of unity, versus the open system incorporation into secondary aragonite with K_D of 2.4. The implication of this result is that continuous precipitation of secondary aragonite over ∼1000 yr of reef submergence would reduce the coral porosity by 5% and can produce an apparent lowering of the calculated U/Ca - SST by ∼1°C and apparent age rejuvenation effect of 7%, with no measurable effect on the calculated initial U isotopic composition.All modern and some Holocene corals (with and without aragonite cement) from Elat yielded uniform δ²³⁴U = 144 ± 5, similar to the Gulf of Aqaba and modern ocean values. Elevated δ²³⁴U values of ∼180 were measured only in mid-Holocene corals (∼5000 yr) from the buried reef. The values can reflect the interaction of the coral skeleton with ²³⁴U-enriched ground-seawater that washes the adjacent granitic basement rocks.We conclude that pore filling by secondary aragonite during reef submergence can produce small but measurable effects on the U/Ca thermometry and the U-Th ages. This emphasizes the critical importance of using pristine corals where the original mineralogy and porosity are preserved in paleooceanographic tracing and dating.  相似文献   

Botryococcus—A planktonic green alga, the source of petroleum through the ages: Transmission electron microscopical studies of oil shales and petroleum source rocks     

Miryam Glikson  Kay Lindsay  John Saxby 《Organic Geochemistry》1989,14(6)

The hydrocarbon secreting alga Botryococcus has been identified in organic remains of sediments ranging from Precambrian to Recent, and is believed to have been a major source material for petroleum generation throughout the geological time. In some petroleum source rocks of Lower Palaeozoic and Precambrian age, identification of the alga is only possible by electron microscopy. Transmission electron microscopy (TEM) has been used in the present study to identify microstructures of the algal remains in a range of oil shales and petroleum source rocks. It has been established that Botryococcus is the predominant alga in the Kukersite oil shale of Estonia. Similarly, the alga has been shown to be a major contributor to petroleum source rocks in Cambrian and Precambrian sedimentary basins in Australia. TEM has been applied to observations of Botryococcus in torbanites and to products from simulated maturation experiments on torbanite. A comparison with algal remains from Cambrian and Precambrian sediments ranging from undermature to overmature, enabled the distinction of organic matter in various stages of oil generation. Maturation/thermal effects on alginite have been established by reflectance and fluorescence, and compared with experimental results.  相似文献   

Further studies on torbanites and coorongite using transmission electron microscopy and C-isotope analysis     

Miryam Glikson 《Organic Geochemistry》1984,7(2):151-160

Transmission electron microscopy of torbanites from various localities in eastern Australia has revealed micro-organisms of possible methanogenic affinity. Botryococcus remains in the torbanites displayed close resemblance to the rubbery B. braunii accumulations deposited in recent bodies of freshwater origin. Compaction and collapse of structure seem to be the major visible alteration to the algal colonies. C-isotope compositions of the torbanites favour methanogenic activity. Comparison with recent botroyococcal accumulations support diagenetic alteration at a very early stage of deposition.  相似文献   

Response of the Nile and its catchment to millennial-scale climatic change since the LGM from Sr isotopes and major elements of East Mediterranean sediments   总被引：1，自引：0，他引：1  

M.R. Box  M.D. Krom  R.A. Cliff  M. Bar-Matthews  A. Almogi-Labin  A. Ayalon  M. Paterne 《Quaternary Science Reviews》2011,30(3-4):431-442

Changes in ⁸⁷Sr/⁸⁶Sr and major element geochemistry, from two sediment cores (9509 and 9501) in the Eastern Mediterranean (EM), were used to resolve changes in sediment provenance and, hence, determine climate changes in the Nile catchment and Eastern Sahara desert over the past 25 ka. The sediment was described by a three end-member system comprising Blue Nile (BN; ⁸⁷Sr/⁸⁶Sr = 0.7506; Sr = 210 ppm), White Nile (WN; ⁸⁷Sr/⁸⁶Sr = 0.7094; Sr = 72.5 ppm) and Saharan dust (SD; ⁸⁷Sr/⁸⁶Sr = 0.7183; Sr = 99 ppm). The sedimentary record of these cores represents the suspended load carried down the Nile river and discharged into the S.E. Levantine basin and thus records palaeoclimatically controlled changes in erosion and transport in the catchment. During arid periods (0–5 ka BP) and prior to 11 ka BP, fluxes of BN sediment at 9509 (～6 g/cm²/yr & 10–12 g/cm²/yr, respectively) were greater than during the peak of the African Humid Period (AHP) from 5 to 11 ka BP (<2 g/cm²/yr); this latter period witnessed the deposition of the youngest organic-rich sediment, termed sapropel (S-1), in the EM basin. By contrast the flux of WN increased during the AHP from ～5 g/cm²/yr at ～13 ka BP to >15 g/cm²/yr. In the Ethiopian Highlands (BN catchment) increases in the amount and duration of the monsoon during the AHP caused more vegetation to grow resulting in less soil erosion. In the WN catchment increased rainfall caused more catchment erosion and higher sediment flux through the Sudd marshes. The sedimentation rate in core 9509 increased during the AHP because of the greater importance of the WN sediment flux relative to the BN sediment flux. Saharan dust flux also decreased during the AHP reaching a minimum at ～6 ka BP (core 9509) due to ‘greening’ of the Sahara desert. At the onset of S-1, the changes in Nile flow as determined by ⁸⁷Sr/⁸⁶Sr and climatic changes in the EM basin determined by δ¹⁸O of planktonic foraminifera were simultaneous, confirming that such isotopic tracers cannot be used directly to determine the cause of the circulation changes in the EM at this time. The increase in the proportion of BN sediment at 9509 with a somewhat higher grain size during the H-1 period (15–17 ka BP) was caused by erosion and redistribution of sediment from the Nile delta and/or the Israeli coast as sea-level rose.  相似文献   

Speleothem record of the last 180 ka in Villars cave (SW France): Investigation of a large δ18O shift between MIS6 and MIS5     

K. Wainer  D. Genty  D. Blamart  M. Daëron  M. Bar-Matthews  H. Vonhof  Y. Dublyansky  E. Pons-Branchu  L. Thomas  P. van Calsteren  Yves Quinif  N. Caillon 《Quaternary Science Reviews》2011,30(1-2):130-146

The Vil-car-1 flowstone core from Villars cave (SW France) provides one of the first European speleothem records extending back to 180 ka, based on U–Th TIMS and MC-ICP-MS measurements. The core offers a continuous record of Termination II and the Last Interglacial. The penultimate deglaciation is characterized by a prominent 5‰ depletion in calcite δ¹⁸O. Determining which specific environmental factors controlled such a large oxygen isotopic shift offers the opportunity to assess the impact of various factors influencing δ¹⁸O variations in speleothem calcite.Oxygen isotope analyses of fluid inclusions indicate that drip water δ¹⁸O remained within a very narrow range of ±1‰ from Late MIS6 to the MIS5 δ¹⁸O optimum. The possibility of such a stable behaviour is supported by simple calculations of various effects influencing seepage water δ¹⁸O.Although this could suggest that the isotopic shift in calcite is mainly driven by temperature increase, attempts to quantify the temperature shift from Late MIS6 to the MIS5 δ¹⁸O optimum by assuming an equilibrium relationship between calcite and fluid inclusion δ¹⁸O yield unreasonably high estimates of ～20 °C warming and Late MIS6 cave temperatures below 0 °C; this suggests that the flowstone calcite precipitated out of thermodynamic equilibrium at this site.Using a method proposed by Guo et al. (submitted for publication) combining clumped isotope measurements, fluid inclusion and modern calcite δ¹⁸O analyses, it is possible to quantitatively correct for isotopic disequilibrium and estimate absolute paleotemperatures. Although the precision of these absolute temperature reconstructions is limited by analytical uncertainties, the temperature rise between Late MIS6 and the MIS5 optimum can be robustly constrained between 13.2 ± 2.6 and 14.6 ± 2.6 °C (1σ), consistent with existing estimates from Western Europe pollen and sea-surface temperature records.  相似文献