Browsing by Author "Matmon, A"

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    10Be exposure ages of ancient desert pavements reveal Quaternary evolution of the Dead Sea drainage basin and rift margin tilting
    (Elsevier, 2010-02-15) Guralnik, B; Matmon, A; Avni, Y; Fink, D
    Early to late Pleistocene 10Be exposure ages of abandoned surfaces in the Negev desert reveal the regional drainage evolution history and its relationship with the subsidence of the western margin of the Dead Sea Rift. The dated desert paved surfaces have developed over originally westward-flowing rivers, which were abandoned by early Pleistocene and whose relicts are now progressively tilted towards the rift axis. The slow and non-destructive subsidence coupled with extreme hyperaridity enabled the preservation of these ancient surfaces along some of the main water divides in the Negev, nearly irrespective of their distance from the rift axis. Constraints on the tilting history are obtained from analyzing the spatial pattern of the exposure ages, suggesting subsidence rates as low as 120–300 m Ma–1 in the southern Arava Valley since the late Pliocene. It is shown that the transition from the Pliocene to current drainage pattern occurred over a short period during the early Pleistocene, and that the governing fluvial response that followed the delineation of current basins is represented by a continuous spectrum of ages of inset terraces.
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    Asynchronous glaciations in arid continental climate
    (Elsevier, 2018-02-15) Batbaatar, J; Gillespie, AR; Fink, D; Matmon, A; Fujioka, T
    Mountain glaciers at ∼26–19 ka, during the global Last Glacial Maximum near the end of the last 105 yr glacial cycle, are commonly considered on the basis of dating and field mapping in several well-studied areas to have been the largest of the late Quaternary and to have advanced synchronously from region to region. However, a numerical sensitivity model (Rupper and Roe, 2008) predicts that the fraction of ablation due to melting varies across Central Asia in proportion to the annual precipitation. The equilibrium-line altitude of glaciers across this region likely varies accordingly: in high altitude, cold and arid regions sublimation can ablate most of the ice, whereas glaciers fed by high precipitation cannot ablate completely due to sublimation alone, but extend downhill until higher temperatures there cause them to melt. We have conducted field studies and 10Be dating at five glaciated sites along a precipitation gradient in Mongolia to test the Rupper/Roe model. The sites are located in nearby 1.875 × 1.875° cells of the Rupper/Roe model, each with a different melt fraction, in this little-studied region. The modern environment of the sites ranges from dry subhumid in the north (47.7° N) to arid in the south (45° N). Our findings show that the maximum local advances in the dry subhumid conditions predated the global Last Glacial Maximum and were likely from MIS 3. However, we also found that at ∼8–7 ka a cirque glacier in one mountain range of the arid Gobi desert grew to a magnitude comparable to that of the local maximum extent. This Holocene maximum occurred during a regional pluvial period thousands of years after the retreat of the Pleistocene glaciers globally. This asynchronous behavior is not predicted by the prevailing and generally correct presumption that glacier advances are dominantly driven by temperature, although precipitation also plays a role. Our findings are consistent with and support the Rupper/Roe model, which calls for glaciation in arid conditions only at high altitudes of sub-freezing temperatures, where the melt fraction in ablation is low. We expect a heterogeneous pattern of glacial responses to a changing modern climate in cold arid regions; an individual glacier advance should not be necessarily interpreted as evidence of cooling climate.© 2017 Elsevier Ltd.
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    Constraining the evolution of river terraces with integrated OSL and cosmogenic nuclide data
    (Elsevier, 2011-02) Guralnik, B; Matmon, A; Avni, Y; Porat, N; Fink, D
    We present a framework for consistent incorporation of optically-stimulated luminescence dates with cosmogenic radionuclide concentrations measured in a single alluvial section, and apply it on two late Quaternary terraces in the Negev Desert, Israel, to derive constraints on their evolution. We solve an integrated, self-consistent and co-dependant set of equations to reproduce either dataset based on three model parameters of (i) uniform cosmogenic inheritance, (ii) constant terrace aggradation rate and (iii) subsequent exposure time. A subset of all possible parameter combinations, which approximates the measurements within the uncertainties of their best-fits, yields a better constraint of the alluvial history than that obtained by any of these dating proxies alone. The derived set of common solutions indicates similar paleo-inheritances of ~ 1 × 105 10Be atoms g−1 in both terraces; progressive deposition of the higher terrace (T2) began at ~250 ka, lasted for a period of ~80 ka, was abandoned at ~170 ka and since that time has remained intact; the lower terrace (T1) was most likely deposited at ~3 ka and rapidly abandoned by ~2 ka. In an alternative interpretation for T2, which treats the two geochronometers separately, this terrace might have experienced discrete events of aggradation at (216 ± 13) ka and deep truncation at 118 +42 -29 ka, significantly separated in time. In the currently active channel of the Neqarot canyon, contemporary stripping of the lowest terrace located along the stream is suggested by decreasing values of 10Be downstream along the river channel. © 2010, Elsevier Ltd.
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    Dating lacustrine sediments in the central Jordan Valley, Israel: Implications for cosmogenic burial dating
    (18th INQUA Congress, 2011-07-21) Davis, M; Matmon, A; Ron, H; Fink, D; Niedermann, S; Rood, DH
    We apply the cosmogenic two isotope burial method to Pliocene to Pleistocene lacustrine sediments (Erk-El-Ahmar (EEA) formation) in the central Jordan Valley, Israel, in the attempt to extend the applicability of the method to common geological settings in which exposure-burial histories are not well constrained. Previous estimates attributed an age of ~1.8 Ma to the bottom of the EEA formation. 26Al and 10Be concentrations were measured in 11 samples collected from the 170 m tectonically-tilted section. 21Ne concentrations were measured in two of these samples. All samples yielded burial ages that range between 3.5 and 5.3 Ma, much older than the previously estimated age of the EEA formation. All three isotopic pairs (26Al/10Be, 26Al/21Ne, and 10Be/21Ne) yielded similar burial ages within 1?. Samples of identical age that were collected from a specific horizon are presently located at decreasing depths below the surface due to the tectonic tilting. Nevertheless, they yielded identical burial ages suggesting rapid recent erosion in this tectonically active region and insignificant production of cosmogenic isotopes at depth by muons. All samples were found to contain two distinct populations of grains (chert and quartz) mixed at various ratios. These two grain-types were eroded from different sources with significantly different pre-burial exposure histories. The cosmogenic nuclide concentrations in the samples are in accordance with those expected for the mixing of two such sources. Calculations of two-source mixing show that initial 26Al/10Be ratios may be lower relative to the expected surface ratios and result in burial ages overestimated by as much as 500 ka. Our burial ages suggest that the water body that deposited the EEA sediments was contained within the initial topographic depression that formed along the central Jordan Valley segment of the Dead Sea rift. Copyright (c) 2011 INQUA 18
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    Dating Pliocene lacustrine sediments in the central Jordan Valley, Israel - Implications for cosmogenic burial dating
    (Elsevier, 2011-05-15) Davis, M; Matmon, A; Fink, D; Ron, H; Niedermann, S
    Cosmogenic burial dating of sediments is usually used at sites with relatively simple or known exposure-burial histories, such as in caves. In an attempt to extend the applicability of the method to other common geological settings (i.e. the dating of late Neogene sedimentary formations), where much less is known about the exposure-burial history, we apply the cosmogenic burial method on Pliocene-early Pleistocene (1.5-4.5 Ma) lacustrine sediments in the central Jordan Valley, Israel. (26)Al, (10)Be, and (21)Ne concentrations in quartz were obtained from a 170 m tectonically-tilted section. Assuming fast burial and no post-burial production we obtained burial ages which range between 3.5 and 5.3 Ma. Integrating simple geological reasoning and the cosmogenic nuclide data, post burial production is found to be insignificant. We also found that the samples contain two distinct populations of grains (chert and quartz) from two different sources which experienced different pre-burial exposure histories. The cosmogenic nuclide concentrations in the samples are in accordance with those expected for the mixing of two sources, and the burial ages computed for both end members agree. Theoretical calculations of two-source mixing show that initial (26)Al/(10)Be ratios are depressed relative to the expected surface ratios and may result in burial ages overestimated by as much as 500 ka. Using ages derived from cosmogenic nuclides, independent age constraints, and magnetostratigraphy we correlate the bottom of the section to the Cochiti Normal magnetic subchron (4.19-4.30 Ma) within the Reverse Gilbert chron, and the top of the section to the Reverse subchron at the top of the Gilbert chron (3.60-4.19 Ma). (C) 2011 Elsevier B.V.
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    Glacier development in continental climate regions of central Asia
    (GeoScienceWorld, 2021-04-07) Batbaatar, J; Gillespie, AR; Koppes, M; Clark, DH; Chadwick, OA; Fink, D; Matmon, A; Rupper, S
    Glaciers in central Asia that developed under a range of climatic conditions from arid to humid provide an excellent opportunity to test glacial responses to changes in climate. To do this, we mapped and dated glacial deposits at 11 sites spread over five mountain ranges in central Asia: the Altai, Tian Shan, Altyn Tagh, Qilian Shan, and Kunlun. The glacial chronologies for these sites were determined from new 10Be and 26Al exposure ages for the mapped moraines, in addition to 10Be ages available in the literature. Paleo–equilibrium-line altitudes were estimated for past glacier extents from the dated moraines. The equilibrium-line altitudes (ELAs) were also estimated for existing glaciers to characterize the spatial pattern in modern climate across the study region. Differences between the modern and paleo-ELAs (∆ELAs) were used to explore the climatic reasons for variations in the glacier sensitivities and responses to past changes in climate. The results show that the glaciers in more humid regions advanced to their maximum during marine oxygen-isotope stage (MIS) 3–2 with ΔELAs of ~1100–600 m. However, glaciers in the arid interior of central Asia, in the rain shadows of the Karakorum and Pamir ranges and in the Gobi Desert ranges, reached their maximum between MIS 6 and 4, and glacier extents during the subsequent colder/drier MIS 3–2 were significantly smaller or did not extend beyond their cirques. Comparisons of our results and the sensitivity analysis of modern glaciers suggest that depression of air temperature was the primary driver of glacier advances in central Asia but that precipitation played a major role in shaping the spatial and temporal heterogeneity of glacier advances. Precipitation was especially important in hyperarid conditions. Therefore, inferences about paleoclimate parameters from past glacial extents must be made after careful consideration of the climatic setting in which the glaciers are found, as well as their sensitivity to climatic factors. © 2020 The Geological Society of America.
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    New chronology for the southern Kalahari Group sediments with implications for sediment-cycle dynamics and early hominin occupation
    (Cambridge University Press, 2017-01-20) Matmon, A; Hidy, AJ; Vainer, S; Crouvi, O; Fink, D; Erel, Y; ASTER Team; Arnold, M; Aumaître, G; Bourlès, D; Keddadouche, K; Horwitz, LK; Chazan, M
    Kalahari Group sediments accumulated in the Kalahari basin, which started forming during the breakup of Gondwana in the early Cretaceous. These sediments cover an extensive part of southern Africa and form a low-relief landscape. Current models assume that the Kalahari Group accumulated throughout the entire Cenozoic. However, chronology has been restricted to early–middle Cenozoic biostratigraphic correlations and to OSL dating of only the past ~ 300 ka. We present a new chronological framework that reveals a dynamic nature of sedimentation in the southern Kalahari. Cosmogenic burial ages obtained from a 55 m section of Kalahari Group sediments from the Mamatwan Mine, southern Kalahari, indicate that the majority of deposition at this location occurred rapidly at 1–1.2 Ma. This Pleistocene sequence overlies the Archaean basement, forming a significant hiatus that permits the possibility of many Phanerozoic cycles of deposition and erosion no longer preserved in the sedimentary record. Our data also establish the existence of a shallow early–middle Pleistocene water body that persisted for > 450 ka prior to this rapid period of deposition. Evidence from neighboring archeological excavations in southern Africa suggests an association of high-density hominin occupation with this water body. © University of Washington
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    New chronology for the southern Kalahari Group sediments: implications for sediment cycle dynamics and early hominin occupation
    (The Geological Society of America, 2014-10-19) Matmon, A; Hiny, AJ; Crouvi, O; Fink, D; Erel, Y; Arnold, M; Aumaître, G; Bourlès, D; Keddadouche, K; Horwitz, LK; Chazan, M
    The Kalahari Group covers an extensive part of the southern African continent and forms a low-relief landscape dominated by extensive unconsolidated sand. Current depositional models assume that the Kalahari Group sediments accumulated gradually throughout the Cenozoic, but an absence of absolute chronology beyond ~60 ka has left this premise untested. Here, we challenge this age model with new cosmogenic burial ages obtained from a 55 m section of Kalahari Group sediments at Mamatwan Mine near the southern edge of the Kalahari basin. Our results indicate that the majority of the existing section was emplaced rapidly at ~1 Ma. At this time the basin filled to its present level and established the Kalahari sand belts, which fostered the modern savannah. Our data suggest a dynamic landscape, with punctuated cycles of erosion and deposition, in contrast to the accepted concept of a stable basin filling slowly throughout the Cenozoic. The sedimentology and cosmogenic nuclide measurements from the lower Mamatwan Mine section reveal the existence of an extensive Early to Middle Pleistocene water body, persisting at least 420 ka prior to the rapid filling event at ~1 Ma. This water body is contemporaneous with a significant hominin occupation as evidenced by neighboring archaeological excavations. We thus provide the first evidence of association of the high-density hominin occupation in southern Africa with an extensive water body. © 2014 The Geological Society of America (GSA)
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    Revealing sediment sources, mixing and transport during erosional crater evolution in the hyperarid Negev Desert, Israel
    (Elsevier, 2011-11-15) Fruchter, N; Matmon, A; Avni, Y; Fink, D
    To better understand the sedimentary history of the erosional crater of Makhtesh Hazera in the hyper-arid Negev Desert of southern Israel we have measured concentrations of in situ (10)Be in alluvial sediments from the active drainage system and from abandoned alluvial terraces and dated them using optically stimulated luminescence (OSL). These sedimentary sequences suggest changes in the drainage system behavior over time and show a periodic pattern in which periods of sediment aggradation alternate with periods of degradation through incision and erosion. In alluvial terrace sediments, (10)Be concentrations were combined with OSL ages to gain insight of the temporal framework of sediment deposition and shed light on the process of sediment storage. OSL and simple I Be exposure ages of terrace sediments give deposition ages between similar to 340 ka to similar to 50 ka, at which time the youngest alluvial terrace was incised. Deposition was interrupted twice, at similar to 300 ka and similar to 160 ka, when periods of rapid incision caused the abandonment of the active fluvial surface and the stabilization of a younger and lower fluvial surface. In the active drainage system, (10)Beconcentrations suggest several possible quartz sources, of which the Lower Cretaceous sandstone bedrock exposed at the base of the cliff enclosing the Makhtesh is the most dominant. The results suggest that sediment eroding form these cliffs are conveyed through the active alluvial channels without significant sediment contribution from alluvial terraces or from eroded bedrock exposed within the Makhtesh. In contrast to our measurements in the active drainage system, (10)Be concentrations in alluvial terrace sediments record significant storage within the Makhtesh. We suggest that the geometry of the Makhtesh, mainly the disproportion between the size of the Makhtesh and its narrow outlet, leads to significant accumulation of sediment within the Makhtesh. Episodic breaching of the barrier is followed by rapid and short-lived incision into the stored sediment. The long residence time of sediment within the Makhtesh results in high measured (10)Be concentrations. At the end of each of these short incision episodes, when channels are already carved into the alluvial sediment and terraces are formed, the channels only convey sediment directly eroded from the bounding cliff of the Makhtesh; a situation presently observed. (C) 2011 Elsevier B.V.
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    Sediment source and mixing and the cycle of sediment transport: an example from NE Negev Desert, Israel
    (Copernicus Publications, 2010-05-02) Fruchter, N; Matmon, A; Zilberman, E; Avni, Y; Fink, D
    Alluvial terraces represent the end product of sedimentary cycles; each includes sediment generation, transport, accumulation, and the ultimate incision that forms abandoned alluvial surfaces. We examine the middle Pleistocene to recent drainage system evolution in Makhtesh Hazera, Negev Desert, southern Israel and compare the characteristics of erosion and sediment transport in the present system with those expressed by the alluvial terraces. The Hazera drainage basin lies at the margins of the arid to hyper-arid Dead Sea rift (DSR). Makhtesh (crater) Hazera is a deeply incised erosional structure (5X7 km) that has been excavated since the early Pliocene into the crest of the Hazera asymmetric anticline. The Makhtesh floor is surrounded by cliffs rising more than 400 meters high. The cliffs are built of Upper Cretaceous hard carbonates caprocks overlying Lower Cretaceous friable quartz sandstones. Bedrock knickpoints isolate the drainage basin in the Makhtesh and above it from a direct influence of the terminal base level of the DSR. Thus, the accumulation of sediment and abandonment of terraces are controlled by climate and bedrock barriers located at the Makhtesh outlet. We use cosmogenic isotope concentrations to determine bedrock denudation rates, ages of alluvial terraces, and basin wide erosion rates in different channels throughout the basin. The use of cosmogenic isotopes enables us to determine sediment sources and reconstruct sedimentary cycles. OSL dating was used to determine the accumulation ages of alluvial sediment in alluvial terraces. These two methods enable quantitative evaluation of fluvial processes. Bedrock erosion rates suggest a strong dependence of erosion on lithology. While the Lower Cretaceous sandstone erodes at >100 mm ky-1, the overlying hard carbonate caprock yielded cosmogenic isotope concentrations that correspond to erosion rates of 1-3 mm ky-1. This significant difference in erosion rates maintains the dramatic relief of the Hazera drainage basin. We find that the quartz sediment in the present fluvial system of Makhtesh Hazera originates from two predominant sources. One is the Lower Cretaceous sandstone that crops out along the base of the Makhtesh cliffs. The second source are un consolidated Miocene sands that fill the syncline which is located north west of the Makhtesh and is drained into it. 10Be concentrations in successive samples indicate that the Miocene sand is gradually diluted by Lower Cretaceous sand as it flows down stream and the mixing of sediment from both sources is good. Alluvial terraces and bedrock units exposed inside the Makhtesh do not contribute a significant amount of sediment to the present drainage system. Three major alluvial terrace levels were identified. The highest terrace level (MKT0) was abandoned at 279±19 ky. This level probably covered most of the Makhtesh surface. The deposition of the two lower levels, MKT1 and MKT2 (which were abandoned at 160±6 and 47±9 ky, respectively), was confined to the present drainage system. Analysis of cosmogenic depth profiles from the terraces suggests significant recycling of sediment within the Mekhtesh. This is in contrast to the present system that lacks recycled sediment. We explain this difference by the fact that the terraces are the final product of a sedimentary cycle while the present drainage system presents a “snapshot” in time which does not represent the entire cycle only the present state of the system which is expressed by rapid incision and very little lateral migration. © Author(s) 2009
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    Seismic origin of the Atacama Desert boulder fields
    (Elsevier BV, 2015-02-15) Matmon, A; Quade, J; Placzek, CJ; Fink, D; Arnold, M; Aumaître, G; Bourlès, D; Keddadouche, K; Copeland, A; Neilson, JW
    Extensive fields of large boulders are common around the base of hills in the Atacama Desert. How these boulders are transported from nearby hillslopes is unclear given the lack of rainfall of the region. Here we document the central role of seismicity, not runoff, in transporting and smoothing >1 ton boulders all across the hyperarid core of the Atacama Desert. The generally granitoid boulders emerge as corestones on hillslopes at an erosion rate of 0.1-1 m Ma(-1). Thereafter, physical and cosmogenic isotopic evidence suggests that boulders slide and bounce rather than roll down hills and onto adjacent flats. In the transport process, the largest boulders are split and the smaller ones are weathered to grus, narrowing average boulder mass to similar to 2 tons (<1 m(3)). At the base of hills, the boulders bunch together and rub during the frequent earthquakes in the region, producing distinctive smoothing around boulder mid-sections, and silt moats around the boulder bases. Our measurements show a strong correlation between boulder field density and rubbing, and only when the density exceeds 60-70% does rubbing become common. Except for slow removal by rubbing, the boulders seem to undergo no further erosion while in the flats. Exposure times for some boulders are >12 Ma, making them among the oldest continuously exposed features on the Earth. Boulder rubbing is just one geologic feature among many in the Atacama that underscore the role that seismicity probably plays in shaping landscapes of the waterless worlds of the solar system. © 2015, Elsevier B.V.
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    Unraveling rift margin evolution and escarpment development ages along the Dead Sea fault using cosmogenic burial ages
    (Elsevier Inc., 2014-07-01) Matmon, A; Fink, D; Davis, M; Niedermann, S; Rood, DH; Frumkin, A
    The Dead Sea fault (DSF) is one of the most active plate boundaries in the world. Understanding the Quaternary history and sediments of the DSF requires investigation into the Neogene development of this plate boundary. DSF lateral motion preceded significant extension and rift morphology by -10 Ma. Sediments of the Sedom Formation, dated here between 5.0 0.5 Ma and 6.2 +/- 451 Ma, yielded extremely lowl Be concentrations and 26A1 is absent. These reflect the antiquity of the sediments, deposited in the Sedom Lagoon, which evolved in a subdued landscape and was connected to the Mediterranean Sea. The base of the overlying Amora Formation, deposited in the terminal Amora Lake which developed under increasing relief that promoted escarpment incision, was dated at 3.311 Ma. Burial ages of fluvial sediments within caves (3.4 +/- 0.2 Ma and 3.6 +/- 0.4 Ma) represent the timing of initial incision. Initial DSF topography coincides with the earliest Red Sea MORB's and the East Anatolian fault initiation. These suggest a change in the relative Arabian-African plate motion. This change introduced the rifting component to the DSF followed by a significant subsidence, margin uplift, and a reorganization of relief and drainage pattern in the region resulting in the topographic framework observed today. (C) 2014 University of Washington. © 2014, Elsevier Inc.