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Darryl E. Granger, Multiple cosmogenic nuclides with different decay rates can be used to date exposure and burial of rocks over the timescales of radioactive decay. Two classes of terrestrial applications are discussed in detail. The first involves the use of 26 Al and 10 Be in rock or sediment that has experienced a complex history of repeated exposure and burial.

Finally, the half-lives of 26 Al and 10 Be are discussed, with special attention given to discrepant estimates of the 10 Be half-life. It is shown that geologic data are consistent with either half-life estimate of 1.

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Book Chapter. Author s. Granger Darryl E. Google Scholar. Get Permissions. You do not currently have access to this chapter. The production rate for a particular nuclide is a function of geomagnetic latitude, the amount of sky that can be seen from the point that is sampled, elevation, sample depth, and density of the material in which the sample is embedded. Decay rates are given by the decay constants of the nuclides. These equations can be combined to give the total concentration of cosmogenic radionuclides in a sample as a function of age.

The two most frequently measured cosmogenic nuclides are beryllium and aluminum These nuclides are particularly useful to geologists because they are produced when cosmic rays strike oxygen and siliconrespectively.

The parent isotopes are the most abundant of these elements, and are common in crustal material, whereas the radioactive daughter nuclei are not commonly produced by other processes.

As oxygen is also common in the atmosphere, the contribution to the beryllium concentration from material deposited rather than created in situ must be taken into account. Each of these nuclides is produced at a different rate. Both can be used individually to date how long the material has been exposed at the surface. Because there are two radionuclides decaying, the ratio of concentrations of these two nuclides can be used without any other knowledge to determine an age at which the sample was buried past the production depth typically meters.

Chlorine nuclides are also measured to date surface rocks. This isotope may be produced by cosmic ray spallation of calcium or potassium. From Wikipedia, the free encyclopedia.

Although we assumed a simple burial history, sediments farther into the foreland may have had significant preburial histories, because the sediment could be sourced not only from the headwaters of the rivers, but also from nearby uplifted Neogene strata.

Because of the age of these source sediments, the 26 Al and 10 Be concentrations were likely very low, having had sufficient time for the isotopes to decay to near zero, and the only measurable concentration results from the most recent period of exhumation and erosion.

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This reasoning would imply that the ages from these sites must be interpreted as maximum ages. However, clast counts of the Xiyu strata in the Bieertuokuoyi Basin Thompson et al. From these data, we contend that most of the sediment is likely being derived from the exhumed granitic domes and Paleozoic limestone in the nearby mountains, and there may not be a significant contribution from the recently uplifted foreland basin sediments.

Postdepositional production can commonly be ignored if the sample was buried deeply until recent exposure of a sample site, but additional observations and analysis can provide the necessary information needed to calculate additional production and modify ages appropriately.

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Importantly, in regions with high source-area erosion rates, and hence lower incoming concentrations, the same duration of postdepositional production will have a larger effect on a sample with a lower initial concentration.

Therefore, samples in basins that bound rapidly eroding source areas, such as the western Tarim Basin, could be more susceptible to younger apparent ages. If a value higher than the true density were used, postdepositional production would be underestimated, resulting in an apparently older age than the true age.

If a value lower than the true density were used, additional postdepositional production of the isotopes would increase the isotope concentrations, resulting in an younger apparent age. Our new burial ages, combined with previously published magnetostratigraphic sections, provide new dates for the minimum initiation of several structures in the Pamir-Tian Shan convergence zone Table 3 ; Figs.

These new data, when integrated with low-temperature thermochronology and magnetostratigraphic data from other studies, illustrate the Neogene-Quaternary propagation of deformation into the western Tarim Basin Fig.

On the northeast Pamir margin, deformation appears to have been distributed on several structures simultaneously Thompson et al. Moreover, the presence of growth strata within an uplifted alluvial fan, possibly of Pleistocene age? Restorations using seismic reflection data line B, Fig. The Kenenbierte thrust Fig.

Furthermore, evidence from the Bieertuokuoyi piggyback basin supports synchronous deformation on the Takegai and Pamir Frontal thrusts between and 1. Furthermore, the average shortening rate since initiation on the Mushi anticline is 0. On the southern margin of the Tian Shan, deformation is clearly younger southward into the foreland Fig.

On the western southern Tian Shan, deformation stepped basinward in four primary phases Fig. The South Tian Shan fault, which initiated ca. In addition, an increase in sediment-accumulation rates ca. This age is supported by an increase in the sediment-accumulation rate of middle Miocene sediments ca.

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Because we do not know the total shortening accommodated by the Kelatuo anticline, we assume it has a similar magnitude of shortening to folds farther east that involve similar stratigraphy.

The third stage is the initiation of the Atushi fault, which we constrain in this study at ca. The final stage of migration of the deformation front is the initiation of the Mingyaole anticline ca. Farther east, Heermance et al.

During stage 2, the initiation of the Kashi Basin thrust began at ca. The initiation of the Tashipishake anticline at We observed a west-to-east younging of ages on folds within the Pamir-Tian Shan forelands Fig. Older ages and both higher structural and greater topographic relief Scharer et al. Such lateral propagation could be expected during oblique closure between these nonparallel mountain fronts, where the western ends of the faults and folds are already pinned, inhibiting westward propagation of deformation e.

Most of the Neogene-Quaternary folds display eastward lateral propagation Fig. However, we caution that the ages at the Kelatuo and Atushi anticlines may be maximum ages because we do not know their preburial cosmogenic history. On the northeast Pamir margin, the PFT appears older at its western end, with a late Miocene initiation age Thompson et al.

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Approximately 40 km toward the east at the western end of the Mushi and Aismaola anticlines, seismic reflection data line B, Fig.

Moreover, the Xiyu Formation merges with the modern alluvial piedmont at the eastern end of the PFT and constitutes the present-day piggyback basin, suggesting it has a younger age than the older, deformed and incised piggyback basin to the west Thompson et al. Alternatively, the apparently younger age of the PFT to the east may be due to increased erosion that led to beveling of topography and the change in strike of the fault from approximately east-west to northwest-southeast at its far eastern end Figs.

The Mushi anticline emerges topographically where the surface expression of the PFT ends, indicating deformation may be transferred onto the younger Mushi fold farther east in the foreland Fig. The Mushi anticline initiated 2. Topography, structural relief, and eastward-tilted fluvial terraces support eastward propagation of the Mushi anticline until ca. Together, these data indicate deformation is propagating southward from the Tian Shan, northward from the Pamir into the foreland, and eastward into the Tarim Basin, as the impinging orogens zipper the intervening Tarim Basin closed.

Moreover, the available data also indicate: 1 deformation along the NE Pamir margin did not step unidirectionally outward, but it instead displays perhaps alternating and synchronous deformation on the Main Pamir, Takegai, and Pamir Frontal thrusts Fig. These data support models that suggest out-of-sequence thrusting and hinterland deformation are required to maintain a critically tapered wedge on the margins of growing orogens experiencing hinterland denudation Davis et al.

Numerical Naylor and Sinclair, and sandbox Gutscher et al.

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The activity of any given thrust fault in the system is then dictated by the convergence-parallel length of the thrust sheet, i. The timing of forward propagation of thrust faults and fault-related folds in the foreland approximately match these time scales Figs.

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However, these models may vary for forelands with variable structural styles, such as the Tian Shan foreland, where the structural style changes from steep thrust faults on the margins to detachment folds in the foreland Heermance et al.

We speculate that the difference in the deformation propagation timing and rates between the hinterland thrusts and the folds in the foreland is related to the stratigraphic units involved and the structural styles, in addition to the inherent tectonic variability factors discussed above.

This paper reviews the development of such dating methods over the past ?50 years, beginning with a historical perspective on early meteorite studies, and later focusing on recent examples in the terrestrial field using the 26 Al- 10 Be pair in quartz. Two classes of terrestrial applications are discussed in detail. Because quartz derived from surface erosion and then buried by sediment accumulation is common, the method is widely applicable for dating Plio-Pleistocene clastic sediments. All (terrestrial) applications of burial dating so far have used the 26 Al- 10 Be benjamingaleschreck.com by: Applications of 26Al /10Be burial dating and magnetostratigraphy to active deformation within sedimentary basins: field examples from the western Tarim Basin, NW China - NASA/ADS Sedimentary basins adjacent to growing orogens hold key information .

The transition from steeply dipping basement thrusts within strong Paleozoic and Mesozoic rock units to fault-related folds and more gentle thrusts i.

Although not the focus of our targeted sampling, our new burial ages also date the Miocene-Pleistocene Xiyu Formation around the margins of the western Tarim Basin Fig. The deposition of the Xiyu conglomerate was apparently continuous and prograded south over time in the Tian Shan. Similar ages of initial local deposition of the Xiyu conglomerates have been documented on the NE Pamir margin, with ages ranging from ca. As in the southern Tian Shan, a similar depositional history emerges in the northeast Pamir, with the Xiyu conglomerate prograding northward since ca.

Moreover, Xiyu deposition appears to have occurred repeatedly in the same position in the foreland e.

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Dating coarse-grained growth strata on the flanks of folds remains a challenge in areas with few volcanic units and sparse biostratigraphy. Burial dating has emerged as a unique way to date such strata in late Cenozoic basins.

Using these ages, we demonstrate an innovative use of burial dating to place multiple age constraints on depositional sequences and to define the initiation of activity on individual structures, especially large-scale folds, on the margins of growing orogens.

These samples were strategically collected from within or just beneath growth strata and from sedimentary units in the footwalls of young faults, thereby placing maximum ages on the initiation of deformation of individual structures within the basin. Burial ages are most reliable when they derive from slowly eroding source terranes, have been deeply and rapidly buried, and have only been exhumed very recently.

Placing constraints on any of the commonly unknown variables, such as the rate of sediment burial, time in transport in the fluvial system, or the timing of recent incision and postdepositional exposure, helps to limit the uncertainties associated with burial ages.

Where feasible, we combined our burial ages with magnetostratigraphic sections to place further constraints on the deposition of the sediments in the basins and the deformation of nearby structures.

The U. We thank Burch Fisher, Zhareen Bulalacao, Yuan Zhaode, Yang Xiaodong, and Benjamin Melosh for assistance in the field and with sample collection and processing, and Richard Heermance and Aaron Bufe for valuable discussions on an earlier version of this manuscript.

Oct 22, Cosmogenic burial dating enables dating of coarse-grained, Pliocene-Pleistocene sedimentary units that are typically difficult to date with traditional methods, such as magnetostratigraphy. In the actively deforming western Tarim Basin in NW China, Pliocene-Pleistocene conglomerates were dated at eight sites, integrating 26 Al/ 10 Be burial dating with previously published Cited by: 8. Quaternary Geochronology Volume 55, February , The first radiometric age by isochron 26 Al/10 Be burial dating for the Early Pleistocene Yuanmou hominin site, southern China LanLuoab Darryl benjamingaleschreck.comrbd HuaTuc ZhongpingLaic GuanjunShend Christopher benjamingaleschreck.com XuepingJif JianhuiLiufAuthor: Lan Luo, Lan Luo, Darryl E. Granger, Darryl E. Granger, Hua Tu, Zhongping Lai, Guanjun Shen, Christo. Surface exposure dating is a collection of geochronological techniques for estimating the length of time that a rock has been exposed at or near Earth's surface. Surface exposure dating is used to date glacial advances and retreats, erosion history, lava flows, meteorite impacts, rock slides, fault scarps, cave development, and other geological events.

We thank two anonymous reviewers for their constructive feedback that helped to improve this manuscript. A Simplified geologic map of the western Tarim Basin. Inset map marks location in Central Asia. Map is modified from Li et al.

Magnetostratigraphic sections discussed in text include: 1- Tang et al. B Interpretation of seismic reflection data across the southern Tian Shan, line A, modified from Heermance et al. C Interpretation of seismic reflection data across the northeastern Pamir, line B, from Chen et al. Regional stratigraphy, depositional environments, and tectonic events of the western Tarim Basin.

Stratigraphic descriptions and interpreted depositional environments are from Carroll et al.

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Timing of regional tectonic events is from Sobel and Dumitru ; Sobel et al. Note growth and pregrowth strata, and the units that form the hanging walls of major thrusts in the hinterlands.

Schematic diagram of the erosion, transport, and burial history of sediments in a basin. Top: Quartz grains are exhumed and eroded on hillslopes in the source area, transported through the fluvial system, and deposited and buried in the adjacent basin.

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After some length of time that is much greater at least an order of magnitude than the previous steps, the sediments may be exhumed, uplifted, and incised such that sampling is feasible. Bottom: Schematic chart illustrating the concentration of 10 Be or 26 Al through time. The concentration increases during initial exhumation and erosion on the hillslopes. The sediments accumulate a minor additional concentration during burial, termed synburial production.

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Once buried, the concentrations decrease as 10 Be and 26 Al decay during shielding. If the sediments are sampled following rapid exhumation, a simple burial age has occurred. If exhumation is slow, such that considerable new nuclide production occurs, concentrations of 10 Be and 26 Al will have increased during exhumation such that postdepositional production should be accounted for in the burial age calculations.

Abbreviation: magstrat age-magnetostratigraphic age.

The half-life of 26Al is half that of 10Be, so the 26Al/10Be ratio decreases over time and can be used to date the burial event. Because quartz derived from surface erosion and then buried by. Mar 12, Here we report cosmogenic 26 Al/ 10 Be burial dating of quartz sediments and artefacts from the lower strata of Locality 1 in the southwestern suburb of Beijing, China, where early representatives. Feb 23, This paper reports the application of 26Al/10Be burial dating as an independent check. Two quartz samples from a lower cultural horizon give a weighted mean age of Ma (million years, 1?). The site is thus younger than ka at 95confidence, which is at variance with the previous paleomagnetic results.

Axes are schematic and not to scale. Red star depicts location of Oytag OYT sample. Sample is projected to where it would appear in the section across the valley. D Cross section across the MPT and splays.

The burial sample, noted by the red star, was collected in a syncline between the MPT and a fault splay. A Simplified geologic map of the Bieertuokuoyi Basin. B Cross section of the Bieertuokuoyi anticline.

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C Lithology, paleomagnetic data VGP-virtual geomagnetic poleresulting magnetic polarity, and correlation to the geomagnetic polarity time scale GPTS; Ogg, of the magnetostratigraphic magstrat section Thompson et al. The red stars mark the location of the cosmogenic burial samples within the section.

Here, we report the first application of a radio-isotopic dating method to the site. 26Al/10Be burial dating results derived from two sand samples from the fossiliferous deposits show that the.

PFT-Pamir Frontal thrust. B Cross section across the Mushi anticline, illustrating the subsurface structure. A Simplified geologic map of the southern end of the Kelatuo anticline.

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B Cross section across the Kelatuo anticline, illustrating the subsurface structure on its southern limb. Abbreviation: magstrat-magnetostratigraphic age. E Photo interpretation on D, showing growth strata on the southern flank of the Kelatuo anticline. F Magnetostratigraphic section from Liu et al. A Simplified geologic map of the Atushi anticline and Atushi fault. B Photo of the sample site, collected from an overhang within an incised valley. D Cross section across the Atushi anticline and Atushi fault.

B Field photo and interpretation of structure of the southern limb of the anticline. C Cross section of the Mingyaole anticline. D Lithology, paleomagnetic data VGP-virtual geomagnetic poleresulting magnetic polarity, and correlation to the geomagnetic polarity time scale GPTS; Ogg, of the magnetostratigraphic section of the Mingyaole anticline Chen et al. The red star marks the location of the cosmogenic burial sample MING within the magnetostratigraphic section.

The resulting magnetostratigraphic correlation indicates the growth strata date to ca. Radioactive decay of the isotopes black dashed lines at different initial source area erosion rates and million-year isochrons for sediment burial following steady erosion are shown.

A Depositional ages of the Xiyu Formation in the western Tarim Basin, including previous studies; magstrat-magnetostratigraphic, TCN-terrestrial cosmogenic nuclides. B Initiation ages of different structures within the western Tarim Basin, illustrating basinward propagation of the orogenic fronts. White square represents unreset apatite fission-track AFT ages.

Data are from Sobel and Dumitru ; Chen et al.

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Initiation ages, average shortening rates, and deformation front migration rates for three transects: A northeastern Pamir, B western southern Tian Shan, and C eastern southern Tian Shan.

See Figure 12 for location of each transect. Top panel shows the initiation ages Ma of different structures from the margin of the orogen toward the foreland.

Thrusts and folds are shown in boxes with abbreviated location. Black vertical arrows mark sedimentation rate increases from magnetostratigraphic sections in the basin.

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Shortening rates assume a total magnitude of shortening from previous studies, described in text, and ages from this and previous studies. Different shades of gray represent different shortening stages, described in text.

Bottom panel shows variations in the deformation front migration rate, measured from the closest basin-bounding fault. Data from the eastern Southern Tian Shan are from Heermance et al.

Gray lines and lighter coloring on eastern ends of Atushi and Kashi folds indicate speculative propagation based on the lack of surface expression of deformation. Abbreviations: magstrat-magnetostratigraphic; TCN-terrestrial cosmogenic nuclides; OSL-optically stimulated luminescence.

Data are from this study, Chen et al. Sign In or Create an Account. User Tools. Sign In. Advanced Search. Article Navigation.



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