10Be Terrestrial Cosmogenic Nuclide Research Articles

Erosion rates and morphogenesis of the El Peñol de Guatapé inselberg, northern Andes (Colombia), inferred from geomorphic analyses and cosmogenic 10Be measurements

Inselbergs are isolated rock bodies that develop as a result of differential weathering and erosion advances during topographic etchplain formation. The timing and rate of inselberg growth are key for constraining external controls on landscape evolution, particularly in etching terrains associated with elevated plateaus carved on granitic lithologies, and in tectonically active provinces in tropical climate zones (e.g., Antioqueño Plateau, AP). We applied new morphostratigraphic and geomorphometric analyses, along with 10Be terrestrial cosmogenic nuclide (TCN) measurements, to in situ rock samples from the Peñol de Guatapé Inselberg (PGI), in the AP of the Colombian Andes to address the chronological framework of bornhardt formation in this tropical setting. The PGI is located in a rejuvenated landscape between middle Miocene to late Mio-Pliocene erosion surfaces. Erosion rates inferred from 10Be analyses ranged between ∼0.0024 ± 0.0001 and 0.24 ± 0.0283 mm/yr. This broad range is consistent with the long-term erosion rate of ∼0.04 mm/yr and mid-term erosion rates of 0.01–0.08 mm/yr previously documented for the region using low-temperature thermochronology. Our findings indicate that the PGI emerged as an important landscape feature over a period of ∼0.5–2.0 Myr and has protruded high above the average AP surface since the Pliocene. The new TCN-derived erosion-rate estimates for the AP Inselberg enable us to better understand the role of weathering and erosional processes that controlled the evolution of landscape surfaces during Andean orogenic cycles documented in the region.

Reconstraining the Quaternary glacial history of Lahaul Himalaya, northern India

The study reports new progress in the glacial chronology from new sites of the Chandrabhaga basin (CBB), in the transition between the monsoon-dominated Pir-Panjal and westerly-dominated Trans-Himalaya, in Lahaul Himalaya, northern India. In Lahaul, asynchronous timing and extent of late Quaternary glaciation have been reported (Owen et al., 1996, 1997, 2001; Eugster et al., 2016). The established oldest and most extensive Chandra glacial stage remains undated and speculative. We reconstrain the late Quaternary glacial history of the CBB using geomorphological mapping, Infrared Stimulated Luminescence (IRSL), and 10Be Terrestrial Cosmogenic Nuclide (TCN) surface exposure dating. Four local glacial stages, the Chandra, Batal, Dali, and Mayar, are dated to 152 ± 37 ka, 43 ± 3 ka, 21 ± 2 ka, and Little Ice Age (LIA), respectively. The Chandra glacial stage occurred during the late Marine Isotope Stage 6 (MIS 6; 186 ± 30 – 113 ± 10 ka), characterized by thick lacustrine deposits, rock benches, and ice-polished bedrock along the trunk valleys. We provide the first account of the numerical dating for the much-awaited timing of the oldest Chandra glacial stage (Local Last Glacial Maxima; LLGM) in the region (Owen et al., 1996, 1997, 2001). The LLGM in the CBB is much older than previously thought, consistent with some north-western Himalayan glacial records (Owen et al., 2006; Dortch et al., 2010; Hedrick et al., 2011; Orr et al., 2017, 2018). The Batal glacial stage occurred during the early MIS 3 and is dated from 47 ± 2 to 41 ± 2 ka, represented by the thick lacustrine deposits and impressive terraces. The Dali glacial stage occurred during the Global Last Glacial Maxima (GLGM), characterized by a series of latero-frontal recession moraines, and is dated from 33 ± 3 to 13 ± 1 ka. The Mayar advance is characterized by confined tributary valley glaciers, possibly linked to the LIA advance reported in the Kulti valley (Saha et al., 2019). The equilibrium line altitude (ELA) rose by ∼486 m from the Chandra stage to the present day. Reconstructed ELA altitudes and glacial landforms demonstrate that the glaciations have become progressively less extensive through time for this part of the western Himalayas. The change of glaciation pattern during the later part of the Quaternary is like other regions of the orogen, such pattern of glaciation reflects regional climatic forcing.

Linear Inversion of Fluvial Topography in the Northern Apennines: Comparison of Base‐Level Fall to Crustal Shortening

AbstractFluvial terraces, longitudinal river profiles, and growth strata carry comparable records of the deformation history in tectonically active mountain belts. In the northern Apennines, these markers are preserved across an actively uplifting, steep mountain front. We take advantage of this setting to model base‐level fall histories reconstructed from a linear inversion of fluvial topography on six transverse catchments spanning 110 km along the strike from Bologna to Parma. We compare these histories to records of crustal shortening preserved in growth strata. The fluvial inversion model is based on the detachment‐limited stream‐power model and considers the variable erodibility of bedrock lithology. Uplift is assumed to be spatially uniform at the catchment scale and crudely in balance with long‐term 10Be terrestrial cosmogenic nuclide (TCN) erosion rates that range from ∼0.3 to 0.7 mm yr−1. The model predicts rates of base‐level fall that are comparable with published rates of fault slip from growth strata and incision from terrace deposits. The modeling demonstrates how orogenic shortening and topographic growth are nonuniform and partitioned along the strike of the Apennine mountain front. Rivers record steady uplift in the last ∼1 Myrs, temporally coincident with overfilling of the Po Plain and reduction of shallow fault slip, supporting a proposed switch from thin‐to thick‐skinned crustal shortening. These results are a novel example of base‐level fall records assembled from both the erosional source and depositional sink and highlight the versatility and challenges of fluvial inversion modeling.

Terrestrial cosmogenic 10Be dating of the Última Esperanza ice lobe moraines (52°S, Patagonia) indicates the global Last Glacial Maximum (LGM) extent was half of the local LGM

Whether glaciers in the southern hemisphere were asynchronous to those in the north during the global Last Glacial Maximum (gLGM; 26.5–19 ka) is still debated. In Patagonia (South America), numerous ice lobes attained their maximum extents during diverse episodes of the last glacial cycle. To understand the variations in the gLGM vs local LGM record, we studied the Lago Aníbal Pinto area (52°00′ S, 72°40′ E; Chile), where several moraine belts were deposited by one of the eastward-flowing southern Patagonian Ice Sheet (PIS) outlet ice lobes; the Última Esperanza. We report eight 10Be terrestrial cosmogenic nuclides (TCN) surface ages from granitic moraine boulders. Our weighted average age obtained from the southern part of the Río Turbio moraine belt yields 50.7 ± 2.4 ka (oldest boulder age; 53.8 ± 5.3 ka) and confirms the greatest extent of the local Last Glacial Maximum (lLGM) during Marine Isotope Stage 3 (MIS 3) in the previously dated northern moraines from the same belt. Our 10Be TCN age (32.6 ± 2.2 ka) derived from the Dos Lagunas moraine, which makes up the northernmost margin of the Última Esperanza ice lobe's Arauco advance, also validates the MIS 3 timing. Following the formation of Arauco moraines, the Última Esperanza ice lobe was split into three main tributaries in the south, which formed three restricted and previously undated moraine complexes. We dated one of them, the Aníbal Pinto moraine complex. Whereas the highest moraine yielded the oldest age (28.3 ± 2.2 ka), lower moraine's surface that was later truncated as a lacustrine erosional platform, yielded younger boulder ages (weighted average age = 18.9 ± 1.0 ka; oldest boulder age = 19.0 ± 1.5 ka), indicating they were deposited under the Pinto Lake level. Our new age data allow us to propose a new chronology for the Aníbal Pinto moraine complex and consolidate previously published ages from other moraine belts. We attribute the Aníbal Pinto moraine complex to early gLGM (MIS 2), emphasising that the gLGM was half the extent of lLGM in the Última Esperanza ice lobe that underpins its interhemispheric asynchronous character.

Late Quaternary Intraplate Deformation Defined by the Las Chacras Fault Zone, West‐Central Argentina

AbstractSeveral major (up to MW 7.5) earthquakes over the past 320 years have shaken the thick‐skinned Sierras Pampeanas region of Argentina, despite exhibiting much lower GPS‐shortening rates than across the thin‐skinned Precordillera region to its west. Whether geodetic shortening rates indicate an actual long‐term shortening gradient, and whether shortening rates translate to higher uplift rates due to steeper faults in the Sierras Pampeanas, remain uncertain due to the limited spatio‐temporal coverage and the inherently large error in the vertical component of deformation of GPS measurements. We measure geomorphic offsets and use 10Be terrestrial cosmogenic nuclide surface exposure dating to determine slip rates on the Las Chacras Fault Zone (LCFZ)—an ∼30 km long, NNW‐trending, steeply dipping (55–65°E) reverse fault that branches off of the longest, westernmost, thick‐skinned Valle Fértil range‐front fault in the western Sierras Pampeanas. Average shortening and uplift rates measured on the LCFZ are ∼0.2 and ∼0.3–0.4 mm/yr, respectively. Despite an uplift rate similar to most other faults in the region, the LCFZ shortening rate is lower than faults to its west; this is in agreement with the inferred west‐east decrease in shortening rates from GPS data, indicating consistent regional deformation patterns since the Late Pleistocene. The decrease in shortening to the east coincides spatially with the termination of the flat portion of the subducted Nazca plate between 67 and 68°W. From scaling relationships among magnitude, slip rate, and fault length, the LCFZ is capable of generating earthquakes of MW 6.7–7.1.

Late Pleistocene slip rate of the Chaman fault based on 10Be exposure dating of offset geomorphic surfaces near Kabul, Afghanistan

We report the first late Pleistocene left-lateral slip rate of the northern Chaman fault in Afghanistan based on 10Be dating of offset alluvial fan surfaces. Field mapping complemented with the analysis of CORONA and ALOS PRISM satellite images and shaded relief and topographic data allows us to identify piercing points across the fault zone at two displaced alluvial fans (Ghat Bandakul and Azadkhail) at Wardak Province south of Kabul. We constrain the ages of offset alluvial fans based on 10Be terrestrial cosmogenic nuclides (TCN) dating of well-embedded quartzite sandstone boulders and cobbles. The Ghat Bandakul alluvial fans are offset at 165 ± 15 m and 235 ± 24 m, for which 10Be TCN model ages average 46.9 ± 3.5 kyr and 66.6 ± 4.9 kyr, respectively, yielding a slip rate of 3.5 ± 0.4 mm/yr. At the Azadkhail site, we identified two offset terraces. Based on 500 ± 50 m offset of a geomorphic surface with 111.2 ± 10.5 kyr age, we obtain a slip rate of 4.5 ± 0.6 mm/yr. Combining the 800 ± 70 m left-lateral offset matching with an average age of 176.8 ± 17.1 kyr for the fan yields the same geomorphic slip rate of 4.5 ± 0.6 mm/yr. These slip rates are considerably lower than geologically, geomorphologically, and geodetically defined slip rates previously obtained along the southern Chaman fault. These results show a clear trend of decreasing fault slip rate with increasing distance to the northeast. The observations suggest that the southern portion of the fault accommodates most of the fault-parallel component of relative motion between the Indian and Eurasian plates. The lower slip rate of the Chaman fault in Afghanistan may be explained by the transfer of the left-lateral shear onto the Gardez and Mokur faults that splay northward from the Chaman fault.

Antarctic erosion history reconstructed by Terre Adélie moraine geochronology

AbstractWe report apatite fission-track and 10Be terrestrial cosmogenic nuclide (TCN) dating of 14 moraine boulders originating from inland Terre Adélie, East Antarctica. These data show cooling of the Proterozoic Terre Adélie craton at < ~120°C between 350 and 300 Ma, suggesting > 4 km temperate glacial erosion during the Late Palaeozoic Ice Age, followed by nearly null Mesozoic erosion and low glacial erosion (< 2 km) in the Cenozoic. Based on glacial flux maps, the origin of the boulders may be located ~400 km upstream. Preliminary TCN (10Be) datings of moraine boulders cluster within the last 30 ka. Cosmogenic ages from the Lacroix Nunatak suggest a main deglaciation after the Younger Dryas at c. 10 ka, while those of Cap Prud'homme mostly cluster at 0.6 ka, in agreement with an exhumation of boulders during the Little Ice Age.

Late Quaternary fluvial landform evolution and controlling factors along the Yulin River on the Northern Tibetan Plateau

The Yulin River in the northern Tibetan Plateau, consists of multiple geomorphological features, including alluvial fans, fluvial terraces, and river profile knickpoints. Collectively, these provide a natural laboratory for exploring the late Quaternary fluvial landform evolution in response to both climatic change and tectonic activities in the region of the Altyn Tagh Fault. In this study, we investigated the distribution, sequences and sediment characteristics of the fluvial landforms along the Yulin River based on high-precision (0.5 m-resolution) Worldview satellite images and field observations. Mid-Pleistocene alluvial fans formed the highest fluvial landform surface into which ten major inset fluvial terraces were developed, distributed along three stream segments. Real-time kinematic global positioning system (RTK-GPS) measurement of terrace surfaces and the modern river longitudinal profiles was conducted across the Dongbatu Shan to show fluvial landform geometry and tectonic deformation. Fluvial terrace surfaces were deformed due to fault uplift as illustrated by spatially variable surface geometries. The chronological sequences of terraces along the Yulin River since 160 ka were reconstructed based on 10Be terrestrial cosmogenic nuclides (TCNs) dating. Results indicated that river incision occurred mainly during periods of climate transition, suggesting that terrace evolution was partly controlled by climate changes. Moreover, terrace exposure ages showed an upstream younging trend along the river, demonstrating a probable response to knickpoint retreat. Combined with terrace deformation and ages, fault uplift rates were constrained, which were lower than the river incision rates during the Late Quaternary, indicating that crustal shortening was mainly absorbed by the growth of the regional anticline. Collectively, our results suggest that the evolution of fluvial landforms along the Yulin River is a function of interplay between regional tectonic activities and climatic changes, which is significant to understand the NW-outward splay of the Altyn Tagh Fault.

Terrestrial cosmogenic surface exposure dating of moraines at Lake Tahoe in the Sierra Nevada of California and slip rate estimate for the West Tahoe Fault

Two sets of Pleistocene moraines (Tioga and Tahoe) are preserved at Cascade Lake along the west side of Lake Tahoe. The 10Be terrestrial cosmogenic nuclide surface exposure ages for two younger Tioga moraines yield an average age of 22.3±1.2ka, coincident with the global Last Glacial Maximum. The ages suggest that the Tioga glaciation may have reached its maximum several thousand years earlier in the Lake Tahoe basin than to the south along the east flank of the Sierra Nevada. The oldest 10Be age (120±8ka) determined for an additional suite of 10 boulders exhibiting significant scatter in 10Be ages is interpreted to be the minimum age of formation for older Tahoe moraines in the Tahoe basin, suggesting they were deposited during marine oxygen isotope stage 6. The moraines at Cascade Lake are displaced by the West Tahoe Fault that strikes northward for 45km along the western edge of the Lake Tahoe basin. Vertical displacements of the crests of the Tahoe and Tioga moraines are 59±10 and 32±12m respectively. Averaged over the time since the formation of the Tahoe and Tioga moraines, the average vertical separation rates are <0.5±0.1 and ~1.4±0.7mm/y respectively. The measured vertical separation across the broad graben on the Tioga moraine may be accentuated by its deposition on a preexisting scarp and, in this regard, the increase in slip rate since the Tioga glaciation may be apparent rather than real. The fault slip rate and accompanying horizontal rate of extension averaged over the time since the formation of the older Tahoe moraines are respectively 0.6±0.2 and 0.3±0.2mm/y. The slip rate averaged over the time since emplacement of the Tahoe moraine is in general accord with prior geologic studies reporting slip rate estimates elsewhere along the fault, and the horizontal extension rate is at the lower end of extension rates estimated by others with geodesy across the Tahoe basin.

Plateau reduction by drainage divide migration in the Eastern Cordillera of Colombia defined by morphometry and 10Be terrestrial cosmogenic nuclides

AbstractCatchment‐wide erosion rates were defined using 10Be terrestrial cosmogenic nuclides for the Eastern Cordillera of the Colombian Andes to help determine the nature of drainage development and landscape evolution. The Eastern Cordillera, characterized by a smooth axial plateau bordered by steep flanks, has a mean erosion rate of 11 ± 1 mm/ka across the plateau and 70 ± 10 mm/ka on its flanks, with local high rates &gt;400 mm/ka. The erosional contrast between the plateau and its flanks was produced by the increase in the orogen regional slope, derived from the progressive shortening and thickening of the Eastern Cordillera. The erosion rates together with digital topographic analysis show that the drainage network is dynamic and confirms the view that drainage divides in the Eastern Cordillera are migrating towards the interior of the mountain belt resulting in progressive drainage reorganization from longitudinal to transverse‐dominated rivers and areal reduction of the Sabana de Bogotá plateau. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Repeated large‐magnitude earthquakes in a tectonically active, low‐strain continental interior: The northern Tien Shan, Kyrgyzstan

AbstractThe northern Tien Shan of Kyrgyzstan and Kazakhstan has been affected by a series of major earthquakes in the late 19th and early 20th centuries. To assess the significance of such a pulse of strain release in a continental interior, it is important to analyze and quantify strain release over multiple time scales. We have undertaken paleoseismological investigations at two geomorphically distinct sites (Panfilovkoe and Rot Front) near the Kyrgyz capital Bishkek. Although located near the historic epicenters, both sites were not affected by these earthquakes. Trenching was accompanied by dating stratigraphy and offset surfaces using luminescence, radiocarbon, and 10Be terrestrial cosmogenic nuclide methods. At Rot Front, trenching of a small scarp did not reveal evidence for surface rupture during the last 5000 years. The scarp rather resembles an extensive debris‐flow lobe. At Panfilovkoe, we estimate a Late Pleistocene minimum slip rate of 0.2 ± 0.1 mm/a, averaged over at least two, probably three earthquake cycles. Dip‐slip reverse motion along segmented, moderately steep faults resulted in hanging wall collapse scarps during different events. The most recent earthquake occurred around 3.6 ± 1.3 kyr ago (1σ), with dip‐slip offsets between 1.2 and 1.4 m. We calculate a probabilistic paleomagnitude to be between 6.7 and 7.2, which is in agreement with regional data from the Kyrgyz range. The morphotectonic signals in the northern Tien Shan are a prime example of deformation in a tectonically active intracontinental mountain belt and as such can help understand the longer‐term coevolution of topography and seismogenic processes in similar structural settings worldwide.

Understanding erosion rates in the Himalayan orogen: A case study from the Arun Valley

AbstractUnderstanding the rates and pattern of erosion is a key aspect of deciphering the impacts of climate and tectonics on landscape evolution. Denudation rates derived from terrestrial cosmogenic nuclides (TCNs) are commonly used to quantify erosion and bridge tectonic (Myr) and climatic (up to several kiloyears) time scales. However, how the processes of erosion in active orogens are ultimately reflected in 10Be TCN samples remains a topic of discussion. We investigate this problem in the Arun Valley of eastern Nepal with 34 new 10Be‐derived catchment‐mean denudation rates. The Arun Valley is characterized by steep north‐south gradients in topography and climate. Locally, denudation rates increase northward, from &lt;0.2 mm yr−1 to ~1.5 mm yr−1 in tributary samples, while main stem samples appear to increase downstream from ~0.2 mm yr−1 at the border with Tibet to 0.91 mm yr−1 in the foreland. Denudation rates most strongly correlate with normalized channel steepness (R2 = 0.67), which has been commonly interpreted to indicate tectonic activity. Significant downstream decrease of 10Be concentration in the main stem Arun suggests that upstream sediment grains are fining to the point that they are operationally excluded from the processed sample. This results in 10Be concentrations and denudation rates that do not uniformly represent the upstream catchment area. We observe strong impacts on 10Be concentrations from local, nonfluvial geomorphic processes, such as glaciation and landsliding coinciding with areas of peak rainfall rates, pointing toward climatic modulation of predominantly tectonically driven denudation rates.

Reconstructing the timing of flash floods using 10Be surface exposure dating at Leidy Creek alluvial fan and valley, White Mountains, California–Nevada, USA

Large alluvial fans characterize the piedmonts of the White Mountains, California–Nevada, USA, with large boulders strewn across their surfaces. The boulders are interpreted as flash floods deposits with an unclear trigger for the transport process. Several triggers are possible, including glacial lake outburst floods (GLOFs), thunderstorms or rainfall on snow cover. From a paleoenvironmental perspective, the origin of the flash floods is of fundamental importance. The alluvial fans that flank the White Mountains at Leidy Creek display particularly impressive examples of these deposits. The boulder deposits and the source catchment at Leidy Creek were examined using 10Be terrestrial cosmogenic nuclide (TCN) surface exposure dating to help elucidate their age and origin. All boulders dated on the alluvial fans date to the Holocene. This is in accordance with the geomorphic analyses of the Leidy Creek catchment and its terraces and sediment ridges, which were also dated to the Holocene using optically stimulated luminescence (OSL) and 10Be surface exposure. The results suggest that the boulders on the alluvial fan were deposited by flash floods during thunderstorm events affecting the catchment of the Leidy Creek valley. Paleomonsoonal-induced mid-Holocene flash floods are the most plausible explanation for the discharges needed for these boulder aggradations, but a regional dataset is needed to confirm this explanation.

Climatically controlled formation of river terraces in a tectonically active region along the southern piedmont of the Tian Shan, NW China

Combined tectonic uplift and Quaternary climate variability control the deposition and abandonment of terraces along the southern Tian Shan in northwest China. Several preserved terraces have been deformed by an actively growing anticline within the uplifted frontal thrust system of the southern Tian Shan. We combine geomorphic mapping, topographic surveys of the deformed terrace surfaces, 10Be terrestrial cosmogenic nuclide (TCN) depth profile dating, and optically stimulated luminescence (OSL) dating to develop a new chronology for the terraces along the Huangshui He since 550ka. Our in situ 10Be dating of fluvial gravels capping strath terraces suggests a relationship between the formation and abandonment of the terraces and glacial climate cycles since the middle-late Pleistocene. These data indicate that the formation of the four terraces occurred at ~550, ~ 430, ~ 350, and ~60ka. We suggest that episodes of aggradation were facilitated by high sediment supply during glacial periods, followed by subsequent incision that led to abandonment of these terraces during deglaciation. We also estimate that tectonically induced river incision may account for about 60–70% of the total incision. However, during the intervening time between 350ka and present, only one terrace was formed and preserved. We suggest that this record might be caused by a gradually decreasing uplift rate of the anticline through time and thus has influenced the preservation of terraces. Therefore, our results demonstrate the utility of chronologic records from southern Tian Shan for deconvolving the effects of tectonics and climate on fluvial incision.

Timing and climatic drivers for glaciation across monsoon-influenced regions of the Himalayan–Tibetan orogen

Mapping and thirty-eight 10Be terrestrial cosmogenic nuclide (TCN) ages help define the timing of glaciation in the monsoon-influenced Greater Himalaya in central Garwhal, India. Glacial landforms in central Garwhal are present only within a few kilometers of the present glaciers and all date to less than ∼12.5 ka. This suggests that the Lateglacial and/or Holocene glacial advances were more extensive than their predecessors and hence destroyed or buried evidence for earlier glaciation or that other processes, such as intensive fluvial erosion and/or hillslope mass movements, have destroyed evidence of earlier glaciation. Prominent laterofrontal moraines date to the Lateglacial, the Early Holocene, and the Neoglaciation. Moraines next to the active ice and boulders on contemporary glaciers date to 101–102 years before present. This suggests only a minor glacial advance during the Little Ice Age occurred in central Garhwal. These young ages indicate that inheritance of TCNs in areas that were recently glaciated is very small and likely has little effect when considering TCN ages on moraines older than the global Last Glacial Maximum. The new 10Be ages are combined with 1081 recalculated 10Be ages from previous studies to develop a regional framework of glaciation across the monsoon-influenced and adjacent regions of the Himalayan–Tibetan orogen. We separate what appears to be continuous glaciation into 27 regional glacial stages (plus 2 tentative glacial stages) that are termed monsoonal Himalayan–Tibetan stages (MOHITS). The regional glacial stages cover a wide chronologic range that includes: five regional glacial stages older than the Last Glacial cycle (MOHITS 13 at 483 ± 38 ka to MOHITS 5E at 122 ± 15 ka); thirteen regional glacial stages within the Last Glacial cycle (MOHITS 5B at 91 ± 15 ka to MOHITS 2A at 12.9 ± 0.9 ka); and eleven regional glacial stages during the Holocene (MOHITS 1k at 11.4 ± 0.7 ka to MOHITS 1A at 0.4 ± 0.1 ka). There are strong correlations both with periods of strong monsoons, and northern hemisphere events throughout the entire chronologic range with 16 stages linked to the monsoon, 11 stages linked to the mid-latitude westerlies, and two unassigned because of large age uncertainties. Overall, we see a complex pattern of glaciation influenced by two climatic systems throughout the mid/late Quaternary.

Late Quaternary alluvial fans at the eastern end of the San Bernardino Mountains, Southern California

Alluvial fans at the eastern end of the San Bernardino Mountains in Southern California provide a record of climate modulated sediment transfer and erosion, and are deformed and displaced in places by active faults. Alluvial fans within two study areas, the Mission Creek and the Whitewater River drainages, were examined using geomorphic, sedimentological, and 10Be terrestrial cosmogenic nuclide (TCN) surface exposure methods to define the timing of alluvial fan formation and erosion, and to examine the role of climatic, tectonic and autocyclic processes. These alluvial fan complexes were studied because they are amongst the best-preserved successions of alluvial fans in southern California and they are located at the mouths of two of the largest drainages, Whitewater River and Mission Creek, in the San Bernardino Mountains and traverse major faults, the Mission Creek and Banning. The alluvial fans comprise bouldery debris deposits that represent deposition dominated by flash flood and debris flow events. TCN surface exposure dating indicates that abandonment/incision of alluvial fan surfaces date to early in the Last Glacial or more likely the penultimate glacial cycle, to marine isotope stage (MIS) 4, and to the Holocene. The lack of alluvial fan ages during the latter part of the Last Glacial (MIS 2 and 3) suggests that there has been little alluvial fan lobe deposition/incision during that time. This is similar to findings for many other alluvial fans throughout the American Southwest, and supports the view that there is a strong climatic control on alluvial fan formation throughout this region. Furthermore, the oldest alluvial fan surfaces in the Mission Creek region are beheaded by the Whitewater River drainage, showing that the oldest alluvial fans in the Mission Creek region underwent significant capture by the Whitewater River drainage. This shows the autocyclic controls are also important on alluvial fan evolution in this region; but the importance of these processes to alluvial fan development in other regions of the American Southwest needs to be more fully assessed. The alluvial fans in the Mission Creek area traverse the Mission Creek fault, but are not deformed by it, which suggests that there may have been little if any movement along this fault since at least MIS 4. In contrast, alluvial fans in the Whitewater River study are displaced by active faults highlighting the influence of tectonism on alluvial fan development in this region. In addition to illustrating the importance of climatic controls on the development of alluvial fans in the American Southwest, a classic region for alluvial fan studies, this study illustrates the complex mixture of autocyclic and allocyclic factors that force alluvial fan development in tectonically active settings.

Investigation of late-Holocene moraines in the western Southern Alps, New Zealand, applying Schmidt-hammer exposure-age dating

Chronological studies applying Schmidt-hammer exposure-age dating (SHD) were performed on six glacier forelands in the western part of the Southern Alps, New Zealand. Although lithological heterogeneity prevented a regional age-calibration curve to be established, local age-calibration curves for La Perouse Glacier and Strauchon Glacier could be derived. They show similar linear equations and trends/slopes and enabled a preliminary assessment of the representativeness of individual 10Be terrestrial cosmogenic nuclide dating (TCND)-ages obtained from the other forelands. No mid- and early-Holocene advance periods were detected. Clusters of moraine ages date around 2800, 1850–1450, and 1100–900 years ago, followed by the ‘Little Ice Age’ commencing c. 500 years ago. There is no good agreement with earlier radiocarbon-based studies and recently published TCND-chronologies. As it will be outlined, this partly could be the result of different approaches to the palaeoclimatic interpretation of the dated samples. The results obtained from this recent study do not support an elsewhere proposed general asynchronous glacier behaviour between the mid-latitudinal Northern and Southern hemispheres.

Timing and nature of alluvial fan and strath terrace formation in the Eastern Precordillera of Argentina

Sixty-eight 10Be terrestrial cosmogenic nuclide (TCN) surface exposure ages are presented to define the timing of alluvial fan and strath terrace formation in the hyper-arid San Juan region of the Argentine Precordillera. This region is tectonically active, and numerous fault scarps traverse Quaternary landforms. The three study sites, Marquesado strath complex, Loma Negra alluvial fan and Carpintería strath complex reveal a history of alluvial fan and strath terrace development over the past ∼225 ka. The Marquesado complex Q3m surface dates to ∼17 ± 3 ka, whereas the Loma Negra Q1ln, Q2ln, Q3ln, Q4ln, and Q5ln surfaces date to ∼24 ± 3 ka, ∼48 ± 2 ka, ∼65 ± 13 ka, ∼105 ± 21 ka, and ∼181 ± 29 ka, respectively. The Carpintería complex comprises eight surfaces that have been dated and include the Q1c (∼23 ± 3 ka), Q2c (∼5 ± 5 ka), Q3ac (∼25 ± 12 ka), Q3bc (∼29 ± 15 ka), Q4c (∼61 ± 12 ka), Q5c (∼98 ± 18 ka), Q6c (∼93 ± 18 ka), and Q7c (∼212 ± 37 ka). 10Be TCN depth profile data for the Loma Negra alluvial fan complex and Carpintería strath terrace complex, as well as OSL ages on some Carpintería deposits, aid in refining surface ages for comparison with local and global climate proxies, and additionally offer insights into inheritance and erosion rate values for TCNs (∼10 × 10410Be atoms/g of SiO2 and ∼5 m Ma−1, respectively). Comparison with other alluvial fan studies in the region show that less dynamic and older preserved surfaces occur in the Carpintería and Loma Negra areas with only younger alluvial fan surfaces preserved both to the north and south. These data in combination with that of other studies illustrate broad regional agreement between alluvial fan and strath terrace ages, which suggests that climate is the dominant forcing agent in the timing of terrace formation in this region.

Paleoseismic study of the east Kalpintage fault in southwest Tianshan based on deformation of alluvial fans and 10Be dating

Multiple earthquakes produced by thrusting deformation have been recorded over the last century in the Tianshan area. Paleoseismic studies are very important in the exploration of the active quaternary tectonics and the risk assessment of great earthquakes in the Tianshan orogenic region. However, in this area, paleoseismic research is still lacking because of the lack of samples dated by 14C or optically stimulated luminescence (OSL) methods. We determined the ages of the alluvial fans by 10Be terrestrial cosmogenic nuclide (TCN) dating, measured the surface deformation of the fault scarp in a GPS survey, and evaluated the vertical displacements of the events in trenches in the east Kalpintage fault in the southwest Tianshan region. We estimated the displacement and recurrence intervals of the paleoseismic events and constrained the errors of the 10Be ages and slip rates using a Monte Carlo simulation method. Our study suggests that each paleoseismic event shows a similar displacement of ~1.5 m with a recurrence interval of ~5 kyr in the east Kalpintage fault. The calculated slip rate is 0.31(+0.21/−0.18) mm/yr. In such arid regions with large areas of coarse gravel that lack 14C or OSL samples, the integration of TCN dating, geomorphic deformation survey, and trenching methods is a reliable alternative for studying the active regional tectonics.

Nature and timing of large landslides within an active orogen, eastern Pamir, China

Large-scale landsliding (involving ≫106m3 in volume) is important in landscape development in high mountains. To assess the importance of large landslides in high mountains, four large landslides (Bulunkou, Muztagh, Taheman, and Yimake) were mapped in the NE Chinese Pamir at the westernmost end of the Himalayan–Tibetan orogen and dated using 10Be terrestrial cosmogenic nuclides. The Bulunkou landslide at the southernmost end of Muji Valley is composed of ~1.7×107m3 of landslide debris and has an age of 2.0±0.1ka. The Muztagh landslide, located on the SW side of the massif Muztagh Ata, is composed of ~4.7×108m3 of debris, and has an age of 14.3±0.8ka. The Taheman landslide, located south of Muztagh Ata, is composed of ~2.6×108m3 of landslide debris and has an age of 6.8±0.2ka. The Yimake landslide, on the northern frontal range of the Pamir at the southwestern end of the Tarim basin, is composed of ~1.4×109m3 of landslide debris and has an age of 7.1±0.6ka. Two other large landslides are present in the region, the Aerpa Aigezi (on a tributary of the Gez River) and the Bile Jiyi (on the Yarkand River) landslides, and are composed of ~1.6×107m3 and ~5.2×106m3 of landslide debris, respectively. However, the Aerpa Aigezi and Bile Jiyi landslides were not studied in as much detail or dated because of their inaccessibility. Given the tectonically active nature of this region, with numerous active faults, and the morphology of the landslides, these landslides were likely triggered by earthquakes. However, other causes — including long-term increased precipitation and geologic bedrock structure — could be important contributing factors in their formation.