Joel Q. Spencer

Timing and style of Late Quaternary glaciation in northeastern Tibet

Glacial successions in the Anyemaqen and Nianbaoyeze Mountains of northeastern Tibet are reassessed and new glacial chronologies are presented for these regions. Cosmogenic radionuclide and optically stimulated luminescence dating indicates that two glacial advances occurred in marine isotope stage (MIS)-3 and MIS-2. In the Anyemaqen Mountains, a third advance occurred in the Early Holocene. We suggest that glaciation was synchronous in the Anyemaqen and Nianbaoyeze Mountains, as well as in other glaciated areas of Tibet and the Himalaya that are influenced by the Asian monsoon. The maximum extent of glaciation occurred early in the last glacial cycle (MIS-3) during a time of increased insolation when the monsoon intensified and supplied abundant precipitation, as snow at high altitude, to feed high-altitude glaciers. This suggests that precipitation, as snow, is fundamental in controlling glaciation in these regions. However, the occurrence of glacial advances during the insolation minimum of MIS-2 suggests that, despite reduced precipitation at this time, the annual temperatures were cold enough to maintain positive glacier mass balances. The numerically defined chronologies for the Anyemaqen and Nianbaoyeze Mountains presented here provide a framework for comparing glacial advances in other parts of high Asia.

Timing of late Quaternary glaciations south of Mount Everest in the Khumbu Himal, Nepal

Moraines south of Mount Everest in the Khumbu Himal were dated using optically stimulated luminescence. Clustering of ages and morphostratigraphy allowed three advances to be dated: (1) the Periche Glacial Stage (ca. 18‐25 ka), (2) the Chhukung Glacial Stage (ca. 10 ka), and (3) the Lobuche Stage (ca. 1‐2 ka). The Periche Stage is coincident with Oxygen Isotope Stage 2; the Chhukung Stage represents a late glacial or early Holocene glacial advance; and the Lobuche Stage is a late Holocene glacial advance that predates the Little Ice Age.

Holocene slip rates along the Owens Valley fault, California: Implications for the recent evolution of the Eastern California Shear Zone

One of the largest historical earthquakes in California occurred in 1872 along the Owens Valley fault located along the western margin of the Eastern California Shear Zone. New paleoseismic and optically stimulated luminescence data are the first to bracket the timing of the pre-1872 rupture to between 3.3 ± 0.3 and 3.8 ± 0.3 ka. These data yield an earthquake recurrence interval between 4100 and 3000 yr, under the assumption of uniform return, and indicate a Holocene slip rate between 1.8 ± 0.3 and 3.6 ± 0.2 mm/ yr. Our data are broadly consistent with a model proposed for the space-time evolution of the Eastern California Shear Zone. Our Holocene slip-rate estimates for the Owens Valley fault are slower than present-day slip rates determined from elastic half-space models of geodetic data. This discrepancy is reduced by using the recurrence interval estimated here and a viscoelastic model of geodetic data or by including geologic slip rates from adjacent faults.

Optically stimulated luminescence dating of Late Quaternary glaciogenic sediments in the upper Hunza valley: validating the timing of glaciation and assessing dating methods

We present a comprehensive comparison of optically stimulated luminescence (OSL) ages with cosmogenic radionuclide (CRN) ages, and the first study to validate CRN dates from boulders on moraine ridges using luminescence dates from glaciogenic sediments from associated moraines, accomplished from both direct and stratigraphic relationships between CRN and OSL sampling sites. Both quartz and K-feldspars extracted from 12 Late Quaternary glaciogenic sediments were studied using single-aliquot OSL techniques. Rapid signal saturation in preliminary additive-dose infrared-stimulated K-feldspar luminescence growth data was interpreted as evidence of insufficiently bleached latent luminescence, and these data gave rise to overestimated ages in the majority of samples. Further analysis concentrated on replicated single-aliquot regenerative-dose (SAR) measurements of quartz minerals using blue-green stimulation. The SAR sensitivity correction method repeatedly failed in two of the samples and a further sample exhibited significant thermal transfer. Nevertheless, three of the eight glacial successions in the upper Hunza valley were defined using quartz-luminescence. Although we discuss the possibility of inherited components in the CRN data, in terms of paleoclimatic interpretations both dating techniques give concordant results.

Using uplifted Holocene beach berms for paleoseismic analysis on the Santa Maria Island, south-central Chile

Major earthquakes ( M > 8) have repeatedly ruptured the Nazca-South America plate interface of south-central Chile involving meter scale land-level changes. Earthquake recurrence intervals, however, extending beyond limited historical records are virtually unknown, but would provide crucial data on the tectonic behavior of forearcs. We analyzed the spatiotemporal pattern of Holocene earthquakes on Santa Maria Island (SMI; 37 degrees S), located 20 km off the Chilean coast and approximately 70 km east of the trench. SMI hosts a minimum of 21 uplifted beach berms, of which a subset were dated to calculate a mean uplift rate of 2.3 +/- 0.2 m/ky and a tilting rate of 0.022 +/- 0.002 degrees/ky. The inferred recurrence interval of strandline-forming earthquakes is similar to 180 years. Combining coseismic uplift and aseismic subsidence during an earthquake cycle, the net gain in strandline elevation in this environment is similar to 0.4 m per event

Luminescence dating of alluvial fans in intramontane basins of NW Argentina

Abstract Alluvial fans are sensitive recorders of both climatic change and tectonic activity. The ability to constrain the age of alluvial-fan sequences, individual sedimentary events and the rates of sediment accumulation are key for constraining which mechanisms most control their formation. Recent advances in optically stimulated luminescence (OSL) measurement and analysis have resulted in vast improvements in the dating technique and reliability of age determinations, particularly for OSL dating of quartz grains, and routine application to a wide variety of depositional environments is now possible. Here we apply OSL methods to date a variety of deposits within Late Pleistocene conglomeratic alluvial sequences in NW Argentina. The ages obtained range from 39 to 83 ka and were determined from debris-flow- and fluvial-dominated deposits and lacustrine sequences in intramontane basins bounded by tectonically active mountain ranges with as much as 2 km of relief. With careful choice of facies and sample collection, OSL techniques can be used to date Late Pleistocene, predominately matrix-supported, cobble-conglomerate alluvial deposits.

Assessing mixed dose distributions in young sediments identified using small aliquots and a simple two-step SAR procedure: the F-statistic as a diagnostic tool

Abstract In this study we have investigated the apparent dose (D e ∗ ) distribution in four samples of young sedimentary quartz from different depositional environments, and on standard quartz comprised of artificial binary-dose mixtures. We have used a simplified two-step single-aliquot regenerative-dose (SAR) approach to rapidly measure D e ∗ from a large number of small aliquots (∼50–100 grains), with a small sub-set subjected to routine SAR measurements to enable monitoring of luminescence characteristics. We have used an F-ratio analysis to interpret D e ∗ distributions. This analysis is sensitive to structure, the leading edge and modal data in D e ∗ distributions, indicated by inflections and plateaux in F-ratio plots. We cautiously suggest that F-ratios at or approaching unity may indicate a single dose component.

Tectonic geomorphology of marine terraces: Santa Barbara fold belt, California

Uplifted marine terraces are common landforms in coastal regions where active tectonics are an important component of landscape evolution, such as along the coastal stretches of southern California. The pattern and elevation of shoreline angles on active folds provide information about rates of uplift and fold growth, which is important for defining tectonic models. A particularly impressive succession of marine terraces are developed across the Santa Barbara fold belt (SBFB) in southern California, which comprises an east-west linear zone of active folds and (mostly) blind faults on the coastal piedmont and in the Santa Barbara Channel. The fold belt is characterized by several flights of emergent late Pleistocene marine terraces uplifted and preserved on the flanks of active anticlines. At several locations along the fold belt, the first emergent marine terrace is numerically dated by methods that include uranium-series dating on terrace corals, 14 C dating on terrace shells and detrital charcoal, optically stimulated luminescence of marine terrace sands, and oxygen isotopic signatures (δ 18 O) of mollusks. Individual marine terraces have as many as four ages, using up to three different dating methods, providing confidence in terrace chronology. Ages of higher terraces are estimated assuming a constant rate of uplift for a particular flight. Of the 31 terraces, 22 formed during a time of falling sea level, with 9 forming at or near marine oxygen isotope stage (MIS) 3 or 5 highstands. Ages and rates of uplift of the first emergent terrace vary systematically from west (younger and higher) to east (older and lower). The first emergent marine terraces in the westernmost SBFB are approximately 45 ka (MIS 3), and the rate of local surface uplift is ∼2 m/k.y. In the central part of the belt, first emergent terraces date to 60–70 ka (MIS 5), and uplift rates decrease to ∼1.2 m/k.y. First emergent marine terraces preserved in the easternmost fold belt range from 70 ka to 105 ka (MIS 5), with rates of local surface uplift of ∼0.5 m/k.y. Lower rates of uplift in the eastern end of the fold belt result from the MIS 5 terrace being tilted down into the Carpinteria syncline. Rates of vertical uplift in the western end of the fold belt are about six times higher than previously reported, suggesting the seismic hazard is also greater.

Landscape response to late Pleistocene climate change in NW Argentina: Sediment flux modulated by basin geometry and connectivity

Citation: Schildgen, T. F., Robinson, R. A. J., Savi, S., Phillips, W. M., Spencer, J. Q. G., Bookhagen, B., . . . Strecker, M. R. (2016). Landscape response to late Pleistocene climate change in NW Argentina: Sediment flux modulated by basin geometry and connectivity. Journal of Geophysical Research-Earth Surface, 121(2), 392-414. doi:10.1002/2015jf003607

Mapping thermal exposure by luminescence thermometry

Abstract It has been shown in previous studies that residual geological thermoluminescence (TL) signals can be used to assess fire damage and thermal exposure, both of which are of some interest in archaeological contexts. Detailed studies of the removal of TL from pure alkali feldspars have shown systematic relations between measured glow curve parameters and the temperatures and durations of isothermal annealing. However, in most archaeological cases, the temperature-time profile is variable and unknown. To examine the relationship between TL characteristics and thermal history under more realistic conditions, a model hearthstone was constructed containing a three-dimensional matrix of 64 thermocouple and the spatial variations in temperature monitored during the course of two experimental fires. Cores were removed from the stone at 18 locations where direct thermocouple correlations could be made, and at a further two locations, to interpolate the radial temperature distribution. Each core was sectioned and samples extracted for TL and PSL analysis, thus providing a representative set of samples which had been exposed to different maximum temperatures and a dynamic thermal exposure. TL measurements were made from room temperature to 700°C using a UV-filtered reader, and PSL measurements were made using a high sensitivity infrared pulsed diode array. The TL results, parametrized in terms of the position of the residual geological signal, are compared with thermocouple data integrated with respect to time over the course of the known thermal exposure, taking account of the empirical form of the complementary temperature-time relationships deduced from studies of pure minerals. This provides a means of quantifying thermal exposure for a generalized thermal event, which can be directly related to measured luminescence indicators.