Optical Dating Sediments from Coastal British Columbia: Successes, Challenges, and Plans for the Future (original) (raw)
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Quaternary Geochronology, 2014
The Quaternary geology of the central coast of British Columbia contains a rich and complex record of glacial activity, post-glacial sea level and landscape change, and early human occupation spanning the last~10,000 years. At present, however, this region remains a largely understudied portion of coastal North America. This study describes the luminescence characteristics of quartz and K-feldspar from coastal dune and beach sands on Calvert Island and develops a suitable optical dating protocol that will allow for a more rigorous chronology for post-glacial landscape evolution and human occupation on British Columbia's central coast. Luminescence signals from Calvert Island quartz are dim, and appear to lack the so-called "fast" component that is most desirable for optical dating. K-feldspar signals are sufficiently bright for optical dating. We test and refine a single-aliquot regenerative-dose (SAR) protocol for K-feldspar specific to Calvert Island samples through a series of dose recovery and preheat plateau tests. Two approaches for correcting a sample age for anomalous fading are compared and a correction for phototransfer is introduced and applied. Measured fading rates vary from sample to sample implying that, in this region, it is not sufficient to rely on two or three representative fading rates as has sometimes been done elsewhere. Refined age estimates show consistency with independent radiocarbon dating control and help identify radiocarbon-dated organic-rich sediments that have been reworked.
Optical Dating of Tsunami-Laid Sands
Quaternary Research, 1996
; Clague and Bo-The ages of some tsunami deposits can be determined by optical browsky, 1994b; Darienzo et al., 1994; Dawson, 1994). dating, a key requirement being that the deposits are derived from Commonly, sandy or gravelly tsunami sediment is deposited sediment that was reworked and exposed to daylight by tidal curin tidal marshes, bogs, and lakes, where it is covered by peat rents, waves, wind, or bioturbation during the last years before the or mud and thus preserved as part of a stratigraphic sequence. tsunami. Measurements have been made using 1.4 eV (infrared) Study of such deposits can provide information on tsunami excitation of K-feldspar grains separated from samples of prehisrecurrence and local run-up which, in turn, is useful in astoric tsunami sand sheets and modern analogs of tsunami source sessing tsunami and earthquake hazards. sediments at four sites in Washington state and British Columbia. Prehistoric tsunamis generally have been dated by radio-Source sands gave equivalent doses indicative of recent exposure carbon analysis of detrital and growth-position plant fossils to daylight. Tsunami sand at Cultus Bay, Washington, yielded an and shells, either within the tsunami deposit or in bounding optical age of 1285 { 95 yr (calendric years before A.D. 1995, sediments. However, there are several problems with such {1s). At 2s, this age overlaps the range of from 1030 to 1100 yr determined through a combination of high-precision radiocarbon dating. One is uncertainty about the age relation of the tsudating and stratigraphic correlation. Tsunami sands at three sites nami and the dated material. Detrital wood or shell within near Tofino and Port Alberni on Vancouver Island, British Columor beneath a tsunami deposit may be reworked and thus bia, have optical ages of 260 { 20, 325 { 25, and 335 { 45 yr. predate the tsunami, and detritus above the tsunami deposit Historical records and radiocarbon dating show that the sand at could either predate or postdate the event. This problem can each of the three sites is between 150 and 400 yr old. These optical be minimized by dating growth-position plant fossils at the ages support the hypothesis that the Vancouver Island sands were base of, or within, the tsunami deposit; the assumption is deposited by a tsunami generated by a large earthquake on that the dated plants were killed by, or began to grow soon the Cascadia subduction zone about 300 yr ago. ᭧ 1996 University of after, the tsunami. Unfortunately, most tsunami deposits lack Washington. such fossils. A second problem is that uncertainties associated with radiocarbon ages usually expand upon conversion to calendric ages, giving rise to a range of calendric ages of
Photonic dating of Holocene back-barrier coastal dunes, northern North Carolina, USA
Quaternary Science Reviews, 2003
We have made the first application of luminescence sediment dating methods to coastal dunes from the barrier-island system in North Carolina. As part of a larger study of the timing of activation and stabilization of coastal dunes of northern North Carolina and southern Virginia that employed ground-penetrating radar, trenching, 14 C dating, and analysis of soils, we applied photonic dating to seven samples from four sites: Jockeys Ridge, Nags Head Woods, Penney Hill, and Run Hill. We used fine-sand-sized potassium feldspar from the four samples with sufficient feldspar concentrations, and quartz from all samples. We applied the multialiquot infrared-stimulated luminescence thermal-transfer-correction additive-dose (ADD), and the late-light-subtraction ADD methods to the feldspars. We applied the single-aliquot regenerative-dose (SAR) method with 470 nm stimulation to the quartz.
The Holocene, 2014
. Towards more robust chronologies of coastal progradation: optically stimulated luminescence ages for the coastal plain at Moruya, south-eastern Australia. The Holocene: a major interdisciplinary journal focusing on recent environmental change, 25 (3), 536-546. Towards more robust chronologies of coastal progradation: optically stimulated luminescence ages for the coastal plain at Moruya, southeastern Australia Abstract Accurate chronologies are fundamental for detailed analysis of palaeoenvironmental conditions, archaeological reconstructions and investigations of Holocene coastal morphological changes. Chronological data enable estimation of rates of shoreline progradation, and provide appropriate context for forecasting future coastal changes. A previously reported radiocarbon chronology for the Moruya coastal plain in southeastern Australia indicated a decelerating overall rate of progradation with minimal net seaward shoreline movement in the past ~2500 years. Single-grain and multi-grain aliquot optically stimulated luminescence (OSL) analyses demonstrate that marine sands from this region have excellent luminescence characteristics. A series of OSL ages across this coastal barrier indicates a remarkably linear trend of Holocene shoreline progradation. The linear trend of seaward shoreline movement indicates that the barrier has grown at an average rate of 0.27 m/yr with successive ridge formation every ~110 years. The oldest ridge on the barrier appears to correspond to cessation of rapid post-glacial sea-level rise, and the large foredune at the seaward margin of the barrier is chronologies, in Australia and around the world, where they have been based on radiocarbon dating of shell hash.
A revised burial dose estimation procedure for optical dating of youngand modern-age sediments
Quaternary Geochronology, 2009
The presence of genuinely zero-age or near-zero-age grains in modern-age and very young samples poses a problem for many existing burial dose estimation procedures used in optical (optically stimulated luminescence, OSL) dating. This difficulty currently necessitates consideration of relatively simplistic and statistically inferior age models. In this study, we investigate the potential for using modified versions of the statistical age models of Galbraith et al. [Galbraith, R.F., Roberts, R.G., Laslett, G.M., Yoshida, H., Olley, J.M., 1999. Optical dating of single and multiple grains of quartz from Jinmium rock shelter, northern Australia: Part I, experimental design and statistical models. Archaeometry 41, 339-364.] to provide reliable equivalent dose (D e ) estimates for young and modern-age samples that display negative, zero or near-zero D e estimates. For this purpose, we have revised the original versions of the central and minimum age models, which are based on log-transformed D e values, so that they can be applied to unlogged D e estimates and their associated absolute standard errors. The suitability of these 'un-logged' age models is tested using a series of known-age fluvial samples deposited within two arroyo systems from the American Southwest. The un-logged age models provide accurate burial doses and final OSL ages for roughly three-quarters of the total number of samples considered in this study. Sensitivity tests reveal that the un-logged versions of the central and minimum age models are capable of producing accurate burial dose estimates for modern-age and very young (<350 yr) fluvial samples that contain (i) more than 20% of well-bleached grains in their D e distributions, or (ii) smaller sub-populations of wellbleached grains for which the D e values are known with high precision. Our results indicate that the original (log-transformed) versions of the central and minimum age models are still preferable for most routine dating applications, since these age models are better suited to the statistical properties of typical single-grain and multi-grain single-aliquot D e datasets. However, the unique error properties of modernage samples, combined with the problems of calculating natural logarithms of negative or zero-Gy D e values, mean that the un-logged versions of the central and minimum age models currently offer the most suitable means of deriving accurate burial dose estimates for very young and modern-age samples.
Optical dating of tsunami-laid sand from an Oregon coastal lake
Quaternary Science Reviews, 2001
Optical ages for five samples of tsunami-laid sand from an Oregon coastal lake were determined using an infrared optical-dating method on K-feldspar separates and, as a test of accuracy, compared to ages determined by AMS 14 C dating of detrital plant fragments found in the same beds. Two optical ages were about 20% younger than calibrated 14 C ages of about 3.1 and 4.3 ka. Correction of the optical ages using measured anomalous fading rates brings them into agreement with the 14 C ages. The approach used holds significant promise for improving the accuracy of infrared optical-dating methods.
New quartz SAR-OSL ages from the stranded beach dune sequence in south-east South Australia
Quaternary Science Reviews, 2003
A sequence of stranded coastal barriers in south-east South Australia preserves a record of sea-level variations over the past 800 ka. Huntley et al. (Quat. Sci. Rev. 12 (1993a) 1; Quat. Sci. Rev. 13 (1994a) 201) attempted to test thermoluminescence (TL) dating methods and found good agreement between quartz TL ages with independent ages for these dunes. We investigate the accuracy of the single-aliquot regenerative-dose (SAR) procedure (Radiat. Meas. 32 over an extended age range of 0-250 ka, by comparing SAR-OSL ages determined on quartz extracts from these dunes with the existing chronology. We show that Robe II range is B60 ka, and that Robe III is 100 ka old. Not surprisingly, the OSL ages increase monotonically from the Robe II range to the West Naracoorte range. For the younger dunes (o240 ka), the SAR-OSL ages agree with the expected ages within 1s errors, whereas for the older dunes the SAR ages are consistent with independent ages within 2s error limits. We consider these results to be very promising, and lend support to the large number of quartz SAR-OSL ages being presented in the literature, where such comparisons with independent chronology are not usually possible. r
Rock-walled archaeological features are notoriously hard to date, largely because of the absence of suitable organic material for radiocarbon dating. This study demonstrates the efficacy of dating clam garden wall construction using optical dating, and uses optical ages to determine how sedimentation rates in the intertidal zone are affected by clam garden construction. Clam gardens are rock-walled, intertidal terraces that were constructed and maintained by coastal First Nation peoples to increase bivalve habitat and productivity. These features are evidence of ancient shellfish mariculture on the Pacific Northwest and, based on radiocarbon dating, date to at least the late Holocene. Optical dating exploits the luminescence signals of quartz or feldspar minerals to determine the last time the minerals were exposed to sunlight (i.e., their burial age), and thus does not require the presence of organic material. Optical ages were obtained from three clam garden sites on northern Quadra Island, British Columbia, and their reliability was assessed by comparing them to radiocarbon ages derived from shells underneath the clam garden walls, as well as below the terrace sediments. Our optical and radiocarbon ages suggest that construction of these clam garden walls commenced between ~1000 and ~1700 years ago, and our optical ages suggest that construction of the walls was likely incremental and increased sedimentation rates in the intertidal zone by up to fourfold. Results of this study show that when site characteristics are not amenable to radiocarbon dating, optical dating may be the only viable geochronometer. Furthermore, dating rock-walled marine management features and their geomorphic impact can lead to significant advances in our understanding of the intimate relationships that Indigenous peoples worldwide developed with their seascapes.