Merging chironomid training sets: implications for palaeoclimate reconstructions

Icelandic and Norwegian chironomid calibration or training sets were merged to investigate whether a larger combined training set would be useful to apply to subfossil chironomid data from Iceland for periods such as the early Holocene, the Holocene Thermal Maximum and the Little Ice Age, when temperatures can be expected to be outside the current temperature range of the Icelandic training set. Following taxonomic harmonisation, the Icelandic and Norwegian data sets were compared before being merged to form a combined Norwegian-Icelandic training set. Analyses showed that it was biologically and statistically valid to merge the two data sets. The resulting combined inference model for mean July air temperature had improved performance statistics (r²_jack = 0.87; RMSEP_jack = 1.13) when compared to the best performing Icelandic model (r²_jack = 0.61; RMSEP_jack = 0.83), due to the longer environmental gradient covered (Icelandic 6–11 °C; combined 3.5–16 °C), and to the increased number of samples (Icelandic = 53 lakes; combined = 207 lakes) and taxa (Icelandic = 47 taxa; combined = 133 taxa) present within the combined training set. The inference models were applied to an early Holocene chironomid sequence from Vatnamýri, north Iceland, and a 450-year recent record from Myfluguvatn, north-west Iceland, to compare the reconstructions produced. The various inference models produced similar trends and patterns of temperature reconstruction, but the inference model based on the combined training set produced a larger range of reconstructed temperatures than the Icelandic model. It was found that different inference models produced more variation in the reconstruction than when different training sets were used. A comparison of the Myfluguvatn reconstructions with meteorological observations showed that the combined Norwegian–Icelandic inference model produced more reliable results than the Icelandic or Norwegian inference models alone.     

Landscape development in an hyperarid sandstone environment along the margins of the Dead Sea fault: Implications from dated rock falls

In this study, we explored the spatial and temporal relations between boulders and their original in-situ locations on sandstone bedrock cliffs. This was accomplished by combining field observations with dating methods using cosmogenic isotopes (¹⁰Be and ¹⁴C) and optically stimulated luminescence (OSL). Our conclusions bear both on the landscape evolution and cliff retreat process in the hyperarid region of Timna and on the methodology of estimating exposure ages using cosmogenic isotopes.

We recognize three discrete rock fall events, at 31 ka, 15 ka, and 4 ka. In this hyperarid region, the most plausible triggering mechanism for rock fall events is strong ground acceleration caused by earthquakes generated by the nearby Dead Sea fault (DSF). Our record, however, under represents the regional earthquake record implying that ongoing development of detachment cracks prior to the triggering event might be slower than the earthquake cycle.

Cliff retreat rates calculated using the timing of rock fall events and estimated thickness of rock removed in each event range between 0.14 m ky^− 1 and 2 m ky^− 1. When only full cycles are considered, we derive a more realistic range of 0.4 m ky^− 1 to 0.7 m ky^− 1. These rates are an order of magnitude faster than the calculated rate of surface lowering in the area. We conclude that sandstone cliffs at Timna retreat through episodic rock fall events that preserve the sharp, imposing, landscape characteristic to this region and that ongoing weathering of the cliff faces is minor.

A 10%–20% difference in the ¹⁰Be concentrations in samples from matching boulder and cliff faces that have identical exposure histories and are located only a few meters apart indicates that cosmogenic nuclide production rates are sensitive to shielding and vary spatially over short distances. However, uncertainties associated with age calculations yielded boulder and matching cliff face ages that are similar within 1 σ . The use of external constraints in the form of field relations and OSL dating helped to establish each pair's age. The agreement between calculated ¹⁴C and ¹⁰Be ages indicates that the accumulation of ¹⁰Be at depth by the capture of slow deep-penetrating muons was properly accounted for in the study.     

Surface ruptures induced by the devastating 1068 AD earthquake in the southern Arava valley, Dead Sea Rift, Israel

The Elat fault (a segment of the Dead Sea Transform) runs along the southern Arava valley (part of the Dead Sea Rift, Israel) forming a complex fault zone that displays a time-dependent seismic behaviour. Paleoseismic evidence shows that this fault zone has generated at least 15 earthquakes of magnitude larger than M 6 during the late Pleistocene and the Holocene. However, at present the Elat fault is one of the quietest segments of the Dead Sea Transform, lacking even microsesimicity. The last event detected in the southern Arava valley occurred in the Avrona playa and was strong enough to have deformed the playa and to change it from a closed basin with internal drainage into an open basin draining to the south.Paleoseismological, geophysical and archaeological evidences indicate that this event was the historical devastating earthquake, which occurred in 1068 AD in the eastern Mediterranean region. According to the present study this event was strong enough to rupture the surface, reactivate at least two fault branches of the Elat fault and vertically displace the surface and an early Islamic irrigation system by at least 1 m. In addition, the playa area was uplifted between 2.5 and 3 m along the eastern part of the Elat fault shear zone. Such values are compatible with an earthquake magnitude ranging between M 6.6 and 7. Since the average recurrence interval of strong earthquakes during the Holocene along the Elat fault is about 1.2 ± 0.3 ky and the last earthquake occurred more about 1000 years ago, the possibility of a very strong earthquake in this area in the future should be seriously considered in assessing seismic hazards.     

Complex exposure histories of chert clasts in the late Pleistocene shorelines of Lake Lisan,southern Israel

Activities of ²⁶Al and ¹⁰Be in five chert clasts sampled from two beach ridges of late Pleistocene Lake Lisan, precursor of the Dead Sea in southern Israel, indicate low rates of chert bedrock erosion and complex exposure, burial, and by inference, transport histories. The chert clasts were derived from the Senonian Mishash Formation, a chert‐bearing chalk, which is widely exposed in the Nahal Zin drainage basin, the drainage system that supplied most of the material to the beach ridges. Simple exposure ages, assuming only exposure at the beach ridge sampling sites, range from 35 to 354 ky; using the ratio ²⁶Al/¹⁰Be, total clast histories range from 0·46 to 4·3 My, unrelated to the clasts' current position and exposure period on the late Pleistocene beach ridges, 160–177 m below sea level. Optically stimulated luminescence dating of fine sediments from the same and nearby beach ridges yielded ages of 20·0 ± 1·4 ka and 36·1 ± 3·3 ka. These ages are supported by the degree of soil development on the beach ridges and correspond well with previously determined ages of Lake Lisan, which suggest that the lake reached its highest stand around 27 000 cal. years BP . If the clasts were exposed only once and than buried beyond the range of significant cosmogenic nuclide production, then the minimum initial exposure and the total burial times before delivery to the beach ridge are in the ranges 50–1300 ky and 390–3130 ky respectively. Alternatively, the initial cosmogenic dosing could have occurred during steady erosion of the source bedrock. Back calculating such rates of rock erosion suggests values between 0·4 and 12 m My^?1. The relatively long burial periods indicate extended sediment storage as colluvium on slopes and/or as alluvial deposits in river terraces. Some clasts may have been stored for long periods in abandoned Pliocene and early Pleistocene routes of Nahal Zin to the Mediterranean before being transported again back into the Nahal Zin drainage system and washed on to the shores of Lake Lisan during the late Pleistocene. Copyright © 2003 John Wiley & Sons, Ltd.     

Electron spin resonance dating of burned flint from Kebara Cave,Israel

Electron spin resonance (ESR) measurements of heated flint from Kebara cave show the presence of two radiation sensitive signals: E' and Al. Both are strongly interfered with by organic signals produced during heating of the flint. The signal subtraction method of Porat and Schwarcz (1991) was used to determine equivalent doses for flint samples from levels VII-XII, for which thermoluminescence (TL) ages on the same samples are known. Ages were determined using dose rates based on analyses of the flint and TLD measurements of external dose rates. The average E' age of 48.5 ± 5.1 ka is much less than the average TL age (62.2 ± 4.3 ka), whereas the average age of 64.6 ± 12 ka given by the Al signal is in good agreement with the TL age, but with much larger dispersion. © 1994 John Wiley & Sons, Inc.     

The geoid in southeastern Brazil and adjacent regions: new constraints on density distribution and thermal state of the lithosphere

Least-squares collocation technique was used to process regional gravity data of the SE South American lithospheric plate in order to map intermediate (10–2000 km) wavelength geoid anomalies. The area between 35–10° S and 60–25° W includes the Paraná CFB Province, the Southern São Francisco Craton and its marginal fold/thrust belts, the Brazilian continental margin and oceanic basins. The main features in the geoid anomaly map are: (a) Paraná CFB Province is characterized by a 1000 km long and 500 km wide, NE-trending, 9 m-amplitude negative anomaly which correlates with the distribution of sediments and basalts within the Paraná basin. (b) A circular (600–800 km in diameter) positive, 8 m-amplitude geoid anomaly is located in the southern S. Francisco craton and extends into the northeastern border of the Paraná CFB Province. This anomaly partially correlates with Alto Paranaíba Igneous Province (APIP), where alkalic volcanism and tholeiitic dikes of ages younger than 80 Ma are found and where a low-velocity zone in the mantle has been mapped using seismic tomography. This positive geoid anomaly extends towards the continental margin at latitude 21° S and joins a linear sequence of short wavelength positive geoid anomalies associated with Vitoria–Trindade seamounts. (c) A NE-trending, 1000 km long and 800 km wide, 4 m-amplitude, positive geoid anomaly, which is located along the southeastern coast of Brazil, from latitude 24 to 35° S. The northern part of this anomaly correlates with the Ponta Grossa Arch and Florianopolis dyke swarm provinces. The age of this intrusive volcanism is 130–120 Ma. (d) A circular positive anomaly with 9 m of amplitude, located over the Rio Grande and Uruguay shields and offshore Pelotas basin. Few alkaline intrusives with ages between 65 and 80 Ma are found in the region and apatite fission track ages in basement rocks indicates cooling at around 30 Ma. A semi-quantitative analysis of the observed geoid anomalies using isostatic considerations suggests that the mechanism which generated Paraná CFB Province did not change, in a significant manner, the lithospheric thermal structure, since the same geoid pattern observed within this province continues northward over the Neoproterozoic fold/thrust belts systems separating the São Francisco and Amazon cratons. Therefore, this observation favours Anderson’s idea of rapid basaltic outpouring through a pull-apart mechanism along a major suture zone. A thermal component may still be present in the Southern São Francisco Craton and in the Rio Grande Shield and contiguous continental margins, sites of Tertiary thermal and magmatic reactivations.     

Charting the territory: Exploring stakeholder reactions to the prospect of seafloor exploration and mining in Australia

Geological surveys of Australia’s marine territory have revealed significant potential for development of a marine resource industry. As onshore mineral deposits become harder to find, less accessible to their market and more challenging to extract, seafloor exploration and mining becomes an economically viable option. However, evidence from industry and environmental literature suggests that social acceptance will be important in determining the future of this industry in Australia. This paper reports on findings from research investigating the social viability of seafloor mining in Australia. A combination of interviews and focus groups were used to explore industry and community reactions to the possible development of seafloor mining in Australia. Although stakeholders’ reactions were variable, the majority of the participants were reluctant to see development of seafloor mining in Australia, primarily because of concerns about the industry’s potential environmental impact. All stakeholders sought further information about the benefits and costs associated with the industry suggesting that they did not yet have a fixed attitude towards the industry. Stakeholders favoured a precautionary approach towards the industry, supported by rigorous scientific analysis of the potential environmental impacts, transparent and socially responsive management processes and meaningful engagement with stakeholders.     

From mass‐wasting to slope stabilization – putting constrains on a tectonically induced transition in slope erosion mode: a case study in the Judea Hills,Israel

Calcrete‐coated remnants of landslide debris and alluvial deposits are exposed along the presently stable hillslopes of the Soreq drainage, Judea Hills, Israel. These remnants indicate that a transition from landslide‐dominated terrain to dissolution‐controlled hillslope erosion had occurred. This transition possibly occurred due to the significant decrease in tectonic uplift during the late Cenozoic. The study area is characterized by sub‐humid Mediterranean climate. The drainage hillslopes are typically mantled by thick calcrete crusts overlying Upper Cretaceous marine carbonate rocks. Using TT‐OSL dating of aeolian quartz grains incorporated in the calcrete which cements an ancient landslide deposit, we conclude that incision of ~100 m occurred from 1056 ± 262 to 688 ± 86 ka due to ~0·3° westward tilt of the region; such incision invoked high frequency of landslide activity in the drainage. The ages of a younger landslide remnant, alluvial terrace, and alluvial fan, all situated only a few meters above the present level of the active streambed, range between 688 ± 86 ka and 244 ± 25 ka and indicate that since 688 ± 86 the Soreq base level had stabilized and that landslide activity decreased significantly by the middle Pleistocene. Copyright © 2012 John Wiley & Sons, Ltd.