In this paper we synthesise existing palaeoenvironmental data from the arid and semi-arid interior of the Australian continent for the period 40–0 ka. Moisture is the predominant variable controlling ...environmental change in the arid zone. Landscapes in this region respond more noticeably to changes in precipitation than to temperature. Depending on their location, arid zone records broadly respond to tropical monsoon-influenced climate regimes, the temperate latitude westerly systems, or a combination of both.
The timing and extent of relatively arid and humid phases vary across the continent, in particular between the westerly wind-controlled temperate latitudes, and the interior and north which are influenced by tropically sourced precipitation. Relatively humid phases in the Murray-Darling Basin on the semi-arid margins, which were characterised by large rivers most likely fed by snow melt, prevailed from 40 ka to the Last Glacial Maximum (LGM), and from the deglacial to the mid Holocene. By contrast, the Lake Eyre basin in central Australia remained relatively dry throughout the last 40 ka, with lake high stands at Lake Frome around 35–30 ka, and parts of the deglacial period and the mid-Holocene. The LGM was characterised by widespread relative aridity and colder conditions, as evidenced by extensive desert dune activity and dust transport, lake level fall, and reduced but episodic fluvial activity. The climate of the deglacial period was spatially divergent. The southern part of the continent experienced a brief humid phase around ∼17–15 ka, followed by increased dune activity around ∼14–10 ka. This contrasts with the post-LGM persistence of arid conditions in the north, associated with a lapsed monsoon and reflected in lake level lows and reduced fluvial activity, followed by intensification of the monsoon and increasingly effective precipitation from ∼14 ka. Palaeoenvironmental change during the Holocene was also spatially variable. The early to mid-Holocene was, however, generally characterised by moderately humid conditions, demonstrated by lake level rise, source-bordering dune activity, and speleothem growth, persisting at different times across the continent. Increasingly arid conditions developed into the late Holocene, particularly in the central arid zone.
► 40 ka of palaeoenvironmental change interpreted from Australian drylands. ► Arid zone responds to influence of tropical monsoon, temperate westerlies, or a combination of both. ► 40 ka to LGM experienced relative humidity on the semi-arid margins, but remained dry in the arid core. ► LGM characterised by widespread relative aridity and cooler conditions. ► Early-mid Holocene saw moderately humid conditions, followed by late Holocene intensified aridity.
Abstract
The Marine Isotope Stage (MIS) 2 is considered the coldest, driest and stormiest period during the last Glacial-Interglacial cycle in large parts of Eurasia. This resulted from strongly ...decreased northern hemisphere temperature and related maximum extension of northern ice sheets that strongly reinforced large-scale circulation modes such as westerlies and East Asian Winter Monsoon driven by the Siberian High. Normally, this intensified circulation is reflected by maximum loess deposition in numerous loess regions spanning Europe and Asia. However, here we present a new loess record from the Caucasus region in NE-Armenia providing evidence in support of heavily reduced or even lacking loess formation during the MIS-2. Owing to implementations of comprehensible luminescence dating work and a provenance survey using rock magnetic and geochemical data, we are able to define distinct loess formation phases and to retrace sediment transport pathways. By comparing our results to other Eurasian palaeo-records, we unveil general atmospheric circulation modes that are most likely responsible for loess formation in the Southern Caucasus. Moreover, we try to test different scenarios to explain lacking loess formation during MIS-2. In line with other archive information, we suggest that loess formation was hampered by higher regional moisture conditions caused by a southward-shift of westerlies and renewed moisture absorption over the Black Sea. Our results show that modifications of MIS-2 circulation modes induced a very heterogeneous moisture distribution, particularly in the lower mid-latitudes of Eurasia producing a juxtaposition of very dry (morphodynamically active) and moderately dry (morphodynamically stable) areas.
In the northern Alpine foreland, there was a shift at the transition from the Early Bronze Age (EBA, 2200–1600 BCE) to the Middle Bronze Age (MBA, 1600–1250 BCE). This shift was associated with a ...widespread abandonment of the pile-dwelling settlements around the pre-Alpine lakes and an expansion and intensification of low- and mid-altitude inland settlements. A research gap exists regarding the nature of MBA subsistence in these inland areas, which are considered unfavourable for agriculture.
We analysed multi-layered colluvial and alluvial deposits in the agriculturally unfavourable Western Allgäu region to gain insights into MBA subsistence farming. Phases of deposition were determined by optically stimulated luminescence (OSL) technique and AMS radiocarbon (14C) measurements of charcoal. They provide a chronostratigraphic framework that is correlated to the local archaeological record. Subsistence farming was reconstructed using land use proxies such as phytoliths, charcoal spectra, urease activity to microbial biomass carbon (Cmic) ratios, faecal biomarkers, polycyclic aromatic hydrocarbons (PAHs) and heavy metals.
The OSL and 14C ages indicate phases of deposition and land use during the MBA. They correlate with two recently excavated MBA inland settlements in the Western Allgäu. Human-induced vegetation change promoted open woodland comprising of Juniperus and Quercus at the expense of Abies and Fagus. The accumulation of charcoal and PAHs in MBA related colluvial horizons is most likely associated with the use of fire to maintain an open landscape. Partially increased urease activity to Cmic ratios and the appearance of Juniperus indicate the importance of livestock farming within the MBA subsistence.
Our results show that there was an extensive and diversified subsistence economy in the Western Allgäu during the MBA. They thus reflect an adaptation of MBA farmers to the harsher climatic conditions of the Western Allgäu, where crop yields were certainly less predictable than, for example, in regions near Lake Constance.
•The MBA period marks the onset of intensive colluviation in the Western Allgäu.•Land use proxies from sedimentary archives indicate MBA subsistence farming.•The predominant land use includes vegetation changes and silvopastoral practices.•MBA land use in agriculturally favourable and unfavourable areas was comparable.
The loess-palaeosol section Achajur is part of the Sevkar loess area in north-eastern Armenia and comprises three prominent pedocomplexes with intercalated loess units, probably spanning at least ...three glacial-interglacial cycles. With its central position between the Black Sea and the Caspian Sea, the Sevkar loess area serves as important bridge between loess sections in southeastern Europe and Central Asia. Establishing a numerical chronology of the Achajur loess section enables correlation with other loess-palaeosol sections and a palaeoenvironmental reconstruction of the region. In this paper, we focus on the chronology of the last glacial-interglacial cycle using luminescence dating on fine grain (4–11 µm) material. We compare two post-IR-IRSL protocols on polymineral fine grain using different stimulation temperatures, in order to evaluate the influence of fading and potential unbleachable residuals on our samples. For a backup of the younger ages (<50 ka), we also applied a single aliquot protocol on the quartz fine grain fraction. The results indicate that the upper loess unit was deposited during MIS3 and 4, while MIS2 ages are not present. The underlying pedocomplex and loess unit fall into MIS5 and MIS6, respectively. This confirms that the loess was deposited during dry phases and pedocomplexes formed during wetter phases, as is also shown by comparison with other palaeoenvironmental proxies from the area.
The loess section Krems-Wachtberg (Lower Austria) is well known for its Upper Palaeolithic find layer, which contains a double and a single infant burial. The layer containing the grave ...(archaeological horizon AH 4.4) was dated to 26,580 ± 160 14C BP (Einwögerer et al., 2006), corresponding to ca. 31 ka cal BP and is embedded in an 8 m thick loess sequence. In order to provide a chronostratigraphy of the entire section, 38 samples for luminescence dating were taken at high resolution from below and above the find layer. The samples were dated using the quartz coarse grain fraction, the quartz fine grain fraction and/or the polymineral fine grain fraction. The resulting ages are in correct chronostratigraphic order and, in case samples were measured with different protocols, agree within errors with each other and with the radiocarbon age of the find layer. The polymineral fine grain ages are systematically slightly lower than the quartz ages, although no fading could be detected in laboratory experiments. Loess deposition at the site commenced ca. 40 ka ago and reaches up to ca. 22 ka. The ages indicate nearly continuous loess sedimentation throughout this time span. Short breaks in sedimentation probably exist but cannot be resolved due to the uncertainties of luminescence ages.
Experimental results from ESR dose recovery tests using Ti-related absorption lines in sedimentary quartz will be presented and discussed. The tests were performed on two Late Pleistocene Australian ...dune sands with a known burial dose based on OSL measurements. The regenerative dose technique (after thermal annealing) was used to detect any differences between ESR estimates of the natural dose, and ESR estimates of an equal laboratory gamma-dose. The studied absorption lines show consistent results with regard to the laboratory dose, but inconsistencies regarding the recovery of the natural dose. Line-shape changes between the natural and artificially induced ESR signals are a matter of concern. These changes are probably the result of the different relative abundance of Ti–H and Ti–Li centres in the naturally irradiated and artificially irradiated sample.
During the penultimate glaciation vast areas of the Alps were glaciated, with piedmont glaciers protruding into the foreland. In the easternmost part of the northward draining valleys of the Alps, ...the glaciers did not reach the foreland, but formed valley glaciers confined by the mountainous terrain. This also applies to the Ybbs valley, where samples for luminescence dating out of glaciofluvial gravel accumulations were taken at three locations along the present day river course. In a highly dynamic depositional environment, such as a glacier-fed river system, incomplete resetting of the luminescence signal is possible, in particular when transport distances are short. In such cases, quartz usually is the preferred mineral over feldspar, especially if dose rates are low and may theoretically allow obtaining quartz ages beyond 150 ka. Because previous research has shown, and as corroborated within this study, quartz from the research area exhibits analytical problems in the high age range. Therefore luminescence properties of coarse grain (100–200 μm) quartz and in addition K-rich feldspar were investigated with the aim to reconstruct the chronology of the glacial processes within the Ybbs catchment area. Issues of incomplete bleaching were pIRIR225 encountered and addressed by comparing quartz OSL, fading corrected K feldspar IR50 and pIRIR225 to identify reliable ages. Depositional ages based on quartz OSL and feldspar pIRIR225 signals revealed deposition of ice marginal kame terraces and glaciofluvial foreland terraces during late to middle MIS 6. In combination with results from previous studies, we could reconstruct the valley evolution during the Riss glaciation. Newly gained luminescence ages of the deglaciation in the easternmost Alps coincide with OSL dated deglaciation events in the Western Alps, indicating that climatic change along the north side of the Alps happened simultaneously.
Archaeological surveys of the Negev Highlands show that the settlement history of this arid environment oscillated widely over time. This observation is almost entirely based on scant sherd ...assemblages from surveys, with only a few chronometric ages from one or two archaeological features at a given site. The reasons for the scarcity of chronometric ages include insufficient attention to radiocarbon dating in past research, low amounts of datable organic material for radiocarbon dating and issues related to low rate of site accumulation, and incomplete preservation of activity remains. In order to overcome these problems, we present here the results of a detailed chronometric radiocarbon and optically stimulated luminescence (OSL) dating study exploring the development of Negev archaeological sites in the third millennium BCE. The study included micromorphological analyses to aid identification of sedimentological and post-depositional processes at the studied sites. At Nahal Boqer 66, one of many small Negev third millennium BCE sites, seven radiocarbon ages were determined from archaeological contexts that suggest repeated discontinuous activity throughout the Early Bronze (EB) and early part of the Intermediate Bronze Age (IBA) (c. 3300–2350 BCE). At Ein Ziq – one of a few large sites in the region – seven samples were dated; they show a very short period of activity in the beginning of the IBA (c. 2450–2200 BCE). OSL age determinations at this site provided evidence for the rapidity of site burial by sediment accumulation. Also, OSL ages from secure depositional contexts – verified via micromorphology – are in agreement with those obtained by radiocarbon dating. Taken together, the results provide new systematic evidence for the timing of EB–IBA activity in the arid Negev Highlands.
•Combination of OSL, radiocarbon and micromorphology to clarify deposition and activity sequences in arid sites.•New chronometric ages (radiocarbon and OSL) from late 4th and early 3rd millennium BCE sites in the Negev Highlands.•Intermediate Bronze Age activity in the Negev Highlands restricted to 2450–2200 BCE.
PDF
