New insights into the late Middle Stone Age occupation of Oued el Akarit, southern Tunisia

This article reports on a new project to investigate the activities of early Homo sapiens in the area of the Chotts ‘megalake’ in southern Tunisia. Excavations in 2015 and 2019 at Oued el Akarit revealed one of a number of Middle Stone Age (MSA) horizons near the top of a long sequence of Upper Pleistocene deposits. The site identified as Oued el Akarit (Sondage 8) consists of lithic artefacts, bone fragments of large ungulates and pieces of ostrich eggshell. Many of the objects are burnt. Excavation of about nine square metres revealed that these were associated with a lightly trampled and combusted occupation surface. Amongst the identified artefacts were Levallois flakes some of which could be refitted, thereby indicating the generally undisturbed nature of the occupation. The lithic finds also included side scrapers and other tools diagnostic of the MSA but significantly no bifacial or tanged tools. OSL (Optically Stimulated Luminescence) dating of the sediments and AMS (Accelerator Mass Spectrometry) radiocarbon dating of ostrich eggshell have produced uncalibrated age determinations in the range 37,000–40,000 years ago, one of the youngest ages for MSA sites in the region. This is the first example of a securely dated later MSA occupation in a riparian environment in south-eastern Tunisia.

Paleoseismological Findings at a New Trench Indicate the 1714 M8.1 Earthquake Ruptured the Main Frontal Thrust Over all the Bhutan Himalaya

The 1714 Bhutan earthquake was one of the largest in the Himalaya in the last millennium. We show that the surface rupture caused by this earthquake extended further to the east than previously known, it was at least 175 km long, with slip exceeding 11 m at our study site. The age of the surface rupture was constrained by a combination of radiocarbon and traditional optically stimulated luminescence dating of affected river sediments. Computations using empirical scaling relationships, fitting historical observations and paleoseismic data, yielded a plausible magnitude of Mw 8.1 ± 0.4 and placed the hypocentre of the 1714 Bhutan earthquake on the flat segment of the Main Himalayan Thrust (MHT), the basal décollement of the Himalayan orogen. Calculations of Coulomb stress transfer indicate that great earthquakes along the leading part of the MHT would cause surface rupture. In contrast, distal earthquakes may not immediately trigger surface rupture, although they would increase the stresses in the leading part of the MHT, facilitating future surface-rupturing earthquakes. Frontal earthquakes would also transfer stress into the modern foreland basin facilitating southward propagation of the MHT as a blind basal décollement. In conclusion, studies of surface-rupturing events alone likely underestimate the seismic slip along the Himalayan megathrust.

Blowout Morphometrics and Mass Balances

The Gonghe Basin on the Qinghai-Tibet Plateau has a cold, arid climate and has suffered severe land degradation. Climate change as well as anthropogenic activities including overgrazing have resulted in widespread blowout development and the formation of some of Earth’s largest blowouts. The blowouts are part of an aeolian dominated landscape that passes from deflation zone to grass covered plain, and then through blowouts of increasing size and complexity to transverse barchanoid dunes that are migrating into the valley of the Yellow River. A combination of structure-from-motion (SfM) optical drone mapping, ground-penetrating radar (GPR) and soil pits are used to investigate blowout scour hollows and depositional lobes. Comparisons of the volumes of sediment removed from the scour hollows with the volumes of sediment deposited within adjacent lobes varies between sites. The lobe volume is invariably less than the volume of the scour hollow. This can, in part, be attributed to aeolian reworking of the lobe, distributing sand further downwind and uplifting of dust. However, much of the difference in volumes between the scour and lobe can be attributed to the measurement technique, particularly where GPR was employed to calculate lobe volumes. The wavelength of the GPR limits its ability to resolve thin layers of sand resulting in an underestimate of the deposited sand at the margins of a lobe where the sand thickness is equal to, or less than, the wavelength of the GPR. For thin sand layers, beneath the resolution of the GPR, soil pits suggest a closer match between the volume of sand eroded from the scour and the volume of the lobe, albeit with large measurement uncertainty. We put forth two hypotheses to explain the spatio-temporal evolution of the blowout dune field. The downwind increase in blowout dune size could either reflect a downwind propagation of aeolian instability; or it could result from an upwind propagation of the instability, which started at the highest points in the landscape and has subsequently migrated in a northwesterly direction, towards lower elevations. Recent optically stimulated luminescence dating appear to support the latter hypothesis.

Late-Holocene landscape evolution of a delta from the foredune ridges: Seyhan Delta, the Eastern Mediterranean, Turkey

The Çukurova Delta Complex, formed by the Seyhan, Ceyhan, and Berdan rivers, is the second-largest delta system in the Mediterranean. The delta complex is a major depocenter that contains sediments transported from the Taurus Mountain belt since the Miocene. Studies on the Quaternary landscape evolution of the Çukurova Delta Complex are scarce, and in particular, the Holocene evolution of the Seyhan Delta section of the Çukurova Delta Complex has been poorly understood. Sedimentological analysis, high-resolution digital elevation models derived using structure from motion, and optically stimulated luminescence dating of the foredune ridges in the Seyhan Delta help define the lesser-known nature of Late-Holocene paleoenvironmental and landscape evolution of the Seyhan section of the Çukurova Delta Complex. The foredune ridges provide evidence that the Akyatan Lagoon, one of Turkey’s largest lagoon, formed at the beginning of the last millennium. The ridges bordering the north and south of Tuzla Lagoon show that the lagoon completed its formation between the 11th and 14th centuries when the ancient delta was to the east. The Seyhan River flowed 10 km east from its current course until at least the 16th Century, and its ancient delta was active until that time. After the 16th Century, the Seyhan River shifted to its current course in the west and began to build the modern delta and the youngest foredune ridges were formed by a combination of aeolian and littoral processes. The contemporary delta continued to prograde until the construction of the Seyhan Dam in AD 1956. Since the construction of the Seyhan Dam, the delta shoreline at the river mouth retreated drastically and foredune formation stopped. In the past few decades, most of the foredune ridges have been eroded away by coastal processes and agricultural activities.

Age of sediments on Danube terraces of the Pest Plain (Hungary) based on optically stimulated luminescence dating of quartz and feldspar

The numerical ages available for the sediments on the Danube terraces in the Pest Plain are scarce. In this study, we present quartz OSL and K feldspar post-IR IRSL290 ages for the sandy fluvial, aeolian and slope sediments collected from Danube terraces IIb, III and V.The feldspar post-IR IRSL290 ages without residual dose subtraction are older than the quartz OSL ages, except for one sample, but the two sets of ages are overlapping within one or two sigma errors.In the bleaching experiment under natural sunlight during summer, an unbleachable component ranging from 2.5±0.7 Gy to 5.2±0.3 Gy after 30 h exposure to bright sunshine is observed and it corresponds to 3−8% of the measured K feldspar post-IR IRSL290 equivalent doses. These facts indicate that residual dose subtraction would be necessary before age calculation, in most cases.The saturated fluvial gravelly sand of terrace V of the Danube is older than ~ 296 ka based on feldspar post-IR IRSL290 measurements. This age does not contradict the traditional terrace chronology and the earlier published age data of this terrace. The other studied sediments on the surface of the terraces V, III and IIb deposited much later than the formation of these terraces. They infer aeolian activity and fluvial sedimentation of small streams during the MIS 3 and MIS 2 periods. The age of the dated dune sands with coeval aeolian sediments in Hungary indicate the cold and dry periods with strong wind activity of the Late Weichselian.