Pleistocene Holocene Research Articles

ПОЗДНЕМИОЦЕН-ПЛИОЦЕНОВАЯ ТРАНСФОРМНАЯ ОКРАИНА КАМЧАТКИ

Testing of the geochemical compositions of the Late Cenozoic volcanites of Kamchatka on new discriminant diagrams confirmed the idea of the existence of different geodynamic regimes at this time. It is shown that the Late Miocene (~6 Ma)-Pliocene volcanites of Eastern Kamchatka and the Central Kamchatka Depression, as well as the Late Pliocene (~3.5 Ma)-Holocene alkaline, calcareous-alkaline, and adakite volcanites of the central part of the Middle Ridge are similar to the volcanites of the transform margins of the Pacific type. At the same time, the Miocene–Holocene volcanites of Southern Kamchatka, the Miocene-Early Pliocene volcanites of the Middle Ridge, and the Pleistocene–Holocene volcanites of Eastern Kamchatka are similar to the volcanites of the convergent margins. In the central part of Kamchatka (from the coast to the Middle Ridge), at the end of the Miocene-Pliocene, during the collision of the Kronotsky terrane of the island arc and the slip of the Pacific plate, magmatic complexes typical of the transform margin were formed in this area. The geochemistry of the transform margin volcanites is due to the upwelling of the subslab asthenosphere both into the collision zone and into the zone of the volcanic arc of the Middle Ridge, after the rupture and subsequent separation of the Komandor-Kronotsky microplate slab.

Weathering and paleoprecipitation indices in a Late Pleistocene–Holocene loess–paleosol sequence in central Argentina

A Late Pleistocene–Holocene loess–paleosol sequence in central Argentina was studied to obtain a weathering insight and to probe geochemical tools as paleoclimatic proxies. Three paleosols and a buried soil interlayered with loess mantles compose Corralito I sequence (32°00′7″ S, 64°11′08″ W, 469 m a.s.l). Several weathering indices (CIA, CIA-K, and LWI) and elemental ratios (∑Bases/Al2O3, Rb/Sr, CaO/TiO2, Na2O/TiO2) were calculated. An incipient weathering degree throughout the sequence was detected, denoting that the parent material (i.e., loess mantles) has not been substantially modified by pedogenesis. Although a statistically significant correlation between magnetic susceptibility and several weathering indices was identified, the weathering intensity was not strong enough to produce a decrease in the magnetic signal of the paleosols, which is, in part, inherited from the detrital fraction. Paleoprecipitation indices, calculated using geochemical data, suggest slightly wetter conditions during paleosol formation when compared to loess. Paleosols were formed during humid conditions (paleosols II and II during MIS 5e, and paleosol I during MIS 3) with sedimentation pause and soil development, whereas loess layers were deposited during more arid conditions.

Late Pleistocene-Holocene sedimentary evolution in the coastal zone of the Red River Delta

The Red River Delta is considered one of the largest megadelta systems in Asia. The formation of this delta has been controlled by the continent-ocean interaction and sea-level fluctuation during the Cenozoic. In this study, we present a new sequence stratigraphic framework of the Red River Delta based on borehole lithofacies analysis and high resolution seismic data. The Late Pleistocene–Holocene sediments in the coastal zone of the Red River Delta were subdivided into three systems tracts: (1) the lowstand systems tract (LST) is characterized by a Late Pleistocene alluvial silty sand facies complex (arLSTQ13b); (2) the transgressive systems tract (TST) is illustrated by the coastal marsh facies complex and the lagoonal greenish-gray clay facies of Early-Middle Holocene (amt, mtTSTQ21−2); and (3) the highstand systems tract (HST) is composed of the Middle-Late Holocene deltaic clayish silt facies complex (amhHSTQ22−3). The boundaries between these three systems tracts are not isochronous, namely: (1) The LST-HST boundary has been associated with the Würm 2 Glaciation, which occurred at ~40-18 Ka.; (2) The TST-LST boundary is identified by a transgressive erosion surface, whose age ranges from ~12-5 Ka.; and (3) the HST-TST boundary is an unconformity between the submarine deltaic facies complex and the Middle Holocene marine flooding plain.

Upper Pleistocene and Holocene stratigraphy in the Kola Peninsula and Northern Karelia (N–W Russia): Marine and glacial units

Data on litho- and biostratigraphy of major sedimentary sequences and their geochronological records were compiled and summarized to describe the Late Pleistocene–Holocene marine and glacial events in the Kola-Northern Karelia region. In the coastal Kola Peninsula and its inner part, three marine units and two glacial events were identified in the Upper Pleistocene sequences. The first marine unit (Ponoi Beds in the regional stratigraphy) can be definitely referred to the significant Late Pleistocene transgression known as the Boreal in northern Eurasia. Data on the Kola Peninsula show that the warm-water Boreal transgression was longer than the Eemian one in western Europe, comprising at least MIS 5e-d (from 130–120 to 105–100 ka BP) in the White Sea depression and MIS 5e-c (earlier at least 90 ka BP) in the Barents Sea. Forested environments dominated on the Kola Peninsula at that time. The second Interglacial marine unit (Strelna Beds) attributed to the subsequent Belomorian transgression was deposited in relatively cold settings at the final phase of the Mikulinian Interglacial (MIS 5), about 100 to 70–80 ka BP. Adjacent areas were covered with open forest and tundra. The third marine unit referred to the Interstadial Leningrad Group was formed 60–40 ka BP in rather a cold marine reservoir, when the environmental conditions were more severe than now. The Late Pleistocene glacial events are correlated to the Podporozhie and Ostashkov Groups (MIS 4 and 2). The Podporozhian glacial unit seems to be associated with the Barents-Kara Ice Sheet and its melting caused the glacioeustatic transgression in the White Sea during the Leningradian Substage (MIS 3).During the Late Glacial and Holocene, a periglacial freshwater lake, brackish-water basin and marine reservoir successively appeared in the White Sea depression successively. Two marine events are suggested here based on the key sedimentary sequences from the coastal isolated lake, i.e. the Late Glacial transgression and the early-middle Holocene (Tapes) transgression.

The distribution of the guanaco (Lama guanicoe) in Patagonia during Late Pleistocene–Holocene and its importance for prehistoric human diet

The great importance of the guanaco ( Lama guanicoe) for the subsistence of the human populations of Patagonia during the Holocene has been demonstrated in numerous studies. This species is considered as the main prey of the hunter-gatherer groups of the Patagonian interior, indicating the existence of a strong ecological relationship of predator-prey type. Despite the importance of this ungulate for prehistoric human populations, its spatial distribution throughout the Holocene has not been systematically explored, assuming that it was ubiquitously distributed in almost all of Patagonia. In this work, the spatial distribution of the guanaco in Patagonia during different periods of the final Pleistocene and Holocene is explored using zooarchaeological and paleontological evidence together with species distribution models and paleoclimatic reconstructions. Likewise, the spatial variation in the importance of this species for the diet of human populations is assessed. The results show that there were large differences in the distribution of guanaco in Patagonia over time. In general terms, this camelid suffered a constant contraction in range since the Late Pleistocene period to the present. There is an Andean range and peri-cordilleran core of population distribution that remains observable during all this time. Human subsistence was strongly influenced by this pattern of distribution. The differences in the guanaco distribution described in this work are important not only for archaeological and paleontological problems, but also for the current conservation of guanacos.

Palaeoenvironmental conditions of the Palaeolithic–Neolithic transition in the Fergana Valley (Central Asia) – New data inferred from fossil mollusсs in Obishir-V rockshelter (Kyrgyzstan)

In the Fergana Valley and the surrounding territories, the number of archaeological sites increased during the Early Holocene. The coincidence of this cultural event, represented by the Obishirian archaeological unit with the onset of the Holocene, suggests that this growing intensity of human activity was driven by climate change, in particular warming and/or wetting. To test this hypothesis, we used fossil terrestrial molluscs from Obishir-V, the eponymic Obishirian site in southern Kyrgyzstan, as a proxy of palaeoenvironmental conditions. We studied pre-Obishirian loess-like deposits from the final Pleistocene and the Early–Middle Holocene sequence of Obishirian-bearing deposits. We analysed taxonomic composition of the mollusc assemblages and used it to infer palaeoecological characteristics, namely preferences in temperature and humidity as well as in differing habitats. Our results showed that the palaeolandscapes and the vegetation during the accumulation of the studied deposits remained almost unchanged. The mollusc assemblages reveal constant dry and warm climatic conditions and stable steppe-like vegetation. Our observations of rather stable climatic conditions in the Fergana Valley during the Pleistocene–Holocene turnover suggests that climate was only a minor driver of the rapid demographic change in Central Asia during those times. Some other factors beyond the changes of humidity must have played an important role. On the basis of our data derived from fossil mollusc assemblages at Obishir-V, we propose to consider the hypothesis that the factor responsible for the intense human occupation of the Fergana Valley during the Early Holocene had not an environmental, but rather a cultural background, such as the neolithization process, such as introduction of domestic livestock.

A woman hunter in the early Andes

Archaeology The ethnographic record of modern hunter-gatherers indicates that men were the primary, almost exclusive, hunters of big game. However, to what extent this pattern existed in prehistory has been challenged on both empirical and theoretical grounds. To examine this question, Haas et al. studied the artifacts recovered from a burial of a young woman at a site on the Andean Altiplano dated to more than 8000 years ago. Found with her was a tool kit used in animal processing and numerous projectile points, strongly indicating that she hunted. Additional examples of female hunters at late Pleistocene and early Holocene sites in the Americas were also identified, findings that support a model of relatively undifferentiated subsistence labor among early populations in the Americas. Sci. Adv. 10.1126/sciadv.abd0310 (2020).

The use of iron chemical analysis of podzols to date the Late Pleistocene–Holocene deglaciation history of the Central Italian Alps

ABSTRACTPodzols that have developed on glacial and periglacial features provide the opportunity to reconstruct glacial evolution after the Last Glacial Maximum (LGM) using different soil indices. Analysing 17 soils classified as podzol, we used the crystallinity ratio of free iron oxides (CRF) on both the A and Bs horizons, and absolute ages for the same landforms containing the soil profile, to create dating curves. Two equations were generated: age = 4566.9 × ln (CRF) + 1760 (1), and age = 3907 × ln (CRF) + 3508.2 (2). The reliability of the curves was evaluated with the Feo/Fed ratio, and with the difference of ages calculated using both equations. Equation (2) is considered more reliable because the A horizon may be influenced by new pedogenesis on the pre‐existing podzol, leading to the development of a new type of soil. By dating the soils, we reconstructed the glacial history of the three main upper branches of the LGM Adda Glacier in the Central Italian Alps, specifically the Stelvio Pass area (ST), Gavia Pass area (GV), and the Val Viola valley (VV). Seven glacial advances were identified at 16.7–14.7 ka (phase I), 12.3 ka (phase II), 11 ka (phase III), 10–9.7 ka (phase IV), 9 ka (phase V), 7.5 ka (phase VI) and 5.3 ka (phase VII). The first five phases are chronologically similar to the main Late Pleistocene–Early Holocene phases recorded in the Central European Alps. The last two Holocene phases, which are both longer in duration than the Little Ice Age, are recorded in ST and GV. Interestingly, these phases generally are not recorded in the rest of the Central European Alps, where the late Holocene glaciers were smaller than their present size.

Sequence modeling in zircon double-dating of early Holocene Mt. Erciyes domes (Central Anatolia)

Abstract Mt. Erciyes (3917 m), the highest stratovolcano in Central Anatolia, Turkey, is considered active based on three recently dated early Holocene dome eruptions that were also correlated with tephras in the Mediterranean and the Black Sea. Despite the demonstrated Holocene activity of Mt. Erciyes, the eruptive chronostratigraphy of these events and their hazard potential for the nearby Kayseri metropolitan area (population ~1.4 million) remain poorly constrained. Here, we apply zircon double-dating (ZDD) based on (U–Th)/He thermochronology and U–Th–Pb crystallization ages, where intra-grain crystallization age differences were used for disequilibrium correction. Individual ZDD ages were refined via sequence modeling to reconstruct the eruption timing of four early Holocene domes peripheral to Mt. Erciyes. Sequence modeling, which incorporated petrological, volcanological, and stratigraphic constraints, yielded the following eruption ages (uncertainties stated at 1σ): 8.8 ± 0.8 ka for stratigraphically directly superimposed Perikartin and Karagullu, 8.9 ± 0.5 ka for Dikkartin, and 9.4 ± 1.3 ka for previously undated Yilanli Dag, located within the perimeter of Kayseri. A model where all four early Holocene domes are assumed to have erupted simultaneously suggests an age of 8.9 ± 0.4 ka. Earlier eruptive phases of Mt. Erciyes were identified by ZDD at ca. 85–88 ka (fall-out deposits and Carik Tepe lava) and at ca. 105 ka (xenoliths from two peripheral scoria cones). Zircon crystallization ages reveal protracted magmatic activity beneath Mt. Erciyes since ca. 800 ka, in agreement with dated volcanic activity, and preceding magmatic phases at ca. 2–3 Ma that included the eruption of the widespread Valibaba Tepe Ignimbrite with a U–Pb zircon age of 2.73 ± 0.02 Ma. A volume estimate for the Quaternary edifice of ~300 km3 translates into an integrated long-term eruptive magma flux of ~0.4 km3/ka for post-collisional Mt. Erciyes, within uncertainty of the Late Pleistocene–Holocene flux estimate of >0.1 km3/ka based on dome volumes and eruption ages. The near-synchronous eruptions of a suite of four evolved domes, in three cases with sizable early explosive venting, calls for a hazard assessment that combines the impact of multiple simultaneous eruptions.

Climate Signals in the Late Quaternary Bottom Sediments of Lake Baunt (Northern Transbaikalia)

Abstract —The bottom sediments of lakes with different mineralization located in the basins of inland areas are high-resolution archives of climate and environmental changes. We present results of study of the Late Pleistocene–Holocene sediments of freshwater Lake Baunt, one of the lakes of the Baunt (Tsipa) depression in the permafrost zone in northern Buryatia. The sediments were studied by XRD, IR spectroscopy, laser granulometry, elemental analysis, AMS dating, etc. Mineral analysis of the bottom sediments with an age of ~18 ka has revealed predominant phyllosilicates, quartz, and feldspars. Mathematical modeling of complex XRD spectra made it possible to identify chlorite, muscovite, illite, mixed-layer illite–smectite and chlorite–smectite, and kaolinite among the phyllosilicates. We have determined their structural and crystal-chemical features and quantitative proportions in the section (800 cm long core), which vary in accordance with the climate cycles and lake level fluctuations. The results obtained helped to reconstruct the evolution of the Lake Baunt basin controlled by the regional climate throughout the Late Pleistocene–Holocene. This paper continues a series of our publications concerned with the reconstruction of the Late Pleistocene–Holocene climate in East Siberia by comprehensive studies of the mineral composition of sedimentary sections of small lakes.

Специфика пространственно-временной организации островных геосистем в плейстоцене–голоцене

На основе эволюции обстановок осадконакопления проанализирована специфика обособления природно-территориальных комплексов (ПТК) низкого топологического ранга в условиях островной суши и роль литогенной основы как главного фактора дифференциации территории на фоне влияния других ландшафтообразующих процессов. Информация о состоянии ПТК и факторах, обусловливающих их динамику в хроноинтервале несколько сотен–тысяч лет, заключена в разрезах рыхлых отложений и может быть получена только палеогеографическими методами. Определена роль литогенной основы в пределах разновозрастных ПТК и ее влияние на особенности развития других природных компонентов. На основе ретроспективного анализа показаны возрастные различия ландшафтов разных типологических уровней. Выявлено, что с увеличением ранга ПТК увеличивается степень гетерохронности и их возраст по сравнению с возрастом составляющих их геокомплексов более низкого ранга. На островах эта закономерность проявляется еще ярче, поскольку они находятся в зоне взаимодействия суши и океана, где очень активны геоморфологические процессы, связанные с климатическими изменениями и колебаниями уровня моря, а также эти территории характеризуются высокой степенью проявления азональных факторов. Изменение литогенной основы в ходе климатических осцилляций вызывало перестройку в первую очередь гидрологического режима и биотических компонентов. Зависимость биотических компонентов от изменения режима увлажнения особенно наглядно проявляется в ландшафтных сменах в пределах болотных массивов, развитие которых во многом контролировалось уровнем грунтовых вод. Неравномерный характер проявления катастрофических процессов на изученных островах определил их разное ландшафтообразующее значение на протяжении плейстоцена–голоцена. We analyze the evolution of sedimentary environments for the specific isolated geocomplexes of a low topological rank on the islands and the role of the lithogenic base (relief, parent rocks and deposits) as the factor in differentiation of the area against the background of the influence of other landscape-forming processes. The information on the geocomplex genesis and the factors determining their dynamics in the chrono-interval of several hundreds to thousands years was recorded in sections of loose deposits and can only be obtained by paleogeographic methods. The role of the lithogenic base within the framework of different age geocomplexes and its influence on the features of the development of other natural components are analyzed. A retrospective analysis allows us to determine the age-related differences of landscapes of different typological levels within the studied islands. It was revealed that with an increase in the grade of geocomplexes, their age increases compared to the age of the lower rank geocomplexes constituting them and the degree of heterochronism. On the islands, this pattern appears even brighter, since they are in the zone of interaction between land and ocean, where geomorphological processes associated with climatic changes and sea level fluctuations were very active, as well as these territories are characterized by a high degree of manifestation of azonal factors. A change in the lithogenic basis during climatic oscillations caused a restructuring of the components and, first of all, the hydrological regime and biotic components. The dependence of the biotic components of the landscape on changes in the moisture regime is especially evident in landscape shifts within the peatlands, the development of which was largely controlled by the level of groundwater. The uneven nature of the manifestation of catastrophic processes on the studied islands determined their different landscape-forming significance during the Pleistocene-Holocene.

Late Pleistocene–Holocene environmental and climatic history of a freshwater paramo ecosystem in the northern Andes

ABSTRACTThis study presents the first multi‐proxy palaeoenvironmental and palaeoclimatic history for northern South America based on the palaeolimnological reconstruction of a pond located in a dry paramo at 3570 masl. During the Last Glacial Maximum (LGM), the study area was under glacial conditions, then during global events Heinrich Stadial 1 (HS1), Bølling–Allerød (BA), and the Younger Dryas (YD), the pond expanded, accumulation rates and proxies for erosion reached the highest values, indicative of humid conditions, with maxima in humidity during the BA and YD. Dry conditions and pond desiccation occurred in the Greenlandian–Northgrippian and by 6010 cal a bp the area was transformed into the mire of today. Comparisons with records from other sites in South America indicate that changes in humidity are most likely controlled by the Intertropical Convergence Zone, mainly during the glacial and postglacial, and by changes in the Pacific Ocean, more pronounced after the YD.

Faces in the Stone: Further Finds of Anthropomorphic Engravings Suggest a Discrete Artistic Tradition Flourished in Timor-Leste in the Terminal Pleistocene

Engraving sites are rare in mainland and Island Southeast Asia (ISEA) where painted art dominates the prehistoric artistic record. Here we report two new engraving sites from the Tutuala region of Timor-Leste comprising mostly humanoid forms carved into speleothem columns in rock-shelters. Engraved face motifs have previously been reported from Lene Hara Cave in this same region, and one was dated to the Pleistocene–Holocene transition using the Uranium–Thorium method. We discuss the engravings in relation to changes in technology and material culture that took place in the terminal Pleistocene and early Holocene archaeological records in this region of Timor as well as neighbouring islands. We suggest that the engravings may have been produced as markers of territorial and social identity within the context of population expansion and greater inter-group contacts at this time.

Impact of Pleistocene–Holocene climate shifts on vegetation and fire dynamics and its implications for Prearchaic humans in the central Great Basin, USA

ABSTRACTThe effects of climate change during the Terminal Pleistocene–Early Holocene transition on ecosystems and early Prearchaic hunter‐gatherers in the central Great Basin of North America are not well understood. We present a palynological reconstruction of regional vegetation and fire history in Grass Valley, central Nevada, from ~14 to ~7.5k cal a BP showing that Pinus‐dominated woodlands were replaced by dry‐adapted steppe and desert vegetation accompanied by an increase in regional fire activity at the beginning of the Holocene, in response to summer warming and a drying climate. Following a severe drought period peaking ~10.2–9.3k cal a BP, Pinus woodlands partially recovered contemporaneously with the 8.2k cal a BP climate anomaly. Local wetlands provided important resource patches for human foraging societies, and periodic declines of wetlands in response to changing local hydrological conditions may have necessitated adjustments in subsistence and settlement practices and technology.

The upper limb skeleton and behavioral lateralization of modern humans from Zhaoguo Cave, southwestern China.

Aims of the study are to initially describe and comparatively evaluate the morphology of the new Zhaoguo M1 upper limb remains, and contextualize upper limb functional adaptations among those of other worldwide Upper Paleolithic (UP) humans to make inferences about subsistence-related activity patterns in southwestern China at the Pleistocene-Holocene boundary. The preserved Zhaoguo M1 skeletal remains include paired humeri, ulnae, and radii, among others. These specimens were scanned using micro-computed tomography to evaluate internal structural properties, while external osteometric dimensions of the Zhaoguo M1 upper limb elements also were acquired. Both sets of measurements were compared to published data on Neandertals, and Middle and Upper Paleolithic modern humans. The upper limb elements of Zhaoguo M1 display a suite of characteristics that generally resemble those of other contemporary Late UP (LUP) modern humans, while robusticity indices generally fall within the upper range of LUP variation. The Zhaoguo M1 upper limb elements display fewer traits resembling those of late archaic humans. The Zhaoguo M1 individual exhibits diaphyseal asymmetry in several upper limb elements suggesting left hand dominance. When evaluating the full range of magnitudes of humeral bilateral asymmetry in the comparative sample, Zhaoguo M1 falls at the lower end overall, but yet is relatively higher than contemporary LUP modern humans specifically from East Eurasia. The Zhaoguo M1 individual suggests typical LUP modern human upper limb morphology persisted in southwest China until the end of the last glacial period. Upper limb bone asymmetry of Zhaoguo M1 also indicates that behavioral activities attributed to a hunter-gatherer tradition apparently extended through the Pleistocene-Holocene transition in this region.

Origin, extinction and ancient DNA of a new fossil insular viper: molecular clues of overseas immigration

Abstract Viperinae is a subfamily of viperid snakes whose fossil record in the Mediterranean islands is, until now, restricted to 12 palaeontological deposits on seven islands. Revision of the material excavated 30 years ago from the Middle/Late Pleistocene–Holocene deposit of Es Pouàs [Eivissa (= Ibiza), Balearic Islands, western Mediterranean] revealed about 6000 bones of a small-sized viper across different stratigraphic levels. Its morphological characteristics are different enough to known species of Vipera to warrant the description of a new species, but the nearly complete mitochondrial genome obtained from this snake based on a sample dated to 16 130 ± 45 bp, suggested it belonged to a new insular population of Lataste’s viper (Vipera latastei), Vipera latastei ebusitana subsp. nov. Phylogenetic analysis indicates that the dispersal of the ancestors of V. l. ebusitana to Eivissa, most probably from a north-east Iberian population, occurred via overwater colonization < 1.5 Mya, well after the Messinian Salinity Crisis (5.97–5.32 Mya) when land bridges allowed terrestrial colonization of the Balearic Islands by mainland faunas. The morphological differences between V. l. ebusitana and the Iberian populations suggest that it is a new dwarf taxon resulting from insular evolutionary processes, becoming extinct shortly after the first human arrival to this island about 4000 years ago.

Water Provenance at the Old River Bed Inland Delta and Ground Water Flow from the Sevier Basin of Central Utah during the Pleistocene-Holocene Transition

AbstractTo ascertain the provenance of water reaching wetlands in an area sustaining a population of Pleistocene–Holocene foragers, 87-strontium/86-strontium isotopic ratios (87Sr/86Sr) of mollusks from channels of the Old River Bed inland delta of central Utah were measured. Potential provenances examined included overflow from Pleistocene–Holocene Lake Gunnison, ground water flow from the Sevier basin, ground water discharge from piedmont aquifers infiltrated by Lake Bonneville, and ground waters from local regional aquifers. Old River Bed inland delta channels active from ~13.2 cal ka BP until ~11.2 cal ka BP have87Sr/86Sr values of 0.70930–0.71049 that are consistent with water sourced from Lake Gunnison in the Sevier basin. Inland delta channels active from ~11.2 cal ka BP until shortly after ~9.3 cal ka BP have87Sr/86Sr values of 0.70977–0.71033, suggesting ground water flowed from the Sevier basin during the early Holocene. Ratios of87Sr/86Sr did not match known values for Lake Bonneville, but the youngest Old River Bed inland delta channel system has an87Sr/86Sr ratio consistent with a local ground water source, perhaps Government Creek. Consistent ground water discharge may explain the persistence of foragers in the region despite the increasingly arid climate of the Great Basin.

Time‐Invariant Late Quaternary Slip Rates Along the Agua Blanca Fault, Northern Baja California, Mexico

AbstractFault slip rates inform models of strain accumulation and release, which over geologic time may vary or remain constant depending on factors like structural complexity, fault strength, deformation rates, and proximity to other faults. In this study, we present a Late Pleistocene–Holocene slip history based on four new geologic slip rates for the Agua Blanca Fault (ABF), which transfers Pacific‐North American dextral plate boundary motion across the Peninsular Ranges of northern Baja California. Time‐averaged slip rates from three sites are 2.8 + 0.8/−0.6 mm/a since ~65.1 ka, 3.0 + 1.4/−0.8 mm/a since ~21.8 ka, 3.2 + 1.0/−0.6 mm/a since ~12.5 ka, and 3.5 + 5.1/−2.0 mm/a since ~1.4 ka; however, the actual slip rate may be closer to 4 mm/a when off‐fault slip and age interpretation uncertainties are considered. Significantly, although the ABF has more in common in terms of length, net offset, and slip rate with known variable slip rate faults, the most straightforward age and offset interpretations for the ABF suggest constant slip rates over ~10 kyr time scales. As with other constant slip rate faults, comparable neighboring faults that might modulate the ABF slip rate are absent, suggesting that fault interaction, or lack thereof, may be a more significant factor controlling fault behavior on this and potentially other faults. The new rates indicate that the ABF accommodates at least half of total slip across the Peninsular Ranges, clarifying strain partitioning for seismic forecasting models that previously lacked modern geologic slip rate constraints for this domain of the plate boundary.

The archaeology of submerged prehistoric sites on the North Pacific Coast of North America

We review the history of underwater archaeological investigations of submerged prehistoric remains on the North Pacific Coast of North America, divided into three phases: Phase 1 (1960s–1981) – hypotheses and “wet-site archaeology”; Phase 2 (1981–1994) – operationalized scuba explorations of submerged anchor stone accumulations and the Montague Harbour Underwater Archaeology Project; and Phase 3 (1995–present) – refined modeling of regional sea beds for areas of high archaeological potential on submerged relict shorelines with limited testing and identification of late Pleistocene and early Holocene archaeological deposits on near-shore intertidal and interior upland strandlines. The latter part of Phase 3 also saw the potential for submerged prehistoric cultural resources integrated into consideration of development project assessments. Finally, the Coastal Migration Route for early migration to the Americas shifted from a peripheral proposition to a central complimentary paradigm. These multiple streams of theory, modeling, and pragmatic effort are poised to converge in a new era of practical underwater archaeological research on the North Pacific Coast.

Tectonics of the Asela‐Langano Margin, Main Ethiopian Rift (East Africa)

AbstractWe provide insights into the tectonics of the Asela‐Langano margin, at the eastern boundary of the central Main Ethiopian Rift, East Africa, by combining field structural data, remote sensing, analysis of the distribution of faults, new dating of faulted material, and analysis of seismicity. The area is characterized by the occurrence of two fault sets: boundary and axial (Wonji) faults, oriented NE‐SW and NNE‐SSW, respectively. Boundary faults show a complex arrangement in the lake Langano area where they display a rhomboidal pattern, due to the presence of NW‐SE‐trending structures, likely related to preexisting transverse fabrics (the so‐called Langano Rhomboidal Fault System). Overall, our analysis supports a structure of the margin characterized by a monocline affected by a series of minor horsts and grabens; this confirms a marked asymmetry of the central Main Ethiopian Rift, with a master fault system on the opposite, western margin. Cumulative paleostress analysis indicates an overall N115°E extension across the Asela‐Langano margin; however, a local variation of the extension direction from axial (Wonji) faults (∼N90°E) to the boundary faults (∼N115°E) can be observed, pointing to a stress reorientation at rift margins. New 14C dating of faulted material and seismicity analysis indicate Late Pleistocene–Holocene and current activity on several normal faults affecting the margin. This suggests that extensional deformation in the central Main Ethiopian Rift is accommodated at the rift margins, with subordinate activity on axial faults, supporting that this rift sector reflects an intermediate stage of rift evolution.