Terminal Pleistocene change in mammal communities in southeastern Washington State,USA

Small mammal communities in western North America experienced declines in taxonomic richness across the late Pleistocene to Holocene transition (PHT), a recent natural global warming event. One community also experienced a decline in evenness and others replaced one species with a congener. Variability in response of small mammal communities to PHT warming is apparent. At the presently arid and xeric Marmes site in the Columbia Basin of southeastern Washington State, megafauna were absent by about 13,000 cal yr BP, evenness of small mammals declined about 11,700 cal yr BP and again about 11,400 cal yr BP whereas richness declined about 11,400 cal BP. Regional faunal turnover was, however, minimal among small-bodied taxa. Local mammal communities are depauperate as a result of megafaunal extinctions and subsequent decreases in small-mammal richness and evenness. The latter chronologically corresponds with a decrease in primary productivity driven by increasing warmth and aridity. More faunas must be studied in order to fully document the range of variability in the responses of mammalian communities to PHT warming. Documentation of patterns in those responses will facilitate understanding and enhance predictive accuracy with respect to responses of mammalian communities to modern global warming.     

Within-taxon morphological diversity in late-Quaternary Neotoma as a paleoenvironmental indicator, Bonneville Basin, Northwestern Utah, USA

Ecological data indicate that as the amount of precipitation in an arid areas increases, so too does mammalian taxonomic richness. This correspondence has been found in two late-Quaternary mammalian faunas from Utah, one from Homestead Cave in the Bonneville Basin. We use the remains of two species of woodrat (Neotoma cinerea and Neotoma lepida) from Homestead Cave to test the hypothesis that as the amount of precipitation in an arid area increases, so too does morphological diversity within individual mammalian taxa. Morphological diversity is measured as corrected coefficients of variation and as richness of size classes of mandibular alveolar lengths. Coefficients of variation for N. cinerea are few and coincide with moisture history if temporally successive small samples are lumped together. More abundant coefficients of variation for N. lepida coincide only loosely with moisture history, likely because such coefficients measure dispersion but not necessarily other aspects of variation. Richness of size classes of N. lepida is high during the early and late Holocene when moisture was high, and lowest during the middle Holocene when climate was most arid.     

Biodiversity,taxonomic richness and specialists-generalists during Late Pleistocene/Early Holocene times in Pampa and Patagonia (Argentina,Southern South America)

Human subsistence systems in the Pampa and Patagonia regions evolved from generalists during the Late Pleistocene/Early Holocene to specialists during the Middle Holocene, according to diversity and relative taxonomic richness counts. The general hypothesis is summarized as follows: 1) at the end of the Pleistocene and beginning of the Holocene (interval between 13.0 and 8.5 ka), the Pampean and Patagonian landscape was different from the present one, with a mammal biodiversity larger than in the Middle Holocene; 2) during the Middle Holocene, the highest mammal taxonomic richness corresponds to one species, Lama guanicoe. Although available biomass was the same for the hunter-gatherers, it was due to the larger abundance of individuals of that single species; 3) the emerged continental surface during the Late Pleistocene/Early Holocene was more extensive than during the Middle Holocene. In ecological terms, this greater land mass is reflected in an equally larger biodiversity, even assuming that populations of Pleistocenic megafauna were diminishing in number since ca. 13,500 years BP.Based on the analysis of our own information and published data, we state that the human groups which colonized the Pampean and Patagonian regions towards the end of the Pleistocene and beginning of the Holocene used generalist strategies encompassing a wide range of faunal resources (birds and mammals, especially of terrestrial habitats). Plasticity of hunter-gatherer societies, plus a complex technology, a higher social mobility and unfilled territories, allowed them to rapidly replace one resource for another in conditions of environmental stress. This lifestyle resulted in the occupation of different ecological zones (niches) and the evolution to specialized systems, based on one or a few mammal species, once the colonization and support in the different environments were successful and the resources of the Late Pleistocene/Early Holocene disappeared.     

Late Pleistocene and Holocene small- and large-mammal faunas from the Northern Urals

Data from the mammal fauna of the North Urals during the Late Pleistocene and Holocene are synthesised. Analysis of differentiation the degree of small- and large-mammal faunas during this time has been undertaken. Only differences of mammal species composition were significant between the Late Pleistocene and Holocene complexes, and within these complexes, the distinction between faunas was insignificant. The transition from the Late Pleistocene to the Holocene complex small-mammal faunas occurred in the Middle Late Valdai due to expansion of the forest species. In large-mammal faunas, the process was recorded later (in Dryas 3-Early Holocene) because of the extinction of some species and others that changed their areas of occupation.     

Late Quaternary stratigraphy and geochronology of the western Killpecker Dunes, Wyoming, USA

New stratigraphic and geochronologic data from the Killpecker Dunes in southwestern Wyoming facilitate a more precise understanding of the dune field’s history. Prior investigations suggested that evidence for late Pleistocene eolian activity in the dune field was lacking. However, luminescence ages from eolian sand of ∼15,000 yr, as well as Folsom (12,950-11,950 cal yr B.P.) and Agate Basin (12,600-10,700 cal yr) artifacts overlying eolian sand, indicate the dune field existed at least during the latest Pleistocene, with initial eolian sedimentation probably occurring under a dry periglacial climate. The period between ∼13,000 and 8900 cal yr B.P. was characterized by relatively slow eolian sedimentation concomitant with soil formation. Erosion occurred between ∼8182 and 6600 cal yr B.P. on the upwind region of the dune field, followed by relative stability and soil formation between ∼5900 and 2700 cal yr B.P. The first of at least two latest Holocene episodes of eolian sedimentation occurred between ∼2000 and 1500 yr, followed by a brief (∼500 yr) episode of soil formation; a second episode of sedimentation, occurring by at least ∼700 yr, may coincide with a hypothesized Medieval warm period. Recent stabilization of the western Killpecker Dunes likely occurred during the Little Ice Age (∼350-100 yr B.P.). The eolian chronology of the western Killpecker Dunes correlates reasonably well with those of other major dune fields in the Wyoming Basin, suggesting that dune field reactivation resulted primarily due to departures toward aridity during the late Quaternary. Similar to dune fields on the central Great Plains, dune fields in the Wyoming Basin have been active under a periglacial climate during the late Pleistocene, as well as under near-modern conditions during the latest Holocene.     

Late Pleistocene and early Holocene rivers and wetlands in the Bonneville basin of western North America

Field investigations at Dugway Proving Ground in western Utah have produced new data on the chronology and human occupation of late Pleistocene and early Holocene lakes, rivers, and wetlands in the Lake Bonneville basin. We have classified paleo-river channels of these ages as “gravel channels” and “sand channels.” Gravel channels are straight to curved, digitate, and have abrupt bulbous ends. They are composed of fine gravel and coarse sand, and are topographically inverted (i.e., they stand higher than the surrounding mudflats). Sand channels are younger and sand filled, with well-developed meander-scroll morphology that is truncated by deflated mudflat surfaces. Gravel channels were formed by a river that originated as overflow from the Sevier basin along the Old River Bed during the late regressive phases of Lake Bonneville (after 12,500 and prior to 11,000 ¹⁴C yr B.P.). Dated samples from sand channels and associated fluvial overbank and wetland deposits range in age from 11,000 to 8800 ¹⁴C yr B.P., and are probably related to continued Sevier-basin overflow and to groundwater discharge. Paleoarchaic foragers occupied numerous sites on gravel-channel landforms and adjacent to sand channels in the extensive early Holocene wetland habitats. Reworking of tools and limited toolstone diversity is consistent with theoretical models suggesting Paleoarchaic foragers in the Old River Bed delta were less mobile than elsewhere in the Great Basin.     

Cenozoic Climates of the Great basin

The Great Basin in the western United States consists of almost level desert basins and alternating parallel mountain ranges. It has sparse, mostly interior, drainage and a few permanent lakes. The climate is arid and semiarid. Fairly large areas are true deserts. The main Cenozoic climatic changes have been: 1. a general cooling during the Tertiary and the early Pleistocene, 2. a progressive drying from the early Miocene into the Pleistocene as a consequence of rise of the Sierra Nevada and the Cascades, and 3. Pleistocene fluctuations between cold-moist and warm-dry ages.The Ice Age left known records of three or four major glaciations, the last of which had two maxima. The glaciations were relatively extensive on the eastern flank of the Sierra Nevada and just east of the Great Basin, and glaciers existed on several ranges in northeastern Nevada. Each glacial was accompanied by a pluvial, which culminated just after the glacial maximum. The pluvial lakes were largest on Lat. 40°. The histories of the huge lakes Bonneville and Lahontan are incompletely known. During the Mankato-Tioga-Provo'glacio-pluvial maximum the temperature in the Great Basin seems to have been only 2.5–3 C° lower, and the precipitation on the surface of Lake Lahontan (Dendritic Lake) twice as large as now.The Neothermal (Postglacial, Postpluvial), the equivalent of the interglacials, is with long-distance correlation in view subdivided on the basis of the major temperature changes into the Ana-,.Alti-, and Medithermal ages. However, in the dry country of the Great Basin the changes in moisture are more apparent and important. The Altithermal was distinctly drier than the present, and nearly all the basins went dry. About 2000 B.C. several basins began again to contain lakes which remained permanent through some acute brief droughts. These recentmodern lakes attained very moderate maxima some time before Christ, while the glaciers in the adjacent mountains probably reached their greatest extent since the Anathermal during the last centuries.     

Late Pleistocene highstand and recession of a small, high-altitude pluvial lake, Jakes Valley, central Great Basin, USA

Models of factors controlling late Pleistocene pluvial lake-level fluctuations in the Great Basin are evaluated by dating lake levels in Jakes Valley. “Jakes Lake” rose to a highstand at 13,870 ± 50 ¹⁴C Yr B.P., receded to a stillstand at 12,440 ± 50 ¹⁴C yr B.P., and receded steadily to desiccation thereafter. The Jakes Lake highstand is roughly coincident with highstands of lakes Bonneville, Lahontan and Russell. The rise to highstand and recession of Jakes Lake were most likely controlled by a storm track steered by the polar jet stream. The final stillstand of Jakes Lake helps constrain timing of northward retreat of the polar jet stream during the Pleistocene-Holocene transition.     

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

The 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.     

Holocene Moisture Variation Recorded by Aeolian Sand-Palaeosol Sequences of the Gonghe Basin, Northeastern Qinghai-Tibetan Plateau, China

The northeastern Qinghai-Tibetan Plateau(QTP) of China is located at the triple junction of the Asian winter and summer monsoons and the westerlies, where paleoclimatic evolution has an important scientific significance for recognizing the spatial-temporal pattern of Asian monsoons in the past and predicting environmental change in the future. Nevertheless, the framework of the Holocene moisture variation and related mechanisms remain controversial, owing to complex hydroclimatic conditions triggered by the landform of the large mountain-arid basin. Here, we employed geochemical proxies from typical aeolian sand-palaeosol sequences in the Gonghe Basin, northeastern QTP, together with Optically Stimulated Luminescence(OSL) dating, to reconstruct the pattern of effective moisture variation and associated mechanisms in this region. Our results indicate that the regional effective moisture was at its lowest until 9–8 ka, and approached a maximum during 8–4/3 ka of the middle Holocene. Afterwards, the climate became relatively dry in general, but with a transient humid interval around 2–1 ka. Our geochemical evidence indicates that the dry early Holocene probably can be attributed to a strong winter monsoon forced by remnant ice sheet, combined with the high evaporation caused by solar insolation. Also, shifts of humid-dry are closely linked to the Asian summer monsoonal strength and therefore the balance of evaporation-precipitation in the middle and late Holocene. Thus, the pattern of the Holocene effective moisture variation is characterized as the ‘monsoon model' in a closed intermontane arid and semi-arid basin near the western Asian monsoonal limit.     

Speleothem and glacier records of latest Pleistocene–early Holocene climate change in the western North American interior

Rapid and high-magnitude North Atlantic climate oscillations following the Last Glacial Maximum have been correlated to climate change events in western North America. However, the strength of teleconnections between the North Atlantic and the interior of western North America remains poorly understood. We present a U-series calibrated speleothem record from Timpanogos Cave National Monument, located at 2040 m asl in the Wasatch Mountains of Utah, spanning 13.5–10.6 ka. Additionally, we carried out a climate reconstruction for a coeval glacier advance in the Wind River Range of Wyoming. Our results indicate that between 13.5 and 12.8 ka, the Wasatch was probably first cool and dry and then warmed. After 12.8 ka, our record suggests cool and/or wetter conditions followed by reduced moisture until 11.8 ka, followed by an early Holocene wet period. The Timpanogos record exhibits few similarities with those from the North Atlantic. Climate reconstructions of the Titcomb Basin glacier suggest modest temperature depressions relative to modern (<−3 °C) were necessary to sustain the glacier with a moderate increase in precipitation (>150%). The high-altitude speleothem record presented here provides a valuable basis for understanding latest Pleistocene–early Holocene glacial episodes in western North America.     

Late Pleistocene and late Holocene lake highstands in the Pyramid Lake subbasin of Lake Lahontan, Nevada, USA

Shoreline geomorphology, shoreline stratigraphy, and radiocarbon dates of organic material incorporated in constructional beach ridges record large lakes during the late Pleistocene and late Holocene in the Pyramid Lake subbasin of Lake Lahontan, Nevada, USA. During the late Holocene, a transgression began at or after 3595 ± 35 ¹⁴C yr B.P. and continued, perhaps in pulses, through 2635 ± 40 ¹⁴C yr B.P., resulting in a lake as high as 1199 m. During the latest Pleistocene and overlapping with the earliest part of the Younger Dryas interval, a lake stood at approximately 1212 m at 10,820 ± 35 ¹⁴C yr B.P. and a geomorphically and stratigraphically distinct suite of constructional shorelines associated with this lake can be traced to 1230 m. These two lake highstands correspond to periods of elevated regional wetness in the western Basin and Range that are not clearly represented in existing northern Sierra Nevada climate proxy records.     

Loess record of the Pleistocene–Holocene transition on the northern and central Great Plains, USA

Various lines of evidence support conflicting interpretations of the timing, abruptness, and nature of climate change in the Great Plains during the Pleistocene–Holocene transition. Loess deposits and paleosols on both the central and northern Great Plains provide a valuable record that can help address these issues. A synthesis of new and previously reported optical and radiocarbon ages indicates that the Brady Soil, which marks the boundary between late Pleistocene Peoria Loess and Holocene Bignell Loess, began forming after a reduction in the rate of Peoria Loess accumulation that most likely occurred between 13.5 and 15 cal ka. Brady Soil formation spanned all or part of the Bølling-Allerød episode (approximately 14.7–12.9 cal ka) and all of the Younger Dryas episode (12.9–11.5 cal ka) and extended at least 1000 years beyond the end of the Younger Dryas. The Brady Soil was buried by Bignell Loess sedimentation beginning around 10.5–9 cal ka, and continuing episodically through the Holocene. Evidence for a brief increase in loess influx during the Younger Dryas is noteworthy but very limited. Most late Quaternary loess accumulation in the central Great Plains was nonglacigenic and was under relatively direct climatic control. Thus, Brady Soil formation records climatic conditions that minimized eolian activity and allowed effective pedogenesis, probably through relatively high effective moisture.Optical dating of loess in North Dakota supports correlation of the Leonard Paleosol on the northern Great Plains with the Brady Soil. Thick loess in North Dakota was primarily derived from the Missouri River floodplain; thus, its stratigraphy may in part reflect glacial influence on the Missouri River. Nonetheless, the persistence of minimal loess accumulation and soil formation until 10 cal ka at our North Dakota study site is best explained by a prolonged interval of high effective moisture correlative with the conditions that favored Brady Soil formation. Burial of both the Brady Soil and the Leonard Paleosol by renewed loess influx probably represents eolian system response that occurred when gradual change toward a drier climate eventually crossed the threshold for eolian activity. Overall, the loess–paleosol sequences of the central and northern Great Plains record a broad peak of high effective moisture across the late Pleistocene to Holocene boundary, rather than well-defined climatic episodes corresponding to the Bølling-Allerød and Younger Dryas episodes in the North Atlantic region.     

临夏盆地晚新生代哺乳动物群演替与青藏高原隆升背景

临夏盆地的晚新生代沉积中富含哺乳动物化石,以晚渐新世巨犀动物群、中中新世铲齿象动物群、晚中新世三趾马动物群和早更新世真马动物群的化石最为丰富。晚新生代是青藏高原快速隆升的时期,临夏盆地的4个主要哺乳动物群在构造剧烈变化的背景下发生了显著的更替。通过对不同动物群所代表的生态特征的分析,恢复了临夏盆地晚新生代以来的气候环境演变过程:晚渐新世以温暖湿润的森林环境为主,间杂有一些开阔地带;中中新世的森林更加茂密,水体更加丰富;晚中新世演变为炎热半干旱的稀树草原环境,季节性变化加强;早更新世气候寒冷而干燥,并伴有显著的海拔升高。青藏高原在晚渐新世的隆升幅度还不足以阻挡大型哺乳动物在高原南北的交流,但到中中新世已成为明显的障碍,至晚中新世对动物迁徙的阻碍作用更加突出,而临夏盆地在早更新世已经达到相当大的高度,产生了一个高原或高山的动物群     

Late Pleistocene and Early Holocene lake‐level fluctuations in the Lahontan Basin,Nevada: Implications for the distribution of archaeological sites

The Great Basin of the western U.S. contains a rich record of Late Pleistocene and Holocene lake‐level fluctuations as well as an extensive record of human occupation during the same time frame. We compare spatial‐temporal relationships between these records in the Lahontan basin to consider whether lake‐level fluctuations across the Pleistocene‐Holocene transition controlled distribution of archaeological sites. We use the reasonably well‐dated archaeological record from caves and rockshelters as well as results from new pedestrian surveys to investigate this problem. Although lake levels probably reached maximum elevations of about 1230–1235 m in the different subbasins of Lahontan during the Younger Dryas (YD) period, the duration that the lakes occupied the highest levels was brief. Paleoindian and Early Archaic archaeological sites are concentrated on somewhat lower and slightly younger shorelines (_1220–1225 m) that also date from the Younger Dryas period. This study suggests that Paleoindians often concentrated their activities adjacent to large lakes and wetland resources soon after they first entered the Great Basin. © 2008 Wiley Periodicals, Inc.     

Episodic Late Holocene dune movements on the sand-sheet area, Great Sand Dunes National Park and Preserve, San Luis Valley, Colorado, USA

The Great Sand Dunes National Park and Preserve (GSDNPP) in the San Luis Valley, Colorado, contains a variety of eolian landforms that reflect Holocene drought variability. The most spectacular is a dune mass banked against the Sangre de Cristo Mountains, which is fronted by an extensive sand sheet with stabilized parabolic dunes. Stratigraphic exposures of parabolic dunes and associated luminescence dating of quartz grains by single-aliquot regeneration (SAR) protocols indicate eolian deposition of unknown magnitude occurred ca. 1290-940, 715 ± 80, 320 ± 30, and 200-120 yr ago and in the 20th century. There are 11 drought intervals inferred from the tree-ring record in the past 1300 yr at GSDNPP potentially associated with dune movement, though only five eolian depositional events are currently recognized in the stratigraphic record. There is evidence for eolian transport associated with dune movement in the 13th century, which may coincide with the “Great Drought”, a 26-yr-long dry interval identified in the tree ring record, and associated with migration of Anasazi people from the Four Corners areas to wetter areas in southern New Mexico. This nascent chronology indicates that the transport of eolian sand across San Luis Valley was episodic in the late Holocene with appreciable dune migration in the 8th, 10-13th, and 19th centuries, which ultimately nourished the dune mass against the Sangre de Cristo Mountains.     

The relation of social evolution and dispersal in ungulates during the Pleistocene,with emphasis on the old world deer and the genus Bison

The evolution of Pleistocene mammals is characterized by giantism and in the ungulates by the appearance of huge and often bizarre horns, antlers, ossicones, and tusks. An earlier study of sheep (Ovis) led to a theory explaining these phenomena. This theory, termed the “dispersal theory,” is described briefly and then applied to the evolution of Old World deer (Cervinea, Baird, 1857). It is shown that the zoogeography and physical characteristics of Old World deer follow the predictions of this theory. Attention is drawn to the parallels in zoogeography and convergent evolutionary changes between Old World deer and other ungulates such as New World deer, the goats and sheep and the genus Bison. The application of the “dispersal theory” to the evolution of the genus Bison shows that it is compatible with known facts and that it explains aspects of Bison morphology not usually considered. It also suggested a new and testable hypothesis of the origin of present-day Bison. In general the “dispersal theory” applied to Pleistocene conditions predicts that a specialization of social behavior and social organs leading to giantism, altered body proportions and bizarre hornlike organs occurs during postglacial dispersal into new habitat. It also describes the characteristics of these early, pioneering populations. In so doing it links the disciplines of animal behavior, ecology, animal science, population dynamics, and zoogeography into a functional whole. In particular it shows the relationship between ecology and social behavior. Finally, the “dispersal theory” is shown to be a general theory, applicable to Pleistocene and pre-Pleistocene conditions. In the tropics or pre-Pleistocene conditions social evolution follows ecological specialization, while in the periglacial zones social evolution only reflects the colonization history of the species. It is shown that the “dispersal theory” unites the apparently contradictory views on evolution and zoogeography of Matthews and Darlington. Matthews' views apply largely to Pleistocene conditions and Darlington's to pre-Pleistocene conditions. A preliminary application of the “dispersal theory” to pre-Pleistocene mammals suggests that it predicts correctly.     

Human responses to Middle Holocene climate change on California's Channel Islands

High-resolution archaeological and paleoenvironmental records from California's Channel Islands provide a unique opportunity to examine potential relationships between climatically induced environmental changes and prehistoric human behavioral responses. Available climate records in western North America (7–3.8 ka) indicate a severe dry interval between 6.3 and 4.8 ka embedded within a generally warm and dry Middle Holocene. Very dry conditions in western North America between 6.3 and 4.8 ka correlate with cold to moderate sea-surface temperatures (SST) along the southern California Coast evident in Ocean Drilling Program (ODP) Core 893A/B (Santa Barbara Basin). An episode of inferred high marine productivity between 6.3 and 5.8 ka corresponds with the coldest estimated SSTs of the Middle Holocene, otherwise marked by warm/low productivity marine conditions (7.5–3.8 ka). The impact of this severe aridity on humans was different between the northern and southern Channel Islands, apparently related to degree of island isolation, size and productivity of islands relative to population, fresh water availability, and on-going social relationships between island and continental populations. Northern Channel Islanders seem to have been largely unaffected by this severe arid phase. In contrast, cultural changes on the southern Channel Islands were likely influenced by the climatically induced environmental changes. We suggest that productive marine conditions coupled with a dry terrestrial climate between 6.3 and 5.8 ka stimulated early village development and intensified fishing on the more remote southern islands. Contact with people on the adjacent southern California Coast increased during this time with increased participation in a down-the-line trade network extending into the western Great Basin and central Oregon. Genetic similarities between Middle Holocene burial populations on the southern Channel Islands and modern California Uto-Aztecan populations suggest Middle Holocene movement of people at this time from southern California desert environs westward to the southern islands, a migration perhaps stimulated by increased continental aridity.     

A framework of Holocene and Late Pleistocene environmental change in eastern Iran inferred from the dating of periods of alluvial fan abandonment,river terracing,and lake deposition

We review studies of the Holocene and Late Pleistocene stratigraphy of eastern Iran to infer past changes in the environment within this presently arid region. We build a scenario of widespread, and presumably climatically driven, evolution of the landscape through the Holocene. Six sites, covering a 10° range in latitude, indicate a regional abandonment of alluvial fan surfaces at ～10 ± 3 ka, with the younger (～9 ka) end of this age range supported by several of the best-constrained studies. Incision of rivers into the fan surfaces has occurred in discrete stages in the early to mid-Holocene (～9–7 ka) leading to the formation of flights of river terraces. Detailed records of lakebed deposition in the presently arid interior of Iran are rare, though the available data indicate lake highstand conditions at <7.8 ka at South Golbaf in SE Iran and at < 8.7 ± 1.1 ka at the Nimbluk plain in NE Iran. The major periods of Holocene landscape development hence correlate with a period of time where water was more abundant than at present, with incision of rivers into thick alluvial deposits possibly occurring due to a combination of decreased sediment supply and high levels of precipitation, and with the formation of inset river terraces possibly responding to century-scale fluctuations in precipitation. No major geomorphic changes are identified within the later part of the Holocene, from which we infer that increased aridity has slowed evolution of the landscape. A decrease in precipitation in the mid-Holocene may have had a detrimental effect on bronze age societies in eastern Iran as has been inferred elsewhere in the eastern Mediterranean region. The pre-Holocene environmental changes in eastern Iran are less well constrained, though there are suggestions of alluvial fan abandonment at 40–60 ka, at ～80 ka, and at ～120 ka.     

A review of Macoma balthica (L) as a stratigraphic marker in the Pleistocene sediments of the southern North Sea Basin

The first occurrence and presence of the bivalve Macoma balthica in the Pleistocene shallow marine sediments (Crags) of East Anglia has long been used to characterise the youngest “Weybourne” or “Wroxham” Crag Formation of Early to early Middle Pleistocene age. A review of recent work on the morphological variation and genetic lineages of living populations of the species and of work on fossil discoveries in East Greenland suggests that the current palaeontological species definition is too narrow, that the species arrived in the Atlantic about 2.4 Ma and much earlier than is envisaged from the studies of the North Sea Basin, and that there were several trans-Arctic migrations of the species during the Pleistocene. This paper reviews these findings and concludes that: (i) detailed morphometric analyses of fossil Macoma species from the Crag need to be undertaken and the species definitions comprehensively reviewed to take account of the morphological and genetic variation seen in modern populations; (ii) detailed morphometric analysis of modern M. balthica should be undertaken and tied to the different genetic lineages, and (iii) the current palaeontological definition of Macoma balthica should not be relied on as the basis for a First Appearance Datum (FAD) in the Southern North Sea basin.