Late Quaternary History Research Articles

Late Quaternary history of the Kerch Strait — the stratotype region for the Black Sea

The Kerch Strait has periodically connected to the Black, Azov, and Caspian seas throughout its Late Quaternary history. The strait's deposits reflect the changes in the natural environment of the entire Ponto-Caspian region, which are a response to global climate change. Several studies have been done on the region's stratigraphy, biostratigraphy, geomorphology, and paleogeography. However, most of the current knowledge about the paleogeography of the area is based on the analysis of empirical data collected more than 25 years ago, and due to the lack of detailed geochronological studies, many palaeogeographical problems remain unresolved.This paper presents a reconstruction of environmental change in the Kerch Strait during the Late Quaternary. The reconstruction is based on the results of a comprehensive study of the sedimentary sequences in the Kerch Strait carried out by the author and colleagues over the past ten years. The study examines the deposits of two stratotype sections of the Karangatian (Eemian) transgression and the four boreholes’ sections in Tuzla Island in the central part of the strait.A biostratigraphic division of the Upper Quaternary deposits of the Kerch Strait was carried out based on a malacofaunal study. Mollusc assemblages corresponding to various paleogeographic stages of development were identified, and their paleoecological characteristics were described. Luminescence and radiocarbon ages made it possible to determine the time intervals of established paleogeographic stages in the strait's history. Detailed luminescence dating of the Karangatian transgression sediments of the Eltigen and Tuzla stratotype sections has been carried out for the first time.Six main stages in the Kerch Strait natural environment development were established in the Late Quaternary and correlated with global and regional climatic events: Karangatian, with three stages (MIS 5e-c); Tarkhankutian (MIS 5a); Post-Karangatian (MIS 4); Surozh (MIS 3); Neoeuxinian, with two stages (MIS 2); and Chernomorian (MIS 1). Two episodes of the Caspian waters flowing through the Kerch Strait into the Black Sea were identified in MIS 5c and at the end of MIS 2.

Historical Demography and Climate Driven Range Shifts in the Blue-spotted Salamander Under the Climate Change Scenarios

This study integrates phylogeography with distributional analysis to understand the demographic history and range dynamics of a limited dispersal capacity amphibian species, Blue-spotted Salamander (Ambystoma laterale), under several climate change scenarios. For this we used an ecological niche modeling approach, together with Bayesian based demographic analysis, to develop inferences regarding this species' demographic history and range dynamics. The current model output was mostly congruent with the present distribution of the Blue-spotted Salamander. However, under both the Last Interglacial and the Last Glacial Maximum bioclimatic conditions, the model predicted a substantially narrower distribution than the present. These predictions showed almost no suitable area in the current distribution range of the species during almost the last 22.000 y before present (ybp). The predictions indicated that the distribution of this species shifted from eastern coast of northern North America to the southern part of the current distribution range of the species. The Bayesian Skyline Plot analysis, which provided good resolution of the effective population size changes over the Blue-spotted Salamander history, was mostly congruent with ecological niche modeling predictions for this species. This study provides the first investigation of the Blue-spotted Salamander’s late-Quaternary history based on ecological niche modeling and Bayesian-based demographic analysis. In terms of the main result of this study, we found that the species' present genetic structure has been substantially affected by past climate changes, and this species has reached current distribution range almost from nothing since the Last Glacial Maximum.

Geomorphology and Late Quaternary evolution of Lake Manicouagan, a deep impounded impact crater-fjord-lake of the eastern Canadian Shield hinterland

A geophysical survey of Manicouagan Reservoir (51.5°N; 68.3°W) has been undertaken using high-resolution swath bathymetry and acoustic subbottom profiling to explore the flooded Lake Manicouagan, Manikuakan in the Innu language. The drowned lake is a 60-km long arc-shaped basin lying within the Manicouagan impact crater, the so-called ‘Eye of Québec’. This dataset unravels the geomorphology and the late Quaternary environmental history of one of the deepest lakes in North America, which reached a natural depth > 320 m prior to the impoundment (> 100 m below modern sea level). The swath bathymetry imaged subaqueous landforms attributed to terrestrial inputs (e.g., sediment waves on drowned deltas, submerged ravines, deep lateral channels, subaqueous fans), slope features (e.g., gullies, slide scars, compression ridges), and water-level changes (terraces). The morphosedimentary record of Lake Manicouagan has no equivalent in regional fjord-lake surveys. The morphosedimentary record documents the successive paleoenvironments since the northward retreat of the Laurentide Ice Sheet margin 7.5 ka ago. The Late Quaternary history deduced from the acoustic dataset shows a three-stage evolution: deglacial, paraglacial/postglacial, and anthropogenic after the construction of the Manic-5 dam and the filling of the associated reservoir by ~140 m of water during the 1960s. The deposition of asymmetrical laminated infills during the paraglacial/postglacial stage probably resulted from the deflection of turbidity currents by the steep and sinuous sidewalls inherited from the impact structure, possibly under the joint influence of the Coriolis and centrifugal forces. Long-distance seismic source and/or large amplitude water-level fluctuations, either natural or man-made, are two potential triggers for lake-wide record of mass-movements initiated under and above the submerged shores. The 3D imagery of the drowned lakeshore is a means to promote a cultural landscape and preserve the memory of a heritage site for the Pessamiulnuat, the Innu of Pessamit, who occupied the lakeshore prior to the impoundment.

Late Quaternary history of the Gumants catchment, Papua New Guinea

The Gumants River, rising on the eastern flank of the Mount Hagen stratovolcano, forms part of the headwater catchment of the Wahgi River in the central highlands of Papua New Guinea. The late Quaternary history of the catchment was shaped by a massive debris avalanche with an estimated volume >15 km3 that most likely occurred 400 ± 100 ka. The Upper Gumants River, which occupies about one-quarter of the 420 km2 catchment and underlain almost entirely by volcanic deposits including the avalanche, lahars and widespread airfall tephras that ceased falling ca 200 ka, once flowed directly to the Wahgi River through the Guga subcatchment rather than through the rest of the Gumants Basin. The Kuk Swamp part of the Guga catchment, intensively investigated for evidence of agriculture stretching back 10 ka, was added to the UNESCO World Heritage List in 2008. Nearly 40% of the 79 km2 of the Kugimi Basin is underlain by at least 30 m of swamp deposits with all but the uppermost few metres of the varied swamp and alluvial deposits beyond the range of radiocarbon dating. The Muga Basin forms nearly half of the Gumants catchment with about 50 km2 of swamp deposits and colluvial/alluvial sediments, which have been accumulating rapidly in the last few hundred years but are still underlain at a depth of a few metres by ancient sediments and, by inference, debris avalanche deposits that extend downvalley beyond the junction of the Gumants River with the Wahgi River. While there has been speculation for decades that the Wahgi River once flowed westward, it is now clear that the Gumants River has always flowed eastward, and it seems very likely that that is also true of the Wahgi River.

A complex insight into the Late Quaternary history of Bohemian-Moravian Highlands summit

Peat is an important archive allowing the reconstruction of past mire environments and surrounding vegetation. The Pihoviny site, one of the oldest peat deposits in the Bohemian-Moravian Highlands, was analysed for macrofossils and pollen and compared with other profiles in the region. The local mire development started in the Late Glacial as sedge-moss quaking fen with tundra elements characterised by high mineral richness and groundwater level. During the Early Holocene, it developed through the rich fen with hummocks, willow and reed stage to the waterlogged spruce forest, which persisted for thousands of years until the post-mediaeval deforestation. The recent mire vegetation developed 300 years ago due to human-induced deforestation. Further, we revealed high regional synchronicity among pollen profiles in the Early-Holocene (10,000–9000 cal BP), when open-canopy pine-birch forests transformed into closed-canopy deciduous forests due to climate improvement. Contrary, the Late-Holocene transformation to beech-fir forests was not synchronous, suggesting another driver than climate, likely human activities. Although pollen of both late-successional trees occurred since the Early Holocene, their expansion began much later, 5500–3500 (beech) and 3500–2500 cal BP (fir). Numerous spruce macrofossils suggest its pollen's local origin in the waterlogged spruce forest. Our results support the need for active management to sustain open mire vegetation and prevent spontaneous forest regrowth, recently boosted by climate warming. Palaeoecological analyses reconstructed a mosaic of waterlogged spruce and terrestrial beech-fir forests in the landscape, which should be restored to increase forest resistance against bark-beetle breakdowns and other disturbances in future.

Late Quaternary evolution of Daihai Lake in northern China and implications to the variation of the East Asian summer monsoon

Global warming over the past decades has resulted in desiccation of lakes in arid and semi-arid northern China. However, the mechanisms responsible for the sharp fluctuations in water levels for these lakes in this region are still unclear. The water level fluctuations in geological time can provide an analogue to better understand current lake levels’ response to global warming. In this study, a combination of quartz and feldspar luminescence dating techniques was applied to establish the chronologies of two sedimentary sequences related to lake level in the catchment of Daihai Lake, located on the fringe of the East Asian summer monsoon (EASM) domain. Our objective is to reconstruct the late Quaternary history of lake level fluctuations and provide the interpretations of their causes. The results indicate that two lake-level highstands existed during 130–120 ka and 8-4 ka, at least ∼38 m and 40 m above the current lake level, respectively. We interpret that the lake level variations on multiple timescales in the monsoonal marginal area have primarily been regulated by the EASM intensity and corresponding monsoonal precipitation, while temperature changes may have played a minor role. Moreover, a compilation of existing lake level data reveals that EASM intensity has a complex response to changes in Northern Hemisphere summer insolation on millennial-orbital timescales. Combining precipitation records in central and southern China, the character of rainfall across East Asia during MIS 5 exhibits a dominant tripolar pattern.

Late Quaternary history of Siberian stone pine as revealed by genetic and paleoecological data

Late Quaternary history of Siberian stone pine as revealed by genetic and paleoecological data

Quaternary Stratigraphy and Geomorphic History of the Flatwoods Region of Owen and Monroe Counties, Indiana

The Flatwoods region of Owen and Monroe Counties, Indiana is an archetype of late Quaternary history of the southern Midwest. We compile decades of field observations and sampling, including soil cores, a deep test hole, and hundreds of water well, seismic, and other data sources, to construct a detailed Quaternary stratigraphy and geomorphic history of the region, including a model of the preglacial bedrock topography. Optically stimulated luminescence (OSL) techniques provide the first numerical ages of the sediments and reveal the Illinois Episode glacier advanced into the region between 111-175 ka. Gray, calcareous Illinois Episode sediments dominate the valley fill, but highly weathered red glaciogenic sediments in the eastern part of the region may be related to a pre-Illinois Episode glacial event. Fine-grained stratified lake sediments indicate the southwestward draining bedrock valley was flooded as glacial ice entered the drainage basin. Sandy outwash covers the lake sediment marking the advance of glacier ice that ultimately crossed the basin and deposited till. Till is found in several ice-marginal ridges interpreted to be moraines marking the glacial limit. The Flatwoods valley routed water to the east end of the region where it spilled over one or more cols into Raccoon Creek, then continued toward the Ohio River in a glacial drainage system developed along the glacier margin. The Sangamon Geosol is a pervasive soil stratigraphic unit developed into Illinois Episode sediments, eroded only in modern stream valleys. The Geosol is well expressed morphologically, noted mostly by deep leaching of carbonates, red colors, and weathered mineralogy. Wisconsin Episode glaciation is represented by eolian sediments, including a thin increment of silty sediment incorporated into the upper solum of the Sangamon Geosol. Windblown Peoria Loess, deposited between ~27-16 ka, blankets the entire Flatwoods region, with greatest thicknesses preserved on flat lake or outwash plain landforms. Supplemental DataGeodatabase: The geodatabase includes locations of water-well records, borehole and outcrop sites, geophysical (gamma-ray) logs, refraction seismic surveys, passive seismic (horizontal-to-vertical spectral ratio [HVSR]) surveys, and data from the geological literature.Metadata: FGDC-compliant metadata for geodatabase.Data: Analytical data and other geological information include: a downhole geophysical (gamma-ray); data from the 2019 test hole, including clay mineralogy, core photographs, a downhole gamma-ray log, and particle size analysis; Indiana Geological and Water Survey (IGWS) archive data, which is comprised of borehole descriptions; a copy of Jacobs' (1994) Ph.D. dissertation; scanned profile description sheets and core stratigraphy from Jacobs (1994); and supplementary optically stimulated luminescence (OSL) data.ReadMe: Detailed file directory explaination of items within each of the supplemental data item ZIP files.

Testing the ‘Vineyard Geologic Identity’ concept in Marquette-producing vineyards in the Champlain Valley, Vermont, USA

ABSTRACT The recently formalized concept of ‘Vineyard Geological Identity’ (VGI) was applied to two vineyards in the Champlain Valley of Vermont, USA. The vineyards studied, LP and SV, both produce the hybrid grape known as ‘Marquette’, are at equivalent elevations, have a similar macroclimate, and were inundated by proglacial Lake Vermont during the last deglaciation. In contrast, the bedrock differs beneath the two sites, and SV was under shallow marine water immediately after Lake Vermont drained. The hypothesis tested was that despite their similar physical settings, the VGI of the two vineyards would vary as a result of differences in their late-Quaternary histories. Samples of soil and sediment were evaluated for grain size distribution, thermogravimetric analysis, mineralogy, major element chemistry, and standard soil fertility assessments, and a map of soil conductivity was made for each site. Results reveal that base cations and silt are significantly more abundant at LP. Conversely, at SV, Na is significantly more abundant, samples are coarser and soil conductivity is higher. These results illuminate the utility of VGI for defining the fingerprint of individual vineyards, and establish a physical foundation for future work evaluating the role of physical setting in controlling aspects of Marquette wines.

Range shift and loss of genetic diversity under climate change in the red-backed fairywren (Malurus melanocephalus), an Australian endemic bird species

AbstractClimatic variability is the most important force influencing the distribution dynamics of common and widespread species, with significant effects on their current biogeographical patterns. In this study, phylogeography was integrated with ecological niche modelling to understand the range dynamics of an Australian bird species, the red-backed fairywren (Malurus melanocephalus), under various climate change scenarios. Specifically, an ecological niche modelling approach with Bayesian-based phylogeographical analysis was used to develop robust inferences regarding the demographic history of the species. The predictions of the model were mostly consistent with the present distribution of the species. However, under the Last Interglacial bioclimatic conditions, the model predicted a significantly narrower distribution than today, indicating the existence of allopatric refugia. Predictions for the Last Glacial Maximum indicated that the species had a wider distribution, extending northwards. Additionally, predictions for the future (2050 and 2070) indicated that the species will probably have a narrower distribution than at present, which will be shifted eastwards. The extended Bayesian skyline plot analysis, which provides a robust analysis of fluctuations in the effective population size throughout the evolutionary history of a species, produced results highly consistent with the ecological niche modelling predictions for the red-backed fairywren. This is the first study to investigate the Late Quaternary history of an endemic avian taxon from Australia using ecological niche modelling and Bayesian-based demographic analysis.

Shedding light on the timing of the largest Late Quaternary transgression of the Caspian Sea

The Late Quaternary history of the Caspian Sea remains controversial. One of the major disagreements in this debate concerns the stratigraphic correlation of various deposits in the Caspian Basin. In this paper we identify and date, for the first time, the Enotaevka regression, lying between the two major phases of the largest Late Quaternary Caspian Sea transgression, the Khvalynian transgressive epoch, and provide a minimum estimate of sea level decrease during this regression. The River Volga is the major source of water to the Caspian; the Lower Volga region is unique in its record of palaeogeographic events, and this provides the opportunity to build a single stratigraphic and palaeogeographic history for the Pleistocene of Central Eurasia. Here we use luminescence to establish a new chronology for the largest Late Quaternary transgressive epoch of the Caspian Sea. The existing radiocarbon chronology does not allow the resolution of the two transgressive phases of this epoch (Early and Late Khvalynian). Based on clear palaeontological and geomorphological evidence, these must be very different in age, but shells associated with both transgressions gave very scattered ages of between 8 and 50 ka. This ambiguity has led to considerable discussion concerning the existence or otherwise of a deep Enotaevka regression phase between the two Khvalynian transgressions. Recently we have again identified these deposits at Kosika, on the right valley side of the Volga River. The new luminescence chronology described here, based on quartz OSL and K-feldspar pIRIR 290 ages, allows us to reconstruct the complicated history of Late Quaternary sedimentation in the southern part of the Lower Volga valley. The Kosika section reflects the following major stages: (1) the earlier Khazarian transgressive epoch; (2) a decrease in the sea level with the development of a freshwater lake/lagoon in the Volga valley; and (3) the Khvalynian transgressive-regressive epoch, including both the Early and Late Khvalynian transgressive periods, and the intercalated Enotaevka regression. Sea level during the early stage of the Khvalynian transgression reached Kosika at about 23–22 ka (approx. −1 to −2 m asl). This event is of the same age as the “grey clay” strata at the base of the Leninsk section marine unit (Kurbanov et al., 2021), also formed at the beginning of the Early Khvalynian transgression. Around 15–14 ka the Khvalynian basin moved to a regressive stage, and in the northern part of the Lower Volga the top part of the well-known ‘Chocolate Clay’ accumulated. In the southern part of the valley marine accumulation stopped at about 12–13 ka. This allows us to reconstruct a decrease in Early Khvalynian basin sea level between 15–14 ka and 13–12 ka ago, of about ∼15 m. At the Kosika section sediments derived from the Enotayevka regression are visible as a weakly developed palaeosol with evidence of surficial erosion, and these sediments are now dated to 13–12 ka. At 8.6 ± 0.5 ka, during the period of the Mangyshlak regression, aeolian deflation processes reworked sediments deposited by immediately preceding Late Khvalynian transgression.

Late quaternary alluvial history of the Brazos River in central Texas

The late Quaternary history of the bedrock-controlled Brazos River system in central Texas is poorly understood as to the complex interplay between bedrock and climate on episodes of channel incision and aggradation. Through geomorphic assessment, sediment core analysis, and luminescence dating (OSL) we map the alluvial terrace and floodplain deposits in the Steinbeck Bend study area in central Texas. Five stratigraphic (allostratigraphic) units were identified beneath four alluvial terrace-sediment complexes (T3-Unit I, T2a-Unit II, T2b-Unit III, T1a-Unit IV, T1b-Unit V) and the current floodplain (T0-Unit VI) of the Brazos River, with the accompanying OSL geochronology ranging from >60 to 0.3 ka. Channel incision appears to have occurred during the transition to cooler and wetter intervals at the beginning of MIS 4 and MIS 2. Alluvial deposition proceeded mainly during the latter stages of the warmer MIS 5 and during the first half of MIS 3, both characterized by a slight warming trend. The alluvial architecture of all units was formed by single story, mixed load meandering channels migrating laterally across Cretaceous marls. Upstream from the study area, the bedrock valley narrows because of the presence of more resistant limestones forming the bedrock channel floor and valley walls. In the Steinbeck Bend study area, the incised meanders develop into larger radius of curvatures as the Brazos River migrates across less resistant Cretaceous marls. Below the study area in the weakly consolidated Tertiary coastal plain deposits, the Brazos River becomes freely meandering, cutting laterally and vertically through previously deposited alluvium interceded by channel avulsions.

Mid- to Late-Quaternary Geomorphic and Paleoseismic Event History, Cheraw Fault, Southeastern Colorado

ABSTRACT Despite its subdued expression and isolated location within the Great Plains of southeastern Colorado, the 80 km long Cheraw fault may be one of the most active faults in North America east of the Rocky Mountains. We present geomorphic analyses, geochronology, and paleoseismic trenching data to (1) document the rupture history of the ∼45 km long southwestern section of the Cheraw fault over the past ∼19 ka, and (2) evaluate slip rate changes for the entire fault over the past ∼200 ka. Results from new trenches excavated at the Old Ranch site show evidence of four surface rupture events since ∼19 ka, each with an average vertical displacement of 0.75 ± 0.15 m. An additional event is likely only slightly older than ∼19 ka. Evidence for relatively small displacements at and near the Old Ranch site indicates that most of these earthquakes were magnitude (M) 7 or less and likely did not rupture the full length of the Cheraw fault. Since ∼19 ka, the average slip rate is ∼0.16 ± 0.3 mm/yr near the Old Ranch site with an average interevent time of 3–5 ka. New geochronologic data for mid- to late-Quaternary geomorphic surfaces cut by the Cheraw fault imply rapid incision by local Arkansas River tributaries from ∼145 to ∼100 ka. Maximum vertical offsets of 7–9 m for these surfaces indicate that from ∼19 to >200 ka the average slip rate was no greater than ∼0.03 mm/yr. The accelerated slip rate since ∼19 ka indicates a possible response to rapid erosional unloading and/or a limited late Cenozoic, <40 ka, paleoseismic history for the Cheraw fault.

Revised ΔR values for the Barents Sea and its archipelagos as a pre-requisite for accurate and robust marine-based 14C chronologies

The calibration of marine 14C dates requires the incorporation of regionally specific marine reservoir offsets known as ΔR, essential for accurate and meaningful inter-archive comparisons. Revised, regional ΔR (‘ΔRR’) values for the Barents Sea are presented for molluscs and cetaceans for the two latest iterations of the marine calibration curve, based on previously published pre-bomb live-collected and radiocarbon-dated samples (‘ΔRL’; molluscs: n = 16; cetaceans: n = 18). Molluscan ΔRR, determined for four broad regional oceanographic settings, are: western Svalbard (including Bjørnøya), −61 ± 37 14C yrs (Marine20), 94 ± 38 14C yrs (Marine13); Franz Josef Land, −277 ± 57 14C yrs (Marine20), −122 ± 38 14C yrs (Marine13); Novaya Zemlya, −156 ± 73 14C yrs (Marine20), 0 ± 76 14C yrs (Marine13); northern Norway, −86 ± 39 14C yrs (Marine20), 74 ± 24 14C yrs (Marine13). Molluscan ΔRR values are considered applicable to other marine carbonate materials (e.g., foraminifera, ostracods). Cetacean ΔRR are determined for toothed (n = 10) and baleen (n = 8) whales, and a combined toothed-baleen group (n = 18): toothed, −161 ± 41 14C yrs (Marine20), 1 ± 41 14C yrs (Marine13); baleen, −158 ± 43 14C yrs (Marine20), 8 ± 41 14C yrs (Marine13); combined baleen-toothed whales, −160 ± 41 14C yrs (Marine20), 4 ± 49 14C yrs (Marine13). Where identification and separation of baleen and toothed whales is impossible the combined ΔRR term may be used. However, we explicitly discourage the application of existing cetacean ΔRR terms to other marine mammals. Our new ΔRR values are applicable for as long as those broad oceanographic conditions (circulation and ventilation) have persisted, i.e., through the Holocene. We recommend using the latest iteration of the marine calibration curve, Marine20, which seems to better capture the time-variant nature of R compared to Marine13. More ΔRL datapoints for both molluscs and cetaceans would improve the accuracy and precision of ΔRR. In the meantime, our new ΔR terms facilitate the calibration of marine 14C dates across the region, paving the way for meaningful and accurate late Quaternary histories and inter-regional comparisons.

Interplay of Holocene surface faulting and climate in the Central Po Plain, Italy

AbstractUnderstanding the recent events marking the late Quaternary history of the Po Plain (N-Italy) is of overriding importance to decipher the record of depositional versus erosional phases, and their interplay with climatic, tectonic, and human forcing. We reconstructed the structural setting and chronostratigraphy of a Holocene succession crosscut by a thrust fault located south of Montodine (Cremona, Italy) within the Po Plain. The fault shows a maximum displacement up to one meter. Radiocarbon dating fixes a minimum age of 11.9 cal ka BP for the postglacial river entrenchment and constrains the fault movement age between 5.9 and 3.4 cal ka BP. Undeformed Late Medieval coarse gravels cover the faulted succession. Due to the outcrop position, lying above the buried frontal thrusts of the Southern Alps and North Apennines, we propose that faulting results from secondary surface effects induced by seismic shaking. We discuss two main mechanisms, both related to lateral spreading, that can result in the formation of reverse faults close to the surface. The Soncino area, recording one of the strongest historical earthquakes of the central Po Plain (1802), is considered as a possible source for seismic shaking. The results of this study are a contribution for the assessment of the potential seismic hazard in one of the most populated regions of Europe.

The Late Quaternary geological history of the lower Sydney estuary (Australia)

Sydney estuary is a dendritic, drowned river valley on the mid-east coast of Australia and comprises an upper and central section of narrow, sinusoidal channels and embayments and a wide, more marine lower estuary. The current work considered only the lower estuary.Minimal research has been undertaken into the structure of the lower Sydney estuary and previous attempts to integrate geologic and geophysical information are limited. The current study combines previously uninterpreted seismic records and poorly-accessible borehole data into a Late Quaternary history of the lower estuary.High-resolution, continuous reflection seismic (212-line km) interpretation matched borehole-based stratigraphy reasonably well. A bedrock paleo-valley deepened from approximately 40 m below present sea level (bpsl) at the Sydney Harbour Bridge (SHB) to > 90 m bpsl at the estuary mouth. Stratigraphy was dominated by two estuarine sequences, which, in the lower part of the estuary comprised mainly fine-grained, organic-rich sediments with peat, that manifest as multiple, strong dark and light-reflectors on seismic. At the SHB, the upper estuarine sequence developed into a transgressive marine to tidal delta deposit. A thin veneer (up to 10 m) of Modern estuarine sands mantled most of the lower estuary. The elevation of the estuarine sediments at approximately present-day levels and at 20 to 30 m bpsl respectively, strongly indicated deposition during periods of high-level marine transgression, i.e. the Last Interglacial (Marine Isotope Stage, MIS 5.5) event at 130 kyPB to 115 kyBP and the Penultimate Interstadial event (MIS 5.1 at 110–80 kyBP), respectively.Late Pleistocene aeolian sands contributed sediment in the south of the estuary, and remobilisation may have dispersed these sediments more widely. Present-day bathymetric features frequently reflected subsurface erosional structures due to starvation of bedload sediment.

The dynamics of historical and recent range shifts in the ruffed grouse (Bonasa umbellus)

Climate variability is the most important force affecting distributional range dynamics of common and widespread species with important impacts on biogeographic patterns. This study integrates phylogeography with distributional analyses to understand the demographic history and range dynamics of a widespread bird species, the Ruffed Grouse (Bonasa umbellus), under several climate change scenarios. For this, I used an ecological niche modeling approach, together with Bayesian based phylogeographic analysis and landscape genetics, to develop robust inferences regarding this species’ demographic history and range dynamics. The model’s predictions were mostly congruent with the present distribution of the Ruffed Grouse. However, under the Last Glacial Maximum bioclimatic conditions, the model predicted a substantially narrower distribution than the present. The predictions for the Last Glacial Maximum also showed three allopatric refugia in south-eastern and west-coast North America, and a cryptic refugium in Alaska. The prediction for the Last Interglacial showed two separate distributions to the west and east of the Rocky Mountains. In addition, the predictions for 2050 and 2070 indicated that the Ruffed Grouse will most likely show slight range shifts to the north and will become more widely distributed than in the past or present. At present, effective population connectivity throughout North America was weakly positively correlated with Fst values. That is, the species’ distribution range showed a weak isolation-by-resistance pattern. The extended Bayesian Skyline Plot analysis, which provided good resolution of the effective population size changes over the Ruffed Grouse’s history, was mostly congruent with ecological niche modelling predictions for this species. This study offers the first investigation of the late-Quaternary history of the Ruffed Grouse based on ecological niche modelling and Bayesian based demographic analysis. The species’ present genetic structure is significantly affected by past climate changes, particularly during the last 130 kybp. That is, this study offers valuable evidence of the ‘expansion–contraction’ model of North America’s Pleistocene biogeography.

River channel response to dam removals on the lower Penobscot River, Maine, United States

AbstractMost geomorphology studies of dam removals have focused on sites with appreciable quantities of stored sediments. There is great interest in channel responses to sediment releases because of potential effects on aquatic and riparian habitats and human uses of these areas. Yet, behind many dams in the Northeast U.S. and other regions of the world only minor accumulations of sediment are present because of small impoundments, run‐of‐river dam design and management (inflow ≈ outflow), low watershed sediment yield, and/or channel beds dominated by coarse sediment and/or bedrock. The two lowermost dams on the Penobscot River in Maine, United States, removed in 2012–2013, exemplified those conditions. Great Works and Veazie dams were about 6 and 10 m high, respectively. Pre‐project geophysical surveys showed coarse substrates dominated the reservoir beds and little sediment was stored in either impoundment—functions of reach geology, late Quaternary history, and upstream dams. Repeat cross‐section surveys in each impoundment, as well as the upstream and downstream reaches, were completed from 2009 to 2015 to evaluate channel morphology responses to the removals. Bed‐sediment grain size and turbidity were also measured to characterize changes in bed texture and suspended sediment. Pre‐ and post‐removal survey comparisons confirmed the expectation that bed elevations, channel shapes, and channel positions would not change substantially. Changes were often within, or close to, our estimated random measurement error. Our study shows that large‐scale physical changes are likely to be minimal when impoundments storing relatively little sediment are removed from erosion‐resistant streambeds. Many dams eligible for removal have these characteristics, making these observations an important case study that is largely unrepresented in the dam removal literature.

Relating pollen representation to an evolving Amazonian landscape between the last glacial maximum and Late Holocene

AbstractIn contrast to temperate regions, relationships between basin characteristics (e.g., type/size) and fossil pollen archives have received little attention in Amazonia. Here, we compare fossil pollen records of a small palm swamp (Cuatro Vientos; CV) and a nearby large lake (Laguna Chaplin, LCH) in Bolivian Amazonia, demonstrating that palm swamps can yield Quaternary pollen archives recording the history of terrestrial vegetation beyond the basin margin, rather than merely a history of localized swamp vegetation dynamics. The pollen assemblages from these two contrasting basins display remarkable agreement throughout their late Quaternary history, indicating past drier climates supported savanna landscape during the last glacial maximum (LGM; 24,000–18,000 cal yr BP) and savanna/semideciduous forest mosaic during the middle Holocene (7000-4750 cal yr BP) at both regional (inferred from LCH) and local (inferred from CV) spatial scales. Additionally, the local-scale catchment of CV and the basin's proximity to the riverine forests of the Río Paraguá enables exploration of the extent of gallery/riverine forests during the LGM and middle Holocene. We show that, between 24,000–4000 cal yr BP, riverine/gallery rainforests were substantially reduced compared with present, challenging the hypothesis that gallery rainforests were important refugia for rainforest species during the drier LGM and middle Holocene.

Late Quaternary history of Lammefjorden, north-west Sjælland, Denmark

Lammefjorden is a reclaimed fjord in north-west Sjælland, Denmark. Sediment cores from the area were collected to study its development after the last deglaciation, in particular the sea-level history. Late glacial and Early Holocene lake and bog deposits occur below marine deposits. Sparse late glacial fossil assemblages indicate tree-less environments with dwarf-shrub heaths. Early Holocene deposits contain remains of Betula sec. Albae sp. and Pinus sylvestris, which indicate open forests. The wetland flora comprised the calciphilous reed plant Cladium mariscus and the water plant Najas marina. Marine gyttja from basins is characterised by sparse benthic faunas, probably due to high sedimentation rates. In some areas, shell-rich deposits were found, with large shells of Ostrea edulis, indicative of high summer temperatures, high salinity and strong tidal currents. A marine shell dated to 6.7 cal. ka provides a minimum age for the marine transgression of Lammefjorden.