Pliocene Glaciation Research Articles

Pliocene CO2 rise due to sea-level fall as a mechanism for the delayed ice age

Global sea level fell progressively during the Pliocene in response to the growth of ice sheets at high northern latitudes. However, not until ∼2.7 Ma did the climate system actually generate and maintain major ice sheets in the Northern Hemisphere. A decline in atmospheric CO2 levels (pCO2) is thought to be responsible for the Pleistocene ice ages. However, the link between pCO2 and Pliocene glaciations, or their delay, is not well understood, mainly because the magnitude of pCO2 remains uncertain beyond the maximum age of ice cores (∼0.8 Ma). Here, we develop a carbonate clumped isotope (∆47) geothermometer specifically for pedogenic carbonate in Chinese loess, which we use to reconstruct temperatures in northern China, and pCO2, for the past 7.24 Ma. The palaeotemperature results show an oscillatory cooling trend over time in the East Asian monsoon region, in good agreement with coeval tropical sea surface temperature records. The pCO2 reconstruction using the pedogenic carbonate palaeobarometer reveals low values (150–325 ppmv) during the intervals of 7.24–4.3 Ma and 2.6–0 Ma. In contrast, there is a three-step rise in pCO2 up to 535 ppmv from 4.3 to 2.6 Ma, coincident with an oscillatory decrease in sea level and in benthic δ13C. We suggest that the Pliocene CO2 rise was causally related to the sea-level fall and associated organic carbon oxidation on exposed continental shelves, thereby delaying the onset of the ice age. This implies a negative feedback mechanism induced by long-term cooling since the Late Miocene, which may have delayed the onset of the ice age but did not prevent it.

Assessing diversity of King Crab Lithodes spp. in the south-eastern pacific using phylogeny and molecular species delimitation methods.

The purpose of this study was to test the hypothesis that the genetic diversity of commercially significant species of King Crabs (Lithodes spp.) along the south‐eastern Pacific (SEP) comprises different independent evolutionary units (IEUs) with spatially isolated distribution. Nine localities from inner and open waters along the SEP Chilean coast (39°S‐55°S) were sampled. We analyzed sequences from 173 individuals for the mitochondrial gene Cytochrome oxidase I (COX‐I), 151 individuals for the Internal Transcribed Spacer 1 (ITS) and 135 for the structural ribosomal RNA (28S). Genetic delimitation was performed through three analytical methods: ABGD, GMYC, and its Bayesian implementation, bGMYC. Bayesian phylogenetic analyses and haplotype networks were also performed. Divergence time between clades was assessed for the COX‐I marker and estimated from known evolutionary rates for this marker in other crustacean species and fossil calibration from other Anomuran species. Delimitation analyses, phylogenetic analyses, and mitochondrial haplotype networks suggested the presence of two deeply divergent mitochondrial lineages of Lithodes in the SEP, referred to as Clade1 and Clade 2. Nuclear markers showed low phylogenetic resolution and therefore were unsuitable for molecular species delimitation. Divergence time analysis of the mitochondrial lineages suggests a separation between Clades of approximately 2.3 Mya. The divergence time obtained suggested that Pliocene glaciations and deglaciations cycles could be involved in hybridization events between Lithodes IEUs at southern tip of South American coasts. The different frequencies of Lithodes haplotypes in inner and open water environments along SEP coasts could be explained by events such as the last glacial maximum or by differences in the adaptation of each clade to different environments. These findings support the necessity of evaluating the taxonomic status of Lithodes individuals found along SEP coasts under an integrative taxonomy approach or through markers with other evolution rates than those already used.

Sinkholes and their impacts on karst hydrogeology in a peatland complex of Northern Ontario, Canada

Pliocene glaciations, post-glacial Tyrrell Sea deposition, peatland formation, and continuous isostatic uplift have created a unique environment for karst development on the Paleozoic carbonate rocks within the James Bay Lowland of Canada. Four types of sinkhole and two karst hydrogeological systems have been recognized in the study area. The hydrogeologically active karst system consists of solution sinkholes, solutionally enlarged fractures, and collapse sinkholes that have developed after the area emerged from the Tyrrell Sea approximately 4400 years ago. The active karst system encompasses the exposed reefal limestone of the Silurian Attawapiskat Formation along the Attawapiskat River and Nayshkootayaow River and isolated bioherms that protrude above the surrounding flat but poorly drained peatland between the two major rivers. The second karst system is in the form of paleokarst formed in the underlying limestone but buried beneath the peat and marine sediments. Although these buried sinkholes were only visible at excavation sites where these features were exposed, it is likely that they underlie most of the study area. Another form of paleokarst is the Bedrock Trench that cut through most of the Paleozoic formation to a depth of approximately 200 m. The bedrock trench encompassed an area of more than 3 km2, was filled with unconsolidated materials, and did not have strong hydraulic connections to the active karst system. Formation mechanism of this bedrock trench is inconclusive but may result from polygenetic processes including glacial scouring and bedrock dissolution. Recognition of these two karst systems helps understand potential hydrogeological changes in response to continuous isostatic uplift and dewatering activities in this region.

The amplifying effect of Indonesian Throughflow heat transport on Late Pliocene Southern Hemisphere climate cooling

An unusually short glaciation interrupted the warm Pliocene around 3.3 Ma (Marine Isotope Stage (MIS) M2). Different hypotheses exist to explain why this glaciation event was so pronounced, and why the global climate system returned to warm Pliocene conditions relatively quickly afterwards. One of these proposed mechanisms is a reduced equator-to-pole heat transfer, in response to a tectonically reduced Indonesian Throughflow (ITF). The ITF is a critical part of the global thermohaline ocean circulation, transporting heat from the Indo-Pacific Warm Pool to the Indian Ocean. When ITF connectivity is reduced, the water and heat supply for the Leeuwin Current, flowing poleward along Australia's west coast, is also diminished. To assess the possible relationship between mid-Pliocene glaciations and latitudinal heat transport through the Indonesian Throughflow, we constructed a multi-proxy orbital-scale record for the 3.7–2.8 Ma interval from International Ocean Discovery Program (IODP) Site U1463, off northwest Australia. The comparison of the Site U1463 record with paleoclimate records from nearby Site 763 and West Pacific Warm Pool Site 806 allows for a detailed regional reconstruction of Pliocene paleoceanography and thus for testing the proposed hypothesis.An astronomically-paced decrease in potassium content characterizes the late Pliocene interval of U1463. This record documents the increasing aridity of northwest Australia, periodically alleviated by reinforced summer monsoon precipitation under summer insolation maxima. The δ18O record of the planktonic foraminifer Globigerinoides sacculifer correlates exceptionally well with the sea surface temperature (SST) record from Site 806 in the West Pacific Warm Pool, even during MIS M2. Hence, Site U1463 preserves an uninterrupted ITF signal even during Pliocene glaciations. However, the U1463 δ18OG.sacculifer record exhibits a 0.5‰ offset with the nearby Site 763A record around MIS M2. This implies that Site 763A, about 500 km west of U1463, more closely tracks Indian Ocean SST records across MIS M2. The U1463 data reveal that heat-transport through the Indonesian Throughflow did not shut down completely during MIS M2, but rather its intensity decreased prior to and during MIS M2, causing Site 763A to temporarily reflect an Indian Ocean, rather than an ITF signal. We conclude that ITF variability significantly influenced latitudinal heat transport by means of the Leeuwin Current and hence contributed to the relative intensity of MIS M2. We propose the ITF valve between the Pacific and Indian Ocean as a positive feedback mechanism, in which an initial sea level lowering reduces ITF heat transport, in turn amplifying global cooling by advancing the thermal isolation of Antarctica.

Paleoceanography of the east equatorial Pacific over the past 16 Myr and Pacific–Atlantic comparison: High resolution benthic foraminiferal δ18O and δ13C records at IODP Site U1337

We present astronomically tuned high resolution (∼3–4 Kyr) 15.8-Myr long benthic foraminiferal δ18O and δ13C records from IODP Site U1337 in the east equatorial Pacific, which provide a reference standard for stratigraphic correlation of deep sea sediments. A long-term glaciation history over the past 15.8 Myr has been recorded in the δ18O. Two of the most significant glaciation events include the East Antarctic Ice Sheet expansion (EAIE) at 13.8 Ma and the final onset of the Northern Hemisphere Glaciation (NHG) in 3.3–2.5 Ma. A series of Miocene and Pliocene glaciation events exist between the EAIE and NHG, which are important glaciation attempts before the Earth finally entered the full “icehouse” world in the late Pleistocene. A long-term ocean carbon isotope decrease over the past 15.8 Myr has been recorded in the δ13C. Ocean circulation change was the major cause of the ocean carbon isotope decrease in 9.4–8.1 Ma and 4–0 Ma, whereas strengthened continental chemical weathering controlled the long-term ocean carbon isotope decrease in most of the time of the past 15.8 Myr. The divergence in benthic foraminiferal δ13C and εNd provides strong evidence of significant ocean circulation change between 12.1 and 9.2 Ma which was probably related to the formation of the Isthmus of Panama. The internal feedbacks such as continental weathering and sea surface temperature change have great potential for modulating the weak 100 and 400 Kyr signals in astronomical forcing into strong 100 and 400 Kyr signals in global ice volume and carbon cycle.

Pliocene erosional pulse and glacier-landscape feedbacks in the western Alaska Range

Pliocene–Pleistocene glaciation modified the topography and erosion of most middle- and high-latitude mountain belts, because the evolution of catchment topography controls long-term glacier mass balance and erosion. Hence, characterizing how erosion rates change during repeated glaciations can help test hypothesized glacier erosion-landscape feedbacks across a range of settings. To better understand how glaciations and landscapes coevolve on geologic timescales, I quantify erosion rates in the glaciated western Alaska Range with low-temperature thermochronometric data and modeling. Zircon (U–Th)/He and apatite fission track data suggest mountain-building was underway by the early Miocene. In contrast, lower-temperature apatite (U–Th)/He age-elevation and grain age-kinetic data indicate that erosion accelerated coincident with regional Pliocene glaciation ca. 4 Ma. Furthermore, erosion rates calculated within an eroding half-space indicate slow erosion at a rate ≤0.3 km/m.y. before 4.2 Ma, an initial pulse of rapid erosion at a rate of 1.0–1.6 km/m.y. during 4.2–2.9 Ma, and more moderate erosion at a rate of 0.4–0.7 km/m.y. since 2.9 Ma. The initial erosion pulse suggests a significant transient landscape adjustment to the introduction of efficient glacial erosion. The subsequent decrease in Pleistocene erosion rates is consistent with a negative feedback between continuing glaciation and glacier size/erosivity: If glacial erosion outpaces rock uplift, glacier erosion decreases over time as topography, mass balance, valley gradients, and ice flux are reduced. These findings imply that in areas of moderate rock uplift rates, the onset of local Plio–Pleistocene glaciation may have been punctuated by an initial pulse of rapid landscape change, after which change became more gradual.

Landscape antiquity and Cenozoic drainage development of southern Yukon, through restoration modeling of the Tintina Fault

The impact of Tintina Fault displacement on the development of the Yukon River and drainage basins of central Yukon is investigated through geophysical and hydrological modeling of digital terrain model data. Regional geological evidence suggests that the age of the planation of the Klondike Plateau is at least Late Cretaceous, rather than Neogene as previously assumed, and that surprisingly there has been little net incision in the region since the late Mesozoic. The Tintina Fault has been previously interpreted to have experienced ∼430 km of dextral displacement, primarily during the Eocene. However, the alignment of river channels across the fault at specific displacements, coupled with recent seismic events and related fault activity, suggests that the fault may have moved in stages over a longer time span. Topographic restoration and hydrological models show that the drainage of the Yukon River northwestward into Alaska via the ancestral Kwikhpak River was only possible at restored displacements of up to ∼50–55 km on the Tintina Fault. We interpret the published drainage reversals convincingly attributed to the effects of Pliocene glaciation as an overprint on earlier Yukon River reversals attributed to tectonic displacements along the Tintina Fault. At restored displacements between 230 and 430 km, our models illustrate that paleo-Yukon River drainage may have flowed eastward into the continental interior via an ancestral Liard River. The revised drainage evolution has wide-reaching implications for surficial geology deposits, the flow direction and channel geometries of the region’s ancient rivers, and importantly, for exploration of placer gold deposits.

Molecular phylogenetics of the glass frog Hyalinobatrachium orientale (Anura: Centrolenidae): evidence for Pliocene connections between mainland Venezuela and the island of Tobago

The presence of Hyalinobatrachium orientale in Tobago and in northeastern Venezuela is puzzling as this species is unknown from the island of Trinidad, an island often hypothesized to be a stepping-stone for the mainland fauna to colonize Tobago. A period of extended isolation on Tobago could result in the Hyalinobatrachium population becoming distinct from the mainland H. orientale. Here, we use 12S and 16S rDNA gene fragments from nine H. orientale specimens from Tobago and the mainland to assess their relationship and taxonomy, as well as the tempo and mode of speciation. The results suggest H. orientale from Venezuela and Tobago are monophyletic and the two populations diverged about 3 million years ago. This estimate corresponds with the drier climate and lower sea levels of the Pliocene glaciation periods. We hypothesize that lower sea levels resulted in land-bridge formations connecting the mainland and Tobago, with a corridor of habitat allowing H. orientale to colonize Tobago to the west of Trinidad.

How lizards survived blizzards: phylogeography of theLiolaemus lineomaculatusgroup (Liolaemidae) reveals multiple breaks and refugia in southernPatagonia and their concordance with other codistributed taxa

Patagonia was shaped by a complex geological history, including the Miocene uplift of the Andes, followed by volcanism, marine introgressions, and extreme climatic oscillations during Pliocene-Pleistocene glaciation-deglaciation cycles. The distributional patterns and phylogenetic relationships of southern patagonian animals and plants were affected in different ways, and those imprints are reflected in the seven phylogeographic breaks and eight refugia that have been previously proposed. In this study, we estimated time-calibrated phylogenetic/phylogeographic patterns in lizards of the Liolaemus lineomaculatus group and relate them to historical Miocene-to-Pleistocene events of Patagonia and the previously proposed phylogeographic patterns. Individuals from 51 localities were sequenced for the mitochondrial marker (cyt-b) and a subsample of individuals from each mitochondrial lineage was sequenced for one nuclear (LDA12D) and one slow evolving mitochondrial gene (12S). Our analyses revealed strong phylogeographic structure among lineages and, in most cases, no signal of demographic changes through time. The lineomaculatus group is composed of three strongly supported clades (lineomaculatus, hatcheri and kolengh + silvanae), and divergence estimates suggested their origins associated with the oldest known Patagonian glaciation (7-5 Ma); subsequent diversification within the lineomaculatus clade coincided with the large Pliocene glaciations (~3.5 Ma). The lineomaculatus clade includes nine strongly genetically and geographically structured lineages, five of which are interpreted as candidate species. Our findings suggest that some Liolaemus lineages have persisted in situ, each of them in a different refugium, through several glaciation-deglaciation cycles without demographic fluctuations. We also summarize and update qualitative evidence of some shared phylogeographic breaks and refugia among plants, rodents and lizards.

A chronological framework for the Clyde Foreland Formation, Eastern Canadian Arctic, derived from amino acid racemization and cosmogenic radionuclides

The most extensive terrestrial outcrops of glacial and glaciomarine deposits in the Eastern Canadian Arctic are exposed in sea cliffs along the Clyde Foreland and Qivitu Peninsula of Baffin Island. Collectively known as the Clyde Foreland Formation (CFF), these stacked deposits record at least seven glacial advances. Despite having been the focus of numerous investigations spanning nearly 50 years, no numerical chronological framework for the age of the deposits has been established. Previous studies relied on biostratigraphy and amino acid racemization (AAR) geochronology and postulated that the oldest units were Late Pliocene to Mid-Pleistocene in age. In this paper, we use a cosmogenic radionuclide isochron approach to determine a minimum age for the burial of a paleosol preserved within the CFF. Abundant palynomorphs in the paleosol are dominated by cool-climate taxa. Combining the paleosol burial age with a compilation of published and new CFF AAR data for marine bivalves Hiatella arctica and Mya truncata, we statistically define seven CFF aminozones and develop a piecewise isoleucine AAR calibration model for Baffin Island. From this, we estimate the minimum age of each aminozone, although the propagation of errors through all calculations produces large uncertainties for each age estimate. The youngest three CFF units, known as the Kogalu, Kuvinilk, and Cape Christian members, were most likely deposited during glaciations in the Mid- to Late-Pleistocene. The paleosol formed prior to 1.15 ± 0.20 Ma, and the underlying aminozones represent sedimentation during Early Pleistocene or latest Pliocene glaciations and record early advances of Laurentide ice across Baffin Island.

Pliocene glaciation

Pliocene glaciation

Late Pliocene age of glacial deposits at Heidemann Valley, East Antarctica: evidence for the last major glaciation in the Vestfold Hills

A Pliocene (2.6–3.5 Ma) age is determined from glacial sediments studied in a 20 m long, 4 m deep trench excavated in Heidemann Valley, Vestfold Hills, East Antarctica. The age determination is based on a combined study of amino acid racemization, diatoms, foraminifera, and magnetic polarity, and supports earlier estimates of the age of the sedimentary section; all are beyond 14C range. Four till units are recognized and documented, and 16 subunits are identified. All are ascribed to deposition during a Late Pliocene glaciation that was probably the last time the entire Vestfold Hills was covered by an enlarged East Antarctic Ice Sheet (EAIS). Evidence for other more recent glacial events of the ‘Vestfold Glaciation’ may have been due to lateral expansion of the Sørsdal Glacier and limited expansion of the icesheet margin during the Last Glacial Maximum rather than a major expansion of the EAIS. The deposit appears to correlate with a marine deposition event recorded in Ocean Drilling Program Site 1166 in Prydz Bay, possibly with the Bardin Bluffs Formation of the Prince Charles Mountains and with part of the time represented in the ANDRILL AND-1B core in the Ross Sea.

Climate change and evolution of the New World pitviper genus Agkistrodon (Viperidae)

AbstractAim We derived phylogenies, phylogeographies, and population demographies for two North American pitvipers, Agkistrodon contortrix (Linnaeus, 1766) and A. piscivorus (Lacépède, 1789) (Viperidae: Crotalinae), as a mechanism to evaluate the impact of rapid climatic change on these taxa.Location Midwestern and eastern North America.Methods We reconstructed maximum parsimony (MP) and maximum likelihood (ML) relationships based on 846 base pairs of mitochondrial DNA (mtDNA) ATPase 8 and ATPase 6 genes sequenced over 178 individuals. We quantified range expansions, demographic histories, divergence dates and potential size differences among clades since their last period of rapid expansion. We used the Shimodaira–Hasegawa (SH) test to compare our ML tree against three biogeographical hypotheses.Results A significant SH test supported diversification of A. contortrix from northeastern Mexico into midwestern–eastern North America, where its trajectory was sundered by two vicariant events. The first (c. 5.1 Ma) segregated clades at 3.1% sequence divergence (SD) along a continental east–west moisture gradient. The second (c. 1.4 Ma) segregated clades at 2.4% SD along the Mississippi River, coincident with the formation of the modern Ohio River as a major meltwater tributary. A single glacial refugium was detected within the Apalachicola region of southeastern North America. Significant support was also found for a hypothesis of trans‐Gulf rafting by the common ancestor of A. piscivorus from eastern Mexico (possibly the Yucatan Peninsula) to northern Florida. There, a Mid–Late Pliocene marine transgression separated it at 4.8% SD from mainland North America. Significant range expansions followed compressive glacial effects in three (of four) A. contortrix clades and in two (of three) A. piscivorus clades, with the Florida A. piscivorus clade exhibiting significant distributional stasis.Main conclusions Pliocene glaciations, rapidly developing western aridity, and Pleistocene glacial meltwaters seemingly led to the diversification of A. contortrix and A. piscivorus in North America. Both species were pushed southwards by Pleistocene climate change, with subsequent northward expansions uninhibited topographically. The subspecific taxonomy used for A. contortrix and A. piscivorus today, however, appear non‐representative. The monophyletic Florida subspecies of A. piscivorus may be a distinct species (at 4.8% SD), whereas two western subspecies of A. contortrix also appear to constitute a single distinct species, pending additional analyses. We conclude that both species of Agkistrodon can be used as suitable ectothermic models to gauge impacts of future climate change.

Origin and development of ideas on Pliocene and Quaternary glaciations in northern and eastern Europe, Iceland, Caucasus and Siberia

Abstract A personal account, illustrated by the author's sketches, of ideas about glaciation, neotectonics and Quaternary geology, discussing the author's observations made during the course of his work undertaken in eastern Europe and Siberia, the Caucasus and Iceland. The paper is at the same time a contribution to autobiographical literature and to studies in the history of geoscience. The author's discovery of evidence for Pliocene glaciation in the Caucasus is noteworthy.

A review of the Tripterygion tripteronotus (Risso, 1810) complex, with a description of a new species from the Mediterranean Sea (Teleostei: Tripterygiidae)

We compared specimens of Tripterygion tripteronotus from 52 localities of the Mediterranean Sea and adjacent waters, using four gene sequences (12S rRNA, tRNA-valine, 16S rRNA and COI) and morphological characters. Two well-differentiated clades with a mean genetic divergence of 6.89±0.73% were found with molecular data, indicating the existence of two different species. These two species have disjunctive geographic distribution areas without any molecular hybrid populations. Subtle but diagnostic morphological differences were also present between the two species. T. tripteronotus is restricted to the northern Mediterranean basin, from the NE coast of Spain to Greece and Turkey, including the islands of Malta and Cyprus. T. tartessicum n. sp. is geographically distributed along the southern coast of Spain, from Cape of La Nao to the Gulf of Cadiz, the Balearic Islands and northern Africa, from Morocco to Tunisia. According to molecular data, these two species could have diverged during the Pliocene glaciations 2.7-3.6 Mya.

Late Pliocene glaciation and landscape evolution of Vestfirðir, Northwest Iceland

Vestfirðir, Northwest Iceland, has been extensively modified by glacial activity, but the timing and landscape impact of pre-Last Glacial Maximum (LGM) glacial activity is not well known. We present new geochemical and chronological data from two tephras, Óþoli and Hjallanes, which constrain the age of high altitude ice-dammed lake sediments near the plateau surface of Skagafjall, located on the outer westernmost fjords of Vestfirðir. Our findings provide the first dated evidence of Late Pliocene glaciation on Vestfirðir. The 2.26±0.11 Ma fission-track age of the airfall rhyolitic Óþoli tephra is compatible with reversed palaeomagnetic polarity data and suggests an ice-dammed lake existed on Skagafjall at broadly the same time as a major and well-documented Late Pliocene downturn in global climate. We assess the likely impact of Late Pliocene and subsequent glacial activity on Vestfirðir landscapes and propose that: (1) geomorphological features and sedimentary deposits on or near the Skagafjall plateau surface could have survived beneath relatively low basal velocity areas and/or relatively non-erosive areas of glacial maxima ice sheets on Vestfirðir at glacial maxima, and (2) the heavily incised fjord network, the principal macroscale landscape feature of Vestfirðir, existed in the Late Pliocene.

Rapid radiation and cryptic speciation in mediterranean triplefin blennies (Pisces: Tripterygiidae) combining multiple genes

The genus Tripterygion is the unique genus of the family Tripterygiidae in the Mediterranean Sea and in the northeastern Atlantic coast. Three species and four subspecies had been described: Tripterygion tripteronotus and Tripterygion melanurus ( T. m. melanurus and T. m. minor) are endemic of the Mediterranean, and T. delaisi ( T. d. delaisi and T. d. xanthosoma) is found in both areas. We used five different genes (12S, 16S, tRNA-val, COI, and 18S) to elucidate their taxonomy status and their phylogenetic relationships. We employed different phylogenetic reconstructions that yielded different tree topologies. This discrepancy may be caused by the speciation process making difficult the reconstruction of a highly supported tree. All pair comparisons between these three species showed the same genetic divergence indicating that the speciation process could have been resolved by a rapid radiation event after the Messinian Salinity Crisis (5.2 Mya) leading to a trichotomy. Our molecular data revealed two clearly supported clades within T. tripteronotus, whose divergence largely exceeded that found between other fish species, consequently these two groups should be considered two cryptic species diverging 2.75–3.32 Mya along the Pliocene glaciations. On the contrary, none of the genes studied supported the existence of two subspecies of T. melanurus. Finally, the two subspecies of T. delaisi were validated and probably originated during the Quaternary climatic fluctuations (1.10–1.23 Mya), however their distribution ranges should be redefined.

Volcanic triggering of late Pliocene glaciation: evidence from the flux of volcanic glass and ice-rafted debris to the North Pacific Ocean

Mass accumulation rates (MAR) of different components of North Pacific deep-sea sediment provide detailed information about the timing of the onset of major Northern Hemisphere glaciation that occurred at 2.65 Ma. An increase in explosive volcanism in the Kamchatka–Kurile and Aleutian arcs occurred at this same time, suggesting a link between volcanism and glaciation. Sediments recovered by piston-coring techniques during ODP Leg 145 provide a unique opportunity to undertake a detailed test of this possibility. Here we use volcanic glass as a proxy for explosive volcanism and ice-rafted debris (IRD) as a proxy for glaciation. The MAR of both glass and IRD increase markedly at 2.65 Ma. Further, the flux of the volcanic glass increased just prior to the flux of ice-rafted material, suggesting that the cooling resulting from explosive volcanic eruptions may have been the ultimate trigger for the mid-Pliocene glacial intensification.

Geologic evolution of the Yukon River: implications for placer gold

The greatest placer potential in northwest Canada lies in preglacial drainage systems. The largest placer gold deposits are associated with Pliocene pre-glacial fluvial gravels of the Dawson Range (in particular Klondike Plateau) of west-central Yukon. The abundance and/or the lack of gold concentration in this area were controlled by the ability of the streams to aggrade in response to changes caused by extensional faulting in the Tintina Trench, differential uplift, and regional denudation. Gold bearing gravels in the northern and eastern slopes of the Dawson Range are found in low order tributaries of the pre-glacial south-flowing Yukon River. Glaciation played an important role in masking and changing the direction of drainage, and creating new channels in this region. The earliest known drainage changes relate to Late Miocene formation of the Tintina Trench, and Early Pliocene uplift of the St. Elias Mountains. Prior to these events the Yukon River drained south into the Gulf of Alaska. Initial regional glaciation (2.6–2.9 Ma) diverted the southward drainage toward the northwest, becoming part of the Kwikhpak River in Alaska. The present Yukon River drainage basin is about 27.5% larger than the ancestral Kwikhpak River basin. The evolution of the river is described here in three stages (1) drainage in pre-Late Miocene, (2) drainage in Early Pliocene and (3) drainage after earliest Pliocene glaciation.

Late Pliocene sand ridges at the western margin of the Barents Sea—do they monitor Late Pliocene glaciations?

Seismic data combined with core analysis of the northwesternmost exploration well on the Norwegian continental margin, well 7316/5-1, has been used to map and discuss the genesis of three well-defined sand ridges. The sand ridges have a NE-SW to N-S orientation and are of Late Pliocene age. The dimensions of the ridges are: height 40 m, length 2–4 km and width 0.5–1 km. In relation to the glaciation models of the Barents Sea, the position of well 7316/5-1, and especially information from a core that penetrated one of the sand ridges, provide important information. The ridges are not, in themselves, diagnostic for grounded glaciers at the margin of the Barents Sea shelf during the Late Pliocene, although the presence of pebbles in a cored section of the ridges may represent ice-dropped material. Whether the possible influx of glaciogenic material is related to local or regional glaciations on the Barents Shelf remains to be evaluated.