Non-glacial Periods Research Articles

Spatiotemporal Distribution and Source Analysis of Heavy Metals in Surface Sediments in Lake Ulansuhai Based on PCA-APCS-MLR Model

To explore the spatial and temporal distribution characteristics of heavy metals in the surface sediments of lakes in cold regions during ice-sealing and non-ice-sealing periods, we analyzed the potential ecological risk degree and the pollution sources. A total of 20 sampling sites in Lake Ulansuhai in cold regions were collected from 2020 to 2021, and 120 surface sediment samples were collected during different periods. The contents of As, Cd, Cr, Cu, Ni, Pb, Zn, and Hg were determined. Correlation analysis, principal component analysis, and the absolute factor score-multiple linear regression (APCS-MLR) receptor model were used to trace the source of heavy metal pollution. The results showed that:① the distribution of heavy metals in lake surface sediments was different between the ice-sealing period and the non-ice-sealing period. The distribution of heavy metals during the ice-sealing period was higher in the north and lower in the south. Cd and Hg were mainly distributed in the central and southern lakes during the non-glacial period. ② Hg, Cd, and As were moderately polluted, and Ni was mildly polluted in the surface sediments of the lake. The overall performance was at a high risk level, and the pollution level during the non-ice-sealing period was higher than that during the ice-sealing period. The main environmental risk factors were Hg and Cd, which showed high risk and moderate risk, respectively. ③ The sources of heavy metals in lake surface sediments were mainly industrial sources from mining and transportation, agricultural sources, and natural sources. As, Ni, Pb, and Hg were mainly affected by industrial sources, with contribution rates of 62.67%, 75.31%, 77.47%, and 80.11%, respectively. The main sources of Cu and Zn were natural sources, and Cd was greatly affected by agricultural sources. The contribution rate was 81.57%. The source of Cr was mainly affected by natural factors, and the influence of human activities and unknown sources require further attention.

Low-latitude climate change linked to high-latitude glaciation during the late paleozoic ice age: Evidence from terrigenous detrital kaolinite

The Late Paleozoic Ice Age (LPIA; ca. 335–260 million years ago) was one of the most significant glacial events in Earth’s history. It records cycles of ice advance and retreat in southern high-latitude Gondwana and provides a deep-time perspective for climate–glaciation coevolution. However, climate records using clay mineral proxies from the LIPA are poorly developed in low latitudes, particularly in the North China Plate (NCP) on the eastern Paleo-Tethys. We address this through a detailed mineralogical study of the marine–continental sedimentary succession in the Yuzhou Coalfield from the southern NCP. We apply biostratigraphy and high-resolution clay mineral composition to reconstruct the latest Carboniferous to early Permian chronostratigraphy and climate change. The Benxi, Taiyuan, and Shanxi formations in the study area are assigned to the Gzhelian, Asselian–Artinskian, and Kungurian-Roadian stages, respectively, and the Carboniferous and Permian lithostratigraphic units across the NCP recognized as widely diachronous. Under scanning electron microscopy, the detrital micromorphology of kaolinite is mostly found as irregular fragments with sizes of 1–5 μm. Illite crystallization varies from 0.22 to 1.88 ∆°/2θ (x̄ = 0.49 ∆°/2θ) and indicates changes in kaolinite content to be a robust proxy for paleoclimate reconstruction. Kaolinite data show alternating warm-humid and cool-humid climate conditions that are roughly consistent with the calibrated glaciations and nonglacial interval successions recognized in high-latitude Gondwana. These include the Asselian-early Sakmarian and late Sakmarian-early Artinskian glacials and the climatic transition to glacial P3 during the Roadian. Our results indicate a comparatively cool-humid and warm-humid climate mode in low-latitude NCP during glacial and nonglacial periods, respectively. This is a significant step toward connecting climate change in low-latitude to high-latitude glaciation during the LPIA in eastern Paleo-Tethys.

Geochemical characteristics of organic-rich intervals within the Cryogenian non-glacial Datangpo Formation in southeastern Yangtze Block-implications for paleoenvironment and its control on organic matter accumulation

To understand the mechanism of organic matter enrichment in the organic-rich intervals of the Cryogenian non-glacial strata, we report high-resolution geochemical data of the well-developed non-glacial Datangpo Formation at a section in the southeastern margin of the Yangtze Block, including iron (Fe) speciation, sulfur and organic carbon isotopic compositions and elemental contents. The organic-rich intervals are mainly distributed in the basal manganese (Mn) carbonate and Mn-bearing shales (intervalⅠ), and overlying black shales (intervalⅡ). The paleo-redox reconstruction shows a transition from ferruginous-dominated watermass during deposition of the IntervalⅠto euxinic-dominated watermass during deposition of the IntervalⅡ, which provides good conditions for the preservation of organic matter. A variety of geochemical indicators demonstrate that during deposition of the IntervalⅠ, elevated primary productivity in the surface water driven by hydrothermal activities and improved post-glacial basinal watermass exchange, coupled with some organic carbon influx from the dissolved organic carbon reservoir, collectively promoted the enrichment of organic matter. For the interval Ⅱ, enhanced chemical weathering accompanied by persistently warm climatic conditions exerted a major control on the organic matter enrichment by importing abundant nutrients, resulting in enhanced surface-water primary productivity. In addition, favorable sedimentation rates also made positive contributions to the organic-rich black shales in the intervalⅡ. Based on a combined analysis of paleoclimates, hydrological conditions and hydrothermal activities, this study puts forward organic matter enrichment models for the organic-rich intervals deposited during the Cryogenian non-glacial period.

Sedimentary noise and sea levels linked to land\u2013ocean water exchange and obliquity forcing

In ancient hothouses lacking ice sheets, the origins of large, million-year (myr)-scale sea-level oscillations remain a mystery, challenging current models of sea-level change. To address this mystery, we develop a sedimentary noise model for sea-level changes that simultaneously estimates geologic time and sea level from astronomically forced marginal marine stratigraphy. The noise model involves two complementary approaches: dynamic noise after orbital tuning (DYNOT) and lag-1 autocorrelation coefficient (ρ1). Noise modeling of Lower Triassic marine slope stratigraphy in South China reveal evidence for global sea-level variations in the Early Triassic hothouse that are anti-phased with continental water storage variations in the Germanic Basin. This supports the hypothesis that long-period (1-2 myr) astronomically forced water mass exchange between land and ocean reservoirs is a missing link for reconciling geological records and models for sea-level change during non-glacial periods.

The SE sector of the Middle Weichselian Eurasian Ice Sheet was much smaller than assumed

Quaternary climatic and glacial history must be known in order to understand future environments. Reconstructions of the last Weichselian glacial cycle 117,000–11,700 years (kyr) ago propose that S Finland, adjacent Russia and the Baltic countries in the SE sector of the Eurasian Ice Sheet (EIS), were glaciated during the Middle Weichselian time [marine isotope stage (MIS) 4, 71–57kyr ago] and that this glaciation was preceded in S Finland by an Early Weichselian interstadial (MIS 5c, 105–93kyr ago) with pine forest. We apply glacial sequence stratigraphy to isolated Late Pleistocene onshore outcrop sections and show, that these events did not take place. The one Late Weichselian glaciation (MIS 2, 29–11kyr ago) was preceded in S Finland by a nearly 90kyr non-glacial period, featuring tundra with permafrost and probably birch forest. Our new Middle Weichselian paleoenvironmental scenario revises the configuration and hydrology of the S part of EIS and gives new setting for the evolution of Scandinavian biota. If future development during the coming glacial cycle proves to be similar, the high-level nuclear waste stored in the bedrock of SW Finland should be located deeper than currently planned, i.e. below any possible future permafrost.

Geomorphological evolution and sediment transfer in the Piave River system (northeastern Italy) since the Last Glacial Maximum

The study deals with sediment production, transfer and deposition in the Piave River basin from the Last Glacial Maximum (LGM) to the Present. It aims at defining the temporal relationships between the late Pleistocene and Holocene glacial phases and sedimentary phases in the Piave hydrosystem, and analyzing modes and timing of sediment transfer within the system. The highest sediment production was at the peak of LGM; immediately after deglaciation, until about 8 ka 14C BP, alluvial sediments were mostly trapped in the terminal tracts of the Alpine valleys and in the Vallone Bellunese. The whole alluvial plain experienced a severe erosive phase between Lateglacial and early Holocene; downcutting in the Vallone Bellunese, after ca. 8 ka 14C BP, re-mobilized the alluvial sediments and contributed to delta formationon the Adriatic coast since 6 ka 14C BP. Post-glacial aggradation in the distal tract of the Nervesa megafan started only at about 4-3 ka 14C BP. In Roman times the fluvial system was rather stable, while between the 5th and 10th century AD there were several major avulsions in the distal Nervesa megafan. The last 100 years are characterized by a dramatic decrease of sediment transport due to a range of human activities (e.g. sediment mining and dams). The transition from a glacial to a non-glacial period controlled both sediment production in the catchment and sea-level change but local factors, i.e. large landslides and valley topography, had a major impact on sediment transfer, while the impact of human activities on the fluvial system has increased through time.

Transient hydrodynamics within intercratonic sedimentary basins during glacial cycles

The hydrodynamic consequences of a glaciation/deglaciation cycle within an intercratonic sedimentary basin on subsurface transport processes is assessed using numerical models. In our analysis we consider the effects of mechanical ice sheet loading, permafrost formation, variable density fluids, and lithospheric flexure on solute/isotope transport, groundwater residence times, and transient hydraulic head distributions. The simulations are intended to apply, in a generic sense, to intercratonic sedimentary basins that would have been near the southern limit of the Laurentide Ice Sheet during the last glacial maximum (∼20 ka B.P.), such as the Williston, Michigan, and Illinois basins. We show that in such basins fluid flow and recharge rates are strongly elevated during glaciation as compared to nonglacial periods. Furthermore, our results illustrate that steady state hydrodynamic conditions in these basins are probably never reached during a 32.5 ka cycle of advance and retreat of a wet‐based ice sheet. Present‐day hydrogeological conditions across formerly glaciated areas are likely to still reflect the impact of the last glaciation and associated processes that ended locally more than 10 ka B.P. Our results reveal characteristic spatial patterns of underpressure and overpressure that occur in aquitards and aquifers, respectively, as a result of recent glaciation. The calculated emplacement of low salinity, isotopically light glacial meltwater along basin margins is roughly consistent with observations from formerly glaciated basins in North America. The modeling presented in this study will help to improve the management of groundwater resources in formerly glaciated basins as well as to evaluate the viability on geological timescales of nuclear waste repositories located at high latitudes.

Snow-contact volcanic facies and their use in determining past eruptive environments at Nevados de Chillán volcano, Chile

Studies of the eruptive products from volcanoes with variable ice and snow cover and a long history of activity enable reconstruction of erupted palaeoenvironments, as well as highlighting the hazards associated with meltwater production, such as jokulhlaups and magma-water interaction. Existing difficulties include estimation of ice/snow thicknesses and discrimination between ice- and snow-contact lithofacies. We present field evidence from the Cerro Blanco subcomplex of Nevados de Chillan stratovolcano, central Chile, which has erupted numerous times in glacial and non-glacial periods and most recently produced andesitic lava flows in the 1861–1865 eruption from the Santa Gertrudis cone on the northwest flank of the volcano. The main period of lava effusion occurred during the winter of 1861 when the upper flanks of the volcano were reportedly covered in snow and ice. The bases and margins of the first lava flows produced are cut by arcuate fractures, which are interpreted as snow-contact features formed when steam generated from the melting of snow entered tensional fractures at the flow base. In contrast, the interiors and upper parts of these flows, as well as the overlying flow units, have autobrecciated and blocky textures typical of subaerial conditions, due to insulation by the underlying lava. Similar textures found in a lava flow dated at 90.0±0.6 ka that was emplaced on the northwest flank of Cerro Blanco, are also inferred to be ice and snow-contact features. These textures have been used to infer that a small valley glacier, overlain by snow, existed in the Santa Gertrudis Valley at the time of the eruption. Such reconstructions are important for determining the long-term evolution of the volcano as well as assessing future hazards at seasonally snow-covered volcanoes.

Fibrous calcite from the Ordovician of Tennessee: preservation of marine oxygen isotopic composition and its implications

ABSTRACTThree categories of fibrous calcite from early to middle Caradoc platform‐marginal buildups in east Tennessee can be delineated using cathodoluminescent microscopy, minor element chemistry and stable C‐O isotopic composition. Bright luminescent fibrous cement has elevated Mn (>1000 p.p.m.), negative δ13C and intermediate δ18O values relative to other types of fibrous calcite. This cement reflects fibrous calcite that interacted with reducing Mn‐rich fluids. Dully luminescent fibrous cement has elevated Fe (>400 p.p.m.), positive δ13C and negative δ18O values relative to other fibrous cements. This cement was stabilized by burial fluids. Nonluminescent fibrous cement has low Mn and Fe (generally below 400 p.p.m.) and positive δ13C and δ18O values relative to other types of fibrous calcite. The latter cement is interpreted to be the best material for determining the isotopic composition of calcite precipitated in equilibrium with early to middle Caradoc seawater, which is δ13C=1% PDB and δ18O=−4 to −5‰ PDB. Results from this study and Ashgillian brachiopods indicate that the average δ18O composition of the Ordovician ocean, during nonglacial periods, was probably never more negative than −3‰ SMOW. Assuming an Ordovician seawater δ18O value of −1‰ SMOW, Holston Formation fibrous cements would have precipitated at temperatures between 27 and 36 °C, which is near the upper temperature limit for metazoans. A seawater δ18O value of −2‰ SMOW yields temperatures ranging from 23 to 31 °C, while a −3‰ SMOW value yields temperatures of 18–26 °C.

Stratigraphic Context of Old Crow Tephra, Holitna Lowland, Interior Southwest Alaska

A thick deposit of Old Crow tephra was discovered in a bluff exposure along the middle Holitna River near the Kulukbuk Hills (61°20′N latitude, 157°10′W longitude) in interior southwest Alaska. This locality is the southwesternmost-known deposit of Old Crow tephra in Alaska. Thickness and grain-size data from this site support a source volcano in the eastern Aleutian arc. Pleistocene stratigraphic sequences in the lowland are dominated by upward-fining eolian sand-sheet deposits and loess separated by organic silt. These deposits record at least two episodes of regional glaciation and an intervening nonglacial period (marine oxygen isotope stage 3, stage 5, or both). Old Crow tephra crops out near the top of the lower upward-fining eolian unit, indicating that the ash erupted near the end of an interval of periglacial eolian sedimentation. The sequence of eolian deposits that contain Old Crow tephra probably accumulated during the latter part of marine oxygen isotope stage 6, whereas the overlying eolian sequence formed during the last glaciation (stage 2). This stratigraphic position is consistent with other stratigraphic contexts for the tephra and with fission-track and thermoluminescence ages of ca. 140,000 ± 10,000 yr B.P.

Northwest European palaeoclimate as indicated by growth frequency variations of secondary calcite deposits

A compilationn for the northwest of Europe of over 500 uranium-series speleothen and travertine dates is presented using a cumulative distributed error frequency approach. These secondary carbonate deposits require both significant groundwater supply and a biogenic soil carbon dioxide source for their growth. During glacial periods soil CO 2 production is inhibited and the water supply is ice locked, therefore growth is slowed significantly if not stopped. Thus deposits can be used on a chronological basis to give a signal of glacial and non-glacial periods. However, sensitivity to the groundwater supply modifies this signal, with growth also limited in times of high aridity, the palaeoclimatic signal is thus complex. The compilation presented is used both as a chronology for comparison with the orbitally tuned marine oxygen isotope record, and as a palaeoclimatic indicator. Attention is focused on two periods of the last glacial / interglacial cycle where the record provides a significantly different palaeoclimatic record to other terrestrial and oceanic records. These are the isotope stages 5/4 transition, for which a relatively low cumulative growth frequency indicates an earlier increase in aridity than observed elsewhere; and isotope stage 3, the pleniglacial, where both statistically significant high (49–62 ka) and low (22–35, 44–46 ka) levels of growth are observed, and can be used to constrain the timing of many of the interstadial events within this period.

Unforced Oscillations in a Freeboard and Basin Model: Analogue to Glacial/Climate Oscillators?

A mass conservation model for paleo-ice sheet cyclicity provides a conceptual analogue for modeling sedimentary cycles. In particular, the relative snowline instability in glacial models suggests a general motif for stratigraphic cyclicity: relative baselevel instability. A simple sedimentary basin model is constructed along these lines that produces free oscillations with no external forcing. All previous models have attributed sedimentary cyclicity to external forcing: eustatic sea level changes, sediment supply rate changes (or rate of sea level changes), or tectonic subsidence rate changes. Such forcing is seriously challenged when confronted with (possibly) global synchronous high frequency cycles of large amplitude during non-glacial periods. Weakly coupled nonlinear oscillators tend often to synchronize. This may be a promising way of understanding widespread synchroneity in the stratigraphic record.

Interaction between hemipelagic sediment and a hydrothermal system: Middle Valley, northern Juan de Fuca Ridge, subarctic northeast Pacific

Slightly hydrothermally altered sediments were recovered from a sedimented rift valley with active hydrothermal discharge. The sediment consists mainly of terrigenous material with a low content of biogenic components. In spite of the alteration, glacial and non-glacial periods are still discernable based on lithology, mineralogy, carbonate content and bulk sediment geochemistry. In the vicinity of the core studied, extremely high heat flow anomalies and the presence of active black smokers suggest a rapid discharge of hydrothermal fluids along discrete pathways such as coarse-grained turbidite layers or faults. In the biogenic-rich fine-grained sediments, diffuse transport can supply the components and allow the time necessary for the formation of authigenic phases such as carbonate concretions, gypsum, barite, often Mg-rich amorphous silica and Mg-rich silicates (stevensite). Mg-rich amorphous silica could be the precursor of the Mg-rich silicates commonly found associated with hydrothermal deposits. Carbon and oxygen isotopic results on the carbonate nodules suggest (1) that the carbon in the nodules could be partly derived from methane which would have been oxidized at the oxic-anoxic boundary and in the sulphate reduction zone and (2) that successive cycles of hydrothermal fluid migration through the sediment could explain the variability in the results.

Sea level changes at active plate margins: processes and products

A joint IAS/Geological Society of London meeting, organized by the British Sedimentological Research Group, was held in London at the Geological Society on 9-11 May 1989, to address the problem of recognizing the controls on, and effects of sea level change at active plate margins. The conference consisted of 48 talks and 11 poster presentations, with about 170 delegates attending. The conference was introduced by the convenor D. I. M. Macdonald (BAS, Cambridge), followed by a short opening session on tectonics, eustasy and stratigraphy. B. U. Haq (NSF) introduced the concept of sequence stratigraphy, and the now familiar global cycle charts, arguing that systems tracts and sequences could be used for regional and inter-regional correlation. J. F. Dewey & W. C. Pitman III (Oxford and Lamont Doherty) considered the problem of the mechanics behind eustatic sea level changes, suggesting that changing ocean basin volume, due to fluctuations in spreading rate, may provide a way of generating the long-term cycles seen. However, such processes were gradual and could not produce the rapid short-term cycles. These short-term cycles could be attributed to changing ice-volume during periods of known glaciation; but how are they generated during non-glacial periods? Sea level changes at Neogene and Recent margins were discussed in the second session. M. Dobson (Aberystwyth) suggested that the control on sedimentation at the Aleutian arc was more a function of separate block activity, rather than arc-wide tectonics or eustatic controls. R. D. Larter & P. Barker (BAS, Cambridge) provided evidence for post-collision uplift

Clay mineralogy of late Cenozoic sediments in the CESAR cores, Alpha Ridge, central Arctic Ocean

The clay-sized (< 2 μm) fraction of the silty and arenaceous lutites constituting CESAR cores 14 and 103 (Alpha Ridge, central Arctic Ocean) is composed predominantly of mica (40–60%), with subequal percentages (10–20%) of kaolinite and chlorite and lesser amounts (< 5%) of smectite, quartz, plagioclase, and potassium feldspar. Calcite and dolomite also occur, but only intermittently in the upper 1.2 m; dissolution is probably responsible for their absence in other units. The silty lutites have a constant mineralogy throughout the 4.5 m long (~ 4.25 Ma) section, whereas some of the arenaceous intervals in the upper 2.1 m have markedly higher amounts of kaolinite, calcite, dolomite, and, to a lesser extent, smectite. The silty lutites were most likely derived from the Beaufort Sea shelf during nonglacial periods, whereas the distinctive components in the sandy layers suggest that they were transported from the Canadian Arctic Islands and Greenland by glacial ice. The absence of kaolinite peaks in the lower half of the core implies that the western Arctic Islands were not glaciated prior to 2.1 Ma, a conclusion supporting previous findings that the climate of the Arctic was warmer in the Pliocene.

The Quaternary stratigraphic record of British Columbia—evidence for episodic sedimentation and erosion controlled by glaciation

The terrestrial Quaternary stratigraphic record of British Columbia is largely a product of brief depositional events separated by long periods of nondeposition and erosion. Thick, stratified Quaternary sediments are present mainly in valleys and coastal lowlands and accumulated during periods of growth and decay of the Cordilleran Ice Sheet. At glacial maxima, till was deposited over large areas of low and moderate relief. However, at the same time, much of the landscape was eroded by glaciers.Sedimentation has been more restricted and has occurred at lower rates during nonglacial periods than during glaciations. On land, the only important sediment accumulation sites during nonglacials have been lakes, floodplains, and fans. However, large amounts of sediment have accumulated offshore, especially in fjords and basins such as the Strait of Georgia. Because of the restricted aspect of sedimentation during nonglacials, the stratigraphic record of these periods is meagre. In most places, true nonglacial units are thin and discontinuous, or they are absent altogether. Commonly, a nonglacial period is recorded only by an unconformity produced when streams incised valley fills shortly after the end of the preceding glaciation.

Summary of Quaternary Stratigraphy and history, Eastern Canada

Deposits of three Wisconsinan substages, Sangamonian Stage, and older Quaternary stratigraphic units are recognized in Eastern Canada. The age assignment of these units is based on radiocarbon dating and correlation of events. Quaternary deposits older than Sangamonian are recognized locally in Eastern Canada. In southern Ontario glacial deposits directly underlie Sangamonian sediments and are referred to as Illinoian in age. In other areas the ages of older sediments are largely unknown. Offshore core stratigraphy suggests that a major glaciation took place about 436 ka and that the Illinoian (oxygen isotope stage 6) was also a time of extensive glaciation. In this report Sangamonian is used as the name for the chronostratigraphic stage that includes all of deep-sea oxygen isotope stage 5 and consequently, on a regional basis, it includes warm interglacial deposits, glacial deposits and cool interglacial deposits. In southern Ontario the warm interglacial deposits are represented by the Don Formation, the stadial deposits by the Scarborough Formation and the cool interglacial deposits by the Pottery Road Formation. Warm interglacial deposits have not been recognized in Quebec (unless they are part of the pre-Johnville Sediments); the Becancour Till is included as glacial Sangamonian sediments, and the St. Pierre Sediments are recognized as cool interglacial sediments. The Early Wisconsinan appears to have been the time of maximum Wisconsinan glaciation in Eastern Canada with ice moving south of the International Boundary and well out onto the continental shelf. The Middle Wisconsinan was primarily a nonglacial period in southern Ontario and a glacial stade elsewhere in Eastern Canada. In southern Ontario the Middle Wisconsinan record has been subdivided into two interstades (Port Talbot and Plum Point), separated by a stade (Cherrytree). The Port Talbot Interstade began before the limit of radiocarbon dating (before 48 ka) and ended about 40 ka; glacial or near glacial conditions of the Cherrytree Stage lasted from about 40 to 35 ka ago, and the Plum Point Interstade was from about 35 to 23 ka ago. Central St. Lawrence Lowland was occupied by ice throughout the Middle Wisconsinan, but southeastern Quebec and the Montreal area were briefly deglaciated. Scattered evidence in Atlantic Canada suggests local deglaciation of coastal areas during Middle Wisconsinan but extensive ice remained on the continental shelf and ice from centres located on the shelf flowed onto land in at least two areas. Glacial conditions predominated throughout Eastern Canada during the Late Wisconsinan. At the Late Wisconsinan maximum, through-moving ice deposited the Catfish Creek Drift in southern Ontario but ice lobes, which developed in the basins of the Great Lakes after 15.5 ka, controlled ice flow during a period of ice margin oscillation and retreat. A calving bay developed in lower St. Lawrence valley, after the Late Wisconsinan maximum, causing a reversal of flow on the south shore of the St. Lawrence and replacing ice in the valley with the Champlain Sea about 12 ka. Late Wisconsinan glaciers were largely limited to land areas in Atlantic Canada. Local ice caps dominated with complicated patterns of flow and retreat developing as centres of accumulation shifted and competing ice centres achieved dominance. The period of Late Wisconsinan retreat in Atlantic Canada appears to have lasted from about 14 to 10 ka.

The submarine Quaternary stratigraphy of northern Spencer Gulf, South Australia

The seafloor morphology and lithology of northern Spencer Gulf, South Australia, is related to successive transgressions and regressions accompanying glacial and non-glacial periods. Vibrocoring has revealed a veneer of Holocene bioclastics and a sequence of Pleistocene marine strata which display varying degrees of pedogenesis, oxidation, decalcification and clay illuviation. The contact between the Holocene and Pleistocene sediments is marked by either a thin alluvial or aeolian horizon or by a soil horizon of variable development. The Pleistocene marine strata have been assigned to four Formations (older Pleistocene marine beds, Mambray Fm., False Bay Fm., and Lowly Point Fm.) based on superposition of lithofacies and intervening pedogenic horizons. A sequence of slightly altered, laminated lagoonal clays (Lowly Point Formation) and bryozoan rich limestones (False Bay Formation) has been encountered in deeper parts of the Gulf. Stratigraphically below these is a widespread, weathered marine unit (Mambray Formation) which contains abundant remains of the bivalve Anadara trapezia and the foraminifer Marginopora vertebralis, species absent from the present biota. This unit, in turn, is underlain by a sedimentary sequence strongly altered by pedogenesis and clay illuviation (older Pleistocene marine beds); its original marine character has been largely obliterated. A dearth of fluvial gravels and sand from the vibrocores, as well as evidence from palaeosols, indicate that a predominantly semi-arid to arid climate has persisted in the northern Gulf region since ca. 125,000 yrs ago, and that there has been little subsequent terrigenous material transported to the Gulf.

Effects of glaciations upon karst aquifers in Canada

In Canada there are ∼5.7 · 10 5 km 2 of limestone and marble outcrop, ∼6 · 10 5 km 2 of dolomite and ∼8 · 10 4 km 2 of sulfate rocks. In addition, halite subscrops beneath 5 · 10 5 km 2 of the central Prairie region and interacts with modern groundwater circulation to a varying extent. More than 90% of the total outcrop-subcrop has been repeatedly glaciated. The most recent glaciation (Late Wisconsin) terminated 13,000–5000 yrs. B.P. in different areas. Carbonate terrains still partly buried by glacier ice may be inspected in the Rocky Mountains. Nine distinct effects of glacial action upon the propagation and efficiency of karst aquifers are recognized. Destructive effects include erasure, dissection, infilling and injection. Bedrock solution may be inhibited during non-glacial periods by a cover of glacial drift rich in carbonate clasts. Glacial burial may also preserve an aquifer and enhance its storage characteristics. Aquifer expansion may be stimulated by raising the hydrostatic head or steepening hydraulic gradients, or by crustal flexure during deglacial isostatic rebound. The differing effects make general prediction of the state of an aquifer in glaciated terrains difficult.

Late Pleistocene stratigraphy of south-central British Columbia

The late Pleistocene deposits of south-central British Columbia record two major glacial and two major nonglacial periods of deposition. The oldest recognized Pleistocene deposits, called Westwold Sediments, were deposited during a nonglacial interval more than 60 000 years ago. Little information is available on the climate of this period, but permafrost may have been present at one time during final stages of deposition of Westwold Sediments. The latter part of this nonglacial period is probably correlative with the early Wisconsin Substage of the Great Lakes – St. Lawrence Valley area. However, deposition of the Westwold Sediments may have begun during the Sangamon Interglacial.Okanagan Centre Drift is the name applied to sediments deposited during the glaciation that followed deposition of Westwold Sediments. Okanagan Centre Drift is known to be older than 43 800 years BP and probably is older than 51 000. It is considered to correlate with an early Wisconsin glacial period.Bessette Sediments were deposited during the last major nonglacial period, which in south-central British Columbia persisted from at least 43 800 years BP (possibly more than 51 000) to about 19 000 years BP. This episode corresponds to Olympia Interglaciation of the Pacific Coast region and the mid-Wisconsin Substage of the Great Lakes – St. Lawrence Valley area. During parts of Olympia Interglaciation the climate was probably as warm as the present-day climate in the interior of British Columbia. Information from coastal regions indicates that there may have been periods of cooler and moister climate.Kamloops Lake Drift was deposited during the last major glaciation of south-central British Columbia. Ice occupied lowland areas from approximately 19 000 to 10 000 years BP. This period corresponds approximately to the Fraser Glaciation of the Pacific Coast region and the late Wisconsin Substage of central and eastern parts of North America.