Post-glacial Climatic Amelioration Research Articles

The age and depositional environments of the lower Karoo Moatize Coalfield of Mozambique: insights into the postglacial history of central Gondwana

The Moatize Coalfield belongs to a network of continental Karoo basins of central Mozambique, known as the Zambezi Basin. Palynological and sedimentological studies were performed on four coal exploration boreholes to determine the age, depositional settings, and overall geological evolution of its extensive coal deposits. Clastic formations recognised in this coalfield, in ascending order, are the Vúzi, Moatize and Matinde formations. Palynomorph assemblages indicate that the Moatize Coalfield succession ranges from Roadian (lower Guadalupian) to Changhsingian (upper Lopingian) in age. Two main depositional phases are identified, whose initiation and development are attributed to regional tectonic events and climate amelioration. The first phase formed towards the end of the deglacial period, characterised initially by fan deltas, represented by the upper Vúzi Formation, and the shift to lake–delta environments, represented by the lower part of the Moatize Formation. This phase took place from Roadian to the Wordian times. The lake–delta settings indicate a sediment aggradation trend with high subsidence rates in the lake basin, which, together with the associated post-glacial climate amelioration, led to the accumulation of coal deposits in swamps of the delta top and lake margins. The second depositional phase took place from Capitanian to Changhsingian times and related to fluvial environments initiated by uplift that reorganised the depocenter into alluvial plains characterised by bedload dominated rivers (braided) and overbank floodplains. Results obtained in this study provide critical information for the onset of the deglaciation events and the age of coal deposits in this part of Gondwana, important for wider stratigraphic correlation of these events in Africa and throughout the Gondwana.

Fusulinid-bearing oolites from the Tengchong Block in western Yunnan, SW China: Early Permian warming signal in the eastern peri-Gondwana

Discovery of fusulinid-bearing oolites from the Tengchong Block in western Yunnan, China, provides new insights into Permian paleoclimatic history of the eastern peri-Gondwana. In the northern Tengchong Block, new carbonate samples from the lower part of the Dadongchang Formation yield a monotonous fusulinid assemblage, comprising Eoparafusulina tschernyschewi tschernyschewi, E. tschernyschewi oblonga, E. tibetica, E. aff. tschernyschewi tschernyschewi and E. aff. laudoni. This assemblage correlates well to late Sakmarian–Artinskian fusulinids widespread among the Cimmerian blocks in peri-Gondwana, which were characterized by low diversity and dominance of cosmopolitan taxa. Such fusulinids have been interpreted to indicate temperate-water environment in the aftermath of late Paleozoic glaciation. Moreover, the eastern Cimmerian region has been suggested, by both paleontological and sedimentological data, to be even cooler than the western region especially during the Early Permian. However, the fusulinids of this study unexpectedly occur within oolites, as ooids diagnostic for warm-water settings, have never been recorded from Early Permian strata of any eastern Cimmerian block. This new finding in the northern Tengchong Block indicate that the shallow marine there was warm enough to accommodate not only poorly diversified fusulinids but also oolites, even immediately posterior to the late Paleozoic glaciation. The appearance of these oolites is more likely ascribed to a warming pulse of sea-surface temperature in the context of post-glacial climatic amelioration than to the northward drift of the Tengchong Block.

Southwestern Gondwana’s Permian climate amelioration recorded in coal-bearing deposits of the Moatize sub-basin (Mozambique)

The postglacial climate history of Gondwana represents the most prominent climate amelioration in the Phanerozoic, ranging from severe icehouse conditions in the Late Carboniferous (Pennsylvanian) to extreme hothouse conditions in the Early Triassic. Here we report new sedimentological and palynological data from a 350m thick coal-bearing succession intersected by borehole 945L_0022, drilled in the eastern Tete Province of Mozambique, which documents southwestern Gondwana’s Permian postglacial climate amelioration. Palynofacies data further support the environmental reconstructions interpreted from the sedimentary succession. Changes in the palynomorph assemblage document a shift from cold, to cool-temperate, to warm-temperate climatic conditions. This climate signature corresponds with observations from other depositional environments elsewhere in southern Africa, and thus enables correlation on a regional to interregional scale. Thick lacustrine deposits are described within the lower coal-bearing succession, reflecting the final glacial retreat, with melt waters supplying fresh water to the incipient lacustrine system. Lakes as characteristic postglacial sedimentary sinks are excellent palaeoclimate archives and the high Total Organic Carbon content of these fine-grained clastic sediments also makes them potential source rock targets for oil and gas.

Diatoms from Lake Kushu: A pilot study to test the potential of a Late Quaternary palaeoenvironmental archive from Rebun Island (Hokkaido Region, Japan)

Rebun Island is a key research area for the Baikal-Hokkaido Archaeology Project to better understand the dynamics of the Neolithic hunter–gatherers in the NW Pacific region. Hence, the ca. 19.5m sediment core RK12 spanning the last ca. 16.6cal. kyr BP was obtained from Lake Kushu. Our aim is to test its potential as a high-resolution multi-proxy archive. Here, we used diatoms to investigate the modern ecosystem of Lake Kushu and its surrounding area on Rebun Island and of Hime-numa Pond on Rishiri Island and selected core samples for comparison. Modern diatom and stable isotope analyses show well-mixed freshwater bodies with eutrophic, alkaline conditions. The fossil diatom and geochemical sediment analyses display three phases that represent major changes in the lake development: (i) a marshy phase (ca. 16.6–10cal. kyr BP); (ii) a brackish water lagoon phase (ca. 10–6.6cal. kyr BP); and (iii) a freshwater lake phase (since ca. 6.6cal. kyr BP). This shows the major role of the post-glacial climate amelioration, global sea-level rise and marine transgression in the development of this landscape. Further analyses will provide a palaeolimnological record at (sub-)decadal resolution that will facilitate the interpretation of the hunter–gatherer dynamics.

The late Paleozoic palynological diversity in southernmost Paraná (Uruguay), Claromecó and Paganzo basins (Argentina), Western Gondwana

This study explores the changes in palynoflora diversity of the late Paleozoic in boreholes DI.NA.MI.GE. 254 (26 samples) and DI.NA.MI.GE. 221 (14 samples) of the Paraná Basin in Uruguay and in 18 surface samples of the La Deheza Formation (Paganzo Basin) and 10 samples of borehole UTAL.CMM1.La Estrella.x-1 (Claromecó Basin) in Argentina. Possible relationships among biostratigraphic zones, diversity levels, facies and climatic evolution patterns in Western Gondwana are studied. Diversity curves of boreholes 221 and 254 and the La Deheza Formation outcrop exhibit similar diversity evolution patterns, i.e., an increase in lower strata diversity and a decrease in upper strata diversity. The disappearance events are determined to be more prominent in biozones of the Cisuralian to the Guadalupian age and less prominent in biozones of the early Cisuralian age. The number of genera raises from the glaciomarine facies, through the deltaic and the marine facies, up to the shallow marine or lagoon facies, in which the disappearance rates become more prominent. . The diversity of the lower part of the La Estrella borehole is lesser than that of the other sequences These diversity, disappearance and appearance behaviors may reflect post-glacial climatic amelioration patterns and the beginning of an arid phase.

Formation of paleovalleys in the Central Himalaya during valley aggradation

The formation of paleovalleys in mountainous regions is considered to result from extreme events such as landslides and glacial or landslide lake outburst floods. According to IPCC (2012) the extreme events are rarest of the rare weather/climatic events when the climate/weather variable is significantly above or below the defined threshold value. The present study suggests that paleovalleys can also form during years long periods of valley aggradation. A series of paleovalleys thus formed runs parallel to the present river course. In this study, we suggest that paleovalleys in the Alaknanda valley of the Central Himalaya have formed in two ways: 1) major valley aggradation and 2) local events of landsliding and lake breaching. Most of the paleovalleys in the Alaknanda valley formed during a major valley aggradation phase (between 15 and 8ka). Paleovalleys formed due to local landsliding also formed around 8ka. Local landslides were triggered due to high rainfall in lower valley reaches during unstable climatic conditions. Therefore, the formation of paleovalleys both by regional and local mode within 15–8ka indicates that the valley was receiving excess sediment from upper catchment as well as from lower reaches during this period. This phase of excess sediment supply and valley aggradation coincides well with post glacial climatic amelioration. Therefore the study underlines the role of climate in the time scales of 103 years in shaping the landscape of an active mountain like the Himalaya. The role of other landscape changing agencies such as tectonics and erosion is not accounted in the present study.

First discovery of Pleistocene orangutan (Pongo sp.) fossils in Peninsular Malaysia: Biogeographic and paleoenvironmental implications

Nine isolated fossil Pongo teeth from two cave sites in Peninsular Malaysia are reported. These are the first fossil Pongo specimens recorded in Peninsular Malaysia and represent significant southward extensions of the ancient Southeast Asian continental range of fossil Pongo during two key periods of the Quaternary. These new records from Peninsular Malaysia show that ancestral Pongo successfully passed the major biogeographical divide between mainland continental Southeast Asia and the Sunda subregion before 500 ka (thousand years ago).If the presence of Pongo remains in fossil assemblages indicates prevailing forest habitat, then the persistence of Pongo at Batu Caves until 60 ka implies that during the Last Glacial Phase sufficient forest cover persisted in the west coast plain of what is now Peninsular Malaysia at least ten millennia after a presumed corridor of desiccation had extended to central and east Java. Ultimately, environmental conditions of the peninsula during the Last Glacial Maximum evidently became inhospitable for Pongo, causing local extinction. Following post-glacial climatic amelioration and reforestation, a renewed sea barrier prevented re-colonization from the rainforest refugium in Sumatra, accounting for the present day absence of Pongo in apparently hospitable lowland evergreen rainforest of Peninsular Malaysia. The new teeth provide further evidence that Pongo did not undergo a consistent trend toward dental size reduction over time.

Amphibian phylogeography: a model for understanding historical aspects of species distributions

Phylogeographic analysis has become a major tool for investigating historical aspects of biogeography and population genetic structure. Anuran amphibians are particularly informative subjects for phylogeographic research on account of their global distribution, high degree of population genetic structure and ease of sampling. Studies on all the world's inhabited continents have demonstrated the nature and locations of refugia, including the Gulf Coast in North America and the Mediterranean peninsulas in Europe during the Pleistocene glaciations; the importance of vicariance events such as the uplift of the Andes in shaping modern distributions; and colonization routes in temperate zones during postglacial climatic amelioration. Features identified as important to amphibian biogeography, notably mountain ranges, large rivers such as the Amazon and climatic fluctuations, are common to many other taxa. New analytical methods based on coalescent, Bayesian and likelihood approaches permit more rigorous hypothesis testing than has hitherto been possible and offer the prospect of even more detailed insights into species and population history in future work.

Phylogeography of the Tree Hymenaea stigonocarpa (Fabaceae: Caesalpinioideae) and the Influence of Quaternary Climate Changes in the Brazilian Cerrado

Hymenaea stigonocarpa (Fabaceae: Caesalpinioideae) is an endemic tree from the Brazilian cerrado (savanna vegetation), a biome classified as a hotspot for conservation priority. This study investigates the phylogeographic structure of H. stigonocarpa, in order to understand the processes that have led to its current spatial genetic pattern. The polymorphism level and spatial distribution of variants of the plastid non-coding region between the genes psbC and trnS were investigated in 175 individuals from 17 populations, covering the greater part of the total distribution of the species. Molecular diversity indices were calculated and intra-specific relationships were inferred by the construction of haplotype networks using the median-joining method. Genetic differentiation among populations and main geographical groups was evaluated using spatial analysis of molecular variance (SAMOVA). Twenty-three different haplotypes were identified. The level of differentiation among the populations analysed was relatively high (F(ST) = 0.692). Phylogeographic analyses showed a clear association between the haplotype network and geographic distribution of populations, revealing three main geographical groups: western, central and eastern. SAMOVA corroborated this finding, indicating that most of the variation can be attributed to differences among these three groups (58.8 %), with little difference among populations within groups (F(SC) = 0.252). The subdivision of the geographic distribution of H. stigonocarpa populations into three genetically differentiated groups can be associated with Quaternary climatic changes. The data suggest that during glacial times H. stigonocarpa populations became extinct in most parts of the southern present-day cerrado area. Milder climatic conditions in the north and eastern portions of the cerrado resulted in maintenance of populations in these regions. Thus it is inferred that the most southern part of the present-day cerrado was re-colonized by different lineages from northern parts of this biome, after postglacial climate amelioration.

The vegetation history of the last glacial–interglacial cycle in eastern New South Wales, Australia

AbstractWe present a reconstruction of the vegetation history of the last glacial–interglacial cycle (ca. 75 k cal. yr BP–present) at Redhead Lagoon, an enclosed lake basin in coastal, eastern New South Wales, Australia. The sequence of vegetation change at the site is broadly comparable with the pattern of climatically induced changes observed in many other pollen records in southeast Australia. Open woodland–herbland and woodland–forest communities correspond with glacial and interglacial periods respectively, with an additional change towards a more open understorey vegetation assemblage over the last 40 000 yr. The driest conditions appear to have occurred during the height of the last glacial (some time between 30 and 20 k cal. yr BP). This is consistent with other records from southeast Australia, and provides support for a poleward shift in the subtropical anticyclone belt and, less certainly, for the thesis that the Southern Hemisphere westerlies intensified during this period. In marked contrast to most sites in southeast Australia, Casuarinaceae dominates the pollen record through the height of the last glacial period and into the Holocene. The postglacial climatic amelioration is accompanied by the general reappearance of tree pollen in the record, by the disappearance of several open and disturbed environment indicator taxa, by increases in organic sediment deposition and pollen taxon diversity, and by higher water balances. While climate appears to have been the major control on patterns of vegetation change at this site throughout most of the last glacial–interglacial cycle, changes in depositional environment and hydrology have also played a role. Significantly, substantial increases in the rate and magnitude of many indicators of environmental disturbance since European settlement suggest that humans are now the most important mechanism for environmental change. Copyright © 2006 John Wiley & Sons, Ltd.

Late Quaternary climate change and spatial genetic structure in the shrubBanksia hookeriana

Spatial genetic variation within species is influenced by both contemporary and historical factors. We attempted to assess the impact of increased aridity and lower temperatures associated with the last glacial maximum on possible refugia and the structuring of genetic variation in Banksia hookeriana, a shrub species restricted to deep sands on the Eneabba sandplain and adjacent Gingin Scarp/Dandaragan Plateau, centred 300 km north of Perth, Western Australia. We used optically stimulated luminescence (OSL) dating to estimate the last time these sands were mobile, as well as amplified fragment length polymorphisms (AFLP) to infer spatial patterns and the phylogeographical history of genetic variation among 15 populations of B. hookeriana. While genetic variation at the species level was high, with 96.6% of 238 AFLP markers polymorphic, average within population gene diversity was low (H(pop) = 0.16). Of the total genetic variation, an analysis of molecular variance (amova) partitioned 70% within populations, 24% among populations within substrate and 6% between substrates. There was an isolation-by-distance effect among populations within the same substrate, but not across substrates, and ordination highlighted genetic differentiation between the sandplain and scarp/plateau populations. A neighbour-joining tree identified the sandplain populations as a distinct clade, with the exception of the most northern sandplain population, which clustered with two northern and eastern plateau populations. The most southern plateau populations formed a clade sister to the sandplain clade. OSL dating of sand at six extant populations suggested that dunes were last mobile 15,000-35,000 years ago, with no clear difference in the ages of sandplain and plateau dunes. These data are consistent with a historical scenario of (re)colonization from isolated refugia of smaller populations either within the patchily vegetated sandplain and/or refugia at the northern, eastern and southern sandplain/scarp margins following postglacial climate amelioration and dune stabilization. Historic interpretations were confounded by the possible effects of long-distance dispersal, natural selection by substrate, and weak and/or ancient introgression with the sister species, Banksia prionotes.

Late Pleistocene and early Holocene climate and limnological changes in the Sierra Nevada, California, USA inferred from midges (Insecta: Diptera: Chironomidae)

Chironomid and stratigraphic analyses of a lake sediment core recovered from a high-elevation lake in the central Sierra Nevada, California, USA, was undertaken to assess chironomid community development during the Pleistocene–Holocene transition and to quantitatively reconstruct the thermal regime that existed during this interval. Between 14 800 cal yr BP and 13 700 cal yr BP the chironomid community consisted almost exclusively of Heterotrissocladius, suggesting this period was characterized by extremely cold climatic conditions. Evidence of post-glacial climatic amelioration, as manifested by increases in thermophilous chironomid taxa, head capsule concentrations, and taxon richness and diversity, commenced at approximately 13 300 cal yr BP. In order to quantify the magnitude of the water temperature changes associated with post-glacial climatic amelioration, a recently developed chironomid-based inference model for surface water temperature was applied to the subfossil chironomid assemblages. The one-component, weighted-averaging partial least squares (WA-PLS) model has an r2jack=0.72, RMSEPjack=1.1°C and a maximum bias of 1.24°C. The reconstructed surface water temperatures suggest a minimum warming of approximately 4.7°C occurred during the Pleistocene–Holocene transition. However, warming during this interval may not have been monotonic. Evidence of the Younger Dryas has been previously discovered in the study area and adjacent regions; Our research indicates that changes in chironomid community composition and an inferred short-term cooling event occurred between 12 000 cal yr BP and 11 500 cal yr BP, which may represent a local manifestation of the Younger Dryas. Chironomid community development during the Pleistocene–Holocene transition appears to primarily reflect the influence of changing climate conditions.

Genetic Variation and Biogeographic History in the Restricted Southwestern Australian Shrub, Banksia Hookeriana

Banksia hookeriana (Proteaceae) is an endemic, fire-killed, shrub of southwestern (SW) Australian Mediterranean-type shrublands restricted to acid sandplains and dunes over a geographic range of only 80 x 30 km. Amplified fragment length polymorphism (AFLP) markers were used to characterize genetic variation within and among six populations encompassing the species extant geographic range. Populations from the north, east, and south of the species range were located on deep sands over laterite on the Gingin Scarp (90-180 m a.s.l.), while three populations were on lowland dunes of the Eneabba Plain (50-80 m a.s.l.). The geomorphic history of the acid sands upon which the species occurs is poorly understood. Regardless of their origins, at least some of these sands may have been mobile during the arid phase of the last glacial-interglacial cycle. A high level of genetic variation was detected, with 94.4% of 231 AFLP markers polymorphic. Significant genetic differentiation among most populations suggested an overall low level of gene flow and the accumulation of genetic differences within relatively genetically isolated populations. A phylogeographic analysis produced a clear dichotomy between upland and lowland populations. Preliminary interpretation suggests that populations on the Eneabba Plain may have expanded there from refugia on the Gingin Scarp following postglacial climate amelioration and dune stabilization. However, the tree is unrooted and differences between upland and plains populations may also reflect different selection pressures reflecting habitat variation.

The 2.7–2.0 Ga volcano-sedimentary record of Africa, India and Australia: evidence for global and local changes in sea level and continental freeboard

The 2.7–2.0 Ga volcano-sedimentary records of the African, Indian and Australian cratons indicate two broadly defined periods of extensive drowning of the emergent continental areas, concomitant with lowered freeboard. Carbonate-banded iron formation (BIF) platforms characterised the first such event, at ca 2.6–2.4 Ga (Africa and Australia) to 2.7 Ga (India). These earlier globally enhanced sea levels are ascribed to increased mid-ocean ridge activity, possibly related to breakup of a postulated Late Archaean ‘southern’ supercontinent. Alternatively, a transition from global-scale catastrophic mantle overturn events to the onset of plate tectonics may have occurred in the Late Archaean (Nelson, 1998. Earth Planet. Sci. Lett. 158, 109–119). Both explanations of increased mid-ocean ridge activity are compatible with significant Early to Middle Archaean crustal growth (Armstrong, 1981. Phil. Trans. R Soc. London A 301, 443–472), with the emergent high freeboard cratons being subjected to aggressive weathering and erosion. Enhanced continental crustal growth near the Archaean–Proterozoic boundary (McLennan and Taylor, 1982. J. Geol. 90, 347–361), related to the development of significant island arc complexes, would have resulted in common lowered freeboard–enhanced sea level conditions at the passive margins of the ‘southern’ cratons. The diachronous nature of these earlier transgressions in the various cratons may reflect the effect of local tectonic movements and/or the thermal state of the cratons. From ca 2.4–2.2 Ga, cratons that make up the present-day continents of India, Africa and Australia had relatively high continental freeboard and lowered sea levels. Glacigenic deposits are preserved on the Kaapvaal (Africa), Singhbhum (India) and Pilbara (Australia) cratons. The second broadly defined drowning event, at ca <2.2 and >2.15 Ga, was probably due to post-glacial climatic amelioration. Freeboard was reduced by the combination of eustatic rise and the reestablishment of aggressive weathering as warmer palaeoclimates returned. In India, carbonates were more prominent than the siliciclastic sediments (including prominent black shales) seen in Africa and Australia.

Environmental changes during the Late Glacial and Post-Glacial in the central Pyrenees (France): new charcoal analysis and archaeological data

The archaeological site at Troubat (Troubat, départment of Hautes Pyrénées) has provided the first long charcoal sequence in the central Pyrenees. It offers information concerning the transformations in the vegetation cover due primarily to climate, from the Late Glacial Bölling–Alleröd interstadial to the middle of the Post-Glacial. Four main phases illustrate the changes in vegetation recorded in the charcoal data. Between about 13,000 B.P. and 11,320±410 B.P. (phase T1) a vegetation with Juniperus, some Rosaceae ( Prunus types 1, 2, 3), Rhamnus alpina, R. cathartica/saxatilis, R. pumila, Hippophae rhamnoides and Betula verrucosa is evidence of an open environment with colonising shrub cover established in a climate of dry mountain or even subalpine type. This change is correlated with the Late Glacial interstadial. At about 10,770±100 B.P., a reduction of the Juniperus pioneer stage cover, which developed thanks to the Bölling/Alleröd warming, together with an increase of Rhamnus and Rosaceae, which would be a response of the vegetation to the first cooling of the Younger Dryas (phase T2). Around 9700±80 B.P., a phase of forest colonisation by Corylus and the establishment of deciduous oak forests which corresponds to the Post-Glacial climatic amelioration is noted (phase T3). Then, at about 8625±80 B.P., there is affirmation of an increase in deciduous oak forests of «collinean» type. Pinus sylvestris, whose role is minor at Troubat, as well as Corylus, see their frequency diminish in response to an increasingly dense forest environment (phase T4).

Post-Glacial Climatic Amelioration and the Extinction of Bison taylori

Post-Glacial Climatic Amelioration and the Extinction of <i>Bison taylori</i>