Petrology of palaeosols and other terrestrial sediments on Aldabra, Western Indian Ocean

1975 ◽  
Vol 273 (921) ◽  
pp. 1-32 ◽  
Keyword(s):  
Environmental Changes ◽  
Climatic Factors ◽  
Western Indian Ocean ◽  
Time Interval ◽  
Discrete Events ◽  
Rock Unit ◽  
Faecal Pellets ◽  
Marine Deposits ◽  
Large Numbers ◽  
Terrestrial Sediments

Rocks exposed on Aldabra include at least six groups of marine deposits separated by terrestrial horizons. Sediments considered are divided into three major groups following important marine formations, the Picard Calcarenites, the Takamaka Limestone and the Aldabra Limestone. Seven textural groups have been identified (1) homogeneous textures in unmodified sediments, (2) crumb-like aggregates of micrite believed to have developed in a dry system, (3) fractured sediments, resulting from drying of wet coherent micrites, (4) vesicular structures, (5) glaebular textures, including concentric glaebules, faecal pellets and bodies formed by inorganic processes of surface accretion, (6) pedotubules, resulting from penetration by rootlets or burrowing organisms and (7) laminate structures formed by incremental deposition of sediment controlled by organisms or, possibly, climatic factors. Identification of the environments of deposition is confirmed by the presence of terrestrial faunas, but textures might be used alone to identify similar horizons within sequences where fossils are absent. Deposits overlying the Picard Calcarenites include unmodified sediments consisting of marine bioclasts but containing terrestrial snails ( Trophidophora ), tortoise bones and rootlet horizons. With these are associated yellow-brown sometimes laminate soils with distinctive textures and a fauna which includes Succinea . The Takamaka Limestone is overlain by deposits which include dense micrites containing well preserved rootlets, and texturally disorganized materials with cavities which have opened by shrinkage and differential compaction. Some are again strongly laminated. Multiphase cementation sequences are present in limited areas. At least two discrete terrestrial events followed the formation of widespread marine erosion surfaces. The emergence which halted deposition of the Aldabra Limestone brought about the formation of laminated crusts, solution cavity fillings (some containing large numbers of tortoise and other bones), cave deposits, stromatolites and soils, probably in a series of discrete events rather than during a single extended time interval. Within the terrestrial sediments diagenetic evidence proves unreliable in indicating the complexity or frequency of environmental changes of individual samples. Once a stable mineralogy is established the potential for alteration is confined to the periphery of the rock unit. Mineralogically most of the sediments are calcite but small quantities of chlorites and phosphates have been detected. Insoluble residues appear not to contain clays and the bulk are believed to be derived ultimately from organic sources.

scholarly journals Current understanding on the Cambrian Explosion: questions and answers

PalZ ◽  
2021 ◽  
Author(s):  
Xingliang Zhang ◽  
Degan Shu
Keyword(s):  
Environmental Changes ◽  
Size Variation ◽  
Progressive Increase ◽  
Cambrian Explosion ◽  
Time Interval ◽  
Early Cambrian ◽  
Ecological Processes ◽  
Questions And Answers ◽  
Evolutionary Event ◽  
History Of

AbstractThe Cambrian Explosion by nature is a three-phased explosion of animal body plans alongside episodic biomineralization, pulsed change of generic diversity, body size variation, and progressive increase of ecosystem complexity. The Cambrian was a time of crown groups nested by numbers of stem groups with a high-rank taxonomy of Linnaean system (classes and above). Some stem groups temporarily succeeded while others were ephemeral and underrepresented by few taxa. The high number of stem groups in the early history of animals is a major reason for morphological gaps across phyla that we see today. Most phylum-level clades achieved their maximal disparity (or morphological breadth) during the time interval close to their first appearance in the fossil record during the early Cambrian, whereas others, principally arthropods and chordates, exhibit a progressive exploration of morphospace in subsequent Phanerozoic. The overall envelope of metazoan morphospace occupation was already broad in the early Cambrian though it did not reach maximal disparity nor has diminished significantly as a consequence of extinction since the Cambrian. Intrinsic and extrinsic causes were extensively discussed but they are merely prerequisites for the Cambrian Explosion. Without the molecular evolution, there could be no Cambrian Explosion. However, the developmental system is alone insufficient to explain Cambrian Explosion. Time-equivalent environmental changes were often considered as extrinsic causes, but the time coincidence is also insufficient to establish causality. Like any other evolutionary event, it is the ecology that make the Cambrian Explosion possible though ecological processes failed to cause a burst of new body plans in the subsequent evolutionary radiations. The Cambrian Explosion is a polythetic event in natural history and manifested in many aspects. No simple, single cause can explain the entire phenomenon.

Interactions betweenTrypanosoma bruceiandBabesiaspp. andPlasmodiumspp. in mice

Parasitology ◽  
1985 ◽  
Vol 90 (2) ◽  
pp. 241-254 ◽  
Author(s):  
Stephanie M. Millott ◽  
F. E. G. Cox
Keyword(s):  
Trypanosoma Brucei ◽  
Babesia Microti ◽  
Cell Populations ◽  
Time Interval ◽  
Oxygen Species ◽  
Plasmodium Chabaudi ◽  
Subsequent Infection ◽  
Activated Oxygen ◽  
Large Numbers ◽  
Intracellular Parasites

Swiss mice with chronicTrypanosoma bruceiinfections become refractory to subsequent infection withBabesia microtiandB. rodhaini. Infection withB. microti7 days afterT. bruceiresulted in an obvious inhibition of the babesia parasitaemias and this inhibition became more profound as the time interval between the infections increased, until at 17–20 days the parasitaemias were totally abolished. Even after intravenous injection of large numbers of parasites parasitaemias were inhibited. Similar inhibition was obtained in BALB/c mice but not in C57BL/6 mice. Mice with establishedT. bruceiinfections also showed reduced susceptibility toB. rodhaini. In mice similarly infected withT. bruceiand the malaria parasitesPlasmodium chabaudi chabaudiandP. c. adamithe pre-patent periods were noticeably prolonged but the subsequent parasitaemias were unaffected. Infections withP. yoeliiwere unaffected.Trypanosoma bruceiinfections were not affected by the intracellular parasites. Among the mechanisms investigated to explain these findings were changes in red blood cell populations, cross-reacting antigens, the release of toxic factors and the generation of activated oxygen species. None of these could account for the inhibition observed.

The ecology of immature phases of Trichostrongyle nematodes: II. The effect of climatic factors on the availability of the infective larvae of Trichostrongylus retortaeformis to the host

Parasitology ◽  
1948 ◽  
Vol 39 (1-2) ◽  
pp. 26-38 ◽  
Author(s):  
H. D. Crofton
Keyword(s):  
Climatic Factors ◽  
Faecal Pellet ◽  
Cold Weather ◽  
Maximum Temperature ◽  
Infective Stage ◽  
Faecal Pellets ◽  
Infective Larvae ◽  
High Death ◽  
Maximum Temperatures ◽  
Rate Of Evaporation

1. Eggs and larvae of Trichostrongylus retortaeformis were used.2. The rate of hatching of eggs was shown to be mainly related to temperature. From November to March, when maximum temperatures were below 50° F., there was no hatching. When maximum temperatures of 50–55° F. occurred eggs hatched on or before the fifteenth day, but never during the first 8 days. Eggs hatched in 8 days or less when maximum temperatures of 60–80° F. occurred.3. When the rate of evaporation in the air was high, eggs still hatched and reached the infective stage, the grass blades reducing the rate of loss of moisture from the faecal pellet. Laboratory experiments show that eggs may not develop to the infective stage if the faecal pellets are on a grassless portion of the pasture. This is most likely to occur when the rate of evaporation is high and the temperature low.4. Hatching may be delayed by cold conditions, but some eggs remain viable for long periods and they hatch when the temperature rises. Eggs passed by the host in the autumn can survive a cold winter and hatch in the spring, but eggs passed during the coldest period die.5. During periods when the maximum temperature never exceeded 55° F., little or no migration of larvae occurred. When temperatures rose above 55° F. the number of larvae migrating increased; but rise of temperature was associated with increase in the rate of evaporation. High rates of evaporation reduced the number of larvae migrating on the grass blades.6. Some infective larvae died soon after exposure on grass plots, but a small number survived long periods. In cold weather some larvae were still alive after 20 weeks. A high death-rate occurred in warm weather. A large proportion of the larvae died during periods in which the rate of evaporation was high; in one of these periods 95% of the larvae were dead at the end of 4 weeks' exposure.7. The number of larvae on grass blades of a pasture was shown to be dependent, at any time, upon the climate at that time, and upon past conditions which had influenced hatching and survival:

Quaternary Climatic Changes and Landscape Evolution

2005 ◽  
Author(s):  
Jürgen Ehlers
Keyword(s):  
Climatic Change ◽  
Large Scale ◽  
Western Europe ◽  
Ice Sheets ◽  
Climatic Changes ◽  
Mountain Glaciers ◽  
Marine Deposits ◽  
The North ◽  
Terrestrial Sediments ◽  
International Geological Congress

The last 2–3 Ma have witnessed climatic changes of a scale unknown to the preceding 300 Ma. In the cold periods vegetation was reduced to a steppe, giving rise to large-scale aeolian deposition of sand and loess and river sands and gravels. In the warm stages, flora and fauna recolonized the region. Parts of Europe were repeatedly covered by mountain glaciers or continental ice sheets which brought along huge amounts of unweathered rock debris from their source areas. The ice sheets dammed rivers and redirected drainage towards the North Sea. They created a new, glacial landscape. This chapter presents an outline of the climatic history, and in particular the glacial processes involved in shaping the landscapes of western Europe. By convention, geologists generally tend to draw stratigraphical boundaries in marine deposits because they are more likely to represent continuous sedimentation and relatively consistent environments in comparison to terrestrial sediments. However, marine deposits from the period in question are relatively rarely exposed at the surface. According to a conclusion of the International Geological Congress 1948 the Tertiary/Quaternary boundary was defined as the base of the marine deposits of the Calabrian in southern Italy. In the Calabrian sediments fossils are found that reflect a very distinct climatic cooling (amongst others the foraminifer Hyalinea baltica). This climatic change roughly coincides with a reversal of the earth’s magnetic field; it is situated at the upper boundary of what is called the Olduvai Event. Consequently, it is relatively easy to identify; its age is today estimated at 1.77 Ma (Shackleton et al. 1990). However, in contrast to the older parts of the earth’s history, the significant changes within the Quaternary are not changes in faunal composition but changes in climate. For reasons of long-term climatic evolution the base of the Calabrian is not a very suitable global boundary. Its adoption excludes some of the major glaciations from the Quaternary. Therefore, in major parts of Europe another Tertiary/Quaternary boundary is in use, based on the stratigraphy of the Lower Rhine area (e.g. Zagwijn 1989). Here the most significant climatic change is already recorded as far back as the Gauss/Matuyama magnetic reversal (some 2.6 Ma ago).

Using Diatoms as Ecological and Paleoecological Indicators in Riverine Environments

2007 ◽  
Vol 13 ◽  
pp. 121-130
Author(s):  
Jeffery R. Stone
Keyword(s):  
Spatial Distribution ◽  
Environmental Changes ◽  
Climatic Factors ◽  
Diatom Assemblages ◽  
Meandering River ◽  
Rates Of Change ◽  
Terminal Lakes ◽  
Riverine Systems ◽  
The Impact ◽  
Selection Of

Fossil diatom assemblages are useful for reconstructing past environmental changes in riverine systems. However, few studies have attempted to utilize paleolimnological techniques in these settings. Analysis of sediments from riverine environments can provide key information predating the impact of human development, which cannot be acquired by other means. Paleolimnological techniques can be used to determine the natural variability in these systems and to estimate the magnitude and rates of change that the environment may have undergone as a result of anthropogenic or climatic factors, and to provide realistic goals for management of negatively-impacted systems.Reconstructing past riverine settings requires an understanding of the factors that control the spatial distribution of diatoms in riverine settings; this paper discusses the impact of resources, stressors, and disturbance events, which are the primary controls on the distribution of benthic diatoms in modern riverine environments. A selection of case studies that utilize paleolimnological techniques to infer past stream hydrology are also discussed; these examples encompass the use of fossil diatom assemblages from sediments recovered from lowland floodplain and meandering river systems, estuarine environments, fluvial lakes, arctic deltaic environments, and terminal lakes.

scholarly journals Monitoring the Spatial and Temporal Variations in The Water Surface and Floating Algal Bloom Areas in Dongting Lake Using a Long-Term MODIS Image Time Series

2020 ◽  
Vol 12 (21) ◽  
pp. 3622
Author(s):  
Mengmeng Cao ◽  
Kebiao Mao ◽  
Xinyi Shen ◽  
Tongren Xu ◽  
Yibo Yan ◽  
...  
Keyword(s):  
Water Quality ◽  
Human Activities ◽  
Water Surface ◽  
Algal Bloom ◽  
Environmental Changes ◽  
Climatic Factors ◽  
Dongting Lake ◽  
Dynamic Learning ◽  
Traditional Methods

Significant water quality changes have been observed in the Dongting Lake region due to environmental changes and the strong influence of human activities. To protect and manage Dongting Lake, the long-term dynamics of the water surface and algal bloom areas were systematically analyzed and quantified for the first time based on 17 years of Moderate Resolution Imaging Spectroradiometer (MODIS) observations. The traditional methods (index-based threshold algorithms) were optimized by a dynamic learning neural network (DL-NN) to extract and identify the water surface area and algal bloom area while reducing the extraction complexity and improving the extraction accuracy. The extraction accuracy exceeded 94.5% for the water and algal bloom areas, and the analysis showed decreases in the algal bloom and water surface areas from 2001–2017. Additionally, the variations in the water surface and algal bloom areas are greatly affected by human activities and climatic factors. The results of these analyses can help us better monitor human contamination in Dongting Lake and take measures to control the water quality during certain periods, which is crucial for future management. Moreover, the traditional methods optimized by the DL-NN used in this study can be extended to other inland lakes to assess and monitor long-term temporal and spatial variations in algal bloom areas and can also be used to acquire baseline information for future assessments of the water quality of lakes.

scholarly journals The impact of African aridity on the isotopic signature of Atlantic deep waters across the Middle Pleistocene Transition

2012 ◽  
Vol 77 (1) ◽  
pp. 182-191 ◽  
Author(s):  
Bruno Malaizé ◽  
Elsa Jullien ◽  
Amandine Tisserand ◽  
Charlotte Skonieczny ◽  
E. Francis Grousset ◽  
...  
Keyword(s):  
Deep Water ◽  
Benthic Foraminifera ◽  
Environmental Changes ◽  
Phase Relationship ◽  
Isotopic Signature ◽  
Middle Pleistocene ◽  
Time Interval ◽  
Deep Waters ◽  
Time Period ◽  
The Impact

A high resolution analysis of benthic foraminifera as well as of aeolian terrigenous proxies extracted from a 37 m-long marine core located off the Mauritanian margin spanning the last ~ 1.2 Ma, documents the possible link between major continental environmental changes with a shift in the isotopic signature of deep waters around 1.0–0.9 Ma, within the so-called Mid-Pleistocene Transition (MPT) time period. The increase in the oxygen isotopic composition of deep waters, as seen through the benthic foraminifera δ18O values, is consistent with the growth of larger ice sheets known to have occurred during this transition. Deep-water mass δ13C changes, also estimated from benthic foraminifera, show a strong depletion for the same time interval. This drastic change in δ13C values is concomitant with a worldwide 0.3‰ decrease observed in the major deep oceanic waters for the MPT time period. The phase relationship between aeolian terrigeneous signal increase and this δ13C decrease in our record, as well as in other paleorecords, supports the hypothesis of a global aridification amongst others processes to explain the deep-water masses isotopic signature changes during the MPT. In any case, the isotopic shifts imply major changes in the end-member δ18O and δ13C values of deep waters.

scholarly journals Circum-Antarctic coastal environmental shifts during the Late Quaternary reflected by emerged marine deposits

1998 ◽  
Vol 10 (3) ◽  
pp. 345-362 ◽  
Author(s):  
Paul A. Berkman ◽  
John T. Andrews ◽  
Svante Björck ◽  
Eric A. Colhoun ◽  
Steven D. Emslie ◽  
...  
Keyword(s):  
Environmental Changes ◽  
Late Quaternary ◽  
Marine Species ◽  
Coastal Areas ◽  
The Arctic ◽  
Marine Habitat ◽  
Marine Deposits ◽  
Quaternary Climate ◽  
Antarctic Marine ◽  
The Antarctic

This review assesses the circumpolar occurrence of emerged marine macrofossils and sediments from Antarctic coastal areas in relation to Late Quaternary climate changes. Radiocarbon ages of the macrofossils, which are interpreted in view of the complexities of the Antarctic marine radiocarbon reservoir and resolution of this dating technique, show a bimodal distribution. The data indicate that marine species inhabited coastal environments from at least 35 000 to 20 000 yr BP, during Marine Isotope Stage 3 when extensive iceberg calving created a ‘meltwater lid’ over the Southern Ocean. The general absence of these marine species from 20 000 to 8500 yr BP coincides with the subsequent advance of the Antarctic ice sheets during the Last Glacial Maximum. Synchronous re-appearance of the Antarctic marine fossils in emerged beaches around the continent, all of which have Holocene marine-limit elevations an order of magnitude lower than those in the Arctic, reflect minimal isostatic rebound as relative sea-level rise decelerated. Antarctic coastal marine habitat changes around the continent also coincided with increasing sea-ice extent and outlet glacial advances during the mid-Holocene. In view of the diverse environmental changes that occurred around the Earth during this period, it is suggested that Antarctic coastal areas were responding to a mid-Holocene climatic shift associated with the hydrological cycle. This synthesis of Late Quaternary emerged marine deposits demonstrates the application of evaluating circum-Antarctic phenomena from the glacial-terrestrial-marine transition zone.

scholarly journals Changes in the structure of bird communities over 10 years in the Ecological Corridor of Paraguay River, Pantanal wetland

2021 ◽  
Vol 12 (3) ◽  
pp. 111-125
Author(s):  
Rafaella Ferreira Neres de Queiroz ◽  
Breno Dias Vitorino ◽  
Angélica Vilas Boas da Frota ◽  
Carolina Joana da Silva ◽  
Solange Kimie Ikeda Castrillon ◽  
...  
Keyword(s):  
Environmental Changes ◽  
Hydrological Cycle ◽  
Bird Community ◽  
Bird Communities ◽  
Time Interval ◽  
Sampling Point ◽  
Generalist Species ◽  
Paraguay River ◽  
Temporal Space ◽  
Effective Decision Making

Studies with bird communities related to the hydrogeomorphological characteristics of climatic rivers associated with flood areas are important to identify short and long term temporal space changes. In this perspective, this research aims to evaluate the structure of the bird community of the Paraguay River, through the richness of descriptors, the quantity and the diversity and equability index over an interval of 10 years, 2008 / 9-2018 / 19 , considering the economies of the hydrological cycle, floods, floods, emptiness and drought and sampled macrohabitats. The study was developed addressing a connected hydrology of the Paraguay River, in the longitudinal and lateral dimensions. A study area comprised of three functional sectors of the Paraguay River, meandering, rectilinear and transitional, beginning in the urban period of the municipality of Cáceres-MT, up to a Descalvada Farm, with a 134 km course of the river, with 13 points in total. Each functional sector of the river, had a sampling point and 10 parental bays, with different degrees of lateral connectivity, were sampled. A survey analyzed and compared two hydrological sampling cycles, the first between June 2008 and March 2009, and the second between August 2018 and April 2019. The protocol for the sampling consisted of four campaigns corresponding to the hydrological drought studies, flood, full and ebb. The results pointed to a distinction in the community structure between the two cycles 2008/2009 - 2018/2019 show a difference in the relative scope and in the composition of the species in the sampled locations. The main change registered between the two cycles (2008/2009 and 2018/2019) was the disappearance of three nests - habitat for feeding and reproduction of colonial birds, identified in the first and without registration in the second cycle. The dominance of Mycteria americana is highlighted, a species sensitive to environmental changes, not observed in the first cycle of studies. The absence of nests in 2018/2019, coupled with the dominance of Pitangus sulphuratus, a generalist species, may indicate anthropic changes that occurred along the Paraguay River in this time interval. It is hoped that the results of this comparison will be able to subsidize or influence the effective decision-making for the conservation of the biodiversity of birds and the Paraguay and Pantanal river itself.

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