55 research outputs found
Evaluating the fidelity of the cerium paleoredox tracer during variable carbonate diagenesis on the Great Bahamas Bank
Inferring redox conditions for ancient marine environments is critical to our understanding of biogeochemical cycles over Earth history. Because of the redox sensitivity of cerium (Ce) relative to other rare earth elements (REEs) and its uptake in marine carbonates, the Ce anomaly (Ce/Ce*) is widely applied to ancient carbonates as a proxy for local redox conditions in the water column. However, carbonate sediments and rocks are particularly vulnerable to multiple stages and styles of post-depositional diagenetic alteration where the diagenetic redox conditions and fluid compositions can vary widely from overlying seawater. Evaluations of the effects of this post-depositional alteration for the Ce anomaly have mostly been limited to ancient carbonate rocks rather than recent, well-characterized analog facies. Here, we report on analyses of REE plus yttrium concentrations (REY) and Ce anomalies in bulk carbonate samples from drill cores collected in the Bahamas (Clino and Unda) that allow us to track loss or retention of primary signals of initial oxic deposition through a range of subsequent alteration scenarios mostly under anoxic conditions. Specifically, these materials have experienced well-constrained overprints linked to meteoric processes and marine burial diagenesis, including dolomitization. Our results show that, regardless of mineralogy, diagenetic fluid composition, and redox state, the REY patterns in these carbonates, including the Ce anomaly, are similar to those of modern oxic seawater, indicating that they likely record the seawater signatures of primary deposition. As such, the Ce anomaly in shallow marine carbonates has the potential to preserve records of primary deposition even when subject to multiple stages and styles of diagenetic alteration, confirming its utility in studies of ancient marine redox
Studies in demyelinating diseases of sheep associated with copper deficiency. I. "Lamkruis," a demyelinating disease of lambs occurring in South Africa. II. A biochemical investigation on the incidence of " Lamkruis " in lambs in the Saldanha Bay, Vredenburg, and St. Helena Bay environs. III. Experimental studies, treatment and control measures
It cannot be claimed that the observations recorded have led to specific information
as to the cause of the disease known as "lamkruis", yet valuable information
has been obtained which makes it clear that the factors originally suspected, i.e.
phosphorus and copper deficiency, can now be disregarded as the primary aetiologic
factors.
An ataxia of lambs called "lamkruis" or "litsiekte" was found to occur
on the south and west coast of South Africa, mostly on the calcareous soils of
recent origin but also on soils of partly granitic origin. Clinically it is a non-febrile
disease characterized by a swaying gait in the hindquarters. When the lambs are
driven they stumble easily and fall on to their sides. The striking pathologic
feature is destruction of the myelin in the nervous system, and, in extreme cases,
symmetrical areas of softening or cavity formation occur in both cerebral hemispheres. The white brain substance is principally affected. Cavity formation is
extremely rare in the spinal cord.
Lamkruis is probably identical with other demyelinating diseases affecting
lambs in various parts of the world, for instance, enzootic ataxia or ataxia of young
lambs in Australia and New Zealand, " swayback" or "singback", or "warfa"
in England and Scotland, and "renguera" in Peru, Patagonia and the Argentine.
"Lamkruis" as we know it in this country only develops in the progeny of
ewes subjected to a pasture of a "low" copper content. Without a single
exception the liver copper value of both ewes and their Jambs was of a low order.
There is evidence, however, that a low copper content of the liver is not pathognomonic
for Lamkruis.
Presumably, therefore, the ataxia is not necessarily caused primarily by a
copper deficiency.
The ataxia is, therefore, probably not due to a copper deficiency alone. In
this respect it differs from enzootic ataxia or ataxia of young lambs and is similar
to swayback and renguera. It is assumed that copper may only be a link of a chain
of contributory causes. The process of demyelination cannot be ascribed to a
single factor such as a copper deficiency.
It has been shown that, although the common lesion-demyelination is an
anatomical entity, its aetiology need not necessarily be identical in each case. The
view is expressed that in the case of " lamkruis" the lesions must be correlated
with a circulatory disturbance and / or a possible defective tissue anabolism brought
about by a deficiency of circulating copper. The bilateral symmetry of the lesions
suggests a systemic involvement.
The beneficial effect of administering copper salts to pregnant ewes in reducing
or preventing the appearance of "lamkruis" in their progeny has been demonstrated. In this respect our findings are in close agreement with those of the
other demyelinating diseases of lambs. l\It cannot be claimed, however, that the
administration of copper salt has a curative effect on diseased lambs.
The administration of copper salts to affected lambs may seem to have a
curative effect in some cases. It should be remembered however that a number of
animals may recover without any treatment at all. Apparent or total recovery,
probably depends on the extent and degree of the lesion and the affected structure.
Presumably in "lamkruis" the demyelination is due to a patho-physiologic
process and the beneficial effects of copper may be ascribed to its physiologic or
therapeutic properties rather than to its direct association with myelination.
The ataxia seen in "lamkruis" is presumably not associated with the lesions in
the cerebral hemispheres, since there was no relationship between the severity of
the clinical symptoms and the extent of the lesions. The possibility that the ataxia
is associated with alterations in the cerebellum or brain-stem or both, must be
considered.
The high concentration of iron and the low copper level in the livers of adult
sheep and lambs on "affected" properties indicate a disturbance in the iron
metabolism and may possibly be due to the absence from the food supply
of some factor (cobalt) necessary for its utilization as is the case in enzootic marasmus.
Presumably most of this iron is immobilized and stored in the organs, since
only a very small amount is demonstrable in sections stained with •Berliner Blue
and this does not occur principally in the form of haemosiderin.
The haemoglobin values for both ewes and lambs may reasonably be considered
to be of a low order. However, the magnitude of the values obtained is not such
that one is justified in stating that haemoglobin synthesis and haemopoiesis have
seriously been affected, since a very low blood copper level (less than 0•1 p.p.m.)
apparently does not interfere with normal haemopoiesis.
Evidence has been produced suggesting that a gradual rehabilitation to a
normal iron-copper metabolism may take place but that the intra-uterine injury to
the central nervous system may be permanent.
It seems that the biochemical processes concerned in the copper and iron
metabolism of the body may proceed normally, in spite of a marked depletion of
the copper stores of the ewes and the developing lamb, and the condition may
further be complicated by a significant deviation of the iron stores of the body
from the normal.
Based on the present evidence we wish to emphasise a post-natal as well
as a pre-natal onset for " lamkruis" and related diseases. Possibly all cases
developing within three months after birth may be looked upon as "delayed"
pre-natal cases, whereas those occurring later are most likely post-natal. Although
the end results may be identical, the pathogenesis in the various forms may differ
in several respects.
A reduced phosphorus content was demonstrated in the soil the vegetation,
the blood and tissues of stock grazing on the " Strandveld" (Bredasdorp, Riversdale
and Swellendam areas) and this was reflected in softness and fragility of the
bones of the animals concerned, whereas no evidence of an apparent phosphorus
deficiency was obtained in the vicinity of Saldanha Bay and Vredenburg.
Phosphorus deficiency is probably a contributory factor of the disease called
"heupsiekte" in cattle and that which was mistakenly termed " lamkruis " in
older sheep by former investigators. The disease described by us has nothing
in common with the previously mentioned condition.
In some of these coastal areas several diseases, such as "duinesiekte" of
sheep and young cattle, paratyphoid of calves, and " broken wind" in draught
animals (called “ruksiekte" or "benoudebors") or "bighead" (osteofibrosis) in
horses, may be very prevalent. The possibility of greater susceptibility of animals
to diseases under conditions prevailing in these coastal regions is a problem that
requires further investigation.
Other diseases, for instance "slapsiekte" of lambs and donkeys, affections of
lambs and goats due to Coenurus cerebralis, and "Malkop" occurring more inland
and characterized by nervous symptoms, have been described. In addition some
demyelinating diseases affecting man and presumably not associated with a copper
deficiency have been mentioned. Evidence has been thereby produced indicating
that diseases with similar clinical symptoms and morbid changes need not necessarily
have the same aetiology. However, there may be some common factor
responsible for their similarity.
" Lamkruis " is not related to imperfect osteogenesis nor to a degeneration
of the musculature as that seen in " white muscle" disease. The alterations in the
central nervous system are not those of aplasia of the white substance of the
brain nor of an inflammatory nature, but must be ascribed to an encephalomyelopathy
or a diffuse leucoencephalopathy without sclerosis. The process in cavity
formation appears to be that of autolysis occurring intra vitam. It is characterized
by a scarcity of fat and "gitter cells". In this respect "lamkruis" differs significantly
from Schilder's Disease, but is in close agreement with diffuse leucoencephalopathy
of man (Josephy and Lichtenstein, 1943). Post mortem changes can
be eliminated since the specimens were placed into formalin within a few minutes
after slaughtering of the animals. Deficiencies of copper, phosphorus and vitamins
may be excluded as primary causes, but they probably act as contributory factors.
Apparently poisonous plants and fungi do not play a role in the aetiology of this
disease.
As the disease may occur intra-uterine it is essential that the placental circulation
(maternal and foetal) and the chemical changes occurring in the foetal brain
should receive more attention than in the past. Progress in elucidating the
pathogenesis of "Jamkruis " and other related diseases may be expected, if the
significance of these two factors will be fully appreciated.
It is well-known that several demyelinating diseases occur in man and that
demyelination can be produced experimentally by a number of variable factors
and not necessarily by a copper deficiency.
Our cases, as well as those mentioned in the literature, point to the necessity
for careful neurologic study in all cases of "lamkruis " and similar conditions.
The distribution and character of cerebral lesions in " lamkruis " are indicative of
circulatory disturbances and the resultant alterations in the affected localities. More
attention should be given to less pronounced changes, especially in the cerebellum,
brain-stem and other organs, for instance the adrenal.The articles have been scanned in colour with a HP Scanjet 5590; 300dpi.
Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format
Continental-scale variation in otolith geochemistry of juvenile American shad (Alosa sapidissima)
Author Posting. © NRC Research Press, 2008. This article is posted here by permission of NRC Research Press for personal use, not for redistribution. The definitive version was published in Canadian Journal of Fisheries and Aquatic Sciences 65 (2008): 2623-2635, doi:10.1139/F08-164.We assembled a comprehensive atlas of geochemical signatures in juvenile American shad (Alosa sapidissima) to discriminate natal river origins on a large spatial scale and at a high spatial resolution. Otoliths and (or) water samples were collected from 20 major spawning rivers from Florida to Quebec and were analyzed for elemental (Mg:Ca, Mn:Ca, Sr:Ca, and Ba:Ca) and isotope (87Sr:86Sr and δ18O) ratios. We examined correlations between water chemistry and otolith composition for five rivers where both were sampled. While Sr:Ca, Ba:Ca, 87Sr:86Sr, and δ18O values in otoliths reflected those ratios in ambient waters, Mg:Ca and Mn:Ca ratios in otoliths varied independently of water chemistry. Geochemical signatures were highly distinct among rivers, with an average classification accuracy of 93% using only those variables where otolith values were accurately predicted from water chemistry data. The study represents the largest assembled database of otolith signatures from the entire native range of a species, encompassing approximately 2700 km of coastline and 19 degrees of latitude and including all major extant spawning populations. This database will allow reliable estimates of natal origins of migrating ocean-phase American shad from the 2004 annual cohort in the future.This work was funded by National Science
Foundation (NSF) grants OCE-0215905 and OCE-0134998
to SRT and by an American Museum of Natural History
Lerner–Gray Grant for Marine Research and a scholarship
from SEASPACE, Inc., to BDW
Subduction initiation in the Scotia Sea region and opening of the Drake Passage: When and why?
During evolution of the South Sandwich subduction zone, which has consumed South American Plate oceanic lithosphere, somehow continental crust of both the South American and Antarctic plates have become incorporated into its upper plate. Continental fragments of both plates are currently separated by small oceanic basins in the upper plate above the South Sandwich subduction zone, in the Scotia Sea region, but how fragments of both continents became incorporated in the same upper plate remains enigmatic. Here we present an updated kinematic reconstruction of the Scotia Sea region using the latest published marine magnetic anomaly constraints, and place this in a South America-Africa-Antarctica plate circuit in which we take intracontinental deformation into account. We show that a change in marine magnetic anomaly orientation in the Weddell Sea requires that previously inferred initiation of subduction of South American oceanic crust of the northern Weddell Sea below the eastern margin of South Orkney Islands continental crust, then still attached to the Antarctic Peninsula, already occurred around 80 Ma. Subsequently, between ~71–50 Ma, we propose that the trench propagated northwards into South America by delamination of South American lithosphere: this resulted in the transfer of delaminated South American continental crust to the overriding plate of the South Sandwich subduction zone. We show that continental delamination may have been facilitated by absolute southward motion of South America that was resisted by South Sandwich slab dragging. Pre-drift extension preceding the oceanic Scotia Sea basins led around 50 Ma to opening of the Drake Passage, preconditioning the southern ocean for the Antarctic Circumpolar Current. This 50 Ma extension was concurrent with a strong change in absolute plate motion of the South American Plate that changed from S to WNW, leading to upper plate retreat relative to the more or less mantle stationary South Sandwich Trench that did not partake in the absolute plate motion change. While subduction continued, this mantle-stationary trench setting lasted until ~30 Ma, after which rollback started to contribute to back-arc extension. We find that roll-back and upper plate retreat have contributed more or less equally to the total amount of ~2000 km of extension accommodated in the Scotia Sea basins. We highlight that viewing tectonic motions in a context of absolute plate motion is key for identifying slab motion (e.g., rollback, trench-parallel slab dragging) and consequently mantle-forcing of geological processes
Corrigendum to “Carbonate delta drift: A new sediment drift type” [Mar. Geol. 401 (2018) 98–111]
The authors regret the mistake in the drawing of the delta drift architecture in figure 11. The authors would like to apologise for any inconvenience caused. [Figure presented
A reevaluation of facies on Great Bahama Bank II: Variations in the d13C, d18O, and mineralogy of surface sediments
Recommended from our members
Sequence and style in scleractinian coral preservation in reefs and associated facies
Studies of reefs and proximal facies in the Pleistocene of East Africa, and in the Tertiary and Miocene of Bahrain yield predictable sequences of coral sediment distribution patterns. These can be sub-divided into micro-facies ranging from the supratidal to at least −33 m. Many of these suites are comparable with facies found today around Heron Island, on the Australian Great Barrier Reef, upon which a series of facies and fabric models are reconstructed. In depths of less than −15 m five main types of facies-linked preservational styles of corals are recognised and their chemical properties are analysed experimentally: (1) essentially unaltered; (2) red-algal encrusted; (3) moldic rhodoliths after sponge borings; (4) intensely endolithically bored intertidal debris; and (5) sterile, internally zoned, leached and abraded skeletons from the strand-line. These represent a linear sequence from off-shore to the storm ridge, which are modelled into transgressive and regressive cycles. The probability of their preservation and the relative proportion of their products, from any one time interval, increase in a landward direction.
Scleractinian standards are established by tracing six taxonomically distinguishable groups represented amongst Astrocoeniina, Fungiina and Faviina in the quasi-fossil strandline shingle to their origins. Each coral or coral-fragment acquires a distinct suite of epibionts on the host's death, and undergoes characteristic chemical alteration related to its micro-environment. Consequently, the same genus develops various modifications reflecting its history of postmortem transport prior to ultimate burial. Thus, the chemical integrity of the skeleton never remains completely intact, as those specimens that are not subject to encrustation and the influences of endo- and epilithic biota are the more susceptible to diagenetic exchange with percolating pore waters. Preferred pathways for interstitial trace-element enrichment are detected by means of dosing the sea-water with uranium: these are best developed at skeletal margins and along trabecular axes in sterilised specimens.
The applicability of these data to bore-hole records is tested by reference to the Heron Island core log. While the implications for the analysis of diagenetically advanced material is demonstrated by Jurassic and Carboniferous examples, these data have profound implications for assessing the reliability of isotope geochemistry and radiometric dating
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