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Xiaofeng Wang - One of the best experts on this subject based on the ideXlab platform.
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cowpea chlorotic mottle bromovirus replication proteins support template selective rna replication in saccharomyces cerevisiae
PLOS ONE, 2018Co-Authors: Bryan S. Sibert, Amanda K. Navine, Janice G Pennington, Xiaofeng WangAbstract:Positive-strand RNA viruses generally assemble RNA replication complexes on rearranged host membranes. Alphaviruses, other members of the alpha-like virus superfamily, and many other positive-strand RNA viruses invaginate host membrane into vesicular RNA replication compartments, known as Spherules, whose interior is connected to the cytoplasm. Brome mosaic virus (BMV) and its close relative, cowpea chlorotic mottle virus (CCMV), form Spherules along the endoplasmic reticulum. BMV spherule formation and RNA replication can be fully reconstituted in S. cerevisiae, enabling many studies identifying host factors and viral interactions essential for these processes. To better define and understand the conserved, core pathways of bromovirus RNA replication, we tested the ability of CCMV to similarly support spherule formation and RNA replication in yeast. Paralleling BMV, we found that CCMV RNA replication protein 1a was the only viral factor necessary to induce spherule membrane rearrangements and to recruit the viral 2a polymerase (2apol) to the endoplasmic reticulum. CCMV 1a and 2apol also replicated CCMV and BMV genomic RNA2, demonstrating core functionality of CCMV 1a and 2apol in yeast. However, while BMV and CCMV 1a/2apol strongly replicate each others' genomic RNA3 in plants, neither supported detectable CCMV RNA3 replication in yeast. Moreover, in contrast to plant cells, in yeast CCMV 1a/2apol supported only limited replication of BMV RNA3 (<5% of that by BMV 1a/2apol). In keeping with this, we found that in yeast CCMV 1a was significantly impaired in recruiting BMV or CCMV RNA3 to the replication complex. Overall, we show that many 1a and 2apol functions essential for replication complex assembly, and their ability to be reconstituted in yeast, are conserved between BMV and CCMV. However, restrictions of CCMV RNA replication in yeast reveal previously unknown 1a-linked, RNA-selective host contributions to the essential early process of recruiting viral RNA templates to the replication complex.
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Host ESCRT proteins are required for bromovirus RNA replication compartment assembly and function.
PLOS Pathogens, 2015Co-Authors: Jiantao Zhang, Abigail Ollwerther, Arturo Diaz, Xiaofeng WangAbstract:Positive-strand RNA viruses genome replication invariably is associated with vesicles or other rearranged cellular membranes. Brome mosaic virus (BMV) RNA replication occurs on perinuclear endoplasmic reticulum (ER) membranes in ~70 nm vesicular invaginations (Spherules). BMV RNA replication vesicles show multiple parallels with membrane-enveloped, budding retrovirus virions, whose envelopment and release depend on the host ESCRT (endosomal sorting complexes required for transport) membrane-remodeling machinery. We now find that deleting components of the ESCRT pathway results in at least two distinct BMV phenotypes. One group of genes regulate RNA replication and the frequency of viral replication complex formation, but had no effect on spherule size, while a second group of genes regulate RNA replication in a way or ways independent of spherule formation. In particular, deleting SNF7 inhibits BMV RNA replication > 25-fold and abolishes detectable BMV spherule formation, even though the BMV RNA replication proteins accumulate and localize normally on perinuclear ER membranes. Moreover, BMV ESCRT recruitment and spherule assembly depend on different sets of protein-protein interactions from those used by multivesicular body vesicles, HIV-1 virion budding, or tomato bushy stunt virus (TBSV) spherule formation. These and other data demonstrate that BMV requires cellular ESCRT components for proper formation and function of its vesicular RNA replication compartments. The results highlight growing but diverse interactions of ESCRT factors with many viruses and viral processes, and potential value of the ESCRT pathway as a target for broad-spectrum antiviral resistance.
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Bromovirus-induced remodeling of host membranes during viral RNA replication.
Current Opinion in Virology, 2014Co-Authors: Arturo Diaz, Xiaofeng WangAbstract:With its high yield, small genome, and ability to replicate in the yeast Saccharomyces cerevisiae, Brome mosaic virus (BMV) has served as a productive model to study the general features of positive-strand RNA virus infection. BMV RNA is replicated in Spherules, vesicle-like invaginations of the outer perinuclear endoplasmic reticulum membrane that remain connected to the cytoplasm via a neck-like opening. Each spherule contains the viral replicase proteins as well as genomic RNAs. Recent advances indicate that multiple interactions between the viral proteins with themselves, cellular membranes, and host factors play crucial roles in BMV-mediated spherule formation. These findings are probably applicable to other positive-strand RNA viruses and might potentially provide new targets for antiviral treatments.
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host acyl coenzyme a binding protein regulates replication complex assembly and activity of a positive strand rna virus
Journal of Virology, 2012Co-Authors: Jiantao Zhang, Paul Ahlquist, Arturo Diaz, Lan Mao, Xiaofeng WangAbstract:All positive-strand RNA viruses reorganize host intracellular membranes to assemble their replication complexes. Similarly, brome mosaic virus (BMV) induces two alternate forms of membrane-bound RNA replication complexes: vesicular Spherules and stacks of appressed double-membrane layers. The mechanisms by which these membrane rearrangements are induced, however, remain unclear. We report here that host ACB1-encoded acyl coenzyme A (acyl-CoA) binding protein (ACBP) is required for the assembly and activity of both BMV RNA replication complexes. ACBP is highly conserved among eukaryotes, specifically binds to long-chain fatty acyl-CoA, and promotes general lipid synthesis. Deleting ACB1 inhibited BMV RNA replication up to 30-fold and resulted in formation of Spherules that were ∼50% smaller but ∼4-fold more abundant than those in wild-type (wt) cells, consistent with the idea that BMV 1a invaginates and maintains viral Spherules by coating the inner spherule membrane. Furthermore, smaller and more frequent Spherules were preferentially formed under conditions that induce layer formation in wt cells. Conversely, cellular karmella structures, which are arrays of endoplasmic reticulum (ER) membranes formed upon overexpression of certain cellular ER membrane proteins, were formed normally, indicating a selective inhibition of 1a-induced membrane rearrangements. Restoring altered lipid composition largely complemented the BMV RNA replication defect, suggesting that ACBP was required for maintaining lipid homeostasis. Smaller and more frequent Spherules are also induced by 1a mutants with specific substitutions in a membrane-anchoring amphipathic α-helix, implying that the 1a-lipid interactions play critical roles in viral replication complex assembly.
Tero Ahola - One of the best experts on this subject based on the ideXlab platform.
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partially uncleaved alphavirus replicase forms spherule structures in the presence and absence of rna template
Journal of Virology, 2017Co-Authors: Kirsi Hellstrom, Katri Kallio, Age Utt, Tania Quirin, Eija Jokitalo, Andres Merits, Tero AholaAbstract:Alphaviruses are positive-strand RNA viruses expressing their replicase as a polyprotein, P1234, which is cleaved to four final products, nonstructural proteins nsP1 to nsP4. The replicase proteins together with viral RNA and host factors form membrane invaginations termed Spherules, which act as the replication complexes producing progeny RNAs. We have previously shown that the wild-type alphavirus replicase requires a functional RNA template and active polymerase to generate spherule structures. However, we now find that specific partially processed forms of the replicase proteins alone can give rise to membrane invaginations in the absence of RNA or replication. The minimal requirement for spherule formation was the expression of properly cleaved nsP4, together with either uncleaved P123 or with the combination of nsP1 and uncleaved P23. These inactive Spherules were morphologically less regular than replication-induced Spherules. In the presence of template, nsP1 plus uncleaved P23 plus nsP4 could efficiently assemble active replication Spherules producing both negative-sense and positive-sense RNA strands. P23 alone did not have membrane affinity, but could be recruited to membrane sites in the presence of nsP1 and nsP4. These results define the set of viral components required for alphavirus replication complex assembly and suggest the possibility that it could be reconstituted from separately expressed nonstructural proteins.IMPORTANCE All positive-strand RNA viruses extensively modify host cell membranes to serve as efficient platforms for viral RNA replication. Alphaviruses and several other groups induce protective membrane invaginations (Spherules) as their genome factories. Most positive-strand viruses produce their replicase as a polyprotein precursor, which is further processed through precise and regulated cleavages. We show here that specific cleavage intermediates of the alphavirus replicase can give rise to spherule structures in the absence of viral RNA. In the presence of template RNA, the same intermediates yield active replication complexes. Thus, partially cleaved replicase proteins play key roles that connect replication complex assembly, membrane deformation, and the different stages of RNA synthesis.
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template rna length determines the size of replication complex Spherules for semliki forest virus
Journal of Virology, 2013Co-Authors: Katri Kallio, Kirsi Hellstrom, Eija Jokitalo, Pirjo Spuul, Giuseppe Balistreri, Tero AholaAbstract:The replication complexes of positive-strand RNA viruses are always associated with cellular membranes. The morphology of the replication-associated membranes is altered in different ways in different viral systems, but many viruses induce small membrane invaginations known as Spherules as their replication sites. We show here that for Semliki Forest virus (SFV), an alphavirus, the size of the Spherules is tightly connected with the length of the replicating RNA template. Cells with different model templates, expressed in trans and copied by the viral replicase, were analyzed with correlative light and electron microscopy. It was demonstrated that the viral-genome-sized template of 11.5 kb induced Spherules that were ∼58 nm in diameter, whereas a template of 6 kb yielded ∼39-nm Spherules. Different sizes of viral templates were replicated efficiently in trans, as assessed by radioactive labeling and Northern blotting. The replication of two different templates, in cis and trans, yielded two size classes of Spherules in the same cell. These results indicate that RNA plays a crucial determining role in spherule assembly for SFV, in direct contrast with results from other positive-strand RNA viruses, in which either the presence of viral RNA or the RNA size do not contribute to spherule formation.
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phosphatidylinositol 3 kinase actin and microtubule dependent transport of semliki forest virus replication complexes from the plasma membrane to modified lysosomes
Journal of Virology, 2010Co-Authors: Pirjo Spuul, Giuseppe Balistreri, Leevi Kaariainen, Tero AholaAbstract:Like other positive-strand RNA viruses, alphaviruses replicate their genomes in association with modified intracellular membranes. Alphavirus replication sites consist of numerous bulb-shaped membrane invaginations (Spherules), which contain the double-stranded replication intermediates. Time course studies with Semliki Forest virus (SFV)-infected cells were combined with live-cell imaging and electron microscopy to reveal that the replication complex Spherules of SFV undergo an unprecedented large-scale movement between cellular compartments. The Spherules first accumulated at the plasma membrane and were then internalized using an endocytic process that required a functional actin-myosin network, as shown by blebbistatin treatment. Wortmannin and other inhibitors indicated that the internalization of Spherules also required the activity of phosphatidylinositol 3-kinase. The Spherules therefore represent an unusual type of endocytic cargo. After endocytosis, spherule-containing vesicles were highly dynamic and had a neutral pH. These primary carriers fused with acidic endosomes and moved long distances on microtubules, in a manner prevented by nocodazole. The result of the large-scale migration was the formation of a very stable compartment, where the Spherules were accumulated on the outer surfaces of unusually large and static acidic vacuoles localized in the pericentriolar region. Our work highlights both fundamental similarities and important differences in the processes that lead to the modified membrane compartments in cells infected by distinct groups of positive-sense RNA viruses.
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Transport of Semliki Forest Virus Replication Complexes from the Plasma Membrane to Modified Lysosomes†
2010Co-Authors: Pirjo Spuul, Tero AholaAbstract:Like other positive-strand RNA viruses, alphaviruses replicate their genomes in association with modified intracellular membranes. Alphavirus replication sites consist of numerous bulb-shaped membrane invagina-tions (Spherules), which contain the double-stranded replication intermediates. Time course studies with Semliki Forest virus (SFV)-infected cells were combined with live-cell imaging and electron microscopy to reveal that the replication complex Spherules of SFV undergo an unprecedented large-scale movement between cellular compartments. The Spherules first accumulated at the plasma membrane and were then internalized using an endocytic process that required a functional actin-myosin network, as shown by blebbistatin treat-ment. Wortmannin and other inhibitors indicated that the internalization of Spherules also required the activity of phosphatidylinositol 3-kinase. The Spherules therefore represent an unusual type of endocytic cargo. After endocytosis, spherule-containing vesicles were highly dynamic and had a neutral pH. These primary carriers fused with acidic endosomes and moved long distances on microtubules, in a manner prevented by nocodazole. The result of the large-scale migration was the formation of a very stable compartment, where the Spherules were accumulated on the outer surfaces of unusually large and static acidic vacuoles localized in the pericentriolar region. Our work highlights both fundamental similarities and important differences in the pro-cesses that lead to the modified membrane compartments in cells infected by distinct groups of positive-sens
Arturo Diaz - One of the best experts on this subject based on the ideXlab platform.
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RESEARCH ARTICLE Host ESCRT Proteins Are Required for Bromovirus RNA Replication Compartment Assembly and Function
2016Co-Authors: Jiantao Zhang, Abigail Ollwerther, Paul Ahlquist, Arturo DiazAbstract:Positive-strand RNA viruses genome replication invariably is associated with vesicles or other rearranged cellular membranes. Brome mosaic virus (BMV) RNA replication occurs on perinuclear endoplasmic reticulum (ER) membranes in ~70 nm vesicular invaginations (Spherules). BMV RNA replication vesicles show multiple parallels with membrane-enveloped, budding retrovirus virions, whose envelopment and release depend on the host ESCRT (endosomal sorting complexes required for transport) membrane-remodeling ma-chinery. We now find that deleting components of the ESCRT pathway results in at least two distinct BMV phenotypes. One group of genes regulate RNA replication and the fre-quency of viral replication complex formation, but had no effect on spherule size, while a second group of genes regulate RNA replication in a way or ways independent of spherule formation. In particular, deleting SNF7 inhibits BMV RNA replication> 25-fold and abolishes detectable BMV spherule formation, even though the BMV RNA replication proteins accu-mulate and localize normally on perinuclear ER membranes. Moreover, BMV ESCRT re-cruitment and spherule assembly depend on different sets of protein-protein interaction
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Host ESCRT proteins are required for bromovirus RNA replication compartment assembly and function.
PLOS Pathogens, 2015Co-Authors: Jiantao Zhang, Abigail Ollwerther, Arturo Diaz, Xiaofeng WangAbstract:Positive-strand RNA viruses genome replication invariably is associated with vesicles or other rearranged cellular membranes. Brome mosaic virus (BMV) RNA replication occurs on perinuclear endoplasmic reticulum (ER) membranes in ~70 nm vesicular invaginations (Spherules). BMV RNA replication vesicles show multiple parallels with membrane-enveloped, budding retrovirus virions, whose envelopment and release depend on the host ESCRT (endosomal sorting complexes required for transport) membrane-remodeling machinery. We now find that deleting components of the ESCRT pathway results in at least two distinct BMV phenotypes. One group of genes regulate RNA replication and the frequency of viral replication complex formation, but had no effect on spherule size, while a second group of genes regulate RNA replication in a way or ways independent of spherule formation. In particular, deleting SNF7 inhibits BMV RNA replication > 25-fold and abolishes detectable BMV spherule formation, even though the BMV RNA replication proteins accumulate and localize normally on perinuclear ER membranes. Moreover, BMV ESCRT recruitment and spherule assembly depend on different sets of protein-protein interactions from those used by multivesicular body vesicles, HIV-1 virion budding, or tomato bushy stunt virus (TBSV) spherule formation. These and other data demonstrate that BMV requires cellular ESCRT components for proper formation and function of its vesicular RNA replication compartments. The results highlight growing but diverse interactions of ESCRT factors with many viruses and viral processes, and potential value of the ESCRT pathway as a target for broad-spectrum antiviral resistance.
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Bromovirus-induced remodeling of host membranes during viral RNA replication.
Current Opinion in Virology, 2014Co-Authors: Arturo Diaz, Xiaofeng WangAbstract:With its high yield, small genome, and ability to replicate in the yeast Saccharomyces cerevisiae, Brome mosaic virus (BMV) has served as a productive model to study the general features of positive-strand RNA virus infection. BMV RNA is replicated in Spherules, vesicle-like invaginations of the outer perinuclear endoplasmic reticulum membrane that remain connected to the cytoplasm via a neck-like opening. Each spherule contains the viral replicase proteins as well as genomic RNAs. Recent advances indicate that multiple interactions between the viral proteins with themselves, cellular membranes, and host factors play crucial roles in BMV-mediated spherule formation. These findings are probably applicable to other positive-strand RNA viruses and might potentially provide new targets for antiviral treatments.
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host acyl coenzyme a binding protein regulates replication complex assembly and activity of a positive strand rna virus
Journal of Virology, 2012Co-Authors: Jiantao Zhang, Paul Ahlquist, Arturo Diaz, Lan Mao, Xiaofeng WangAbstract:All positive-strand RNA viruses reorganize host intracellular membranes to assemble their replication complexes. Similarly, brome mosaic virus (BMV) induces two alternate forms of membrane-bound RNA replication complexes: vesicular Spherules and stacks of appressed double-membrane layers. The mechanisms by which these membrane rearrangements are induced, however, remain unclear. We report here that host ACB1-encoded acyl coenzyme A (acyl-CoA) binding protein (ACBP) is required for the assembly and activity of both BMV RNA replication complexes. ACBP is highly conserved among eukaryotes, specifically binds to long-chain fatty acyl-CoA, and promotes general lipid synthesis. Deleting ACB1 inhibited BMV RNA replication up to 30-fold and resulted in formation of Spherules that were ∼50% smaller but ∼4-fold more abundant than those in wild-type (wt) cells, consistent with the idea that BMV 1a invaginates and maintains viral Spherules by coating the inner spherule membrane. Furthermore, smaller and more frequent Spherules were preferentially formed under conditions that induce layer formation in wt cells. Conversely, cellular karmella structures, which are arrays of endoplasmic reticulum (ER) membranes formed upon overexpression of certain cellular ER membrane proteins, were formed normally, indicating a selective inhibition of 1a-induced membrane rearrangements. Restoring altered lipid composition largely complemented the BMV RNA replication defect, suggesting that ACBP was required for maintaining lipid homeostasis. Smaller and more frequent Spherules are also induced by 1a mutants with specific substitutions in a membrane-anchoring amphipathic α-helix, implying that the 1a-lipid interactions play critical roles in viral replication complex assembly.
Janice G Pennington - One of the best experts on this subject based on the ideXlab platform.
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Cowpea chlorotic mottle bromovirus replication proteins support template-selective RNA replication in Saccharomyces cerevisiae
PLOS ONE, 2018Co-Authors: Bryan S. Sibert, Amanda K. Navine, Janice G PenningtonAbstract:Positive-strand RNA viruses generally assemble RNA replication complexes on rearranged host membranes. Alphaviruses, other members of the alpha-like virus superfamily, and many other positive-strand RNA viruses invaginate host membrane into vesicular RNA replication compartments, known as Spherules, whose interior is connected to the cytoplasm. Brome mosaic virus (BMV) and its close relative, cowpea chlorotic mottle virus (CCMV), form Spherules along the endoplasmic reticulum. BMV spherule formation and RNA replication can be fully reconstituted in S. cerevisiae, enabling many studies identifying host factors and viral interactions essential for these processes. To better define and understand the conserved, core pathways of bromovirus RNA replication, we tested the ability of CCMV to similarly support spherule formation and RNA replication in yeast. Paralleling BMV, we found that CCMV RNA replication protein 1a was the only viral factor necessary to induce spherule membrane rearrangements and to recruit the viral 2a polymerase (2apol) to the endoplasmic reticulum. CCMV 1a and 2apol also replicated CCMV and BMV genomic RNA2, demonstrating core functionality of CCMV 1a and 2apol in yeast. However, while BMV and CCMV 1a/2apol strongly replicate each others' genomic RNA3 in plants, neither supported detectable CCMV RNA3 replication in yeast. Moreover, in contrast to plant cells, in yeast CCMV 1a/2apol supported only limited replication of BMV RNA3 (
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cowpea chlorotic mottle bromovirus replication proteins support template selective rna replication in saccharomyces cerevisiae
PLOS ONE, 2018Co-Authors: Bryan S. Sibert, Amanda K. Navine, Janice G Pennington, Xiaofeng WangAbstract:Positive-strand RNA viruses generally assemble RNA replication complexes on rearranged host membranes. Alphaviruses, other members of the alpha-like virus superfamily, and many other positive-strand RNA viruses invaginate host membrane into vesicular RNA replication compartments, known as Spherules, whose interior is connected to the cytoplasm. Brome mosaic virus (BMV) and its close relative, cowpea chlorotic mottle virus (CCMV), form Spherules along the endoplasmic reticulum. BMV spherule formation and RNA replication can be fully reconstituted in S. cerevisiae, enabling many studies identifying host factors and viral interactions essential for these processes. To better define and understand the conserved, core pathways of bromovirus RNA replication, we tested the ability of CCMV to similarly support spherule formation and RNA replication in yeast. Paralleling BMV, we found that CCMV RNA replication protein 1a was the only viral factor necessary to induce spherule membrane rearrangements and to recruit the viral 2a polymerase (2apol) to the endoplasmic reticulum. CCMV 1a and 2apol also replicated CCMV and BMV genomic RNA2, demonstrating core functionality of CCMV 1a and 2apol in yeast. However, while BMV and CCMV 1a/2apol strongly replicate each others' genomic RNA3 in plants, neither supported detectable CCMV RNA3 replication in yeast. Moreover, in contrast to plant cells, in yeast CCMV 1a/2apol supported only limited replication of BMV RNA3 (<5% of that by BMV 1a/2apol). In keeping with this, we found that in yeast CCMV 1a was significantly impaired in recruiting BMV or CCMV RNA3 to the replication complex. Overall, we show that many 1a and 2apol functions essential for replication complex assembly, and their ability to be reconstituted in yeast, are conserved between BMV and CCMV. However, restrictions of CCMV RNA replication in yeast reveal previously unknown 1a-linked, RNA-selective host contributions to the essential early process of recruiting viral RNA templates to the replication complex.
Bruce M Simonson - One of the best experts on this subject based on the ideXlab platform.
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shock metamorphosed rutile grains containing the high pressure polymorph tio2 ii in four neoarchean spherule layers
Geology, 2016Co-Authors: Frank C Smith, Bruce M Simonson, B.p. Glass, Alexandra E Krulldavatzes, Joseph P Smith, Karl S BookshAbstract:At least 17 spherule layers are presently known within stratigraphic units deposited between ca. 3.47 and 2.49 Ga. The spherule layers contain varying amounts of formerly molten, millimeter-sized and smaller Spherules. The aggregate thickness of Spherules in these layers commonly ranges from ∼1 cm to as much as a few decimeters. Several lines of evidence support the interpretation that the spherule layers represent distal impact ejecta layers. Previously, only one shock-metamorphosed grain (quartz) had been documented from the spherule layers. Therefore, a key diagnostic criterion for the impact origin of these layers has remained elusive for 30 years. We report the discovery, using micro-Raman spectroscopy, of shock-induced TiO 2 -II, a high-pressure polymorph of TiO 2 , in 34 grains from four Neoarchean spherule layers deposited between ca. 2.65 and 2.54 Ga. As all the TiO 2 -II-bearing grains contain rutile, we interpret them as shock-metamorphosed rutile grains. Shock-metamorphosed rutile grains, which may be more abundant in the upper parts of three of the layers, provide unambiguous physical evidence to further support an impact origin for these four layers. Our results demonstrate that TiO 2 -II can survive for >2.5 b.y. in supracrustal successions that have undergone low-grade metamorphism. Because TiO 2 -II transforms to rutile at a temperature ≥440 °C, TiO 2 -II in impact ejecta layers is a potential geothermometer. To our knowledge, this is the first report of a shock-induced, high-pressure polymorph formed by an Archean impact.
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spherule layers crater scaling laws and the population of ancient terrestrial impactors
Icarus, 2016Co-Authors: B C Johnson, Bruce M Simonson, G S Collins, David A Minton, T J Bowling, Maria T ZuberAbstract:Abstract Ancient layers of impact Spherules provide a record of Earth's early bombardment history. Here, we compare different bombardment histories to the spherule layer record and show that 3.2–3.5 Ga the flux of large impactors (10–100 km in diameter) was likely 20–40 times higher than today. The E-belt model of early Solar System dynamics suggests that an increased impactor flux during the Archean is the result of the destabilization of an inward extension of the main asteroid belt (Bottke et al., 2012). Here, we find that the nominal flux predicted by the E-belt model is 7–19 times too low to explain the spherule layer record. Moreover, rather than making most lunar basins younger than 4.1 Gyr old, the nominal E-belt model, coupled with a corrected crater diameter scaling law, only produces two lunar basins larger than 300 km in diameter. We also show that the spherule layer record when coupled with the lunar cratering record and careful consideration of crater scaling laws can constrain the size distribution of ancient terrestrial impactors. The preferred population is main-belt-like up to ∼50 km in diameter transitioning to a steep distribution going to larger sizes.
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first detection of extraterrestrial material in ca 2 49 ga impact spherule layer in kuruman iron formation south africa
Geology, 2015Co-Authors: Bruce M Simonson, Steven Goderis, Nicolas J BeukesAbstract:Thin layers rich in formerly molten Spherules interpreted as distal ejecta from large impacts by extraterrestrial bodies have been found in 8 stratigraphic units deposited between ca. 2.63 Ga and 2.49 Ga and attributed to a minimum of 4 separate impacts. Here we report geochemical evidence of extraterrestrial material in the only one of these spherule layers where it has not been previously reported, the Kuruman spherule layer (KSL) in the Kuruman Iron Formation, a banded iron formation (BIF) in the Griqualand West Basin (South Africa). We identified the KSL in 3 drill cores separated by as much as ∼350 km and analyzed 2 core samples that have a mean Ir concentration of ∼12.9 ppb and nearly chondritic interelement ratios of platinum group elements Ir, Ru, Pt, and Rh. This suggests that the samples contain ∼1%–3% by mass extraterrestrial material even though the Spherules are highly diluted by ambient sediment. Our geochemical data strongly support the correlation of the KSL with the Dales Gorge spherule layer (DGSL) in a penecontemporaneous BIF in the Hamersley Basin (Western Australia). The KSL and DGSL are close matches in terms of major and various trace element contents and the DGSL has a comparable Ir content of ∼11.5 ppb. Therefore it is very likely the KSL and DGSL are distal ejecta from a ca. 2.49 Ga impact by a single extraterrestrial object >10 km across. The lack of any significant changes in the stratigraphic succession in either basin also implies that large impacts alone are not sufficient to cause long-term changes in Earth’s surface environments.
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paleozoic impact spherule ejecta layers
2013Co-Authors: B.p. Glass, Bruce M SimonsonAbstract:Although the Paleozoic Era lasted nearly five times longer than the Cenozoic, the number of Paleozoic distal impact ejecta layers that have been identified is much smaller (compare Table 6.1 with Table 4.1). Two probable Late Devonian distal impact ejecta layers have been reported. The youngest is a silicate glass spherule (microtektite?) layer and Ir anomaly found in Qidong (southern China) in Late Devonian deposits, about 1.5 to 2.0 Ma younger than the Frasnian–Famennian boundary. The second is an older layer of silicate glass Spherules (microtektites) found just above the Frasnian–Famennian boundary at two sites (Senzeille and Hony) in Belgium. Four additional spherule occurrences of Frasnian to Famennian age have been reported in southern China: one above the Frasnian–Famennian boundary, one at the boundary, and two below the boundary. The most intensely studied Paleozoic ‘ejecta’ layer is at the Permian–Triassic boundary, but as of 2011, the impact origin of this boundary layer had not been established.
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paraburdoo spherule layer hamersley basin western australia distal ejecta from a fourth large impact near the archean proterozoic boundary
Geology, 2011Co-Authors: Scott W Hassler, Bruce M Simonson, D Y Sumner, Louis BodinAbstract:We report the discovery of the Paraburdoo spherule layer, which consists entirely of replaced impact-produced melt Spherules. It is distal ejecta from a large impact close to the Archean-Proterozoic boundary in the Hamersley Basin of Western Australia. The spherule layer occurs in the Paraburdoo Member of the Wittenoom Formation and was deposited ca. 2.57 Ga (date via U-Pb age interpolation) in a deep shelf environment. The layer consists of microkrystites rich in plagioclase and ferromagnesian crystals, replaced by K-feldspar and a phlogopite-like sheet silicate, respectively. The skeletal textures indicate rapid cooling of a melt with mafic to ultramafic composition and suggest oceanic target rocks. The Paraburdoo spherule layer is 2 cm thick, normally graded, and was probably deposited by suspension settling, as there is no evidence of reworking; it is strikingly similar to the Reivilo spherule layer in the Griqualand West Basin (South Africa), appears to provide a third impact-related high-resolution stratigraphic correlation between these two basins, and points to a high frequency of large impacts around the Archean-Proterozoic boundary.
