Abstract 2219: Reference materials for ctDNA-based measurable residual disease (MRD) assay development and validation

Monitoring measurable residual disease (MRD) via liquid biopsy is a promising method for catching early stage cancer and disease relapse long before traditional diagnostics, which generally require significant disease progression for detection. Assays in development include those that target patient-specific variants and fixed panels for all patients. Regardless, detection of variant allele frequencies at extremely low levels, well below the limit of detection of typical circulating tumor DNA (ctDNA) assays, presents a challenge that can be surmounted with well-designed reference materials that allow for assessment of sensitivity and specificity. We developed the Seraseq® ctDNA MRD Panel kit composed of 4 tumor fractions at decreasing levels to meet validation needs of both patient-specific and fixed panel targeted cfDNA NGS MRD assays. Genomic DNA from tumor and their SNP-matched normal cell lines, characterized by whole exome sequencing (WES), was fragmented to approximate the size of circulating cell free DNA (ccfDNA). This DNA was blended at tumor fractions (TF) of 0.5%, 0.05%, and 0.005% and biosynthetic DNA fragments containing more common and clinically relevant variants were spiked in at similar TF levels. A normal (0% tumor) ctDNA reference material was produced for comparison and identification of background variants. The VAFs for the biosynthetic variants were determined by digital PCR (BioRad QX200) and targeted cfDNA NGS assay (ArcherDx LiquidPlex) in the 0.5% TF mix. Somatic variants from the tumor DNA were assessed using a custom Agilent SureSelect XT HS2 assay targeting ~100 variants in the MRD panel mix using 50 ng as input. Variants were called at 1 observation. All biosynthetic variants were detectable in the TF 0.5% mix at anticipated VAFs (dPCR: 0.43% ± 0.12% and NGS: 0.33% ± 0.15%). Somatic VAFs of the ctDNA MRD panel mixes were measured at expected levels although not all variants were detected below 0.05% due to sampling. Agilent SureSelect XT HS2 libraries had ~25% incorporation efficiency and ~ 72% on-target. The 0.5% and 0.05% mixes showed evidence of more of the somatic variants at 1 or more copies than the other samples. The 0.005% mix showed evidence of more of the somatic variants than the 0% mix. The Seraseq ctDNA MRD Panel Mixes have been designed to provide a broad range of DNA mutations from tumor-normal matched cell lines and spike-in variants to aid sensitivity and specificity when applied to MRD evaluation of patient-specific and fixed panel cfDNA NGS MRD assays.

Citation Format: Dana Ruminski Lowe, Benedicta Forson, Matthew G. Butler, Yves Konigshofer, Catherine Huang, Omoshile Clement, Russell K. Garlick, Bharathi Anekella. Reference materials for ctDNA-based measurable residual disease (MRD) assay development and validation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2219.

Abstract 1024: The challenge of standardizing the measurement of an imprecise biomarker like HRD

Here we present data on the characterization and implementation of a set of reference materials for the standardization of homologous recombination deficiency (HRD) assessment. The safety and effectiveness profile of a drug can be improved by using it in patients where that drug is most likely to be effective. While PARP inhibitors are indicated for use in some patients with ovarian, breast, pancreatic, and prostate cancer, patients with other cancers that are deficient in homologous recombination repair (HRR) might also benefit from their use. However, determining whether a cancer is HRD-positive is neither trivial nor precise. While clinical trials have shown that patients with deleterious mutations in BRCA2 and BRCA1 are most likely to benefit from PARP inhibitors, determining that a given BRCA mutation (or set of such mutations) is in fact deleterious is frequently not straightforward. Therefore, assays are now looking for signs of HRD, such as genomic instability consistent with non-homologous end joining (NHEJ) being used for the repair of double-stranded breaks in DNA as opposed to HRR. For example, some assays look at the combination of loss of heterozygosity (LOH) and large-scale state transitions (LST) across chromosomes as well as telomeric allelic imbalance (TAI) when determining whether a cancer is HRD-positive, while other assays use alternative approaches. How those characteristics are measured, integrated, and distilled into a final determination of whether HRD is present or absent varies, which can create uncertainty around treatment options and enrollment into clinical trials. This also makes the path of follow-on companion diagnostics challenging because perfect agreement between imprecise measurements is unlikely. In order to enable more standardized reporting of HRD and to enable the assessment of HRD assays, we created a set of characterized reference materials composed of HRD negative, borderline, and positive tumor/normal matched cell lines that were analyzed using both array-based and next generation sequencing-based assays in order to characterize chromosomal changes across their genomes and obtain HRD scores. Because of differences in the results, assay imprecision should be taken into account in clinical trials that implement cutoffs in order to establish safety data for patients who are biomarker-negative but may be biomarker-positive in a future assay, which is similar to what is done for complementary diagnostics.

Citation Format: Yves Konigshofer, Matthew G. Butler, Krystyna Nahlik, Dana Ruminski Lowe, Catherine Huang, Omoshile Clement, Russell K. Garlick. The challenge of standardizing the measurement of an imprecise biomarker like HRD [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1024.

Abstract 537: Development of blood TMB (bTMB) reference materials for validation of cfDNA-based targeted NGS assays that measure tumor mutational burden (TMB) in patient blood samples

TMB is a biomarker with potential for predicting positive patient response to immune checkpoint inhibitors. TMB measurements can be determined using genomic DNA extracted from FFPE-preserved tissue biopsy samples. However, assessment of TMB from a liquid biopsy, or blood TMB (bTMB), is an attractive alternative clinical diagnostic tool that would allow clinicians and patients to avoid the invasive challenge of tissue biopsies. Accurately measuring bTMB with targeted gene panels has been problematic, thus we have developed the new Seraseq® bTMB reference materials at various mutational burden levels from genomic DNA extracted from tumor-derived and SNP-matched normal cell lines. Somatic variants were identified in each cell line by whole exome sequencing (WES). TMB assessments were made by an in-house developed TMB bioinformatics pipeline based on recommendations by the Friends of Cancer Research (FoCR) TMB Harmonization Consortium. DNA from tumor and normal cell lines were blended at 0%, 0.5%, and 2% tumor fractions and fragmented to approximate the size of cell free DNA (cfDNA). The resulting bTMB mixes were enriched with the TruSight™ Oncology 500 ctDNA Assay (2x151 bp), in triplicate, and sequenced on a NovaSeq™ 6000. Blood TMB scores were determined using the DRAGEN™ TruSight Oncology 500 ctDNA Analysis Software v1.1. The observed bTMB scores for the tumor-containing materials were slightly lower in the TF 0.5% mix versus the TF 2% mix due to variants moving below the limit of detection of the TSO500 ctDNA assay (Table 1). As is the case with patient samples and clonal hematopoiesis, there are background variants in 0% tumor content material that may elevate apparent bTMB scores, thus adjusted bTMB scores are shown. The Seraseq Blood TMB Score reference materials provide a tumor-normal matched blood TMB control to aid development, validation and QC of cfDNA NGS assays for accurate determination of bTMB Scores.

Table 1. Average bTMB scores and adjusted bTMB scores for each mix. Mix Average bTMB Score (mutations/megabase ± 1 SD) Adjusted bTMB Score (mutations/megabase ± 1 SD) Score 7 0% 7.5 ± 1.7 0 Score 7 0.5% 13.1 ± 2.6 5.6 ± 3.1 Score 7 2% 17.9 ± 1.3 10.4 ± 2.1 Score 13 0% 4.6 ± 0.5 0 Score 13 0.5% 18.7 ± 2.1 14.1 ± 2.2 Score 13 2% 24.6 ± 0.8 20.0 ± 0.9 Score 20 0% 7.5 ± 1.4 0 Score 20 0.5% 26.0 ± 2.3 18.5 ± 2.7 Score 20 2% 35.6 ± 1.0 28.1 ± 1.7 Score 26 0% 6.0 ± 0.5 0 Score 26 0.5% 20.7 ± 5.5 14.7 ± 5.5 Score 26 2% 30.4 ± 1.5 24.4 ± 1.9

Citation Format: Dana Ruminski Lowe, Benedicta Forson, Matthew G. Butler, Yves Konigshofer, Catherine Huang, Omoshile Clement, Russell K. Garlick, Bharathi Anekella. Development of blood TMB (bTMB) reference materials for validation of cfDNA-based targeted NGS assays that measure tumor mutational burden (TMB) in patient blood samples [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 537.

Abstract 756: Comprehensive NGS-based reference materials for variant detection in lymphoid cancer

Next Generation Sequencing (NGS) is an important technology to identify genetic changes involved in lymphoid malignancies. Genome-level understanding of these changes can aid in diagnosis, prognosis, and therapy selection. Cancer biopsies are often preserved by formalin-fixed, paraffin-embedding (FFPE) procedures which provide long-term preservation but introduce damage to nucleic acids that are present in tissue including double strand breaks, nicks, and oxidation. The gold standard for Lymphoma diagnosis is surgical removal of the lymph node making FFPE the preferred sample format for analysis. To address the need for high quality reference materials for tumor profiling assays for these patients, we developed two multiplexed, biosynthetic reference materials: the Seraseq® FFPE Lymphoma DNA Reference Material and the Seraseq® Lymphoma DNA Mutation Mix. Both contain 26 plasmids containing important SNVs, INDELs, and gene fusions in lymphoid disease. For the FFPE format, plasmids were pooled at equal concentrations and introduced into the GM24385 reference human cell line. Engineered cells were diluted to achieve desired allele frequencies (AFs) as determined by digital PCR (dPCR). The cells were processed with a proprietary FFPE protocol that mimics damage in patient samples. The QIAamp DNA FFPE Tissue Kit and the Maxwell RSC DNA FFPE Kit were used for DNA isolation. DNA was quantified by the Qubit dsDNA HS Assay and quality assessed by the Agilent TapeStation. AFs were determined by dPCR for QIAamp-extracted DNA and a custom ArcherDX VariantPlex NGS panel for DNA extracted by both kits. DNA yield was similar, 193±44 ng (QIAamp) and 124±11 ng (Maxwell); however, a higher DNA integrity number was observed with the QIAamp kit (6.1 vs 2.7). The average % AF by dPCR was 9.6±1.8 (QIAamp) (target ≥5%). The average % AF by NGS was 7.6±2.8 (QIAamp) and 3.3±1.1 (Maxwell). For the DNA mix format, the same plasmids were pooled and blended with total purified genomic DNA from GM24385 cells. The average % AF was 8.4±0.6 by dPCR (target 5-10%) and 8.2±1.6 for the ArcherDX VariantPlex NGS panel. Overall, there was good concordance between AFs measured by dPCR and NGS for the DNA and FFPE formats. We noted that overall sample performance may be impacted by the FFPE DNA extraction method used. In conclusion, these reference materials allow for monitoring of a broad range of somatic mutations and gene fusions which can aid testing laboratories in accurately detecting and quantifying various genetic events in Lymphoid patient samples. The FFPE format can serve as an extraction control in assay development, while the DNA mix format allows laboratories to go directly into NGS library preparation and dPCR. A complementary circulating tumor DNA (ctDNA) version of these reference materials would aid laboratories in detecting minimal residual disease in patient blood resulting in less invasive lymphoid testing and therapeutic response monitoring.

Citation Format: Tonya N. Watkins, Benedicta Forson, Dana Ruminski Lowe, Yves Konigshofer, Catherine Huang, Omoshile Clement, Bharathi Anekella. Comprehensive NGS-based reference materials for variant detection in lymphoid cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 756.

Abstract 4540: Development of well characterized breast, lung, and brain cancer copy number variation reference materials

Introduction: Copy number variation (CNV), including gene amplification and deletion, can be a key driver of oncogenesis. Pathogenic CNVs are often associated with unfavorable prognosis and drug resistance, therefore detection of these types of genetic changes will be important for personalized treatment. Many tumor profiling workflows can detect CNVs in addition to somatic mutations, but well-characterized reference materials for CNVs are not widely available, which makes it difficult to assess accuracy and sensitivity. CNV content of cell lines can be variable and may change with passages, the genomic background may not be diploid, and germline and somatic variants may not be well characterized. Remnant patient samples often lack characterization and the volumes needed for such characterization and larger validation studies. Therefore, we developed and evaluated Seraseq CNV reference materials to serve as accuracy, precision, and limit-of-detection (LOD) controls for tumor profiling assay development and validation. By providing a consistent source of purified DNA with stable CNV content, these reference materials allow for repeatable assessment of clinical diagnostic assays targeting CNVs. Methods: Seraseq CNV reference materials were prepared by mixing genomic DNA with additional copies of target genes from the well-characterized cell line GM24385. Copies of ERBB2, FGFR3, and MYC were combined with genomic DNA to simulate CNVs found in breast cancer, while sequences for EGFR, MET, and MYCN were used to mimic lung and brain cancer CNVs. Three levels of amplification were targeted: +3, +6, and +12 additional copies. The copy number of each gene was precisely quantified using digital PCR and confirmed on several NGS-based assays internally and externally. Results & Conclusions: Testing revealed CNVs of each target gene were close to the expected copy number. Good correlation was observed between digital PCR data and NGS data generated internally with the Archer VariantPlex Solid Tumor assay. In addition, internal and external NGS data showed correlation and broad assay compatibility. While CNVs observed clinically can be upwards of 50 additional copies and more easily detectable, LOD controls such as those described here are imperative in evaluating assay performance. Collectively, the data demonstrate the utility of biosynthetic Seraseq CNV reference materials, which serve as superior alternatives to DNA from cell lines or patient-derived material.

Citation Format: Dana Ruminski Lowe, Jessica Dickens, Catherine Huang, Yves Konigshofer, Bharathi Anekella. Development of well characterized breast, lung, and brain cancer copy number variation reference materials [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4540.

Integration of biochemical, histochemical and toxicogenomic indices for the assessment of health status of mussels from the Tamar Estuary, U.K

The aim of this study was to examine whether a combination of biochemical, histopathological and toxicogenomic data could be used as a valuable tool for the assessment of biological risk associated with pollutants within the Tamar River and Estuary, S.W. England, U.K. Accordingly, biochemical and histopathological biomarkers (protein carbonyls, lipofuscin, neutral lipids, lysosomal stability [N-acetyl-β-hexosaminidase and neutral red], lysosomal volume, ferric reducing antioxidant power [FRAP] and malonaldehyde [MDA]) and gene expression profiles were assessed in 5 sites from the Tamar River and Estuary (Neal Point, Town Quay, Wilcove, Cremyll Ferry and Whitsand; and a reference site, Trebarwith Strand, N. Cornwall). PAHs were measured in mussel tissue and sediment and metals were measured in mussel tissue only. Data from the biomarkers was integrated into a Mussel Expert System (MES) model to produce a simple assessment of mussel stress. Clear gradients of mussel toxicity were identified by the biomarkers (with the exception of neutral lipids) with the highest impacted animals found furthest up the Tamar, whilst the MES was unable to identify a gradient of effect. Gene expression profiles also indicated a gradient of stress with the greatest number of significantly up- or down- regulated genes found at the uppermost 2 sites. The MES did, however, determine that mussels from all sites, except the reference site, were highly stressed; a conclusion that could not be inferred from the biomarker data alone. It is concluded that the MES is a valuable tool that permits integration and interpretation of complex sets of biomarker data by identifying the biological meaning of biomarker changes.

Quantification of the effects of secondary matrix on the analysis of sandstone composition, and a petrographic-chemical technique for retrieving original framework grain modes of altered sandstones

Most studies of sandstone provenance involve modal analysis of framework grains using techniques that exclude the fine-grained breakdown products of labile mineral grains and rock fragments, usually termed secondary matrix or pseudomatrix. However, the data presented here demonstrate that, when the proportion of pseudomatrix in a sandstone exceeds 10%, standard petrographic analysis can lead to incorrect provenance interpretation. Petrographic schemes for provenance analysis such as QFL and QFR should not therefore be applied to sandstones containing more than 10% secondary matrix. Pseudomatrix is commonly abundant in sandstones, and this is therefore a problem for provenance analysis. The difficulty can be alleviated by the use of whole-rock chemistry in addition to petrographic analysis. Combination of chemical and point-count data permits the construction of normative compositions that approximate original framework grain compositions. Provenance analysis is also complicated in many cases by fundamental compositional alteration during weathering and transport. Many sandstones, particularly shallow marine deposits, have undergone vigorous reworking, which may destroy unstable mineral grains and rock fragments. In such cases it may not be possible to retrieve provenance information by either petrographic or chemical means. Because of this, pseudomatrix-rich sandstones should be routinely included in chemical-petrological provenance analysis. Because of the many factors, both pre- and post-depositional, that operate to increase the compositional maturity of sandstones, petrologic studies must include a complete inventory of matrix proportions, grain size and sorting parameters, and an assessment of depositional setting.

A conceptual review of regional-scale controls on the composition of clastic sediment and the co-evolution of continental blocks and their sedimentary cover

Both sediment recycling and first-cycle input influence the composition of clastic material in sedimentary systems. This paper examines conceptually the roles played by these processes in governing the composition of clastic sediment on a regional scale by outlining the expected effects on sediment composition of protracted sediment recycling and of continuous first-cycle input on a maturing continental block. Generally speaking, long-term recycling tends to enrich sediments in the most chemically and mechanically stable components: quartz in the sand and silt size fractions, and illite among the clay minerals. Sandstones trend towards pure quartz arenites, and mudrocks become more potassic and aluminous. The average grain size of clastic sediment decreases by a combination of progressive attrition of sand grains and ongoing breakdown of primary silicate minerals to finer-grained clay minerals and oxides. Sandstones derived by continuous first-cycle input from an evolving continental crustal source also become increasingly rich in quartz, but in addition become more feldspathic as the proportion of granitic material in the upper continental crust increases during crustal stabilization. Associated mudrocks also become richer in potassium and aluminum, but will have higher K2O/Al2O3 ratios than recycled muds. The average grain size of the sediment may increase with time as the proportion of sand-prone granitic source rocks increases at the expense of more mud-prone volcanic sources. In general, except in instances where chemical weathering is extreme, first-cycle sediments lack the compositional maturity of recycled detritus, and are characterized by the presence of a variety of primary silicate minerals. Sedimentary systems are not usually completely dominated by either recycling or first-cycle detritus. Generally, however, sedimentary systems associated with the earliest phases of formation and accretion of continental crust are characterized by first-cycle input from igneous and metamorphic rocks, whereas those associated with more mature cratons tend to be dominated by recycled sedimentary material.

Accretionary history of the Archean Barberton Greenstone Belt (3.55-3.22 Ga), southern Africa

The 3.55-3.22 Ga Barberton Greenstone Belt, South Africa and Swaziland, and surrounding coeval plutons can be divided into four tectono-stratigraphic blocks that become younger toward the northwest. Each block formed through early mafic to ultramafic volcanism (Onverwacht Group), probably in oceanic extensional, island, or plateau settings. Volcanism was followed by magmatic quiescence and deposition of fine-grained sediments, possibly in an intraplate setting. Late evolution involved underplating of the mafic crust by tonalitic intrusions along a subduction-related magmatic arc, yielding a thickened, buoyant protocontinental block. The growth of larger continental domains occurred both through magmatic accretion, as new protocontinental blocks developed along the margins of older blocks, and when previously separate blocks were amalgamated through tectonic accretion. Evolution of the Barberton Belt may reflect an Early Archean plate tectonic cycle that characterized a world with few or no large, stabilized blocks of sialic crust.

Abiological origin of described stromatolites older than 3.2 Ga

The three well-documented occurrences of three-dimensional stromatolites older than 3.2 Ga meet most criteria for biogenicity except the presence of fossil bacteria. However, they also show features more consistent with nonbiological origins. Small conical structures in the Strelley Pool chert in the upper part of the Warrawoona Group (3.5-3.2 Ga), Western Australia, lack the structure typical of stromatolites and probably formed mainly through evaporitc precipitation. A domal structure from the North Pole chert, Warrawoona Group, formed by soft-sediment deformation or originally flat layers. Laminated chert containing domal and pseudocolumnar structures in the Onverwacht Group (3.5-3.3 Ga), Barberton Greenstone Belt, South Africa, extends downward into veins and cavities, where it formed through inorganic precipitation. Although bacterial communities were widespread on Earth prior to 3.2 Ga, these particular three-dimensional structures are probably abiotic in origin and do not provide information on the paleobiology or paleoecology of early organisms. The paucity of Archean stromatolites older than 3.2 Ga probably reflects the paucity of known and possibly extant carbonate deposits of this age.

Sm-Nd dating of Fig Tree clay minerals of the Barberton greenstone belt, South Africa

Sm-Nd isotopic data from carbonate-derived clay minerals of the 3.22-3.25 Ga Fig Tree Group, Barberton greenstone belt, South Africa, form a linear array corresponding to an age of 3102 +/- 64 Ma, making these minerals the oldest dated clays on Earth. The obtained age is 120-160 m.y. younger than the depositional age determined by zircon geochronology. Nd model ages for the clays range from approximately 3.39 to 3.44 Ga and almost cover the age variation of the Barberton greenstone belt rocks, consistent with independent evidence that the clay minerals are derived from material of the belt. The combined isotopic and mineralogical data provide evidence for a cryptic thermal overprint in the sediments of the belt. However, the highest temperature reached by the samples since the time of clay-mineral formation was <300 degrees C, lower than virtually any known early Archean supracrustal sequence.

Depositional and tectonic setting of the Archean Moodies Group, Barberton Greenstone Belt, South Africa

The 3.22-3.10 Ga old Moodies Group, uppermost unit of the Swaziland Supergroup in the Barberton Greenstone Belt (BGB), is the oldest exposed, well-preserved quartz-rich sedimentary sequence on earth. It is preserved in structurally separate blocks in a heavily deformed fold-and-thrust belt. North of the Inyoka Fault, Moodies strata reach up to 3700 m in thickness. Detailed mapping, correlation of measured sections, and systematic analysis of paleocurrents show that the lower Moodies Group north of the Inyoka Fault forms a deepening- and fining-upward sequence from a basal alluvial conglomerate through braided fluvial, tidal, and deltaic sandstones to offshore sandy shelf deposits. The basal conglomerate and overlying fluvial facies were derived from the north and include abundant detritus eroded from underlying Fig Tree Group dacitic volcanic rocks. Shoreline-parallel transport and extensive reworking dominate overlying deltaic, tidal, and marine facies. The lithologies and arrangement of Moodies Group facies, sandstone petrology, the unconformable relationship between Moodies strata and older deformed rocks, presence of at least one syndepositional normal fault, and presence of basaltic flow rocks and airfall fall tuffs interbedded with the terrestrial strata collectively suggest that the lower Moodies Group was deposited in one or more intramontane basins in an extensional setting. Thinner Moodies sections south of the Inyoka Fault, generally less than 1000 m thick, may be correlative with the basal Moodies Group north of the Inyoka Fault and were probably deposited in separate basins. A northerly derived, southward-thinning fan-delta conglomerate in the upper part of the Moodies Group in the central BGB overlies lower strata with an angular unconformity. This and associated upper Moodies conglomerates mark the beginning of basin shortening by south- to southeast-directed thrust faulting along the northern margin of the BGB and suggest that the upper Moodies Group was deposited in a foreland basin. Timing, orientation, and style of shortening suggest that this deformation eventually incorporated most of the BGB into a major fold-and-thrust belt.

3.4-Billion-year-old biogenic pyrites from Barberton, South Africa: sulfur isotope evidence

Laser ablation mass spectroscopy analyses of sulfur isotopic compositions of microscopic-sized grains of pyrite that formed about 3.4 billion years ago in the Barberton Greenstone Belt, South Africa, show that the pyrite formed by bacterial reduction of seawater sulfate. These data imply that by about 3.4 billion years ago sulfate-reducing bacteria had become active, the oceans were rich in sulfate, and the atmosphere contained appreciable amounts (>>10(-13) of the present atmospheric level) of free oxygen.

Noble metal abundances in an Early Archean impact deposit

We report detailed analyses on the concentrations of the noble metals Pd, Os, Ir, Pt, and Au in an early Archean spherule bed (S4) of probable impact origin from the lower Fig Tree Group, Barberton Greenstone Belt, South Africa. Compared to other sedimentary deposits of known or suspected impact origin, some noble metals are present in exceptionally high concentrations. Noble metal abundances are fractionated relative to abundances in chondrites with ratios of Os/Ir, Pt/Ir, Pd/Ir, and Au/Ir at only 80, 80, 41, and 2% of these values in CI chondrites. Although an extraterrestrial source is favored for the noble metal enrichment, the most plausible cause of the fractionation is by regional hydrothermal/metasomatic alteration.

Chronology of early Archaean granite-greenstone evolution in the Barberton Mountain Land, South Africa, based on precise dating by single zircon evaporation

We report precise 207Pb/206Pb single zircon evaporation ages for low-grade felsic metavolcanic rocks within the Onverwacht and Fig Tree Groups of the Barberton Greenstone Belt (BGB), South Africa, and from granitoid plutons bordering the belt. Dacitic tuffs of the Hooggenoeg Formation in the upper part of the Onverwacht Group yield ages between 3445 +/- 3 and 3416 +/- 5 Ma and contain older crustal components represented by a 3504 +/- 4 Ma old zircon xenocryst. Fig Tree dacitic tuffs and agglomerates have euhedral zircons between 3259 +/- 5 and 3225 +/- 3 Ma in age which we interpret to reflect the time of crystallization. A surprisingly complex xenocryst population in one sample documents ages from 3323 +/- 4 to 3522 +/- 4 Ma. We suspect that these xenocrysts were inherited, during the passage of the felsic melts to the surface, from various sources such as greenstones and granitoid rocks now exposed in the form of tonalite-trondhjemite plutons along the southern and western margins of the BGB, and units predating any of the exposed greenstone or intrusive rocks. Several of the granitoids along the southern margin of the belt have zircon populations with ages between 3490 and 3440 Ma. coeval with or slightly older than Onverwacht felsic volcanism, while the Kaap Valley pluton along the northwestern margin of the belt is coeval with Fig Tree dacitic volcanism. These results emphasize the comagmatic relationships between greenstone felsic volcanic units and the surrounding plutonic suites. Some of the volcanic plutonic units contain zircon xenocrysts older than any exposed rocks. These indicate the existence of still older units, possibly stratigraphically lower and older portions of the greenstone sequence itself, older granitoid intrusive rocks, or bodies of older, unrelated crustal material. Our data show that the Onverwacht and Fig Tree felsic units have distinctly different ages and therefore do not represent a single, tectonically repeated unit as proposed by others. Unlike the late Archaean Abitibi greenstone belt in Canada, which formed over about 30 Ma. exposed rocks in the BGB formed over a period of at least 220 Ma. The complex zircon populations encountered in this study imply that conventional multigrain zircon dating may not accurately identify the time of felsic volcanic activity in ancient greenstones. A surprising similarity in rock types, tectonic evolution, and ages of the BGB in the Kaapvaal craton of southern Africa and greenstones in the Pilbara Block of Western Australia suggests that these two terrains may have been part of a larger crustal unit in early Archaean times.

Loss of carbamazepine suspension through nasogastric feeding tubes

The apparent loss of carbamazepine suspension during administration through polyvinyl chloride nasogastric feeding tubes in vitro was studied. Twelve methods of administering carbamazepine suspension (100 mg/5 mL) were tested; the methods differed with respect to nasogastric tube size, presence and type of diluent, and type of flush solution. Undiluted or 50% diluted carbamazepine suspension 200 mg was drawn up in a syringe and forced through adult or pediatric nasogastric feeding tubes. The tubes were immediately flushed twice with 50 mL of sterile water, 0.9% sodium chloride solution, or 5% dextrose solution, by using the same syringe used to administer the suspension. Samples were collected and analyzed for carbamazepine concentration by high-performance liquid chromatography. Each administration method was tested six times, and the results were subjected to analysis of variance. Significant loss of carbamazepine was noted for four of the six methods in which undiluted suspension was administered. In these methods, adult and pediatric tubes were flushed with sterile water or 0.9% sodium chloride. No significant loss of drug occurred for any of the methods involving the use of diluent. Significant losses were associated with diluent and flush solution but not nasogastric tube size. Carbamazepine suspension should be mixed with an equal volume of diluent before being administered through nasogastric feeding tubes.

Geological and Geochemical Record of 3400-Million-Year-Old Terrestrial Meteorite Impacts

Beds of sand-sized spherules in the 3400-million-year-old Fig Tree Group, Barberton Greenstone belt, South Africa, formed by the fall of quenched liquid silicate droplets into a range of shallow-to deep-water depositional environments. The regional extent of the layers, their compositional complexity, and lack of included volcanic debris suggest that they are not products of volcanic activity. The layers are greatly enriched in iridium and other platinum group elements in roughly chondritic proportions. Geochemical modeling based on immobile element abundances suggests that the original average spherule composition can be approximated by a mixture of fractionated tholeiitic basalt, komatiite, and CI carbonaceous chondrite. The spherules are thought to be the products of large meteorite impacts on the Archean earth.

Stability of carbamazepine suspension after repackaging into four types of single-dose containers

The stability of carbamazepine in commercially available suspension that had been repackaged in various single-dose containers was studied. Carbamazepine suspension was repackaged in 2-mL and 8-mL aliquots in amber glass vials, polypropylene vials, and amber polypropylene syringes and in 2-mL aliquots in amber glass oral syringes. Containers were stored at room temperature and continuously exposed to fluorescent light for up to 12 weeks. Samples from each container type and volume were assayed for carbamazepine content by high-performance liquid chromatography at various intervals during storage. Carbamazepine concentrations in the samples were compared with the carbamazepine concentration in the original manufacturer's container. The pH of the samples was also determined, and the suspensions were inspected for color, odor, and large particles. There was no significant decrease in carbamazepine concentration of more than 10% in samples stored for up to eight weeks. After 12 weeks, significant decreases in concentration were observed in all but one container type. No changes in color, odor, or consistency were observed during the 12 weeks, and there were no significant changes in pH. In commercially available suspension repackaged in volumes corresponding to common pediatric doses, carbamazepine (20 mg/mL) is stable for at least eight weeks when stored at room temperature in the containers tested.

Geochemistry of Precambrian carbonates: II. Archean greenstone belts and Archean sea water

Carbonate rocks with geological attributes of marine sediments are a minor component of the Archean greenstone belts. Despite their relative scarcity, these rocks are important because they record chemical and isotopic properties of coeval oceans. The greenstones containing such carbonates appear to cluster at approximately 2.8 +/- 0.2 and approximately 3.5 +/- 0.1 Ga ago. The samples for the younger group are from the Abitibi, Yellowknife, Wabigoon (Steep Rock Lake), Michipicoten and Uchi greenstone belts of Canada and the "Upper Greenstones" of Zimbabwe. The older group includes the Swaziland Supergroup of South Africa, Warrawoona Group of Australia and the Sargur marbles of India. Mineralogically, the carbonates of the younger greenstones are mostly limestones and of the older ones, ferroan dolomites (ankerites); the latter with some affinities to hydrothermal carbonates. In mineralized areas with iron ores, the carbonate minerals are siderite +/- ankerite, irrespective of the age of the greenstones. Iron-poor dolomites represent a later phase of carbonate generation, related to post-depositional tectonic faulting. The original mineralogy of limestone sequences appears to have been an Sr-rich aragonite. The Archean carbonates yield near-mantle Sr isotopic values, with (87Sr/86Sr)o of 0.7025 +/- 0.0015 and 0.7031 +/- 0.0008 for younger and older greenstones, respectively. The best preserved samples give delta 13C of +1.5 +/- 1.5% PDB, comparable to their Phanerozoic counterparts. In contrast, the best estimate for delta 18O is -7% PDB. Archean limestones, compared to Phanerozoic examples, are enriched in 16O as well as in Mn2+ and Fe2+, and these differences are not a consequence of post-depositional alteration phenomena. The mineralogical and chemical attributes of Archean carbonates (hence sea water) are consistent with the proposition that the composition of the coeval oceans may have been buffered by a pervasive interaction with the "mantle", that is, with the oceanic crust and the coeval ubiquitous volcanosedimentary piles derived from mantle sources.

Turbidity Current Activity in a British Columbia Fjord

A year-long monitoring program within an elongated channel-fan system in Bute Inlet of British Columbia, Canada, detected active sand-transporting turbidity currents. Measurements of bottom velocities and sediment collected in traps, as well as damage to moorings and equipment, captured the signatures of frequent energetic events. Maximum calculated velocities achieved were 335 centimeters per second, with flow thicknesses of more than 30 meters. Coarse sand was transported at least 6 to 7.5 meters above the sea floor. Turbidity currents flowed a minimum distance of 25.9 kilometers, but possibly as far as 40 to 50 kilometers, over bottom slopes of generally less than 1 degrees.

Eruption of the Nevado del Ruiz Volcano, Colombia, on 13 November 1985: Gas Flux and Fluid Geochemistry

The 13 November 1985 eruption of Nevado del Ruiz volcano, in Colombia, released a small volume of pyroclastic material and a disproportionately large volume of volcanic gas. Before the eruption, summit fumarole gases became less water-rich, and the sulfur/chlorine ratio increased. Remote measurements of sulfur dioxide flux after the eruption indicated active degassing at levels associated with eruptive or inter-eruptive stages of other volcanoes. Thermal water analyses revealed increases in magnesium, calcium, and potassium and an increase in the magnesium/chlorine ratio, suggesting that these elements may have been leached from new magma. Ash leachate data showed sulfate and chloride concentrations and ratios that would be expected for the late stages ofa major Plinian eruption. Water from the lahar contained high concentrations of sulfate and had a sulfur/chlorine ratio of 4.67, suggesting that water ejected from the crater lake and turbulent mixing of pyroclasts and glacial ice triggered the lahar. Microprobe analyses of pumice from this eruption and the most recent previous event showed similar mixed andesites. The uniform composition of the pumices and the unusually high ratio of gas to magma suggest that, although a new batch of magma triggered this eruption, the pumice that erupted may actually be old. Large volumes of new magma and glacial ice make the volcano dangerous and should stimulate development of an integrated long-term monitoring program to include Tolima volcano, 25 kilometers to the south.

Toxicological findings in amoxapine overdose

Tissue concentrations of amoxapine, a new antidepressant with antipsychotic properties, were determined in two cases in which amoxapine was taken in overdose. Two extractions and GLC procedures, UV spectra, and TLC properties of amoxapine are described. The concentrations of amoxapine are described. The concentrations of amoxapine in brain tissue (52 micrograms/g and 53.2 micrograms/g) were about equal to concentrations found in liver (77 micrograms/g and 50 micrograms/g) and higher than blood concentrations (6 micrograms/mL and 1.5 micrograms/mL). The two metabolites of amoxapine, 8-hydroxyamoxapine and 7-hydroxyamoxapine, were not detected by TLC or GLC.