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1. Interpreting and reporting 40Ar/39Ar geochronologic data

Author

Schaen, AJ, Jicha, BR, Hodges, K, Vermeesch, P, Stelten, ME, Mercer, CM, Phillips, D, Rivera, TA, Jourdan, F, Matchan, EL, Hemming, SR, Morgan, LE, Kelley, SP, Cassata, WS, Heizler, MT, Vasconcelos, PM, Benowitz, JA, Koppers, AAP, Mark, DF, Niespolo, EM, Sprain, CJ, Hames, WE, Kuiper, KF, Turrin, BD, Renne, PR, Ross, J, Nomade, S, Guillou, H, Webb, LE, Cohen, BA, Calvert, AT, Joyce, N, Ganerod, M, Wijbrans, J, Ishizuka, O, He, H, Ramirez, A, Pfander, JA, Lopez-Martinez, M, Qiu, H, Singer, BS, Schaen, AJ, Jicha, BR, Hodges, K, Vermeesch, P, Stelten, ME, Mercer, CM, Phillips, D, Rivera, TA, Jourdan, F, Matchan, EL, Hemming, SR, Morgan, LE, Kelley, SP, Cassata, WS, Heizler, MT, Vasconcelos, PM, Benowitz, JA, Koppers, AAP, Mark, DF, Niespolo, EM, Sprain, CJ, Hames, WE, Kuiper, KF, Turrin, BD, Renne, PR, Ross, J, Nomade, S, Guillou, H, Webb, LE, Cohen, BA, Calvert, AT, Joyce, N, Ganerod, M, Wijbrans, J, Ishizuka, O, He, H, Ramirez, A, Pfander, JA, Lopez-Martinez, M, Qiu, H, and Singer, BS

Abstract

The 40Ar/39Ar dating method is among the most versatile of geochronometers, having the potential to date a broad variety of K-bearing materials spanning from the time of Earth’s formation into the historical realm. Measurements using modern noble-gas mass spectrometers are now producing 40Ar/39Ar dates with analytical uncertainties of ∼0.1%, thereby providing precise time constraints for a wide range of geologic and extraterrestrial processes. Analyses of increasingly smaller subsamples have revealed age dispersion in many materials, including some minerals used as neutron fluence monitors. Accordingly, interpretive strategies are evolving to address observed dispersion in dates from a single sample. Moreover, inferring a geologically meaningful “age” from a measured “date” or set of dates is dependent on the geological problem being addressed and the salient assumptions associated with each set of data. We highlight requirements for collateral information that will better constrain the interpretation of 40Ar/39Ar data sets, including those associated with single-crystal fusion analyses, incremental heating experiments, and in situ analyses of microsampled domains. To ensure the utility and viability of published results, we emphasize previous recommendations for reporting 40Ar/39Ar data and the related essential metadata, with the amendment that data conform to evolving standards of being findable, accessible, interoperable, and reusable (FAIR) by both humans and computers. Our examples provide guidance for the presentation and interpretation of 40Ar/39Ar dates to maximize their interdisciplinary usage, reproducibility, and longevity.

Published
2021

2. P3.162 Developing a clinical prediction rule to target sti testing and contraception to women in community settings: implications for sexual health surveys

Author

Mercer Cm, Jackie Cassell, Natalie Edelman, and De Visser Ro

Subjects
medicine.medical_specialty, education.field_of_study, business.industry, Public health, Population, Absolute risk reduction, Psychological intervention, Risk management tools, Family medicine, medicine, Risk assessment, business, Psychiatry, education, Psychosocial, Reproductive health
Abstract

Introduction Applied sexual health surveys investigate associations between psychosocial and demographic factors, sexual risk behaviour, uptake of interventions and sexual morbidity. This work improves clinical and public health understandings of sexual morbidity but may not be easily translated into practice. We seek to identify key features of research surveys that would make them more relevant to the development and use of risk assessment and targeting tools. Methods To support the development of clinically-embedded risk assessment tools we undertook a systematic review of population surveys reporting on sexual risk and morbidity. We identified aspects of sexual health research questionnaire items and their reporting which could be adapted to better serve public health and clinical services to identify patients for targeted intervention. Results Four key deficiencies were identified: 1.The degree to which sexual risk behaviours such as multiple partnerships and inconsistent contraception use predict adverse outcomes remains under-investigated; 2.Surveys frequently use composite measures with complex scoring systems; 3. Analyses often fail to report on non-response to individual items and the prevalence of exposures; 4. Sexual risk behaviours and morbidity are often reported without measures of absolute risk. Conclusion There is a strategic need to exploit survey research better in order to embed investigation of risk factors in clinical risk prediction tools. Survey analyses should investigate which sexual risk behaviours warrant different sexual health interventions, and use measures of absolute risk. Researchers should favour questionnaire items that are concise and easy to score, and should report on item non-response and prevalence of exposures. These steps would facilitate the development of brief, acceptable and adequately predictive tools.

Published
2017
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5. P3.163 Differences between women attending specialist sexual health clinics and those attending general practices: implications for targeting sti testing

Author

Edelman, Natalie, Mercer, CM, Cassell, J, and Visser, RO De

Abstract

IntroductionIn Britain sexual health interventions are increasingly provided in community settings such as General Practices (GPs), while Genito-Urinary Medicine clinics have largely been replaced by Sexual Health and for Contraception clinics (SHACs). This study compared women attending GPs with those attending SHAC in an urban setting to investigate how much these populations differ and to assess the extent of sexual risk behaviour in GP populations.MethodsA convenience sample of women aged 16–44 years attending GP and SHAC services in the city of Brighton and Hove was invited to complete a short questionnaire about socio-demographic, psychosocial and sexual behavioural factors.Results1288 participated from GPs and 552 women from SHAC. 11.2% of GP participants and 3.4% of SHAC participants (p<0.0001) reported no male sexual partners in the last year. GP participants were less likely than SHAC participants to report 2 or more male sexual partners in the last year (2PP) (21.5% versus 60.9% p<0.0001) and to report non-use of condoms with two partners in the last year 6.9% versus 24.2% p<0.0001.These associations remained after adjusting for the smaller proportion of women≤24 years among GP participants compared to SHAC (21.7% v. 44.5% p<0.0001). Binge drinking alcohol in the last week was associated with 2PP (p<0.0001) and was more common among SHAC participants≤24 years than GP participants≤24 years (49.8% versus 37.9% p=0.009). However, it did not differ across sites for women aged 25–44 years (33.3% versus 36.3% p=0.362).ConclusionAlthough women attending GPs are less likely than those attending SHAC to report sexual risk behaviour in the last year, a substantial minority may benefit from sexual health promotion, STI testing and alcohol awareness. This supports the development of a risk prediction tool to target sexual health and adjunct interventions in community settings among women aged 16–44 years.

Published
2017
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6. Refining lunar impact chronology through high spatial resolution (40)Ar/(39)Ar dating of impact melts.

Author

Mercer CM, Young KE, Weirich JR, Hodges KV, Jolliff BL, Wartho JA, and van Soest MC

Abstract

Quantitative constraints on the ages of melt-forming impact events on the Moon are based primarily on isotope geochronology of returned samples. However, interpreting the results of such studies can often be difficult because the provenance region of any sample returned from the lunar surface may have experienced multiple impact events over the course of billions of years of bombardment. We illustrate this problem with new laser microprobe (40)Ar/(39)Ar data for two Apollo 17 impact melt breccias. Whereas one sample yields a straightforward result, indicating a single melt-forming event at ca. 3.83 Ga, data from the other sample document multiple impact melt-forming events between ca. 3.81 Ga and at least as young as ca. 3.27 Ga. Notably, published zircon U/Pb data indicate the existence of even older melt products in the same sample. The revelation of multiple impact events through (40)Ar/(39)Ar geochronology is likely not to have been possible using standard incremental heating methods alone, demonstrating the complementarity of the laser microprobe technique. Evidence for 3.83 Ga to 3.81 Ga melt components in these samples reinforces emerging interpretations that Apollo 17 impact breccia samples include a significant component of ejecta from the Imbrium basin impact. Collectively, our results underscore the need to quantitatively resolve the ages of different melt generations from multiple samples to improve our current understanding of the lunar impact record, and to establish the absolute ages of important impact structures encountered during future exploration missions in the inner Solar System.

Published
2015
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