B. Schubert, J. Samuels, J. Chatters, J. Arroyo‐Cabrales
Several years ago, a new genus and species of peccary, “Muknalia minima”, was described from the Pleistocene of Mexico. We previously examined that specimen and concluded that it was synonymous with the extant collared peccary, Pecari tajacu, but that taxonomic revision is rejected by the authors of the original study (this volume). Here, we provide further analysis of “Muknalia” and expand on previous evidence from both morphology and taphonomy that support synonymy with P. tajacu. We argue that morphological features, both in terms of size and shape, that were used to diagnose “Muknalia” all fall within the range of variation of the extant P. tajacu, or are a consequence of taphonomic modification, including human handling.
{"title":"Muknalia is a Collared Peccary (Pecari tajacu): A Reply to Stinnesbeck et al.","authors":"B. Schubert, J. Samuels, J. Chatters, J. Arroyo‐Cabrales","doi":"10.5334/oq.98","DOIUrl":"https://doi.org/10.5334/oq.98","url":null,"abstract":"Several years ago, a new genus and species of peccary, “Muknalia minima”, was described from the Pleistocene of Mexico. We previously examined that specimen and concluded that it was synonymous with the extant collared peccary, Pecari tajacu, but that taxonomic revision is rejected by the authors of the original study (this volume). Here, we provide further analysis of “Muknalia” and expand on previous evidence from both morphology and taphonomy that support synonymy with P. tajacu. We argue that morphological features, both in terms of size and shape, that were used to diagnose “Muknalia” all fall within the range of variation of the extant P. tajacu, or are a consequence of taphonomic modification, including human handling.","PeriodicalId":37172,"journal":{"name":"Open Quaternary","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-06-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42703082","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Reconstructions of postglacial sea-level rise have provided key insight into the rapid disintegration of ice-sheets and the discharge of large meltwater pulses during the last deglaciation. The most complete reconstruction is from Barbados where thick, backstepping sequences of the reef-crest coral Acropora palmata have been recovered in cores from the insular shelf and slope off the Island’s south coast. Differences in the depth, timing, and magnitude of meltwater pulses between the Barbados reconstruction and other reefal records, however, has led to significant uncertainty in their origin, and the consequent timing of ice-sheet collapse. Here we re-analyse the published sedimentary, stratigraphic, and chronological data from Barbados, and find evidence for ex-situ data which indicates that reefal sequences contain coral clasts generated during hurricanes. By adjusting for biases caused by these ex-situ data, we provide a revised sea-level reconstruction which shows that MWP-1b was an 8–11 m rise from –53 m in ~250 years starting at 11.3 ka, which is 5 m smaller, and 150 years younger than previous estimates. It also shows that the onset of MWP-1a cannot be determined at Barbados because the downslope core sequences are not reef-crest deposits due to their association with deeper coral assemblages and lack of depositional relief. The end of this meltwater pulse can however be determined from the upslope reef, and occurred at a similar time and depth to that documented from Tahiti.
{"title":"Revised Postglacial Sea-Level Rise and Meltwater Pulses from Barbados","authors":"Paul Blanchon, A. E. Medina-Valmaseda, F. Hibbert","doi":"10.5334/OQ.87","DOIUrl":"https://doi.org/10.5334/OQ.87","url":null,"abstract":"Reconstructions of postglacial sea-level rise have provided key insight into the rapid disintegration of ice-sheets and the discharge of large meltwater pulses during the last deglaciation. The most complete reconstruction is from Barbados where thick, backstepping sequences of the reef-crest coral Acropora palmata have been recovered in cores from the insular shelf and slope off the Island’s south coast. Differences in the depth, timing, and magnitude of meltwater pulses between the Barbados reconstruction and other reefal records, however, has led to significant uncertainty in their origin, and the consequent timing of ice-sheet collapse. Here we re-analyse the published sedimentary, stratigraphic, and chronological data from Barbados, and find evidence for ex-situ data which indicates that reefal sequences contain coral clasts generated during hurricanes. By adjusting for biases caused by these ex-situ data, we provide a revised sea-level reconstruction which shows that MWP-1b was an 8–11 m rise from –53 m in ~250 years starting at 11.3 ka, which is 5 m smaller, and 150 years younger than previous estimates. It also shows that the onset of MWP-1a cannot be determined at Barbados because the downslope core sequences are not reef-crest deposits due to their association with deeper coral assemblages and lack of depositional relief. The end of this meltwater pulse can however be determined from the upslope reef, and occurred at a similar time and depth to that documented from Tahiti.","PeriodicalId":37172,"journal":{"name":"Open Quaternary","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44136904","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
“ Orbital, the Box” provides an interactive tool with graphical user interface (GUI) for stimulating active, visual learning for understanding of astronomical climate forcing. This cross-platform tool can be run locally on a personal computer using a standard web browser environment with no need for plugins, thus maximising accessibility for students and teachers alike. The tool facilitates in the development of a holistic and quantitative understanding of astronomical climate forcing by allowing students to independently vary orbital parameters, after which they can instantaneously see the resulting effect upon the seasonal and latitudinal distribution of solar irradiance arriving at the top of the Earth’s atmosphere. Such an approach follows a classic controlled experimental design whereby one parameter can be changed while all others are kept constant. This experimental tool can be deployed as a virtual laboratory, including within a flipped classroom setting, to promote active learning of traditionally challenging concepts such as the roles of eccentricity and precession in astronomical climate forcing, and in particular their interaction with Kepler’s second law and the subsequent consequences for season length.
{"title":"Orbital, the Box - An interactive educational tool for in-depth understanding of astronomical climate forcing.","authors":"B. Lougheed","doi":"10.31223/x57310","DOIUrl":"https://doi.org/10.31223/x57310","url":null,"abstract":"“ Orbital, the Box” provides an interactive tool with graphical user interface (GUI) for stimulating active, visual learning for understanding of astronomical climate forcing. This cross-platform tool can be run locally on a personal computer using a standard web browser environment with no need for plugins, thus maximising accessibility for students and teachers alike. The tool facilitates in the development of a holistic and quantitative understanding of astronomical climate forcing by allowing students to independently vary orbital parameters, after which they can instantaneously see the resulting effect upon the seasonal and latitudinal distribution of solar irradiance arriving at the top of the Earth’s atmosphere. Such an approach follows a classic controlled experimental design whereby one parameter can be changed while all others are kept constant. This experimental tool can be deployed as a virtual laboratory, including within a flipped classroom setting, to promote active learning of traditionally challenging concepts such as the roles of eccentricity and precession in astronomical climate forcing, and in particular their interaction with Kepler’s second law and the subsequent consequences for season length.","PeriodicalId":37172,"journal":{"name":"Open Quaternary","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49353684","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Poetry as a Tool For Outreach in Quaternary Science: Examples From the 20th INQUA Congress","authors":"H. Griffiths","doi":"10.5334/oq.103","DOIUrl":"https://doi.org/10.5334/oq.103","url":null,"abstract":"","PeriodicalId":37172,"journal":{"name":"Open Quaternary","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70694767","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Sarah R. Stinnesbeck, W. Stinnesbeck, E. Frey, Jerónimo Avíles Olguín, A. González
{"title":"Comment on Schubert et al. 2020. Muknalia minima from the Yucatán of Mexico is synonymous with the collared peccary, Pecari tajacu (Artiodactyla: Tayassuidae). Open Quaternary, 6: 8, pp. 1–9. DOI: https://doi.org/10.5334/oq.84","authors":"Sarah R. Stinnesbeck, W. Stinnesbeck, E. Frey, Jerónimo Avíles Olguín, A. González","doi":"10.5334/oq.89","DOIUrl":"https://doi.org/10.5334/oq.89","url":null,"abstract":"","PeriodicalId":37172,"journal":{"name":"Open Quaternary","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70695251","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Duval, K. Westaway, J. Zaim, Y. Rizal, Aswan, M. Puspaningrum, Agus Trihascaryo, P. Albers, Holly E. Smith, Gerrell M. Drawhorn, G. Price, Julien Louys
{"title":"New Chronological Constraints for the Late Pleistocene Fossil Assemblage and Associated Breccia from Ngalau Sampit, Sumatra","authors":"M. Duval, K. Westaway, J. Zaim, Y. Rizal, Aswan, M. Puspaningrum, Agus Trihascaryo, P. Albers, Holly E. Smith, Gerrell M. Drawhorn, G. Price, Julien Louys","doi":"10.5334/oq.96","DOIUrl":"https://doi.org/10.5334/oq.96","url":null,"abstract":"","PeriodicalId":37172,"journal":{"name":"Open Quaternary","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70695378","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Karst-derived breccia is the most analysed deposit in fossil-bearing Southeast Asian caves due to its superior preservation potential for human, faunal, archaeological, and palaeontological data. The study of breccia can provide a better understanding of human and faunal histories, and an opportunity to investigate site taphonomy and insights into environments of deposition and post-depositional processes. We review the literature on approaches used to improve the taphonomic understanding of cave deposits in Southeast Asia and how these deposits fit into a cave’s life history. We discuss common methods used to extract taphonomic data retained in Southeast Asian cave deposits and the associated opportunities to discern the mechanisms of cave formation, depositional history, and faunal accumulation. While attempts have previously been made to discern the taphonomic characteristics of Pleistocene vertebrate remains in the region, there has been no comprehensive review outlining methods used to understand taphonomic histories and the biases introduced through these processes. We illustrate the challenges of researching cave breccias in Southeast Asia and the knowledge gaps brought about by conventional methodologies. Uncertainties exist about the extent to which breccia can be examined to infer the taphonomic history of a vertebrate assemblage. These uncertainties exist in part because of dating complexities. This review demonstrates that a taphonomic analysis of breccia in complex long-term accumulations requires a multi-disciplinary approach. We recommend using digital techniques to record spatial distribution data for a thorough interpretation of taphonomic characteristics.
{"title":"Taphonomic Analyses of Cave Breccia in Southeast Asia: A Review and Future Directions","authors":"Holly E. Smith, Mike W. Morley, Julien Louys","doi":"10.5334/oq.75","DOIUrl":"https://doi.org/10.5334/oq.75","url":null,"abstract":"Karst-derived breccia is the most analysed deposit in fossil-bearing Southeast Asian caves due to its superior preservation potential for human, faunal, archaeological, and palaeontological data. The study of breccia can provide a better understanding of human and faunal histories, and an opportunity to investigate site taphonomy and insights into environments of deposition and post-depositional processes. We review the literature on approaches used to improve the taphonomic understanding of cave deposits in Southeast Asia and how these deposits fit into a cave’s life history. We discuss common methods used to extract taphonomic data retained in Southeast Asian cave deposits and the associated opportunities to discern the mechanisms of cave formation, depositional history, and faunal accumulation. While attempts have previously been made to discern the taphonomic characteristics of Pleistocene vertebrate remains in the region, there has been no comprehensive review outlining methods used to understand taphonomic histories and the biases introduced through these processes. We illustrate the challenges of researching cave breccias in Southeast Asia and the knowledge gaps brought about by conventional methodologies. Uncertainties exist about the extent to which breccia can be examined to infer the taphonomic history of a vertebrate assemblage. These uncertainties exist in part because of dating complexities. This review demonstrates that a taphonomic analysis of breccia in complex long-term accumulations requires a multi-disciplinary approach. We recommend using digital techniques to record spatial distribution data for a thorough interpretation of taphonomic characteristics.","PeriodicalId":37172,"journal":{"name":"Open Quaternary","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-12-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49550228","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J. Hennekam, V. Herridge, L. Costeur, C. Patti, P. Cox
The endemic dormouse Leithia melitensis from the Pleistocene of Sicily is considered an insular giant, whose body size is exceptionally large in comparison to that of any extant dormouse species. However, knowledge of the skull morphology of this giant glirid species is limited as cranial material is rare and mostly fragmentary. A fossil conglomerate representing a cave floor segment from Poggio Schinaldo, Sicily, presented an exceptional opportunity to reconstruct the cranium of Leithia melitensis. Following microCT scanning, five partial crania were digitally extracted from the conglomerate. A composite skull of the partial crania was then reconstructed with the use of merging and warping techniques, resulting in the best approximation to the complete skull morphology of this species thus far. All major structures except for the nasal bone are present in the composite model, indicating very robust morphology, especially in the zygomatic area and the pterygoid flange. This model could potentially be very important for our understanding of the morphology and ecology of this gigantic dormouse, as well as for providing valuable data for understanding the phenomenon of insular gigantism more generally.
{"title":"Virtual Cranial Reconstruction of the Endemic Gigantic Dormouse Leithia melitensis (Rodentia, Gliridae) from Poggio Schinaldo, Sicily","authors":"J. Hennekam, V. Herridge, L. Costeur, C. Patti, P. Cox","doi":"10.5334/oq.79","DOIUrl":"https://doi.org/10.5334/oq.79","url":null,"abstract":"The endemic dormouse Leithia melitensis from the Pleistocene of Sicily is considered an insular giant, whose body size is exceptionally large in comparison to that of any extant dormouse species. However, knowledge of the skull morphology of this giant glirid species is limited as cranial material is rare and mostly fragmentary. A fossil conglomerate representing a cave floor segment from Poggio Schinaldo, Sicily, presented an exceptional opportunity to reconstruct the cranium of Leithia melitensis. Following microCT scanning, five partial crania were digitally extracted from the conglomerate. A composite skull of the partial crania was then reconstructed with the use of merging and warping techniques, resulting in the best approximation to the complete skull morphology of this species thus far. All major structures except for the nasal bone are present in the composite model, indicating very robust morphology, especially in the zygomatic area and the pterygoid flange. This model could potentially be very important for our understanding of the morphology and ecology of this gigantic dormouse, as well as for providing valuable data for understanding the phenomenon of insular gigantism more generally.","PeriodicalId":37172,"journal":{"name":"Open Quaternary","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45313261","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Huixian Chen, T. Shaw, Jianhua Wang, S. Engelhart, D. Nikitina, J. Pilarczyk, J. Walker, Ane García-Artola, B. Horton
We investigated foraminiferal distributions from two salt-marsh sites at Thunderbolt and Georgetown, in mainland northern Georgia, U.S. Atlantic coast. We analyzed modern epifaunal foraminiferal assemblages across multiple transects consisting of 54 surface samples. Multivariate statistical analysis (Partitioning Around Medoids and Detrended Correspondence Analysis) revealed that dead foraminiferal assemblages are divided into three faunal zones, which are elevation-dependent and site-specific. At Thunderbolt, an intermediate salinity marsh (17‰), high marsh assemblages are dominated by Haplophragmoides spp. with an elevational range of 1.19 to 1.68 m mean tide level (MTL) between Mean Higher High Water (MHHW) to Highest Astronomical Tide (HAT). Low marsh assemblages are dominated by Miliammina fusca and Ammobaculites spp. with an elevational range of – 0.05 to 1.14 m MTL (between MTL and MHHW). At Georgetown, a low salinity marsh (6‰), the assemblages are dominated by Ammoastuta inepta with an elevational range of 0.43 to 1.16 m MTL (between MTL and MHHW). We also enumerated living infaunal foraminiferal populations from six 50-cm sediment cores from the two salt marshes to assess implications for interpretations of sea-level change. Peak concentrations of living foraminiferal populations occur in the upper 1-cm surface sediment in five of the six cores. An exception was observed in high marsh settings of Thunderbolt, where Haplophragmoides spp. and Arenoparrella mexicana were observed living down to 40 cm depth and both the live and dead abundance peaked (32 and 520 specimens per 10 cc respectively) between depths of 15–35 cm in the core. The dominant infaunal species were similar to those observed in modern surface samples, and the total number of infaunal foraminifera was typically less than 15% compared to the total number of dead specimens in the surface samples. Finally, we compared the down-core patterns of living and dead foraminiferal abundance that suggest that 90% of the tests were removed within the upper 10 cm of sediment in most cores. This may be due to taphonomic alteration from bioturbation and/or microbial processes. Selective preservation between resistant species such as A. mexicana and fragile species like M. fusca and Ammobaculites spp. can change the subsurface foraminiferal assemblage. This has the potential to cause errors in sea-level reconstructions using foraminiferal assemblage from low marsh sediments. This study highlights the modern vertical distribution of salt-marsh foraminifera in mainland northern Georgia and their potential as modern analogues for fossil counterparts in reconstructing sea-level changes. Taphonomic processes may cause the absence of foraminiferal tests or differences between modern and fossil assemblages, which could be problematic when performing RSL reconstructions in low marsh environment.
我们调查了美国大西洋沿岸乔治亚州北部大陆Thunderbolt和Georgetown两个盐沼地点的有孔虫分布。我们分析了由54个表面样本组成的多个样带的现代趾外有孔虫组合。多元统计分析(Partitioning Around medium - ids和dettrend Correspondence analysis)表明，有孔虫死亡群落可划分为3个区系带，这些区系带具有海拔依赖性和地点特异性。Thunderbolt是一个中等盐度的沼泽(17‰)，在平均高高潮(MHHW)到最高天文潮(HAT)之间的平均潮位(MTL)高度范围为1.19 ~ 1.68 m，高沼泽组合以Haplophragmoides spp.为主。低洼沼泽群落以富丝米纳(milammina fusca)和水蛭属(Ammobaculites)为主，海拔范围为- 0.05 ~ 1.14 m MTL(介于MTL和MHHW之间)。在低盐度(6‰)的Georgetown，以Ammoastuta inepta为主，海拔范围为0.43 ~ 1.16 m MTL(介于MTL和MHHW之间)。我们还从两个盐沼的6个50厘米沉积物岩心中枚举了活的有孔虫种群，以评估对海平面变化解释的影响。在6个岩心中，有孔虫种群的峰值出现在1厘米以上的表层沉积物中。在Thunderbolt的高沼泽环境中观察到一个例外，在那里观察到Haplophragmoides spp.和arenopparrella mexicana生活在40 cm的深度，并且在15-35 cm的核心深度之间，活和死的丰度达到峰值(每10 cc分别有32和520个标本)。优势虫种与现代地表标本相似，有孔虫总数通常少于地表标本死亡总数的15%。最后，我们比较了活的和死的有孔虫丰度的下核模式，结果表明，在大多数岩心中，90%的测试是在沉积物的上部10厘米内被移除的。这可能是由于生物扰动和/或微生物过程引起的语音学改变。耐药物种如A. mexicana和脆弱物种如M. fusca和Ammobaculites之间的选择性保存可以改变地下有孔虫的组合。这有可能导致使用来自低地沼泽沉积物的有孔虫组合进行海平面重建时出现错误。这项研究强调了乔治亚州北部大陆盐沼泽有孔虫的现代垂直分布，以及它们作为重建海平面变化的化石化石对应物的现代类似物的潜力。地形学过程可能导致有孔虫测试的缺失或现代和化石组合之间的差异，这在低沼泽环境中进行RSL重建时可能会出现问题。
{"title":"Salt-Marsh Foraminiferal Distributions from Mainland Northern Georgia, USA: An Assessment of Their Viability for Sea-Level Studies","authors":"Huixian Chen, T. Shaw, Jianhua Wang, S. Engelhart, D. Nikitina, J. Pilarczyk, J. Walker, Ane García-Artola, B. Horton","doi":"10.5334/oq.80","DOIUrl":"https://doi.org/10.5334/oq.80","url":null,"abstract":"We investigated foraminiferal distributions from two salt-marsh sites at Thunderbolt and Georgetown, in mainland northern Georgia, U.S. Atlantic coast. We analyzed modern epifaunal foraminiferal assemblages across multiple transects consisting of 54 surface samples. Multivariate statistical analysis (Partitioning Around Medoids and Detrended Correspondence Analysis) revealed that dead foraminiferal assemblages are divided into three faunal zones, which are elevation-dependent and site-specific. At Thunderbolt, an intermediate salinity marsh (17‰), high marsh assemblages are dominated by Haplophragmoides spp. with an elevational range of 1.19 to 1.68 m mean tide level (MTL) between Mean Higher High Water (MHHW) to Highest Astronomical Tide (HAT). Low marsh assemblages are dominated by Miliammina fusca and Ammobaculites spp. with an elevational range of – 0.05 to 1.14 m MTL (between MTL and MHHW). At Georgetown, a low salinity marsh (6‰), the assemblages are dominated by Ammoastuta inepta with an elevational range of 0.43 to 1.16 m MTL (between MTL and MHHW). We also enumerated living infaunal foraminiferal populations from six 50-cm sediment cores from the two salt marshes to assess implications for interpretations of sea-level change. Peak concentrations of living foraminiferal populations occur in the upper 1-cm surface sediment in five of the six cores. An exception was observed in high marsh settings of Thunderbolt, where Haplophragmoides spp. and Arenoparrella mexicana were observed living down to 40 cm depth and both the live and dead abundance peaked (32 and 520 specimens per 10 cc respectively) between depths of 15–35 cm in the core. The dominant infaunal species were similar to those observed in modern surface samples, and the total number of infaunal foraminifera was typically less than 15% compared to the total number of dead specimens in the surface samples. Finally, we compared the down-core patterns of living and dead foraminiferal abundance that suggest that 90% of the tests were removed within the upper 10 cm of sediment in most cores. This may be due to taphonomic alteration from bioturbation and/or microbial processes. Selective preservation between resistant species such as A. mexicana and fragile species like M. fusca and Ammobaculites spp. can change the subsurface foraminiferal assemblage. This has the potential to cause errors in sea-level reconstructions using foraminiferal assemblage from low marsh sediments. This study highlights the modern vertical distribution of salt-marsh foraminifera in mainland northern Georgia and their potential as modern analogues for fossil counterparts in reconstructing sea-level changes. Taphonomic processes may cause the absence of foraminiferal tests or differences between modern and fossil assemblages, which could be problematic when performing RSL reconstructions in low marsh environment.","PeriodicalId":37172,"journal":{"name":"Open Quaternary","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42025271","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Nelson, A. Hawkes, Y. Sawai, S. Engelhart, R. Witter, Wendy C. Grant-Walter, L. Bradley, T. Dura, N. Cahill, B. Horton
We infer a history of three great megathrust earthquakes during the past 2000 years at the Nehalem River estuary based on the lateral extent of sharp (≤3 mm) peat-mud stratigraphic contacts in cores and outcrops, coseismic subsidence as interpreted from fossil diatom assemblages and reconstructed with foraminiferal assemblages using a Bayesian transfer function, and regional correlation of 14C-modeled ages for the times of subsidence. A subsidence contact from 1700 CE (contact A), sometimes overlain by tsunami-deposited sand, can be traced over distances of 7 km. Contacts B and D, which record subsidence during two earlier megathrust earthquakes, are much less extensive but are traced across a 700-m by 270-m tidal marsh. Although some other Cascadia studies report evidence for an earthquake between contacts B and D, our lack of extensive evidence for such an earthquake may result from the complexities of preserving identifiable evidence of it in the rapidly shifting shoreline environments of the lower river and bay. Ages (95% intervals) and subsidence for contacts are: A, 1700 CE (1.1 ± 0.5 m); B, 942–764 cal a BP (0.7 ± 0.4 m and 1.0 m ± 0.4 m); and D, 1568–1361 cal a BP (1.0 m ± 0.4 m). Comparisons of contact subsidence and the degree of overlap of their modeled ages with ages for other Cascadia sites are consistent with megathrust ruptures many hundreds of kilometers long. But these data cannot conclusively distinguish among different types or lengths of ruptures recorded by the three great earthquake contacts at the Nehalem River estuary.
根据岩心和露头中尖锐(≤3 mm)泥炭-泥浆地层接触的横向范围、硅藻化石组合解释的同震沉降以及利用贝叶斯传递函数与有孔虫组合重建的同震沉降，以及14c模拟年龄的区域对比，推断了Nehalem河口近2000年来三次大逆冲地震的历史。从公元1700年开始的沉降接触点(接触点A)，有时被海啸沉积的沙子覆盖，可以在7公里的距离上追踪到。接触点B和接触点D记录了早期两次大逆冲地震期间的沉降，范围要小得多，但可以追溯到700米乘270米的潮汐沼泽。虽然其他一些卡斯卡迪亚研究报告了在接触点B和接触点D之间发生地震的证据，但我们缺乏关于这种地震的广泛证据，可能是因为在下游河流和海湾快速变化的海岸线环境中保存可识别的证据很复杂。触点年龄(95%间隔)和沉降为:A, 1700 CE(1.1±0.5 m);B, 942-764 cal a BP(0.7±0.4 m和1.0 m±0.4 m);和D, 1568-1361 cal a BP (1.0 m±0.4 m)。与其他卡斯卡迪亚遗址的年龄相比，接触沉降及其模拟年龄的重叠程度与数百公里长的巨型逆冲断裂一致。但这些数据不能决定性地区分Nehalem河河口三次大地震接触记录的不同类型或长度的破裂。
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