Atlantic Geology最新文献

{"title":"New Cryogenian, Neoproterozoic, and middle Paleozoic U–Pb zircon ages from the Caledonia terrane, southern New Brunswick, Canada: better constrained but more complex volcanic stratigraphy","authors":"S. Barr, S. C. Johnson, G. Dunning, C. White, A. Park, M. Wälle, A. Langille","doi":"10.4138/ATLGEOL.2020.007","DOIUrl":"https://doi.org/10.4138/ATLGEOL.2020.007","url":null,"abstract":"New U–Pb zircon ages from volcanic, plutonic, and sedimentary units in the Avalonian Caledonia terrane of southern New Brunswick provide better timing constraints in this geologically complex area. Previous ca. 620 Ma ages from the Broad River Group are now corroborated by additional dates from felsic tuff in the Gordon Falls Formation and rhyolite in the former Fairfield (now East Branch Black River) Formation of 620 ± 5 Ma and 622 ± 1.9 Ma, respectively. Combined with ages ranging from ca. 625 Ma to 615 Ma from crosscutting plutons, the data suggest that the minimum age of the Broad River Group is about 615 Ma. A quartzfeldspar porphyry dyke in mafic volcanic rocks of the previously undated Long Beach Formation yielded an igneous crystallization age of 685 ± 10 Ma, the oldest unit yet dated in the Caledonia terrane but similar in age to porphyry in the Stirling belt in the Avalonian Mira terrane of Nova Scotia. The age of the Coldbrook Group was constrained previously by U–Pb (zircon) ages of volcanic rocks between 560 and 550 Ma as well as by similar ages from comagmatic plutons. Five additional samples from both volcanic and plutonic units lie in the same range of 560–550 Ma, including errors, demonstrating that the Coldbrook Group and related plutons formed in less than 10 million years. Such a large volume of mainly felsic magma erupted and emplaced in a short time span suggests a “supereruption/supervolcano” environment such as the late Cenozoic southwestern USA but not yet recognized at ca. 560–550 Ma elsewhere in Avalonia. Two units yielded Paleozoic ages: felsite of the Bloomsbury Mountain Formation with a zircon population at 427 ± 9 Ma, indicating a Silurian maximum emplacement age, and dacite of the Grassy Lake Formation with several zircon grains at 382.8 ± 8.3 Ma, indicating a maximum age of middle Devonian, the first rocks of this age to be identified in the Caledonia terrane.","PeriodicalId":49235,"journal":{"name":"Atlantic Geology","volume":"56 1","pages":"163-187"},"PeriodicalIF":1.6,"publicationDate":"2020-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47718979","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Deglaciation of Penobscot Bay, Maine, USA","authors":"Emmy A. Wrobleski, R. Hooke","doi":"10.4138/ATLGEOL.2020.006","DOIUrl":"https://doi.org/10.4138/ATLGEOL.2020.006","url":null,"abstract":"The Pond Ridge and Pineo Ridge moraines in downeast Maine likely formed at ~16.1 and ~15.7 ka respectively, during cold episodes recorded by δ18O dips in the GRIP ice core. The elapsed time between these ages is broadly consistent with retreat rates recorded by intervening De Geer moraines, which are readily visible on LiDAR imagery and are believed to be approximately annual. North-northwestward from the southwesterly extension of the Pond Ridge moraine there are three pairs of prominent moraines that are relatively continuous across the study area and could be reliably extrapolated across intervening water bodies. Retreat rates recorded by De Geer moraines suggest that these pairs formed at 15.7-15.8 ka, 15.5-15.6 ka, and ~15.5 ka. Although retreat appears to have occurred slightly faster across Penobscot Bay, a significant calving bay does not seem to have developed there. Instead, the ice margin remained relatively straight, retreating to the north-northwest. De Geer moraines become more widely spaced northward and vanish after ~15.5 ka when the ice margin was north of the head of Penobscot Bay and of Pineo Ridge. This likely reflects higher retreat rates during the initial phases of the Bølling warm period. Just south of Pineo Ridge there were two ice lobes; one retreated to the north and one to the northwest. The latter retreated more rapidly, while the former experienced numerous minor readvances and stillstands until finally pausing at the location of Pineo Ridge. A stillstand of this lobe then resulted in deposition of the Pineo Ridge moraine complex.","PeriodicalId":49235,"journal":{"name":"Atlantic Geology","volume":"56 1","pages":"147-161"},"PeriodicalIF":1.6,"publicationDate":"2020-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44459285","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Alethopteris and Neuralethopteris from the lower Westphalian (Middle Pennsylvanian) of Nova Scotia and New Brunswick, Maritime Provinces, Canada","authors":"C. Álvarez-Vázquez","doi":"10.4138/atlgeol.2020.005","DOIUrl":"https://doi.org/10.4138/atlgeol.2020.005","url":null,"abstract":"A systematic revision of Alethopteris and Neuralethopteris from upper Namurian and lower Westphalian (Middle Pennsylvanian) strata of Nova Scotia and New Brunswick, eastern Canada, has demonstrated the presence of eight species: Alethopteris bertrandii, Alethopteris decurrens, Alethopteris cf. havlenae, Alethopteris urophylla, Alethopteris cf. valida, Neuralethopteris pocahontas, Neuralethopteris schlehanii and Neuralethopteris smithsii. Restudy of the Canadian material has led to new illustrations, observations and refined descriptions of these species. Detailed synonymies focus on records from Canada and the United States. As with other groups reviewed in earlier articles in this series, it is clear that insufficient attention has been paid to material reposited in Canadian institutions in the European literature. The present study emphasizes the similarity of the North American flora with that of western Europe, especially through the synonymies.","PeriodicalId":49235,"journal":{"name":"Atlantic Geology","volume":"56 1","pages":"111-145"},"PeriodicalIF":1.6,"publicationDate":"2020-06-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42559694","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geological Association of Canada, Newfoundland and Labrador Section Abstracts: Technical Meeting 2020","authors":"N. E. A. L. A. S T . J OHN'S, Zsuzsanna Magyarosi, Jared Butler, James Conliffe, Shawn Duquet, Nic Capps, Sarah Hashmi, Annie Parrell, Roderick Smith, Eric Thiessen, Nic Lachance, GAC-NL, M. A. A. Rshian, A. L. L. Eitch, H. A. A. S. Andeman, I. A. W. .. H. Onsberger, G. U. B. Arré, C. R. L. Aflamme, D. E. W. Ilton, D. A. D. Iekrup, A. L. M. H. Inchey, G. R. W. S. Parkes, J. O. G. H. Inchey, K. Y. K. Ennedy, S. T. P. Iercey, D. A. C. O. d, A. Y. A. Zad, J. K. I. K HORASANI, W. E. A. Lison, M. Alcolm","doi":"10.4138/atlgeol.2020.004","DOIUrl":"https://doi.org/10.4138/atlgeol.2020.004","url":null,"abstract":"The primary aim of this study is to determine the sub-surface structure of coastal roads in three key areas prone to erosion in the town of Bay Bulls, Newfoundland and Labrador. Information about the subsurface can facilitate the development of long-term strategies to reduce coastal exposure to the effects of climate change. Three sites of potential concern for coastal erosion are on roads built on steep slopes. On the north side of the bay, at the Bread and Cheese site, the road faces the risk of being undercut by waves, whereas the Cliff site road has a wooden retaining wall which is starting to slump sideways. At the Quays, located on the south side of Bay Bulls, the road runs very close to narrow inlets within steep cliffs. Three geophysical techniques—ground-penetrating radar (GPR), direct current resistivity (DCR), and real-time kinematic (RTK) analysis — were utilized for this purpose, along with geological and coastal geomorphological observations. The GPR survey operates by sending a radar pulse down and recording reflections. The method revealed the extent of the fractured region at Bread and Cheese, the bedrock and rock structure interfaces on Quays road, and the location of bedrock and support beams at the Cliff site. DCR surveys measure the resistivity of the ground by sending an electric current into the ground. DCR identified the general structure of the ground, in terms of higher and lower resistivity blocks, which were then correlated with layers of stronger and weaker bedrock. In general, the Bay Bulls area is fortunate to be located in strong bedrock that is relatively resistant to wave action. Areas where the rock is fractured, or roads lie on Quaternary cover are most vulnerable to degradation.","PeriodicalId":49235,"journal":{"name":"Atlantic Geology","volume":" ","pages":""},"PeriodicalIF":1.6,"publicationDate":"2020-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44069817","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"INTERPRETATION OF LINEAMENTS AND FAULTS NEAR SUMMERVILLE, SOUTH CAROLINA, USA, USING LIDAR DATA: IMPLICATIONS FOR THE CAUSE OF THE 1886 CHARLESTON, SOUTH CAROLINA, EARTHQUAKE","authors":"R. Marple, J. Hurd","doi":"10.4138/atlgeol.2020.003","DOIUrl":"https://doi.org/10.4138/atlgeol.2020.003","url":null,"abstract":"LiDAR (light detection and ranging) data acquired near Summerville, South Carolina, reveal numerous lineaments trending in various directions across the Middleton Place-Summerville seismic zone (MPSSZ) and surrounding area. These lineaments are defined by linear depressions and stream valleys that are developed within late Eocene to Holocene marine, marginal marine, and fluvial sediments of the Atlantic Coastal Plain. The 40-kmlong, ENE-WSW-oriented Deer Park lineament coincides with the Woodstock epicenter of the 1886 Charleston earthquake, suggesting that the main shock may have occurred along a fault associated with this lineament. The proximity of the 17-km-long, ENE-WSW-oriented Middleton Place lineament to the Middleton Place epicenter suggests that it too may have ruptured in 1886. Several E-W-oriented topographic scarps are also located near the area of modern seismicity, including the 3- to 5-km-long, south-facing McChune and Summerwood scarps. The McChune scarp is aligned with the E-W-trending portion of the Summerville scarp to the west, suggesting that both scarps may be from uplift to the north along the same fault. The McChune scarp and the Otranto and Middleton Place lineaments coincide with faults interpreted from previously acquired seismic-reflection profiles, suggesting that these features are surface expressions of Quaternary faults. Other lineaments east of the MPSSZ are associated with Neogene structural domes, indicating that the interpreted faults along these lineaments have been active during the late Cenozoic. The LiDAR data also revealed a ~350-m dextral offset of a middle Pleistocene beach ridge along the Woodstock fault and a ~20-km-long, NW-SE-oriented lineament to the east (Canterhilllineament) that appears to be the surface expression of the Charleston fault.","PeriodicalId":49235,"journal":{"name":"Atlantic Geology","volume":" ","pages":""},"PeriodicalIF":1.6,"publicationDate":"2020-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47593267","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Field relations and petrology of the Trafalgar Plutonic Suite and comparisons with other Devonian granitoid plutons in the Meguma terrane, Nova Scotia, Canada","authors":"Raya C. Puchalski, S. Barr, C. White","doi":"10.4138/ATLGEOL.2020.001","DOIUrl":"https://doi.org/10.4138/ATLGEOL.2020.001","url":null,"abstract":"The Trafalgar Plutonic Suite intruded metasedimentary rocks of the Goldenville and Halifax groups in the northeastern part of the Meguma terrane of southern Nova Scotia at about 374 Ma, based on previously published U–Pb and 40Ar/39Ar mineral ages. Using field and petrographic observations, the suite is divided into 20 different plutons on the combined basis of variations in grain size (fine, medium, or coarse), texture (equigranular or porphyritic) and modal mineralogy (quartz diorite/tonalite, granodiorite, monzogranite, and syenogranite). The granodiorite, monzogranite, and syenogranite plutons are relatively uniform in composition with little variation in mineralogy or chemistry within each pluton or between plutons of the same lithology. In contrast the quartz diorite/tonalite plutons show mineralogical and chemical variation, both within and between plutons. The granodiorite, monzogranite, and syenogranite plutons closely resemble other peraluminous granitoid plutons characteristic of the Meguma terrane. The quartz diorite/tonalite plutons are varied but chemically resemble minor Devonian mafic intrusions elsewhere in the Meguma terrane. Like other plutons of the Meguma terrane, the Trafalgar Plutonic Suite has chemical characteristics of volcanic-arc to syn-collisional granitoid rocks and likely has experienced extensive contamination by metasedimentary material as documented by previous studies of plutons in the Meguma terrane. The minor quartz diorite/tonalite plutons are additional examples of the mafic rocks that have been proposed in tectonic models of the Meguma terrane to have facilitated melting of the lower crust to generate granodioritic parent magmas, followed by crystal fractionation and extensive contamination by metasedimentary material.","PeriodicalId":49235,"journal":{"name":"Atlantic Geology","volume":"15 1","pages":"001-017"},"PeriodicalIF":1.6,"publicationDate":"2020-04-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41261380","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Atlantic Geoscience Society Abstracts: 46th Annual Colloquium & General Meeting 2020","authors":"C. White","doi":"10.4138/ATLGEOL.2020.002","DOIUrl":"https://doi.org/10.4138/ATLGEOL.2020.002","url":null,"abstract":"","PeriodicalId":49235,"journal":{"name":"Atlantic Geology","volume":" ","pages":""},"PeriodicalIF":1.6,"publicationDate":"2020-04-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46860023","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Conopsoides Hitchcock 1858: an ichnological chimera of Acanthichnus and Bifurculapes","authors":"P. Getty, J. Burnett","doi":"10.4138/atlgeol.2019.014","DOIUrl":"https://doi.org/10.4138/atlgeol.2019.014","url":null,"abstract":"The ichnogenus Conopsoides, established in the Nineteenth Century, was differentiated from other ichnogenera by the presence of mounds of sediment associated with the tracks, but this characteristic is now considered an invalid ichnotaxobase by some invertebrate ichnologists. Consequently, Conopsoides has been compared to other ichnogenera in the Hitchcock collection in order to determine if other characteristics could be used to differentiate it. As a result, the morphologies exhibited by Conopsoides are seen in two other ichnogenera, Acanthichnus and Bifurculapes. Specifically, the morphologies seen in the type species, Conopsoides larvalis, are observed in Acanthichnus cursorius and Acanthichnus saltatorius, and therefore different specimens of Conopsoides larvalis are considered to belong to these two ichnospecies. Similarly, the morphology observed in Conopsoides curtus is observed in Bifurculapes laqueatus, so the former ichnospecies is considered a junior subjective synonym of the latter.","PeriodicalId":49235,"journal":{"name":"Atlantic Geology","volume":" ","pages":""},"PeriodicalIF":1.6,"publicationDate":"2019-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48027737","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Atlantic Universities Geoscience Conference 2019","authors":"C. White","doi":"10.4138/atlgeol.2019.013","DOIUrl":"https://doi.org/10.4138/atlgeol.2019.013","url":null,"abstract":"s from the Atlantic Universities Geoscience Conference (AUGC) are published annually in Atlantic Geoscience. Such publication provides a permanent record of the abstracts","PeriodicalId":49235,"journal":{"name":"Atlantic Geology","volume":" ","pages":""},"PeriodicalIF":1.6,"publicationDate":"2019-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46993450","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The Lac au Renard Tephra Cluster: a record of Lochkovian (Lower Devonian) volcanism in the Indian Point Formation, Gaspe Peninsula, Quebec, Canada","authors":"J. Ebert, D. K. Matteson","doi":"10.4138/atlgeol.2019.012","DOIUrl":"https://doi.org/10.4138/atlgeol.2019.012","url":null,"abstract":"Approximately twenty tephra beds, comprising the Lac au Renard Tephra Cluster (new), occur in the Rosebush Cove and Petit Portage members of the Indian Point Formation (Chaleurs Group) on the Gaspe Peninsula of Quebec, Canada. The tephra beds range in thickness from <1.0 cm to 82 cm and occur in a mudrock-dominated sequence with coarser tempestite interbeds. Mineralogically and texturally graded accumulations of phenocrysts mark the bases of the thickest tephra beds. Early diagenetic concretions in one composite tephra preserve pre-compaction fabrics and original hypocrystalline textures with microphenocrysts and devitrified glass shards. The presence of plagioclase, quartz, K-feldspar, biotite, apatite, and zircon suggest a rhyolitic source. The coarseness of the microphenocrysts in the basal accumulations, along with the abundance and thickness of the tephras, suggest that deposition in the Gaspe area was in a proximal position relative to the volcanic source. The zonal graptolites Monograptus praehercynicus and Monograptus aequabilis ssp. from the Petit Portage Member indicate a middle Lochkovian age for the Lac au Renard Tephra Cluster of the Indian Point Formation. Correlation with the tephra cluster that includes the Judds Falls Bentonite in the New Scotland Formation and other possible tephras in the Kalkberg Formation (Helderberg Group) of New York and the Corriganville and Mandata formations of Pennsylvania is likely. The graptolite fauna of the Indian Point and probable correlations to New York may provide additional biostratigraphic constraints on a U–Pb zircon radiometric age determination of 417.6 Ma from New York that has been used to estimate the age of the Silurian–Devonian boundary.","PeriodicalId":49235,"journal":{"name":"Atlantic Geology","volume":" ","pages":""},"PeriodicalIF":1.6,"publicationDate":"2019-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47327716","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}