Pub Date : 2020-07-09DOI: 10.4138/ATLGEOL.2020.007
S. Barr, S. C. Johnson, G. Dunning, C. White, A. Park, M. Wälle, A. Langille
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.
来自新不伦瑞克省南部阿瓦洛尼亚喀里多尼亚地体的火山、深成岩和沉积单元的新U-Pb锆石年龄为该地质复杂地区提供了更好的时间约束。先前来自Broad River Group的约620 Ma的年龄现在被Gordon Falls组的长英质凝灰岩和前Fairfield组(现为Black River East Branch)的流纹岩的620±5 Ma和622±1.9 Ma的年龄所证实。结合横切岩体约625 ~ 615 Ma的年龄，认为Broad River群的最小年龄约为615 Ma。长滩组基性火山岩中的石英长石斑岩岩脉的火成岩结晶年龄为685±10 Ma，是喀里多尼亚地体中最古老的单位，但其年龄与新斯科舍省阿瓦洛尼亚米拉地体中斯特林带的斑岩相似。Coldbrook群的年龄先前受到560 ~ 550 Ma火山岩的U-Pb(锆石)年龄以及岩浆岩体的类似年龄的限制。另外5个来自火山和深部岩体单元的样品位于560-550 Ma的相同范围内，包括误差，表明Coldbrook群和相关的深部岩体形成时间不到1000万年。如此大量的长英质岩浆在短时间内喷发和就位，表明美国西南部是晚新生代的“超级喷发/超级火山”环境，但在阿瓦洛尼亚其他地区约560-550 Ma尚未发现。两个单元测定了古生代的年龄:布卢姆斯伯里山组英安岩的锆石数量为427±9 Ma，表明其最大侵位年龄为志留纪;草湖组英安岩的锆石数量为382.8±8.3 Ma，表明其最大侵位年龄为中泥盆世，这是加里东尼亚地体中首次鉴定出该时代的岩石。
{"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}
Pub Date : 2020-07-05DOI: 10.4138/ATLGEOL.2020.006
Emmy A. Wrobleski, R. Hooke
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.
{"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}
Pub Date : 2020-06-02DOI: 10.4138/atlgeol.2020.005
C. Álvarez-Vázquez
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.
{"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}
Pub Date : 2020-05-27DOI: 10.4138/atlgeol.2020.004
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
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.
本研究的主要目的是确定Bay Bulls镇、Newfoundland镇和Labrador镇三个易受侵蚀的关键地区沿海道路的亚表面结构。关于地下的信息可以促进制定长期战略，减少沿海地区受气候变化影响的程度。三个可能引起海岸侵蚀的地点位于陡峭斜坡上的道路上。在海湾的北侧，在面包和奶酪遗址，道路面临着被海浪侵蚀的风险，而悬崖遗址的道路有一堵木制挡土墙，开始向侧面坍塌。在位于海湾公牛队南侧的码头，这条路非常靠近陡峭悬崖内的狭窄入口。为此，利用了三种地球物理技术——探地雷达（GPR）、直流电阻率（DCR）和实时运动学（RTK）分析，以及地质和海岸地貌观测。探地雷达探测通过发送雷达脉冲并记录反射来进行。该方法揭示了Bread and Cheese断裂区域的范围、Quays路的基岩和岩石结构界面，以及悬崖现场基岩和支撑梁的位置。DCR测量通过向地面发送电流来测量地面电阻率。DCR确定了地面的一般结构，即电阻率较高和较低的块体，然后将其与较强和较弱的基岩层相关联。总的来说，海湾公牛地区幸运地位于相对抵抗波浪作用的坚固基岩中。岩石断裂或道路位于第四纪覆盖层上的区域最容易退化。
{"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}
Pub Date : 2020-05-22DOI: 10.4138/atlgeol.2020.003
R. Marple, J. Hurd
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.
在南卡罗来纳州萨默维尔附近采集的激光雷达（光探测和测距）数据显示，Middleton Place Summerville地震带（MPSSZ）及其周边地区存在多条不同方向的线性构造。这些线性构造由大西洋海岸平原始新世晚期至全新世海洋、边缘海洋和河流沉积物中发育的线性凹陷和河谷定义。40公里长、东北-西南走向的鹿公园线理与1886年查尔斯顿地震的伍德斯托克震中重合，这表明主震可能发生在与该线理相关的断层沿线。Middleton Place线理17公里长，北东-西南走向，靠近Middleton Place震中，这表明它也可能在1886年破裂。现代地震活动区附近也有几个E-W方向的地形陡崖，包括3至5公里长、朝南的McChune和Summerwood陡崖。McChune陡崖与西面Summerville陡崖的E-W走向部分对齐，这表明两个陡崖可能沿着同一断层从隆起向北。McChune陡崖、Otranto和Middleton Place线性构造与先前获得的地震反射剖面中解释的断层一致，表明这些特征是第四纪断层的表面表现。MPSSZ以东的其他线性构造与第三纪构造穹丘有关，表明这些线性构造沿线的解释断层在新生代晚期一直很活跃。激光雷达数据还揭示了伍德斯托克断层沿线更新世中期海滩山脊的约350米右旋偏移，以及东部约20公里长的西北-东南向线性构造（Canterhill线性构造），似乎是查尔斯顿断层的表面表现。
{"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}
Pub Date : 2020-04-18DOI: 10.4138/ATLGEOL.2020.001
Raya C. Puchalski, S. Barr, C. White
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.
{"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}
Pub Date : 2019-12-08DOI: 10.4138/atlgeol.2019.014
P. Getty, J. Burnett
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.
{"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}
Pub Date : 2019-11-20DOI: 10.4138/atlgeol.2019.013
C. White
s from the Atlantic Universities Geoscience Conference (AUGC) are published annually in Atlantic Geoscience. Such publication provides a permanent record of the abstracts
{"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}
Pub Date : 2019-11-09DOI: 10.4138/atlgeol.2019.012
J. Ebert, D. K. Matteson
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.
加拿大魁北克省加斯佩半岛印第安角组（Chaleurs群）的Rosebush Cove和Petit Portage成员中，约有20个火山床，包括Lac au Renard tephra群（新）。火山灰岩层厚度在<1.0 cm至82 cm之间，以泥岩为主，具有较粗的风暴岩互层。斑晶的矿物和质地分级堆积标志着最厚的火山灰岩层的基底。一个复合火山灰岩中的早成岩结核保留了预压实组构和原始的次晶结构，具有微晶和失透玻璃碎片。斜长石、石英、钾长石、黑云母、磷灰石和锆石的存在表明其来源于流纹岩。基底堆积物中微晶的粗糙度，以及火山灰岩的丰度和厚度，表明加斯佩地区的沉积相对于火山源位于近端位置。带状笔石Monograptus praehercynicus和Monograpus aequabilis ssp。来自Petit Portage段，表明印第安角组Lac au Renard Tephra群的Lochkovian中期。可能与包括新苏格兰组的Judds Falls膨润土和纽约Kalkberg组（Helderberg群）以及宾夕法尼亚州Corriganville和Mandata组的其他可能的火山灰岩的火山灰带群相关。Indian Point的笔石动物群以及与纽约的可能相关性可能会为纽约417.6 Ma的U–Pb锆石辐射年龄测定提供额外的生物地层学限制，该年龄测定已用于估计志留纪-泥盆纪边界的年龄。
{"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}
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