Pub Date : 2024-07-11DOI: 10.1016/j.margeo.2024.107360
Bing Li , Jixin Wang , Chuanshun Li , Sai Wang , Lei Fan , Jun Ye , Yuan Dang , Quanshu Yan , Xuefa Shi
Numerous investigations into the northern Mid-Atlantic Ridge (the NMAR), a typical slow-spreading mid-ocean ridge, have revealed that NMAR is favorable for the development of long-lived detachment faults and the formation of oceanic core complexes (OCCs). OCCs are often conducive to the development of ultramafic-hosted hydrothermal deposits with significant resource potential. However, as a counterpart of the NMAR on the Southern Hemisphere, the southern Mid-Atlantic Ridge (SMAR), also belonging to the class of slow-spreading ridges, has only received very limited investigation. This prompts the inquiry as to whether the SMAR, like the NMAR, can foster the development of OCC and associated hydrothermal deposit. To address this issue, we present the identification of an OCC (named as Kaifeng OCC) at the intersection of the SMAR and the Martin Vaz transform fault (∼23°S). This discovery is accompanied by evidence detailing a new detachment fault breakaway on an old detachment footwall. Collected samples reveal indications of hydrothermal activity, encompassing (1) residual sulfide containing chalcopyrite within honeycomb-like structures, (2) reddish-brown Fe oxides and atacamite, partially concretized by dolomite, and (3) a dark gray Mn-oxide crust. These mineralogical features indicate the presence of gossans, commonly iron oxide-dominated cover layers that envelope the outer surface of weathered seafloor sulfide deposits, which subsequently undergo modifications due to subsequent hydrothermal activities. Our work proves the existence of OCC and associated hydrothermal deposits at a ridge-transform intersection of the SMAR.
{"title":"An oceanic core complex and its associated weathered hydrothermal deposit on a ridge-transform intersection zone at 23°S, Southern Mid-Atlantic Ridge","authors":"Bing Li , Jixin Wang , Chuanshun Li , Sai Wang , Lei Fan , Jun Ye , Yuan Dang , Quanshu Yan , Xuefa Shi","doi":"10.1016/j.margeo.2024.107360","DOIUrl":"https://doi.org/10.1016/j.margeo.2024.107360","url":null,"abstract":"<div><p>Numerous investigations into the northern Mid-Atlantic Ridge (the NMAR), a typical slow-spreading mid-ocean ridge, have revealed that NMAR is favorable for the development of long-lived detachment faults and the formation of oceanic core complexes (OCCs). OCCs are often conducive to the development of ultramafic-hosted hydrothermal deposits with significant resource potential. However, as a counterpart of the NMAR on the Southern Hemisphere, the southern Mid-Atlantic Ridge (SMAR), also belonging to the class of slow-spreading ridges, has only received very limited investigation. This prompts the inquiry as to whether the SMAR, like the NMAR, can foster the development of OCC and associated hydrothermal deposit. To address this issue, we present the identification of an OCC (named as Kaifeng OCC) at the intersection of the SMAR and the Martin Vaz transform fault (∼23°S). This discovery is accompanied by evidence detailing a new detachment fault breakaway on an old detachment footwall. Collected samples reveal indications of hydrothermal activity, encompassing (1) residual sulfide containing chalcopyrite within honeycomb-like structures, (2) reddish-brown Fe oxides and atacamite, partially concretized by dolomite, and (3) a dark gray Mn-oxide crust. These mineralogical features indicate the presence of gossans, commonly iron oxide-dominated cover layers that envelope the outer surface of weathered seafloor sulfide deposits, which subsequently undergo modifications due to subsequent hydrothermal activities. Our work proves the existence of OCC and associated hydrothermal deposits at a ridge-transform intersection of the SMAR.</p></div>","PeriodicalId":18229,"journal":{"name":"Marine Geology","volume":"475 ","pages":"Article 107360"},"PeriodicalIF":2.6,"publicationDate":"2024-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141607322","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Recent high-resolution multibeam bathymetry and seismic data from the platform-top to the abyssal plain of the Zhongsha Platform allow for a detailed investigation of the morphologies, spatial distribution, and trigger mechanisms of submarine canyons, submarine landslides, and associated sedimentary features along modern isolated carbonate slopes. The newly observed Zhongsha Canyon System provides a natural laboratory for reconstructing the source-to-sink sedimentary processes in a pure carbonate setting. This study reveals that there are thirty-four submarine canyons at water depths between 300 and 4100 m on the northern and western slopes of the Zhongsha Platform. Two morphologically different submarine canyon types are identified: (1) dendritic canyons, which exhibit abundant tributaries with scallop-shaped failures at the canyon heads, and (2) linear canyons, which feature rare tributaries with elongated failures at the canyon heads. The dendritic canyons are more complex in morphology than the linear canyons as a result of the interaction among numerous tributaries. Canyon initiation and evolution pass through three phases: (1) initial stage: off-platform sediment transport and platform margin failures contribute to erosive gravity flows; (2) developmental stage: initiation and incision of submarine canyons along platform margin failures; and (3) mature stage: numerous mature canyons along the platform margin. Off-platform sediment transport, density cascading, gravity flows, monsoon currents, and deep circulation play an essential role in shaping the slope morphologies. In addition, submarine landslides are extensively observed along the entire slope of the Zhongsha Platform at water depths of 600 to 4200 m, including canyon-wall failures, slope landslides, canyon-front landslides, and slope-toe failures based on their location and genesis. These processes can steepen the platform slopes by upward retrogressive and downward progressive erosion. On a larger scale, the persistent submarine canyons and occurrence of landslides around the Zhongsha Platform contribute to the uniqueness of this landscape among modern carbonate slopes. The morphologies and evolutionary processes of Zhongsha Canyon System present significant differences from the global carbonate submarine canyons in terms of their dimensions and trigger mechanisms. The findings of this work provide novel insights into the morphological features and sedimentary processes of submarine canyons in modern isolated carbonate platform settings.
{"title":"Morphology and evolution of submarine canyons around the Zhongsha Platform, South China Sea: Implications for sedimentary processes in a modern isolated carbonate setting","authors":"Junjin Chen , Shiguo Wu , Qi Li , Chenglong Wei , Guowei Fu , Wanli Chen , Yongpeng Qin , Umair Khan , Songlin Wu","doi":"10.1016/j.margeo.2024.107362","DOIUrl":"10.1016/j.margeo.2024.107362","url":null,"abstract":"<div><p>Recent high-resolution multibeam bathymetry and seismic data from the platform-top to the abyssal plain of the Zhongsha Platform allow for a detailed investigation of the morphologies, spatial distribution, and trigger mechanisms of submarine canyons, submarine landslides, and associated sedimentary features along modern isolated carbonate slopes. The newly observed Zhongsha Canyon System provides a natural laboratory for reconstructing the source-to-sink sedimentary processes in a pure carbonate setting. This study reveals that there are thirty-four submarine canyons at water depths between 300 and 4100 m on the northern and western slopes of the Zhongsha Platform. Two morphologically different submarine canyon types are identified: (1) dendritic canyons, which exhibit abundant tributaries with scallop-shaped failures at the canyon heads, and (2) linear canyons, which feature rare tributaries with elongated failures at the canyon heads. The dendritic canyons are more complex in morphology than the linear canyons as a result of the interaction among numerous tributaries. Canyon initiation and evolution pass through three phases: (1) initial stage: off-platform sediment transport and platform margin failures contribute to erosive gravity flows; (2) developmental stage: initiation and incision of submarine canyons along platform margin failures; and (3) mature stage: numerous mature canyons along the platform margin. Off-platform sediment transport, density cascading, gravity flows, monsoon currents, and deep circulation play an essential role in shaping the slope morphologies. In addition, submarine landslides are extensively observed along the entire slope of the Zhongsha Platform at water depths of 600 to 4200 m, including canyon-wall failures, slope landslides, canyon-front landslides, and slope-toe failures based on their location and genesis. These processes can steepen the platform slopes by upward retrogressive and downward progressive erosion. On a larger scale, the persistent submarine canyons and occurrence of landslides around the Zhongsha Platform contribute to the uniqueness of this landscape among modern carbonate slopes. The morphologies and evolutionary processes of Zhongsha Canyon System present significant differences from the global carbonate submarine canyons in terms of their dimensions and trigger mechanisms. The findings of this work provide novel insights into the morphological features and sedimentary processes of submarine canyons in modern isolated carbonate platform settings.</p></div>","PeriodicalId":18229,"journal":{"name":"Marine Geology","volume":"475 ","pages":"Article 107362"},"PeriodicalIF":2.6,"publicationDate":"2024-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141691879","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2024-07-10DOI: 10.1016/j.margeo.2024.107357
Huikun Yao , Xiaoqiang Liu , Maotian Li , Weihua Li , Yan Song , Zijie Tan , Wenyan Zhang , Dan Peng , Yan Liu , Jing Chen , Said A. Shetaia
Annually 5–6 typhoons strike the Yangtze Estuary (YE) as extreme events. However, their high energy and importance for sediment transportation and geomorphic changes are still not fully understood. In this study, high-resolution observations of wind, wave, flow velocity, and suspended sediment concentration (SSC) at two in-situ stations were carried out during the 2022 Hinnamnor typhoon. Additionally, we simulated the change in SSC, estuarine bed erosion/deposition, and flow and sediment transport with and without a typhoon in the YE using MIKE3 numerical model. The findings revealed that the Hinnamnor typhoon-induced waves increased the SSC of the turbidity maximum zone (TMZ) by a factor of 5.6 times (maximum is 2.8 kg/m3). The TMZ area also extended by 2.68 times (maximum is 7880km2, 70.4% of YE) in the YE. Moreover, the typhoon caused a dramatic change in sediment transport and bed erosion/deposition in the YE. First, in the delta front area where the mean water depth is >5 m, the typhoon significantly increased the southward flux of residual flow and sediment, causing sediment transport into Hangzhou Bay to abruptly increase 26.3 times (increase of 52 million tons, accounting for 1/3 of the present annual flux of the Yangtze River (150 million tons)) during a single spring-neap period. The net erosional area and volume extended to 6770km2 (60.4% of YE) and 91.18 × 106 m3. Second, in the delta shoals (where the mean water depth is <5 m, including east Chongming Shoal, Hengsha Shoal, Jiuduansha Shoal, and east-south Nanhui Shoal), residual flow and sediment flux decreased northward from the typhoon and resulted in the erosion of the shoal. Third, in channels with trumpet-shaped mouths (North Branch (NB), North Channel (NC) and South Passage (SP), except for North Passage (NP)), the upward flux of residual flow and sediment increased due to the typhoon, resulting in bed deposition in these channels (NB, NC and SP). This study highlights the important influence of typhoons on flow and sediment transport and bed erosion in estuarine areas.
{"title":"Effect of typhoon on suspended sediment concentration, bed erosion and sediment transport in the Yangtze Estuary","authors":"Huikun Yao , Xiaoqiang Liu , Maotian Li , Weihua Li , Yan Song , Zijie Tan , Wenyan Zhang , Dan Peng , Yan Liu , Jing Chen , Said A. Shetaia","doi":"10.1016/j.margeo.2024.107357","DOIUrl":"10.1016/j.margeo.2024.107357","url":null,"abstract":"<div><p>Annually 5–6 typhoons strike the Yangtze Estuary (YE) as extreme events. However, their high energy and importance for sediment transportation and geomorphic changes are still not fully understood. In this study, high-resolution observations of wind, wave, flow velocity, and suspended sediment concentration (SSC) at two in-situ stations were carried out during the 2022 Hinnamnor typhoon. Additionally, we simulated the change in SSC, estuarine bed erosion/deposition, and flow and sediment transport with and without a typhoon in the YE using MIKE3 numerical model. The findings revealed that the Hinnamnor typhoon-induced waves increased the SSC of the turbidity maximum zone (TMZ) by a factor of 5.6 times (maximum is 2.8 kg/m<sup>3</sup>). The TMZ area also extended by 2.68 times (maximum is 7880km<sup>2</sup>, 70.4% of YE) in the YE. Moreover, the typhoon caused a dramatic change in sediment transport and bed erosion/deposition in the YE. First, in the delta front area where the mean water depth is >5 m, the typhoon significantly increased the southward flux of residual flow and sediment, causing sediment transport into Hangzhou Bay to abruptly increase 26.3 times (increase of 52 million tons, accounting for 1/3 of the present annual flux of the Yangtze River (150 million tons)) during a single spring-neap period. The net erosional area and volume extended to 6770km<sup>2</sup> (60.4% of YE) and 91.18 × 10<sup>6</sup> m<sup>3</sup>. Second, in the delta shoals (where the mean water depth is <5 m, including east Chongming Shoal, Hengsha Shoal, Jiuduansha Shoal, and east-south Nanhui Shoal), residual flow and sediment flux decreased northward from the typhoon and resulted in the erosion of the shoal. Third, in channels with trumpet-shaped mouths (North Branch (NB), North Channel (NC) and South Passage (SP), except for North Passage (NP)), the upward flux of residual flow and sediment increased due to the typhoon, resulting in bed deposition in these channels (NB, NC and SP). This study highlights the important influence of typhoons on flow and sediment transport and bed erosion in estuarine areas.</p></div>","PeriodicalId":18229,"journal":{"name":"Marine Geology","volume":"475 ","pages":"Article 107357"},"PeriodicalIF":2.6,"publicationDate":"2024-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141639122","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2024-07-08DOI: 10.1016/j.margeo.2024.107359
Carson B. Miller , John A. Goff , Sean P.S. Gulick , Davin J. Wallace , Christopher M. Lowery
Barrier islands are rarely preserved on continental shelves following sea-level rise. Proxies like overwash deposits, tidal inlets, and wave ravinements identify the location of paleo-barrier islands through time. Barrier island remnants are potential sand resources for beach nourishment to combat shoreline erosion from increasing rates of sea-level rise. Additionally, understanding the conditions that lead to barrier island drowning can be used to advise coastal policy makers. This study aims to identify barrier island signatures and deposits to understand the coastal processes that maximize preservation of paleo-barrier island remnants. We employed high resolution chirp sub-bottom data coupled with legacy sediment cores collected over Heald and Sabine Banks, on the east Texas shelf, which have been identified as possible preserved barrier island associated facies. Heald Bank exhibits a predominantly homogenous, low-amplitude facies with few low-amplitude internal horizons overlying the transgressive ravinement, whereas Sabine Bank consists of high-amplitude, landward-dipping reflectors beneath this surface, likely indicative of preserved subaqueous overwash deposits. This stratigraphy suggests Sabine Bank includes barrier island associated facies, whereas Heald Bank is mostly a marine sand bank. The overwash unit of Sabine Bank displays landward-thinning and landward-dipping deposits with reflections increasing in amplitude and displaying lower slopes to the NW. We hypothesize that higher slopes to the SE indicate proximity to the former barrier island. The Sabine River paleo-valley is mostly filled with estuarine sediment, leaving only ∼4 m of antecedent accommodation in a limited area of the NE portion of the paleo-valley. The low shelf gradient, which increases accommodation, and initially high sediment supply that decreased during the drowning of Sabine Bank are the major factors controlling partial preservation of the subaqueous portion of the paleo-barrier island.
海平面上升后,大陆架上很少保留屏障岛。冲刷沉积物、潮汐入海口和波浪冲积物等代用资料可以确定古屏障岛的位置。壁垒岛遗迹是潜在的海沙资源,可用于滋养海滩,以应对海平面上升导致的海岸线侵蚀。此外,了解导致屏障岛溺水的条件还可以为沿海决策者提供建议。这项研究旨在识别屏障岛的特征和沉积物,以了解最大限度地保存古屏障岛遗迹的沿岸过程。我们采用了高分辨率啁啾底层数据,以及在得克萨斯州东部大陆架 Heald Bank 和 Sabine Banks 采集的遗留沉积物岩芯,这些沉积物被确定为可能保存下来的屏障岛相关岩层。希尔德浅滩主要呈现出同质、低振幅的地层,很少有低振幅的内部地层覆盖在横向沟壑上,而萨宾湾浅滩则由高振幅、向陆地倾斜的反射体组成,很可能是保留下来的水下冲刷沉积物。这种地层学表明,萨宾河岸包括与屏障岛相关的地层,而希尔德河岸则主要是海洋沙岸。Sabine Bank 的冲刷单元显示了向陆地稀疏和向陆地倾斜的沉积物,反射振幅增大,并向西北方向显示了较低的斜坡。我们推测,向东南方倾斜的坡度较高,表明靠近前屏障岛。萨宾河古河谷大部分被河口沉积物填满,只在古河谷东北部的有限区域内留下了 4 米左右的前生容积。陆架坡度低,增加了容积,最初沉积物供应量大,但在萨宾河岸淹没过程中沉积物供应量减少,这些都是控制古屏障岛水下部分部分保存的主要因素。
{"title":"Internal sand bank seismic stratigraphy provides insight into paleo-barrier island preservation","authors":"Carson B. Miller , John A. Goff , Sean P.S. Gulick , Davin J. Wallace , Christopher M. Lowery","doi":"10.1016/j.margeo.2024.107359","DOIUrl":"10.1016/j.margeo.2024.107359","url":null,"abstract":"<div><p>Barrier islands are rarely preserved on continental shelves following sea-level rise. Proxies like overwash deposits, tidal inlets, and wave ravinements identify the location of paleo-barrier islands through time. Barrier island remnants are potential sand resources for beach nourishment to combat shoreline erosion from increasing rates of sea-level rise. Additionally, understanding the conditions that lead to barrier island drowning can be used to advise coastal policy makers. This study aims to identify barrier island signatures and deposits to understand the coastal processes that maximize preservation of paleo-barrier island remnants. We employed high resolution chirp sub-bottom data coupled with legacy sediment cores collected over Heald and Sabine Banks, on the east Texas shelf, which have been identified as possible preserved barrier island associated facies. Heald Bank exhibits a predominantly homogenous, low-amplitude facies with few low-amplitude internal horizons overlying the transgressive ravinement, whereas Sabine Bank consists of high-amplitude, landward-dipping reflectors beneath this surface, likely indicative of preserved subaqueous overwash deposits. This stratigraphy suggests Sabine Bank includes barrier island associated facies, whereas Heald Bank is mostly a marine sand bank. The overwash unit of Sabine Bank displays landward-thinning and landward-dipping deposits with reflections increasing in amplitude and displaying lower slopes to the NW. We hypothesize that higher slopes to the SE indicate proximity to the former barrier island. The Sabine River paleo-valley is mostly filled with estuarine sediment, leaving only ∼4 m of antecedent accommodation in a limited area of the NE portion of the paleo-valley. The low shelf gradient, which increases accommodation, and initially high sediment supply that decreased during the drowning of Sabine Bank are the major factors controlling partial preservation of the subaqueous portion of the paleo-barrier island.</p></div>","PeriodicalId":18229,"journal":{"name":"Marine Geology","volume":"475 ","pages":"Article 107359"},"PeriodicalIF":2.6,"publicationDate":"2024-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141689956","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2024-07-08DOI: 10.1016/j.margeo.2024.107358
Fanxing Kong , Xiting Liu , Anchun Li , Jiang Dong , Houjie Wang , Guangchao Zhuang , Zihu Zhang , Chao Li
The East China Sea (ECS) is located between the Eurasian continent and the Pacific Ocean with a wide continental shelf, which acts as a potential source of reactive iron in the Western Pacific. However, the source and fate of reactive iron in continental shelf sediments of the ECS remain poorly constrained. Here, we examined the influence of the depositional environment on the fate of reactive iron on the continental shelf of the ECS since the last deglaciation. The contents of redox-sensitive elements (U and Mo) indicate that the sediments in the ECS inner shelf have primarily deposited in oxic and suboxic environments since 18.5 ka. The ratio of reactive iron to total iron (FeHR/FeT) ranges from 0.24 to 0.41, and the ratio of total iron to aluminum (FeT/Al) is approximately 0.55 ± 0.11. These ratios suggest that the majority of reactive iron is derived from fine-grained terrestrial sediments discharged by the Changjiang River. The contents of Fepy and Fecarb exhibit opposite trends with depth in the core, indicating competition between carbonate (bicarbonate) ions and sulfide ions for ferrous ions. This competition is primarily controlled by the depositional environment and redox state since 18.5 ka. The Fecarb is the dominant iron speciation throughout the core sediments, but its abundance declined since 13.2 ka when the ECS inner shelf was influenced by seawater transgression due to deglacial sea-level rise. The Fepy content reached its maximum when the ECS inner shelf was fully flooded. Our study highlights the depositional control on the source-sink processes of reactive iron, providing new insights into the fate of reactive iron on continental shelves in response to environmental evolution.
{"title":"Depositional control on the fate of reactive iron in shelf sediments since the last deglaciation: A case study of the East China Sea","authors":"Fanxing Kong , Xiting Liu , Anchun Li , Jiang Dong , Houjie Wang , Guangchao Zhuang , Zihu Zhang , Chao Li","doi":"10.1016/j.margeo.2024.107358","DOIUrl":"https://doi.org/10.1016/j.margeo.2024.107358","url":null,"abstract":"<div><p>The East China Sea (ECS) is located between the Eurasian continent and the Pacific Ocean with a wide continental shelf, which acts as a potential source of reactive iron in the Western Pacific. However, the source and fate of reactive iron in continental shelf sediments of the ECS remain poorly constrained. Here, we examined the influence of the depositional environment on the fate of reactive iron on the continental shelf of the ECS since the last deglaciation. The contents of redox-sensitive elements (U and Mo) indicate that the sediments in the ECS inner shelf have primarily deposited in oxic and suboxic environments since 18.5 ka. The ratio of reactive iron to total iron (Fe<sub>HR</sub>/Fe<sub>T</sub>) ranges from 0.24 to 0.41, and the ratio of total iron to aluminum (Fe<sub>T</sub>/Al) is approximately 0.55 ± 0.11. These ratios suggest that the majority of reactive iron is derived from fine-grained terrestrial sediments discharged by the Changjiang River. The contents of Fe<sub>py</sub> and Fe<sub>carb</sub> exhibit opposite trends with depth in the core, indicating competition between carbonate (bicarbonate) ions and sulfide ions for ferrous ions. This competition is primarily controlled by the depositional environment and redox state since 18.5 ka. The Fe<sub>carb</sub> is the dominant iron speciation throughout the core sediments, but its abundance declined since 13.2 ka when the ECS inner shelf was influenced by seawater transgression due to deglacial sea-level rise. The Fe<sub>py</sub> content reached its maximum when the ECS inner shelf was fully flooded. Our study highlights the depositional control on the source-sink processes of reactive iron, providing new insights into the fate of reactive iron on continental shelves in response to environmental evolution.</p></div>","PeriodicalId":18229,"journal":{"name":"Marine Geology","volume":"475 ","pages":"Article 107358"},"PeriodicalIF":2.6,"publicationDate":"2024-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141593015","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2024-07-06DOI: 10.1016/j.margeo.2024.107347
Elmar Albers , Nele Behrendt , Alexander Diehl , Felix Genske , Patrick Monien , Simone A. Kasemann , Autun Purser , Antje Boetius , Wolfgang Bach
Volcanic centers are characteristic features of ultraslow-spreading mid-ocean ridges, the least-explored parts of the global ridge system. Volcanic centers can provide insights into deep magmatic and metamorphic processes at these ridges. Here, we present data from the largest volcanic center on the Gakkel Ridge, the Langseth Ridge, situated at 60–62°E. Langseth is ∼10 km wide, consisting of three peaks that rise to 585 m water depth, some 3–4 km above the surrounding seafloor. It strikes perpendicular to Gakkel's spreading direction and can be traced for ∼40 km, which translates to an age of ∼8 Myr. Seafloor imaging revealed abundant (pillow) basalt but also fissures and geologic faults across the Langseth Ridge. Basaltic rocks were sampled at all summits and diabase at the slope of the northern summit that dips into the rift valley.
Our samples are of normal to depleted mid-ocean ridge basalt composition and exhibit a wide range of major and trace element contents, due to magmatic processes, accumulation of macrocrysts, and hydrothermal alteration. Radiogenic isotope ratios, most notably 143Nd/144Nd and 208Pb/206Pb, trend from typical rift valley compositions to isotopically enriched values with increasing distance to the rift valley. This trend may imply melt pooling from different sources, potentially representing a shift from shallow melting beneath the rift valley to deeper melting of enriched sources and higher degrees of melting underneath Langseth. Mineral compositions and plagioclase sieve textures imply prolonged storage of magma at depth prior to eruption. Hydrothermal alteration occurred over a range of conditions. Basalt from the summits is weakly altered at temperatures ≪100 °C, which likely occurred in situ at the summit sites. Diabase samples experienced chloritization and albitization and display epidote and quartz veins, which formed at >300 °C. These assemblages and temperatures are typical for lower crustal levels and imply uplift of the samples of >1 km. Diabase samples from the Afanasenkov Seamount, another volcanic center on the Gakkel Ridge that we investigated for comparison, were altered under comparable conditions.
Our findings suggest a combined volcanic–tectonic origin of the studied volcanic centers, potentially implying that such complexes may generally form due to the interplay of magmatism and tectonics. Researching volcanic centers has the potential to further our understanding of both deep and shallow crustal processes at ultraslow-spreading ridges, providing further insights into the role of these centers as linkages between lithosphere and hydrosphere and the (deep) biosphere they sustain.
{"title":"Formation and hydrothermal alteration of a volcanic center: Melt pooling and mass transfers at Langseth Ridge (Gakkel Ridge, Arctic Ocean)","authors":"Elmar Albers , Nele Behrendt , Alexander Diehl , Felix Genske , Patrick Monien , Simone A. Kasemann , Autun Purser , Antje Boetius , Wolfgang Bach","doi":"10.1016/j.margeo.2024.107347","DOIUrl":"10.1016/j.margeo.2024.107347","url":null,"abstract":"<div><p>Volcanic centers are characteristic features of ultraslow-spreading mid-ocean ridges, the least-explored parts of the global ridge system. Volcanic centers can provide insights into deep magmatic and metamorphic processes at these ridges. Here, we present data from the largest volcanic center on the Gakkel Ridge, the Langseth Ridge, situated at 60–62°E. Langseth is ∼10 km wide, consisting of three peaks that rise to 585 m water depth, some 3–4 km above the surrounding seafloor. It strikes perpendicular to Gakkel's spreading direction and can be traced for ∼40 km, which translates to an age of ∼8 Myr. Seafloor imaging revealed abundant (pillow) basalt but also fissures and geologic faults across the Langseth Ridge. Basaltic rocks were sampled at all summits and diabase at the slope of the northern summit that dips into the rift valley.</p><p>Our samples are of normal to depleted mid-ocean ridge basalt composition and exhibit a wide range of major and trace element contents, due to magmatic processes, accumulation of macrocrysts, and hydrothermal alteration. Radiogenic isotope ratios, most notably <sup>143</sup>Nd/<sup>144</sup>Nd and <sup>208</sup>Pb/<sup>206</sup>Pb, trend from typical rift valley compositions to isotopically enriched values with increasing distance to the rift valley. This trend may imply melt pooling from different sources, potentially representing a shift from shallow melting beneath the rift valley to deeper melting of enriched sources and higher degrees of melting underneath Langseth. Mineral compositions and plagioclase sieve textures imply prolonged storage of magma at depth prior to eruption. Hydrothermal alteration occurred over a range of conditions. Basalt from the summits is weakly altered at temperatures ≪100 °C, which likely occurred in situ at the summit sites. Diabase samples experienced chloritization and albitization and display epidote and quartz veins, which formed at >300 °C. These assemblages and temperatures are typical for lower crustal levels and imply uplift of the samples of >1 km. Diabase samples from the Afanasenkov Seamount, another volcanic center on the Gakkel Ridge that we investigated for comparison, were altered under comparable conditions.</p><p>Our findings suggest a combined volcanic–tectonic origin of the studied volcanic centers, potentially implying that such complexes may generally form due to the interplay of magmatism and tectonics. Researching volcanic centers has the potential to further our understanding of both deep and shallow crustal processes at ultraslow-spreading ridges, providing further insights into the role of these centers as linkages between lithosphere and hydrosphere and the (deep) biosphere they sustain.</p></div>","PeriodicalId":18229,"journal":{"name":"Marine Geology","volume":"475 ","pages":"Article 107347"},"PeriodicalIF":2.6,"publicationDate":"2024-07-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0025322724001312/pdfft?md5=2ebd8d3becc213c8ce46dae6b2bb5ff5&pid=1-s2.0-S0025322724001312-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141639123","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-04DOI: 10.1016/j.margeo.2024.107345
P. Standring , C.M. Lowery , J. Burstein , J. Swartz , J.A. Goff , S.P.S. Gulick , C.B. Miller
Regional variability of global sea-level rise remains an important area of study given the vulnerability of sediment-starved coastlines to coastal inundation, especially those in proximity to large population centers. Galveston Bay, Texas, is currently experiencing more than double the global rate of sea-level rise and is particularly vulnerable to storm inundation that will further destabilize the coastline. Limitations in instrumental observations necessitate the use of the geologic record preserved offshore modern Galveston Bay to understand how this particular coastline responds to periods of rapid sea-level rise. We present micropaleontological analysis of sediment cores combined with high-resolution seismic data to reconstruct the Holocene paleoestuary offshore Galveston Bay and its evolution since initial inundation ∼10 ka through marine transgression ∼6 ka. We find that despite rapid sea-level rise, the Galveston paleoestuary maintained relatively stable outer boundaries, and within the bay environmental shifts occurred as a result of probable marine incursions due to tidal inlet migrations. Paleoenvironmental changes in the early Holocene coincide with flooding events within other Texas Gulf Coast bays suggesting global sea-level rise played a prominent role. Middle to late Holocene changes occurred when rates of sea-level rise slowed, suggesting regional hydroclimate change played a more dominant role.
全球海平面上升的区域变异性仍然是一个重要的研究领域,因为沉积物匮乏的海岸线很 容易被沿海洪水淹没,特别是那些靠近大型人口中心的海岸线。得克萨斯州加尔维斯顿湾目前的海平面上升速度是全球上升速度的两倍多,特别容易被风暴淹没,从而进一步破坏海岸线的稳定。由于仪器观测的局限性,有必要利用现代加尔维斯顿湾近海保存的地质记录来了解这条特殊的海岸线是如何应对海平面快速上升时期的。我们结合高分辨率地震数据,对沉积物岩芯进行了微古生物学分析,重建了加尔维斯顿湾近海全新世古河口及其自 10 ka ka 初期淹没至 6 ka 海洋侵蚀的演变过程。我们发现,尽管海平面迅速上升,但加尔维斯顿古河口仍保持着相对稳定的外部边界,而海湾内部的环境变化则可能是潮汐入口迁移造成的海洋入侵的结果。全新世早期的古环境变化与得克萨斯州海湾沿岸其他海湾的洪水事件相吻合,这表明全球海平面上升起到了重要作用。全新世中期到晚期的变化发生在海平面上升速度放缓之时,这表明区域水文气候的变化发挥了更主要的作用。
{"title":"Foraminiferal analysis of Holocene sea-level rise within the Trinity River Incised Paleo-Valley, Offshore Galveston Bay, Texas","authors":"P. Standring , C.M. Lowery , J. Burstein , J. Swartz , J.A. Goff , S.P.S. Gulick , C.B. Miller","doi":"10.1016/j.margeo.2024.107345","DOIUrl":"10.1016/j.margeo.2024.107345","url":null,"abstract":"<div><p>Regional variability of global sea-level rise remains an important area of study given the vulnerability of sediment-starved coastlines to coastal inundation, especially those in proximity to large population centers. Galveston Bay, Texas, is currently experiencing more than double the global rate of sea-level rise and is particularly vulnerable to storm inundation that will further destabilize the coastline. Limitations in instrumental observations necessitate the use of the geologic record preserved offshore modern Galveston Bay to understand how this particular coastline responds to periods of rapid sea-level rise. We present micropaleontological analysis of sediment cores combined with high-resolution seismic data to reconstruct the Holocene paleoestuary offshore Galveston Bay and its evolution since initial inundation ∼10 ka through marine transgression ∼6 ka. We find that despite rapid sea-level rise, the Galveston paleoestuary maintained relatively stable outer boundaries, and within the bay environmental shifts occurred as a result of probable marine incursions due to tidal inlet migrations. Paleoenvironmental changes in the early Holocene coincide with flooding events within other Texas Gulf Coast bays suggesting global sea-level rise played a prominent role. Middle to late Holocene changes occurred when rates of sea-level rise slowed, suggesting regional hydroclimate change played a more dominant role.</p></div>","PeriodicalId":18229,"journal":{"name":"Marine Geology","volume":"475 ","pages":"Article 107345"},"PeriodicalIF":2.6,"publicationDate":"2024-07-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141623493","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2024-07-02DOI: 10.1016/j.margeo.2024.107348
Jie Sheng , Shuqing Qiao , Xuefa Shi , Jianguo Liu , Yanguang Liu , Shengfa Liu , Kunshan Wang , Che Abd Rahim Mohamed , Somkiat Khokiattiwong , Narumol Kornkanitnan
Sedimentation rates and sediment budgets are important agents to understand the source-to-sink dynamics in marginal seas. As a classical representative of mega-river dominated marginal seas globally, the South China Sea (SCS) receives huge amounts of fluvial input from mega rivers covering different climate zones. Despite its well-documented prevalence, quantifying the spatial distribution of sedimentation rate and sediment budget over the entire SCS remains a challenge due to limited data availability. In this study, we employed a comprehensive approach to quantify the modern sedimentation rates and sediment budget in the SCS. This approach combined 210Pb measurements from 409 cores, AMS14C data from 112 cores, and 33 sediment trap observations. Our results show that higher sedimentation rates >0.3 cm/a mainly occur in deltas, shelf mud areas, and upper continental slope that connects the submarine canyon. In the subaqueous Mekong Delta, for example, the sedimentation rates can exceed 10 cm/a. In contrast, there is no substantial modern sedimentation in sandy and gravelly areas of the shelf due to strong erosion by a combination of waves, tides and ocean currents. We further compare these results with the eastern China seas including the Bohai Sea, Yellow Sea and East China Sea. A similar spatial distribution of sedimentation rates can be observed in the continental shelf of the eastern China seas. The Holocene sedimentation rates in the deep-water regions of the SCS are generally <100 cm/ka. The basin floor experiences the slowest accumulation, with rates below 3 cm/ka. In contrast, sedimentation rates on the eastern island slopes range from 3 to 8 cm/ka, while the northern, western, and southern continental slopes accumulate sediment most rapidly, exceeding 25 cm/ka. Approximately 1191.1 × 106 t of fine-grained sediment is deposited annually in the continental mud areas of the SCS, with a comparable amount of 1185.4 × 106 t/a deposited on the continental shelf of the eastern China seas. The continental slope accumulates sediment at a significantly higher rate (∼161.0–239.4 × 106 t/a) compared to the deep-water basin (∼16.5–20.1 × 106 t/a) in the SCS. Most of the modern sediments (>98%) are deposited on the continental shelf and slope. In the SCS, fluvial inputs dominates modern sediment sources, contributing over 80% of the total. Coastal/seabed erosion and biogenic deposition account for approximately ∼18%, with eolian dust contributing less than <2%. The findings presented here are critical for elucidating the sources, transport pathways, and deposition patterns of modern sediments in marginal seas.
{"title":"Modern sedimentation and sediment budget in the South China Sea and their comparisons with the eastern China seas","authors":"Jie Sheng , Shuqing Qiao , Xuefa Shi , Jianguo Liu , Yanguang Liu , Shengfa Liu , Kunshan Wang , Che Abd Rahim Mohamed , Somkiat Khokiattiwong , Narumol Kornkanitnan","doi":"10.1016/j.margeo.2024.107348","DOIUrl":"https://doi.org/10.1016/j.margeo.2024.107348","url":null,"abstract":"<div><p>Sedimentation rates and sediment budgets are important agents to understand the source-to-sink dynamics in marginal seas. As a classical representative of mega-river dominated marginal seas globally, the South China Sea (SCS) receives huge amounts of fluvial input from mega rivers covering different climate zones. Despite its well-documented prevalence, quantifying the spatial distribution of sedimentation rate and sediment budget over the entire SCS remains a challenge due to limited data availability. In this study, we employed a comprehensive approach to quantify the modern sedimentation rates and sediment budget in the SCS. This approach combined <sup>210</sup>Pb measurements from 409 cores, AMS<sup>14</sup>C data from 112 cores, and 33 sediment trap observations. Our results show that higher sedimentation rates >0.3 cm/a mainly occur in deltas, shelf mud areas, and upper continental slope that connects the submarine canyon. In the subaqueous Mekong Delta, for example, the sedimentation rates can exceed 10 cm/a. In contrast, there is no substantial modern sedimentation in sandy and gravelly areas of the shelf due to strong erosion by a combination of waves, tides and ocean currents. We further compare these results with the eastern China seas including the Bohai Sea, Yellow Sea and East China Sea. A similar spatial distribution of sedimentation rates can be observed in the continental shelf of the eastern China seas. The Holocene sedimentation rates in the deep-water regions of the SCS are generally <100 cm/ka. The basin floor experiences the slowest accumulation, with rates below 3 cm/ka. In contrast, sedimentation rates on the eastern island slopes range from 3 to 8 cm/ka, while the northern, western, and southern continental slopes accumulate sediment most rapidly, exceeding 25 cm/ka. Approximately 1191.1 × 10<sup>6</sup> t of fine-grained sediment is deposited annually in the continental mud areas of the SCS, with a comparable amount of 1185.4 × 10<sup>6</sup> t/a deposited on the continental shelf of the eastern China seas. The continental slope accumulates sediment at a significantly higher rate (∼161.0–239.4 × 10<sup>6</sup> t/a) compared to the deep-water basin (∼16.5–20.1 × 10<sup>6</sup> t/a) in the SCS. Most of the modern sediments (>98%) are deposited on the continental shelf and slope. In the SCS, fluvial inputs dominates modern sediment sources, contributing over 80% of the total. Coastal/seabed erosion and biogenic deposition account for approximately ∼18%, with eolian dust contributing less than <2%. The findings presented here are critical for elucidating the sources, transport pathways, and deposition patterns of modern sediments in marginal seas.</p></div>","PeriodicalId":18229,"journal":{"name":"Marine Geology","volume":"475 ","pages":"Article 107348"},"PeriodicalIF":2.6,"publicationDate":"2024-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141607321","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2024-06-30DOI: 10.1016/j.margeo.2024.107346
Paul Michael Nii Anang Okoe , Elírio Ernestino Toldo Júnior , Cristiano Fick , Eduardo Puhl , Maria Luiza Correa da Camara Rosa , José Carlos Rodrigues Nunes , Francisco Eduardo G. Cruz , Vinicius Carbone B. de Oliveira
For the past decade, giant deepwater oil discoveries in the pre-salt section of the Campos and Santos basins of Brazil, have brought significant attention to offshore exploration activities along the South Atlantic margins. The prolific Cretaceous coquina deposits in these basins are part of the pre-salt rock record and constitute an effective but complex and heterogeneous hydrocarbon reservoir difficult to predict and model. Parting from this context, an evaluation of the sedimentological, structural and taphonomic criteria for coquinas are essential to better understand and predict the facies distribution and depositional models of the pre-salt coquinas strata. Based on this premise, the present work aims to genetically interpret 133 mixed carbonate-siliciclastic bottom sediments of the Albardão shelf – a modern marine coquina analogue, using facies description, investigating the relationship with hydrodynamic forces, and accessing the influence of morphology and structural framework on their deposition. From these analyses, we recognized a hybrid facies, three modern carbonate facies in analogy to the carbonate rock classification and four siliciclastic facies. These eight facies were then grouped into three facies associations representing high, moderate, and low energy facies. The high energy facies association comprises rudstones (Rf) and grainstones (Gf) with highly fragmented bivalve shells and barnacles abundantly present in the beach system, above the fair-weather wave base limit (FWWB). These facies also occur offshore on bathymetric highs above the storm wave base limit (SWB) but display less reworking than the coastal high energy facies above the FWWB due to wave shoaling. The moderate energy facies association consists of hybrid sand (Hs), sand (S) and muddy sand (mS) occurring between the FWWB and SWB limits in the offshore transition zone with extensive winnowing action and low rate of reworking. The low energy facies association includes sandy mud (sM), mud (M) and micritic mud (Mc), characterized by the decantation of the fine sediments below the offshore SWB limit. The results confirm a bottom facies distribution controlled by depth, shelf profile morphology and energy from incident waves. The fragmented rudstone and fragmented grainstone facies are the best-recognized reservoirs with both having high porosity and high permeability.
{"title":"Depositional model of the Holocene coquinas - Albardão platform, southern Brazil","authors":"Paul Michael Nii Anang Okoe , Elírio Ernestino Toldo Júnior , Cristiano Fick , Eduardo Puhl , Maria Luiza Correa da Camara Rosa , José Carlos Rodrigues Nunes , Francisco Eduardo G. Cruz , Vinicius Carbone B. de Oliveira","doi":"10.1016/j.margeo.2024.107346","DOIUrl":"https://doi.org/10.1016/j.margeo.2024.107346","url":null,"abstract":"<div><p>For the past decade, giant deepwater oil discoveries in the pre-salt section of the Campos and Santos basins of Brazil, have brought significant attention to offshore exploration activities along the South Atlantic margins. The prolific Cretaceous coquina deposits in these basins are part of the pre-salt rock record and constitute an effective but complex and heterogeneous hydrocarbon reservoir difficult to predict and model. Parting from this context, an evaluation of the sedimentological, structural and taphonomic criteria for coquinas are essential to better understand and predict the facies distribution and depositional models of the pre-salt coquinas strata. Based on this premise, the present work aims to genetically interpret 133 mixed carbonate-siliciclastic bottom sediments of the Albardão shelf – a modern marine coquina analogue, using facies description, investigating the relationship with hydrodynamic forces, and accessing the influence of morphology and structural framework on their deposition. From these analyses, we recognized a hybrid facies, three modern carbonate facies in analogy to the carbonate rock classification and four siliciclastic facies. These eight facies were then grouped into three facies associations representing high, moderate, and low energy facies. The high energy facies association comprises rudstones (Rf) and grainstones (Gf) with highly fragmented bivalve shells and barnacles abundantly present in the beach system, above the fair-weather wave base limit (FWWB). These facies also occur offshore on bathymetric highs above the storm wave base limit (SWB) but display less reworking than the coastal high energy facies above the FWWB due to wave shoaling. The moderate energy facies association consists of hybrid sand (Hs), sand (S) and muddy sand (mS) occurring between the FWWB and SWB limits in the offshore transition zone with extensive winnowing action and low rate of reworking. The low energy facies association includes sandy mud (sM), mud (M) and micritic mud (Mc), characterized by the decantation of the fine sediments below the offshore SWB limit. The results confirm a bottom facies distribution controlled by depth, shelf profile morphology and energy from incident waves. The fragmented rudstone and fragmented grainstone facies are the best-recognized reservoirs with both having high porosity and high permeability.</p></div>","PeriodicalId":18229,"journal":{"name":"Marine Geology","volume":"475 ","pages":"Article 107346"},"PeriodicalIF":2.6,"publicationDate":"2024-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141540837","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2024-06-26DOI: 10.1016/j.margeo.2024.107344
Chufeng Guo , Yong Tang , Yinxia Fang , Chunyang Wang , Xiaodong Wei , He Li , Peng Chao , Tianyi Yang , Zhibin Song , Jianye Ren , Jiabiao Li
The Nansha Trough (NT) is part of the southern continental margin boundary of the South China Sea (SCS). It has undergone complex tectonic superposition and evolutionary processes involving the subduction demise of the Proto-SCS and subsequent spreading of the SCS. This study provides the first systematic identification and analysis of igneous bodies and seamounts along the NT, based on a multi-channel seismic profile (NDL1) recently acquired along it. The seamounts within the trough are of magmatic origin and the carbonate build-ups observed at the summits of some seamounts exhibit a substantial thickness. Igneous bodies within the trough are consistently associated with high P-wave anomalies. Furthermore, at the eastern and western sides, there are distinct gravity-magnetic-anomaly patterns. On the eastern side, Yinqing Seamount, Nanle Hill and volcanic mounds show high gravity and strong negative magnetic anomalies. In contrast, on the western side, Jinghong Seamount, Yangshu Hill and intrusive bodies show less pronounced magnetic anomalies. This difference may be related to differences in magmatic periods. Unlike the extensive post-spreading magmatism in the SCS's northern margin and deep basin, the most widespread magmatic activity in the NT occurred at ca. 16 Ma before decreasing during the Miocene. This decrease may be closely related to subduction cessation in the Proto-SCS and the collision between the Nansha Block and Borneo. The identification and analysis of NT igneous bodies and their evolutionary processes help delineate the southern boundary of magmatism at the SCS margin. They also provide crucial information for constraining the magmatic processes of Proto-SCS subduction termination and SCS spreading evolution.
南沙海槽(NT)是中国南海(SCS)南部大陆边边界的一部分。它经历了复杂的构造叠加和演化过程,包括原南中国海的俯冲消亡和随后南中国海的扩张。本研究根据最近获得的沿北部湾多道地震剖面(NDL1),首次对北部湾沿岸的火成岩体和海山进行了系统识别和分析。海槽内的海山源于岩浆,在一些海山山顶观测到的碳酸盐堆积厚度很大。海槽内的火成岩体始终与高 P 波异常有关。此外,在东西两侧,重力-磁异常模式截然不同。在东侧,银清海山、南乐山和火山丘呈现高重力和强负磁异常。相比之下,西侧的景洪海山、羊蹄山和侵入体的磁异常不明显。这种差异可能与岩浆期的不同有关。与南中国海北缘和深海盆地广泛的扩张后岩浆活动不同,北部最广泛的岩浆活动发生在约16Ma,然后在中生代逐渐减少。16Ma,然后在中新世逐渐减少。这种活动的减少可能与原南中国海俯冲停止以及南沙区块与婆罗洲的碰撞密切相关。对NT火成岩体及其演化过程的识别和分析有助于划定南中国海边缘岩浆活动的南部边界。它们还为制约原南中国海俯冲终止和南中国海扩张演化的岩浆过程提供了重要信息。
{"title":"Magmatism along the Nansha Trough on the southern continental margin of the South China Sea: Recent evidence from along-strike seismic profile","authors":"Chufeng Guo , Yong Tang , Yinxia Fang , Chunyang Wang , Xiaodong Wei , He Li , Peng Chao , Tianyi Yang , Zhibin Song , Jianye Ren , Jiabiao Li","doi":"10.1016/j.margeo.2024.107344","DOIUrl":"https://doi.org/10.1016/j.margeo.2024.107344","url":null,"abstract":"<div><p>The Nansha Trough (NT) is part of the southern continental margin boundary of the South China Sea (SCS). It has undergone complex tectonic superposition and evolutionary processes involving the subduction demise of the Proto-SCS and subsequent spreading of the SCS. This study provides the first systematic identification and analysis of igneous bodies and seamounts along the NT, based on a multi-channel seismic profile (NDL1) recently acquired along it. The seamounts within the trough are of magmatic origin and the carbonate build-ups observed at the summits of some seamounts exhibit a substantial thickness. Igneous bodies within the trough are consistently associated with high P-wave anomalies. Furthermore, at the eastern and western sides, there are distinct gravity-magnetic-anomaly patterns. On the eastern side, Yinqing Seamount, Nanle Hill and volcanic mounds show high gravity and strong negative magnetic anomalies. In contrast, on the western side, Jinghong Seamount, Yangshu Hill and intrusive bodies show less pronounced magnetic anomalies. This difference may be related to differences in magmatic periods. Unlike the extensive post-spreading magmatism in the SCS's northern margin and deep basin, the most widespread magmatic activity in the NT occurred at ca. 16 Ma before decreasing during the Miocene. This decrease may be closely related to subduction cessation in the Proto-SCS and the collision between the Nansha Block and Borneo. The identification and analysis of NT igneous bodies and their evolutionary processes help delineate the southern boundary of magmatism at the SCS margin. They also provide crucial information for constraining the magmatic processes of Proto-SCS subduction termination and SCS spreading evolution.</p></div>","PeriodicalId":18229,"journal":{"name":"Marine Geology","volume":"475 ","pages":"Article 107344"},"PeriodicalIF":2.6,"publicationDate":"2024-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141540836","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}