Evolving Earth最新文献_第2页

Tectonic significance of meso-microscopic porphyritic granitic structures along Phulad shear zone, Rajasthan, NW India 印度拉贾斯坦邦Phulad剪切带细观斑状花岗岩构造的构造意义

Evolving Earth

Pub Date : 2025-12-10 DOI: 10.1016/j.eve.2025.100096

Alip Roy , Sadhana M. Chatterjee , Ayan Kumar Sarkar , Anirban Manna

The Phulad Shear Zone (PSZ) in northwestern India is a major crustal-scale transpressional structure striking NE-SW, which separates the South Delhi Fold Belt (SDFB) to the east from the Marwar Craton to the west. Although several porphyritic granites, traditionally called “Erinpura Granite,” are reported adjacent to the PSZ, their relationship to deformation and tectonic events remains debated. This study combines detailed field observations, mesoscopic and microscopic structural analyses, and Fractal Dimension Analysis (FDA) to clarify the tectonic evolution of the granites near the PSZ. Two distinct granitic bodies are identified: (i) the Megacrystic Granite (MG) to the west and (ii) the Phulad Granite (PG) within and near the PSZ. The MG preserves an early foliation (S1_MG) that predates PSZ shearing and shows signs of being fully crystallized and tectonically rigid during PSZ deformation. These features, along with existing geochronological data, suggest that the MG is a pre-tectonic granite forming part of the stable footwall of the Marwar Craton. Conversely, the PG displays both magmatic and solid-state foliations aligned with the mylonitic fabric of the PSZ, indicating syn-tectonic emplacement during shearing (820-810 Ma). FDA findings support the variation in strain intensity and deformation conditions between these two granite units. Overall, the results show that suturing along the PSZ occurs after the emplacement of MG and that PG was emplaced during active transpressional deformation. Therefore, MG serves as a pre-tectonic granite associated with the Marwar Craton, while PG is a syn-tectonic granite linked to the PSZ suturing event.

印度西北部的普拉德剪切带（PSZ）是一条北东-西向的重要的地壳尺度的反扭构造，东隔南德里褶皱带（SDFB），西隔马尔瓦尔克拉通（Marwar克拉通）。尽管在PSZ附近发现了几种斑岩花岗岩，传统上称为“Erinpura花岗岩”，但它们与变形和构造事件的关系仍存在争议。本研究结合详细的野外观测、细观和微观构造分析以及分形维数分析（FDA）来阐明PSZ附近花岗岩的构造演化。确定了两个不同的花岗岩体：(i)西部的巨型花岗岩（MG）和（ii） PSZ内及其附近的Phulad花岗岩（PG）。MG保留了早于PSZ剪切的早期片理（S1MG），并在PSZ变形期间显示出完全结晶和构造刚性的迹象。这些特征，连同现有的地质年代学数据，表明MG是一个构造前的花岗岩，形成了马尔瓦尔克拉通稳定下盘的一部分。相反，PG显示岩浆和固态片理与PSZ糜棱岩结构排列一致，表明剪切（820-810 Ma）期间的同构造侵位。FDA的调查结果支持这两个花岗岩单元之间应变强度和变形条件的变化。总的来说，结果表明沿PSZ方向的缝合发生在MG植入之后，PG是在主动跨压变形期间植入的。MG为与马尔瓦尔克拉通有关的构造前花岗岩，PG为与PSZ缝合事件有关的同构造花岗岩。

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引用次数: 0

Chaotic behaviour of the Earth System in the Anthropocene 人类世地球系统的混沌行为

Evolving Earth

Pub Date : 2025-01-01 DOI: 10.1016/j.eve.2025.100060

A.E. Bernardini , O. Bertolami , F. Francisco

It is shown that the Earth System (ES) can, due to the impact of human activities, behave in a chaotic fashion. Our arguments are based on the assumption that the ES can be described by a Landau–Ginzburg model, which on its own allows for predicting that the ES evolves, through regular trajectories in the phase space, towards a Hothouse Earth scenario for a finite amount of human-driven impact. Furthermore, we find that the equilibrium point for temperature fluctuations can exhibit bifurcations and a chaotic pattern if the human impact follows a logistic map. Our final analysis includes interactions between different terms of the planetary boundaries (PB) in order to gauge the predictability of our model.

研究表明，由于人类活动的影响，地球系统（ES）可以以混沌的方式运行。我们的论点是基于这样一个假设，即ES可以用朗道-金兹堡模型来描述，该模型本身就可以预测ES的演变，通过相空间中的规则轨迹，在有限数量的人类驱动的影响下，向温室地球的方向发展。此外，我们发现，如果人类的影响遵循逻辑映射，温度波动的平衡点会出现分岔和混沌模式。我们的最终分析包括行星边界（PB）不同项之间的相互作用，以衡量我们模型的可预测性。

引用次数: 0

Glacial-interglacial and millennial-scale changes in terrigenous supply and ocean circulation in the western South Atlantic 南大西洋西部冰期-间冰期和千年尺度的陆源供应和海洋环流变化

Evolving Earth

Pub Date : 2025-01-01 DOI: 10.1016/j.eve.2025.100066

Igor M. Venancio , João M. Ballalai , Douglas V.O. Lessa , Thiago S. Figueiredo , Raissa Tayt-Sohn , Marianna C. Motta , Aurélio F. Silva , Nathalia O. de Lima , Beatriz C.O.D.S.S. da Silva , Rut Díaz , Manuel Moreira , Anderson G. de Almeida , Ana Luiza S. Albuquerque

Oceanic circulation changes play a fundamental role in shaping past climate variability in northeastern Brazil, influencing precipitation patterns and sediment transport on glacial-interglacial and millennial timescales. However, the extent to which these processes vary across different water depths and their geochemical imprints in marine sediments remain poorly constrained. Here, we present multiproxy geochemical records from three sediment cores in the Sergipe Basin, located off northeastern Brazil, spanning the last 45,000 years. Variations in Fe/Ca, Zr/Rb, TOC, CaCO₃, and sulfur content reveal distinct glacial-interglacial shifts, with enhanced terrigenous input and reduced carbonate deposition during glacials, likely linked to lower sea level and changes in ocean circulation. Millennial-scale fluctuations in sulfur and Zr/Rb suggest variations in deep-water ventilation and bottom-current speed. These results provide new insights into the regional paleoceanographic evolution of the western South Atlantic and reinforce mechanisms driving sedimentary responses to past climate variability.

海洋环流变化在塑造巴西东北部过去的气候变率中发挥了基本作用，影响了冰期-间冰期和千年时间尺度上的降水模式和沉积物输运。然而，这些过程在不同水深的变化程度及其在海洋沉积物中的地球化学印记仍然知之甚少。在这里，我们展示了来自巴西东北部Sergipe盆地三个沉积物岩心的多代理地球化学记录，这些岩心跨越了过去的45,000年。Fe/Ca、Zr/Rb、TOC、CaCO3和硫含量的变化显示出明显的冰期-间冰期变化，冰期陆源输入增强，碳酸盐沉积减少，可能与海平面下降和海洋环流变化有关。硫和Zr/Rb在千年尺度上的波动表明深水通风和底流速度的变化。这些结果为南大西洋西部区域古海洋学演化提供了新的见解，并强化了驱动沉积响应过去气候变率的机制。

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引用次数: 0

Unravelling paleoenvironmental dynamics across the cretaceous-paleogene (K-Pg) boundary in the offshore Mannar Basin of the Northern Indian Ocean 北印度洋曼纳尔近海盆地白垩纪-古近纪（K-Pg）边界的古环境动力学揭示

Evolving Earth

Pub Date : 2025-01-01 DOI: 10.1016/j.eve.2025.100062

S.S. Nawarathna , P.L. Dharmapriya , A.U. Wijenayake , E.K.C.W. Kularathna

Reconstructing the sedimentary environment and comprehension of the process of mineral enrichment rely significantly on lithofacies, which can be considered a proxy for the paleoenvironment. This study investigates the lithostratigraphic characteristics of the Late Cretaceous to Early Paleocene period, spanning the pivotal Cretaceous-Paleogene (K-Pg) boundary, in the Mannar Basin. Utilizing 25 drill cutting samples from the Dorado exploration well at intervals of 10 m, ranging from 2800 m to 3040 m in depth, various lithofacies were identified using Scanning Electron Microscope (SEM), polarizing microscope, and X-ray diffraction (XRD) analysis. Petrographic examinations revealed a diverse mineral arrangement, ranging from very fine to coarse-grained textures. Dominant minerals identified through XRD analysis include Quartz, Feldspar, Carbonate, and various clay minerals, facilitating shale classification. Five distinct lithofacies were delineated, encompassing calcareous, clayey, calcareous siliceous mixed, calcareous clayey mixed shales, and siliceous rocks. Noteworthy mineralogical compositions include abundant kaolinite, chlorite, and hematite minerals in the Maastrichtian succession, transitioning to montmorillonite, illite, and pyrite dominance in the Early Maastrichtian succession. Through clay mineralogy, this study discerns significant shifts in paleoenvironmental conditions, ranging from anoxic, arid to semi-arid climates during the Campanian to warm/wet, oxidizing environments during Maastrichtian, and finally to arid/semi-arid conditions during the early Paleocene. Additionally, evidence of early burial diagenesis and Late Maastrichtian sea-level regression is identified, contributing to a comprehensive understanding of environmental dynamics during this critical geological period in the Mannar Basin in the Equatorial Margin of the Northern Indian Ocean.

沉积环境的重建和矿物富集过程的认识在很大程度上依赖于岩相，岩相可以被认为是古环境的代表。本文研究了马纳尔盆地晚白垩世至早古新世的岩石地层特征，跨越了关键的白垩纪-古近纪（K-Pg）边界。利用Dorado探井在2800m至3040m深度的10 m区间内的25个钻切样品，利用扫描电镜（SEM）、偏光显微镜（polarmicroscope）和x射线衍射（XRD）分析确定了不同的岩相。岩石学检查显示矿物排列多样，从极细到粗粒结构。通过XRD分析确定的优势矿物包括石英、长石、碳酸盐和各种粘土矿物，有助于页岩分类。圈定了5种不同的岩相：钙质岩相、粘土岩相、钙质-硅质混合岩相、钙质-粘土混合页岩相和硅质岩相。值得注意的矿物组成包括丰富的高岭石、绿泥石和赤铁矿矿物，在马斯特里赫特演替早期过渡到蒙脱石、伊利石和黄铁矿为主。通过粘土矿物学研究，发现了古环境条件的显著变化，从坎帕尼亚期的缺氧、干旱到半干旱气候，到马斯特里赫特期的温暖/潮湿、氧化环境，再到古新世早期的干旱/半干旱环境。此外，还发现了早期埋藏成岩作用和马斯垂克晚期海平面回归的证据，有助于全面了解北印度洋赤道边缘马纳尔盆地这一关键地质时期的环境动力学。

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引用次数: 0

Magnetostratigraphic perspectives and palaeoenvironmental implications of Deccan volcano-sedimentary succession within the Malwa subprovince, Central India 印度中部马尔瓦省德干火山-沉积演替的磁地层透视及其古环境意义

Evolving Earth

Pub Date : 2025-01-01 DOI: 10.1016/j.eve.2025.100061

Sarvendra Pratap Singh , Mohammad Arif , Arvind Kumar Singh , Shreya Mishra , Vivesh Vir Kapur , Vandana Prasad , Mamilla Venkateshwarlu , Amiya Shankar Naik

The present study examines a composite section representing four basaltic and three intertrappean successions at Gujri locality, Malwa subprovince, Central India. An integrated palaeomagnetic, sedimentological, mineralogical, and palaeontological approach has been utilized to understand the palaeoenvironmental changes in a stratigraphic context. The palaeomagnetic results reveal the presence of C30n/C29r and C29r/C29n magnetic reversals providing the C30n-C29r-C29n magnetostratigraphy for the region that spans almost the entire eruption history of the Deccan volcanism. As the Malwa lava flows contain C30n magnetochron, it represents the earliest basalt flows of Deccan volcanism compared to the Western Ghats sequences. Additionally, the record of the younger C29n magnetochron suggests that the Malwa and Mandla lava flows are magnetostratigraphically correlatable and experienced synchronous volcanic activity with the Western Ghats sequences during the main (C29r) and late (C29n) phases of Deccan volcanic eruption. Sedimentological and palaeontological data support that the intertrappean sediments at the Gujri locality were deposited in a dominantly low to moderate-energy freshwater palustrine-lacustrine environment under tropical to sub-tropical humid conditions with seasonal precipitation. However, data from the topmost intertrappean unit at Gujri possibly hints at ‘Mock’ aridity across the C29r/C29n transition.

本研究考察了印度中部马尔瓦省古杰里地区的一个复合剖面，该剖面代表了四个玄武岩和三个圈层间序列。综合运用古地磁、沉积学、矿物学和古生物学的方法，在地层背景下了解古环境的变化。古地磁结果显示C30n/C29r和C29r/C29n磁倒转的存在，为该地区的C30n-C29r-C29n磁地层学提供了几乎跨越整个德干火山喷发史的磁地层学。由于马尔瓦熔岩流含有C30n磁时线，与西高止山脉序列相比，它代表了德干火山活动中最早的玄武岩流。此外，C29n期较年轻的磁时线记录表明，马尔瓦和曼德拉熔岩流与德干火山喷发主期（C29r）和晚期（C29n）的西高止山脉序列具有磁地层相关性，并经历了同步的火山活动。沉积学和古生物学资料表明，古日地区盖层间沉积物主要沉积于热带-亚热带湿润、季节性降水条件下的低-中能量淡水湖湖环境。然而，来自Gujri最上层的夹层单元的数据可能暗示在C29r/C29n过渡期间存在“模拟”干旱。

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引用次数: 0

Provenance, paleoweathering and maturity study of shales in the Mundeck Formation of Kribi-Campo sub-basin in the western African margin (A geochemical approach) 西非边缘Kribi-Campo次盆地Mundeck组页岩物源、古风化及成熟度研究（地球化学方法）

Evolving Earth

Pub Date : 2025-01-01 DOI: 10.1016/j.eve.2025.100084

Ashukem Ethel Nkongho , Bokanda Ekoko Eric , Bisse Salomon Betrant , Kwankam Florence Njinto , Philip Fralick , Ikose Franklin , Nzesseu Valentino , Belinga Belinga Cedric , Ekomane Emile

The geochemical investigation of shales from Mundeck Formation of the Kribi-Campo sub-basin was conducted to determine the origin, tectonic setting evolution, paleo-weathering conditions, sediment maturity and cycling. The research included a comprehensive field survey, sample collections, and analysis of a variety of major, trace, and rare-earth elements using inductive couple plasma-atomic emission spectrum (ICP-AES) and inductive couple plasma-mass spectrum (ICP-MS). Provenance plots of La/Sc, Th/Co, Cr/Th, Th/Sc ratios and Zr vs TiO₂, Al₂O₃vs TiO₂ disclosed a felsic to mixed rock composition as the source rock of the studied shales. The felsic to mixed source rock compositions are also supported by an enrichment of LREE/HREE and a negative europium anomaly on chondrite calculation and chondrite normalized diagram. Discriminant diagrams of DF(A-P)M, and DF(A-P)MT used, designate an active marginal source rock for the studied shales. The active margin signature in this work shows the source rocks of the study shales was affected by the tectono thermal events of the Pan African Orogeny also known as the Brasiliano orogeny in South America. The chemical index of alteration (CIA and CIX) and the plagioclase index of alteration (PIA and PIX) suggest weak to extreme intensity. These variations are cause by potassium enrichment and depletion during weathering. The old and new ICV calculated values suggest that the shales are immature to mature. The plots of Zr and (La/Yb)_N, Th/Sc and (Gd/Yb)_N ratios show the studied shales are positive correlated and fall away from the zircon addition domain, thus confirming that they are immature to mature first cycle sediments.

对克里比-坎波亚盆地Mundeck组页岩进行了地球化学调查，以确定其成因、构造背景演化、古风化条件、沉积物成熟度和旋回作用。该研究包括全面的实地调查、样品收集以及使用电感耦合等离子体原子发射光谱（ICP-AES）和电感耦合等离子体质谱（ICP-MS）分析各种主要、痕量和稀土元素。La/Sc、Th/Co、Cr/Th、Th/Sc比值和Zr / TiO2、al2o3 / TiO2的物源图显示，页岩的烃源岩为石英-混合岩。在球粒陨石计算和球粒陨石归一化图上，轻稀土/重稀土富集和负铕异常也支持长英质-混合烃源岩组成。利用DF(A-P)M和DF(A-P)MT的判别图，为所研究的页岩指定了一个活跃的边缘烃源岩。活动边缘特征表明，研究页岩烃源岩受南美泛非造山运动（即Brasiliano造山运动）构造热事件的影响。化学蚀变指数（CIA和CIX）和斜长石蚀变指数（PIA和PIX）显示弱至极端强度。这些变化是由风化过程中钾的富集和耗竭引起的。新旧ICV计算值表明，页岩处于未成熟~成熟阶段。Zr与（La/Yb）N、Th/Sc和（Gd/Yb）N比值图显示，页岩正相关，且偏离了锆石添加域，确定其为未成熟至成熟的第一旋回沉积。

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引用次数: 0

Into thin air: The loss of the pliocene giant volant birds 消失在稀薄的空气中：上新世巨型飞禽的消失

Evolving Earth

Pub Date : 2025-01-01 DOI: 10.1016/j.eve.2024.100055

Alan Cannell , Federico J. Degrange

Four genera of distantly phylogenetically very large volant birds existed for most of the Pliocene: Pelagornithidae seabirds; the large North American Teratornithidae, the stork Leptoptilos falconeri in Africa and Asia, and the gigantic vulture Dryornis pampeanus in Argentina. All became extinct around 2 to 3 Ma. The reasons for their demise are puzzling, as the Pelagornithidae had a world-wide evolutionary history of more than 50 Ma, smaller teratorns were still extant in the Holocene, and smaller stork and vulture species continue to be successful today. Extant large birds have a common critical takeoff airspeed suggesting biomechanical constraints in terms of power, risk and launch speed. Atmospheric mass is not constant over time and estimates for Late Pliocene atmospheric density, based on the difference between marine and terrestrial derived pCO₂ and isotopes in amber, suggest a value equivalent to about 1.2 bar that dropped to the present level over the period from ∼3.3 to 2.0 Ma. Simulations of the flight of these extinct species suggest that in the present atmosphere at sea level (∼1) bar their takeoff airspeeds would have exceeded critical values; however, at 1.2 bar all the extinct species present takeoff airspeeds similar to those of large extant volant birds and which are within their muscle power and kinetic energy limits. A loss in atmospheric density may therefore have caused biomechanical and ecological stress contributing to their extinction and/or evolution of smaller forms.

在上新世的大部分时间里，有四属在系统发育上距离较远的非常大的飞禽：飞禽科海鸟；北美的巨鸟科，非洲和亚洲的狐鹳，以及阿根廷的巨型秃鹫。它们都在2到3 Ma之间灭绝了。它们灭绝的原因令人费解，因为长喙鸟科在世界范围内的进化史超过50万年，较小的角嘴鸟在全新世仍然存在，而较小的鹳和秃鹫物种今天仍然很成功。现存的大型鸟类有一个共同的临界起飞空速，这表明在动力、风险和起飞速度方面存在生物力学限制。大气质量随着时间的推移并不是恒定的，根据海洋和陆地二氧化碳分压和琥珀同位素之间的差异，对上新世晚期大气密度的估计表明，其值相当于1.2巴，在~ 3.3至2.0 Ma期间下降到现在的水平。对这些灭绝物种飞行的模拟表明，在目前海平面（~ 1）bar的大气中，它们的起飞空速将超过临界值；然而，在1.2巴时，所有灭绝的物种的起飞速度与现存的大型飞禽相似，并且在它们的肌肉力量和动能极限内。因此，大气密度的减少可能造成生物力学和生态压力，从而导致它们的灭绝和/或较小形式的进化。

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引用次数: 0

Insights into greener Miocene biomes and globally enhanced terrestrial productivity from fossil leaves 从树叶化石中了解更绿色的中新世生物群落和全球陆地生产力的增强

Evolving Earth

Pub Date : 2025-01-01 DOI: 10.1016/j.eve.2025.100058

Tammo Reichgelt , Christopher K. West

Leaf megafloras represent a snapshot of local environmental conditions in Earth's history. As such, they are an important way to understand terrestrial climate analogues for future warmer climate scenarios. Here, we present paleoclimate, productivity, and biome reconstructions of 108 globally distributed Miocene leaf megafloras using a standardized method based on leaf physiognomy. Our results show that the Miocene had higher than modern zonal temperature, precipitation and net primary productivity (NPP) averages, especially for precipitation at latitudes >30°N/°S, suggesting enhanced poleward moisture transport in both hemispheres and a greener biosphere. There is a dearth of Miocene data in the tropics and notably an absence of data points in equatorial localities that have high modern NPP (rainforests), which makes a direct comparison complicated. 89% of investigated sites underwent a precipitation decrease from the Miocene to modern, whereas 66% underwent a temperature decrease, and 60% underwent both a precipitation and a temperature decrease. 67% of sites had more productive biomes during the Miocene than today. Most notably, forested biomes were replaced by more open woodland/shrubland or grassland biomes. Correspondingly, the average NPP decrease from the Miocene to today of our investigated localities was conservatively ∼250 gC m⁻² yr⁻¹ or ∼450 gC m⁻² yr⁻¹ by comparison of zonal averages. Considered collectively, leaf megafloras reveal an overall greener Miocene world that appears to be largely driven by greater moisture availability.

巨型树叶群代表了地球历史上当地环境状况的缩影。因此，它们是了解未来变暖气候情景的陆地气候类似物的重要途径。本文采用基于叶片地貌的标准化方法，重建了全球分布的108个中新世巨型叶区系的古气候、生产力和生物群系。研究结果表明，中新世的纬向温度、降水和净初级生产力（NPP）平均值高于现代，特别是在纬度>；30°N/°S的降水，表明两个半球向极地的水分输送增强，生物圈更加绿色。热带地区中新世数据的缺乏，特别是赤道地区现代NPP（热带雨林）较高的地区缺乏数据点，这使得直接比较变得复杂。从中新世到现代，89%的研究地点经历了降水减少，66%经历了温度下降，60%经历了降水和温度下降。67%的地点中新世时期的生物群落比现在更多产。最值得注意的是，森林生物群落被更开阔的林地/灌丛或草地生物群落所取代。相应地，与纬向平均值相比，我们研究的地区中新世至今的平均NPP减少保守地为~ 250 gC m−2 yr−1或~ 450 gC m−2 yr−1。综合考虑，叶片巨型植物群揭示了一个整体上更绿色的中新世世界，这似乎主要是由更多的水分可用性驱动的。

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引用次数: 0

Organic petrographical, geochemical, and mineralogical features of the Permian Coalbrook Sub-basin, South Africa: Reconstruction of paleo-depositional conditions 南非二叠系煤溪亚盆地有机岩相、地球化学和矿物学特征：古沉积条件的重建

Evolving Earth

Pub Date : 2025-01-01 DOI: 10.1016/j.eve.2025.100067

F. Zonke Chitlango, Ofentse M. Moroeng, Nicola J. Wagner

Coal samples from four boreholes drilled as part of an exploration project in the Vereeniging-Sasolburg Coalfield, Coalbrook Sub-basin, South Africa, were studied to understand the depositional environments using organic petrography (macerals, microlithotypes, and vitrinite reflectance), inorganic geochemistry, and mineralogy. Given that South Africa is projected to remain reliant on coal for its energy needs in the short-to medium-term, the study aims to expand on the limited knowledge regarding this part of the Main Karoo Basin (MKB). The samples are classified as low-rank A sub-bituminous to medium-rank D bituminous, with variable maceral composition, with very low to moderate vitrinite (5.8–48.0 vol%, mineral matter free basis, mmf) although most samples are dominated by inertinite (from 42.0 to 90.6 vol%, mmf). The vitrinite to inertinite ratio (V/I) varies from 0.06 to 1.14, indicative of generally dry and oxidizing environments with frequent paleofires. The dominant minerals in the studied coals are kaolinite and quartz. Angular to rounded quartz grains suggest a detrital origin, whereas kaolinite is both detrital and authigenic, the latter also occurring within telovitrinite cell lumens. In contrast, detrital kaolinite mainly occurs in association with inertodetrinite, sporinite, and the detrital quartz. This indicates allochthonous deposition for the detrital minerals and the associated organic matter (including charcoal), likely reflecting flooding of the paleomire. The Al₂O₃/TiO₂ ratios indicate that the minerals were mostly derived from intermediate and felsic sources. Total sulphur (TS) values are generally low, suggesting freshwater conditions. The microlithotype facies plot suggests that the Coalbrook Sub-basin coals were deposited in lacustrine and lower deltaic environments, related to the undulating paleotopography at the base of the coalfield owing to the presence of karst features. This distinguishes the Vereeniging-Sasolburg from the other coalfields of the MKB (e.g., Witbank, Highveld, and Ermelo), which have the Dwyka diamictite at their base and formed in deltaic and fluvial environments. The paleotopography of the basement thus had a strong influence on peat accumulation in this coalfield, including in the Coalbrook Sub-basin.

作为南非Coalbrook亚盆地Vereeniging-Sasolburg煤田勘探项目的一部分，研究人员利用有机岩石学（显微岩质、微岩型和镜质组反射率）、无机地球化学和矿物学研究了四个钻孔的煤样，以了解沉积环境。鉴于预计南非在中短期内仍将依赖煤炭满足其能源需求，本研究的目的是扩大对主要卡鲁盆地（MKB）这一部分的有限了解。样品分为低阶A亚沥青至中阶D沥青，显微成分变化，镜质组含量极低至中等（5.8 ~ 48.0 vol%，矿物游离基，mmf），大部分样品以惰质组（42.0 ~ 90.6 vol%, mmf）为主。镜质组与惰质组比值（V/I）在0.06 ~ 1.14之间，表明该区为干燥氧化环境，古火源频繁。研究煤中的优势矿物为高岭石和石英。角状至圆形的石英颗粒表明其为碎屑来源，而高岭石既是碎屑又是自生的，后者也出现在镜质体细胞腔内。碎屑高岭石主要与岩质泥质、孢质岩和碎屑石英伴生。这表明碎屑矿物和伴生有机物（包括木炭）的异位沉积，可能反映了古泥岩的洪水。Al2O3/TiO2比值表明矿物主要来源于中间质和长硅质。总硫（TS）值普遍较低，表明是淡水环境。微岩型相图表明煤溪次盆地煤沉积于湖相和下三角洲环境，与煤田底部岩溶地貌起伏有关。这将Vereeniging-Sasolburg煤田与MKB的其他煤田（例如Witbank， Highveld和Ermelo）区分开来，后者的底部有Dwyka二辉岩，形成于三角洲和河流环境。因此，基底古地形对该煤田包括煤溪次盆地的泥炭聚集有强烈的影响。

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引用次数: 0

Contact metamorphism of coals in the Southern Piceance Basin, USA: Volatile matter generation, pyrolytic carbon accumulation, and δ13C trends 美国南皮尔斯盆地煤的接触变质作用：挥发物生成、热解碳聚集和δ13C趋势

Evolving Earth

Pub Date : 2025-01-01 DOI: 10.1016/j.eve.2025.100063

Susan M. Rimmer , Lois E. Yoksoulian , Darren R. Gröcke

Four transects of coal were studied to determine petrographic, geochemical, and δ¹³C changes due to contact with thin sills. Approaching the sills, vitrinite and coke reflectance increases from ∼0.75% to ∼7%, while volatile matter (VM) and H/C decrease. Despite extensive VM loss, the coals do not follow normal burial maturation pathways. Alteration above the sills exceeds that below, and the width of the contact aureole is large compared to that of the sills. This may suggest prolonged magma transport within the sills. Additionally, multiple fractures contain coke, pyrolytic carbon, and minerals, which suggests migration of fluidized coal, VM, and hot fluids. Incipient mosaic and anisotropic coke structures (fine-grained circular mosaic, with minor medium-grained circular mosaic) are observed within the aureole, consistent with intrusion of a high volatile bituminous coal. Devolatilization vacuoles, more abundant in altered collodetrinite than collotelinite, increase in number and size approaching the sills. Pyrolytic carbon occurs as fracture fills, spherulites, and botryoidal aggregates; spherulitic forms are more abundant at higher maturation levels. δ¹³C of the altered coal/coke varies only minimally from that of the unaltered coal and overall trends are ambiguous. Factors affecting δ¹³C may include maceral composition, rank at the time of intrusion, extent of alteration, size of the carbon reservoir, redeposition of pyrolytic carbon, and openness of the system. It is possible that the rapid heating and high temperatures associated with contact metamorphism limit carbon isotopic fractionation. In turn, this may imply that the intrusion of coal results in minimal liberation of isotopically light CH₄.

研究了4个煤样的岩石学、地球化学和δ13C与薄岩接触的变化。接近井壁时，镜质组和焦炭反射率由~ 0.75%增加到~ 7%，挥发分（VM）和H/C降低。尽管大量VM损失，煤不遵循正常的埋藏成熟途径。技能上方的变化大于技能下方的变化，接触光圈的宽度比技能的宽度大。这可能表明岩浆在岩床内的运输时间延长了。此外，多个裂缝中含有焦炭、热解碳和矿物，这表明流化煤、VM和热流体的迁移。在光晕内观察到早期嵌合和各向异性焦炭结构（细粒圆形嵌合和少量中粒圆形嵌合），与高挥发性烟煤的侵入相一致。脱挥发液泡，在蚀变胶泥岩中比胶泥岩中更丰富，在数量和大小上接近茎尖。热解碳以裂隙填充物、球晶和岩石体聚集体的形式存在；成熟程度越高，球晶形式越丰富。蚀变煤/焦炭的δ13C与未蚀变煤的δ13C变化很小，总体趋势不明确。影响δ13C的因素可能包括显微组分、侵入时的等级、蚀变程度、储层的大小、热解碳的再沉积以及体系的开放性等。与接触变质作用有关的快速加热和高温可能限制了碳同位素分馏。反过来，这可能意味着煤的侵入导致同位素轻CH4的最小释放。

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