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Universal decomposition model: An efficient technique for palaeoenvironmental reconstruction from grain‐size distribution 通用分解模型:一种从粒度分布重建古环境的有效技术
IF 3.5 2区 地球科学 Q1 GEOLOGY Pub Date : 2023-05-13 DOI: 10.1111/sed.13115
Yuming Liu, Ting Wang, Bo Liu, Yi-Jie Long, Xingxing Liu, Youbin Sun
For many years, researchers have used the decomposition of grain‐size distributions to acquire critical information on provenances, transport dynamics and depositional environments. This study presents a novel decomposition method, termed the universal decomposition model, for analysing grain‐size data. The universal decomposition model unifies single‐sample unmixing and end‐member modelling analysis approaches and overcomes their respective limitations. To evaluate the effectiveness of the universal decomposition model, an artificial dataset and borehole data from the west Weihe Basin were analysed. Results indicate that the universal decomposition model algorithm performs proficiently on both datasets. Correlation analysis was employed to compare the abilities of universal decomposition model, single‐sample unmixing and end‐member modelling analysis to extract minor signals, with universal decomposition model and single‐sample unmixing exhibiting greater proficiency. Furthermore, the universal decomposition model provides a broader perspective for contrasting single‐sample unmixing and end‐member modelling analysis. The study highlights the inadequacy of the statistical method for determining the optimal number of components and summarizes an empirical approach. Moreover, disregarding the potential diversity in component shapes of real‐world sediments has been demonstrated to be a sub‐optimal design. Finally, this article presents results of a new investigation into the geological significance of sediment grain sizes revealed by various analytical methods that suggest that the universal decomposition model has enormous potential in reconstructing paleoenvironment.
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引用次数: 0
A mechanistic approach for interpreting hydroclimate from halite‐bearing sediments 从含盐沉积物中解释水文气候的一种机制方法
IF 3.5 2区 地球科学 Q1 GEOLOGY Pub Date : 2023-05-13 DOI: 10.1111/sed.13114
I. Sirota, M. Armon, Yoav Ben Dor, E. Morin, N. Lensky, Y. Enzel
Establishing accurate palaeo‐hydroclimatic reconstructions from lacustrine and marine archives is a long‐standing challenge in palaeoenvironment studies. Closed‐basin evaporites, and especially halite, record episodes of extremely arid conditions during rapid climate change. However, the complex limnological behaviour of deep hypersaline water bodies and the stochastic nature of the hydroclimatic regime and its variations limit detailed palaeo‐hydroclimatic interpretations from such records. Therefore, a mass‐balance model was developed to explore hydrology–limnology–sedimentology relationships in hypersaline environments under both deterministic and stochastic approaches that generates synthetic halite–mud sequences. Applying the model to the Holocene Dead Sea halites yields novel insights into palaeoenvironmental conditions in the Levant. The deterministic framework indicates that: (i) under a series of similar hydroclimatic cycles, the thickness of each subsequent halite interval decreases, due to the depletion of dissolved‐ions storage in the brine; (ii) halite deposition requires lake levels to drop below the minimal lake level of the preceding cycle; (iii) the time interval between halite deposition and the hydrological minimum is increasingly longer in subsequent cycles. Thus, counter‐intuitively, halite deposition mostly takes place as water discharge increases, providing that the water balance is still negative. The stochastic approach produced random sequences comparable to the observed Dead Sea sedimentary record. It demonstrates that some hydrological minima are not represented by halite deposition at all. Furthermore, the thickness and number of halite beds at each hydrological cycle vary substantially, depending on the specific hydrological conditions realized. Finally, these results imply that the major Dead Sea level drop at the pre‐Holocene deglaciation (ca 14 ka bp), previously assumed to be a record minimum, could not have been as pronounced as suggested, and must have been milder than the subsequent drop at the early Holocene (ca 11–10 ka bp).
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引用次数: 0
Deep‐water sand transfer by hyperpycnal flows, the Eocene of Spitsbergen, Arctic Norway 挪威北极斯匹次卑尔根岛始新世深水砂转移
IF 3.5 2区 地球科学 Q1 GEOLOGY Pub Date : 2023-05-11 DOI: 10.1111/sed.13105
S. Grundvåg, W. Helland‐Hansen, E. Johannessen, J. Eggenhuisen, F. Pohl, Yvonne T. Spychala
Flood‐generated hyperpycnal flows are dense, sediment‐laden, turbulent flows that can form long‐lived, bottom‐hugging turbidity currents, which undoubtedly transport large volumes of fine‐grained sediments into the ocean. However, their ability in transferring sand into deep‐water basins is debated. This study presents sedimentological evidence of sandy hyperpycnal flow deposits (hyperpycnites) in a series of basin floor lobe complexes associated with a progradational shelf margin in the Eocene of Spitsbergen, Arctic Norway. Four coexisting types of sediment gravity flow deposits are recognized: (i) sandy hyperpycnites deposited by quasi‐steady hyperpycnal flows; (ii) turbidites deposited by waning, surge‐type turbidity currents; (iii) hybrid event beds deposited by transitional flows; and (iv) mass transport deposits emplaced during rare slope failures. The abundance of thick‐bedded massive sandstones, frequent bed amalgamation, the distribution of hyperpycnites across the lobes and the abundance and systematic occurrence of plant‐rich hybrid event beds and associated climbing ripple cross‐laminated beds in the lobe fringes, suggest that hyperpycnal flow was the most important mechanism driving lobe progradation. Shelf‐edge positioned fluvial channels linked to the basin floor lobe complexes via deeply incised, sandstone‐filled slope channels, suggest that rivers fed directly onto the slopes where their dense, sand‐laden discharges readily generated quasi‐steady hyperpycnal flows that regularly reached the basin floor. The composite architecture and complex waxing–waning flow facies configuration of the hyperpycnites is consistent with sustained and concomitant suspension and traction deposition under fluctuating subcritical to supercritical conditions. Similar sandstone beds occur on the clinoform slopes, indicating that the hyperpycnal flows operated likewise on the slope. Plant‐rich hybrid event beds indicate transformation of initially turbulent flows by relative enrichment of clay and plant material via progressive sand deposition to such an extent that it suppressed turbulence. The multi‐faceted character of the hyperpycnites reported here, challenges traditional beliefs that hyperpycnites assumingly preserve the waxing–waning signal of single‐peaked floods.
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引用次数: 0
Ultra‐long‐distance transport of aeolian sand: The provenance of an intermontane desert, south‐east China 风沙的超长距离运输:中国东南部山间沙漠的物源
IF 3.5 2区 地球科学 Q1 GEOLOGY Pub Date : 2023-05-11 DOI: 10.1111/sed.13106
Shuo Cao, Laiming Zhang, N. Mountney, Jing Ma, Mingang Hao, Chengshan Wang
Intermontane deserts are an important type of arid‐climate sedimentary system. Although rare at present, the sedimentary records of intermontane deserts reveal their widespread development in past greenhouse periods, and they might develop in the near future in response to ongoing global warming. Determination of the provenance of sand supplied for the construction of intermontane deserts is important to gain improved understanding of the potential impact of future climate on environmental evolution in arid and semi‐arid regions. During the Cretaceous, a typical intermontane desert developed in the Xinjiang Basin, south‐east China. In this study, the origin, spatial variability, and transport pathways of both aeolian and alluvial–fluvial sediments in the Xinjiang intermontane desert are investigated by analyses of bulk‐rock petrography and detrital‐zircon U–Pb geochronology. These results demonstrate that the sand in the Xinjiang intermontane desert succession was mainly of extraneous origin and wind‐derived. The nearby South China Block and South China Magmatic Belt were primary sources, and the 1000 km distant western margin of Yangtze Block was an important secondary source. During the Late Cretaceous, the westerlies were stronger in the northern than in the southern hemisphere with doubled wind speeds. In such a climatic context, the results herein suggest that the ultra‐long‐distance aeolian sediment transport was likely further enabled by two factors: (i) the strengthening of intermittent westerly winds during short‐lived glacial episodes; and (ii) the presence of a low‐relief corridor that served as a transport pathway from source to sink.
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引用次数: 0
Shape‐dependent settling velocity of skeletal carbonate grains: Implications for calciturbidites 骨架碳酸盐颗粒的形状依赖沉降速度:对钙厚积石的影响
IF 3.5 2区 地球科学 Q1 GEOLOGY Pub Date : 2023-05-08 DOI: 10.1111/sed.13103
A. Slootman, Max de Kruijf, G. Glatz, J. Eggenhuisen, R. Zühlke, J. Reijmer
Particle transport and deposition in turbidity currents is governed by the balance between turbulent suspension and gravitational settling, with settling velocity becoming dominant during the final rain‐out phases of decelerated turbidity currents on lobes. Differential particle settling velocities play a role in the sorting of grains in turbidity currents; there is a preference of grains with higher settling velocities to be deposited first, yielding a settling‐velocity gradient in vertical and longitudinal cross‐sections through turbidite beds. If sediments contain little variation in particle shape and density (for example, siliciclastics), then settling velocity is dominantly controlled by grain size. Carbonate sediments, in contrast, are composed of non‐skeletal and skeletal grains with various growth structures, producing a wide distribution of particle shapes (from spheroidal to platy, bladed and elongated forms). The present paper aims to constrain the extent to which shape‐dependent differential settling velocities influence sorting mechanisms in carbonate turbidity currents. Experiments using natural skeletal sand were conducted to investigate the settling of carbonate grains in: (i) isolation; (ii) suspension clouds; and (iii) turbidity currents. Size, density and shape parameters, including Corey Shape Factor and Zingg diagrams, were analysed using high‐resolution micro‐computed tomography. The slower settling of non‐spheroidal shapes was quantified. In the sinking suspensions, a sorting mechanism operated through differential velocities yielding an abundance of spheroidal grains at the base and enrichment in less‐spheroidal grains towards the top of suspension deposits. This trend was also observed longitudinally in carbonate turbidity currents, for which enhanced advection lengths caused less spheroidal grains to be transported farther into the basin. The effect of particle shape becomes increasingly significant as grain size increases, in particular above medium sand. Carbonate turbidites may therefore be more poorly sorted than siliciclastic turbidites, which is expected to result in lower primary porosity in calciturbidites compared to siliciclastic turbidites.
浊度流中的粒子输运和沉积受湍流悬浮和重力沉降的平衡控制,沉降速度在叶片上减速浊度流的最终雨出阶段占主导地位。在浊度流中,不同的颗粒沉降速度对颗粒的分选起作用;沉降速度较高的颗粒优先沉积,在浊积层的垂直和纵向截面上产生沉降速度梯度。如果沉积物的颗粒形状和密度变化不大(例如,硅塑料),那么沉降速度主要由颗粒大小控制。相比之下,碳酸盐沉积物由具有不同生长结构的非骨架和骨架颗粒组成,产生了广泛分布的颗粒形状(从球形到板状,叶片状和细长形)。本文旨在限制形状依赖的差分沉降速度在碳酸盐浊度流中影响分选机制的程度。利用天然骨架砂进行了实验,以研究碳酸盐颗粒在以下条件下的沉降:(i)隔离;(ii)悬浮云;(三)浊度流。尺寸、密度和形状参数,包括科里形状因子和青格图,使用高分辨率微计算机断层扫描进行分析。对非球面形状的缓慢沉降进行了量化。在下沉的悬浮物中,通过差速操作的分选机制在悬浮物沉积物的底部产生丰富的球形颗粒,而在悬浮物沉积物的顶部则富集较少的球形颗粒。在纵向上,碳酸盐浊度流也有这种趋势,平流长度的增加导致较少的球状颗粒被输送到盆地内。随着颗粒尺寸的增大,颗粒形状的影响变得越来越显著,特别是在中砂以上。因此,碳酸盐浊积岩可能比硅屑浊积岩分选更差,这可能导致钙质浊积岩的原生孔隙度比硅屑浊积岩低。
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引用次数: 1
Orbitally‐driven Palaeogene to Neogene deposition in the western South Atlantic (Espírito Santo Basin) and its correlation with global sea level 轨道驱动的南大西洋西部(Espírito Santo盆地)古近纪至新近纪沉积及其与全球海平面的相关性
IF 3.5 2区 地球科学 Q1 GEOLOGY Pub Date : 2023-05-08 DOI: 10.1111/sed.13104
T. Santos, Luana Lisboa, Victor Carreira, Fellippe R. A. Bione, I. Venancio, M. Bernardes, A. Belém, R. Díaz, M. Moreira, Alexandre A. O. Lopes, T. L. Santos, I. Souza, A. Spigolon, A. Albuquerque
Over the last 66 million years, Earth has undergone dramatic climate changes, shifting from a warm greenhouse to the more recent cold icehouse with polar ice caps in both hemispheres. Geological records show that the transition between these equilibrium states caused significant long‐term eustatic sea‐level and atmospheric CO2 decline paced by external orbital motions. Such eustatic variability influenced the stacking pattern of sedimentary successions, generating cyclic sequence boundaries that may be globally correlated. However, the impact of such oscillation along the Brazilian margin is largely unknown. This study used the natural gamma‐ray log from a well (ES‐2) at the offshore Espírito Santos Basin (western South Atlantic) measured between late‐Palaeocene and late‐Miocene. Null hypothesis tests ‐ evolutionary Average Spectral Misfit and Correlation Coefficient of no orbital modulation ‐ were executed to confirm the influence of astronomical parameters. The evolutionary Time Optimization algorithm was used to extract the sedimentation rate and depositional time. The anchored timescale shows a chronological interval placed between 58.97 and 7.72 ± 0.1 Ma (mid‐Thanetian – late Tortonian), mostly influenced by long‐eccentricity and short‐eccentricity (405 kyr and ca 100 kyr, respectively) and obliquity (ca 40 kyr) and their respective amplitude modulations (ca 2.4 Myr and 1.2 Myr). Applying the Integrated Prediction Error Filter Analysis and a high‐resolution age model, this study identified main depositional trends through time and correlated them to global sea‐level change. The correlation indicates that several intervals of global sea‐level reduction agree with a regressive trend at the ES‐2 site, but this relation is affected during enhanced regional tectonic activity intervals, as related to the emplacement of the Abrolhos Archipelago. The strategy adopted here is a way to join cyclostratigraphy and sequence stratigraphy, and promotes high‐resolution local‐to‐global correlation by identifying key stratigraphic surfaces. This will be relevant for palaeoclimatic studies and the geoscientific industry.
在过去的6600万年里,地球经历了剧烈的气候变化,从一个温暖的温室转变为最近在两个半球都有极地冰盖的寒冷的冰窖。地质记录表明,这些平衡状态之间的转变导致了显著的长期海平面上升和大气CO2以外轨道运动为节奏的下降。这种上升变率影响了沉积层序的堆积模式,产生了可能具有全球相关性的旋回层序边界。然而,沿着巴西边缘的这种振荡的影响在很大程度上是未知的。本研究使用了在晚古新世和晚中新世之间测量的Espírito Santos盆地(南大西洋西部)海上一口井(ES‐2)的自然伽马射线测井。零假设检验——演化平均光谱失拟和无轨道调制的相关系数——被用来证实天文参数的影响。采用演化时间优化算法提取沉积速率和沉积时间。锚定的时间尺度显示了58.97和7.72±0.1 Ma之间的时间间隔(中Thanetian -晚Tortonian),主要受长偏心率和短偏心率(分别为405 kyr和100 kyr)和倾角(40 kyr)及其各自的振幅调制(2.4 Myr和1.2 Myr)的影响。采用综合预测误差滤波分析和高分辨率年龄模型,确定了主要的沉积趋势,并将其与全球海平面变化进行了关联。相关性表明,全球海平面下降的几个区间与ES - 2站点的回归趋势一致,但这种关系在区域构造活动增强的区间受到影响,与Abrolhos群岛的就位有关。这里采用的策略是一种结合旋回地层学和层序地层学的方法,并通过识别关键地层面来促进高分辨率的局部到全球对比。这将与古气候研究和地球科学产业相关。
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引用次数: 0
Century‐scale sequences and density‐flow deltas of the late Holocene and modern Dead Sea coast, Israel 以色列全新世晚期和现代死海海岸的世纪尺度序列和密度流三角洲
IF 3.5 2区 地球科学 Q1 GEOLOGY Pub Date : 2023-05-08 DOI: 10.1111/sed.13101
M. Moran, J. Holbrook, N. Lensky, Liran Ben Moshe, Z. Mor, H. Eyal, Y. Enzel
Late Holocene Dead Sea rift‐margin strata reveal century‐scale sequences. Sequences are known to form at millennial timescales, but whether they can form at scales as short as centuries (seventh‐order, sensu Vail et al., 1991) was previously unconfirmed. This study maps lithofacies and sequence‐stratigraphic surfaces from a ca 35 m high outcrop of the post‐1500 ad part of the Holocene falling‐stage wedge, and adjacent subaerial environments, along the Nahal Darga of the western Dead Sea coast, using drone images. The study also produces the first maps of subaqueous delta environments from remotely operated vehicle photographs. Comparison of outcrop and remotely operated vehicle data show that delta foresets form by debris‐flow lobes accreting onto the delta face. Debris lobes increase in size with depth, have sorted cobble heads, and stack compensationally. Debris lobes dewater to form mostly erosive turbidity currents that cut channels and obstacle scours down slope. Topsets comprising fluvial, beach‐ridge and lagoonal deposits prograde over these foresets. Surfaces separating foreset and topset elements of this Gilbert‐delta system bind systems tracts and record downstep and upstep of the shoreface associated with base‐level rises and falls. These surfaces match known lake‐level changes in the Dead Sea in magnitude, timing and direction. They confirm Medieval (ca 600 to 1300 ad) and Modern (ca 1300 ad to Modern) century‐scale sequences. These microsequences form in the Dead Sea because this climate‐sensitive lake can generate metres‐scale lake‐level cycles on century timescales, and because depositional systems can, as shown here, reestablish sufficiently rapidly (≤101 years) to record century‐scale cycles with complete systems tracts. Although conditions for generating microsequences are optimal in the Dead Sea, they are not unique. These microsequences pose a challenge to sequence stratigraphy because they typically fall below seismic resolution, may geometrically resemble higher‐order composite sequences and complicate defining of anchor sequences within a sequence hierarchy.
晚全新世死海裂谷边缘地层揭示了世纪尺度的层序。已知序列在千年的时间尺度上形成,但它们是否能在短至几个世纪的尺度上形成(七阶,sensu Vail et al., 1991),以前没有得到证实。本研究利用无人机图像,绘制了死海西岸纳哈尔达尔加地区1500年后、全新世部分跌落期楔形物约35米高的露头岩相和层序地层表面,以及邻近的地面环境。该研究还从远程操作的车辆照片中产生了水下三角洲环境的第一张地图。露头和遥控车辆数据的比较表明,三角洲的森林是由碎屑流瓣在三角洲表面上增生形成的。碎屑裂片的大小随深度的增加而增加,具有分选的卵石头,并具有补偿性堆积。碎屑裂片脱水,形成侵蚀性浊流,切断河道,并沿坡冲刷障碍物。由河流、滩脊和泻湖沉积物组成的顶集在这些森林之上向前推进。分离吉尔伯特三角洲系统的森林和顶部元素的表面结合了系统域,并记录了与基准面上升和下降相关的海岸表面的下降和上升。这些表面在大小、时间和方向上与死海已知的湖泊水位变化相匹配。他们确认了中世纪(公元600年至1300年)和现代(公元1300年至现代)世纪尺度的序列。这些微层序之所以在死海中形成,是因为这个对气候敏感的湖泊可以在世纪时间尺度上产生米级的湖平面旋回,而且沉积系统可以像这里所示的那样,以足够快的速度(≤101年)重建,以完整的系统域记录世纪尺度的旋回。尽管在死海中产生微序列的条件是最佳的,但它们并不是唯一的。这些微层序对层序地层学提出了挑战,因为它们通常低于地震分辨率,在几何上可能类似于高阶复合层序,并且使层序层次中的锚定层序的定义复杂化。
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引用次数: 0
Aptian Oceanic Anoxic Event 1a in the shallow, carbonate‐dominated intrashelf Kazhdumi Basin, Zagros Mountains Zagros山Kazhdumi浅层碳酸盐岩占主导的陆架内盆地Aptian海洋缺氧事件1a
IF 3.5 2区 地球科学 Q1 GEOLOGY Pub Date : 2023-05-07 DOI: 10.1111/sed.13102
A. Jafarian, A. Husinec, Chengshan Wang, Xi Chen, Abdus Saboor, Yalin Li
The early Aptian Selli Oceanic Anoxic Event 1a (ca 120 Ma) is a major Mesozoic episode of biotic, climatic, environmental and geochemical perturbations associated with the extensive burial of organic matter. Based on the new sedimentological, biostratigraphic and carbon‐isotope data from the Kazhdumi Intrashelf Basin, this study tracks the Oceanic Anoxic Event 1a‐associated perturbations along the north‐eastern margin of the Arabian Plate. The studied succession has five complete third‐order sequences with three facies associations: (i) deep open‐marine and intrashelf basin; (ii) shallow open‐marine mid‐ramp; and (iii) inner ramp. The Oceanic Anoxic Event 1a‐equivalent deposits include the former two facies associations – (i) and (ii) – and are 25 to 31 m thick, which corresponds to the accumulation rates of ca 1.9 to 3.1 cm kyr−1 (uncorrected for compaction) based on the 1.0 to 1.3 Myr duration of the event. The interval retained a high‐resolution record of carbon‐isotope and sea‐level fluctuations, which enables correlation across the Arabian Plate and Tethys. The Oceanic Anoxic Event 1a onset is marked by a biotic change from ostreid‐dominated shallow‐marine limestone with abundant foraminifera (Palorbitolina lenticularis and Choffatella decipiens) to dark grey deep‐water planktonic foraminifera‐rich and radiolaria‐rich limestone with chert and organic‐rich shale (Radiolarian Flood Zone). The upper oceanic anoxic event part of 1a is characterized by the shallowing‐upward, backstepping facies marking the return to a shallow open‐marine setting, albeit without recovery of the Palorbitolina–Choffatella association. Deep open‐marine deposition (Kazhdumi Tongue) was restored early during the Oceanic Anoxic Event 1a recovery in the latest early Aptian. A return to shallow open‐marine environments with Mesorbitolina‐rich limestone marks the beginning of the late Aptian, followed by a major sea‐level fall and karstification. This study resolves some of the uncertainties related to the order and timing of the events influencing the environmental disturbances across the eastern Arabian Plate during Oceanic Anoxic Event 1a and stresses the importance of shallow carbonate‐dominated intrashelf basins as faithful recorders of carbon‐isotope and sea‐level oscillations and palaeoenvironmental changes during global oceanic perturbations.
早阿普tian Selli海洋缺氧事件1a(约120 Ma)是中生代生物、气候、环境和地球化学扰动的主要事件,与有机质的广泛埋藏有关。基于新的沉积学、生物地层学和碳同位素数据,本研究追踪了沿阿拉伯板块东北缘的海洋缺氧事件1a相关扰动。研究的层序有5个完整的三级层序,具有3种相组合:(1)深开阔海相和陆架内盆地;(ii)浅海开阔中坡道;(三)内坡道。海洋缺氧事件1a‐等效沉积物包括前两个相组合(i)和(ii),厚度为25至31 m,对应于基于事件持续时间1.0至1.3 Myr的累积速率约1.9至3.1 cm kyr−1(未校正压实)。这段时间保留了碳同位素和海平面波动的高分辨率记录,从而实现了阿拉伯板块和特提斯之间的相关性。海洋缺氧事件1a的发生以生物变化为标志,从以牡蛎为主的浅海石灰岩(含丰富的有孔虫(Palorbitolina lenticularis和Choffatella decipiens))到深灰色的深水浮游有孔虫和富含放射虫的石灰岩(含燧石和富含有机质的页岩)。1a的上层海洋缺氧事件部分的特征是浅水-向上,后退相,标志着浅水-开阔海环境的回归,尽管没有恢复Palorbitolina-Choffatella组合。早阿普tian晚期的海洋缺氧事件1a恢复早期恢复了深海开放海相沉积(Kazhdumi舌)。富含Mesorbitolina的石灰岩的浅海开放环境的回归标志着阿普梯晚期的开始,随后是海平面的大幅下降和岩溶作用。本研究解决了在海洋缺氧事件1a期间影响整个阿拉伯板块东部环境扰动的事件顺序和时间的一些不确定性,并强调了浅层碳酸盐主导的大陆架内盆地作为全球海洋扰动期间碳同位素、海平面振荡和古环境变化的忠实记录者的重要性。
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引用次数: 3
Geomorphic and environmental controls on microbial mat fabrics on Little Ambergris Cay, Turks and Caicos Islands 特克斯和凯科斯群岛小龙涎香礁微生物垫织物的地貌和环境控制
IF 3.5 2区 地球科学 Q1 GEOLOGY Pub Date : 2023-04-13 DOI: 10.1111/sed.13100
N. Stein, J. Grotzinger, D. Quinn, U. Lingappa, T. Present, E. Trower, M. Gomes, E. Orzechowski, M. Cantine, K. Metcalfe, W. Fischer, B. Ehlmann, J. Strauss, A. Knoll
To interpret microbially influenced paleoenvironments in the sedimentary record, it is crucial to understand what processes control the development of microbial mats in modern environments. This article reports results from a multiyear study of Little Ambergris Cay, Turks and Caicos Islands, an uninhabited island floored by broad tracts of well‐developed microbial mats on the wind‐dominated and wave‐dominated Caicos Platform. Uncrewed aerial vehicle‐based imaging, differential global positioning system topographic surveys, radiocarbon data, and in situ sedimentological and microbial ecological observations were integrated to identify and quantify the environmental factors that influence the distribution and morphologies of Little Ambergris Cay microbial mats, including their response to large storm events. Based on these data, this study proposes that Little Ambergris Cay initially developed from the accretion and rapid lithification of carbonate sediment delivered by converging wave fronts in the lee of adjacent Big Ambergris Cay. Broad tracts of microbial mats developed during late Holocene time as the interior became restricted due to beach ridge development. Minor elevation differences regulate subaerial exposure time and lead to three categories of microbial mats, differentiated by surface texture and morphology: smooth mats, polygonal mats and blister mats. The surface texture and morphology of the mats is controlled by subaerial exposure time. In addition to elevation, the spatial distribution of mats is largely controlled by hydrodynamics and sediment transport during large storm events. This detailed assessment of the controls on mat formation and preservation at Little Ambergris Cay provides a framework within which to identify and understand the interactions between microbial communities and sediment transport processes in ancient high‐energy carbonate depositional systems.
为了解释沉积记录中微生物影响的古环境,了解在现代环境中控制微生物席发育的过程是至关重要的。本文报告了对特克斯和凯科斯群岛上的小龙柏香礁(Little Ambergris Cay)多年研究的结果,这是一个无人居住的岛屿,在风主导和波浪主导的凯科斯平台上,有大片发育良好的微生物垫。基于无人机成像、差分全球定位系统地形调查、放射性碳数据以及原位沉积学和微生物生态观测相结合,确定并量化了影响小龙伯格礁微生物垫分布和形态的环境因素,包括它们对大风暴事件的响应。基于这些数据,本研究认为,小龙涎香礁最初是由相邻大龙涎香礁背风处的汇聚波锋传递的碳酸盐沉积物的增生和快速岩化而形成的。在全新世晚期,由于海滩脊的发展,内部受到限制,形成了大面积的微生物席。微小的海拔差异调节着地面暴露时间,形成了按表面纹理和形态区分的三种微生物垫:光滑垫、多边形垫和水泡垫。垫层的表面纹理和形态受地面曝光时间的控制。除了海拔高度外,大风暴期间的水动力和泥沙输运在很大程度上控制了席层的空间分布。对小龙涎香礁席形成和保存控制因素的详细评估为识别和理解古代高能碳酸盐沉积体系中微生物群落与沉积物输运过程之间的相互作用提供了一个框架。
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引用次数: 0
Influence of the grain shape and packing texture on the primary porosity of sandstone: Insights from a numerical simulation 颗粒形状和充填结构对砂岩原生孔隙度的影响:数值模拟的启示
IF 3.5 2区 地球科学 Q1 GEOLOGY Pub Date : 2023-04-11 DOI: 10.1111/sed.13098
Yiming Yan, Liqiang Zhang, Xiaorong Luo, Keyu Liu, Tongye Jia, Yanjun Lu
Sandstone is an important carrier of underground hydrocarbon and the geological sequestration of carbon dioxide. Primary porosity is an important parameter used to predict reservoir quality, and it is influenced by the grain shape, grain‐size distribution and grain packing texture. However, few studies have focused on deriving multivariate equations of the grain size, grain‐size distribution and grain packing texture to predict the primary porosity of sandstone. The natural sedimentary process of sandstones was designed and simulated using a discrete element method. The results confirmed that the primary porosity is influenced by roundness, flatness, elongation, grain‐size distribution and grain packing texture; of the attributes, the mean grain size contributes less to the primary porosity of sandstone. Based on 193 simulated sandstone samples with a one‐component grain packing texture, a mathematical model considering roundness, flatness, elongation, grain packing texture and grain‐size distribution was proposed. The maximum, mean absolute and root mean square errors were 0.71, 0.26 and 0.32, respectively. The correlation coefficient between the simulated results and mathematical predicted results was 0.94. Furthermore, the primary porosity was positively correlated with the kurtosis of the grain‐size distribution in sandstone with the same grain shape but different kurtosis. The primary porosity was found to be independent of the mean grain size and mainly affected by the grain packing texture. Moreover, the primary porosity prediction model for sandstones with different grain‐size distribution curves based on the grain packing texture, which was proposed by the author in a previous study, was verified, and the correlation coefficient between the simulated results and predicted results was >0.92. The new mathematical model proposed in this study is a useful supplement for key parameter acquisition in the previous primary porosity prediction model of sandstone with different grain‐size distribution curves and grain packing texture. A mathematical model considering roundness, flatness, elongation, grain packing texture and grain‐size distribution is of great significance for reservoir quality prediction and conducting a quantitative evaluation of the diagenesis.
砂岩是地下油气的重要载体和二氧化碳的地质封存。原生孔隙度是预测储层质量的重要参数,受颗粒形状、粒度分布和颗粒充填结构的影响。然而,很少有研究关注于建立砂岩的粒度、粒度分布和颗粒堆积结构的多元方程来预测砂岩的原生孔隙度。采用离散元法对砂岩的自然沉积过程进行了设计和模拟。结果表明:原始孔隙率受圆度、平整度、伸长率、晶粒尺寸分布和晶粒堆积织构的影响;其中,平均粒度对砂岩原生孔隙度的影响较小。基于193个单组分颗粒充填结构的砂岩模拟样品,建立了考虑圆度、平整度、伸长率、颗粒充填结构和粒度分布的数学模型。最大误差、平均绝对误差和均方根误差分别为0.71、0.26和0.32。模拟结果与数学预测结果的相关系数为0.94。在相同颗粒形状但不同峰度的砂岩中,原生孔隙度与粒度分布峰度呈正相关。原生孔隙度与平均晶粒尺寸无关,主要受晶粒堆积织构的影响。验证了作者在前人研究中提出的基于颗粒堆积结构的不同粒度分布曲线砂岩孔隙度初步预测模型,模拟结果与预测结果的相关系数>0.92。本文提出的数学模型是对以往不同粒度分布曲线和颗粒充填结构砂岩孔隙度初步预测模型中关键参数获取的有益补充。考虑圆度、平坦度、伸长率、颗粒堆积结构和粒度分布的数学模型对储层质量预测和成岩作用定量评价具有重要意义。
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引用次数: 1
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Sedimentology
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