Mound Growth Research Articles

Scaling of surface roughness in film deposition with height-dependent step edge barriers.

We perform kinetic Monte Carlo simulations of film growth in simple cubic lattices with solid-on-solid conditions, Ehrlich-Schwoebel (ES) barriers at step edges, and a kinetic barrier related to the hidden off-plane diffusion at multilayer steps. Broad ranges of the diffusion-to-deposition ratio R, detachment probability per lateral neighbor, ε, and monolayer step crossing probability P=exp[-E_{ES}/(k_{B}T)] are studied. Without the ES barrier, four possible scaling regimes are shown as the coverage θ increases: nearly layer-by-layer growth with damped roughness oscillations; kinetic roughening in the Villain-Lai-Das Sarma (VLDS) universality class when the roughness is W∼1 (in lattice units); unstable roughening with mound nucleation and growth, where slopes of logW×logθ plots reach values larger than 0.5; and asymptotic statistical growth with W=θ^{1/2} solely due to the kinetic barrier at multilayer steps. If the ES barrier is present, the layer-by-layer growth crosses over directly to the unstable regime, with no transient VLDS scaling. However, in simulations up to θ=10^{4} (typical of films with a few micrometers), low temperatures (small R,ε, or P) may suppress the two or three initial regimes, while high temperatures and P∼1 produce smooth surfaces at all thicknesses. These crossovers help to explain proposals of nonuniversal exponents in previous works. We define a smooth film thickness θ_{c} where W=1 and show that VLDS scaling at that point indicates negligible ES barriers, while rapidly increasing roughness indicates a small ES barrier (E_{ES}∼k_{B}T). θ_{c} scales as ∼exp(const×P^{2/3}) if the other parameters are kept fixed, which represents a high sensitivity on the ES barrier. The analysis of recent experimental data in the light of our results distinguishes cases where E_{ES}/(k_{B}T) is negligible, ∼1, or ≪1.

Contrasting Features and Volcanostratigraphy of the Mafic-Hosted Mandoos and Shinas Volcanogenic Massive Sulfide Deposits, Samail Ophiolite, Oman

AbstractDespite the substantial amount of research on the Cretaceous Samail ophiolite in Oman, the factors controlling the size and metal endowment of the mafic-hosted, Cu-Au(-Zn-Ag) volcanogenic massive sulfide (VMS) deposits remain elusive. This work shows that the volcanostratigraphic position, hydrothermal venting style, and oxidation processes are critical factors controlling the distinct features of the Shinas and Mandoos deposits.Mandoos is a large (8 Mt, 1.8 wt % Cu, 0.18 g/ton Au) orebody preserving abundant primary vent-related features formed via mound growth and collapse within a wide hydrothermal field, overlying a poorly developed stockwork. The smaller Shinas deposit (0.8 Mt, 2.6 wt % Cu, 0.63 g/t Au) represents a higher-temperature system evolving from low fS2/fO2 conditions, locally sealed by jaspers, to a mound growth stage with widespread subseafloor brecciation/replacement with associated zone refining. Mandoos formed at the onset of the postaxial stage (Geotimes-Tholeiitic Alley transition), and Shinas is hosted within the Alley units. Volcanism in Samail was seemingly continuous, and the low ɛNd and Nb/Ta of the Shinas hanging-wall lavas record the onset of significant modifications of the mantle source during the postaxial stage.Mandoos is enriched in Te + As + Se ± Zn ± Ga ± Sb relative to Shinas, where higher Cu + Au + Tl ± Mo grades possibly reflect leaching of protoarc-like lavas. Rare earth element patterns in the ores mimicking the deposit footwall can be employed to constrain volcanostratigraphic positioning and indicate that the footwall lavas may also represent a source of metals. Formation of metal-rich ochres at the sea floor likely led to Cu + Au upgrading in the ores during seawater-induced oxidation, which was enhanced during subaerial gossan formation.

InGaN surface morphology evolution investigated by atomic force microscope with power spectral density analysis

The morphology of thin InGaN layers grown at varying temperature by metalorganic chemical vapor deposition (MOCVD) has been studied by atomic force microscope (AFM). The surface morphology undergoes a transition process from three-dimensional (3D) island growth mode to two-dimensional (2D) nucleated mound and hillock growth mode and finally to layer-by-layer step-meandering and step flow growth mode. The changes in morphology were analyzed from a thermodynamic (mostly based on the BCF theory of crystal growth by Burton, Cabrera and Frank) and kinetic (mostly the ESB theory based on the Ehrlich-Schwöbel barrier) perspective. Power spectral density (PSD) analysis of AFM surface images is used to determine the dominant smoothing mechanisms that contribute to the feature of surface morphology of InGaN, and validate our analysis based on BCF and ESB theories.

Geochemical Characterization of Laminated Crystalline Crust Travertines Formed by Ca2+-Deficient Hot Springs at Sobcha (China)

Travertines formed of crystalline crust have been widely reported, but there has not been focus on their geochemical characteristics. We therefore carefully conducted a series of geochemical investigations and U-Th dating on a travertine mound mainly composed of crystalline crust from Sobcha (southwest China) to determine their geochemical features and geological implications. The Sobcha travertines dominantly consist of granular crystals and fan crystals and show δ13C from 3.4‰ to 4.9‰ V-PDB, δ18O from −26.7‰ to −23.7‰ V-PDB, and 87Sr/86Sr from 0.712458 to 0.712951. When normalized to PASS, the Sobcha travertines exhibit MREE enrichment relative to HREE and LREE, HREE enrichment relative to LREE, and positive Eu anomalies. The δ13C signatures and mother CO2 evaluation of the Sobcha travertines show that the Sobcha travertines were thermogene travertines largely receiving mother CO2 from (upper) mantle (i.e., magmatic CO2) or a mixture of soil-derived CO2 and CO2 related to carbonate decarbonation. The 87Sr/86Sr of the Sobcha travertines is out of the 87Sr/86Sr ranges of local deposits exposed at Sobcha and surrounding areas but is well matched with the mean 87Sr/86Sr of Nadi Kangri volcanic rocks which cropped out to the northeast of the studied travertines (over 20 km away). This might indicate the important role of the Nadi Kangri volcanic rocks in suppling Sr to the studied travertines, but more studies are required. The LREE depletion compared to MREE and HREE in the Sobcha travertines was interpreted to be caused by the difference in geochemical mobility between LREEs and HREEs during water–rock interaction at depth, while the MREE enrichment compared to HREE was considered to be most likely inherited from reservoir/aquifer rocks. The positive Eu anomalies of the Sobcha travertines may result from very high reservoir temperatures and/or preferential dissolution of Eu-rich minerals/rocks (especially plagioclase). The Sobcha travertine mounds displays no or very slight vertical variations in δ13C, 87Sr/86Sr, and REE patterns, indicating the compositional stability of mother CO2 and paleo-fluids. However, a significant vertical increase in δ18O was observed and was explained as the result of gradual water temperature decrease related to climate cooling, self-closure of the vents, or mound vertical growth. The findings in this study might help us better understand the deposition of crystalline crust in Ca2+-deficient hot spring systems.

Power spectral density-based fractal analyses of sputtered yttria-stabilized zirconia thin films

This study provides information about the surface morphology of sputtered yttria-stabilized zirconia (YSZ) thin films from the atomic force microscope (AFM) spectral analyses using the power spectral density (PSD) function at varying annealing temperatures. Applying fractal and k-correlation fitting models to the PSD data, fractal dimension, Hurst exponent, correlation length, and equivalent root mean square roughness are quantified. The PSDs of the films exhibit an inverse power-law variation at high spatial frequency, which points to the existence of the fractal components in the film’s surface. The annealing temperatures up to 900 ∘C decreased fractal dimension from 2.60 to 2. The surface roughness increased from 0.10 to 13.92 nm and from 0.04 to 3.95 nm, obtained from the statistical analyses of AFM images and the k-correlation model. The films annealed from 500 ∘C to 800 ∘C showed fine grain size morphology with Hurst exponent values from 0.40 to 0.53, indicating a homogeneous spatial roughness distribution. While the film annealed at 900 ∘C exhibited large aggregate grains morphology. The growth of a sample annealed at the temperature of 900 ∘C is more likely to be ruled by the step-edge barrier-induced mound growth and inhomogeneous spatial distribution of roughness. In contrast, normal self-affine behaviour is observed at lower annealing temperatures.

Factors controlling the geometry of travertine mounds: Insights from Heinitang (China)

AbstractTravertine mounds are common spring‐constructed landforms with highly variable geometries, but factors controlling their development have not yet been fully understood. To investigate processes linked with their lateral and vertical growth, this study investigated travertine mounds at Heinitang (China) and compared them with typical mounds around the world. Calcium concentration variation modelling and height evaluation of travertine mounds were also performed. The lateral extent of travertine mounds was found to be mainly controlled by Ca2+ and concentrations and water discharge: relatively small metre‐scale mounds, like those from Heinitang, are largely the products of Ca2+‐deficiency (<150 mg L−1, commonly <100 mg L−1) or ‐deficiency (<500 mg L−1) springs with low discharges (<0.1 L s−1), whereas springs with higher Ca2+ and concentrations and discharges give rise to the formation of wider mounds. Additional factors affecting mound lateral development include infiltration, evaporation, micro‐organisms, water cooling, CO2 degassing and flow paths. Height of travertine mounds cannot be simply considered to represent the piezometric surface, because the vertical growth of travertine mounds is also influenced by the water table change triggered by tectonic pulses and climate fluctuations, and the closing of conduits induced by self‐sealing. The extinction of travertine mounds at Heinitang is, for example, probably caused by the water table lowering triggered by earthquakes or climate drying after 4 kyr bp. These findings offer new inputs for the better understanding of factors controlling travertine mound development and might assist in the reconstruction of fluid properties, hydrodynamics, tectonics and climate fluctuations in fossil geothermal systems with travertine mounds.

Feedbacks between hydrodynamics and cold-water coral mound development

Cold-water corals rely on currents to transport food towards them and when external conditions are favourable, they can form coral mounds. These structures, which can be over 300 m high, influence the hydrodynamics around the reefs that grow on the mounds, which feeds back to affect coral- and therefore mound-growth. We investigated these feedbacks at the Logachev coral mound province, by running simulations with a 3D hydrodynamic model (Roms-Agrif), using different seafloor bathymetries that represent consecutive stages of mound development. Simulations ranged from a fully smoothened bathymetry without mounds, to a coral mound (Haas mound) at 1.5 times its current size. The effect of mound height on coral growth was investigated by looking at the baroclinic (internal) tide, turbulent energy dissipation, vertical velocities, and horizontal bottom currents. The simulations suggest that with increasing mound height horizontal velocities increase, while turbulent energy dissipation and vertical velocities around the mound foot decrease. This supposedly limits coral growth at the mound foot and hence lateral mound extension in later stages of development. An increase in turbulent energy dissipation and vertical velocities on the mound top and upper flanks, indicates vertical mound growth at all subsequent stages. Our findings of continued vertical mound growth provide an explanation for recently published data on benthic cover from a transect over Haas mound, that show a dominance of live corals on the mound top. We find areas of increased energy conversion rates from the barotropic (surface) to the baroclinic tide on the bathymetry where we artificially eliminated the mounds from (i.e. smoothened bathymetry). Interestingly, these areas overlap with the region where coral mounds are located at present. So, the baroclinic tide is likely an important mechanism in the process of coral mound establishment. Given the relative ease with which the energy conversion rate from the barotropic to the baroclinic tide can be deduced from hydrodynamic model simulations, our results provide opportunities to investigate where coral mounds may be initiated worldwide.

Development of a Mississippian–Lower Pennsylvanian isolated carbonate platform within the basinal griotte facies of the Cantabrian Mountains, NW Spain

The Valdediezma platform consists of upper Tournaisian to lower Bashkirian (Carboniferous) shallow-water carbonates deposited in the core of the Picos de Europa Province (Cantabrian Mountains, northwest Spain). Although faulted in several thrust sheets, it is the only preserved platform developed in the Mississippian starved basins of the southern branch of the Variscan Orogen that is characterised also by pelagic sedimentation. This unusual platform provides an exceptional opportunity to study the lateral variation from the platform to the typical condensed griotte limestones developed in a starved basin, the origin of such a platform in a particularly unfavourable setting for carbonate accumulation, as well as the nucleation of the subsequent widespread Pennsylvanian carbonate platforms of the Cantabrian Mountains. Sixteen carbonate microfacies are differentiated in the Valdediezma Limestone, from shallow-water to slope to basinal environments. The carbonate production is related to the submarine topography and the rapid rates of microbial mound growth and accumulation, particularly from the upper Viséan to the lower Serpukhovian. A high-elevation platform and steep southern margin occurred during the deposition of condensed cephalopod-bearing limestones in the basin. A higher rate of carbonate accumulation is recognised from the upper Serpukhovian and younger, with similar thicknesses in shallow- and deeper water settings. The thickest part of the succession was coeval with the larger subsidence resulting from the migration of the Variscan deformation at the margin of the foreland basin of the Cantabrian Zone. The migration of deformation along the foreland uplifted the Valdediezma platform from the lower Bashkirian and caused its partial erosion. The Pennsylvanian carbonate platform developed on an exhumed Mississippian platform. Tectonic overloading due to the emplacement of nearby thrust sheets caused the subsidence and burial of the Valdediezma platform in the upper Moscovian.

Integration of superhydrophobicity and high durability in super-rough hard thin films

The development of drag reduction and self-cleaning technologies urgently needs the superhydrophobic films with high durability. However, due to hardness limitation, traditional polymer-based superhydrophobic films cannot achieve high durability. Here, a new strategy of “surface super-roughening of hard inorganic films” was proposed to achieve the integration of durability and hydrophobicity. By inducing the vertical growth of surface mounds, super-rough Ag-doped hafnium nitride films were prepared. This film had superhydrophobicity, high hardness, high wear resistance and high corrosion resistance. In addition, through the combination of experiments and simulations, we explained the microscopic mechanism of the vertical growth of surface mounds.

Modelling Ediacaran metazoan–microbial reef growth

AbstractThroughout the Phanerozoic, sessile metazoans grew in close association with various microbial carbonates to form reefs. The first metazoans with calcareous hard‐parts appeared in the terminal Ediacaran,ca550 million years ago, and these also commonly grew associated with microbial mats, thrombolites and stromatolites, to form the oldest known metazoan–microbial reefs. These hard‐parts also formed the first skeletal (bioclastic) carbonate sediments, which increased to dominate shallow marine carbonate sedimentary production during the Phanerozoic. Here the growth dynamics and sedimentary interactions between Ediacaran microbial–metazoan reefs and their bioclastic products are described based on reef complexes from the Nama Group, Namibia (ca547 Ma), and the first three‐dimensional numerical models are constructed to parametrize these dynamics. These reefs are observed to form large domal mounds and columns neighbouring locally high rates of bioclastic sediment accumulation, and commonly evolve to flat‐topped surfaces overlain by sediment. This model is parsimonious, embodying a single dynamic rule:metazoans attach to microbialite mounds which grow radially into free space shedding bioclasts in proportion to metazoan production. Models evolve mounds into columns due to spatial competition, and produce an oscillating interplay between mound expansion and smothering that results in an inter‐fingering of microbialite mound and detrital sediment. This dynamic is shown to be non‐linear in the proportion of bioclastic sediment produced. Smothering by bioclastic sediment is also demonstrated to both reduce the rate (by volume) of subsequent mound growth, and to overwhelm the growing mat surfaces of stromatolites: after a threshold is reached in the rate of bioclastic sediment deposition, sediment terminates all stromatolite growth. These models show that the general characteristics of field observations can be explained by a single dynamic rule, and that reef‐sourced bioclasts may make an important local contribution to Ediacaran to Cambrian microbial–metazoan reef dynamics – a contribution that remains important throughout the Phanerozoic.

Constraining the formation of authigenic carbonates in a seepage-affected cold-water coral mound by lipid biomarkers.

Cold-water coral (CWC) mounds are build-ups comprised of coral-dominated intervals alternating with a mixed carbonate-siliciclastic matrix. At some locations, CWC mounds are influenced by methane seepage, but the impact of methane on CWC mounds is poorly understood. To constrain the potential impact of methane on CWC mound growth, lipid biomarker investigations were combined with mineralogical and petrographic analyses to investigate the anaerobic oxidation of methane (AOM) and authigenic carbonate formation in sediment from a seep-affected CWC mound in the Gulf of Cadiz. The occurrence of AOM was confirmed by characteristic lipids found within a semi-lithified zone (SLZ) consisting of authigenic aragonite, high-magnesium calcite and calcium-excess dolomite. The formation of high-Mg calcite is attributed to AOM, acting as a lithifying agent. Aragonite is only a minor phase. Ca-excess dolomite in the SLZ and upper parts may be formed by organoclastic sulphate reduction, favouring precipitation by increased alkalinity. The AOM biomarkers in the SLZ include isoprenoid-based archaeal membrane lipids, such as abundant glycerol dibiphytanyl glycerol tetraethers (GDGTs) dominated by GDGT-2. The δ13 C values of GDGT-2, measured as ether-cleaved monocyclic biphytanes, are as low as -100‰ versus V-PDB. Further, bacterial dialkyl glycerol diethers with two anteiso-C15 alkyl chains and δ13 C values of -81‰ are interpreted as biomarkers of sulphate-reducing bacteria. The lipid biomarker signatures and mineralogical patterns suggest that anaerobic methane-oxidizing archaea of the ANME-1 group thrived in the subsurface at times of slow and diffusive methane seepage. Petrographic analyses revealed that the SLZ was exhumed at some point (e.g. signs of bioerosion of the semi-lithified sediment), providing a hard substrate for CWC larval settlement. In addition, this work reveals that AOM-induced semi-lithification likely played a role in mound stabilization. Lipid biomarker analysis proves to be a powerful tool to disentangle early diagenetic processes induced by microbial metabolisms.

In situ growth of ultra-smooth or super-rough thin films by suppression of vertical or horizontal growth of surface mounds

A new method and mechanism were explored for in situ growth of ultra-smooth/super-rough thin films with unique surface properties.

Constraining past environmental changes of cold‐water coral mounds with geochemical proxies in corals and foraminifera

AbstractCold‐water coral (CWC) reefs and mounds are and have been biodiversity hotspots of the deep sea. As their occurrence depends on specific environmental parameters, gaining hindsight on changing ocean conditions under on‐going climate change is the key to a better understanding of CWC mound development through time. A convenient technique for reconstructing the palaeoenvironment during periods of CWC mound growth is by extracting geochemical proxies from biologically mediated carbonates. Here, the focus is on probably the two most abundant calcareous archives, that are, cold‐water Scleractinia and Foraminifera, with an overview of the geochemical proxies (selection) used in these aragonitic and calcitic skeletons from CWC mounds. A particular emphasis is set on constraining proxies for temperature, salinity, seawater density, seawater carbonate systems parameters (pH, CO32−), nutrients, oxygen and water mass tracers.

Tannic acid- and cation-mediated interfacial self-assembly and epitaxial growth of fullerene (nC60) and kaolinite binary graphitic aggregates

In this study, we investigated the tannic acid (TA)-, Ca2+-, and mica-enabled interfacial assembly of nC60 fullerene (FWS) and Na-saturated kaolinite (Na-Kl) with in and ex situ atomic force microscopy (AFM). The epitaxial growth of herringbone motif, two dimensional (2D) chiral clusters and 3D mounds were detected. π-π electron donor-acceptor (EDA) interactions drove the transformation of the FWS, and the symmetry of the muscovite substrate directed the epitaxial ordering of self-assembled herringbone motifs. A ternary mixture of Na-Kl/FWS/TA in the presence of Ca2+ produced double-stranded (ds) helices and 2D platelets of chiral clusters with a nano-porous monolayer on K+-treated muscovite surfaces. The weak hydration of exchangeable K+ and stronger electric fields possibly contributed to the 1D and 2D propagation of aggregates. However, the local increment in carbon content due to the nucleation of functionalized FWS on mica diminished the K+-induced electric field effect and facilitated the 3D growth of helical mounds. The diffusion limited mass-transfer of particulates across the Ehrlich-Schwoebel barrier (ESB) and screw dislocation assisted motion of particulates specifically at higher steps aided mound growth. Thus, the structural incorporation of FWS can substantially impede its interfacial transport and produce hierarchical hybrid mineral-enriched graphitic aggregates.

An examination of scaling behavior in unstable epitaxial mound growth via kinetic Monte Carlo simulations

We investigate the scaling behavior for roughening and coarsening of mounds during unstable epitaxial growth. By using kinetic Monte Carlo (KMC) simulations of two lattice-gas models of crystal surfaces, we find scaling exponents that characterize roughening and coarsening at long times. Our simulation data show that these exponents have a complicated dependence on key model parameters that describe a step edge barrier and downward transport mechanisms. This behavior has not been fully described in previous works. In particular, we find that these scaling exponents vary continuously with parameters controlling the surface current. The kinetic processes of the KMC models that we employ include surface diffusion, edge diffusion, step-edge barriers, and also account for transient kinetics during deposition via downward funneling and transient mobility. Our extensive simulations make evident the salient interplay between step-edge barrier strength and transient kinetic processes.

Han KangThe White Book

most venal, which means that institutionalized corruption simply exacerbates local social inequalities. Further, the carbon offsets , hedges, and funds that reward investment in capital-intensive green industries can only be fully taken advantage of by those who already wield great financial influence. Even worse, such policies, when coupled with regulatory obligations and punitive laws, may drive small and medium enterprises out of business, resulting in concentrations of wealth, resources, and capital in financial oligopolies. Ervine points out, with almost alarming clarity, that the growth built on globalization has a foundation in unsustainable consumerism. The more we build our economies on consumption, the more we produce . It’s a Malthusian disaster, not just in terms of population, but in the logarithmic growth of greenhouse gases, climate change, and mounds of plastics. While the highgrowth industrializing economies of China and India have improved their citizens’ income prospects, they have also spurred consumption. The environmental utopians have claimed a “small is beautiful” solution by limiting consumption. However, Ervine shows the reader just how a transition from a carbon-based consumption-driven economy would spell the collapse of the world’s financial system. However, Ervine does give examples, such as Canada, Costa Rica, and Uruguay, where their economies have established transitions or pathways using renewables. The examples are encouraging, except they do not seem to work without ample alternative energy, infrastructure, and a low level of corruption. Further, successful implementation requires a central government and sufficient funds dedicated to building appropriate architecture and to enforcing energy-transitional behaviors. It’s hard to keep from envisioning a dystopian implementation of a utopian aspiration: surveillance, AI-driven monitoring, “social credit” scores, and worse. In reading Ervine’s text, it is clear we can’t transcend our narratives and their deterministic forms and predictable outcomes . Most narratives used in conjunction with carbon tend to be apocalyptic. There is also the “jeremiad,” which refers to the biblical account of Jeremiah, who urged sinners to repent before the imminent end of the world. The use of the jeremiad facilitates the rise of a charismatic leader, and with his/her emotional appeals comes the blinding of objectivity and a strong need to remain with the group of “true believers.” Other narratives that are employed with the carbon narratives tend to perpetuate cognitive bias and encourage confirmation bias and groupthink. What is masked is the fact that we still are not able to transcend our postmodernist condition of extreme skepticism about the narratives used to construct reality. The narratives used to unify will also be used to subvert. The tight emotional and intellectual control required in the continual manufacture of the dominant culture’s notion of reality contains embedded narratives of resistance and subversion. This is the carbon narrative in operation. Perhaps that is why Ervine’s final section on pathways toward a sustainable future and her statement that “the collective is essential to democratic ecologies” makes one wish she had described the kinds of political structures and incentives needed. Our current institutions have been shown to simply perpetuate or exacerbate social inequality and pollution. So, how do we arrive at a collective ability to implement “climate justice”? Ervine’s book suggests the answer is in pathways to be developed, hopefully soon. To do so, we need to rebuild carbon narratives. University of Oklahoma Susan Smith Nash earned her PhD in English at the University of Oklahoma where her dissertation examined apocalyptic narratives in literary, film, and cultural texts. She has combined her passion for creative expression with petroleum geology to develop programs that promote innovation, science, and technology. Han Kang The White Book Trans. Deborah Smith. New York. Hogarth. 2019. 160 pages. Han Kang’s The White Book is a meditation on grief using a study of white objects in the author’s life to spark memories of events she did—and did not—experience, specifically the birth and deaths of her older sister (and a quickly mentioned older brother, who also succumbed to premature birth) and their mother. The book’s focus on white originates from the little that Kang—the third child of her mother but the first to live beyond a few hours—knew of her onni...

Early Triassic Griesbachian microbial mounds in the Upper Yangtze Region, southwest China: Implications for biotic recovery from the latest Permian mass extinction

Early Triassic microbialites are distributed widely in the shallow marine facies of the Tethys Region, especially in the carbonate platform where they were deposited immediately after the latest Permian mass extinction (LPME). Ten Griesbachian domed microbial mounds were found in an outcrop of the uppermost first member of the Feixianguan (FXG) Formation at Baimiaozi, which is located in Beibei in the Upper Yangtze Region of southwest China. Field investigations and thin-sections analyses indicated that oolitic limestone, bioclastic limestone, microbialite, marl, and mudstone deposits are present in the first and second members of the FXG Formation, among which the thickness of the microbial mound above the massive oolitic limestone at the carbonate platform was approximately 3–4 m. Three facies were identified at the microbial mounds, namely, a mound base, mound body, and mound cap. Irregular laminae were found in the brown-colored microbialite of the mound base. The main mound body, which is composed of gray microbialite, is 1.0–1.5 m high and 2.0–3.0 m in diameter at the base. Dark gray grainstone found in the mound cap is covered by a thin layer of shelly limestone containing intact fossils of bivalves and gastropods, which are indicative of a simple ecosystem consisting of microbes and primary consumers. Brown-colored mudstone and marl layers of the second member of the FXG Formation overlie the microbialite, and this indicates that growth of the microbial mounds was halted by a sudden increase of terrestrial inputs and rapid transgression. Early Griesbachian conodonts of Hindeodus parvus? were identified from the mound limestone and the overlying strata of the second member of the FXG Formation, which is suggestive of the presence of a microbialite-dominated ocean in the Upper Yangtze Region during a certain interval after the LPME.

Temperature control of cold-water coral (Lophelia) mound growth by climate-cycle forcing, Northeast Gulf of Mexico

Chronostratigraphy, of a northern Gulf of Mexico Lophelia pertusa (cold-water coral) mound (Roberts Reef), indicated that mound development included periods of growth and non-growth that are closely tied to Late Pleistocene climate cycles. U/Th and 14C dating of coral fragments in two ~ 16 m cores (mound crest and mound flank) and foraminiferal biostratigraphy provided a stratigraphic framework that identified five mound-growth sequences separated by four hiatuses, a total of ~ 300 ka. Mound growth occurred during interglacials while non-growth and unconformity formation correlates to glacial periods. In each cycle, growth on the mound flank persisted after growth at the crest ceased.Results of our study suggest warming bottom-water as the most probable environmental condition for limiting L. pertusa growth and mound accretion as sea level fell toward a glacial maximum. At highstands of sea level, the mound resided in the Oxygen Minimum Layer with a present temperature range of ~ 9.0–12.8 °C. During falling-to-lowstands of sea level, isotherms of warm, Subtropical Underwater (~ 12.8–21 °C) progressively exposed the mound to water above the thermal range for L. pertusa.A comparison of non-growth periods in the mound cores indicates that coral mortality and suppression of mound growth started at the crest and moved down the flank, a trend that supports progressive immersion of the mound in warm Subtropical Underwater. Multiday episodes of vertical down-mixing may have also transported warm ocean water, above the tolerance level of Lophelia, to the mound.Present average bottom-water temperatures at the mound crest range between 9 and 10.5 °C, ideal for L. pertusa growth in the Gulf of Mexico. Experimental work indicates that relatively short periods (weeks) of L. pertusa exposure to water of ~ 12–14 °C results in mortality. At periods of lowered sea level, the mound is projected to have been immersed in ocean water of ~ 12–14 °C for millennial scale time periods.

Morphology and shallow structure of seafloor mounds in the Canary Basin (Eastern Central Atlantic Ocean)

The increasing volume of high-resolution multibeam bathymetry data collected along continental margins and adjacent deep seafloor regions is providing further opportunities to study new morphological seafloor features in deep water environments. In this paper, seafloor mounds have been imaged in detail with multibeam echosounders and parametric sub-bottom profilers in the deep central area of the Canary Basin (~350–550 km west off El Hierro Island) between 4800 and 5200 mbsl. These features have circular to elongated shapes with heights of 10 to 250 m, diameters of 2–24 km and with flank slopes of 2–50°. Based on their morphological features and the subsurface structures these mounds have been classified into five different types of mounds that follow a linear correlation between height and slope but not between height and size. The first, second (Subgroup A), and third mound-types show heights lower than 80 m and maximum slopes of 35° with extension ranging from 2 to 400 km2 and correspond to domes formed at the surface created by intrusions located at depth that have not outcropped yet. The second (Subgroup B), fourth, and fifth mound-types show higher heights up to 250 m high, maximum slopes of 47° and sizes between 10 and 20 km2 and are related to the expulsion of hot and hydrothermal fluids and/or volcanics from extrusive deep-seated systems. Based on the constraints on their morphological and structural analyses, we suggest that morphostructural types of mounds are intimately linked to a specific origin that leaves its footprint in the morphology of the mounds. We propose a growth model for the five morphostructural types of mounds where different intrusive and extrusive phenomena represent the dominant mechanisms for mound growth evolution. These structures are also affected by tectonics (bulge-like structures clearly deformed by faulting) and mass movements (slide scars and mass transport deposits). In this work, we report how intrusive and extrusive processes may affect the seafloor morphology, identifying a new type of geomorphological feature as ‘intrusive’ domes that have, to date, only been reported in fossil environments but might extend to other oceanic areas.

A novel population of composite mounds: their initiation, growth and demise. San Emiliano Formation, Cantabrian Mountains, Spain

PurposeMounds from the Pennsylvanian aged San Emiliano Formation (Cantabrian Mountains, Spain) are commonly well exposed. These mounds range from 2 to 50 m in height and are observed to be primary geological features. The mounds are described and classified and the factors and controls of mound nucleation, growth and demise have been established.MethodsMicrofacies analysis of 177 thin sections has revealed the composition of the mounds and surrounding carbonates.ResultsComposite mounds, exhibiting characteristic components of both Cluster mounds and Agglutinated Microbial mounds are described. The mounds are skeletal-microbial/pack-wackestones. Peloidal, homogenous and clotted micrites are the main sedimentological constituents of the mounds. Microfossils are dominant with Donezella, Claracrusta, Rothpletzella and Girvanella being common. Small foraminifera, bryozoans, corals and algae are all present within the mounds, but are more common within off-mound carbonates.ConclusionsThe formation of the mounds was controlled by a dynamic relationship between Donezellacean algae, and microscopic encrusters, a bio-mechanism not observed in mud mounds elsewhere. Fluctuating environmental conditions lead to the alternate dominance between the two groups, resulting in accretion and stabilisation of carbonate muds. These mounds are compositionally different to their Pennsylvanian counterparts.