Marine carbonate sedimentation in volcanic settings

Carbonate sediments have been produced and deposited in areas of active volcanism since, at least, the Paleoarchean. Despite early recognition of a significant relationship between volcanism and marine carbonate systems, research in this field has been largely neglected. With increasing recognition of the accelerating effects and significance of anthropogenically-driven climate change on the ocean-atmosphere system, the time is ripe for studying volcanism-influenced carbonates as a natural analogue for future environmental scenarios. We undertake a detailed assessment of the state-of-the-science in our understanding of these systems. We identify significant bilateral division in approaches, with the geological and biological communities rarely interacting. The study of ancient volcanic-carbonate systems, in particular, appears to have ‘fallen-between-two-stools’ with both the volcanic and sedimentological communities shying away from studying these cross-disciplinary systems. Observations of recent volcanic-carbonate interactions are challenging, long periods of volcanic quiescence are punctuated by brief episodes of activity. Recent developments in robust remotely deployable instrumentation offer an opportunity to safely undertake sustained monitoring of these systems before, during and after eruptions. Informed assessment of the likely responses of carbonate ecosystems to future climatic challenges requires the initiation of an integrated, collaborative, cross-disciplinary approach to studying the complex interactions within these challenging mixed depositional systems.

Carbonate fabric diversity and environmental heterogeneity in the late Mesoproterozoic Era

Time-distinctive features within carbonate rocks, specifically the presence, abundance and distribution of stromatolites, molar-tooth fabric and specific morphologies of marine cement, have been identified as potential indicators of global-scale changes in the chemistry of marine environments. Recently, Cantine et al. (2019) introduced a database approach seeking to quantify spatial and temporal patterns in these carbonate features through the Precambrian. Despite the coarse temporal scale, results support earlier inferences of temporal change in carbonate sedimentation. Here, we use original field notes to dissect late Mesoproterozoic (˜1.3 to 1.0 Ga) carbonate strata at a high resolution, analyse time-distinctive carbonate fabrics within a database context and compare sedimentological patterns within this narrow time range to observations of the Proterozoic as a whole. Late Mesoproterozoic strata contain a variety of features (e.g. stromatolites, seafloor precipitates, herringbone carbonate, molar-tooth carbonate), often in close spatial and temporal proximity, that are commonly considered to be temporally restricted during the Precambrian. The spatial distribution of such features within Mesoproterozoic basins demonstrates the importance of recognizing even rare occurrences of time-distinctive facies and permits inference of environmental drivers that may have interacted to affect carbonate precipitation. Such spatial variability reflects a subtle division of Mesoproterozoic carbonate platform environments driven by globally high sea level, elevated carbonate saturation and a low-oxygen water column. The heterogeneous, mosaic nature of environments appears to be a hallmark of Mesoproterozoic carbonate sedimentation and emphasizes the importance of these basins in understanding longer-term trends in carbonate deposition.

Benthic Foraminiferal Assemblages and Rhodolith Facies Evolution in Post-LGM Sediments from the Pontine Archipelago Shelf (Central Tyrrhenian Sea, Italy)

The seabed of the Pontine Archipelago (Tyrrhenian Sea) insular shelf is peculiar as it is characterized by a mixed siliciclastic–carbonate sedimentation. In order to reconstruct the Late Quaternary paleoenvironmental evolution of the Pontine Archipelago, this study investigates the succession of facies recorded by two sediment cores. For this purpose, benthic foraminifera and rhodoliths assemblages were considered. The two cores (post-Last Glacial Maximum in age) were collected at 60 (CS1) and 122 m (Caro1) depth on the insular shelf off Ponza Island. The paleontological data were compared with seismo-stratigraphic and lithological evidence. The cores show a deepening succession, with a transition from a basal rhodolith-rich biodetritic coarse sand to the surface coralline-barren silty sand. This transition is more evident along core Caro1 (from the bottom to the top), collected at a deeper water depth than CS1. In support of this evidence, along Caro1 was recorded a fairly constant increase in the amount of planktonic foraminiferal and a marked change in benthic foraminiferal assemblages (from Asterigerinata mamilla and Lobatula lobatula assemblage to Cassidulina carinata assemblage). Interestingly, the dating of the Caro1 bottom allowed us to extend to more than 13,000 years BP the rhodolith record in the Pontine Archipelago, indicating the possible presence of an active carbonate factory at that time.

Geomorphology and Neotectonics of Southwestern Crimea

—The area of southwestern Crimea includes the ending of the Crimean Mountains that arose during the neotectonic activation at the place of the Cretaceous–Paleogene denudation plain and the adjacent shallow-water carbonate sedimentation basin. The Crimean Mountains are one of the links of the Alpine–Himalayan orogenic belt formed during the collision of the Eurasian, African, and Indo–Australian plates. Their area includes late Cenozoic marine terraces of the complete Mediterranean series and a staircase of Neogene, Paleogene and Cretaceous planation surfaces over them. The planation surfaces of different ages resulted from the successive lowering of the World Ocean level. Their subsequent deformations make it possible to outline the area of the neotectonic uplifting and determine its parameters. The main mechanism of the neotectonic activation was the thrust of the East Black Sea microplate under the Scythian one and the formation of a ramp fold structure. The amplitude of the neotectonic uplifting of southwestern Crimea for the past 2 Myr varies from 0 to 800 m, i.e., is up to 0.04 mm/year. The recent neotectonic structure of the area is formed by the northern flank of the ramp fold; it is a monocline of NW dip consisting of “keys” of NW strike separated by the latest faults with vertical displacements of 10 to 120 m. The uplifting of the area and the lowering of the World Ocean level led to a widespread of denudation surfaces. Their good preservation makes it possible to refine the sequence of neotectonic events, whose first pulses reached the study area in the Oligocene, and the main activation phase began in the Pliocene.

Hardground, gap and thin black shale: spatial heterogeneity of arrested carbonate sedimentation during the Jenkyns Event (T-OAE) in a Tethyan pelagic basin (Gerecse Mts, Hungary)

The Jenkyns Event or Toarcian Oceanic Anoxic Event (T-OAE) was an episode of severe environmental perturbations reflected in carbon isotope and other geochemical anomalies. Although well studied in the epicontinental basins in NW Europe, its effects are less understood in open marine environments. Here we present new geochemical (carbon isotope, CaCO3, [Mn]) and nannofossil biostratigraphic data from the Tölgyhát and Kisgerecse sections in the Gerecse Hills (Hungary). These sections record pelagic carbonate sedimentation near the margin of the Tethys Ocean. A negative carbon isotope excursion of ∼6‰ is observed in the Tölgyhát section, in a condensed clay and black shale layer where the CaCO3 content drops in association with the Jenkyns Event. At Kisgerecse, bio- and chemostratigraphic data suggest a gap in the lower Toarcian. The presence of an uppermost Pliensbachian hardground, absence of the lowermost Toarcian Tenuicostatum ammonite zone, and the condensed record of the Jenkyns Event at Tölgyhát, together with a condensed Tenuicostatum Zone and the missing negative carbon isotope anomaly at Kisgerecse implies arrested carbonate sedimentation. A calcification crisis and sea-level rise together led to a decrease in carbonate production and terrigenous input, suggesting that volcanogenic CO2-driven global warming may have been their common cause.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5355342

Mixed siliciclastic-carbonate sedimentation on the Miocene Pearl River continental shelf, northeastern South China Sea: Implications for exploring lithologic traps

During the Miocene, when the Zhujiang Formation was deposited, the eastern part of the Pearl River Mouth Basin, northern South China Sea, underwent intense mixed siliciclastic and carbonate sedimentation, particularly on the platform of the marginal ramp of the Dongsha Rise, northeastern margin of the South China Sea. Cores and well logs from industrial boreholes were collected and systematically investigated to reveal the sedimentary-petrographic characteristics of the mixed deposits and their formative processes. Four lithotypes were differentiated in the deposits, that is, (1) sandstone, (2) dolomitic sandstone and calcitic sandstone, (3) sandy dolomite and sandy limestone, and (4) dolomite, bioclastic limestone, and micrite limestone, which were formed by three major types of mixing processes: punctuated, facies, and in situ mixing processes. The porosity and permeability of the mixed deposits indicated that the siliciclastic component of the mixed deposits that experienced punctuated mixing formed the most high-quality hydrocarbon reservoirs. Exploration revealed that the lithologic reserves in the study area were mainly developed in mixed sedimentation areas. Our results suggest that the mixed sedimentation area, particularly with pure sandstone sedimentation or bioclastic sandstone, that underwent compaction or structural fracture activities, may be the next preference for lithologic exploration.

Shallow deformation kinematic history, a new insight from carbonates U-Pb direct dating by LA-ICP-MS imaging technique.

<p>This project aims to refine direct dating of carbonates by the U-Pb system, using a new LA-ICP-MS imaging technique that incorporates complementary element and textural analysis information. The direct dating of carbonates in deep time has been considered desirable for decades (e.g. Jahn and Cuvellier, 1994) given their ubiquity in the Earth system, and carbonates are a key phase for dating geological processes such as brittle-ductile deformation in carbonate successions. This new method facilitates detailed (on the scale of tens of microns) mapping of U-Pb isotope and element distributions (cf Drost et al., 2018), and is here applied to carbonate vein dating to constrain local and regional histories of deformation or fluid activity.</p><p>In this presentation we focus on a sample from the Carboniferous North Dublin Basin, Ireland. The basin has been affected by deformation that led to tight chevron folds and kinematically-linked dextral en-echelon vein sets. Additionally bedding-parallel veins and  slickenfibres are common. The deformation has been conventionally assumed to be of Variscan age, and some Variscan U-Pb ages are recorded in this study. However many calcites analysed yield late Eocene ages, a deformation phase that is hitherto undetected on the Irish mainland. Our data indicate repeated fault slip over a peroid of at least c. 4 my during late Eocene times and, thus, demonstrate the ability of the LA-ICP-MS imaging approach to not only unravel complex polyphase deformation histories in carbonates but also to resolve processes on fine temporal and spatial scales.</p><p> </p><p> </p><p>DROST, K., CHEW, D., PETRUS, J. A., SCHOLZE, F., WOODHEAD, J. D., SCHNEIDER, J. W. & HARPER, D. A. T. 2018. An Image Mapping Approach to U-Pb LA-ICP-MS Carbonate Dating and Applications to Direct Dating of Carbonate Sedimentation. Geochemistry, Geophysics, Geosystems, 19<strong>,</strong> 4631-4648.</p><p>JAHN, B.-M. & CUVELLIER, H. 1994. Pb-Pb and U-Pb geochronology of carbonate rocks: an assessment. Chemical Geology, 115<strong>,</strong> 125-151.</p>

Lithium carbonate sedimentation using flocculants with different ionic bases

Lithium has become a metal of enormous interest worldwide. The extensive use of rechargeable batteries for a range of applications has pushed for rapid growth in demand for lithium carbonate. This compound is produced by crystallization, by reaction with lithium chloride (in solution) and by adding sodium carbonate. Low sedimentation rates in the evaporation pools present a problem in the crystallization process. For this reason, in this work, mineral sedimentation tests were carried out with the use of two flocculant types with different ionic charges. The tests were carried out at a laboratory level using different dosages for each flocculant and measurements were performed to obtain the increase in the content of solids in the sediment. The anionic flocculant had better performance as compared to that of the cationic flocculant, increasing the sedimentation rate of lithium carbonate by up to 6.5. However, similar solids contents were obtained with the use of the cationic flocculant at 3.5 times lower dosage making it the flocculant of choice regarding the economic point of view.