Marine Geology最新文献

Tropical storm Pabuk (4th January 2019) struck southern Thailand, causing damage to the low-lying coastal area. The combination of waves, storm surge, and high tide resulted overwash and inundation of regions on the West coast of the Gulf of Thailand (GOT) side. After the event, we conducted a field survey from January 7–10 and 15–20, 2019 to investigate the effect of storm surges and the degree of damage from the site under the eye of storm affected area up to the north 500 km from the landfall sites. This paper investigates how variations in coastal geomorphological features respond to the storm surge generated by tropical storm Pabuk at a regional scale. Coastal damage was observed along the beach from the presence of the scour, beach scarp, knocked down trees, and destroyed buildings and infrastructure. The most damaged area was at Nakhon Si Thammarat (NST), where the tropical storm made landfall with maximum wind speeds of almost 100 km/h and a storm surge height of 5 m. At NST site, the washover deposits extended as far as 80 m from the coastline with a maximum inundation of 330 m. From this study, two types of washover deposits including perched fan and washover terrace were identified. The thickest washover sediment, 60 cm thick, was discovered in a relatively low-lying area adjacent to a small estuary. Mud rip-up clasts, planar stratification, cross stratification, foreset bedding, scouring at base, and sharp and erosional contact are characteristics of sedimentary structures found in storm sediments. Bedform surfaces, such as current ripples with indicated storm surge direction, were well-preserved at several sites. We suggest that the local geomorphological controlling factors, especially coastal elevation have played important roles in the difference of coastal geomorphological responses as well as the type of washover deposits.

Organic carbon (OC) burial in river-dominated ocean margins plays a pivotal role in the global carbon cycle, impacting atmospheric CO₂ levels over the long term. Despite its significance, uncertainties persist regarding the influence of external environmental factors and intrinsic properties on sedimentary OC. In this study, we conducted a comprehensive analysis of surface sediments from the East China Sea, examining geochemical properties (including total OC content [TOC], Δ¹⁴C, δ¹³C, and C/N ratio), terrestrial biomarkers (n-alkanes), and mineral properties (such as specific surface area, Al/Si ratio, and mineral composition). Our aim was to shed light on the fate of sedimentary OC.

The surface sediment's Δ¹⁴C values displayed significant spatial heterogeneity, delineating four distinct sub-regions. Strong positive correlations (all p < 0.01) were found between the ∆¹⁴C values and fine-grained sediments, specific surface area, and clay minerals, suggesting the potentially pivotal role of mineral protection in shaping the fate of sedimentary OC. The proportion of terrestrial OC gradually decreased towards the south, while marine OC proportion increased, corresponding to the enrichment of Δ¹⁴C. The co-variation of Δ¹⁴C values, mineral properties, and OC source proportions suggests that terrestrial OC may undergo progressive replacement by marine OC during southward transport. Temporal variations in ∆¹⁴C values indicated that seabed erosion led to a significant increase in ∆¹⁴C values (p < 0.01) in the coastal mud belt, a phenomenon likely common in river-dominated ocean margins globally due to the new sediment cycle during the Anthropocene.

Atolls in the South China Sea comprise 15% of the world's total in area. In contrast to most reef flats in the Indo-Pacific region, which typically develop up to contemporary sea level, a significant portion of their reef flats in the South China Sea are inundated at depths of 5–20 m. To gain insights into modern processes and determine whether these subtidal reef flats are actively shaped by hydrodynamics, we carried out an in situ observation on a 12 m-deep southwest-facing reef flat over a period of 8 months. The measurements revealed a prevalence of seasonally varying waves and stable tidal currents. While the reef flat remained sheltered from the northeast monsoon (January–May), the southwest monsoon (June–September) led to prolonged reef exposure to substantial waves (mean significant wave height of 1.3 m, with an orbital velocity of 0.22 m/s on average). Such an exposure resulted in the formation of mobile bed ripples and entrainment of coarse-grained coral sands. Estimates of potential bedload transport rate indicated that the combined action of waves and currents caused material loss from the reef flat, with movement into the lagoon or down the fore-reef slope of the atoll. This sediment loss was equivalent to reef bed erosion of up to 28 mm during the observation period. As these potential losses may be compensated by coral reef growth, our measurements implied that modern sediment budgeting has played a significant role in the maintenance of subtidal reef flats, in terms of bed elevation. Hence, the deep reef flat does not necessarily belong to the previously identified give-up pattern; a balance of coral sediment supply and transport-induced loss may result in an equilibrium morphology, or a “lock-up” pattern.

High-resolution multibeam data integrated with seismic reflection profiles are used to identify and characterize the main primary volcanic and erosive-depositional features along the submarine part (about the 80%) of the active Pantelleria volcano located in the Sicily Channel. Volcanic features include lava flows, cones and elongated ridges. Lava flows are mainly recognized over the insular shelf, while volcanic cones and ridges are mostly concentrated along the steep submarine flanks, especially along the wider SE and NW ones. A strong volcano-tectonic interaction is envisaged for their formation, as indicated by their preferential elongation or alignment along the (main) SE-NW and (secondary) SW-NE directions that have controlled the evolution of the whole volcanic edifice. Erosive-depositional features mainly include small-scale landslide scars and narrow gullies affecting the edge of the insular shelf and overlying submarine depositional terraces. Gullies sometimes merge downslope in larger channels, whose formation is primarily controlled by the distribution of volcanic features and/or shelf sectors characterized by different age or lithologies. Based on the marked morphological differences between the different flanks of the Pantelleria volcano, we infer an overall migration of the volcanic activity from SE to NW over time. This migration is apparently in contrast with the presence of a much wider but shallower NW insular shelf with respect to the SE one. This anomaly can be explained through a two-stage model, with the formation, in the NW sector, of a polygenic shelf rejuvenated by volcanic progradation during the last eustatic hemicycle. The different depths of the insular shelf edge around the island also provide insights on vertical deformations that affected the Pantelleria volcano during the Late-Quaternary.

Cerium (Ce) anomalies can be used to distinguish diagenetic and hydrogenetic nodules, making them an important discriminator for the genesis of marine ferromanganese nodules. To understand the enrichment and adsorption mechanisms of Ce in different types of ferromanganese nodules, we conducted mineralogical and geochemical studies on ferromanganese nodule layers formed through both hydrogenetic and early diagenetic processes as well as adsorption experiments on synthetic δ-MnO₂ to monitor the Ce uptake during the different processes. The major and trace element contents of natural ferromanganese nodule layers were investigated by SEM, EPMA and LA-ICP-MS analysis. The marine nodule studied in this study consisted of a core of fish tooth and a rim that could be divided into the hydrogenetic (type I) and early diagenetic (type II) layers based on their mineralogy and Mn/Fe ratios. The Mn oxide mineral assemblage is composed of todorokite, buserite, birnessite, and vernadite (δ-MnO₂) and occurred in both type I and II layers. The type I layer has laminated structures with a low Mn/Fe ratio (1.1–3.2; averaging at 1.7), and low Cu, Ni and Mg contents consistent with a hydrogenetic genesis. The type II layer has a columnar and stromatolitic structure with a high Mn/Fe ratio (5.1–54.0; averaging at 23.3) and high Cu, Ni and Mg contents that are similar to early diagenetic nodules. The ΣREE contents in type I and type II layers are 1405–3506 ppm (averaging at 2091 ppm) and 199–1232 ppm (averaging at 674 ppm), respectively, indicating that the REE is enriched in the hydrogenetic type I layers. Strong positive Ce anomalies are present type I layers ranging from 1.2 to 2.5 (averaging 1.9), but only slightly positive are seen in type II ranging from 0.4 to 2.4 (averaging at 1.0). Synthetic experiments to monitor the Ce uptake process show that Ce can be adsorbed onto δ-MnO₂ with the XRD and FTIR patterns suggesting that the structure of δ-MnO₂ did not change significantly, consistent with Ce behavior in hydrogenetic nodules. The results suggest that Ce is predominantly concentrated in hydrogenetic nodules in an oxic environment, whereas in the early diagenetic layer, there is less oxidation and fixation of Ce due to the suboxic conditions. Our findings are consistent with Ce anomalies in marine Fe-Mn nodules being the result of Mn oxide oxidation adsorption and then fixation (oxidation) after adsorption.

Sediment waves are subaqueous sedimentary figures belonging to the supercritical flow domain and are of growing interest to the scientific community and industry. They are ubiquitously observed on the seafloor of world's oceans, as well as in the stratigraphic record imaged by marine seismic datasets. In this study we focus on the Cenozoic strata offshore Ivory Coast, where giant sediment waves developed at the base of slope range in height and wavelength: 10–100 m and 1–6 km, respectively. Sediment waves fields in this study developed simultaneously and adjacent to wide, rectilinear valleys, filled by mass-transport deposits. Thus, sediment waves serve as a rare example of large-scale deep-water cyclic steps formed through phase transformation (water entrainment and dilution) of laminar debris flows.

The lithological nature of sediment waves can be estimated through the observation of polygonal faulting affecting the sediment waves fields, which suggest a dominant abundance of fine-grained material (clay and silt-prone). This study also shows that wide submarine valleys flanked by sediment waves do not necessarily correspond to sand-prone depositional systems, and that their potential to hold reservoir units for hydrocarbon exploration or CO₂ storage should be evaluated with caution when in lower resolution datasets are used.

The Arabian Sea significantly impacts the global climate due to its hosting of one of the largest sedimentary bodies in the Modern Ocean basin and thickest oxygen minimum zone. It makes the study of fine-scale evolutionary changes in the Arabian Sea imperative to address the ongoing challenges in developing a strong and cohesive model for predicting rapid climate change in the future. Therefore, this study carried out environmental magnetic, grain size, stable isotope, total organic carbon (TOC), trace elements (TE), and rare earth elements (REE) investigations on a well-dated 2.68 m long sediment core from the eastern Arabian Sea to understand the fluctuation in monsoon and non-monsoon-driven sediment supply and associated primary productivity changes during the late Quaternary. The careful observations of chronological changes in the investigated parameters concerning coeval major global events enabled us to successfully identify the response of major global climatic events that occurred around 42.8–28 ka, 17 ka, 14.5 ka, 11.7 ka, 9.7 ka, 8.2 ka, 4.6–3.9, and 2–0.6 ka. These global events also played a crucial role in co-regulating the water column oxygen conditions in the Arabian Sea. Comparing our record with a sedimentary record from off Chennai, Bay of Bengal, suggests that opposite variations (anti-phasing) between southwest (SW) monsoon and northeast (NE) monsoon is a post-25 ka phenomenon. Pre-25 ka SW and NE monsoon showed similar variations (same phase), and we speculate that this anti-phasing between the SW and NE monsoon was cyclically driven by the earth's axial precession cycle.

Grain-size end-member (EM) modelling is a robust statistical approach for identifying and quantifying dominant grain-size distributions. This approach provides a novel perspective for understanding the impact of interactions between depositional processes in complex sedimentary environments. This study examines grain-size distributions of six glacimarine sediment cores collected along an NS transect from the continental shelf to the Wijdefjorden system in northern Svalbard. In addition, we integrate grain-size EMs with lithologic and acoustic facies, allowing us to identify three distinct groups of EMs (EM1–3), each closely associated with specific depositional processes: turbid meltwater discharge (EM1), sediment winnowing by bottom currents (EM2), and the deposition of ice-rafted debris in glacimarine conditions and subglacial till (EM3). An analysis of the three EM groups reveals that the glacial retreat during the last deglaciation and the Atlantic Water inflow significantly impacted depositional changes within the Wijdefjorden system. In contrast, a decrease in the Atlantic Water inflow during the late Holocene corresponds to glacial re-advance, resulting in shifts in the depositional environment. This study demonstrates the utility of EM modelling in deciphering complex grain-size distributions and reconstructing different climate-driven depositional processes in glacimarine sediments in Svalbard fjords. This integrated approach enhances our understanding of the intricate interplay among climate change, glacier dynamics, and oceanic forcing in polar fjord environments.

The sedimentary record of the western South African continental shelf is condensed compared to the continental slope and contains erosional unconformities, owing to periods of non-deposition, eustatic sea-level fluctuations, episodic uplift and intensified continental aridity. Despite this, the sedimentary record of the continental shelf provides important information on the depositional history and palaeoenvironmental evolution of the region. A core retrieved from the western shelf of South Africa was analysed for its sedimentary composition, lithological variation, foraminiferal content and its relation to the palaeoenvironment of the region. Four depositional facies were identified along the core, namely quartzitic sand, sandy mud, and glauco-phosphatic sand and a glauco-phosphatic gravel. The basal facies consisting of quartzitic sand is interpreted to have been deposited between 15.90 and 14.60 Ma, corresponding to the timing of the Mid-Miocene Climatic Optimum (MMCO). The highly quartzitic nature of the sediments indicate a high terrestrial influence from fluvial sources. The overlying sandy mud facies was deposited between 14.60 and 13.90 Ma based on planktic foraminiferal biostratigraphy. Foraminiferal analyses of these two facies that were deposited in the Langhian stage of the middle Miocene point to subtropical sea surface conditions and mesotrophic benthic environments. Sea level was noticeably higher during the MMCO and part of the cooling period following the MMCO. An erosional surface that spans 10.77 Myr, equal to the late Miocene (13.90 Ma) to early Pliocene (3.13 Ma), marks the boundary between the two Langhian facies and the overlying two Pleistocene facies, consisting of coarser grained glauco-phosphatic gravelly sand units. The Pleistocene environment on the shelf is interpreted to contrast with the Langhian environment, where cooler, shallower conditions and a more eutrophic benthic environment was prevalent, during a time that Benguela upwelling intensified with higher frequency and higher amplitude sea level fluctuations. Palaeobathymetric interpretations indicate that middle Miocene sea-level in the region were up to 77 m higher than present day and 101 m lower in the Pleistocene, in-line with previous global studies. Glauco-phosphatic content that increase up-core also marks the shallowing of the environment under high productivity conditions.

Texas receives the second-highest number of tropical cyclone (TC) landfalls per year in the United States. At present, long-term TC projections from climate models remain uncertain due to the short and biased nature of Atlantic TC observations. Sediment archives of past storms can help extend the observational record of TC strikes over the past few millennia. When a TC makes landfall along the central Texas coast, coastal downwelling channels and storm currents transport and deposit coarse sediment to a zone of rapid accumulation along the shelf, known as the Texas Mud Blanket (TMB). This “backwash” process results in expansive storm deposits along the shelf, making this region ideal for paleotempestological reconstructions. Here, we present two sediment cores, located approximately 6 km southeast of Matagorda Island (TX), that collectively yield a ∼4500-year paleohurricane record. ²¹⁰Pb and ¹³⁷Cs are utilized in conjunction with radiocarbon ages to produce high-resolution Bayesian age models. One-centimeter interval grain size analyses are used to identify TC deposits. Two-centimeter interval X-Ray Fluorescence (XRF) is used as an additional measure to verify depositional mechanisms in this shelf environment. We define an intense paleohurricane event threshold through statistical analysis of mean grain size data. The sediment-derived TC record is correlated to Palmer Drought Severity Index (PDSI) data from Paleo Hydrodynamics Data Assimilation (PHYDA) to bolster our interpretation of the TC record, revealing a coupled relationship between PDSI and TCs since ∼300 yr BP. Over the ∼4500-year period, 24 intense TCs were recorded in the sediment record, yielding a long-term annual landfall probability of ∼0.53%. Additionally, comparisons between other TC records within the Atlantic establish a relationship between enhanced TC activity in the Western Gulf of Mexico (GOM) and TCs formed in the Caribbean Sea.