Common-offset common-reflection-surface attributes estimation with differential evolution

Common-reflection surface is a method to describe the shape of seismic events, typically the slopes (dip) and curvature portions (traveltime). The most systematic approach to estimate the common-reflection surface traveltime attributes is to employ a sequence of single-variable search procedures, inheriting the advantage of a low computational cost, but also the disadvantage of a poor estimation quality. A search strategy where the common-reflection surface attributes are globally estimated in a single stage may yield more accurate estimates. In this paper, we propose to use the bio-inspired global optimization algorithm differential evolution to estimate all the two-dimensional common-offset common-reflection surface attributes simultaneously. The differential evolution algorithm can provide accurate estimates for the common-reflection surface traveltime attributes, with the benefit of having a small set of input parameters to be configured. We apply the differential evolution algorithm to estimate the two-dimensional common-reflection surface attributes in the synthetic Marmousi data set, contaminated by noise, and in a land field data with a small fold. By analysing the stacked and coherence sections, we could see that the differential evolution based common-offset common-reflection surface approach presented significant signal-to-noise ratio enhancement.     

Uncovering unnoticed small-scale tsunamis: field survey in Lombok,Indonesia, following the 2018 earthquakes

Natural Hazards - In 2018, Lombok island, Indonesia, was hit by a series of destructive earthquakes that caused thousands of casualties and widespread material damage. In response to those events,...     

Controls on Early Cretaceous desert sediment provenance in south-west Gondwana,Botucatu Formation (Brazil and Uruguay)

The Lower Cretaceous Botucatu Formation records the development of widespread dry–aeolian desert sedimentation throughout the Paraná Basin in south-west Gondwana. To reconstruct the provenance of the aeolian sediment, petrography, granulometric analysis, U-Pb detrital zircon ages have been determined from along the southern basin margin in Rio Grande do Sul state (southern Brazil) and Uruguay (Tacuarembó region). The dataset reveals a mean composition Qt₈₉F₈L₃, comprising very fine to medium-grained quartozose and feldspatho-quartzose framework. Heavy mineral analysis reveals an overall dominance of zircon, tourmaline and rutile grains (mean ZTR_0.84) with sporadic garnet, epidote and pyrolusite occurrences. The detrital zircon U-Pb ages are dominated by Cambrian to Neoproterozoic (515 to 650 Ma), Tonian to Stenian (900 to 1250 Ma) and Orosirian to Rhyacian (1.8 to 2.2 Ga) material. The detrital zircon dataset demonstrates a significant lateral variation in sediment provenance: Cambrian to Neoproterozoic detrital zircons dominate in the east, while Tonian to Stenian and Orosirian to Rhyacian ages predominate in the west of the study area. Sandstones are quartz-rich with dominantly durable zircon, tourmaline and rutile heavy mineral suite, with subtle but statistically significant along-strike differences in heavy mineral populations and detrital mineralogy which are thought to record local sediment input points into the aeolian system. The similar age spectra of Botucatu desert with proximal Paraná Basin units, the predominance of quartzose, and zircon, tourmaline and rutile components, suggests that recycling is the mechanism responsible for the erg feeding.     

New insights from low-temperature thermochronology into the tectonic and geomorphologic evolution of the south-eastern Brazilian highlands and passive margin

The South Atlantic passive margin along the south-eastern Brazilian highlands exhibits a complex landscape,including a northern inselberg area and a southern elevated plateau,separated by the Doce River valley.This landscape is set on the Proterozoic to early Paleozoic rocks of the region that once was the hot core of the Aracuai orogen,in Ediacaran to Ordovician times.Due to the break-up of Gondwana and consequently the opening of the South Atlantic during the Early Cretaceous,those rocks of the Araquai orogen became the basement of a portion of the South Atlantic passive margin and related southeastern Brazilian highlands.Our goal is to provide a new set of constraints on the thermo-tectonic history of this portion of the south-eastern Brazilian margin and related surface processes,and to provide a hypothesis on the geodynamic context since break-up.To this end,we combine the apatite fission track(AFT)and apatite(U-Th)/He(AHe)methods as input for inverse thermal history modelling.All our AFT and AHe central ages are Late Cretaceous to early Paleogene.The AFT ages vary between 62 Ma and90 Ma,with mean track lengths between 12.2μm and 13.6μm.AHe ages are found to be equivalent to AFT ages within uncertainty,albeit with the former exhibiting a lesser degree of confidence.We relate this Late Cretaceous-Paleocene basement cooling to uplift with accelerated denudation at this time.Spatial variation of the denudation time can be linked to differential reactivation of the Precambrian structural network and differential erosion due to a complex interplay with the drainage system.We argue that posterior large-scale sedimentation in the offshore basins may be a result of flexural isostasy combined with an expansion of the drainage network.We put forward the combined compression of the Mid-Atlantic ridge and the Peruvian phase of the Andean orogeny,potentially augmented through the thermal weakening of the lower crust by the Trindade thermal anomaly,as a probable cause for the uplift.     

Analysis of occurrence patterns and biological factors of cetaceans based on long‐term and fine‐scale data from platforms of opportunity: Madeira Island as a case study

Management and conservation issues are addressed through the identification of areas of particular importance, which requires the acquisition of baseline information on species distribution and dynamics. These types of data are particularly difficult to obtain at high resolution for large marine vertebrates like cetaceans, given that dedicated surveys are complex and logistically expensive. This study uses daily presence–absence sighting data of cetaceans collected year‐round from whale‐watching boats to support the theory that fine‐scale data obtained from platforms of opportunity can provide valuable information on species occurrence and group dynamics. Data from 7,551 (daily) sightings comprising 22 species were collected from 3,527 surveyed days over 11 years (mean of 321 days per year, SD = 17) in the pelagic environment of Madeira Island. Cetaceans were observed on 92% of the surveyed days, and a mean of 15.4 (SD = 1.5), 8.2 (SD = 2.0) and 2.1 (SD = 1.2) species were recorded per year, month, and day, respectively. There were significant differences in the number of species per month (p < .001), with the highest diversity recorded in June. At least nine species, comprising 96% of all sightings, were found to use the Madeiran waters on a regular basis, such as the Atlantic spotted dolphin (Stenella frontalis), the short‐beaked common dolphin (Delphinus delphis), the bottlenose dolphin (Tursiops truncatus), and others featured in the Red List of the International Union for Conservation of Nature as Endangered, Vulnerable, and Data Deficient. In addition, 10 species were found to use the Madeiran waters for travelling, feeding, resting, socializing and calving, which suggests that the southern and southeastern waters of Madeira Island constitute an area of interest for cetaceans. This study characterizes the cetaceans’ community structure (occurrence, aggregation sizes, behaviours, proportion of calves, and inter‐specific relationships) of a poorly studied region, providing important information for managers. Finally, the advantages and limitations of using fine‐scale data from a type of platform of opportunity that is increasing along coastlines globally are discussed.     

MTD distribution on a ‘passive’ continental margin: The Espírito Santo Basin (SE Brazil) during the Palaeogene

Mass-wasting on the Brazilian margin during the Mid-Eocene/Oligocene resulted in the accumulation of recurrent Mass Transport Deposits (MTDs) offshore Espírito Santo, SE Brazil. In this paper, we use three-dimensional seismic data to characterize a succession with stacked MTDs (Abrolhos Formation), and to assess the distribution of undeformed stratigraphic packages (i.e. turbidites) with reservoir potential separating the interpreted MTDs. High-amplitude strata in less deformed areas of MTDs reflect their internal heterogeneity, as well as possible regions with a higher sand content. Separating MTDs, turbiditic intervals reach 100 ms Two-Way Travel Time (TWTT), with thicker areas coincident with the flanks of growing diapirs and areas of the basin where mass-wasting is less apparent. Turbiditic strata laterally grade into, or are eroded by MTDs, with transitional strata between MTDs and turbidites being also influenced by the presence of diapirs. MTDs show average thickness values ranging from 58 to 82 ms TWTT and constitute over 50% of Eocene-Oligocene strata along the basin slope. Low average accumulations of 58 ms TWTT in areas of high confinement imposed by diapirs suggest sediment accumulation upslope, and/or bypass into downslope areas. This character was induced by the high sediment input into the basin associated with coastal erosion and growth of the Abrolhos volcanic plateau. Our results suggest that significant amounts of sediment derive from the northwest, and were accumulated in the middle-slope region. Interpretations of (palaeo)-slope profiles led to the establishment of a model of margin progradation by deposition of MTDs, contrasting with the retrogressive erosional margins commonly associated with these settings.     

Building adaptive capacity to climate variability: The case of artisanal fisheries in the estuary of the Patos Lagoon,Brazil

The vulnerabilities of fishing communities to climate and environmental change represent major issues for the governance of fisheries resources which have a direct effect on human security, livelihoods and rights. This paper explores the dynamics of social-ecological systems in the estuary of the Patos Lagoon in southern Brazil. The paper identifies key factors that increase and/or minimize the vulnerabilities of the fishing communities in this lagoon with the objective of understanding: (a) the degree to which fishing communities are able to build adaptive and learning capacities to minimize/reduce vulnerabilities and maintain their livelihoods; and (b) how and under what circumstances external and internal factors may influence and disrupt the social-ecological resilience in this lagoon system. Results show that fishing communities with a higher degree of self-organization are able to create ways to minimize their vulnerability to adverse climatic conditions. However, only a few communities have developed adaptive mechanisms to cope with the influence of climate on resource abundance and availability. Little external institutional support for small-scale fishing communities, erosion of their traditional resource use systems and decreasing fish stocks in recent decades have all led to a gradual increase in the vulnerability of fishing livelihoods in this lagoon. The uncertainties associated with climate are related to increasing vulnerability and influence the degree of resource conservation and exploitation. The lack of public policies to deal with the impact of climate variability on the livelihoods of fishing communities and the presence of weak institutions in resource governance represent major threats to the social security of fishers in this region.     

Quasi-Saturated Layer: Implications for Estimating Recharge and Groundwater Modeling

This study presents an extension of the concept of “quasi-saturation” to a quasi-saturated layer, defined as the uppermost dynamic portion of the saturated zone subject to water table fluctuations. Entrapped air here may cause substantial reductions in the hydraulic conductivity (K) and fillable pore water. Air entrapment is caused by a rising water table, usually as a result of groundwater recharge. The most significant effects of entrapped air are recharge overestimation based on methods that use specific yield (S_y), such as the water table fluctuation method (WTF), and reductions in K values. These effects impact estimation of fluid flow velocities and contaminant migration rates in groundwater. In order to quantify actual groundwater recharge rates and the effects of entrapped air, numerical simulations with the FEFLOW (Version 7.0) groundwater flow model were carried out using a quasi-saturated layer for a pilot area in Rio Claro, Brazil. The calculated recharge rate represented 16% of the average precipitation over an 8-year period, approximately half of estimates using the WTF method. Air entrapment amounted to a fillable porosity of 0.07, significant lower that the value of 0.17 obtained experimentally for S_y. Numerical results showed that the entrapped air volume in the quasi-saturated layer can be very significant (0.58 of the air fraction) and hence can significantly affect estimates of groundwater recharge and groundwater flow rates near the water table.     

The impact of internal waves on upper continental slopes: insights from the Mozambican margin (southwest Indian Ocean)

Evidences of sedimentation affected by oceanic circulation, such as nepheloid layers and contourites are often observed along continental slopes. However, the oceanographic processes controlling sedimentation along continental margins remain poorly understood. Multibeam bathymetry and high-resolution seismic reflection data revealed a contourite depositional system in the Mozambican upper continental slope composed of a contourite terrace (a surface with a gentle seaward slope dominated by erosion) and a plastered drift (a convex-shape sedimentary deposit). A continuous alongslope channel and a field of sand dunes (mainly migrating upslope), formed during Holocene, were identified in the contourite terrace at the present seafloor. Seismic reflection data of the water column show internal waves and boluses propagating in the pycnocline near the upper slope. The channel and the dunes are probably the result of the interaction of the observed internal waves with the seafloor under two different conditions. The alongslope channel is located in a zone where intense barotropic tidal currents may arrest internal solitary waves, generating a hydraulic jump and focused erosion. However, upslope migrating dunes may be formed by bottom currents induced by internal solitary waves of elevation propagating landwards in the pycnocline. These small-scale sedimentary features generated by internal waves are superimposed on large-scale contouritic deposits, such as plastered drifts and contourite terraces, which are related to geostrophic currents. These findings provide new insights into the oceanographic processes that control sedimentation along continental margins that will help interpretation of palaeoceanographic conditions from the sedimentary record. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd     

Sources and transformations of organic matter in surface soils and sediments from a tidal estuary (North Inlet, South Carolina, USA)

Surface soil and sediment samples collected along a forest-brackish marsh-salt marsh transect in a southeastern U.S. estuary were separated into three different fractions (sand, macro-organic matter, and humus) based on size and density. Elemental, stable carbon isotope, and lignin analyses of these samples reveal important contrasts in the quantity, composition, and sources of organic matter, between forest and marsh sites. Elevated nitrogen contents in humus samples suggest nitrogen incorporation during humification is most extensive in forest soils relative to the marsh sites. The lignin compositions of the macro-organic and humus samples reflect the predominant type of vegetation at each site. Lignin phenol ratios indicate that woody and nonwoody litter from, gymnosperm and angiosperms trees (pines and oaks) is the major source of vascular plant-derived organic matter in the forest site and that angiosperm, grasses (Juncus andSpartina) are the major sources of lignin at the marsh sites. The phenol distributions also reveal that oxidative degradation of lignin is most extensive in the forest and brackish marsh zones whereas little lignin decay occurs in the salt marsh samples. In forest soils, most organic matter originates from highly altered forest vegetation while at the brackish marsh site organic matter is a mixture of degradedJuncus materials and microbial/algal remains. Organic matter in the salt marsh appears to be composed of a more complex mixture of sources, including degradedSpartina detritus as well as algal and microbial inputs. Microbial methane oxidation appears to be an important process and a source of¹³C depleted organic carbon in subsurface sediments at this site.