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A decomposition approach to cyclostratigraphic signal processing
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Sedimentary rocks can record signals produced by highly complex processes. These signals are generated by a progressive deposition of sediments which can be affected, mainly through the climate system, by regular astronomical cycles (i.e. Milankovitch cycles), and by irregular oscillations like the El Niño-Southern Oscillation. Also, usually through biological, chemical and/or physical post-depositional processes, the sedimentary records can be affected by pattern-creating heterogeneous processes. The noise in the signals further complicates the records, and the deposition rate (or sedimentation rate) can fluctuate, which greatly reduces the effectiveness of the classical stationary time-series analysis methods commonly used in cyclostratigraphy (i.e. the study of the cycles found in the sedimentary records). Faced with this multiplicity of processes, a common approach used in cyclostratigraphy is to reduce each signal to more manageable sub-signals, either over a given range of frequencies (e.g., by filtering), or by considering a continuum of constant frequencies (e.g., using transforms). This makes it possible to focus on the features of interest, commonly astronomical cycles. However, working with sub-signals is not trivial. Firstly, sub-signals have a certain amount of cross-cancellation when they are summed back to reconstruct the initial signal. This means that in filters and in transforms, wiggles that are not present in the initial signal can appear in the sub-signals. Secondly, the sub-signals considered often cannot be summed to reconstruct the initial signal: this means that there are processes affecting the signal which remain unstudied. It is possible to take cross-cancellation into account and to consider the entire content of a signal by dividing the signal into a decomposition: a set of sub-signals that can be added back together to reconstruct the original signal. We discuss here how to reframe commonly used time-series analysis techniques in the context of decomposition, how they are affected by cross-cancellation, and how adequate they are for comprehending the whole signals. We also show that decomposition can be carried out by non-stationary time-series methods, which can minimise cross-cancellation, and have now reached sufficient maturity to tackle sedimentary records signals. We present novel tools to adapt non-stationary decomposition for cyclostratigraphic purposes, based on the concepts of Empirical Mode Decomposition (EMD) and Instantaneous Frequency (IF), mainly: (1) a fast Ensemble Empirical Mode Decomposition (EEMD) algorithm, (2) quality metrics for decomposition, and (3) plots to visualise instantaneous frequency, amplitude and frequency ratio. We illustrate the use of these tools by applying them on a greyscale signal from the site 926 of the Ocean Drilling Program, at Ceara Rise (western equatorial Atlantic), especially to identify and characterise the expression of astronomical cycles. The main goal is to show that by minimising cross-cancellation, we can apply in real signals what we call the wiggle-in-signal approach: making the sub-signals in the decomposition more representative of the expression, wiggle by wiggle, of all the processes affecting the signal (e.g., astronomical cycles). We finally argue that decomposition could be used as a practical standard output for time-series analysis interpretation of cyclostratigraphic signals.
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RBINS Staff Publications 2021
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A dietary perspective of cat-human interactions in two medieval harbors in Iran and Oman revealed through stable isotope analysis
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Cats are hypercarnivorous, opportunistic animals that have adjusted to anthropogenic environments since the Neolithic period. Through humans, either by direct feeding and/or scavenging on food scraps, the diet of cats has been enriched with animals that they cannot kill themselves (e.g., large mammals, fish). Here, we conducted carbon and nitrogen stable isotope ratio analysis to reconstruct the diet of medieval cats and investigate cat-human interactions in two medieval harbor sites (Qalhât, Oman and Siraf, Iran). The analysis included 28 cat individuals and 100 associated marine and terrestrial faunal samples pertaining to > 30 taxa. The isotopic results indicate a high marine protein-based diet for the cats from Qalhât and a mixed marine-terrestrial (C4) diet for the cats from Siraf. Cats at these sites most likely scavenged on both human food scraps and refuse related to fishing activities, with differences in the two sites most likely associated with the availability of marine resources and/or the living conditions of the cats. By shedding light on the dietary habits of cats from two medieval harbors in the Arabian Gulf and Gulf of Oman, this study illustrates the potential of stable isotope analysis in reconstructing human-cat interactions in the past.
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RBINS Staff Publications 2023
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A Discussion of Gullentops & de Moor (2001): Quaternary lithostratigraphic units (Belgium). 2.2. Remaining marine-estuarinedeposits
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RBINS Staff Publications
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A distinct island population of threatened freshwater fish: to split or lump?
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Freshwater fishes in the Balkans display high percentages of endemic species, many being limited to restricted distributions. Their management, for example, through identification of priority areas for conservation or through re-introduction, is hampered by a poor understanding of their taxonomic diversity and interrelationships. We evaluate the identity of a sand goby belonging to Knipowitschia, limited to a single wetland on the Greek island of Zakynthos. Its representatives morphologically differ sufficiently from their congeners to qualify as a separate species. However, in view of the similarity in mitochondrial ribosomal DNA sequences, the evolutionary plasticity of said morphological characters, and in the absence of a taxonomic revision of the Ionian Ecoregion’s Knipowitschia gobies, describing it as a new species seems unjustified and premature. Rather, we advocate that its unique habitus and its vulnerability as the island’s only resident freshwater fish necessitate conservation efforts as a kind of ‘‘phenotypically significant unit’’. We also propose sand gobies as flagships for wetlands in the region. This case study suggests a possible approach for fish conservation prioritization in the region, taking a precautionary angle in order to avoid taxonomic inflation, which is an imminent risk given the importance of nominal species and endemics in conservation policy.
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RBINS Staff Publications 2016
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A diverse bird assemblage from the Ypresian of Belgium furthers knowledge of Early Eocene avifaunas of the North Sea Basin
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We describe an assemblage of 54 avian bones from early Eocene marine sediments of the Ampe quarry near Egem in Belgium. The fossils belong to at least 20 species in more than 11 higher-level taxa. Well-identifiable specimens are assigned to the Odontopterygiformes, Galliformes, Messelornithidae, Apodiformes, Halcyornithidae, Leptosomiformes (cf.Plesiocathartes), and Coraciiformes (cf. Septencoracias). Further specimens are tentatively referred to the phaethontiform Prophaethontidae and to the Accipitridae, Masillaraptoridae, and Alcediniformes. The threedimensionally preserved fossils from Egem provide new data on the osteology of taxa that are otherwise mainly known from compression fossils with crushed bones. The material also includes specimens that further knowledge of the composition of early Eocene avifaunas of the North Sea Basin. The comparatively well-represented small galliform species is clearly distinguished from the early Eocene Gallinuloididae and most closely resembles Argillipes aurorum, a largely ignored galliform species from the London Clay. The tentatively identified fossils of Accipitridae and Alcediniformes would represent the earliest fossil records of these clades. The bird assemblage from Egem includes relatively few seabirds (Odontopterygiformes, cf. Prophaethontidae) and is dominated by remains of terrestrial species (Galliformes, Messelornithidae). Arboreal birds (Halcyornithidae, Leptosomiformes, cf. Alcediniformes, Coraciiformes) are less abundant and aerial insectivores (Apodiformes) very scarce, which either indicates a taphonomic bias in the composition of the avifauna or particular paleoenvironmental characteristics of the nearshore habitats in that area of the southern North Sea Basin.
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RBINS Staff Publications 2019
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A diverse snake fauna from the early Eocene of Vastan Lignite Mine, Gujarat, India
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RBINS Staff Publications
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A DNA-based approach to validate the identification of exotic mosquito species in Belgium
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RBINS Staff Publications 2019
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A dynamic 2DH flocculation model for coastal domains
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RBINS Staff Publications 2023
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A euenantiornithine bird from the Late Cretaceous Hateg Basin of Romania
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RBINS Staff Publications
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A first, local DNA barcode reference database of the forensically important flies (Diptera) of the island of La Reunion
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RBINS Staff Publications 2017
