Andreas Prokoph

Tempo of the end-Permian event: High-resolution cyclostratigraphy at the Permian-Triassic boundary

The Permian-Triassic (P-T) boundary is marked by the most severe mass extinction in the geologic record. High-resolution cyclostratigraphy on a 10 4 yr scale across the P-T boundary in a core from the Carnic Alps (Austria) revealed significant cycles in the ratio ~40:10:4.7:2.3 m, identified with Milankovitch cycles of ~412:100:40:20 k.y. (eccentricity 1 and 2, obliquity, and precession). Wavelet analysis indicates continuity of deposition across the boundary, with an average accumulation rate of ~10 cm/k.y. The dramatic faunal changes at the P-T boundary can be constrained within an interval of <60 k.y. (possibly <8 k.y.), with the accompanying sharp negative global carbonisotope shift within <30 k.y., suggesting a catastrophic cause.

Geochronology and calibration of global Milankovitch cyclicity at the Cenomanian-Turonian boundary

New 40 Ar/ 39 Ar geochronology and global cyclostratigraphic calibration provide high-resolution insights into the timing of geochemical fluctuations across oceanic anoxic event II (OAE II). Five new 40 Ar/ 39 Ar data from a single section in western Canada suggest an age of 96.4 ± 1 Ma for the Cenomanian-Turonian (C-T) boundary. This is ∼3 m.y. older than previously dated. Time-series analysis (e.g., wavelet transform) reveals that OAE II was synchronously deposited worldwide over a period of ∼320 k.y. The preservation and stationarity of Milankovitch cyclicity in sections across the Atlantic indicates that no major fluctuations in sedimentation rate occur across the OAE II, except for a minor short- term decrease in the rate just before the C-T boundary. A δ 13 C org increase of >2‰ took place at the beginning of OAE II over a period of ∼110 k.y., and likely represents a period of worldwide excessive organic carbon burial during transgression, leading to a 12 C depletion of seawater and sedimentation. This interval was followed by a three-step decrease to pre-OAE II δ 13 C values.

Time-series analysis of large igneous provinces: 3500 Ma to present

We outline an efficient integrated wavelet, a spectral, and a cross‐spectral approach for the time‐series analysis of geologic data. Here these techniques are applied to a database of 154 large igneous provinces (LIPs) in order to test for cycles, trends, and abrupt changes in temporal distribution since 3500 Ma. The average frequency of events is relatively constant and supports an overall model of semicontinuous temporal emplacement of LIPs. However, several weak cycles were obtained in the analysis. Those of longest duration are a ∼170‐m.yr. cycle from 1600 Ma to present and in the late Archean, a ∼330‐m.yr. cycle from about 3000 to 1000 Ma, a cycle decreasing in length from 730 to 550 m.yr. over the interval 3500 Ma to present, and a still weaker cycle increasing from 900 to 1000 m.yr. over the interval 2000 Ma to present. Additional cycles of shorter duration include a ∼250‐m.yr. cycle in the late Archean, a ∼230‐m.yr. cycle in the Phanerozoic, a ∼105‐m.yr. cycle in the early Proterozoic, and several <60‐m.yr. cycles occurring in scattered intervals. The uncertainties in the cycle patterns preclude a simple correlation with previously interpreted forcing functions: a ∼30‐m.yr. cometary impact, a 270‐m.yr. galactic year, a 500–300‐m.yr. supercontinent cycle, and a ∼800‐m.yr. resonance between tidal and free oscillations of the core. However, our ∼170‐m.yr. interval spacing is associated with clusters of LIP events over the past 1500 Ma. Future time‐series analyses on improved versions of the LIP database (and appropriate subsets) will be required to test the robustness of the cycles we observe and to identify underlying forcing functions.

Organization of oscillatory zoning in zircon: analysis, scaling, geochemistry, and model of a zircon from Kipawa, Quebec, Canada

Abstract The character of oscillatory zoning within a zircon crystal from the syenite Kipawa Complex, Quebec, varies with scale of observation. Analysis of an scanning electron microscopy (SEM) back-scatter gray-scale traverse at a resolution of one pixel = 2.43 μm revealed 145 zones over 5130 μm, whereas a detailed high-resolution (one pixel = 0.195 μm) section near the crystal rim revealed 225 zones over 795 μm. In order to mathematically characterize the zoning pattern, wavelet, Fourier, and nonlinear analysis techniques were used on profiles of the SEM gray-scale data, and a series constructed was from the zone widths. Results demonstrate that the zircon oscillatory zoning preserves nonlinear and periodic components. Secondary ion mass spectrometry, electron microprobe, and SEM analyses of trace elements show the SEM back-scatter bright zones are enriched in U, Th, and rare earth elements (REE) in comparison to the darker zones. REE patterns are sharply heavy REE enriched and have negative Eu anomalies and prominent positive Ce anomalies. We model the oscillatory zoning, including a measure of its chemical variation, by use of a periodically forced nonlinear system. Results of this data-driven model are quantitatively similar to the natural data. We envisage that the small-scale oscillatory zoning was the result of a nonlinear feedback process wherein the crystal growth modified the adjacent melt, which in turn affected the crystal composition. The large-scale harmonic zones likely reflect changes in the bulk geochemistry of the system from which the zircon grew.

Wavelet analysis of well-logging data from oil source rock, Egret Member, offshore eastern Canada

Wavelet analysis is a sensitive method for automatically detecting and distinguishing abrupt discontinuities (i.e., faults, unconformities), cyclicity, and gradual changes in sedimentation rate by transforming depth-related sedimentary signals (i.e., gamma-rays) into wavelengths at distinct depth intervals. We used wavelet analysis for evaluation of the spatio-temporal distribution of oil source rocks and for estimating accumulation rates in a sedimentary basin having high resolution. The method was applied to 16 gamma-ray logs from the Jurassic Egret Member (an oil-source rock succession 55 m to 227 m in thickness), offshore eastern Canada. Dominant gamma-ray cycles having wavelengths varying from 2.8 m (western margin of the basin) to 24 m (eastern part of the basin) have been detected by wavelet analysis. The coincidence of the ratio of predominant gamma-ray cycles with the ratio of Milankovitch spectra (about 400, 100, 40, 20 k.y.) suggests that climatic cycles are an important factor controlling sedimentary cyclicity in the Egret Member. Dominant wavelengths likely represent ~100 k.y. eccentricity, giving accumulation times of ~1.9 m.y. for stratigraphically complete sections having 19 successive 2.8 m gamma-ray cycles and giving accumulation times of ~600 k.y. for incomplete successions having only 6 cycles. Up to four discontinuities occur in gamma-ray log cyclicity and separate the Egret Member into subunits. We interpret the discontinuities as unconformities or faults and as related to sediments having low petroleum potential. The stratigraphic completeness of the Egret Member is correlated to total mass of organic carbon and decreasing thickness of non-source rock intervals, having correlation coefficients of r = 0.8 and r = -0.76, respectively.

Trends, cycles and nonstationarities in isotope signals of phanerozoic seawater

Abstract The new set of 87 Sr / 86 Sr , δ 18 O and δ 13 C experimental data for Phanerozoic seawater, the “Bochum/Ottawa Isotope Dataset”, has been tested by wavelet, discontinuity and sliding window correlation dimension analyses for cyclicities and nonstationarities in the isotope signal. The tests indicate discontinuities in the strontium isotope signal at ∼500, 340, 288, 210, 65 and 28 Ma, while for the oxygen and carbon isotopes they are at ∼500, 385, 290, 210 and 65 Ma. These discontinuities, often coincident with major stage boundaries, reflect mostly single (likely tectonic) events that do not affect the structure of the underlying system. The two most pronounced nonstationarities in all isotope systematics are at ∼65 and 210 Ma, respectively, that is at the K/T and Norian/Rhaetian transitions. Wavelet analysis for all three isotope systems yields a long-term quasi-periodicity at ∼94–125 Ma, best developed during the Paleozoic, with superimposed intermittent 48–57 and 29–35 Ma oscillations, all likely a reflection of plate reorganizations within the Caledonian, Hercynian and Alpine tectonic cycles.

Evidence for periodicity and nonlinearity in a high-resolution fossil record of long-term evolution

The application of new signal analysis techniques provides increased insight into the study of the fossil record and processes of evolution. The fossil record of 622 planktic foraminifera contains data from 200 stratigraphic stages of the past 127 m.y. Time-series analyses (wavelet and Fourier transform) of the planktic foraminifera fossil record were used to discern periodic components in long-term evolution. The correlation function analysis was used to distinguish between random and deterministic behavior of the fossil record. The analyses show that stationary ~30 m.y. periodicity and complex deterministic patterns occur in the long-term planktic foraminifera evolution, in particular in the extinction record. Our results suggest that the occurrence of intense diversity fluctuations with 3–10 m.y. periodicity after major extinction events may be attributed to nonlinear, self-organized evolutionary response to the availability of new ecospace. This coupled nonlinear-periodic scenario may explain the repetitive appearance of similar morphotypes in ~30 m.y. intervals.

Is the Solar System's Galactic Motion Imprinted in the Phanerozoic Climate?

A new δ18O Phanerozoic database, based on 24,000 low-Mg calcitic fossil shells, yields a prominent 32 Ma oscillation with a secondary 175 Ma frequency modulation. The periodicities and phases of these oscillations are consistent with parameters postulated for the vertical motion of the solar system across the galactic plane, modulated by the radial epicyclic motion. We propose therefore that the galactic motion left an imprint on the terrestrial climate record. Based on its vertical motion, the effective average galactic density encountered by the solar system is . This suggests the presence of a disk dark matter component.

Application of wavelet and regression analysis in assessing temporal and geographic climate variability: Eastern Ontario, Canada as a case study

Abstract Regression and wavelet analysis have been employed to trace and quantify variation in temporal patterns (e.g., cycles and trends) between the instrument climate records of urban Ottawa and nearby rural areas in eastern Ontario. Possible links between observed climate change at these stations and possible natural and anthropogenic drivers were also investigated. Regression analysis indicates that the temperature in Ottawa increased, on average, at a rate of >0.01°C yr−1 in comparison to adjacent rural areas over the last century. Wavelet analysis shows that this relative urban warming trend was primarily manifested in the form of multidecadal and interseasonal cycles that are likely attributable to gradual increased winter heating in Ottawa (heat island effects) associated with population growth. We estimate that the 1°C increase in the Ottawa temperature is equivalent to an increase in population size of ∼400,000. In contrast, interannual variability correlates well between rural and urban areas with about the same temperature amplitudes.

Are Mantle Plumes Periodic

In the past few years, researchers have uncovered evidence that several kinds of geological and biological events seem to show regular cycles of similar lengths. For example, Rohde and Muller [2005] looked at the record of diversity of marine organisms over the past 540 million years and found evidence for two cycles in the data—a roughly 62-million-year cycle and a longer cycle of about 140 million years. This was followed by reports of an approximately 56-million-year cycle in long-term stratigraphic sequences in sedimentary basins [Meyers and Peters, 2011] and a 59-million-year period in the marine strontium-isotope record [Melott et al., 2012]. A similar period may even exist in atmospheric carbon dioxide over the past 542 million years of the Phanerozoic [Franks et al., 2012]. A cycle of about 140 million years was reported by Veizer et al. [2000] and Mayhew et al. [2008] in long-term fluctuations in global climate.