Milankovitch Cycles in Upper Jurassic and Lower Cretaceous Radiolarites of the Equatorial Pacific: Spectral Analysis and Sedimentation Rate Curves

Abstract

Periodic changes in depositional environments due to Milankovitch astronomical climate cycles can cause cyclic patterns in sedimentation properties as recorded by logging data. Ocean Drilling Program Site 801 recovered Callovian (upper Middle Jurassic) through Valanginian (Lower Cretaceous) clayey radiolarites, originally deposited in a near-equatorial setting. Cycles of variable concentration of radiolarians and clay, and associated changes in degree of silicification were apparent in the geophysical logs, especially in the gamma-ray signal and the Formation MicroScanner. Three-dimensional spectral analysis was performed on the gamma-ray log signal using a 40-m sliding window. The dominant spectral peaks maintain the same relative ratios in frequency as the 413-k.y., 123-k.y., and 95-k.y. Milankovitch periods of eccentricity. The wavelengths of these eccentricity-modulated cycles were used to determine rates and discontinuities in sedimentation with depth.Two sharp discontinuities in sedimentation rate were inferred: (1) Callovian alternations of red radiolarite and claystone, with a sedimentation rate of approximately 14.5 m.y., is terminated by a Callovian/Oxfordian boundary hiatus, and the overlying upper Oxfordian through lowest Tithonian clay-rich radiolarites and the lower Tithonian banded chert have an average sedimentation rate of 7 m/m.y.; (2) a discontinuity of probable late Tithonian-early Berriasian age terminates the Tithonian banded chert; the overlying Berriasian through Valanginian radiolarite has a mean sedimentation rate of 11.5 m/m.y. These computed sedimentation rates and interpreted discontinuities are consistent with the stratigraphy of the recovered sediments and the uncertainties in the geological time scale.Eccentricity cycles identified in the gamma-ray signal were matched to corresponding features on the Formation MicroScanner high-resolution imagery of clay content and degree of silicification. Eccentricity cycles are manifested as groupings of beds of higher radiolarian content and silicification. Milankovitch climate cycles may affect the intensity of equatorial Pacific upwelling, hence the surface productivity of radiolarians, and the amount of eolian dust and clay contributed to the sediments.

Conodont biostratigraphy and faunal assemblages in radiolarian ribbon-banded cherts of the Burubaital Formation, West Balkhash Region, Kazakhstan

“…This rate of sedimentation is comparable with data on the sedimentation rates of different Mesozoic and Cenozoic ribbon-banded radiolarites (Molinie & Ogg, 1992) and comparable with those from zones of modern accumulations of radiolarian oozes, despite the fact that modern oozes contain a significant siliciclasitic input (Sadler, 1981;Schindel, 1980). This rate of sedimentation is comparable with data on the sedimentation rates of different Mesozoic and Cenozoic ribbon-banded radiolarites (Molinie & Ogg, 1992) and comparable with those from zones of modern accumulations of radiolarian oozes, despite the fact that modern oozes contain a significant siliciclasitic input (Sadler, 1981;Schindel, 1980).…”

Takuyo-Daisan Guyot: Depositional History of the Carbonate Platform from Downhole Logs at Site 879 (Outer Rim)

“…This Milankovitch cycle produces cyclic changes in global climate and ocean fertility and temperature (e.g., Molinie andOgg, 1992a, 1992b). The predicted magnitude of these Milankovitch-induced oscillations of sea-level in nonglacial intervals is probably equivalent to the combined effect of ocean thermohaline volume changes (-0.1-10 m, depending upon the magnitude of cyclical heating and cooling of deep ocean waters) and postulated changes in groundwater storage on the continents (up to 10-20 m; Revelle, 1990;Hay and Leslie, 1990;Plint et al, 1992).…”

“…The FMS tool creates high-resolution images of the borehole by measuring the electrical resistivity contrast across an array of small electrodes (Ekstrom et al, 1986;Pezard and Luthi, 1988;Bourke et al, 1989;Molinie and Ogg, 1992b). The ODP FMS has four orthogonal pads containing 16 pad-mounted button electrodes that are pressed against the borehole.…”

“…; 400 k.y.) of Milankovitch climate-oceanographic cooling cycles (e.g., Molinie andOgg, 1992a, 1992b;Ogg et al, 1992). This eccentricity modulation of precession should also cause overall cooling-warming cycles of the deep ocean, thereby creating rises and falls of eustatic sea level (e.g., Revelle, 1990).…”

Análise Da Periodicidade Dos Folhelhos Negros Do Poço DSDP-530 (Bacia De Angola): Um Estudo Comparativoi Entre a Análise Espectral Utilizando Harmônicos E Wavelet

“…Denomina-se neste estudo de índice colorimétrico os dados numéricos que representam as variações de cores das litologias recuperadas no testemunho. Atualmente, existe um grande número de estudos cicloestratigráficos realizados em séries temporais que representam as variações de cores, comprovando a eficiência destas técnicas (Busch, 1991;Molinie & Ogg, 1992;Sageman et al,1997;Yang & Kominz, 1999;Balsam et al, 1999). A análise espectral das curvas que expressam o índice colorimétrico segue o método descrito em Sageman et ai.…”