Orbital frequencies in the carbonate sedimentary record: distorted by diagenesis?

Abstract

The most important archive of Earth's climate change through geologic history is the sedimentary rock record. Rhythmic sedimentary alternations are usually interpreted as a consequence of periodic variations in the orbital parameters of the Earth. This interpretation enables the application of cyclostratigraphy as a very precise chronometer, when based on the assumption that orbital frequencies are faithfully recorded in the sedimentary archive. However, there are numerous uncertainties with the application of this concept. Particularly in carbonates, sediment properties such as mineralogical composition and fossil associations are severely altered during post-depositional alteration (diagenesis). We here point out that the assumption of a 1:1 recording of orbital signals in many cases is questionable for carbonate rhythmites. We use computer simulations to show the effect of diagenetic overprint on records of orbital signals in the carbonate record. Such orbital signals may be distorted in terms of frequency, amplitude, and phase by diagenetic processes, and cycles not present in the insolation record may emerge. This questions the routine use of carbonate rhythmites for chronostratigraphic dating.

Precessional and half-precessional climate forcing of Mid-Devonian monsoon-like dynamics

“…The steplike changes in microfacies can only be represented using multiple additional sine and cosine components during a Fourier transformation, polluting the spectrum (Proakis and Menolakis, 1996;Weedon, 2003). Therefore, spectral analysis on the microfacies curve was carried out using the Walsh and Blackman-Tukey (BT) method for spectral analysis.…”

“…When interpreting cyclic sedimentary alternations as a consequence of periodic changes in the orbital parameters of the Earth, one should be aware of the fact that the assumption of a 1:1 recording of astronomical signals in carbonate sediments is questionable (Westphal et al, 2004). The original astronomical signal can be altered by the climatic system, responding in a nonlinear way to the applied forcing.…”

Stratigraphic continuity and fragmentary sedimentation: the success of cyclostratigraphy as part of integrated stratigraphy

“…Sedimentary cyclicity implies changes in sedimentation rate and is inherent to cyclostratigraphy (Herbert 1994). The result is an uncertain, distorted time scale and frequency dispersal of spectral power (Meyers et al 2001;Westphal et al 2004). The problem leads to elevated false negatives if a is too small.…”

“…Stratigraphic distortion leads to dispersal of spectral power with the emergence of side bands and harmonics as spectral artefacts (Herbert 1994;Meyers et al 2001;Westphal et al 2004). The cycle with the highest frequency (usually related to precession) undergoes the most intense distortion and peak broadening.…”

Los Ciclos de Milankovitch: Origen, Reconocimiento, Aplicaciones en Cicloestratigrafía y el estudio de Sistemas Petroleros

“…Un caso ilustrativo de efectos diagenéticos que generan patrones cíclicos se presenta durante la diagénesis de ciertas secuencias carbonáticas de subsidencia moderada 7 , en donde tienen lugar procesos de disolución, con flujo de iones disueltos hacia estratos suprayacentes donde luego precipitan (Figura 7). Este proceso puede darse sucesivamente a medida que la secuencia es soterrada, generando patrones alternados de cristalización y disolución en forma de ritmitas cíclicas.…”