Geochronology/Orbitally forced cyclicity

"Chemical and physical proxies from sedimentary rock sequences are frequently used for palaeoclimatic studies and for detecting orbitally forced cyclicity in marine Cenozoic sequences and calibrating recognized sedimentary cycles to time-periodicity."[1]

The nature of sediments can vary in a cyclic fashion, and these cycles can be displayed in the sedimentary record - here visible in the colouration and resistance of strata. Credit: Verisimilus.{{free media}}

Magnetic susceptibility edit

"Spectral analysis of the [magnetic susceptibility (MS)] record reveals the presence of the complete suite of orbital frequencies in the precession, obliquity, and eccentricity (95–128 ka and 405 ka) bands with very high amplitude of the precession index cycles originating from [decimeter (dm)] dm-scale couplets."[1]

Ammonites edit

"Ammonite zone duration estimates are made by counting the interpreted precession cycles, and provide an ultra-high resolution assessment of geologic time."[1]

Astronomical tuning edit

An alternative method of calibrating the used standard is astronomical tuning (also known as orbital tuning), which arrives at a slightly different age.[2]

Cyclostratigraphy edit

Cyclostratigraphy is the study of astronomically forced climate cycles within sedimentary successions.[3]

Milankovitch cycles edit

Astronomical cycles (also known as Milankovitch cycles) are variations of the Earth's orbit around the sun due to the gravitational interaction with other masses within the solar system.[4]

Precessions edit

The main orbital cycles are precession with current main periods of 19 and 23 kyr, obliquity with main periods of 41 kyr, and 1.2 Myr, and eccentricity with main periods of around 100 kyr, 405 kyr, and 2.4 Myr.[5]

Eccentricity cycles edit

The 405 kyr eccentricity cycle helps correct chronologies in rocks or sediment cores when variable sedimentation makes them difficult to assign.[4] Indicators of these cycles in sediments include rock magnetism, geochemistry, biological composition, and physical features like color and facies changes.[4][3]

See also edit

References edit

  1. 1.0 1.1 1.2 Slah Boulila, Bruno Galbrun, Linda A. Hinnov, Pierre-Yves Collin (January). "High-resolution cyclostratigraphic analysis from magnetic susceptibility in a Lower Kimmeridgian (Upper Jurassic) marl–limestone succession (La Méouge, Vocontian Basin, France)". Sedimentary Geology 203 (1-2): 54-63. Retrieved 2015-01-27. 
  2. Kuiper, K. F.; Hilgen, F. J.; Steenbrink, J.; Wijbrans, J. R. (2004). "40Ar/39Ar ages of tephras intercalated in astronomically tuned Neogene sedimentary sequences in the eastern Mediterranean". Earth and Planetary Science Letters 222 (2): 583–597. doi:10.1016/j.epsl.2004.03.005. 
  3. 3.0 3.1 Andre Strasser, Frederik Hilgen, Philip H. Heckel. "Cyclostratigraphy - from orbital cycles to geologic time scale". 2008. Cite error: Invalid <ref> tag; name "Strasser" defined multiple times with different content
  4. 4.0 4.1 4.2 Hinnov, Linda A. (2013). "Cyclostratigraphy and its revolutionizing applications in the earth and planetary sciences". Geological Society of America Bulletin 125 (11/12): 1703-1734. doi:10.1130/B30934.1. 
  5. Hinnov L.A. & Ogg J.G. (2007). "Cyclostratigraphy and the Astronomical Time Scale". Stratigraphy 4 (2-3): 239-251. 

External links edit

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