Utilizing Milankovitch Cycles to create high-resolution astrochronologies

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Using Milankovitch Cycles to create high-resolution astrochronologies

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"data-medium-file =" https://i0.wp.com/wattsupwiththat.com/wp-content/uploads/2020/12/134525819_m.jpg?fit=300%2C191&ssl=1 "data-large-file = "https://i0.wp.com/wattsupwiththat.com/wp-content/uploads/2020/12/134525819_m.jpg?fit=700%2C447&ssl=1" load = "lazy" width = "700" height = " 447 "src =" https://i0.wp.com/wattsupwiththat.com/wp-content/uploads/2020/12/134525819_m.jpg?resize=700%2C447&ssl=1 "alt =" "class =" wp- image-6684477 "srcset =" https://i0.wp.com/wattsupwiththat.com/wp-content/uploads/2020/12/134525819_m.jpg?resize=720%2C460&ssl=1 720w, https: // i0. wp.com/wattsupwiththat.com/wp-content/uploads/2020/12/134525819_m.jpg?resize=300%2C191&ssl=1 300w, https://i0.wp.com/wattsupwiththat.com/wp-content/uploads /2020/12/134525819_m.jpg?resize=768%2C490&ssl=1 768w, https://i0.wp.com/wattsupwiththat.com/wp-content/uploads/2020/12/134525819_m.jpg?w=940&ssl= 1 940w "sizes =" (maximum width: 700px) 100vw, 700px "data-recalc-dims =" 1 "/> Close up of petrified wood in Petrified Forest National Park, Arizona

To quote (and H / T) Leif Svalgaard:

This is an interesting application.

From EGU blogs

Lon Abbott November 20, 2020 Stratigraphy, Sedimentology and Paleontology

This year marks the 100th anniversary of Milutin Milankovitch's first paper on the earth's climate. Milankovitch argued that the amount of solar radiation that Earth receives, and therefore its climate, changes cyclically as its orbit changes due to gravitational tugs from the other planets. His climate theory fell into disrepute in the 1950s but was rehabilitated in the 1970s.

Many people today are aware that cyclical changes in the earth's orbit, now known as the Milankovitch cycles, have plunged the earth into and out of glacial episodes repeatedly over the past 2.7 million years. Less known, however, is the control that the same cycles have exercised to form rhythmically oscillating sequences of sediments throughout the Earth's history, thanks to the changes in the deposition conditions they induce. Stratigraphers “tune” the chronology of a rhythmic rock sequence to Milankovitch cycle beats and then anchor those beats to the geological time scale using radiometric and paleomagnetic data to create an astro chronology. Due to their unusually high temporal resolution, such astrochronologies offer deep insights into the development of the earth, its inhabitants and the earth-moon system.

Milankovitch orbital cycles have four primary periods. The Earth's axis of rotation moves in a cycle of approximately 20,000 years and changes its inclination (called skew) in a cycle of approximately 40,000 years. Alternating gravitational tugs from Jupiter and the inner planets cause the eccentricity of our orbit (the elliptical nature of our orbit) to vibrate in two modes, one approximately 100,000 years and the other steady 405,000 years. The remarkable stability of the 405,000 year cycle modulated by Jupiter and Venus makes it the Milankovitch cycle of choice for the construction of astrochronologies.

The stratigraphy of the Newark Basin in the eastern United States enabled scientists to construct an important early example. This Triassic Rift basin is home to rhythmically changing lake and river sediments that reflect the expansion and contraction of the lake in the course of climate change. Scientists tuned the Newark Basin astro-chronology to the 405,000-year-old Milankovitch Cycle and then tied it to the geological timescale using magnetic polarity reversals and high-resolution radiometric data from basalt embedded in the uppermost sedimentary layers. Although the high temporal resolution of the chronology seemed like a big leap forward, some scientists worried about missing cycles due to undetected sediment breaks. They didn't trust astrochronology because it lacked a radiometric datum to anchor the base of the sequence.

It was clear that a test of the accuracy of Newark astrochronology was required. Scientists had to find a comparatively aged section that could be linked to radiometric data above and below. In 2013, they found the ideal candidate: a 500-meter-long core drilled in the Chinle Formation of Petrified Forest National Park in Arizona. This core has cyclical sequences that are deposited in rivers and lakes that drained a volcanically active area. The youngest detrital zircons in each sediment layer likely record the age of that layer. Therefore, the scientists dated these zircons in key layers to provide radiometric points at the top and bottom of the core. The team then applied the same strategy to the core of the Petrified Forest as they did to the Newark Basin. By 2018, they had created an identical astro-chronology that confirms that there are no missing cycles in the Newark Basin section, thus “cementing” its reliability.

The astrochronology of the Petrified Forest / Newark Basin had many important implications. For example, paleontologists have long believed that the Late Triassic fossil record suggests that dinosaurs achieved ecological dominance in mid-to-high latitudes for millions of years before they did in the tropics. However, this conclusion has been controversial due to dating uncertainties. Applying the Astrochronology of the Petrified Forest / Newark Basin to mid-latitude fossil sites in Argentina and Greenland, as well as to low-latitude sites in Canada's Fundy Basin and Petrified Forest, now confirms that the delay in dominance of tropical dinosaurs is real.

GeoLog | Using Milankovitch Cycles to Create High Resolution Astrochronologies – GeoLog (egu.eu)

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