# Geological Cycles

Some geological cycles notes from the past studies of cycles and geology.

**Sedimentary Climate Cycles**

In 1996 Malcolm McClure wrote:

The Geological Sociey London, has just published Special Publication 85 on the subject of sedimentary cycles co-edited by M.R. House. and A.S. Gale It is called Orbital Forcing Timescales and Cyclostratigraphy. In his intro House lists the factors as follows:

1. Earth-Sun distance (perihelion and precession cycles: 19 & 25 ka)

2. Tilt in Earth’s axis with respect to ecliptic (obliquity cycles 41 & 54 ka)

3. Changes in the geometry of earth’s orbit around the sun (eccentricity cycles of 106 and 414 ka)

4. 26 Ma oscillations related to the cosmic year (260 Ma)

(Before anybody asks, House concluded that extinction events are not cyclical.)

Other shorter period cycles are

1. The Earth year (length decreased from 400 to 365.25 days in 400 Ma)

2. The Chandler Wobble (434-436 days, which nobody understands

3. The Lunar perigee (8.85 a)

3. The Solar year (11.0 a)

4 The Lunar Nodal cycle (18.6 a)

5. The Hale cycle (22.0 a of sunspot activity)

This book also corrects the magnetostrat dates during the Neogene.

**Nanocycles Method**

In 1997 Ray Tomes wrote:

[Note: my Russian knowledge is zero and so translation is risky]

In “Nanocycles Method” Professor S. Afansiev of Moscow University describes how he has determined accurately the variations in short term cycles laid down in rock strata. These variations are due to the changing period of the lunar nodal cycle which affects rainfall and hence the variations in thickness of silt deposits in making the rocks.

As well as the nodal cycle itself it is possible to detect the interaction periods of the cycle with the annual cycle of the seasons. Using these interaction periods the nodal cycle period can be determined to high precision, and asthe period varies continuously due to tidal interaction with the earth, the exact date of deposits can be determined. The book contains some 80 pages of tables showing the nodal period and the interaction periods at 0.2 million year intervals for the last 600 million years. A brief summary of the recent values is:

Million years ago 100 80 60 40 20 0 Nodal period (years) 3.278 3.814 4.523 5.504 6.951 9.298

In any given age, the Nodal period interacts with the seasons so as to produce further cycles. The first of these is calculated by dividing the nodal period by its difference from the nearest integer, so that at present the nodal period of 9.298 years would produce an interaction cycle of 9.298/(9.298-9) = 31.2 years. This interaction period is very sensitive to the length of the nodal cycle, for example varying from 46 to 31 years as the nodal cycle varies from 9.2 to 9.3 years, and so measuring it allows the very accurate measure of the nodal cycle and therefore the age of the strata.

Using the established ages in this manner Prof Afansiev was able to determine the periods of other geological cycles in strata to an unprecedented high precision.