Geology Topics

By Darrel Dunn, Ph.D., PG, Geologist

(Professional Synopsis🔳)

The purpose of this web page is to present my comments on geology topics addressed in emails from viewers of this site. These comments are brief statements related to questions and comments in the viewer's emails. They are not comprehensive coverage of the topic.


Foundation Settlement

When a house is located on compressible material such as sand and clay, the amount of settlement depends on the actual compressibility of the material beneath the footings, depth and width of the footings, and the elevation of the water table. If settlement is very small and the structure of the house resists deformation, no cracks or other indications of settlement are noticed. However, in some cases the settlement is noticeable and can produce cracks, tight doors, et cetera. Information on compressibility of geologic materials may be found on the web page titled Aquifer Storativity.

Denver Basin

The following table contains my interpretation of the age of events related to the development of the Denver Basin in Colorado, USA, and the adjacent mountains.

Ma Event (Ma = Million Years before present)

0 Post-Laramide uplift continues (Tectonic and rebound due to erosion. Uplift > 5000 feet)

0.0093 Sudden cooling

0.011 End Wisconsin glaciation (Bull Lake, Pinedale, and Holocene Terraces in Denver Area)

0.1 Begin Wisconsin glaciation

Slocum Alluvium deposited (Sangoman/Illinoian)

0.25 End Illinoisian

0.4 Begin Illinoisian

0.64 Verdos gravel deposited (Age based on volcanic ash bed)

0.75 End Kansan glaciation

0.9 Begin Kansan glaciation

1.65 End Nebraskan glaciation

1.8 Begin Nebraskan glaciation

5 End Post-Laramide magmatism (Left Eocene erosional surface buried under flow and ejecta)

10 Rate of exhumation increases

28 Begin Post-Laramide uplift, extension, and rifting

33.5 End of Eocene

36 Begin Post-Laramide magmatism, faulting, northward tilting of Denver Basin

36.7 Deposition of Castle Rock Conglomerate

Rocky Mountain erosion surface developed (Low relief surface extends east onto deposits)

40 End of Laramide deformation

52 Beginning of D2 deposition

54.8 Beginning of Eocene

64 End of D1 deposition

72 Beginning of Laramide deformation

75 End of Laramie Formation deposition (Laramie deposited by retreating Cretaceous sea)

510 Begin advance of Cambrian sea from west.

1100 Begin Pre-Cambrian erosional period.

Related information is contained in the web page titled Palmer Lake Geology.