Interbedding

Interbedded graywacke-siltstone-slate in the Precambrian of Minnesota, USA. This is an outcrop of slightly metamorphosed rock that was smoothed and striated by glaciers during the Pleistocene Ice Age.

In geology, interbedding occurs when beds (layers of rock) of a particular lithology lie between or alternate with beds of a different lithology.[1] For example, sedimentary rocks may be interbedded if there were sea level variations in their sedimentary depositional environment.[2]

Intercalation is a special case of interbedding where a layer is variably inserted into an already existing sequence; or where two separate depositional environments in close spatial proximity migrate alternately across the contact.

Folded sedimentary rocks (calcareous turbidite sequence) of Lower Carbonferous (Brigantian/Visean) age at Loughshinny, eastern coast of Ireland. The Variscan orogeny is responsible for the folding.

While interbedding has layers that are horizontally flat (or aligned with the angle of the entire stratum), intercalated rock on the other hand has slanted layers that streak through each other (even when it aligns with the stratum). For example intercalated conglomerate and sandstone looks like ripples of different material networked through each other somewhat off the horizontal, as the beds are deposited in a gradient. This is likely due to differing fluvial conditions and gradual changes in sediment transport over time.[3]

  1. ^ UCMP glossary ucmp.berkeley.edu Retrieved on- March 2008
  2. ^ Harper, John A.; Christopher D. Laughrey; Jaime Kostelnik; David P. Gold; Arnold G. Doden (2004-05-26). "Trenton and Black River Carbonates in the Union Furnace Area of Blair and Huntingdon Counties, Pennsylvania : Introduction". Field Trip Guidebook for the Eastern Section AAPG Annual Meeting, September 10, 2003 and the PAPG Spring Field Trip, May 26, 2004. Pennsylvania Geological Survey. Archived from the original on March 28, 2006. Retrieved 2008-06-14.
  3. ^ "Fig. 6. Intercalated conglomerates and sandstones (ICS), northern..." ResearchGate. Retrieved 2019-12-22.