Tennycape Unconformity EarthCache

Tennycape Unconformity

Tennycape is a small community in the Canadian province of Nova Scotia, located in The Municipality of the District of East Hants in Hants County. Tennycape is located on the west coast of Nova Scotia (on the Minas Basin, at the northeast end of the Bay of Fundy).

At this geological site you will find a display of slate tipped to a 90 degree angle on the beach. Regional geographic mapping establishes that much of this area is underlain by undivided layers of the Windsor and Horton groups. Slates occur chiefly among older rocks, although some occur in regions in which comparatively recent rocks have been folded and compressed as a result of mountain-building movements. The direction of cleavage depends upon the direction of the stresses applied during metamorphism.

It is not unusual to observe abrupt contacts between two, seemingly, contiguous rock layers, such as the one at this site. This type of contact is called an unconformity and marks two very distinct times periods, where the rocks formed under very different conditions.

This fault/fold to create the vertical rock formation would be angular unconformity. An angular unconformity is an unconformity where horizontally parallel strata of sedimentary rock are deposited on tilted and eroded layers, producing an angular discordance with the overlying horizontal layers. The whole sequence may later be deformed and tilted by further orogenic activity.

Unconformity

An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval of time before deposition of the younger layer, but the term is used to describe any break in the sedimentary geologic record. 

The rocks above an unconformity are younger than the rocks beneath (unless the sequence has been overturned). An unconformity represents time during which no sediments were preserved in a region. The local record for that time interval is missing and geologists must use other clues to discover that part of the geologic history of that area. The interval of geologic time not represented is called a hiatus. It is a kind of relative dating.

Angular unconformity

Angular Unconformities are those where an older package of sediments has been tilted, truncated by erosion, and than a younger package of sediments was deposited on this erosion surface.  The sequence of events is summarized in the pictures at left.  First: subsidence and sediment deposition occurs; Second: rocks are uplifted and tilted (deformation); Third: erosion removes the uplifted mountain range; Fourth: subsidence occurs, the sea covers the land surface, and new sediments deposition occurs on top the previous land surface.  Then the cycle may repeat.

Rock layers can become tilted in a number of ways. The folding of sedimentary rocks into anticlines and synclines is one way. Tilting can also result when rocks are pushed upward, or uplifted. In some areas of the world, rock layers are so severely tilted that they may be bottom side up.

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Questions: You need to do this at almost low tide.strong>

1. How wide is the area showing the unconformities?

2. What direction are the unconformities going and what angle are they?

3. Using a sample at ground zero, describe the texture and colour of a rock sample? 

4. Post a picture in your log with a personal item or hand in picture to prove you were there.

[REQUIRED] In accordance with the updated guidelines from Geocaching Headquarters published in June 2019, photos are now an acceptable logging requirement and WILL BE REQUIRED TO LOG THIS CACHE. Please provide a photo of yourself or a personal item in the picture to prove you visited the site.