From the posted coordinates to the end of the beach (approximately 200 m) scattered along this section of Myette Beach, is evidence of wave Ripple Marks. Ripple marks are sedimentary structures and indicate agitation by water (current or waves) or wind. Ripple marks are ridges of sediment that form in response to wind blowing along a layer of sediment. Ripple marks form perpendicular to the wind direction and each ridge is roughly equidistant from the ripple mark on either side. Numerous rocks exist with the tell-tale signs of fossilized symmetrical ripple marks. Often found on beaches, symmetrical ripple marks are created by a two way current; for example the waves on a beach swashing and backwash. This creates ripple marks with pointed crested and rounded troughs, which aren't inclined more to a certain direction. Three common sedimentary structures that are created by these processes are herringbone cross stratification, flaser bedding, and interference ripples. As stated, Symmetrical Ripple Marks occur in environments where there is a steady back and forth movement of the water. There are several types:
Straight
Straight ripples generate cross-laminae that all dip in the same direction, and lay in the same plane. These forms of ripples are constructed by unidirectional flow of the current.
Sinuous
Sinuous ripples generate cross-laminae that are curvy. They show a pattern of curving up and down as shown in picture. Sinuous ripples produce trough cross lamination. All laminae formed under this type of ripple dip at an angle to the flow as well as downstream. These laminae are also formed by the unidirectional current.
Catenary
Catenary ripples generate cross-laminae that are curvy but have a unidirectional swoop. They show a pattern similar to what a repeated "W" would look like. Like the sinuous ripples, this form of ripple is created by unidirectional flow with the dip at an angle to the flow as well as downstream.
Linguoid / Lunate
Linguoid ripples have lee slope surfaces that are curved generating a laminae similar to caternary and sinuous ripples. Linguoid ripples generate an angle to the flow as well as downstream. Linguoid ripples have a random shape rather than a "W" shape, as described in the catenary description. Lunate ripples, meaning crescent shaped ripples, are exactly like linguoid ripples except that the stoss sides are curved rather than the lee slope. All other features are the same.
To claim this Earth Cache, please answer the following questions:
1) What types of symmetrical ripple marks can you see in this area? Please review the descriptions provide and pictures in cache gallery.
2) Can you find differences in the colour of the rocks that different types of ripple marks are found in? What kinds of rocks do you think they are?
3) Which direction do you think the wind was predominently blowing to form the ripple marks?
4) Describle the general geology of the area around you? What type of rock do you think is there?
5) Please post a picture of yourself / group holding a sample of the Ripple Mark stones. Please leave the stones behind and be respectful of the geology of the area. Feel free to post the picture in the log but please email me the answers.
6) Bonus: plant fossils are also readily found here. Post pictures of any fossils you find.