CAUTION
1. Be aware of the tides. The cliffs in the area are not scalable in case of emergency, and the waves at high tide crash close to or on the cliff face.
2. The walk along the shore at the foot of Ashburton Head features a long point of land at low tide and a small string of islets at high tide. You do not want to be on these when the tides come in.
3. To access Indian Beach do not attempt to walk the shoreline - use the hiking trails
4. Cliffs themselves can be dangerous as they are eroding, and small rock falls are common place.
5. Cell phone reception, in case of emergency, is spotty.
6. This is not a quick cache, both hikes will take upwards of 3 - 4 hours, each. The difficulty rating reflects this.
Information for access to trails
1. EEL BROOK BEACH (Ashburton Head) https://www.hikingnb.ca/Trails/FundyWest/GrandManan/LighthouseTrail/WhaleToWhistle.html
2. INDIAN BEACH https://www.hikingnb.ca/Trails/FundyWest/GrandManan/LighthouseTrail/WhistleToDark.html
The Grand Manan Rift Basin
The Grand Manan Basin is a small Early Mesozoic rift basin with maximum dimensions around 30 km wide by 70 km long. The basin is bounded on the southeast by the west-dipping Red Point Fault, which bisects Grand Manan island, and on the northwest by a submarine border fault marked by the Murr Escarpment, a bathymetric feature that parallels the coast of Maine. The island of Grand Manan has the only exposed strata and basalt of the Grand Manan Basin. The unmetamorphosed basalt and clastic sedimentary strata on the island have been recognized as Early Mesozoic.
Mesozoic Dark Harbour Basalt
The Triassic Period marked the beginning of major changes that were to take place throughout the Mesozoic Era, particularly in the distribution of continents and geographic distribution due to plate tectonic activity and a period of continental rifting. Mesozoic exposures on western Grand Manan are dominated by Dark Harbour Basalt. The basalt has three members, which from top to bottom are: Ashburton Head Member (> 80 m), Seven Days Work Member (ca. 50 m) and Southwest Head Member (ca. 110 m).
The Ashburton Head, Seven Days Work, and Southwest Head members of the end-Triassic Dark Harbour Basalt cover most of western Grand Manan with a total thickness around 240 m. The basalt flows and sedimentary strata on Grand Manan are generally within a few degrees of horizontal, but with limited areas of wide gentle folds and a few normal faults.
Ashburton Head Member
The Ashburton Head Member is interpreted to be a final and very thick lava flow, which is co-magmatic but caps the entire volcanic sequence in the basin. The basalt of the Ashburton Head Member is partly columnar like the Southwest Head Member, but in this upper member much of the columns are bent and broken perhaps caused by faults, irregular cooling and/or.tectonic forces. The colonnade is deformed and broken by faults. Several normal faults with significant displacements have been observed in shoreline cliffs, particularly here in the northern part of the island. Ashburton Head is bound by a relatively shallow, northeast-dipping normal fault, exposed on beaches at either end, along which the Ashburton Head Member was dropped down against the Seven Days Work Member. A steeper normal fault trends east-southeast from Indian Beach, where it juxtaposes the Southwest Head Member basalt to the south against Seven Days Work and Ashburton Head members to the north.
A low-angle fault at the base of the cliff looks like the upper part was thrust along at a shallow angle. Also look closely at the dark gash that runs at an angle up the cliff, near the head end. It appears to be filled a narrow dolerite dyke, which indicates the continued presence of magma beneath the upper members of the Dark Harbour Basalt.
A low-angle normal fault with thick gouge toward the northern end of the beach separates the Seven Days Work Member from the Ashburton Head Member. Note the physical contrast between the two members. The fault surface dips 49° NE with a trend that curves from about 280° to 330° around Ashburton and Northern Head, emerging at Whistle Beach. The Ashburton Head Member has moved down the fault with a vertical displacement of about 60 m to 80 m, judging from the thickness of the adjacent Seven Days Work Member. The deformation visible in the cliff face may be due to the fault movement as well as from instability over the Fundy lava lake.
A conformable contact between the Seven Days Work Member and overlying Ashburton Head Member is gently dipping at its only observed location at Indian Beach. A high-angle fault under vegetation in the cliff face at Indian Beach separates the lower Southwest Head Member (right side) from Seven Days Work (layered flows, lower left) and upper Ashburton Head (upper left) members of the Dark Harbour Basalt.
In order to log this earthcache, please send a private message to the cache owner with the answers to the following questions:
1. [PHOTOS 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 post a photos in your log of yourself or a personal item with 1. Ashburn Head and Eel Brook Beach in the background and 2. Indian Beach in the background to prove you visited the site.
2. What is co-magmatic?
3. What is fault gouge?
4. How does Fault Gauge Form?
5. At Ashburton Head (Eel Brook Beach) describe the gouge you see.
6. At the Indian Beach observation point please describe the following