Valley in a Valley EarthCache

Valley in a Valley

Truro (Scottish Gaelic: Truru) is a town in central Nova Scotia and is the shire town of Colchester County. It is  located on the south side of the Salmon River floodplain, close to the river's mouth at the eastern end of Cobequid Bay. The area has been home to the Mi'kmaq people for several centuries. The Mi'kmaq name for the Truro area, "Wagobagitik" means "end of the water's flow". Truro is known as the Hub of Nova Scotia as it is located at the junction of many vital communications and transport links.

Victoria Park

In the center of Truro is more than 400 hectares of natural beauty. Step into Victoria Park and you step from the bustle of town into a world of hills, mature forest, wildlife, rocky cliffs and waterfalls. You also step into history: the park was established in 1887, making it one of Nova Scotia’s oldest protected areas. Victoria Park is located on the south side of the Salmon River Valley where Lepper Brook tumbles from higher elevations to a nearly sea level in the upper reaches of the park. The valley of Lepper Brook is a gorge almost 130 feet (40m) deep. At the bandshell (bandstand), the valley consists of a channel for the brook and a broad flat floodplain. A stream that passes over very hard rock will usually have rapids, cascades and waterfalls.

Park Geology

Victoria Park exposes rocks and landforms that show the effects of erosion and the formation of streams. Two ages of rocks are found in the park. The gorge and waterfalls of the upper park have been created by the erosion of the older, red sandstone and shale of the Horton Group. These rocks belong to the Early Carboniferous period and are about 360 million years old.

The younger of the two groups is the Wolfville Formation. These red-orange sandstones and conglomerates are about 220 million years old and are exposed downstream of the Serpentine Drive bridge. They were deposited in often desert-like conditions during the dawn of dinosaurs in the Middle Triassic period.

The two rock units are separated by an unconformity that represents at least 140 million years, when either no rocks were deposited or rocks were deposited but stripped away by erosion. These two rock groups provide an insight into the continuity of geological processes through time and a marvelous view of ancient stream deposits. They also represent two separate periods of earth history when Nova Scotia was undergoing radical changes.

Geological History

The story begins 380 million years ago during the collision of two large crustal plates: one was ancient North America and the other was Gondwana (includes Africa, South America, Australia, Antarctica, India and others). The collision produced a range of mountains now called the Appalachians. As soon as the mountains were created, they began to be weathered and eroded. The gravel, sand, and mud coming from the destruction and erosion of the mountains formed layers of sediment deposited by streams which we now call the Horton Group.

After the deposition of the Horton, many kilometers of mud, limestone, gypsum, salt, sandstone, and coal were deposited on top of it. The region was cut and broken by faults, folded, and eroded. Between 180 and 220 million years ago, what is now Nova Scotia lay near the center of a huge mega continent (Pangea). Beginning approximately 225 million years ago, Pangea began to break apart by rifting. As the cracks widened and deepened into valleys, what is now southern Nova Scotia began to split away from northern Nova Scotia. Large amounts of mud, sand, and gravel were deposited in the deep, wide rift valley. Geologists interpret the rocks of the Wolfville Formation to have formed on the slopes of an alluvial fan in desert like conditions.

Lepper Brook

Lepper Brook flows north and west through the park, over waterfalls and into a deep gorge. Lepper Brook flows throughout the heart of the park and over the eons, has carved the deep gorge. From the gorge riverbed, the terrain rises by nearly 100 meters from north to south. The highest point is located near the entrance to the Railyard Mountain Bike Park, at 120 meters above sea level. Plateaus above the gorge have flatter areas and offer amazing views. Where Lepper Brook crosses the flat ground near park amenities, evidence of another river, this one of Triassic age can be seen in the present day stream bed.

Victoria Park’s Lepper River cuts through Carboniferous sandstones built up in ancient rivers. It probably originated after the end of the last glaciation, approximately 11,000 years ago, as drainage in this area was reestablished. But it flows in a valley whose origins date back to the Triassic period. So, part of the valley where Lepper Brook flows today is quite ancient.

Formations

Lepper Brook exposes deposits of conglomerate (gravel) in the Wolfville Formation (235-222 Ma) that were deposited in an ancient valley cut by Triassic age streams. Old and New Streams and their deposits form the continuity between the present and the geological past. The clues are found in both the valley walls and in the streambed of Lepper Brook. In the lower park near the bandshell (bandstand), the channel of the brook has cut into ancient gravels (now conglomerate) of the Wolfville Formation while the adjacent valley walls expose outcrops of Horton Group (340-335 Ma) shales and sandstones from the Carboniferous period.

In order to have younger rock (Wolfville) restricted to a valley and lower in elevation than the older rock (Horton), the younger rock must have been deposited in an ancient valley. This would mean that part of the Lepper Brook valley was excavated in the Middle Triassic (about 220 million years ago) and filled with gravels and sands (conglomerates and sandstones) of the Wolfville Formation. While the upper part of the brook was formed during the Carboniferous period (about 300 million years ago). Considerable erosion, all that remains of the second valley are the small exposures of Wolfville formations.

To log this Earthcache visit the viewing locations. Please answer the following questions and send in a timely manner to my geocaching profile or email. Answers not received will result in deleted logs.

Questions:

1. What is the elevation at Ref A, First Valley (N 45° 21.276' W 63° 15.711')?

2. What is the elevation at Ground Zero?

3. Based on information obtained, which location is younger, Why?

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.