Name: Reg. lab day: M Tu W Th F Geology 1013 Field trip to Black River Valley (Lab #7, Answer Key)

Drive south on Gaspereau Avenue and stop at the Highway 101 overpass.

Stop 1: HALIFAX GROUP A: Go to the north side of the overpass. slate a) Name the rock exposed in this outcrop. b) What was the original rock before metamorphism? Shale/mudrock c) Was the metamorphism regional or contact? regional d) Use the compass to measure strike & dip of cleavage. 060(240)±20/70±10SE e) Use the compass to measure strike & dip of bedding. 020(200)±20/20±10NW f) Is cleavage parallel to bedding? no g) Plot cleavage and bedding on the attached map using the proper symbols.

B: Go to the south side of the overpass. 060(240)±20/70±10SE a) Use the compass to measure strike & dip of cleavage. 120(300)±20/20±10SW b) Use the compass to measure strike & dip of bedding. c) Is the cleavage orientation similar to that in (d) above? yes d) Is the bedding orientation similar to that in (e) above? no

Drive on through Gaspereau to White Rock. Go through the intersection in White Rock and stop in the big quarry on the right.

Stop 2: WHITE ROCK FORMATION quartzite a) Name the rock. quartz sandstone b) What was the original rock before metamorphism? c) This rock unit is more resistant to weathering than the Halifax Formation. Suggest reasons why.

1. composition (hard, chemically inert mineral) 2. no foliation (no planes of weakness)

Black River Lab – Answer Key Page 2 of 4

Drive back through White Rock, turn south, and stop at the parking area at the Gaspereau River bridge.

Stop 3: KENTVILLE FORMATION The Kentville Formation is exposed in a small outcrop at the parking area. a) Name the rock type. slate b) Why is the Kentville Formation shown as a separate map unit from the Halifax Group even though it is similar in lithology? (Hint: look at the map)

Separated from Halifax Formation by the White Rock formation

Return to the bus. Drive back to White Rock and turn right (east). After 2.5 km turn right (south) and proceed across canal. Turn right on Black River road. Continue about 4.5 km to just before (north of) Lumsden Dam. Stop at outcrop on the east side of the road.

Stop 4: HALIFAX GROUP 050(230)±20/75±10N a) Measure strike & dip of bedding. yes b) Are cleavage and bedding parallel here? c) Plot cleavage & bedding on your map using the correct symbol. d) Find cross-laminations and use them to interpret younging direction — are younger beds to the north or to the south? north

upright e) Is the section upright or overturned? (see sketch below)

Continue driving south about 4 km, turn west to cross Black River and the canal, then south beside the canal. Stop at a roadside outcrop about 0.5 km past the turn. Black River Lab – Answer Key Page 3 of 4

Stop 5: GOLDENVILLE GROUP a) Some beds of this outcrop show cross-bedding. Are younger beds to the north or south? north b) The beds which do not show cross-bedding contain porphyroblasts (large crystals formed during metamorphism) of andalusite (Al2SiO5). Andalusite is characteristic of contact metamorphism of Al-rich sedimentary rocks. Why don't andalusite crystals and cross-bedding occur in the same beds?

Andalusite forms in Al-rich (clay-rich) layers, cross-bedding forms in quartz rich (clay-poor) layers

c) These rocks were subjected to regional metamorphism followed by contact metamorphism. What do you think caused the contact metamorphism? (HINT: look at the map)

South Mountain Batholith

Drive about 1.6 km past the dam at Black River Lake. Notice the large boulders along the road. We have crossed the contact onto the South Mountain Batholith.

Stop 6: SOUTH MOUNTAIN BATHOLITH a) Walk to the power line and look at fresh samples of this rock. Name the four most abundant minerals present: quartz biotite K-feldspar plagioclase b) Describe the texture. Coarse grained

granite c) Name the rock. d) Find xenoliths in the rock. From which of the rock units that you have seen today did they probably come? Goldenville Group e) Is the South Mountain Batholith older or younger than the Goldenville Formation? younger

On your map: 1) Draw in the fold axes using the proper symbol. 2) Label anticlines and synclines. Black River Lab – Answer Key Page 4 of 4