2012 Field Trip 1 Questions
Structural Geology
Name: ____________________________________ Safety
Glasses, PCBC form
Work on these questions in small groups. The instructor will help you.
Safety Rules: Stay away from the road. Only persons with safety glasses with side shields
may use rock hammers. All others stay 10 feet away. No rock face climbing.
We will take 24 (second onramp) toward 287 North.
The valley past Short Hills Mall was a proglacial lake in the Pleistocene.
What is it about glaciers that cause proglacial lakes? ____________________________
______________________________________________________________________
How could you sample the lake sediments, and what sedimentary structures would you
look for to recognize glacial and interglacial lake deposits?______________________
______________________________________________________________________
What microfossils should you use to determine the changing plant ecology from
sediments you have sampled? ______________________________________________
At the crests of Basalt ridges we will look north to see the border fault between the
Triassic/Jurassic Rift Valley and the Precambrian Highlands (our first destination) but on
the way there we won’t see outcrops: the highway department has been busy removing
basalt along 24.
At the end of 24 take the Mahwah exit to 287 north, then take the second exit for Rt. 80.
A. The Highlands
Once we climb up the border fault on Route 80, large rock outcrops will be common.
Prior to our exit onto 15, we will mostly see metamorphosed sediments (hereafter called
“metasediments”) that are Grenvillian in age, about 1.3 to 1.0 billion years old. These
have been metamorphosed to gneisses. What grade of metamorphism is a gneiss? (high,
low)
The Grenville was the last cratonic piece added in the assembly of what would become
Laurentia, part of the Proterozoic supercontinent Rodinia.
Can you see any features in these rocks that look like bedding? ______________. Are the
features likely to be bedding or foliation? ____________________ If they are gneisses,
what is the predominant mineral orientation likely to be? (along sediment bedding planes,
perpendicular to directed pressure)
Suppose you had a large grant and access to a modern geoanalytic laboratory. How could
you distinguish metamorphic rocks that were sediments from metamorphic rocks that
once were basalts and granites? _____________________.
Suppose you were assigned the problem of mapping in the Highlands, and you want to
know, wherever possible, how the original orientation of sediments has been altered by
folding and faulting. If all the rocks are now metamorphosed, what metamorphic rock
type(s) should you look for? ______________________________________________
As we turn onto Route 15 North, we will start to see more rocks that were igneous in
origin. These were once a variety of granitic to basaltic rocks, now metamorphosed.
On top of the PreCambrian rocks are patches of younger Paleozoic sediments. These are
preserved in a few areas along 15. If I am quick, I’ll show you a patch of Silurian Green
Pond Conglomerate that is resistant to weathering. Which is likely to be closer to a source
area, (circle one) a conglomerate or a sandstone?
Logistics Stop. MacDonald’s in Jefferson Twp., NJ, Route 15. We will stop first in the
only MacDonald’s along Route 15. You can purchase food, water, and use the restrooms,
etc. ASK to see the Geologic Map of the area.
Across the driveway is a series of boulders from this region. You may look at them and
try to identify rock types and the common minerals you learned. Can you find gneisses,
granites, and perhaps something close to a migmatite?
List the ways you know of to form rocks that are granitic in composition.
1.____________________________________________________________________
2.____________________________________________________________________
What is a granitic composition, anyway? Define “granitic composition”
______________________________________________________________________
STOP 1. Grenvillian Lake Hopatcong Intrusive Suite. USGS Professional Paper
1565-c discusses the area.We will examine outcrops along an abandoned highway ramp.
We will take the exit where the sign points to the park and ride, about a half mile past
mile marker 10. I’ll park in the back of the park and ride lot. Looking toward Rt. 15,
you will see two rock outcrops. We will first walk along the one on your left. This is
mainly gneisses with granite intrusions, one thick, the rest thin.
There are several lines and breaks in the rock. Can you see dominant directions in the
some of the cracks? Can you find any offset features across the cracks? What about
slickensides? Are these joints or faults? ___________________________________
What mechanical weathering process might cause these?
Using a Compass, you will take strike and dip measurements on a rock face selected by
your instructor. First orient yourself, by asking “Which way is North?” Towards the
_________________(landmark)
What is the Strike of this rock surface? __________ What direction is this surface
dipping? ______________By how much? _____________
Write out the strike and dip in standard notation ____________________________
Are there any other surfaces you can see similar in orientation to this one? _________
Walk down to a second area (where the rock is broken and is different in it’s resistance to
weathering. Using the rock hammer, take samples of the broken low strength rock in the
crack, of the crystalline rock just to the left, and of the gneiss to the left. Label them with
a sharp magic marker as instructed.
Examine the rock samples. Can you suggest what happened in this area? _____________
_______________________________________________________________________
Place your samples in a backpack.
Look behind you at the small rock outcrop. Is this feature continued there? ___________
What does that tell you about the extent of such features here? _____________________
Walk to the end of this wall. A pegmatite is exposed there. Try to find amphiboles,
quartz, feldspars, micas, and some iron oxides. This green surface coatings are the
Sorosilicate Epidote, here apparently formed by retrograde metamorphism.
Turn around and walk along the low outcrops. Can you find any examples of inclusions,
a place where granites have broken off a piece of the local gneiss? ________. Which is
younger, the gneiss or the granite? __________________________________________
Next we will walk back to the parking lot and cross the road to another abandoned
highway exit ramp. Examine the granites and gneisses. What is the orientation of the
gneiss foliation? ___________. How does that compare to your understanding of
foliation direction in gneiss. i.e. which way was the directed pressure?___________ What
Plate Tectonic setting accounts for this area?
_____________________________________________________________
Walk back to the van. We will return to 15 North and will drive a short distance to a
small outcrop.
STOP 2. Large Scale Mafic and Felsic Banding. This contains broad bands of dark and
light rock with pegmatite intrusions. What is the large bunch of dark crystals made of?
_____________________. What minerals might the light colored bands be?
_____________________________________________________________________.
Suggest some possibilities for what has happened here:_________________________
______________________________________________________________________
If the felsic bands melted and recrystallized, what would such a rock be
called?________________.
We will continue north on 15 until the superhighway ends, pass the light and tracks (note
the sign for the Sterling Zinc Mine, a great trip we will run in Mineralogy) and on to the
next light at Houses Corner Road. We will turn left and continue on to the PreCambrian
Franklin Marble.
B. Valley and Ridge
STOP 3 Lime Crest Quarry mines this Precambrian marble as lawn lime and
ornamental gravel. The marble rests unconformably on top of the Grenvillian
metasediments. On the side of the road across from the mine are small piles of gravel
near the mile 6 marker.
How might the formation of extensive limestone deposits effect climate?
________________________________________________________________________
________________________________________________________________________
Besides atmospheric content of greenhouse gasses, what plate tectonic and orbital
conditions are important for extensive continental glaciation?
_______________________________________________________________________
_______________________________________________________________________
There are many small clusters of minerals in the marble. Nearby, many contain minerals
rich in Zinc. What divergent margin process might spread metal ore over the floor of an
ocean? ________________________________________________________________
What is metamorphism involving hot waters called? ____________________________
Next we will head back to Route 15, this time on the southbound side. At the beginning
of the superhighway part we will pass more Franklin Marble, but it is too dangerous to
stop there.
Past the Sparta exit, we will pull over into a parking area just before the overpass where
Cambro-Ordovician carbonates are still preserved.
What does Cambro-Ordovician mean? _______________________________________
STOP 4 Cambro-Ordovician Allentown Formation. Look to your right, there seem to
be one or two crumbled boundaries between stacks of carbonate rocks with different
orientations. What could such a “boundary” be? ___________________________
Can you tell if there is displacement? What would you need? A _______ ________ .
Can you find any slickensides? ___________________________________________
How wide is the fracture zone? ____________ meter.
Check these carbonates for calcite concentration. What carbonate rock do you know of
that behaves in this fashion? __________________. What mineral does it contain?
_______________ How is it different from pure calcite?__________________________
Allentown Formation Sparta NJ (continued) Part 2 mapping.
Measure the strike and dip of the bedding planes at several places on either side of the
broken areas. Keep track of your position with pace and azimuth from the fracture zone.
If you have a GPS, record as much detail on Latitude and Longitude as your instrument
can handle.
Surfaces are available here. Take strike and true dip. Use a flat surface to average the
plane.
1. Rocks to the right (north) Strike N ____o___ and dip______ o towards the ____ at
________ feet from the center of the fracture zone on an azimuth _________,
Latitude N____o______._____’ and Longitude W____o______.______’
2. Rocks to the right (north) Strike N ____o___ and dip______ o towards the ____ at
________ feet from the center of the fracture zone on an azimuth _________,
Latitude N____o______._____’ and Longitude W____o______.______’
3. Rocks to the left (south) Strike N ____o___ and dip______ o towards the _____ at
________ feet from the center of the fracture zone on an azimuth _________,
Latitude N____o______._____’ and Longitude W____o______.______’
4. Rocks to the left (south) Strike N ____o___ and dip______ o towards the _____ at
________ feet from the center of the fracture zone on an azimuth _________,
Latitude N____o______._____’ and Longitude W____o______.______’
5. Rocks to the left (south) Strike N ____o___ and dip______ o towards the _____ at
________ feet from the center of the fracture zone on an azimuth _________,
Latitude N____o______._____’ and Longitude W____o______.______’
Do the rocks on either side of the “boundary” strike and dip the same way? ______
Can you sketch what happened here?
After this stop, and a lunch break near the McDonald’s in Jefferson (the Pizza place
adjacent), we will return to Route 80 and will continue west toward the Delaware Water
Gap. Along the way we will pass Cambrian and Ordovician rocks on top of the
Precambrian Grenville metasediments and intrusives.
Lunch Discussion: The Appalachians: Greville, Taconic, Acadian, and Allegheny
Orogenies.
C. The Valley and Ridge continues along Rt. 80
There are two main types of Paleozoic rocks here: Cambrian and Ordovician carbonates
(shallow water limestones and dolomites), and dark Ordovician shales and slates. Both
are folded in this area.
Do the Precambrian and Paleozoic rocks have the same sized folds? Let’s collect some
data:
Beginning about mile 17:
As we pass sediment outcrops, record the direction of apparent dip by mile marker:
Mile Marker ___ ._ Apparent Dip (ahead OR behind us) Where (Crest, Upslope, downslope, valley)
Mile Marker ___ ._ Apparent Dip (ahead OR behind us) Where (Crest, Upslope, downslope, valley)
Mile Marker ___ ._ Apparent Dip (ahead OR behind us) Where (Crest, Upslope, downslope, valley)
Mile Marker ___ ._ Apparent Dip (ahead OR behind us) Where (Crest, Upslope, downslope, valley)
Mile Marker ___ ._ Apparent Dip (ahead OR behind us) Where (Crest, Upslope, downslope, valley)
Mile Marker ___ ._ Apparent Dip (ahead OR behind us) Where (Crest, Upslope, downslope, valley)
Mile Marker ___ ._ Apparent Dip (ahead OR behind us) Where (Crest, Upslope, downslope, valley)
Do the sediment folds follow the large scale topography? ______. What is this type of
tectonics called? __________- _________________ ____________________. How does
such a tectonic style occur?
Along 80 West on the right side of the road near mile marker 10 are some small scale
folds. LOOK SHARP:
What types of folds did you see? ___________________ and _________________.
How would you describe the carbonate rocks if you were using them as a landmark?
What does a wall of limestone remind you of? ________________________________
What does the symbol for limestone look like? Draw it:
As we drive down the hill towards the water gap, we will discuss the formation of water
gaps and wind gaps in the context of incised streams.
STOP 5 Shawangunk Formation. In New York State the shale and siltstone facies of
the middle to late Ordovician Martinsburg Formation (the dark shales and slates we just
passed on Route 80) can be seen to form an angular unconformity with the overlying
Silurian Shawangunk Formation.
This means that some ___________ occurred after the Martinsburg was deposited, prior
to the deposition of Silurian Shawangunk Formation. Can you think of a collision of the
right age that would account for this? The _______________ Orogeny.
What is the name of this clastic wedge that was deposited during the erosion of the
Taconic Uplift? ___________________________
If the Shawangunk is closest to the source area, what type of detrital sediments do you
expect it to contain? ____________________________________________________
What does it contain? ___________________________________________________
What did the Silurian Green Pond Conglomerate contain? ______________________
Which was closer to the source area? ______________________________________
What is a basin that forms inland from a collision called? __________________
At the Water Gap and elsewhere, there are thin lenses of dark fossiliferous shales that
have been compared to tidal flat streams. They contain large arthropods: eurypterids and
phyllocarids, and plants. In the Shawangunk, instances of mudcracks are known.
The top of the Shawangunk transitions into the base of the Bloomsburg Formation, with
the Bloomsburg redbeds alternating with the Shawangunk Quartzite.
STOP 6 High Falls - Bloomsburg Formation (Silurian) The Bloomsburg Formation
shows fining-upward sequences of non-marine deposits. Flood sequences, stream
deposits with some of the earliest jawless fish (Agnathans) are known from these
deposits. Some levels show fossil soils with root casts, etc..
We will examine the folding in the Shawangunk and Bloomsburg here. Which is
younger, the deposition of the sediments or the folding? _________________________
What is the age of the folding? ______________________________________
Next we will return to Route 80 and cross the bridge into Pennsylvania.
D. The Devonian sediments
Past the toll booth we see more Silurian sediments and then a variety of lower Devonian
marine deposits. Why did the sediments switch from shallow non-marine to marine
deposits? _______________________________________________________________
Where was the main impact of the Acadian Orogeny?____________________________
We will take the exit for Stroudsburg's business district (exit 307) and then follow the
signs for 191 North in a small loop. A few blocks past the light we will turn left onto
Brown and go to the stop sign. Ahead on our left is a small parking lot. Beyond is a small
black outcrop, the middle Devonian Marcellus Shale.
STOP 7 Marcellus Shale. (middle Devonian). To the west of 191 North are small
outcrops of a black shale. Only a few fossils are to be found here. Can you find a
brachiopod? Snails,a straight cephalopod, and byozoans are rare finds.
How many different fossils can you find? ____________________________________
Is the bedding planar, or cross bedded? ______________________________________
How big is the largest ripple? _____________________________________________
Was the water still or gently flowing? ________________________________________
What is the particle size (mud, silt, fine sand, etc.? ____________________________
Why is the sediment black? _______________________________________________
In what environment was this sediment deposited? ____________________________
Why is the diversity of fossils so low? _______________________________________
______________________________________________________________________
We will return to 191 North and drive to an outcrop of a middle Devonian Reef, part of
the Mahantango Formation.
Stop 8. Mahantango Formation (middle Devonian) I have to check in with the private
property owners. Thousands of geology students have benefited from examining this reef,
but the shoulder is narrow and traffic fast. Please keep yourself safe. Loose rock is at the
base. All persons must wear safety glasses.
The Mahantango is a reef with high fossil diversity. The major reef formers are rugose
corals, plus sponges and bryozoans; there are also fragments of crinoids, whole
brachiopods, and the occasional trilobite, especially Phacops rana.
What types of fossils did your group find? _____________________________________
_______________________________________________________________________
Why is the diversity we see here so much higher than in the Marcellus? ______________
________________________________________________________________________
________________________________________________________________________
Why would a coral need shallow water? Why would the other animals need shallows?
Next we will return to 80 North for a short drive (8 miles up to Tannersville, Pa.) past
successively younger beds in the Catskill Formation, a delta deposit. Along the way,
you should keep a record of the colors of the sediments by mile marker. Record how the
colors change as we drive higher in the Upper Devonian section:
Mile Marker:________Colors:______________________________________________
Mile Marker:________Colors:______________________________________________
Mile Marker:________Colors:______________________________________________
Mile Marker:________Colors:______________________________________________
Mile Marker:________Colors:______________________________________________
WHICH WAY ARE THE BEDS DIPPING? ______________ARE WE DRIVING
TOWARDS OLDER OR YOUNGER SEDIMENTS? _______________________
How could you account for different colors (say red and green and black) if the original
sediments were identical in this area?
______________________________________________________________________
Do the colors change abruptly or alternate? ___________________________________
Assume the rock color reflects the oxidation state of Iron in the sediments. What color is
Iron that has been oxidized by the atmosphere? (Hint: think of a nail left outside) ______
Based on this information, which of the three colors had the greatest exposure to high
oxygen levels? Would color would be most likely in very deep water? _______
In very shallow water? ______
Was the water in the Devonian getting deeper or shallower as we pass younger and
younger sediments in the Catskill Formation? ________Why? ________________
__________________________________________________________________
__________________________________________________________________
Take exit 299, ahead across the road is a gas station. We have permission to examine the
rocks on this property. DO NOT CLIMB ON THE ROCKS. Please be courteous to the
owners. Stay close to the rock wall and watch out for cars in the parking lot.
Stop 9. Exit 299, Tannersville, PA. Catskill Formation (Late Devonian). We’ll stop
here to refuel. Behind the gas station is an exposure of Catskill formation redbeds. West
of here, at Red Hill above Hyner, PA, fossil land plants, fish near the ancestry of
amphibians, and the earliest amphibian, Hynerpeton are being collected by scientists at
the Academy of Natural Sciences in Philadelphia. Here in Tannersville bone is very rare,
but the rocks contain interesting sedimentary structures. See if you can find root casts,
ripple marks, mudcracks, sole marks, and clay clasts eroded from other areas. I'll
personally pay $50 to the first person to find fossil bone in these sediments.
What sedimentary environments could have formed the sediments you see before you?
________________________________________________________________________
________________________________________________________________________
Rocks in this area are tilted. Further west at Hyner they are nearly flat. Why? _________
In fact, all rocks older than mid-Pennsylvanian are folded in eastern Pennsylvania. Why?
______________________________________________________________________
What hit us? ____________________________________________________________
What was this Orogeny called? _____________________________________________
You may purchase snacks, use the rest room, etc. When we leave here, our next planned
stop will be the campus.
E. Return throught the Highlands and Triassic\Jurassic Lowlands
We will take 80 back into New Jersey and will pick up Route 206 South within the
Grenvillian Metasediments and Intrusives. Soon afterward on our right we pass a sign for
Gold Mine Road, a reminder of the high metal content of late fractionation waters.
In the valley just before Chester, we will pass through Flanders, New Jersey. Sediments
along this syncline in the Highlands contain patches of the Cambrian and Ordovician
sediments we examined earlier. The rocks are not resistant to erosion, and outcrops are
few, but the carbonates make the waters of the South Branch of the Raritan River mildly
alkaline, and a unique flora and fauna live in the river as a consequence.
Return to route 206 south.
Just south of Chester, off a side road we will not follow, is an exposure of the Lower
Cambrian Hardyston Quartzite, the oldest Paleozoic rock in this area. Just past that road
we will begin our descent down the border fault\escarpment into the western flank of the
Late Triassic\Early Jurassic Rift Valley so familiar to us at Kean. Along 206 we will see
crumbling outcrops of “Brunswick” redbeds. If we had the time, further south in
Princeton we could find black lake beds, and over by the Delaware River we could see
the course Stockton Sandstones and Hammer Creek Conglomerates.
We will travel on 287 briefly, and then will pick up 78 east for the last leg back to Union.
Route 78 runs along the Second Watchung, one north of the basalt lava flow familiar to
us above Route 22. We will see small scale columnar jointing (cf. "devil's post pile") on
our left while passing Bernardsville and Berkeley Heights, and if there is enough light,
will see a huge basalt quarry on our right in Berkeley Heights.
How do we know these are lava flows and not sills? __________________________
____________________________________________________________________
When a lava flow bakes muds underneath it, what is the name we give to the rock that
has been baked in this "contact metamorphism"? ______________________________
Kean University Parking Lot. Keep this paper for class work. DO NOT LOSE IT.