Field Trip Questions

Geology 1200

Name: ______

Work on these questions insmall 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.

There won’t be much to see on the way to Route 80. I’ll point out a valley between Jurassic Basalt ridges that was a proglaviallake 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 ecology in the 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 PrecambrianHighlands (our first destination) but on the way there we won’t see much: the highway department has been busy removing basalt rock along 24. Once we climb up the border fault to Route 80, however, 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 anyfeatures in these rocks that look like bedding? ______. Are the featureslikely 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 couldyou 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.

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 LakeHopatcongIntrusive Suite.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 15, you will see two rock outcrops. We will walk along the one on your left. This is mainly gneisses with granite intrusions.

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 the Brunton 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 thecrack, of the crystalline rock just to the left, and of the gneiss 5 meters to the right. Label them with a sharp magic marker ES0715A-1, 2 and 3 respectively.

Examine the rock samples. Can you suggest what happened in this area? ______

______

Place your samples in a plastic bag labeled ES0715A

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? ______

Does this feature have the same orientation as the surface measured in area 1? ______

Walk to the end of this wall. A pegmatite is exposed there. Try to findamphiboles, quartz, feldspars, micas, and some iron oxides.

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.In the center of the right hand wall the rock has weathered to a vertical black stripe. 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.

STOP 3Lime Crest Quarry mines this Precambrian marble as lawn lime and ornamental gravel. The marble rests unconformably on top of the Grenvillian metasediemnts we saw. 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?

Check these carbonates for calcite concentration. What carbonate rockdo you know of that behaves in this fashion? ______. What mineral does it contain? ______How is it different from pure calcite?______

Measure the strike and dip of the bedding planes on either side of the broken areas.

Rocks to the right (north) Strike N ____o___ and dip______o towards the ____

Rocks to the left (south) Strike N ____o___ and dip______o towards the _____

Do the rocks on either side of the “boundary” strike and dip the same way? ______

Can you sketch what happened here?

After this stop 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.

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 gently folded in this area.

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)

Do the sediment folds follow the 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?______

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.

Logistics stop. MacDonald’s Delaware Water Gap. Rest rooms, lunch as needed.

Discussion, maps.Review Blairstown Surface Geology Map for comparison to Cambro-Ordovician just seen. Note Water Gap geology. Break out Pennsylvania Maps.

STOP 5 Shawangunk Formation.In New YorkState 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 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 eurypterids, 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 Bloomsburg Formation(Silurian) The Bloomsburg Formation 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 a maximum age for the folding? ______

Next we will return to Route 80 and cross the bridge into Pennsylvania.

Past the toll booth we see more Silurian sediments and then a variety of lower Devonianmarine deposits. Why did the sediments switch from shallow non-marineto 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 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? ______

______

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. 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:______

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 that be most likely in very deep or 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 SciencesinPhiladelphia. 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.