Virtual Field Trip 1:
Outcrops near Dalton, Georgia

Dalton is located in the Ridge and Valley Province of Georgia, about 100 miles northwest of Atlanta. The Ridge and Valley is the one area in Georgia that preserves sedimentary rocks that were deposited on the platform of the North American craton during the early Paleozoic. The Paleozoic rocks have been folded and faulted to produce long ridges that trend northeast to southwest. The faults bounding the province are thrust faults where sheets of sandstone, shale, limestone, and dolostone have been pushed northwestward on top of each other. As we will see, however, normal faults also occur in certain rocks of certain time periods. We will examine outcrops at three stops, defining a semicircle beginning on the northeast side of Dalton and ending on the Conasauga River at Tibbs Bridge.

As you can see from the state geological map, the outcrops we will visit lie between the Great Smoky (Cartersville) fault to the east and the Rome fault to the west. Find these two faults either on the above figure or, preferably, on an original copy of the state map which has the map key. Answer the following:



    1. Which map units are found east and west of the Cartersville fault in the vicinity of Carters Dam?



       _______________________________________________________________    


	

    2.  Which map units are found east and west of the Rome fault?



       _______________________________________________________________    



STOP 1 - CHATTANOOGA AVENUE

 

	The field trip begins at the bedrock outcrop at the corner of the North Dalton
        bypass (US 76) and Chattanooga Avenue. To reach the outcrop, you take exit 336
        from I-75. This will put you on US 76, which you take east for approximately 2 miles
        to the intersection with Chattanooga Avenue. The above view is looking west along 
        Chattanooga Avenue from the outcrop. Note the long ridge in the background which
        trends northeast, parallel to the regional strike of the Paleozoic sedimentary
        rocks.

	According to the state geological map, the outcrop at STOP 1 is middle Ordovician, 
        Bays formation or Mocassin limestone (Omb). Siltstone, shale, and limestone all occur.
        Changes in color are quite dramatic but partly due to chemical changes that have
        occurred since the sediments were deposited. Several large faults cut across the
        entire outcrop. The rocks have been smoothed and polished, and there is quartz material
        along the fault planes that formed during the faulting.



	 
    3.  If the bed labeled A is the same on either side of the fault, would this be a reverse or a normal fault?
 


  	______________________________________________________


        How can you tell?



  	______________________________________________________



	In spite of the faulting, the rock retains grain size differences and other
        features that indicate the environment in which the sediment was deposited.
        Sedimentary structures such as those in the images below indicate a setting
        between high and low tide with a moderate degree of bioturbation or disturbance
        by burrowing organisms.  




    4.  Image A shows mudcracks. What do these indicate about the depositional environment?
 


  	______________________________________________________



    5.  Image B shows symmetrical ripple marks. What do these indicate? Is this the top or the bottom of the bed?
 


  	a. ______________________________________                  b. _____________________________________


    6.  Image C shows a filled-in burrow, probably from a worm. Does this mark the top or the bottom of the bed?
 


  	______________________________________________________




STOP 2 - ICHNOFOSSILS IN CONASAUGA SHALE

The outcrop at STOP 2 is in the Conasauga shale (Ccs), according to the state geological map. The rocks at STOP 2 are the most highly metamorphosed of those we examined. The beds in the lower part of the outcrop were the least deformed. Laminar bedding can be seen below the dashed line in the image below.



	The beds in the upper two thirds of the outcrop were thrust over the more laminar beds at the
	base. I measured a strike of N 40 deg E (see my instructions on measuring strike and dip).
	The beds dip at 78 degrees below the horizontal.

	Our main reason for visiting this outcrop was to observe the unique trace fossils ("ichnofossils") which
	Ken Leonard has found on bedding surfaces in this rock. 



	The small circular depressions in the rock immediately above my rock hammer are ichnofossils
	which Ken thinks were made by members of the phylum Cnidaria.




    7. Look in your textbook and find the phylum Cnidaria. What are some modern organisms which are 
       members of this phylum?



  	_________________  _________________  _________________  _________________




    8.  Describe one of the samples of the Conasauga "shale" that we collected from the outcrop at STOP 2:  

	Color(s)  ________________________________________   Hardness _______________

	Texture __________________________________________________________________

	Bedding/Foliation __________________________________________________________




STOP 3 - TIBBS BRIDGE ON THE CONASAUGA RIVER



	Tibbs Bridge on the Conasauga River is reached by taking Tibbs Bridge Road from
	Spring Place on S.R. 225. The river channel makes abrupt right angle bends here 
	so that the channel is either aligned with the bedrock strike or running perpendicular 
	to it. Both limestone and shale are included in the unit shown on the state geological 
	map. The outcrop that we will be looking at is under the bridge on the east bank.
	Shale erodes easily, so that the bank is covered with crumbled pieces of shale.

	If you break off a fresh slab and closely examine the top of each laminar bedding
	plane, you will be rewarded by the discovery of a fossil trilobite.




   9.  Describe one of the samples of the Conasauga shale that we collected from the outcrop at STOP 3:  

	Color(s)  ________________________________________   Hardness _______________

	Texture __________________________________________________________________

	Bedding/Foliation __________________________________________________________



   10.  Now compare your descriptions and the samples from STOP 2 and STOP 3 with each other and with
	samples of shale, slate, and phyllite provided by your instructor. What rock name would you assign to:


	STOP 2 outcrop ___________________________________


	STOP 3 outcrop ___________________________________




REFERENCES

Chowns, T. M., 1972, Sedimentary environments in the Paleozoic rocks of northwest Georgia. Georgia Geological Survey, Atlanta.

Cressler, C. W., 1964, Geology and Ground-Water Resources of the Paleozoic Rock Area, Chattooga County, Georgia. Georgia Geological Survey Information Circular 27, Atlanta.

Pickering, S. M., and Murray, J. B., 1976, Geologic Map of Georgia. Georgia Geological Survey, Atlanta.

Munyan, Arthur Claude, 1951, Geology and mineral resources of the Dalton quadrangle, Georgia-Tennessee. Georgia Geological Survey, Atlanta.


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Copyright Donald M. Thieme
Valdosta State University, Valdosta, GA
Page created June 1, 2009