Introduction

            The purpose of this study was to recreate the paleoecology of the BangorLimestone.  The study was conducted in conjunction with three

other students at the University of North Alabama.  The fossils from each locality were used to conduct the study.  Using the characteristics of

Blastoids, Corals, Brachiopods, Gastropods, Crinoids, Bryozoans, Trilobites, Clams, and Cephalopods the paleoecology during the Mississippian

was interpreted. 

Purpose of Study

            Fossils were collected at three localities.  The fossils were used to recreate the paleoecology during the Mississippian.  Using their

characteristics and the environment in which they lived, the paleoenvironment of Northwest Alabama during the Mississippian was recreated. 

Materials and Methods

            Fossils were collected at three localities in the Bangor Limestone.  The three localities were Fox Trap, Alabama Highway 247, and Coon Dog.  One hour at each locality was spent collecting fossils.  Only fossils that were completely weathered out were collected.  The fossils were then soaked in soapy water, rinsed, and allowed to air dry.  The fossils were then sorted by species and counted.  The totals were then exchanged with the other three classmates.   Any fossils found were assumed to have lived there.  

Stratigraphy

            “The Bangor Limestone was deposited in shallow carbonate shelf and basinal mixed carbonate-clastic settings on the southeastern margin of the North American craton during Late Mississippian (middle and late Chesterian) time” (Alego and Rich, 1992).  “Late in the Mississippian sea levels rose one more time leaving the sediment from the Ouachita mountain-building far back to the west” (Lacefield, 2000).  The Bangor Limestone records marine transgressions, one major and several minor, this affects the shelf margin (Alego and Rich, 1992).

            The Bangor Limestone of Northwest Alabama is overlain by the Pottsville Formation and underlain by the Hartselle Sandstone.  The Bangor Limestone was deposited in three environments: low-energy open marine shelf, a high-energy ooid shoal, and a low-energy back shoal lagoon and tidal flat complex (Alego and Rich, 1992).  The open marine shelf was deposited below the wave base (Alego and Rich, 1992).  This area had normal salinity and formed wackestones and packstones (Alego and Rich, 1992).  This area is dominated by bryozoan-echinoderm wackestone/packstone (Alego and Rich, 1992).  “Bangor high-energy shoals developed where wave base intersected the landward-rising marine shelf, causing wave and tidal-current energy to dissipate through friction” (Alego and Rich, 1992).  This area results in shell fragmentation, abrasion, and sorting (Alego and Rich, 1992).  This area is covered by oolitic grainstone (Alego and Rich, 1992).  The low-energy lagoon and tidal flats were located “shoreward” of the high-energy zone (Alego and Rich, 1992).   

Collecting Area

          The three collecting localities were Fox Trap in Littleville, Alabama; Alabama Highway 247 in Colbert County 8 miles west of the 72 and 43 junction; and Coon Dog in Colbert County1/10 mile off of Alabama Highway 247.  Fox Trap is made up of limestone.  Highway 247 is limestone with interbedded shale.  Limestone is exposed at the bottom.  The limestone layer is the layer the fossils were collected from.  The limestone at the Coon Dog locality was deposited with higher energy.  The evidence comes from the fact the fossils at this locality were more flattened than the other two localities.           

Discussion

            Many things play an important role in determining the environment of deposition.  There are many limiting factors that play a role in determining where an organism lives.  These factors include salinity, temperature, depth, and sediment type.  Below is a brief discussion on some of the limiting factors of each phylum found at the three localities. 

Salinity

Normal salinity is about 35% (Boardman, 1987).  The following table was created from Prothero, 1998:

Organisms that are euryhaline can tolerate wide ranges of salinity, stenohaline means the organism cannot tolerate a wide range of salinity (Dodd, 1990).  The following table summarizes the salinity tolerance of the collected fossils. 

Table compiled from Dodd, 1990

The following chart is a summary of the organisms found at the three localities.

General Information

Bryozoans

• Shallow mud bottom (McKinney and Jackson, 1988).
• Colonial (McKinney and Jackson, 1988).
• Benthic
• Most are marine (Clarkson, 1993).

Crinoids

• Benthic
• Shallow water (Hess, 1999).
• Carbonate sediment (Hess, 1999).
• Can handle a minor variation in salinity (Hess, 1999).
• Need high oxygen content (Hess, 1999).
• Low energy environment (Hess, 1999).
• Occurrence on muddy bottom is unlikely (Prothero, 1998).

Blastoids

• Never abundant (Clarkson, 1993).
• Occurs on reef-knoll and carbonate shelf fauna (Clarkson, 1993).

Trilobites

• Most are benthic (Taylor, 1998).
• “Trilobites lived in shelf and slope environments around continental margins and in the shallow continental seas that covered areas of the earth that today are land masses” (Taylor, 1998).

 Coral

• Important reef builders (Prothero, 1998).
• Clear, shallow water in the photic zone (Prothero, 1998).

Gastropods

• Marine, terrestrial, or freshwater

Clams

• Marine (Clarkson, 1993).
• Benthic (Clarkson, 1993).

Brachiopods

• Benthic
• Shallow water (Clarkson, 1993).
• Shallow shelf (Clarkson, 1993).
• Normal salinity (Prothero, 1998).

Cephalopods

• Marine (Clarkson, 1993).

Possible Environments

            A reef environment is shallow and has normal salinity (Suthern, 2000).  There are three types of reefs (Suthern, 2000).  The three types of reefs are fringing, barrier, and atoll (Suthern, 2000).  A fringing reef is muddy because of the influx of freshwater (Suthern, 2000).  The influx of freshwater would cause a flux in salinity.  A barrier reef has normal salinity and low energy (Suthern, 2000).  An atoll is usually in a volcanic core (Suthern, 2000). The continental shelf can be a low energy environment (Raymond, 2002).    Barrier Islands receive more impact from waves and currents (Author Unknown, 2002).  The salinity of the barrier island environment does not fluxuate (Author Unknown, 2002).          

Conclusion/Summary

            From looking at the above salinity chart the environment must be of a constant salinity because of the organisms that are stenohaline.  Some organisms such as the Bryozoans, Crinoids, and Blastoids prefer a low energy environment, therefore I have concluded that Fox Trap was a continental shelf, Highway 247 was a reef, and Coon Dog was a barrier island.  The evidence to support these claims is stated below.

            The dominant organism at Fox Trap was the brachiopod.  Brachiopods prefer to live on the continental shelf.  Fox Trap also had a lot of crinoids and bryozoans, they prefer a low energy environment.  The continental shelf is a low energy environment. 

            The dominant organisms at highway 247 were brachiopods, crinoids, and bryozoans.  Crinoids and bryozoans prefer a low energy environment, therefore I conclude that highway 247 was a reef.  A reef is an area of low energy.  As stated above a reef has normal salinity, which is preferred by brachiopods. 

The dominant organisms at Coon Dog were crinoids and bryozoans.  The crinoids and bryozoans like a low energy environment, therefore I have concluded that Coon Dog was a barrier island.  The barrier island environment can also have high energy from the waves, and also during storms.  The higher energy concurs with the flattened fossils collected at this locality.

References

1. Author Unknown, 2002, Organisms of the Bay, Retrieved on December 2, 2002, from

World Wide Web: http://www.rice.edu/armadillo/Projects/Ecodillo/Galveston/organisms.html

2. Alego, Thomas J. and Mark Rich, February 1992, Bangor Limestone: Depositional and

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http://alabamamaps.ua.edu/alabama/basemaps/basemap2.jpg