Field AssignmentPart I

By Edward Potter

The Chesapeake Bay is the ria, or drowned valley, of the Susquehanna, meaning that it was where the river flowed when the sea level was lower. It is not a fjord, as the Laurentide Ice Sheet never reached as far south as the northernmost point on the bay.

The bay's geology, its present form, and its very location were created by a bolide impact event at the end of the Eocene (about 35.5 million years ago), forming the Chesapeake Bay impact crater and the Susquehanna river valley much later. The Bay itself was formed starting about 10,000 years ago when rising sea levels at the end of the last ice age flooded the Susquehanna river valley. Parts of the bay, especially the Calvert County, Maryland coastline, are lined by cliffs composed of deposits from receding waters millions of years ago. These cliffs, generally known as Calvert Cliffs, are famous for their fossils, especially fossilized shark teeth, which are commonly found washed up on the beaches next to the cliffs. Scientists' Cliffs is a beach community in Calvert County named for the desire to create a retreat for scientists when the community was founded in 1935.

Much of the bay is quite shallow. At the point where the Susquehanna River flows into the bay, the average depth is 30 feet (9 m), although this soon diminishes to an average of 10 feet (3 m) from the city of Havre de Grace for about 35 miles (56 km), to just north of Annapolis. On average, the depth of the bay is 21 feet (7 m), including tributaries; over 24% of the bay is less than 6 ft (2 m) deep.

The climate of the area surrounding the bay is primarily humid subtropical, with hot, very humid summers and cold to mild winters. Only the area around the mouth of the Susquehanna River is continental in nature, and the mouth of the Susquehanna River and the Susquehanna flats often freeze in winter. It is exceedingly rare for the surface of the bay to freeze in winter, as happened most recently in the winter of 1976–77.

Chesapeake Bay

Igneous rocks are formed from the solidification of molten rock material. There are two basic types: 1)intrusive igneous rocks such as diorite, gabbro, granite and pegmatite that solidify below Earth's surface; and 2) extrusive igneous rocks such as andesite, basalt, obsidian, pumice, rhyolite and scoria that solidify on or above Earth's surface

Igneous Rocks

I BELIEVE THIS ROCK TO BE DIORITE WHICH IS A COARSE-GRAINED, INTRUSIVE IGNEOUS ROCK THAT CONTAINS A MIXTURE OF FELDSPAR, PYROXENE, HORNBLENDE AND SOMETIMES QUARTZ. 

Sample # 1

Metamorphic rocks have been modified by heat, pressure and chemical process usually while buried deep below Earth's surface. Exposure to these extreme conditions has altered the mineralogy, texture and chemical composition of the rocks. There are two basic types of metamorphic rocks: 1) foliated metamorphic rocks such as gneiss, phyllite, schist and slate which have a layered or banded appearance that is produced by exposure to heat and directed pressure; and, 2) non-foliated metamorphic rocks such as marble and quartzite which do not have a layered or banded appearance. 

Metamorphic Rocks

I BELIEVE THIS ROCK TO BE GNEISS, WHICH IS FOLIATED METAMORPHIC ROCK THAT HAS A BANDED APPEARANCE AND IS MADE UP OF GRANULAR MINERAL GRAINS. IT TYPICALLY CONTAINS ABUNDANT QUARTZ OR FELDSPAR MINERALS. 

Sample # 2

Sedimentary Rocks Sedimentary rocks are formed by the

accumulation of sediments. There are three basic types of sedimentary rocks: 1) clastic sedimentary rocks such as breccia, conglomerate, sandstone and shale, that are formed from mechanical weathering debris; 2) chemical sedimentary rocks such as rock salt and some limestones, that form when dissolved materials precipitate from solution; and, 3)organic sedimentary rocks such as coal and some limestones which form from the accumulation of plant or animal debris.

I BELIEVE BOTH OF THESE ROCKS ARE SANDSTONE, WHICH ARE A CLASTIC SEDIMENTARY ROCK MADE UP MAINLY OF SAND-SIZE (1/16 TO 2 MILLIMETER DIAMETER) WEATHERING DEBRIS. ENVIRONMENTS WHERE LARGE AMOUNTS OF SAND CAN ACCUMULATE INCLUDE BEACHES, DESERTS, FLOOD PLAINS AND DELTAS. 

Sample # 3

Sample # 4

I BELIEVE THIS ROCK TO BE CONGLOMERATE WHICH IS A CLASTIC SEDIMENTARY ROCK THAT CONTAINS LARGE (GREATER THEN TWO MILLIMETERS IN DIAMETER) ROUNDED PARTICLES. THE SPACE BETWEEN THE PEBBLES IS GENERALLY FILLED WITH SMALLER PARTICLES AND/OR A CHEMICAL CEMENT THAT BINDS THE ROCK TOGETHER

Sample # 5

REFERENCE PAGE http://en.wikipedia.org/wiki/Chesapeake_Bay http://geology.com/ EARTH, (Tarbuck and Lutgens, 2010)

Researching what types of rock samples I have, was a tough task. I am hoping I got close. This was fun and I had a great time doing it.