Readings for Geologic Background:

In discussing this topic we have several major goals. First, we want to understand the geologic setting of Chesapeake Bay, which is located in the coastal plain on the eastern seaboard of the United States. To differentiate the coastal plain from the Piedmont and the other physiographic provinces of the Appalachian mountains requires some basic geologic history, which involves a brief discussion of the role of plate tectonics in events that go back several hundred million years. You will have some class handouts describing the major physiographic provinces and the geologic time scale so you can keep these events in temporal and spatial perspective. After discussing some basic aspects of the evolution of the Appalachian Mountains we will cover the opening of the modern Atlantic Ocean and the development of the passive continental margin and the sequence of sediments and sedimentary rocks that underlie the Coastal Plain  and the Atlantic seaboard. We will talk about the role played by a meteorite impact 35 million years ago that had a profound influence on Chesapeake Bay, even though Chesapeake itself did not exist until much more recently. That event punctuated a fairly long interval of depositional activity extending throughout the Tertiary period of earth history.

After this we will turn to the evolution of Chesapeake Bay itself, based on what is known about its history during the Pleistocene period, when periods of glaciation and low sea level alternated with interglacial periods and high sea level. The Pleistocene began about 1.8 million years ago. The most recent warming episode brought on the Holocene period of the past 10,000 years or so, and it was during this time that the modern Chesapeake Bay formed. Therefore we need a little bit of paleoclimatic history, and we need to understand how the present Chesapeake Bay and previous incarnations of Chesapeake Bay responded to oscillations in sea level. Some additional information on sea-level rise during the Holocene will be provided in class.The reading by Colman, Halka and Hobbs describes evidence associated with  several sets of buried channels underneath the floor of Chesapeake Bay. These are apparently ancient channels of the Susquehanna River from past glacial periods. Looking at these channels and at when they formed, we can begin to understand the progressive evolution of the Delmarva peninsula and of Chesapeake Bay as we know it today.

Once we have some understanding of the geologic history of the Bay, we still need to discuss the modern geologic processes that sculpture the Bay as we know it today. The reading by Ward and others, provides some discussion of both the recent geologic history and the modern processes, including sea-level rise, shore erosion and sedimentation.

Finally, we will spend some time in class exploring the geomorphic evolution of our modern Bay, focusing on how the fluvial topography inherited from the Pleistocene is inundated by rising sea level, how drainage systems are dismantled, and how the landscape is modified by waves, longshore transport of sediment, marsh growth, and filling of tidal tributaries by sediment coming from upland drainage. There is no single reading that can provide this information, but you should read review the chapter on coasts and shorelines from your basic physical geography or physical geology textbook. (I assume you have taken either Geography 110 or 111; if not, you are responsible to borrow a textbook from someone else and read the appropriate chapter.)   Important topics include waves and wave refraction, longshore drift, coastal erosion, coastal sediment transport and the evolution of beaches, spits and barrier islands, tides, and a general discussion of the evolution of different types of coasts. We will learn more about waves and tides when we get to the topic of estuarine circulation. Once you understand the basic processes, it becomes easier to interpret the landscape as seen from a topographic map or an aerial photograph.

1. Pages from the World Wide Web:

The following pages provide important background on the geologic framework underlying Chesapeake Bay. Notes will indicate what you should focus on. Look through these before going to the pdf files. There are a lot of pages but most of them are quite short, and scrolling through them should give you a good overview.

2. Adobe Acrobat (pdf) files available on line - check the Course Documents folder on Geologic Background: 3. Supplementary notes on estuarine geology and geomorphology