Cape Cod Tidal Flats EarthCache

If the coastal sediments are fine grained, a tidal flat or mud coastline is developed instead of a beach. Tidal flats are of such low slope that the sedimentation is dominated by the tides. Organism interaction with sediments and evaporitic influences may be intense in this environment. Extensive intertidal flats occur in macrotidal areas such as the Yellow Sea of Korea. In North America, similar tidal flats surround Bay of Fundy and occur along the New England coast and the North Sea. Narrower but significant intertidal flats also occur in mesotidal areas and mud shorelines are common off the microtidal, low relief Louisiana shoreline. Mud deposition is typically in protected, low energy environments such as estuaries and lagoons that also have an influx of dominantly fine-grained sediments.

However, mud deposition is not restricted to low-energy environments. Where there is an abundance of fine sediments, muddy deposits can persist even on coasts exposed to stronger wave action. Off the coast of Surinam (South America), muds are deposited in a wave energy environment normally associated with sand deposits (moderate wave power. The mud banks of Surinam resemble linear sand ridges on the shelf of the eastern United States in shape, oblique orientation to the coastline, and orientation with respect to dominant direction of transport processes. They are attached to the shoreline and commonly produce progradation of the coastline. ^{Rine and Ginsburg, 1985} The Surinam coast is just one example in a growing list of relatively high energy, inter-deltaic mud coasts that include the chenier plains of Louisiana, the Yellow Sea between China and Korea ^{Alexander et al., 1991} and the Kerala coast of southwest India where the fine-grained sediments are in such abundance that mud deposition follows.

Tidal flats have three basic environments

• subtidal,
• intertidal, and
• supratidal

The intertidal zone lies between normal low and high tides and is exposed once or twice daily. Coupling the modes of transport with duration of periods of submergence favors deposition of muds in the high tidal flats, interbedded mixed lithologies of mud and sand in the mid-flat zone, and sand in the low tidal flat zone. ^{Beall, Jr., 1968} Suspension transport is dominant in the high intertidal flat zones and the sediments are fine grained silts and clays, which have bioturbation, mudcracks and silty current ripples. The middle part of the intertidal flat is covered for about half of the tidal cycle and the nearly equal periods of suspension and bedload transport generate thin, parallel layered beds of alternating sand and mud with a tendency to coarsen in a seaward direction. Scour and channel sand deposition can cut across the other features of the intertidal flat. Bedload transport and deposition dominate in the low tidal flat zone. Intertidal sand bodies in the lower tidal flat which are exposed at low tide are linear shoals or bars deposited by tidal currents.

The supratidal zone is above high tide and sediment deposits are exposed to subaerial conditions most of the time with flooding only during spring or storm tides. This zone is divided into vegetated and non-vegetated intertidal mud flats and sand bodies. Storm-driven supratidal sediment-charged water creates layers of sediment in a few hours. These storm layers are sandwiched between layers of organic carbon-rich algae, which proliferate between storms. The non-vegetated part of the supralittoral may have algal mat laminar structures (discussed in Chapter 3). The blue-green filamentous algae trap and bind fine-grained sediments in a supratidal algal mat. The layered sequence in the mats results from a sequence of trapping of an influx of sediment, growth of the algae above the surface, and another sequence of sediment trapping. Tidal exposure allows development of mud cracks and curled chips of sediment during the drying out process in this zone. Intraclasts of these chips are eroded and redeposited during storms.

The supralittoral flat may have a growth of marsh grass. The growth of vegetation is the final stage in filling depressions, embayments and other irregularities along coasts and in the leveling of marine delta plains. Filling or preservation of the marsh environment is a result of interaction between the relative sea level rise and rate of sedimentation. ^{Allen, 1990}

To complete this earlcache you must follow the following guidelines:

1) Take a picture of your GPS with the above listed coords displayed

2) Identify the Intertidal and Supratidal areas using the above info and submit photo's of both

3) Identify at least 1 type of Marine Life occupying the tidal flats and submit a photo

4) You can log your visit immediately but please submit all photos either via the Cache Log or directly to the owner via tidalflatsearthcache@gmail.com


This cache was placed to honor the the previous caches "Triple B-Flat (GCJTM1)" and "Triple B-Flat Reprise (GCXBBK)"

The ideal time to search for this cache would be the two hour window of time beginning one-hour before each posted low tide and ending one-hour after the low tide.

This geocache is part of the Gulf of Maine Council Geotour across Nova Scotia, New Brunswick, Maine, New Hampshire and Massachusetts. You can earn a limited edition geocoin for accumulating 100 points in the tour. Details for the geotour can be found at the GOMC website. To play, download the full geotour passport.

Parking