Seismic sections can be divided into stratigraphic units of related strata bounded by unconformities. These units are called seismic sequences. They are categorized according to the relations between the boundaries and the reflections contained in the sequence. In this lab you will practice identifying seismic sequences and use them to come to conclusions about the depositional environment and possible lithologies.

Your assignment is to interpret a seismic section for stratigraphy. You can do all your initial work on one of the supplied (identical) sections, but please copy your final interpretation onto the other supplied section. You are to complete the following steps:

1. Interpret the attached migrated seismic section, using the following steps:

   1. Identify the water bottom multiple and mark it in blue to avoid confusing the geologic interpretation.

   2. Identify cycle terminations caused by onlap, downlap, erosional truncation, and toplap by marking a red arrow on the black half-cycle at the truncation.

   3. With a green pencil, trace the sequence boundaries which are defined by the cycle terminations. As a convention, mark the white half-cycle rather than the black one so the color is easier to see. Experience indicates that with this method the marked sequence boundary will be less than one full cycle away from its true position on the section.

2. Label each sequence with the shorthand notation from the attached handout.

3. Determine the geologic age of the sequences you identified where possible by tying to wells 2 and 3. The wells are plotted on the attached correlation diagram at the same vertical scale as the seismic section.

4. Interpret the depositional environment by:

   1. Tracing the shelf edge from the oldest recognizable sequence to the youngest.

   2. Indicating where sediments from shelf, slope, and deep basin floor environments are deposited.

   3. Showing two estimates of paleobathymetry by drawing lines in a fourth color along the tops of the oldest sequences deposited, and at the tops of a middle aged group of sequences.

5. Compute the vertical and horizontal resolutions of the seismic reflections at the bottom of the Albian, at the locations of the two wells. Note the time scale on the right side of the seismic section is in units of seconds. Use the 5000-foot depth of reflections at 1 s two-way travel time as given on the well correlation diagram to compute an average velocity V above the bottom of the Albian, and report it in units of m/s. Use this velocity also as the interval velocity v.