the florida state university college of arts and sciences evolution of ...

Field Sampling
CHAPTER 3
METHODS
Samples for sediment and geochronologic analyses were collected by two methods.
Vibracores were used to collect deep sediment samples beneath the beach ridges. Additionally,
whenever possible, trenches were excavated into selected ridges. All trenches were oriented
perpendicular to the trend of the ridge crest. A total of 18 trenches were excavated. Samples for
OSL dating were obtained by hammering 0.3 m sections of aluminum irrigation pipe horizontally
into the vertical walls of the trenches or by subsampling sections of the aluminum vibracore
tubes.
For this investigation trenching was the preferred method of sample collection. However,
sediment cores can also provide direct evidence of the lithologic character of the sediment.
Vibracoring is one of many subsurface sediment acquisition techniques. Samples were collected
by vibrating a core barrel into the sediment. By using this method it is possible to obtain cores of
up to 6.0 m in length in unconsolidated sediments. Vibratory corers have been in use for several
decades and techniques have improved through the years as field experience has advanced. They
are relatively simple devices comprised of a frame, coring tube, and drive head that consists of
either a pneumatic, hydraulic or electrical vibrator. For this study a Stow vibrator powered by an
8 horsepower Briggs and Stratton gas motor was used. The unit spins a flexible cable at a high
speed that causes the unevenly weighted head to vibrate. The head was mounted by U bolts to
an adaptor that was clamped to the 8-cm diameter aluminum core barrels. Once maximum
penetration was achieved, the top of the core barrel was filled with water and capped. This
created suction when the core was extracted and prevented the movement of sediment in the core
barrel. A come-along and tripod were used to extract each core out of the ground. For this
investigation, 8-cm diameter aluminum irrigation pipe cut into 3.0 to 6.0 m lengths was used.
Vibracores were not logged because they were opened under reduced light conditions for OSL
sample collection. Figure 3.1 shows the sample collection methods employed in this
investigation.
33