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Open File Report:
Stratigraphy of the Indian River Region |
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Introduction |
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Figure 1:
Location of study area including seismic survey,
well logs, and the subsurface
fault identified by Bermes (1958) and Schiner and others (1988). |
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Introduction
The geology and and hydrology of the central Indian River
region along the central east coast of Florida (Fig. 1) is of
critical concern to the St. Johns River Water Management District
(SJRWMD). In this area the upward migration of deeper, more
saline ground water in the lower Floridan aquifer to the
shallower, fresher ground water of the upper Floridan aquifer and
above, may impact the water quality of this resource. Higher
than normal chloride concentrations occur in wells east of a
reported fault within the Indian River south of Johns Island
(Bermes, 1958). The nature and extent of the fault is not well
defined. High-resolution seismic tools using digital technology
were utilized in collecting geophysical data in an attempt to
identify the fault. Additionally, the data collected exhibits
the benefits of these techniques in understanding the formation
of the upper Florida platform. The application of these
techniques aid in the management of water resources by
identifying the stratigraphy that contain the surface water
bodies and the various aquifer systems.
Physiography and Lithology
Beneath Indian River, the horizons of acoustic impedance are
generally related to lithologic changes between clays and
carbonates within the Hawthorn Group and with the underlying
carbonates of the Ocala Limestone. The Hawthorn Group sediments
are highly variable, layered sediments that range from poorly
indurated sands and shells to clays, and well indurated
carbonates (Scott, 1991). The variable bedding in the sediments
provide multiple reflections. The upper Ocala Limestone contact
is an irregular horizon identified as an erosional karst surface.
The limestone has few bedding planes that have sufficient
velocity contrasts to produce coherent reflections.
Strata above the Hawthorn are comprised of variable,
undifferentiated sediments associated with ridges formed by
Plio-Pleistocene barrier island and dune development. The ridges
form the Cocoa-Sebastian Ridge, the Sebastian-Juniper Ridge and
Upper St. Johns Karst Regions of the Eastern Flatwoods District
physiographic provinces described by Brooks and Merrit (1981).
The ridges have elevations of less than 28 m (90 ft). The Indian
River occupies the interstices of these paleo-ridges and the
modern offshore barrier development.
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