Carbonate Aquifers - Trace Fossils as Indicators of Sedimentary Environments - page 854

FIGURE 8 The uppermost high-frequency cycle of the Miami Limestone, assigned to marine iso-
tope stage 5e ( modified from Halley et al., 1977 ). Conceptual model showing relations between
paleoenvironments, ichnologic parameters, and macroporosity related to Ophiomorpha -dominated
ichnofabrics. In some areas, the Ophiomorpha -related macroporosity is linked to the development of
karst features. The horizontal bars indicate the relative abundance of five ichnotaxa and the ichno-
fabric index scale with increasing line thickness corresponding to increasing abundance (few, mod-
erate, and abundant).
while smaller and relatively less energetic callianassids dominated the shallow
tier of the cycle. The shallow tier may, for instance, have been dominated by
juveniles or maybe a smaller-bodied callianassid species. As shown in
Figure 7 , sonic-log porosity values calculated from the Raymer-Hunt equation
are highest in the lower tiered zone of the Ophiomorpha -dominated ichnofabric
at the base of the HFC assigned to MIS 5e. Also, across this zone, fluid-
conductivity and fluid-temperature logs show marked changes in values, sug-
gesting relatively larger fluid flow either into or out of the borehole over this
interval and, thus, a relatively high permeability. Importantly, the geophysical
logs show potential for concentrated flow of groundwater through deep-tiered
zones of Ophiomorpha -dominated ichnofabric and a higher potential for diffuse
flow in the shallower Ophiomorpha -dominated zone.
3.1.4 Influence of Ichnology on Karst
Stratiform, touching-vug, macroporous, Ophiomorpha -dominated zones can
influence the development of relatively large-scale karst features (caves, sink-
holes, and vertical solution pipes) in the upper HFC of the Miami Limestone
assigned to MIS 5e. Examples of the stratiform, burrowed zones and related
caves have been identified in outcrops of the Miami Limestone within the
oolitic barrier bar and marine sand belt shown in Figure 8 . The cave system