Carbonate Aquifers - Trace Fossils as Indicators of Sedimentary Environments - page 843

to the ichnology of carbonate outcrops in the Biscayne aquifer's unsaturated
zone with taxonomic and comparative analyses.
2. METHODS
This chapter presents existing data on the Biscayne aquifer ( Cunningham and
Sukop, 2011; Cunningham et al., 2004, 2006a,b, 2009, 2010 ) and summarizes
new analyses and computations for carbonate rocks from the Biscayne aquifer
and Edwards-Trinity aquifer system ( Fig. 1 ). The new research includes (1) thin-
section petrography; (2) high-resolution X-ray computed tomography scans of
two carbonate rock samples analyzed at the high-resolution X-ray CT facility
at theUniversity of Texas; (3) LatticeBoltzmann calculation of the permeability;
and (4) quantification of the macroporosity by pixel counting on computer
renderings created from the CT scans. A description of the X-ray tomography
acquisition, Lattice Boltzmann method (LBM; Sukop and Thorne, 2006 ), and
pixel-counting technique can be found in Cunningham et al. (2009, 2010) .
The ichnofabric indices (II) scales of Droser and Bottjer (1986, 1989) were
applied to measurements of the intensity of bioturbation.
3. APPLICATION OF ICHNOLOGY TO
AQUIFER CHARACTERIZATION
Important applications of ichnology, especially the study of ichnofabrics, to car-
bonate aquifer characterization include its use in improving (1) delineation of
cycles, (2) mapping of cycles based on correlation of biogenically altered sur-
faces, (3) mapping of zones of preferential groundwater flow and paleoground-
water flow, and (4) understanding of the origin of karst features where related to
ichnogenic macroporosity and permeability (as defined by Cunningham et al.,
2009 ). These applications are discussed individually for carbonate rocks of the
Biscayne aquifer and Edwards-Trinity aquifer system ( Fig. 1 ). The research
results related to these two groundwater systems strongly reflect the practicality
of integrating ichnology and hydrogeology for the purpose of carbonate aquifer
characterization.
Three case studies are presented ( Fig. 1 ), concentrating on the influence of
thalassinidean or thalassinidean-like crustacean-produced ichnofabrics on car-
bonate aquifer characteristics. The first study focuses on interpretation of multi-
disciplinary data from the Biscayne aquifer and provides evidence for
concentrated groundwater flow through stratiform, touching-vug, macroporous
zones where the macroporosity is related to both, (1) primary intraburrow poros-
ity, and (2) secondary fabric-selective intraburrow and interburrowmacroporos-
ity within Ophiomorpha -dominated ichnofabrics (see Cunningham et al., 2009
for definitions of porosity terms). These pore types occur as the principal
groundwater-flow networks in broad areas of the aquifer. The other two studies
of carbonate rocks that comprise parts of the Edwards-Trinity aquifer system