This item has the following downloads:

PDF ( PDF )

STATE OF FLORIDA
DEPARTMENT OF NATURAL RESOURCES
Don Duden, Acting Executive Director





DIVISION OF RESOURCE MANAGEMENT
Jeremy A. Craft, Director





FLORIDA GEOLOGICAL SURVEY
Walter Schmidt, State Geologist and Chief





Open File Report No. 56



Sarasota County Intermediate Aquifer System
Core Drilling and Analysis

by

Kenneth M. Campbell, Thomas M. Scott,
Richard Green and William L. Evans, III


Florida Geological Survey
Tallahassee, Florida
March 1993









SARASOTA COUNTY INTERMEDIATE AQUIFER SYSTEM
CORE DRILLING AND ANALYSIS

by
Kenneth M. Campbell, P.G. 192, Thomas M. Scott, P.G. 99,
Richard C. Green and William L. Evans III

Introduction

The Florida Geological Survey (FGS), in cooperation with the

U. S. Geological Survey (USGS) and Sarasota County, drilled and

analyzed two core holes in Sarasota County (Figure 1). This in-

vestigation focused on the Neogene stratigraphy of the interme-

diate aquifer system in the two cores which were drilled into the

Oligocene "Suwannee Limestone" and the top of the Floridan aquifer

system. Funding was provided by the FGS with assistance from the

USGS (Purchase Order 047670-92).

The study area is located in southwestern peninsular Florida

approximately centered on the axis of the Florida Platform. Water

resources in Sarasota County are drawn in large part from the in-

termediate aquifer system and the Floridan aquifer system. The

Floridan aquifer system is comprised of Paleogene and earliest

Neogene carbonate sediments. The intermediate aquifer system and

confining unit is composed of Neogene Hawthorn Group sediments.

The Neogene stratigraphic section in this area is incomplete due to

non-deposition and erosion with part of the Miocene and much of the

Plio-Pleistocene missing.

The Carlton Reserve core, FGS W-16782, 580' TD, is located in

the northwest quarter of the northwest quarter of section 31, Town-

ship 38 South, Range 20 East. The South Venice core, FGS W-16814,












R 17 E R 18 E R 19 E R 20 E R 21 E R 22 E


Scaie
0 1 2 3 4 Miles
0 1 2 3 45 6 Kllomrnete
* WELL LOCATION


Figure 1: Location map and core locations.


-N


I








701' TD, is located in the northwest quarter of the northwest quar-

ter section 29, Township 39 South and Range 19 East. Both core-

holes were drilled utilizing a Failing 1500 drill rig. Core sam-

ples were collected from the land surface to the total depth of

each well. Split spoon samples were collected at selected inter-

vals in the unconsolidated sediments for hydraulic conductivity

analysis. The Carlton Reserve well was converted to a four inch

diameter monitor well by plugging the hole back to 190 feet and

installing casing from the land surface to 175 feet. The open hole

interval is from 175-190 feet. The South Venice core was abandoned

after coring, in accordance with Southwest Florida Water Management

District and Sarasota County regulations.

Lithologic descriptions were generated for each core by a FGS

geologist utilizing a binocular microscope. The descriptions

(Appendix 1) follow the standard FGS format and were entered into

the FGS data base via WELL LOG DATA SYSTEM software (Geosys Inc.,

1992). Formation picks were made based on the core samples in con-

junction with the gamma logs for the cores.
Structure

The broad Florida Platform extends southward from the North

American continent, separating the Gulf of Mexico from the Atlantic

Ocean. The exposed portion of the platform forms the State of

Florida with the present day western coast of peninsular Florida

approximating the axis of the Florida Platform. The Sarasota

County study area, located on the southwestern portion of the

Florida peninsula, lies near the center of the southern half of the








platform.

The main structural features that affected Cenozoic deposition

in the study area include the Sarasota Arch, South Florida Basin,

Ocala Platform and Okeechobee Basin. The Sarasota Arch and the

South Florida Basin influenced deposition during the Paleogene

while the Ocala Platform and the Okeechobee Basin affected depo-

sition during the Neogene.

Subsurface investigations in southwestern Florida have en-

countered complex geologic conditions in the Neogene section. Some

researchers have delineated faults disrupting the strata and com-

plicating the hydrostratigraphic and lithostratigraphic interpre-

tations (Sproul et al., 1972; Hutchinson, 1991). Other investi-

gators recognized folding in seismic reflection surveys run paral-

lel to the coastline (Missimer and Gardner, 1976). This has led to

speculation that deep seated faulting was responsible for the near

surface structures. Interesting new data acquired during recent

seismic surveys off the southwestern coast of the state have re-

vealed that the reflectors in the mid-Eocene section are essen-

tially flat lying while reflectors in the Mio-Pliocene section

appear folded (Missimer, personal communication, 1993). Evans and

Hine (1988) discussed the existence of a number of small "basins",

erosional features and "deltas".

Lithostratigraphy

This investigation focused on the stratigraphy of the Neogene

section as recognized in two Florida Geological Survey drilled

coreholes, Carlton Reserve (W-16782) and South Venice (W-16814).








The FGS coreholes were drilled to a depth sufficient to reach the

top of the Oligocene "Suwannee Limestone" and the top of the

Floridan aquifer system (Figures 2-4).

The "Suwannee Limestone" is referred to in quotes as a result

of uncertainties concerning the actual formational identification

of the Oligocene limestones in southern Florida. In the past, the

first carbonate unit below the base of the Tampa Limestone (now

Tampa Member of the Arcadia Formation, Hawthorn Group) was assigned

to the Suwannee Limestone based simply on superposition. There is

concern that these sediments may actually be younger than the type

Suwannee Limestone and, since there is significant lithologic vari-

ation from the type, may be a separate formation. In keeping with

the conventions described on the COSUNA chart for the Gulf Coastal

Region (Braunstein et al., 1988) the name is used in quotes to de-

signate that it is a formal lithostratigraphic unit name that may

be incorrectly used.

The "Suwannee Limestone" occurs at 572 feet and 681 feet

below land surface (bls) in the Carlton Reserve and South Venice

cores, respectively. The carbonate sediments encountered are white

to yellowish-gray, moderately- to well-indurated, fossiliferous

packstones to grainstones. Foraminifera are the most common faunal

constituent followed by molds of mollusks. Traces of clay, pro-

bably washed in to the formation, were noted. Approximately eight

feet of "Suwannee Limestone" was cored at the Carlton Reserve site,

while at South Venice 20 feet was cored.

The "Suwannee Limestone" is unconformably overlain by the
















EXPLANATION




HATCHING PATTERNS


E LL. I r I Ir I | l |" I I I






1/ /7
GRAVEL FINE MEDIUM COARSE
LIMESTONE

..... I / / / / /
L: f [ Il / / /r ,l l l, / I l l
. . . . / / / r / / / 2


DOLOSTONE




SILT FINE MEDIUM COARSE

INTERBEDDED LIMESTONE AND DOLDSTONE



-NTE--'--- A LAIAMAEAAAAA I-----^ A Aaan

CLAY CHERT SHELL BED NO SAMPLE






COMMENTS

M MICRITE T SILT
S SAND C CLAY
P PHOSPHATE GRAVEL Sh SHELL
p PHOSPHATE SAND D DOLOSTONE
O ORGANIC L LIMESTONE
R SPAR H HEAVY MINERALS
I IRON STAIN NO SPL NO SAMPLE
0 QUARTZ G GYPSUM
A ANHYDRITE Py PYRITE
Ch CHERT




Figure 2: Explanation of hatching patterns
and codes used in stratigraphic
columns (Figures 3 and 4).





















W-16782


FEET METERS
0 0



- 50


- 100 -



- 150 -



- 200



- 250



- 300



- 350



-400 -



- 450



- 500



-550 -



- 600


- 20





- 40





- 60





- 80





-100


- -120


- -160


- -180


,hCj.,H Undif, Sand/Clay
, CHp,PM,Sh ______
S:,r Tp,Py -
Sh.S.p,T, Venice clay mbr.
p,T.C,Py
p,S.C.Py
p,Ch

C,p,Ch,Py
p,Ch,Py
P-
p
P,P
p,P
pS,C,Ch,T
p,C
p,S,P,C,Ch
,p,P,0
p,M,P --- >
MS,,R Tampa Mbr. ,
M,R,p n
M,p, P
M,R,p
M,ShMp,P

M,R,pP
R,M,p
M,R,p Nocatee Mbr.
M.C.pP P
RM Sh p
R,M,p,P O
M,R,L,p -
M,p
M,p
M,p
M,p
D,M,p
S,p,'y
p,C,T

C.p
,P
D.C,p,Py
C,p
C,p.Ch
DIp.O,py

p,R,Py
D,p
M,D,p,Py
M,p,fl,Py
M,p

M,p,Py -

'Suwannee Ls.'


0 50 100 150 200

Gamma (CPS) I
Gamma (CPS)


Stratigraphic column and gamma-ray log For
Carlton Reserve Core.


Figure 3:














W-16814


FEET METERS


Figure 4:


p'c Undif, Sand/Clay
O,p,PSh
Mp.-- Ft, Thompson Fm,
M,p.Sh
M,p,Sh
n,p,C Peace River Fm.
D,C,p,P
D,C,p

D.p
P.Py
p,Ch,0 -
,S.D Venice clay mbr.
C.p
p.Ch
p,C,Ch
p
p,Ch


0 -



- 50



- 100 -



-150 -



- 200



-250 -



-300 -



-350



- 400 -



-450



- 500 -



- 550



- 600


-





- 20





- 40


Ls.'


Stratigraphic column and gamma-ray log for
South Venice Core.


S,p,C
C h, CS, p
p.T. Tampa Mbr
p,T,S
M.S
M
M,R,p.S --
M,p,D
MD,p
PO
M,p, D,R
M,pR
M,p

fs'p

p,Py


C,p
Mp


P

Mp.Py
M,p


M,p,L
C,p,M



p,C
D.p.C
M,D.p,C
p.C
M.p,Py
D,p


M
M 'Suwannee


0 100 200


Gamma (CPS)




















I-


- 60


- 80





- 100





- -120





-140





- 160





- -180


650 -200


- 700 -



- 750 -


- -220


r"








Arcadia Formation of the Hawthorn Group. The unconformable contact

resulted from a world-wide mid- to Late Oligocene sea level drop

due to the development of southern hemisphere glaciation. This

unconformity is often difficult to recognize due to similarities in

lithologies between the top of the "Suwannee Limestone" and the

basal Tampa Member or undifferentiated Arcadia Formation. The

occasional difficulty in recognizing the disconformity spawned the

humorous term Suwa-Tampa-Haw to describe the unit. This difficulty

is predominantly related to lithologic descriptions and formational

picks made from well cuttings. Close examination of high-quality

core samples allows the unconformity to be recognized (Appendix 1).

The erosional disconformity forming the upper surface of the

Hawthorn Group shows significant variability. Following the axis

of the Florida Platform northward onto the Ocala Platform, progres-

sively more of the stratigraphic section is removed. In the Tampa

area, for example, most of the Arcadia Formation is missing leaving

the Tampa Member at or near the surface. The converse is true to

the south. The Hawthorn Group sediments thicken to the south as

the axis of the Platform dips in that direction. Down dip on the

eastern flank of the Platform, the Hawthorn Group thickens signi-

ficantly, forming a more complete section.

The Hawthorn Group, in these cores, consists of the Arcadia

Formation with its component Tampa and Nocatee Members and the

Peace River Formation (Scott,1988). The upper Hawthorn Group Peace

River Formation is absent in the Carlton Reserve core due to ero-

sion. The absence of the Peace River Formation in this core is not