Examples of MCUI and MUCIII In North-Central Florida and South-Central Georgia

1. Examples of MCUI and MUCIII In North-Central Florida and South-Central Georgia L.J. Williams U.S. Geological Survey 3/15/2012

2. Middle Confining Units (Miller, 1986) See full presentation about the MCUs at: http://fl.water.usgs.gov/FASWAM/presentations.html 8 subregional middle confining units The MCUs divide the system into the Upper and Lower Floridan aquifers These are named using Roman numerals I to VIII (not 1, 2, 3 ..) The MCUs are a composite of one or more geologic units Units overlap in some areas

3. Middle Confining Unit I Low-permeability zone mostly within rocks of middle Eocene age extending from South Carolina to Florida Keys Separates the Upper and Lower Floridan aquifers Overlaps gypsiferous dolomite of MCU II

4. MCU I: Geologic Units and Lithology Very local mostly here Mostly located in the middle and upper parts the middle Eocene Locally lower part of the Late Eocene Soft micritic limestone and fine-grained dolomitic limestone, both of low porosity Original porosity not greatly affected by pore filling minerals

5. Middle Confining Unit III Low-permeability dense, fossiliferous, gypsiferous, dolomitic limestone Occupies area in south-central Georgia and northern Florida (center on Valdosta)

6. MCU III: Geologic Units and Lithology here Located in the lower and middle part of the middle Eocene Dolomitic limestone Intergranular gypsum (rare layers and lenses of gypsum)

7. The Problem III I MCUI II here MCUI, II, and III all lie in approximately the same stratigraphic position Abrupt termination of the units causes “cliffs” in the surfaces Lumped units across a fairly thick middle Eocene section sometimes causes confusion when mapping them

8. Investigating MCUI and MCUIII in this area We are working with nearly the same set of logs and well cutting descriptions that Jim Miller used to construct the original framework FGS litho database has been exhausted; no returns over the zones of interest is common Some deep exploratory test wells in Georgia and SJRWMD help us to some degree in unraveling the mystery behind these units but we are still lacking data

9. Key Well Locations in Georgia GULF TROUGH We find “MCUIII” type section in these two wells, thus extending the unit to east Previously mapped extent of MCUIII USGS Test Well S.E. Matthews and R.E. Krause WRIR 83-4204 GA-COQ2 (corehole) USGS Test Well R. E. Krause OFR-78-117

10. GA-WA2: Ware County Test Well Showing MCUI and MCUIII Focused (guard) Resistivity Gamma Ray Upper unit is Miller’s MCUI MCU I MCU III Logs from files of the USGS Denotes a geophysical marker bed

11. Normals and Guard Log CAL/ GR My marked up log for GA-WA2 (MP=150’) DT TOP OF SYSTEM Highly Permeable MCUI Highly resistive unit Gyp Pattern MCUIII BASE OF SYSTEM • MCUI: easily identified on elog as a highly-resistive zone on elogs; it is a low-porosity dolomitic LS or dolostone; variably fractured; overlain by highly permeable Ocala LS • MCUIII: less-resistive “spikey” on elog, LS, Dolostone, gypsum • “Gyp Pattern” used for mapping lower unit

12. GA-WA2 (cont’) Like “MCUIII” This unit has much significance in coastal areas Low-sulfate water above High-sulfate water below

13. U.S. Gypsum Core hole – Colquitt Co. Highly Permeable MCUIII 800 ft deep core hole completed by U.S. Gypsum Highly- resistive gypsiferous dolomitic LS interval This is underlain by a lower-resistivity “spikey” MCUIII interval

14. Key Well Locations in Georgia GULF TROUGH We find “MCUIII” type section in these two wells, thus extending the unit to east Previously mapped extent of MCUIII USGS Test Well S.E. Matthews and R.E. Krause WRIR 83-4204 GA-COQ2 (corehole) GGS3115 USGS Test Well R. E. Krause OFR-78-117

15. GGS3115(MP=212’) Highly Permeable UPPER FLORIDAN AQUIFER MCUIII LOWER FLORIDAN AQUIFER Less Permeable (see USGS test well 19E043 in Valdosta) Lowndes Co.

16. GGS107(MP=238’) TOP OF SYSTEM No middle confining unit was previously mapped here but we clearly find MCUIII present UPPER FLORIDAN AQUIFER Like “MCUIII” LOWER FLORIDAN AQUIFER BASE OF SYSTEM Atkinson Co.

17. Comparisons MCUI MCUIIIII U.S. GYPSUM CORE HOLE, COLQUITT CO. USGS TEST WELL GA-WA2, WARE CO.

18. Key Well Locations Florida P59 YY FFFF ZZ P1033 JJ (old) P1015 Previously mapped extent of MCUIII FF (old) AA (old) P1052 KKKK

19. Base of Floridan Aquifer System Hydrogeologic units generally thin across the structural high and subcrop at shallower depths exposing them to greater weathering and dissolution P1033 Ocala “uplift” Note: this is a draft map of the base of system

20. P1033 (MP=21’) This part of the Middle Eocene section is low-permeability and gypsiferous in Valdosta but here no evaps. Indicated from well cuttings TOP OF SYSTEM “MCUI Horizon” “MCUII Horizon” AVON PARK This part of MCUIII is much deeper in the section than seen in Valdosta MCUIII OLDSMAR Note : measuring point is from NGVD29 BASE OF SYSTEM

21. P1033 (MP=21’) TOP OF SYSTEM “MCUI Horizon” (absent) Classic “Gyp” Pattern “MCUII Horizon” MCUIII BASE OF SYSTEM Madison Co.

22. P1015 (MP=10’) SP AND GAMMA RAY INDUCTION DT “MCUI Horizon” UPPER FLORIDAN AQUIFER UPPER GAMMA RAY MARKER “MCUII Horizon” LOWER FLORIDAN AQUIFER MCUIII LOWER GAMMA RAY MARKER Taylor Co.

23. Key Well Locations Florida P59 YY FFFF ZZ P1033 JJ (old) P1015 Previously mapped extent of MCUIII FF (old) AA (old) P1052 KKKK

24. P1052 (MP= 82’) SP AND GAMMA RAY INDUCTION DT MCUIII Glauconite Gamma-Ray Marker (see next slide) Note: This pick south of previously mapped extent of MCUIII Lafayette Co.

25. Glauconite Marker as a Tool to Help Guide placement of MCU’s Northern Extent of mappable Glauconite Gamma-Ray Marker Marker first mapped by Duncan Et. Al. in Brevard and then expanded across central southern Peninsular Florida by Reese and Richardson Reese and Richardson’s northern extent

26. Lets look Even Further South at P66 P1052 -400 MCUI P1 and FL-DIX4 (litho descrips + old elogs) -300 -200 -500 P66 -600 MCUII

27. P66(MP=14’) TOP OF SYSTEM UPPER FLORIDAN AQUIFER ?? MCUII What is this below MCUII? LOWER FLORIDAN AQUIFER BASE OF SYSTEM

28. Unfortunately, gamma-ray log not available to confirm the pick of MCUIII below MCUII but the section only thickens slightly and the pick can be supported by way of correlation P62 (cont’) TOP OF SYSTEM MCUII Lower Floridan below MCUII Further south these rocks form a major confining sequence in the Lower Floridan aquifer and are represented in the revised framework Like “MCUIII” BASE OF SYSTEM

29. Key Well Locations Florida P59 YY FFFF ZZ P1033 JJ (old) P1015 Previously mapped extent of MCUIII FF (old) AA (old) P1052 KKKK

30. P59 (MP=134’ msl) “MCUIA” (semi-confining) “MCUIB” Permeable Zone “MCUIII” Permeable Zone

31. Summary In north-central Florida and south-central Georgia MCUI, MCUIII lie in the middle and upper parts of the Avon Park Formation MCUI is a “leaky” fairly massive dolomitic LS or dolostone characterized by high resistivity on electric logs and low porosity on porosity logs; we find both high and low permeability zones associated with this unit; intergranular gypsum is common in south-central and eastern Georgia MCUIII is a highly gypsiferous unit typically mapped on a “spikey” resistivity pattern; this is a “lumped” geologic unit originally mapped in Valdosta where it starts at top of Avon Park, but is much lower in section in Florida; the upper part of MCUIII in Valdosta is stratigraphically equivalent to MCUII much further south We have a revision for this part of the system that will allow more uniform structural surfaces to incorporate the subregional low-permeability units into the models of the area