html5-img
1 / 41

The Middle Confining Units of the Floridan Aquifer System

The Middle Confining Units of the Floridan Aquifer System. Lester J. Williams 4/21/2011. Outline. Describe characteristics of the 8 middle confining units mapped as part of the Floridan aquifer system Extent of each unit Geologic Unit(s) and Lithology Confining properties

robyn
Download Presentation

The Middle Confining Units of the Floridan Aquifer System

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. The Middle Confining Units of the Floridan Aquifer System Lester J. Williams 4/21/2011

  2. Outline • Describe characteristics of the 8 middle confining units mapped as part of the Floridan aquifer system • Extent of each unit • Geologic Unit(s) and Lithology • Confining properties • Configuration and Thickness • Geophysical Log Characteristics • Mapping Criteria

  3. Middle Confining Units (Miller, 1986) • 8 subregional middle confining units • 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

  4. 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

  5. MCU I: Geologic Units and Lithology • 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 Very local mostly here

  6. MCU I: Confining Properties • Leakiest of all MCUs • Lithology similar to rocks above and below • Minor head differences and water-quality changes suggests acts as a confining bed Leak-o-meter

  7. MCU I: Configuration and Thickness Top of MCU I modified from Miller, 1986 • Generally dips along stratigraphic horizons • Thickest in southeastern Georgia embayment and east-central Florida

  8. MCU I: Geophysical Log Characteristics • High resistivity • Low porosity • Multiple beds may comprise this unit Focused (guard) Resistivity Gamma Ray Waycross, GA

  9. MCU I Mapping Criteria • Lithology • Geophysical log response (low porosity beds) • Position in stratigraphic section • Top of unit is usually picked on the shallowest low-porosity bed in middle Eocene rocks Brunswick, GA MCUI (Miller, 1986)

  10. Middle Confining Unit II • Low-permeability gypsiferous dolomite and dolomitic limestone • Overlapped by MCU I in part of central Florida • Extensive middle Eocene sabkha or tidal flat

  11. MCU II: Geologic Units and Lithology • Located in the middle part of the middle Eocene • Dolomite and dolomitic limestone • Intergranular gypsum makes it a very low-permeability unit here

  12. MCU II: Confining Properties • Non-leaky confining bed • Mineralized water contained in the unit suggests poor connection with freshwater in the overlying Upper Floridan aquifer Leak-o-meter

  13. Configuration and Thickness Top of MCU II modified from Miller, 1986 • Generally dips along stratigraphic horizons • Thickest in the northeast and thins to east • (anomalous thickness in northern Polk)

  14. MCU II: Geophysical Log Characteristics Induction E-Log Sonic • Identified on elogs by its “spiky” high and low resistivity zones • Has very Low porosity (<10%) Upper Floridan 900 MCU II 1300 Lower Floridan Citrus Co. FL

  15. Correlation • Oil and gas test well (Citrus Co.) on left • ROMP core hole (Sumter Co.) on right • These wells are 33 miles apart

  16. MCU II Mapping Criteria • Lithology (evaporites) • Geophysical log response (resistivity and porosity logs) • Position in stratigraphic section • Top of unit is usually picked at first occurrence of persistent evaporites MCU II

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

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

  19. MCU III: Confining Properties • Slightly leaky confining bed • Around edges underlain by permeable strata • Grades downward into low permeability clastic rocks that are part of the aquifer’s lower confining unit Leak-o-meter

  20. Configuration and Thickness Top of MCU II modified from Miller, 1986 • Blob shaped does not conform to any stratigraphic unit • Thickest along northwest edge (near Gulf Trough) Gulf Trough

  21. Middle Confining Unit IV (abbreviated) • Calcareous sand and clay of relatively lower permeability • Limited to a few counties in eastern Panhandle

  22. MCU IV: Geologic Units and Lithology • Equivalent to Lisbon and Tallahatta • Dolomite and dolomitic limestone • Think of it like a tongue of low permeability rocks down dip from the permeable part of the Upper Floridan here

  23. MCU IV: Confining Properties • leaky confining unit • Lower Floridan lies below this unit Leak-o-meter

  24. Middle Confining Unit V (abbreviated) • Low permeability clay bed • Located in Florida’s western Panhandle

  25. MCU V: Geologic Units and Lithology • Bucatunna Formation • Sandy massive, dark gray calcareous soft clay • Thickness more uniform than other MCUs • Readily identified on electric logs here

  26. MCU V: Confining Properties • confining unit • Lower Floridan lies below this unit Leak-o-meter

  27. Middle Confining Unit VI • Low-permeability argillaceous rocks of various lithologies • Extends below MCU II in the northern part of the unit • Overlapped by MCU I in the southeastern part of the unit

  28. MCU VI: Geologic Units and Lithology • Located mainly in the lower part of the middle Eocene • Interbedded finely to coarsely crystalline dolomite and finely pelletal micritic limestone mostly here locally

  29. MCU VI: Confining Properties • Considered an “effective” confining unit based on lithologic character • No hydraulic head data were available to confirm this Leak-o-meter

  30. Configuration and Thickness • Follows stratigraphic horizons in some places but not others • This surface represents a composite of several different geologic units • Thickens to southwest Thin Thickens Top of MCU VI modified from Miller, 1986

  31. MCU VI: Geophysical Log Characteristics Sonic Elogs • Identified by its highly resistive character • Low porosity APPZ 1900 MCU VI Charlotte Co. FL 2300

  32. MCU VI Mapping Criteria • Lithology (dolomite) • Geophysical log response (resistivity and porosity logs) • Position in stratigraphic section • Top of unit is usually picked at high resistivity zones near the base of middle Eocene APPZ 1900 MCU VI 2300

  33. Middle Confining Unit VII (abbreviated) • Narrow northeast trending strip of low-permeability rocks in west-central Georgia • Contiguous and southeast of Gulf Trough • It is suggested that fault grabens have juxtaposed rocks into this position

  34. MCU VII: Geologic Units and Lithology • Southwest boarder: middle Eocene • Central: middle to late Eocene • Micritic to finely crystalline limestone, dolomitized • Lenses, pods, beds of gypsum here

  35. MCU VII: Confining Properties • The southern part of this unit it grades vertically downward into calcareous glauconitic clastic rocks that are part of the lower confining unit • The northern part of this unit it is thin and underlain by permeable limestone Leak-o-meter

  36. Middle Confining Unit VIII • Thick regionally extensive confining unit within the Lower Floridan aquifer • Overlies and extends beyond the boulder zone

  37. MCU VIII: Geologic Units and Lithology • Middle part of rocks of early Eocene age • Micritic finely pelletal limestone and lesser amounts of interbedded finely crystalline dolomite here

  38. MCU VIII: Confining Properties • Thick regionally extensive confining unit • Extensive hydraulic testing of this unit from deep well injection projects over the past 20+ years Leak-o-meter

  39. Configuration and Thickness • In southern part surface seems to be representing more of a horizontal “bed” over BZ • Several different geologic units comprise this unit • Thickest in Palm Beach Co, FL • Thins to north and south Thins Thickest Thins Top of MCU VIII modified from Miller, 1986

  40. MCU VIII: Geophysical Log Characteristics • In some logs it is a very low resistivity unit, other logs very high resistivity unit SP Resistivity 2800 MCU VI Boulder Zone Dade Co. FL 3000

  41. Summary • 8 MCUs were originally defined and mapped when constructing the RASA framework for the Floridan aquifer system • Each of the MCUs is mapped based on lithology, geophysical characteristics, and stratigraphic position • One or more geologic units comprise each unit, therefore some generalizations were made when mapping the tops of these units

More Related