Depositional and Ground-Water Flow Systems of the Carrizo-Upper Wilcox, South Texas

RI0175. Depositional and Ground-Water Flow Systems of the Carrizo-Upper Wilcox, South Texas, by H. S. Hamlin. 61 p., 47 figs., 9 tables, 3 appendices, 1988. ISSN: 008235X: Print.


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ABSTRACT
In the Rio Grande Embayment of South Texas, the Carrizo Formation (lower Eocene) consists of two sand-rich fluvial depositional systems that grade basinward into several deltaic complexes within the upper part of the Wilcox Group. Data from oil, gas, and water wells provide information on Carrizo fluvial and ground-water flow systems, and outcrop and core data help define component lithofacies.

The bed-load channel system contains multistory, multilateral fluvial channel-fill sandstones deposited by broad, sand-rich, dominantly braided streams. Mudstones are mainly thin, laterally discontinuous remnants of abandoned channel fills. Bed-load channel sandstones are most abundant along the major fluvial axes and form the depositional framework of the interval. The mixed alluvial system consists of a more typical suite of coastal-plain facies, which were deposited by meandering streams in a variety of channel and interchannel environments. Mixed-load channel-fill sandstones tend to be isolated and surrounded by overbank mudstones and thin sandstones. Fluvial sediment input converged on the embayment from the west, northwest, and north.

The bed-load channel system is the Carrizo aquifer. Regional ground-water flow is controlled by topography, structural configuration, and, to a lesser extent, sandstone geometry. Rainfall recharges the aquifer at outcrop; ground water flows gravitationally down structural/depositional dip into the deeper subsurface, encounters updip-expulsing formation waters, partly mixes with them, and finally discharges upward, mainly along fault-related permeability pathways. Upward cross-formational leakage, driven by high fluid pressures, is common throughout much of the aquifer.

As Carrizo ground water moves down flow paths from outcrop, a systematic hydrochemical evolution occurs: total dissolved solids gradually increase, and calcium-sodium-bicarbonate-chloride water changes to sodium-bicarbonate water. Local hydrochemical anomalies can be related to variations in recharge characteristics, ground-water mixing, and aquifer lithology. The most important processes controlling hydrochemical evolution within the aquifer are calcite dissolution and cation exchange.

The updip Carrizo Sandstone contains fresh ground water, small oil fields, and uranium deposits. The downdip upper Wilcox trend is an area of active hydrocarbon exploration and production.

Keywords: Carrizo aquifer, Carrizo Formation, Eocene, fluvial sedimentation, ground-water flow, hydrochemistry, hydrogeology, Rio Grande Embayment, Texas, Wilcox Group



CONTENTS

ABSTRACT

INTRODUCTION

Methodology

Previous work

Regional geologic setting

FLUVIAL DEPOSITIONAL SYSTEMS

Sandstone distribution and geometry

Sediment input and dispersal patterns

Depositional systems and facies

Bed-load channel system

Mixed alluvial system

Paleogeography

Depositional history

Summary of depositional systems

GROUND-WATER FLOW SYSTEM

Hydrogeologic setting

Controls on ground-water flow

Hydrogeologic zonation

Physiography

Climate

Aquifer geology and hydraulic conductivity

Ground-water pumpage

Ground-water flow patterns

Potentiometric surface

Topographic effects

Geologic effects

Vertical components of flow

Summary of aquifer hydraulics

Hydrochemistry

Total dissolved solids

Hydrochemical facies

Sodium-bicarbonate water

Bicarbonate and pH

Chloride

Sulfate

Silica

Summary of hydrochemical evolution

ECONOMIC GEOLOGY

Ground water

Uranium

Petroleum

CONCLUSIONS

ACKNOWLEDGMENTS

REFERENCES

 APPENDICES

A. Electric-log data base used in this study

B. Water-well data base used in this study

C. U.S. Geological Survey/Texas Water Commission ground-water reports

Figures

1. Structural elements of the Texas Coastal Plain

2. Generalized dip cross section down the axis of the Rio Grande Embayment

3. Location map of study area showing Carrizo Formation outcrop, surface and subsurface data control, cross-section lines, and location of type log

4. Structural cross section G-G' illustrating the Carrizo-upper Wilcox correlation interval

5. Map of water-well data control

6. Carrizo-upper Wilcox total-interval isopach map

7. Structure map on top of the Carrizo-upper Wilcox interval

8. Carrizo-upper Wilcox sandstone-percent map

9. Carrizo-upper Wilcox net-sandstone map

10. Carrizo-upper Wilcox maximum sand-body thickness map

11. Map of Carrizo-upper Wilcox high-sandstone trends, fluvial axes, and sediment input directions

12. Carrizo-upper Wilcox depositional systems, component facies, and type electric log

13. Geomorphic and sedimentary characteristics of bed-load, mixed-load, and suspended-load channel segments

14. Selected logs from dip cross section L-L' showing correlations and systems distributions along the northeastern fluvial axis

15. Selected logs from strike cross section 1-1' showing correlations, systems distributions, and fluvial axes

16. Selected logs from dip cross section G-G' showing correlations and systems distributions along the central fluvial axis

17. Selected logs from dip cross section C-C' showing correlations and systems distributions along the southwestern fluvial axis

18. Typical measured section in the bed-load channel depositional system illustrating the component facies and internal features of the thick, high-resistivity sand bodies

19. Typical measured section in the mixed alluvial depositional system illustrating the component facies and internal features of the interbedded sandstone/shale sequences

20. Paleogeographic reconstructions showing distributions of systems early, middle, and late in the depositional history of the Carrizo-upper Wilcox interval

21. Map of hydrogeologic zones that coincide with the fluvial axes shown in figure 11 but that also include adjacent interfluvial areas

22. Map showing topographic relief, major drainage, and locations of flowing Carrizo wells

23. Map of potentiometric surface, Carrizo aquifer

24. Structural cross section G-G' showing hydrogeologic features in profile

25. Structural cross section L-L' showing hydrogeologic features in profile

26. Graph showing relationship between land-surface (wellhead) elevation and water levels in the Carrizo aquifer

27. Numerically simulated, computer-generated flow net showing the effects of topography and hydraulic conductivity contrast on ground-water flow

28. Potentiometric-surface elevations in the Carrizo and Queen City aquifers in Frio and Atascosa Counties

29. Map of generalized ground-water flow patterns in the Carrizo aquifer

30. Map of total dissolved solids in Carrizo ground water

31. Graph of total dissolved solids versus depth in Carrizo ground water

32. Piper diagram of Carrizo ground-water chemistry

33. Map of hydrochemical facies in Carrizo ground water

34. Graph of sodium versus total dissolved carbonate in Carrizo ground water

35. Map of sodium percentage of total cation composition in Carrizo ground water

36. Graph of sodium versus calcium in Carrizo ground water

37. Map of pH in Carrizo ground water

38. Graph of pH versus bicarbonate in Carrizo ground water

39. Graph of bicarbonate versus depth in Carrizo ground water

40. Map of bicarbonate concentration in Carrizo ground water

41. Graph of sodium versus chloride in Carrizo ground water

42. Graph of chloride versus .depth in Carrizo ground water

43. Map of chloride concentration in Carrizo ground water

44. Graph of sulfate versus depth in Carrizo ground water

45. Map of sulfate concentration in Carrizo ground water

46. Map of dissolved silica in Carrizo ground water

47. Map of updip oil and gas production in the Carrizo-upper Wilcox interval showing structure and westward limit of Reklaw Shale

 

Tables

1. Paleocene to lower Eocene stratigraphic relationships in South Texas

2. Hydrogeologic properties of the Carrizo aquifer

3. Updip production from the Carrizo-upper Wilcox interval



Citation
Hamlin, H. S., 1988, Depositional and Ground-Water Flow Systems of the Carrizo-Upper Wilcox, South Texas: The University of Texas at Austin, Bureau of Economic Geology, Report of Investigations No. 175, 61 p.