Smackover and Lower Buckner Formations, Jurassic, South Texas: Depositional Systems

RI0112. Smackover and Lower Buckner Formations South Texas: Depositional Systems on a Jurassic Carbonate Ramp, by D. A. Budd and R. G. Loucks. 38 p., 26 figs., 3 tables, 1981. ISSN: 0082335X: Print.


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ABSTRACT
The Smackover and lower part of the Buckner Formations (Oxfordian) comprise a thick regressive sedimentary sequence deposited on a Jurassic carbonate ramp. Four major depositional systems are recognized: (1) basinal, (2) low-energy open shelf, (3) high-energy shoal, and (4) sabkha. Lithofacies boundaries within each system and between systems follow paleobathymetrical contours. High-energy grainstone facies were concentrated landward; muddy low-energy facies were deposited seaward.

Basinal facies are dominated by laminated carbonate mudstones, deposited from suspension, and irregularly laminated carbonate mudstones, the product of sediment reworking by oscillatory bottom currents. The outer-shelf facies is characterized by burrowed carbonate mudstones containing crustacean pellets and a pelagic fauna. The inner-shelf facies is composed of burrowed wackestones containing a benthic fauna. Burrowed oncolite and pellet packstones characterize the outer-shoal system, and crossbedded mixed-allochem, oolite-intraclast, and oolite grainstones compose the high-energy inner shoal system. Increased sorting and decreased grain size within these facies suggest increasing energy levels landward even within the shoal system.

The sabkha system consists of cyclic subtidal to supratidal facies. Subtidal units are represented by burrowed gastropod and pellet wackestones and oolite wackestones to grainstones, whereas the intertidal zone is characterized by cross-laminated sandstones and algal-laminated dolomite mudstones. The supratidal facies consists of anhydrite nodules intercalated with carbonate and terrigenous mud, and siliciclastic sand and silt.

Depositional systems of the Yucatan Shelf of the Gulf of Mexico may be an approximate analogue for those of the Smackover Formation. Smackover moderate-energy packstones may have originated in stabilized grainflats, whereas Smackover grainstones were deposited in mobile sand waves, shoals, spits, spillover lobes, beaches, and eolian dunes. Depositional environments of the Trucial Coast of the Persian Gulf are in part analogous to the Buckner sabkha system. Subtidal units of the lower part of the Buckner Formation were deposited in coastal lagoons, tidal-channel deltas, spits, and beaches. Intertidal facies include sediment deposited in sand flats and algal mat zones. Supratidal facies are characterized by anhydrite nodules.


CONTENTS

ABSTRACT

INTRODUCTION

PURPOSE

METHODS

REGIONAL GEOLOGIC SETTING

STRATIGRAPHIC FRAMEWORK

STRUCTURAL FRAMEWORK

FACIES AND DEPOSITIONAL SYSTEMS

BASINAL SYSTEM

Deep basin

Shallow basin

LOW-ENERGY CARBONATE SHELF SYSTEM

Outer shelf

Inner shelf

HIGH-ENERGY SHOAL SYSTEM

Outer shoal

Inner shoal

Pellet grainstone

Mixed-allochem grainstones

Oolitic quartzarenite

Intraclast, oolite-intraclast, and oolite grainstones

SABKHA SYSTEM

Subtidal

Intertidal

Supratidal

DEPOSITIONAL MODEL

MODERN ANALOGS

Yucatan Shelf

Trucial Coast, Persian Gulf

SMACKOVER MODEL

BASIN EVOLUTION

CONCLUSIONS
ACKNOWLEDGMENTS

REFERENCES

APPENDIX: SOUTH TEXAS SMACKOVER AND BUCKNER WELLS

FIGURES

1. Index map of South Texas study area showing wells that penetrate the Buckner and Smackover Formations

2. Generalized Jurassic stratigraphic nomenclature, Texas Gulf Coast

3. Coastal onlap of Jurassic strata, South Texas

4. Regional dip section A-A', Upper Jurassic strata, South Texas

5. Distinguishing characteristics, lithic composition, and generalized depositional environments of Jurassic strata, northern Gulf Coast Basin

6. Facies map of Smackover Formation, northern Gulf Coast Basin

7. Structural framework, northern Gulf Coast Basin

8. Idealized vertical sequence of Smackover and lower Buckner depositional systems and component facies

9. Interpreted Smackover depositional systems of dip section A-A', South Texas

10. Vertical sequences of lithology, structures, constituents, and fauna within basinal and shelf systems, Smackover Formation

11. Facies and bedding features, basinal system
12. Facies, structures, and characteristic features, shelf system

13. Vertical sequences of lithology, structures, constituents, and fauna within the high-energy shoal system, Smackover Formation

14. Textures and allochems of oncolite and pellet facies

15. Bedding structures of fine-grained oolitic quartzarenite

16. Oolite and intraclast grainstones, high-energy inner shoal

17. Postulated axis of maximum buildup, high-energy Smackover shoal system

18. Vertical sequences of subtidal to supratidal deposits, Buckner sabkha system

19. Subtidal facies and structures, Buckner sabkha system

20. Intertidal facies and structures, Buckner sabkha system
21. Anhydrite textures of supratidal facies, Buckner sabkha system

22. Profile of modern western Yucatan Shelf and facies map of relict Holocene sediment, Yucatan Shelf: modern ramp analogs

23. Facies map, high-energy grainstones, eastern Yucatan Shelf

24. Bathymetric profile, facies sequence, and schematic map of the Trucial Coast, Persian Gulf: modern sabkha analog

25. Depositional model, Smackover and lower Buckner depositional systems, South Texas

26. Interpreted evolution of deposition in the Smackover basin

TABLES

1. Smackover facies and characteristics

2. Lower Buckner facies and characteristics

3. Comparison of the ramp and rimmed shelf models of modern carbonate environments

Keywords: Smackover Formation, Buckner Formation, Jurassic, carbonate, sabkha system, facies, Texas



Citation
Budd, D. A., and Loucks, R. G., 1981, Smackover and Lower Buckner Formations South Texas: Depositional Systems on a Jurassic Carbonate Ramp: The University of Texas at Austin, Bureau of Economic Geology, Report of Investigations No. 112, 38 p.