Salt Tectonics on the Continental Slope, Northeast Green Canyon Area, Northern Gulf of Mexico: Evolution of Stocks

RI0212. Salt Tectonics on the Continental Slope, Northeast Green Canyon Area, Northern Gulf of Mexico: Evolution of Stocks and Massifs from Reactivation of Salt Sheets, by S. J. Seni. 102 p., 59 figs., 4 tables, 1994.  Print.


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ABSTRACT
Data from conventional two- and three-dimensional seismic surveys and wells were used to analyze the morphology of salt structures and to determine the history of salt emplacement in a 1,500-mi² (3,885-km²) region of the continental slope, northeast Green Canyon Area. Salt structures within the region include stocks, massifs, an allochthonous sheet, and remnant-salt structures. Also within this region is a largely salt free area (at least to a depth of 20,000 to 25,000 ft (6,100 to 7,600 m) that coincides with a U-shaped submarine trough. A large graben between an east-northeast-trending zone of growth faults near the shelf margin and a parallel trend of counterregional growth faults located 30 to 40 mi (48 to 64 km) basinward contains the submarine trough, stocks, and massifs. This graben is inferred to have formed from extension and subsidence as burial of the landward portion of a thick salt sheet produced massifs and stocks by downbuilding. Large-displacement counterregional growth faults form the northern, landward margin of a large salt sheet that extends to the Sigsbee Escarpment.

Differential loading separates salt stocks and massifs from the trailing margin of a salt sheet. During sheet burial, the landward margin of the sheet is segmented into discrete, irregular massifs separated by salt-withdrawal basins. These massifs are in turn segmented into stocks. The early stage of salt structural evolution of stocks and massifs is similar. The deeply buried margins of stocks, massifs, and remnant-salt structures are geometrically and structurally analogous to salt rollers, indicating a common pattern of structural evolution. This structural pattern includes initial growth under thin cover in an extensional regime. Strata thin over the crest and onlap the flanks of the structures. Thickness variations indicate syndepositional salt structural evolution under thin (<1,000 ft [<300 m]) cover.

The former presence of salt below the submarine trough is inferred on the basis of remnant-salt structures and a turtle-structure anticline lying on a discontinuity. Where salt is absent, this discontinuity is a salt weld representing suturing of sediments formerly separated by a salt sheet. Age of sediments below the weld indicates that sheet extrusion occurred in late Miocene to early Pliocene (4.6 to 5.3 m.y.a.). The age of sediments above the weld is late Pliocene (2.8 to 3.5 m.y.a.). In the submarine trough, sheet burial began in the late Pliocene and around the massifs burial continued from the early Pleistocene to the Holocene.

Keywords: differential loading, Gulf of Mexico slope, massifs, salt weld, sheet evolution, stocks, turtle structure

CONTENTS

Abstract

Introduction

Objectives

Setting

Salt Morphology

Development of Salt Structures

Methods

Seismic Data

Well Data

Mapping Methods

Quantitative

Geometry and Distribution of Salt Structures

Salt Provinces

Salt-Controlled Bathymetry

Salt Distribution in the Detailed Region

Stocks

Massifs

Sheets

Minor Salt Structures

Remnant-salt structures

Peripheral tongue

Depositional and Postdepositional Features

Salt-Withdrawal Basins Submarine Trough

Submarine-trough structure
Strata and structure near stocks

Submarine-trough strata

Structural inversion

Origin of the submarine trough

Faults

Regional fault patterns

Regional growth faults

Massif- and sheet-flank faults

Evolution of Salt Structures on the Slope

Quantitative Stock Evolution

Palinspastic reconstruction

R'/A' growth curves

Quantitative Massif Evolution

Palinspastic reconstruction

R'/A' growth curves

Quantitative Sheet Evolution

Palinspastic reconstruction

R'/A' growth curves

Qualitative Evolution

Conceptual Model of Salt-Sheet Burial

Integrated Evolution of Salt Structures

Discussion

Associations of Salt Structures
Mechanisms of Salt Movement on the Slope

Evolution of Stocks and Massifs by Sheet Burial

Salt-Sheet Removal

Figures

1. Location map showing Gulf of Mexico, inland salt diapir provinces, and salt structures

2. Schematic view of types of salt structures

3. Stages of evolution of salt structures during progradation of the northern Gulf of Mexico slope

4. Regional map showing distribution of area boundaries, seismic lines, and well control

5. Stratigraphic chart and mapped horizons and correlations with paleontologic zones and eustatic sea-level curves

6. Graph of conversion function for time to depth

7. Seismic line G illustrating correlation horizons, paleontologic horizons, and well log

8. Palinspastic reconstructions using backstripping and decompaction

9. Schematic vertical sections illustrating dome-growth processes

10. Map of major salt structures, basins, and regional faults, northeast Green Canyon Area

11. Map of bathymetry, faults at the seafloor, and shallow salt structures in the detailed region

12. Map of canyons on shelf and projected connection with submarine trough

13. Seiscrop map at 2.8 s of the detailed region

14. Map of time-structure contours of top of salt in the detailed region

15. Isometric block diagram of time-structure contours of salt in the detailed region
16. Map of salt-structure contours of part of the detailed region showing distribution of remnant-salt structures in the submarine trough

17. Seismic line H showing structure and geometry of stocks 2 and 3

18. Isometric block diagram of stocks, northeast Green Canyon Area

19. Seismic line I illustrating geometry of stock 1

20. Isometric block diagram of massifs 2 and 3, northeast Green Canyon Area

21. Seismic line J illustrating massifs 2 and 3

22. Seiscrop maps at 1.8 to 3.8 s showing variations in geometry of massif 3

23. Seismic line B illustrating regionally extensive sheet of salt

24. Interpreted seismic lines C, 0, E, and F of salt sheet

25. Map of top of salt sheet from south of the detailed region to Sigsbee Escarpment

26. Isometric block diagrams of salt sheet extending south of the detailed region to Sigsbee Escarpment

27. Map of bathymetry over salt sheet south of the detailed region to Sigsbee Escarpment

28. Seiscrop map at 4.3 s showing features associated with updip termination of sheet

29. Seismic line G showing geometry of remnant-salt structures in submarine trough

30. Parallel seismic lines K, L, J, and M showing slices through a peripheral tongue

31. Map of synclinal axial traces and location of structural lows of salt-withdrawal basins associated with salt massifs
32. Map of synclinal axial traces and location of structural lows of basins within the submarine trough

33. Seiscrop maps at 2.8 and 4.3 s showing orientation of axial traces

34. Seismic line I and seiscrop map at 2.8 s showing geometry of stock 1 and structure of surrounding strata

35. lsopach map of Pleistocene and Holocene fill in the detailed region

36. Seismic line N illustrating sediment-cored anticline between massifs 1 and 2

37. Time-structure and time-isopach maps illustrating geometry of Pliocene(?) sediment-cored anticline

38. Reconstruction of sediment-cored anticline showing structural reversal

39. Intersecting seismic lines G and N showing a turtle structure and remnant-salt structures overlying the same horizon

40. Maps of time-structure contours, faults, and salt structures in the detailed region
41. Seiscrop maps of strata I patterns at bases of basins 1 and 2

42. Seismic lines A and G showing regional growth-fault geometry

43. Seismic lines G, 0, and P showing possible thrust-fault geometry

44. Graph of growth index of regional growth fault

45. Parallel seismic lines Q-U showing transfer zone across a counterregional fault along northern margin of massif 2

46. Seismic line V illustrating a normal fault and associated graben on landward margin of massif 3
47. Map of peripheral sink basins in submarine trough superimposed on bathymetric map

48. Graph of volume of peripheral sink basins

49. Depth-converted and decompacted palinspastic reconstruction of seismic line 1

50. Incremental R'/A' growth curve of stocks 1, 2, and 3

51. Graph of volume of withdrawal basins 2, 3, and 4

52. Palinspastic reconstruction of seismic line R showing evolution of massif 2

53. R'/A' growth curve of massifs 2 and 3

54. Palinspastic reconstruction of seismic line B illustrating evolution of salt sheet

55. R'/A' growth curve of salt sheet

56. Dip-oriented seismic lines I, M, and R showing assemblage of salt structures

57. Strike-oriented seismic lines V, J, and W showing assemblage of salt structures

58. Conceptual model showing reactivation of salt sheet and table of original model parameters
59. Schematic dip-oriented section integrating evolution of salt structures and majorfeatures in the detailed region

Tables

1. Geometric characteristics of salt stocks in the detailed region

2. Geometric characteristics of salt massifs in the detailed region

3. Geometric characteristics of salt sheets in the detailed region and Sigsbee Escarpment

4. Geometric characteristics of faults in the detailed region

Citation
Seni, S. J., 1994, Salt Tectonics on the Continental Slope, Northeast Green Canyon Area, Northern Gulf of Mexico: Evolution of Stocks and Massifs from Reactivation of Salt Sheets: The University of Texas at Austin, Bureau of Economic Geology, Report of Investigations No. 212, 102 p.