Depositional-Episodes: Their Relationship to the Quaternary Stratigraphic Framework in the NW...Gulf Basin

GC7401. Depositional-Episodes: Their Relationship to the Quaternary Stratigraphic Framework in the Northwestern Portion of the Gulf Basin, by D. E. Frazier. 28 p., 18 figs., 3 tables, 1974. ISSN: 0082-3309. Print.


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ABSTRACT
The stratigraphic record yields evidence that each episode of clastic silicate deposition has been of limited duration and that each has been preceded and followed by a significant hiatus. Evidence for alternations of deposition and nondeposition is readily apparent in the landward portions of Pleistocene deposits along the Gulf Coast, due to the glacio-eustatic changes in sea level; evidence of alternations, although elusive, exists also in the basinward portions of these deposits. The concept of depositional-episodes explains the significance and relationship of these alternating conditions throughout the basin.

The strata attributed to each depositional episode are a composite of several discrete facies sequences and are referred to in this paper as a depositional-complex. Each facies-sequence represents either a single delta lobe within a deltaic progression, or one of the several repetitive sequences deposited in an interdeltaic environment.

Each depositional-complex records and defines a depositional-episode and indicates three phases of development. Deposits of the initial phase record a stillstand of the sea during which each of the several rivers entering the basin prograde a succession of delta lobes and interdeltaic facies sequences across the shelf. The second phase of development (which is penecontemporaneous with the first) is recorded by the intercalation of clastic and organic flood-plain deposits which accumulate on the newly formed coastal plain, and by the deep-water hemipelagc basin sediments which are secondarily derived from unstable sediments deposited in the outermost shelf and uppermost slope environments. The terminal phase is evidenced by sediments deposited during a period of instability when a marine transgression either continuously or intermittently forces estuarine conditions on the rivers entering the basin. Throughout the terminal transgression, the finite zone of active deposition adjacent to the shoreline is shifted landward. Basinward of this active zone of deposition, hiatal conditions are imposed and at the instant of maximum transgression, when the depositional-episode is terminated, all points on the hiatal surface are synchronous.

The bounding surfaces of depositional complexes represent natural stratigraphic breaks over the entire basin and are related to hiatal conditions imposed by marine transgressions. Within the Quaternary section, the repetitive alternation of depositional-episodes and significant hiatuses is due to the glacio-eustatic fluctuations of sea level: as a result, worldwide correlations of the Quaternary depositional complexes and hiatal surfaces may be possible.


Keywords: deposition, Quaternary, stratigraphy, sea level, Gulf Coast

CONTENTS
Abstract

Introduction

Sedimentologic principles

Depositional-episodes-Definitions and discussion

Depositional-events and facies-sequences

Depositional-episodes and depositional-complexes

Glacially controlled depositional-episodes

Clastic deposition

River-mouth deposition

Initial deposition of sediments from suspension

Interdeltaic deposition

Major transgressions and significant hiatal surfaces

Progradation across a hiatal surface

Effects of sediment failure along the upper continental slope

Turbidites

"En masse" sediment transport

Summary

Stratigraphic framework

Rock-stratigraphic units

Relationship of depositional-complexes to formations

Conclusions

References

Appendix

Figures

1. Exposed Quaternary deposits in the northwest region of the Gulf of Mexico

2. Depositional-event

3. Depositional-episode

4. Interdeltaic offlap: chenier plain

5. Deltaic offlap--St. Bernard delta complex

6. Deltaic offlap--Plaquemines delta complex

7. Stratigraphic framework of present depositional-complex

8. Delta lobes formed by Mississippi River in the past 6,000 years

9. Deposition during first glacial cycle

10. Succession of offlapping depositional-complexes

11. Glacially controlled depositional-episodes

12. Sediment distribution on the Gulf floor in the vicinity of the Mississippi delta

13. Specific gravity, turbidity, and salinity (o/oo) of water beyond crest of bar at Southwest Pass, Mississippi River

14. Submarine topography of outer shelf off Mississippi birdfoot delta

15. Precision-depth-recorder section from Southwest Pass of the Mississippi River westward

16. Basinward limit of Recent elastic deposition on the continental shelf

17. Relict, transgressive, shoreline sands exposed on the continental shelf- northwestern Gulf of Mexico

18. Sea level during last 40,000 years--Gulf of Mexico

Tables

1. Radiocarbon age determinations pertinent to eustatic sea level fluctuations in the Gulf of Mexico in the past 40,000 years

2. Radiocarbon age determinations pertinent to glacial advances in North America in the past 40,000 years

3. Radiocarbon age determinations pertinent to warming trends in the Gulf of Mexico in the past 30,000 years

Citation
Frazier, D. E., 1974, Depositional-Episodes: Their Relationship to the Quaternary Stratigraphic Framework in the Northwestern Portion of the Gulf Basin: The University of Texas at Austin, Bureau of Economic Geology, Geological Circular 74-1, 28 p.