Late Quaternary Evolution and Stratigraphic Framework Inflfluence on Coastal Systems along the North-Central Gulf of Mexico, USA

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Late Quaternary Evolution and Stratigraphic Framework Inflfluence
on Coastal Systems along the North-Central Gulf of Mexico, USA, Is A Well-Researched Topic, It Is To Be Used As A Guide Or Framework For Your Research.

ABSTRACT

Coastal systems in the Gulf of Mexico are threatened to reduced sediment supply, storm impacts and relative sea level rise (RSLR). The geologic record can provide insights of geomorphic threshold crossings (formation, progradation, transgression, destruction) to these forcing mechanisms to predict future barrier evolution to climate change. The stratigraphic framework and antecedent topography directly influence
coastal evolution over geologic timescales. This study synthesizes ~2100km of geophysical data, 700+ sediment cores, and 63 radiocarbon dates to regionally map two sequence boundaries, multiple ravinement surfaces and fourteen depositional facies.

One marine isotope stage (MIS) 6 valley’s fill provided up to 300 x106 m3 of sand to modern systems through transgressive ravinement during the Holocene. Repeated storm breaches or tidal inlets correspond to paleotopographic low’s in the MIS 2 surface. A Holocene geomorphic evolutionary model was created for Petit Bois and Dauphin Island from available data, highlighting RSLR rates and sediment supply. As the
MIS 2 surface was flooded, tidal/wave scour supplied sand to migrating marine shoals.

These rapidly transgressing shoals converted drowned paleovalleys to estuaries starting about 9ka. Islands formed in their modern positions about 6ka, when sediment supply was high and RSLR rates were 2mm/yr. Between 4ka-1750 CE. Islands prograded due to RSLR rates of 1-0.4mm/yr and sufficient sand supply from alongshore and inner shelf
sources. Currently, the islands experience RSLR rates of 3.61 mm/yr and reduced sediment supply resulting in barrier degradation. This study provides geologic evidence of coastal geomorphic thresholds related to RSLR, sediment supply and antecedent topography.

TABLE OF CONTENTS

ABSTRACT ………………………………………………………………………………………………………… ii
ACKNOWLEDGMENTS ……………………………………………………………………………………. iii
DEDICATION ……………………………………………………………………………………………………. iv
LIST OF TABLES ………………………………………………………………………………………………. ix
LIST OF ILLUSTRATIONS …………………………………………………………………………………. x
LIST OF ABBREVIATIONS ……………………………………………………………………………….. xi
1-INTRODUCTION …………………………………………………………………………………………….. 1
2-REGIONAL SETTING ……………………………………………………………………………………… 5
2.1 Coastal and Physical Setting …………………………………………………………………………. 5
2.2 Coastal Response to Sea Level ……………………………………………………………………… 6
2.3 Barrier Formation and Evolution …………………………………………………………………… 8
2.4 Shore Oblique Sand Ridges ………………………………………………………………………….. 9
2.5 Mississippi/Alabama Coastal Geology …………………………………………………………. 10
3-METHODS …………………………………………………………………………………………………….. 13
3.1 Geophysical Data ………………………………………………………………………………………. 13
3.2 Sediment Cores …………………………………………………………………………………………. 15
3.3 Radiocarbon Dating Estimates …………………………………………………………………….. 15
3.4 Sand Volume Calculations ………………………………………………………………………….. 17
3.5 Evolutionary Model …………………………………………………………………………………… 18

4-RESULTS ………………………………………………………………………………………………………. 19
4.1 Quaternary Chronostragraphic Framework …………………………………………………… 19
4.1.1 Sequence Boundary 1: Marine Isotope Stage 6 ……………………………………….. 25
4.1.2 Sequence Boundary 2: Marine Isotope Stage 2 ……………………………………….. 27
4.1.3 Unit 1: Pleistocene ………………………………………………………………………………. 27
4.1.4 Unit 2: Fluvial Channel Sands Deposits …………………………………………………. 28
4.1.5 Unit 3: Fluvial Lateral Accretion Deposits ……………………………………………… 28
4.1.6 Unit 4: Marsh Deposits ………………………………………………………………………… 29
4.1.7 Unit 5: Oyster Biostrome ……………………………………………………………………… 30
4.1.8 Unit 6: Estuarine Deposits ……………………………………………………………………. 30
4.1.9 Unit 7: Tidal Inlet Fill or Barrier Spit …………………………………………………….. 31
4.1.10 Unit 8: Flood Tidal Delta Deposits ………………………………………………………. 31
4.1.11 Unit 9: Ebb Tidal Delta Deposits (Modern) ………………………………………….. 32
4.1.12 Unit 10: Shoreface Deposits ……………………………………………………………….. 32
4.1.13 Unit 11: Barrier and Backbarrier Deposits ……………………………………………. 33
4.1.14 Unit 12: Marine Surficial (MAFLA) Sand Sheet …………………………………… 34
4.1.15 Unit 13: Sand Ridge Deposit ………………………………………………………………. 34
4.1.16 Unit 14: Inner Shelf Mud Deposit ……………………………………………………….. 35
4.1.17 Unconformity 1: Transgressive Surface (TS) ………………………………………… 35
4.1.18 Unconformity 2: Wave Ravinement Surface (wRs) ……………………………….. 35

4.1.19 Unconformity 3: Tidal Ravinement Surface (tRs) ………………………………….. 36
4.1.20 Unconformity 4: Bay Ravinement Surface (bRs) …………………………………… 36
4.1.21 Unconformity 5: Sand Ridge Ravinement Surface (sRs) ………………………… 38
4.2 Antecedent Topography and Paleofluvial systems …………………………………………. 38
4.2.1 Sequence Boundary 1: MIS 6 Surface ……………………………………………………. 38
4.2.1.1 Fowl and La Batre Systems ……………………………………………………………. 38
4.2.1.2 Escatawpa/Pascagoula …………………………………………………………………… 39
4.2.2 Sequence Boundary 2: MIS 2 Surface ……………………………………………………. 40
4.2.2.1 MIS 2 Surface Gradient …………………………………………………………………. 40
4.2.2.2 Fowl, La Batre, Escatawpa Systems ………………………………………………… 41
4.2.2.3 Pascagoula System ………………………………………………………………………… 42
4.3 Sand Volume Calculations ………………………………………………………………………….. 44
5-DISCUSSION …………………………………………………………………………………………………. 48
5.1 Pre-Holocene Antecedent Geology and Topography Influences ………………………. 48
5.2 Sediment Sourced through Transgressive Ravinement …………………………………… 50
5.3 Holocene Transgressive Evolutionary Model ………………………………………………… 51
5.3.1 10ka-9ka Transgressing Shoals ……………………………………………………………… 51
5.3.2 8-7ka Transgressing Shoals ………………………………………………………………….. 52
5.3.3 6-5ka: Island Formation and Stabilization ………………………………………………. 55
5.3.4 4-2.5ka: Island Progradation …………………………………………………………………. 55

5.3.5 1750 CE- Modern: Island Degradation …………………………………………………… 57
6-CONCLUSION ………………………………………………………………………………………………. 59
REFERENCES ………………………………………………………………………………………………….. 61

Additional information

Author

Robert Hollis

No of Chapters

6

No of Pages

84

Reference

YES

Format

PDF

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