Marginal-Marine Environments Deltas, Beach and Barrier Island systems,

Marginal Marine Transitional Where land meets the sea Dominated by rivers (fluvial), wave, and tidal processes. High-energy – waves and currents Quiet water – lagoonal, and estuarine

Deltas – Deltaic system Alluvial Delta Subaerial, subaqueous Sediment in a standing body of water

Ancient Delta Deposits Found in all ages of stratigraphic sequences Important petroleum and natural gas deposits, coal, and other mineral resources, uranium is one. Excellent reservoir rocks, cap rocks and traps in this sequence of rocks, stratigraphic traps

Modern deltas Table 9.1 Largest delta plain area = Ganges –Bramaputra Large water discharge = G-P, Irrawaddy, Mississippi

Classification of Deltas

Delta Classification 2 Figure 9.3

Cross-Section of a Delta progradation

Delta formation

Cross-section Gilbert-type deltas, in your book, Figure 9.4

Figure 9.12 Components of a Delta

Sediment Characteristics of Deltas Deltaic plain – subaerial component Subaqueous Deltaic plaine Delta front prodelta

Closer view of the cross-section

Flow and Discharge Jet – discharge of sediment Homopycnal flow – equal density water of river entering basin of equal density water, rapid mixing and abrupt deposition of sediment. Hyperpycnal flow – river water higher density than basin water, flows beneath the basin water, vertically oriented plane-jet flow, forms turbidites on gentle slope of delta. Hypopycnal flow – river water is less dense than the basin water, river flow into marine or saline lake flow on top of basin as a horizontal plane-jet,

Bird-foot Delta

History of the Mississippi Delta

River-Dominated Delta

Wave-dominated Delta

Tidal-dominated Delta

Fan Delta Figure 9.11

Delta Cycles Transgression of sea Progradation of delta seaward – construction phase Coarsening-upward sequence Fine prodelta muds overlain by delta front silt and sand Distributary-mouth sands on top of these Marsh and fluvial deposits Transgression of sea Destruction phase

River – Dominated Strata

Wave-dominated delta Strata

Tide-dominated delta strata

Ancient Delta system - Mississippian What tectonic event would these deltas be associated with of the Appalachian Mountains?

What do you know of the sea? Ocean currents? Rotation? Hurricanes rotate in what direction? What about tides? How many low tides per day? Spring tide? Neap tide?

Surface Currents

Spring Tide and Neap Tide

Beach and Barrier Island Systems Beach is the dominant marginal marine deposit What is the dominant Wentworth’s clast size found on the beach?

Depositional Settings Tidal ranges Microtidal = 0 – 2 m tidal range, barrier islands Mesotidal = 2 – 4 m tidal range Macrotidal = > 4 m tidal range

Beach to Barrier Island Single Beach – attached to the mainland Strand Plain – broad beach-ridge system, multiple parallel beach ridges and parallel swales, lack well-developed lagoons or marshes Chenier Plain – sandy ridges elongated along the coast and separated by coastal mudflat Barrier Island – separated wholly or partly form mainland by a lagoon or marsh

Beach Littoral zone

Breakers

Longshore Current

Rip Current

Prograding Beach Figure 9.25

Barrier Islands and Lagoon

Barrier Island Figure 9.23

Characteristics Beach deposits Backshore Shoreface deposits Fine to medium Sand Heavy-mineral laminae Backshore Eolian sand deposits Storm-wave deposits Shoreface deposits Upper shoreface – bidirectional cross-bedding sets, Skolithos burrows, Middle shoreface – fine to medium sand, shell material, landward and seaward dipping cross-beds, Skolithos and ophiomorpha Lower shoreface – fine to very fine sand, intercalated layers of silt and mud, small scale cross-stratification, horizontal laminations, hummocky cross-stratification

Deposits Back-barrier Washover deposits – sandy deposits in the mud-rich lagoon Tidal-channel deposits – sand and lag deposits, fluvial marine deposit, cross-bedding Tidal delta deposits – sandy deposits, parabolic shape in cross-section Tidal Flat deposits – sand lenses and mud deposit Lagoonal – fine grained muds, organic rich muds Marsh – sandy to silts to muds, peat deposits, bioturbated a lot.

Barrier Islands Figure 9.26

Galveston Island

Delaware Island

Barrier Island Sequence

Back-Barrier Figure 9.27

Pennsylvanian Lagoon

Barrier Island and Lagoon - Estuary

Estuary