Tidal Environments

Tidal environments occur in a wide variety of settings (e.g., directly facing the open sea/ocean, in Estuaries, in lagoons behind barrier islands, near tidal inlets) and contain a supratidal zone, an intertidal zone (tidal flats), and tidal channels.

Tidal channels can be extremely deep and dynamic and are commonly filled with large-scale cross-stratified tidal-bundle sequences and/or laterally accreted heterolithic (sandy and muddy) strata.

Intertidal environments include sandy to muddy tidal flats where tidal rhytmites may form, commonly bordered by salt marshes or mangroves where muddy facies or peats accumulate.

Estuaries are transgressed, drowned, river valleys where fluvial, tide, and wave processes interact; they are characterized by a net landward movement of sediment in their seaward part.

Tide-dominated estuaries contain tidal sand bars at the seaward end, separated from the fluvial zone by relatively fine-grained tidal flats (e.g., salt marshes); fluvial channel deposits exhibit heterolithic characteristics and sometimes tidal-bundle sequences.

Wave-dominated estuaries have a coastal barrier with a tidal inlet and flood- tidal delta, separated from a bayhead delta by a central basin where fine- grained sediments (muds) accumulate.

 

St Michel, France   Tropical Tidal (mangroves)

 

Wave-dominated Tidal Estuary

 

 

Tide-influenced sedimentary structures can take different shapes:

Herringbone cross stratification indicates bipolar flow directions, but it is rare.

 

 

 

 

 

 

 

Mud-draped cross strata are much more common, and are the result of alternating bedform migration during high flow velocities and mud deposition during high or low tide (slackwater).

Tidal bundles are characterized by a sand-mud couplet with varying thickness; tidal bundle sequences consists of a series of bundles that can be related to neap-spring cycles.

Tidal rhytmites can form in fine-grained facies that aggrade vertically, to a large part from suspension, and consist of commonly very thin (mm-scale), but distinct laminae.

 

   

 

Sigmoidal Cross-bedding; Mud-draped cross strata. Thinner, mud draped bundles represent neap-tide, thicker sets represent spring-tide (higher tidal energy). the two bundles represent one month of deposition. Mud-draped cross strata

 

Tidally influenced channel sand, Pre-Cambrian, Kovyktinskoye, E. Siberia

 

Tidal rhytmites Tidal rhytmites