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Michael Walsworth Ryan Sullivan Simi Odueyungbo William Budd

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Michael Walsworth Ryan Sullivan Simi Odueyungbo William Budd Powered By Docstoc
					Michael Walsworth, Ryan Sullivan,
Simi Odueyungbo, William Budd
   Estuarine
    Environment
       At first (Pritchard, 1967),
        an estuary was defined by
        the salinity of the water.
       Then by Clifton (1982) as
        “an inlet of the sea
        reaching into a river
        valley as far as the upper
        limit of tidal rise.”
         By definition also includes
          barrier lagoons and deltaic
          regimes.
   Refined by Dalrympal (1992)
       Basic definition still applied today
       “The seaward portion of a drowned valley system
        which receives sediment from both fluvial and
        marine sources and which contains facies influenced
        by tide, wave and fluvial processes. The estuary is
        considered to extend from the landward limit of
        tidal facies at its head to the seaward limit of coastal
        facies at its mouth” (Dalrympal, et al, 3).
   Fluvial
       Upstream of transition zone
       Purely fluvial processes
   Fluvial-Tidal Transition Zone
     (“that part of the river which lies between the
      landward limit…”)
     Mixture of fluvial and tidal/wave processes

   Estuarine
       Downstream of transition zone
       Feels no effects of fluvial processes
   Transition Zone is defined by Van den Berg as “that
    part of the river which lies between the landward limit
    of observable effects of tidally induced flow
    deceleration on fluvial cross-bedding at low river
    discharge, and the most seaward occurrence of a
    textural or structural fluvial signature at high river
    stage.”
       Extends past measurable dilution of salt water
       Includes river-sea relationships in deltas
   Studies on Rhine and Meuse River System
    (Netherlands/Germany)
       A mesotidal estuaries with a medium-large river system in a
        temperate climatic zone
   Quaternary and Pliocene-aged sediments
   Large-scale dune X-bedding
       Results in foresetting, tend to be approximately
        regularly spaced
   Ripple and Transitions
   Longitudinal Sequences sorting from sands
    upstream to clays downstream
   Dm-scale successions in the vertical
       Cyclic Neap-Spring Successions
         Herringbone X-bedding and alternating sand and mud
         interbedding, indicators of flow reversal
   Inclined linsen and flaser bedding
   Wave-Dominated
   Tidal-Dominated
   Fluvial-Dominated
       Grey area, as at this point the area could be defined
        as a delta rather than an estuary
   Not affected by fluvial processes
   Fine sediments accumulate
   No distinct vertical sequence at meter scale,
    except for the top one to two meters which
    transition into clays and intertidal salts
   In estuarine environments, discontinuities are
    draped with clays in dune X-bedding as
    opposed to peats in transition zone
   Ebb flow is concentrated in channels
   Flood can cross shoal morphology
   Ebb channels dictate the large morphological
    changes
   Tidal signatures in the stratigraphy of fluvial
    sediments allows for the determination of the
    maximum flood surface
   Transition zone is characterized by
    a single meandering channel that
    guides the main flow of both tides
       Results in thick cosets displaying the
        dominant ebb-direction
   Hydraulic and morphological
    characteristics make transition
    zone differ from other
    fluvial/tidal environments


• As flow strength increases the hydraulic roughness of fluvial
  dunes decreases, whereas dune height remains relatively the
  same
• Fluvial-tidal zones contain characteristic Herringbone X-bedding
   - Due to alternating periods of ebb and flood dominance
   Regular vertical alternations
    of flood and ebb directed X-
    lamination present
   The landward limit of the
    transition zone is dictated
    by the turbidity maximum
     Just upstream of the salt
      intrusion (salinity .1-.5%) is   • Deposits
      where the landward                  • Stepwise fining-upward
      transition zone marker
                                            sequence from decimeter to
     This marker is a function of
      discharge rate of the river           meter scale in outcrops
                                          • Mud drapes of silty nature
     In fluvial dominated systems,
      moves to be more seaward            • Peat lump-dominated
      than in tidal dominated
      regimes.
   Typically, tidal influence is small
   2 maxima
       1 at the mouth caused by wave energy and 1 at the head produced by river currents
       Called the “Central Basin”
         Energy minimum in central portion of estuary
         Contains extensive salt marshes and muds
       Mouth
         Mouth of system experiences relatively high wave energy, accumulating marine sand
           Causes the sediment to form a submerged barrier at the mouth, preventing wave energy
            from entering the estuary
       Head
         Sand and gravel deposited at head forming a bay-head delta
   Best examples are Macro-tidal, i.e. Salmon River
   They occur at much smaller tidal ranges if wave action is limited and/or
    tidal prism is large
   Tidal-current exceeds wave energy at mouth
   Elongated sand bars develop and dissipate the wave energy that does exist
    causing it to decrease in cross-sectional area up the estuary
   Energy minimum (Central Basin) is not as pronounced as in wave-
    dominated systems
       Site of finest channels sands
   Deposits
       Regular, vertical repetitions due to alternating spring and neap tides
       Two or more lithologic units with different sedimentary structure and texture (one for
        neap tide, one for spring tide)
       Largest particles are clay pebbles
   Dalrymple, Robert W., Brian A. Zaitlin, and
    Ron Boyd. "Estuarine Facies Models:
    Conceptual Basis and Stratigraphic
    Implications." Journal of Sedimentary Petrology
    62.6 (1992): 1130-146. Print.
   Van Den Berg, J. H., J. R. Boersma, and A. Van
    Gelder. "Diagnostic Sedimentary Structures of
    the Fluvial-Tidal Transition Zone - Evidence
    from Deposits of the Rhine and Meuse."
    Netherladns Journal of Geosciences 86.3 (2001):
    287-306.

				
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