of discharge is often marked by a small sand mound
(“sand volcano”) some 30–50 cm in diameter and up to
10 cm in height.
Methane, hydrogen sulfide, and ammonia gases generated by decomposition of organic matter buried under the
beach can upwell along a preferred conduit, escaping to
the surface of the beach. Such gas upwelling also causes
physical disruption of lamination of beach sediment.
Evaporation, caused by solar radiation or by wind,
results in the loss of moisture. Depending on the depth to
the water table under a beach, evaporation can induce an
increase in salinity by moisture loss and in precipitation
of salt (halite).
During rainfall, meteoric water effects three processes:
dilution of surface water and pellicular water salinity, dissolution of any halite that has precipitated on the surface,
and vadose water-induced infiltration. For the latter, rain
washing onto a beach during its exposure at low tide can
deliver dust or any fine-grained sediment on the beach to
levels lower down the sediment profile. If the beach is
not reworked later by waves and tides, this material can
be preserved as meniscus sediment. Waves and tides
washing over a beach slope on a rising tide can also infiltrate the beach sand vertically and deliver fine-grained
sediment (that was in suspension in the water) into the
beach-sand pore spaces.
In terms of the horizontal sequence of small-scale landforms, sedimentary structures, and processes, sandy
beaches provide excellent examples of the products of
wave and tidal energy intersecting a sloping shore and
illustrate the range of sedimentary products that are developed across the slope gradient from shallow subtidal to
supratidal, in response to the graded effect of waves, tides,
wind, and freshwater seepage (Clifton, 1969; Clifton et al.,
1971; Reineck and Singh, 1980; Semeniuk and Johnson,
1982; Semeniuk, 1997; Brocx and Semeniuk, 2009). For
instance, wave action intersecting a sloping shore is translated from a lower flow regime (varying progressively
upslope) to an upper flow regime, and the resultant
upslope progressive development of rippled beds and perhaps megarippled bedforms further upslope, and plane
beds. Hourly, daily, weekly, and seasonal variation in
wave patterns, coupled with storm effects, tide fluctuation,
and onshore winds, generate lamination, shell layers,
cut-and-fill structures, discontinuities (Mii, 1958), variation in grain size across laminations, and bubble sand.
While the literature cited above on beach processes and
products is derived mainly from beaches on oceanic
shores, the principles of sedimentation and stratigraphic
evolution apply equally to estuarine beaches. Moreover,
the beaches closer to the estuary mouth, particularly in
wide valley-tract, ocean-facing estuaries, have many features in common with oceanic beaches.
The biological processes on beaches are macrobiota
shell production; microbiota test production; burrow
construction; root structuring; general bioturbation; fragmentation; macrofaunal and meiofaunal breakdown of
seagrass, algae, and other plant materials on the beach
face; microbial decomposition; sediment pigmentation
by sulfides; and hydrochemical changes in pH, Eh, and
ionic chemistry effected by microbiota. The conspicuous
products of biological activity result in shell layers, burrows, bioturbation, and pigmentation of sediments.
Shell production results in articulated bivalve shells
being preserved in situ in the sediment (e.g., pipis and
tellinids) or, where shells are disarticulated and locally
transported after death, in shells being scattered in the sediment parallel to lamination usually in a convex-up orientation, though concave-up orientations are possible
(Nagle, 1967; Reineck and Singh, 1980; Savarese,
1994). Gastropods are often predators of bivalves in the
shore environment and are responsible for their death
(the evidence being drill holes in the disarticulated
bivalves; Carriker and van Zandt, 1972; Kabat, 1990),
after which follows disarticulation. Gastropods also scavenge for decaying organic material on beaches. Gastropods contribute shell to beach sediments after their own
death. Often bivalve and gastropod shells form laminae
of shell concentrates in the beach sediment, with the
bivalve shells specifically also forming a platy shell pavement on the surface due to wind deflation or current
winnowing. Microbiota, such as foraminifera and diatoms, contribute tests as fine sand-sized particles that
accumulate as fine-grained calcareous and siliceous particulates in the sediment.
Some of the major products of biogenic processes on
beaches include burrow construction, general bioturbation,
and root-structuring (McCall and Tevesz, 1982). Fauna that
live in permanent burrows on the beach slope create distinct
biogenic structures. Bivalves and beach worms are examples of such fauna (Reineck and Singh, 1980; Brown and
McLachlan, 1990). The burrows may be diffuse, vertical
structures penetrating the beach lamination (formed as the
animal migrated vertically in response to changing groundwater levels), or may be a simple single tube open burrow
that the animal has lined with organic matter or mud to prevent collapse, or may be a u-shaped open burrow. With the
open burrows, remaining open because of their lining, later
sand infiltration into abandoned burrows brought in by
wave swash or tidal currents results in a sand-filled tube that
is penetrative through the beach lamination. Bioturbation of
the sediment is produced by other animals that burrow in
the beach sediment but do not produce permanent tube
dwellings.
Depending on whether physical processes that produce
beach lamination are dominant over biological processes
that produce burrow and bioturbation structures, the beach
sediments can grade from laminated sand and shelly sand
with occasional burrows (i.e., physical processes are dominant), to laminated sand and shelly sand with abundant
burrows and bioturbation structures but within which the
beach lamination is relict and still evident, to thoroughly
bioturbated sand and shelly sand with some sand-filled
vertical burrows evident (i.e., biological processes are
dominant). Figure 8 illustrates this gradation in laminated
sediment to bioturbated sediment.
66
BEACH PROCESSES
(“sand volcano”) some 30–50 cm in diameter and up to
10 cm in height.
Methane, hydrogen sulfide, and ammonia gases generated by decomposition of organic matter buried under the
beach can upwell along a preferred conduit, escaping to
the surface of the beach. Such gas upwelling also causes
physical disruption of lamination of beach sediment.
Evaporation, caused by solar radiation or by wind,
results in the loss of moisture. Depending on the depth to
the water table under a beach, evaporation can induce an
increase in salinity by moisture loss and in precipitation
of salt (halite).
During rainfall, meteoric water effects three processes:
dilution of surface water and pellicular water salinity, dissolution of any halite that has precipitated on the surface,
and vadose water-induced infiltration. For the latter, rain
washing onto a beach during its exposure at low tide can
deliver dust or any fine-grained sediment on the beach to
levels lower down the sediment profile. If the beach is
not reworked later by waves and tides, this material can
be preserved as meniscus sediment. Waves and tides
washing over a beach slope on a rising tide can also infiltrate the beach sand vertically and deliver fine-grained
sediment (that was in suspension in the water) into the
beach-sand pore spaces.
In terms of the horizontal sequence of small-scale landforms, sedimentary structures, and processes, sandy
beaches provide excellent examples of the products of
wave and tidal energy intersecting a sloping shore and
illustrate the range of sedimentary products that are developed across the slope gradient from shallow subtidal to
supratidal, in response to the graded effect of waves, tides,
wind, and freshwater seepage (Clifton, 1969; Clifton et al.,
1971; Reineck and Singh, 1980; Semeniuk and Johnson,
1982; Semeniuk, 1997; Brocx and Semeniuk, 2009). For
instance, wave action intersecting a sloping shore is translated from a lower flow regime (varying progressively
upslope) to an upper flow regime, and the resultant
upslope progressive development of rippled beds and perhaps megarippled bedforms further upslope, and plane
beds. Hourly, daily, weekly, and seasonal variation in
wave patterns, coupled with storm effects, tide fluctuation,
and onshore winds, generate lamination, shell layers,
cut-and-fill structures, discontinuities (Mii, 1958), variation in grain size across laminations, and bubble sand.
While the literature cited above on beach processes and
products is derived mainly from beaches on oceanic
shores, the principles of sedimentation and stratigraphic
evolution apply equally to estuarine beaches. Moreover,
the beaches closer to the estuary mouth, particularly in
wide valley-tract, ocean-facing estuaries, have many features in common with oceanic beaches.
The biological processes on beaches are macrobiota
shell production; microbiota test production; burrow
construction; root structuring; general bioturbation; fragmentation; macrofaunal and meiofaunal breakdown of
seagrass, algae, and other plant materials on the beach
face; microbial decomposition; sediment pigmentation
by sulfides; and hydrochemical changes in pH, Eh, and
ionic chemistry effected by microbiota. The conspicuous
products of biological activity result in shell layers, burrows, bioturbation, and pigmentation of sediments.
Shell production results in articulated bivalve shells
being preserved in situ in the sediment (e.g., pipis and
tellinids) or, where shells are disarticulated and locally
transported after death, in shells being scattered in the sediment parallel to lamination usually in a convex-up orientation, though concave-up orientations are possible
(Nagle, 1967; Reineck and Singh, 1980; Savarese,
1994). Gastropods are often predators of bivalves in the
shore environment and are responsible for their death
(the evidence being drill holes in the disarticulated
bivalves; Carriker and van Zandt, 1972; Kabat, 1990),
after which follows disarticulation. Gastropods also scavenge for decaying organic material on beaches. Gastropods contribute shell to beach sediments after their own
death. Often bivalve and gastropod shells form laminae
of shell concentrates in the beach sediment, with the
bivalve shells specifically also forming a platy shell pavement on the surface due to wind deflation or current
winnowing. Microbiota, such as foraminifera and diatoms, contribute tests as fine sand-sized particles that
accumulate as fine-grained calcareous and siliceous particulates in the sediment.
Some of the major products of biogenic processes on
beaches include burrow construction, general bioturbation,
and root-structuring (McCall and Tevesz, 1982). Fauna that
live in permanent burrows on the beach slope create distinct
biogenic structures. Bivalves and beach worms are examples of such fauna (Reineck and Singh, 1980; Brown and
McLachlan, 1990). The burrows may be diffuse, vertical
structures penetrating the beach lamination (formed as the
animal migrated vertically in response to changing groundwater levels), or may be a simple single tube open burrow
that the animal has lined with organic matter or mud to prevent collapse, or may be a u-shaped open burrow. With the
open burrows, remaining open because of their lining, later
sand infiltration into abandoned burrows brought in by
wave swash or tidal currents results in a sand-filled tube that
is penetrative through the beach lamination. Bioturbation of
the sediment is produced by other animals that burrow in
the beach sediment but do not produce permanent tube
dwellings.
Depending on whether physical processes that produce
beach lamination are dominant over biological processes
that produce burrow and bioturbation structures, the beach
sediments can grade from laminated sand and shelly sand
with occasional burrows (i.e., physical processes are dominant), to laminated sand and shelly sand with abundant
burrows and bioturbation structures but within which the
beach lamination is relict and still evident, to thoroughly
bioturbated sand and shelly sand with some sand-filled
vertical burrows evident (i.e., biological processes are
dominant). Figure 8 illustrates this gradation in laminated
sediment to bioturbated sediment.
66
BEACH PROCESSES