Chapter 4 Sedimentary Structures

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Chapter 4 Sedimentary Structures
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Bed Tabular or lenticular layers of sedimentary
rock that have lithologic, textural, or
structural unity that clearly distinguishes them
form strata above and below. Bedding planes
(Bounding planes) The upper and lower surfaces
of beds. Sedimentation units thickness of
sediments deposited under essentially constant
physical conditions. Laminae layers less than 1
cm thick. Subdivision an informal unit arising
from distinctive associations of sedimentary
structures such as plane or ripple laminae. Lens
Lenticular shaped deposit of different
composition, texture, cementation or color than
that of the surrounding material. Band Similar
to lens but a intermittent, linear deposit that
differs from the surrounding material.
Amalgamation surface a marked discontinuity
between two beds of similar composition. Amalgamat
ed bed a bed separated by an amalgamation
surface. Layer an informal reference to any bed
or stratum of rock.
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• Terms
• Beds
• Bedding planes
• Sedimentation Units
• Laminae
• Subdivision
• Lens
• Band
• Amalgamation surface
• Amalgamated bed
• Layer

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Bedding Surfaces
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Bedsets (Groups of similar beds Simple or
Composite)
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Graded bedding sedimentation units characterized
by distinct gradations in grain size. These can
be normal (larger grains on the bottom gradually
changing to smaller grain on the top, or the
opposite and less-common, reverse grading.
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Bedform development as a function of water flow
velocity
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Pebble Orientation and Current Direction
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Imbrication
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Ripple formation in a flume
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Symmetric ripples (Oscillation ripples) are
formed by wave action.
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Sediment Transport within an antidune
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Tabular cross-bedding cross-bedded units that
are broad in lateral dimensions with respect to
set thickness and that have essentially planar
bounding surfaces. Trough cross-bedding
cross-bedded units in which one or both bounding
surfaces are curved.
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Flaser bedding ripple bedding in which thin
streaks of mud occur between sets of
cross-laminated or ripple laminated sandy or
silty sediment. More sand than mud.
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Lenticular Bedding a structure formed by
interbedded mud and ripple cross-laminated sand
in which the ripples or sand lenses are
discontinuous and isolated in both a vertical and
horizontal direction. More mud than sand.
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Irregular Stratification Convolute bedding and
lamination a structure formed by complex or
intricate crumpling of beds or laminations into
irregular, generally small-scale anticlines and
synclines.
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Flame Structures wavy flame-shaped tongues of
mud that project upward into an overlying layer,
which is commonly sandstone.
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Ball and pillow structures present in the lower
part of sandstone beds and less common in
limestone beds, that overlie shales. They consist
of hemispherical or kidney-shaped masses that
show internal laminations.
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Synsedimentary Folds and Faults (slump structures)
Décollement structure
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Convolute lamination
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Dish and pillar structures
Scour and fill structures
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Bedding-plane markings
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Groove and Flute casts
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Sole markings owing to erosion of a mud bottom
followed by the deposition of coarser material.
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Index Fossils
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Trace Fossils
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Bedding-plane markings Syneresis cracks,
precipitation imprints, mudcracks, rill marks
parting lineation. Syneresis cracks
Precipitation imprints
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Mudcracks
Rill marks
Parting lineation
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Ichnofacies are trace fossil assemblages that
indicate a specific environment. The type of
trace fossils that may be encountered within
ichnofacies include Repichnia crawling or
walking traces (any trace made during
locomotion. Fodichnia feeding structures
(usually infaunal burrows made by deposit feeders
that systematically mine for food.) Domichnia
burrows used primarily for dwelling as opposed to
feeding. Cubichnia behavioral traces including
resting or nesting traces. Pascichnia traces
made by grazing herbavores, usually at the
sediment/water interface.
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Schematic representation of the relationship of
the characteristic trace fossils to sedimentary
faces and depth zones in the ocean.
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Stromatolites organically formed laminated
structures composed of fine silt or clay-sized
sediment, or more rarely, sand-size sediment.
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Paleocurrents