Geoscience 240 – Lab 7 Sedimentary Structures, Facies, Transport, Deformation and Trace Fossils
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LAB 7: SEDIMENTARY STRUCTURES, FACIES, TRANSPORT,
DEFORMATION & TRACE FOSSILS: PART 1
Sediments are often deposited by flowing water or beneath water. As deposited they are usually
saturated (all pore spaces filled by water) but some clayey sediments can be deposited so slowly that they
may hold more water than they do solid mineral matter.
There are two parts to this lab:
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Part 1: Examination, measuring, drawing and interpreting sedimentary structures from diverse
environments including: bedding (laminar, wavy, lenticular), concretions, cross beds, flame
structures, graded beds, hard ground, lode casts, mud cracks, ripple marks, rip up clasts,
sedimentary massive sulphides, sedimentary mineralization, soft sediment deformation,
turbidites and trace fossils (burrows, grazing trails). Note the formation and source of samples.
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Part 2: Exercises from Ancient Environments including:
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A. Clastic sediment evolution on triangular diagrams
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B. Introduction to strip logs for common stratigraphic sequences and depositional facies
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C. Facies maps
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D. Constructing your own strip logs
The 1st part requires access to the rocks, hand lenses and binocular microscopes. The second part is
supported by the out of print lab books and on line copies and facies foldouts. While this secont part may
be done as homework, it helps to work through this in groups so you can discuss the various alternatives
and learn how to think about these concepts with the help of some spare brains!
INTRODUCTION TO COMMON SEDIMENTARY STRUCTURES
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Geoscience 240 – Lab 7 Sedimentary Structures, Facies, Transport, Deformation and Trace Fossils
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Geoscience 240 – Lab 7 Sedimentary Structures, Facies, Transport, Deformation and Trace Fossils
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ICHNOFOSSILS (TRACE FOSSILS)- FORMED BY ANIMALS: CRAWLING, GRAZING,
BURROWING, OXYGEN DEPENDENT.
Fossil/Organism Behaviour
Bathyal Ichnofacies – pelagic/turbidites
(Oxygen limited)
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Geoscience 240 – Lab 7 Sedimentary Structures, Facies, Transport, Deformation and Trace Fossils
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Ichnofacies: Coastal, Shelf (wave base), Bathyal (below wave base), Abyssal (very deep suboxic basins)
SEDIMENT TRANSPORT –HJULSTROM DIAGRAM
 Transport in suspension
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Transport as bedload 
Geoscience 240 – Lab 7 Sedimentary Structures, Facies, Transport, Deformation and Trace Fossils
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HEIGHTS AND WAVELENGTHS OF NATURALLY OCCURRING RIPPLES AND DUNES
PART 1: DESCRIPTION OF SEDIMENTARY STRUCTURES
1. Concretions: Spheres, flattened spheres, dumbbells, septarian, irregular cementation around
organic matter or fossils thereafter. Concretions are low temperature geochemically cemented
portions of sedimentary rock (sandstone, shale, limestone, coal etc. Typically they form below the
water table where oxygen is limited. Often they are cemented by the same common cement
compounds that permineralize or petrify fossils. Spherical or concentric concretions are often
compositionally zoned with different mineral cements in layers. This is through to be controlled by
diffusion and chemical gradients set up around decaying organic matter. Draw & describe 2 different
shapes of concretions. Note what mineral cements are present and whether there are any fossils. (6)
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Geoscience 240 – Lab 7 Sedimentary Structures, Facies, Transport, Deformation and Trace Fossils
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2. Cross Beds. These are generally sandy to gravelly for grain size and are formed by deposition on
the slip face of subaqueous dunes for our specimens. Sketch and describe 2 different specimens with
cross bedding. Are the cross beds curved? What is the way up of your specimen. Which way was the
current flowing that deposited these crossing sand layers and how do you know. If your cross beds
are this tall, how tall was the dune they originally formed on? Be sure to include a scale on your
drawings. (6):
3. Ripple Marks. These form usually out of phase with overlying waves in low flow velocities but in
shallow moving water such as along the edge of a stream or just off the beach face with some wind
stress wave ripple activity. In some instances the flow is unidirectional, in others it is oscillating in
one place. Draw the plan and cross sectional view of a ripple marked specimen and note whether the
ripples are linear or curved and straight or branching? If there are other layers with ripples in the
same specimen are they in the same orientation (alignment)? Why or why not and what does this tell
you about water motion when they formed. Draw a plan view and a cross sectional view and label
whether these ripples are symmetric or asymmetric. (6 )
4. Cruziana (horizontal grazing trails or shallow burrows parallel to the seabed). Try and estimate
whether these were caused by 1 or more than one organism. How big was it? Is there any indication
of how vigorously it could move? Draw one of these specimens and also a set of burrows or burrow
molds. Can you tell the orientation of these and what animal behavior gave rise to them. Compare
and contrast the 2 structures. Sketch and describe with labels. (6):
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5. Bedding variations: turbidites, alternating laminations, wavy, lenticular, bimodal: Often
environments receive different types of sediment or sediment transported via different processes
alternately. Deep slopes fail to generate turbidity currents. As these pass by coarse materials fall first
then fine materials. See Bouma sequence: A, B, C, D and E. Often the setting starts with a muddy
breccia or graded gavel to sand bed and passes upwards into finely laminated silts. Once the tractive
sediment deposits only hemipelagic muds fall so there is a mud or shale cap. Tides are often
asymmetric in their intensity, strong flood and weak ebb. Storms start out big then pacify. Rivers
flood then subside. All of these processes can generate 2 alternating bed types. Draw 2 different
examples, ascertain their lithologies and or cements then try and figure out their way up and
depositional settings. (6)
6. Flame structures: Rapidly deposited successions of sands and muds on delta fronts, continental
slope canyons to abyssal plain fans and deep lakes with sediment accumulation can become loaded
by new sediment causing sediments to dewater, water to escape upwards, and sands can flow. Flame
structures are the result on a fine scale and clastic dykes and sand blows, sand volcanoes can occur on
larger scales especially in tectonic basins which are seismically active.
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Geoscience 240 – Lab 7 Sedimentary Structures, Facies, Transport, Deformation and Trace Fossils
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7. Hard ground: In carbonate islands, atolls etc. when se level falls (regression) from climate cooling,
ice ages, opening of new trenches etc., the drop in sea level shuts down the carbonate deposition.
Above sea level the acid rain dissolves exposed layers and reduces them in thickness down to local
water table. Limestones in bulk may be mostly CaCO3 but windblown silt, hematite, clays and other
insoluble residues left over from chemical weathering accumulate as a reddish hard lag. This type of
hardground differs from submarine cemented aragonite crusts which are depositional in origin. In
any thick succession of carbonate rocks there are wavy, undulating reddish layers. This one was from
a 125 ka (the last marine high stand isotope stage 5E) exposed bed a few metres above sea level on San
Salvador in the Bahamas. Draw and label showing way up and any fine particles and evidence of
dissolution and recementation plus any lags. (6)
8. Ophiomorpha: This was a vertically oriented shrimp burrow (dwelling, hide out for sneaky
attacks, escape structure?). Some shrimp species dwell in muddy carbonate bottoms and secrete a
protein glue to cement the walls of their burrows. Thes structures are like skolithos preserved in sand
beds but here you can see the part that stuck up above the seabed like the rim of a soldier’s fox hole.
Later this recrystallized to interlocking calcite. This one came from a micrite layer 3 m above sea level
on Rum Cay in the Bahamas. Draw the structure in plan view and cross section. Estimate how big the
creature was who built this ~ 125 ka.
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Geoscience 240 – Lab 7 Sedimentary Structures, Facies, Transport, Deformation and Trace Fossils
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9. Krotovina: This is a chunk of “B” horizon orangeish red weathered soil developed on the
floodplain overbank silts of the Mascall Formation along Rattlesnake Creek in Harney Basin Eastern
Oregon. It is riddled with krotovina. This is the soil scientists term for any kind of a burrow in a soil.
While this is now sagebrush arid scrub steppe and rattlesnake country at 7.06 Ma when the overlying
Rattlesnake tuff fell and buried it, there was a humid, forested savannah. Tehse burrows were made
by cicadas (locusts) whose life cycle involves long pupation and root nibbling before the right year to
emerge, fly, sing and breed. Draw the shapes of these and label the weathering minerals and colours
that tell you this was above the water exposed to the air. (6)
10. Lode casts, sediment rolls and rip up clasts: Often sediment is laid down rapidly in sufficient
thicknesses to deform underlying materials as in sandy turbidites over muds or silts. Lode casts form
ont eh bottom of beds and are elongate in the downhill direction of sediment transport. Contrariwise
sometimes slopes get loaded and slough off materials that “roll their own” and can make cohesive
muds to fail and roll up much like rolling up the rug. Rapid increases in flow velocity can also erode
cohesive muds from the underlying beds and fling them downhill like wet curvy potato peelings.
Find, draw and label any 2 of these structures. Use them to show way up on the beds and the
transport direction. (6)
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Geoscience 240 – Lab 7 Sedimentary Structures, Facies, Transport, Deformation and Trace Fossils
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11. Mudcracks: are a type of fissure through a wet, cohesive clay sized sediment bed as it dries out
when exposed to the sun. They typically form on tidal flats at ebb tide and along floodplains or
islands in rivers as flooding abates. In carbonate settings they are often accompanied by cubic molds
salt casts from brine evaporation. The cracks form polygonal networks as mud shrinks in volume and
pulls away in tension from its surroundings to form polygonal networks of cracks. They are
sometimes adorned with raindrop impressions or animal tracks. Subsequent flooding can mobilize
sand to fill in the cracks. Unlike cracks and veins caused by structural deformation, these cracks only
penetrate one bed as only the uppermost bed is wet and drying out. Draw one of these in plan view
and cross section & indicate how you can tell way up even without tracks or raindrop impressions. (6)
12. Sinter/tufa: These are silica rich hotsprings deposits which form by evaporation and
precipitation at the rims of or as crusts atop the edge of thermal springs. These samples come from
Mickey Hotsprings near Steens Mountain in the Alvord desert of SE Oregon. There are often
thermophyllic bacterial mats and in some of these pools and borax deposits. The springs themselves
stand up as raised mounds as the depositon of minerals forms cements and inflates the surrounding
sediment so the water must rise higher to escape a bit like a mound shaped volcano but here the
deposits form gradually. Vugs (trapped air or steam pockets) give the rock a porous appearance.
Crusts formed by thermophyllic bacteria and heat adapted algae are common. How are these
deposits similar to and different from more common evaporates? Draw and label some components
of this sinter and indicate way up. (6)
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13. Economic mineral deposits which form sediments or form in sediments: Sedimentary Massive
Sulphides (SMS) and VMS (Volcanogenic) form where super heated mineral brines hit cold sea water
such as at Black Smokers (Magic Mountain, Tag, Kuroko, Bathurst, Sullivan). The cores here are cross
bedded pyrite, sphalerite and chalcopyrite from the Myra Falls Mine in Strathcona Park above
Campbell River (underground Zn/Cu mine owned by Breakwater Resources). This Myra Formation
was part of a submarine volcano sedimentary system in Devonian, somewhere south in the
Panthallasic Ocean that was destined to become the backbone of Vancouver Island. The layered rock
is an iron rich skarn (tactite) where a Jurassic Granodiorite Intrusion hit cold Quatsino Limestone and
deposited pyrite, chalcopyrite and magnetite. Limestones are typically host to thin contact
metamorphic skarn deposits. The “Pink Rock” was actually a red, mudcracked Middle Proterozoic
mudstone (Prichard Formation) from eastern Washington north of Spokane. It was cut by barite veins
and inflated to a barite industrial mineral deposit. Barite only forms over continents as hydrothermal
fluids alter plagioclase and release its few tens to hundreds of ppm of Ba. Note the veining and
complete destruction of primary bedding. Draw and label any 2 of these rocks keeping in mind that
sometimes sediments get superposed structures and mineralization. (6)
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