EAS 209 - Lecture 28
Triassic (Absaroka Sequence)
Focus of the lecture is the Triassic Period within the Absaroka Sequence.
Previous material covered the Pennsylvanian and Permian.
The Triassic follows the end-Permian mass extinction and is largely a story of biological recovery.
Important questions to consider for any geologic period:
What was Western Canada like during that time?
What formations are preserved?
What rock types occur?
Are the rocks mainly carbonates or siliciclastics?
Are sediments coarse-grained or fine-grained?
What fossils are present?
Frederick August von Alberti
German geologist who lived from 1795–1878.
Important figure in German geology.
Known for coining the term "Triassic."
Worked extensively in mining.
Observed three rock units that consistently occurred together:
Bunter Sandstone.
Muschelkalk.
Keuper.
Named this recurring three-part sequence the "Trias."
The name later became "Triassic."
Also contributed to fossil identification and scientific publications.
ANS: B
Sea-Level Trends During the Triassic
Overall sea level was falling through the Triassic.
Smaller sea-level rises and falls occurred within the larger long-term regression.
A sea-level drop occurred at the Permian-Triassic boundary.
The drop was not large enough to end the Absaroka Sequence.
As sea level fell:
Shorelines migrated westward.
Areas previously underwater became exposed.
Depositional environments shifted progressively west.
End-Permian Mass Extinction
One of the largest extinction events in Earth history.
The Triassic records recovery after this event.
At the beginning of the Triassic:
Fossils are extremely rare.
Biodiversity is greatly reduced.
Similar pattern to the post-Devonian extinction recovery seen previously in the course.
Early Triassic sediments contain:
Siltstones.
Mudstones.
Very fine-grained sandstones.
Some dolomite occurs as transported grains.
Fossils become more common only later in the Triassic as recovery progresses.
Preservation Issues After the Extinction
Lack of fossils does not necessarily mean life was absent.
Oceans are thought to have become highly acidic.
Acidic seawater dissolves shells after organisms die.
Living organisms protect shells using biological coatings.
After death:
Protective coatings disappear.
Shells become exposed to seawater.
Acidic water dissolves shell material.
When organisms are living, they usually have a biological film that protects their shell from exposure to the surrounding seawater. It acts as a buffer.
When they die, this buffer dissolves and dies away.
Evidence includes:
Molds of ammonoids where shells have dissolved away.
Recovery of biodiversity took a very long time.
Biodiversity levels similar to the Permian were not reached again until the Jurassic.
Organisms must have survived somewhere during this interval.
Scientists propose the existence of refugia:
Small isolated pockets where organisms survived.
Populations later expanded outward as conditions improved.
These refugia are difficult to locate in the geologic record because they were geographically limited.
Must have been a global change in climate for so many animals to go extinct.
Evidence of Global Ecological Collapse
Extinction affected:
Microfossils.
Plankton.
Large marine organisms.
Swimming organisms.
Sessile organisms.
Land plants.
Nearly all ecological groups experienced severe declines.
Indicates a global environmental crisis rather than a local event.
Pangaea During the Triassic
Triassic world was dominated by the supercontinent Pangaea.
Earlier in Earth's history:
Rodinia existed.
Continents later separated and reassembled through the Wilson Cycle.
During the Triassic:
Most continental masses were joined together.
Major oceans included:
Panthalassa Ocean.
Paleotethys Ocean.
Western Canada was located much closer to Siberia than today.
Siberian Traps and the Mass Extinction
Siberian Traps are considered a major contributor to the end-Permian extinction.
Consisted of enormous flood basalt eruptions.
Lava erupted continuously over millions of years.
Not a single volcano.
Instead:
Vast regions continuously leaked lava.
Flood basalts spread across enormous areas.
Thickness and volume were immense.
Enough lava exists in the Siberian Traps to cover all of North America with approximately 121 meters of lava.
Eruptions are closely dated to the extinction event.
Environmental Effects of Siberian Trap Volcanism
Released large amounts of:
CO₂.
SO₂.
Chlorine compounds.
Fluorine compounds.
NOx gases.
Consequences included:
Global warming.
Acid rain (when it mixes with water vapour).
Atmospheric changes.
Ocean acidification.
Ash and aerosols:
Reduced sunlight.
Reflected solar radiation back into space.
Contributed to climate instability.
Ocean Acidification
Oceans became more acidic.
Acidic water dissolved shells and skeletal material.
Reduced preservation potential for fossils.
Likely contributed to marine ecosystem collapse.
Ocean Anoxia
Oceans lost large amounts of dissolved oxygen.
Caused by increased organic productivity and decomposition.
Plant die-off increased erosion.
Sediment and nutrients were washed into marine environments.
Nutrients promoted massive algal blooms.
Similar to modern eutrophication in lakes.
When algae died:
Bacteria decomposed the biomass.
Oxygen was consumed.
Oxygen depletion led to widespread marine stress and mortality.
Consumption of biomass which causes ocean anoxia.
Role of Plant Die-Off
Vegetation normally stabilizes soil.
During the extinction:
Plants died in large numbers.
Soil became vulnerable to erosion.
Increased sediment transport to marine environments.
Increased nutrient delivery to oceans.
Helped drive algal blooms and ocean anoxia.
Triassic Environmental Conditions
Conditions near the Siberian Traps were extremely harsh.
Landscapes were barren and volcanic.
Western Canada was thought to be:
More desert-like.
Arid.
Less volcanically active than Siberia.
Overall environment was challenging compared with earlier periods.
Groups Lost During the End-Permian Extinction
Fusulinids disappeared.
Acanthodians disappeared.
Most crinoids disappeared.
Rugose horn corals suffered major losses.
Many marine groups experienced severe declines.
Groups That Survived or Expanded
Marine reptiles appeared and diversified.
Ammonoids became very successful.
Gastropods continued successfully.
Brachiopods persisted.
Evolutionary recovery involved both survivors and newly successful groups.
Triassic Paleogeography and Basin Development
During the Triassic, North America was still part of Pangaea.
Laurentia and Gondwana had previously come together to form the supercontinent.
The Paleotethys Ocean existed alongside the larger Panthalassa Ocean.
Western Canada occupied a position on the western margin of Pangaea.
The region was much closer to Siberia than it is today.
This proximity is important because the Siberian Traps are thought to have played a major role in the end-Permian extinction.
The Triassic of Western Canada is represented mainly within the Peace River Embayment.
The Peace River Embayment formed a major marine connection into the Western Canada Sedimentary Basin.
Sediments were transported into the basin from surrounding source regions.
Ocean currents are interpreted to have flowed generally from north to south.
Material associated with the Siberian region may have been transported along the coastline.
Rivers also contributed sediment into the basin.
Distribution of Triassic Rocks in Western Canada
Triassic rocks occur in both outcrop and subsurface settings.
Major areas include:
Northern Rocky Mountain Outcrop Belt.
Southern Rocky Mountain Outcrop Belt.
Alberta subsurface.
Saskatchewan-Manitoba subsurface.
The Liard Sub-Basin contains extensive Triassic deposits.
The Lower Watrous Sub-Basin occupies parts of Saskatchewan and Manitoba.
The same general area had previously been referred to as the Williston Sub-Basin during discussion of older rocks.
Basin names sometimes change depending on the age interval being studied.
This can create confusion when comparing literature from different geologic periods.
Terrain Accretion During the Triassic
Evidence suggests terrain accretion began during the Late Triassic.
Zircon studies provide evidence for this timing.
By the Jurassic, terrain accretion was definitely occurring.
Accreted terrains represent:
Island arcs.
Oceanic crust fragments.
Continental fragments.
These were progressively added onto western North America.
Compression associated with accretion influenced basin development.
Effect of Falling Sea Level on Triassic Deposits
The Lower Triassic has the greatest geographic extent.
This reflects higher sea levels early in the Triassic.
As sea level fell:
Shorelines migrated westward.
Marine environments retreated.
The area covered by Triassic sediments became progressively smaller.
Younger Triassic units therefore occupy a smaller geographic area than older Triassic units.
Montney Formation
Represents the major Triassic subsurface unit of economic significance.
Extensively targeted for oil and gas development.
Particularly important in:
Northern British Columbia.
Areas around Grande Prairie.
One of the primary reasons for extensive drilling in these regions.
Often developed alongside the Charlie Lake Formation.
Triassic Stratigraphy
Lower Triassic intervals include:
Griesbachian.
Dienerian.
Smithian.
Spathian.
Middle Triassic intervals include:
Anisian.
Ladinian.
Outcrop terminology differs from subsurface terminology.
Sand-dominated shallow and marginal marine successions occur extensively along the Ladian-Carnian coastline of NW Pangea.
Sulphur Mountain Formation
Major Triassic outcrop unit.
Commonly divided into members.
Lower Triassic members:
Vega Member.
Frozo Member.
These are approximately equivalent to the Montney Formation in the subsurface.
Middle Triassic members include:
Whistler Member.
Llama Member.
Whistler Member corresponds to the Doig Formation in the subsurface.
Llama Member corresponds to the Halfway Formation in the subsurface.
Upper Triassic units also occur but were not fully shown on some stratigraphic columns.
Kokina Beds
A notable middle member contains kokina deposits.
Kokina consists largely of shell debris.
Represents accumulation of skeletal material.
Indicates increasing biological recovery through time.
Sediment Sources During the Triassic
Sediment transport and source still predominantly from the east (Shield, not Cordillera), except for: Scholar Meosin Ridge.
Most sediment came from the Canadian Shield.
The Cordillera had not yet developed into the major mountain system seen today.
Therefore, western mountains were not the primary sediment source.
Rivers transported sediment from shield areas into the basin.
Scholar Meosin Ridge (Proposed High)
A hypothesized topographic high existed in western portions of the basin.
Which explains why we have a thickening of subsurface deposits going westward.
Considered to be a fault-bound rock and may have risen from terrane accretion.
In subsurface mapping:
Sediments thin away from known source areas.
Unexpectedly begin thickening again farther west.
This thickening requires an additional sediment source.
Proposed explanation:
An uplifted island or structural high shed sediment into the basin.
The feature may have been:
Fault bounded.
Uplifted by compression associated with terrain accretion.
Direct preservation of the feature does not exist.
Interpretation is based on sediment-thickness patterns.
Montney Basin:
Restricted inland seaway with openings to north and south.
Western ridge is interpreted to be a fault-bound block from the autochthon which may have risen in response to terrane collision.
As exploration proceeds westwards, the possibility of sediment sourced form a western ridge must be considered.
Triassic Climate
Climate was generally:
Temperate to subtropical.
Arid.
Mid-temperate to slightly subtropical, and arid.
Alberta and British Columbia were thought to be relatively dry.
Red beds are common indicators of these conditions.
Red coloration reflects oxidizing environments.
Triassic Red Beds
Well-developed in Saskatchewan and Manitoba.
Characterized by:
Red mudstones.
Red sandstones.
Excellent exposures occur in the Rocky Mountains.
Example from Banff:
Triassic Spray River red beds overlie Pennsylvanian clastic rocks.
Exposure occurs in a large anticline structure.
Carboniferous rocks form the core.
Triassic red beds occur on the flanks.
Complete Triassic Stratigraphic Succession
Lower Triassic:
Vega.
Frozo.
Middle Triassic:
Whistler.
Llama.
Upper Triassic:
Starlight Evaporite.
Charlie Lake Formation.
Baldonnel Formation.
Pardonet Formation.
Charlie Lake and Montney are major hydrocarbon-producing units (oil and gas).
Pardonet Formation is mostly restricted to British Columbia.
Baldonnel Formation occurs in limited areas of Alberta.
Lithology Through the Triassic
Much of the Triassic succession is siliciclastic.
Upper Triassic contains significant evaporite deposits.
Carbonates become more common near the top of the succession.
Sulphur Mountain Formation
Sulphur Mountain Formation is one of the most important Triassic units in outcrop.
Widely exposed throughout the Rocky Mountains.
Consists primarily of:
Siltstone.
Mudstone.
Very fine-grained sandstone.
Represents deposition shortly after the end-Permian extinction.
Records the early stages of biological recovery.
Economically important as a building stone.
Commonly marketed as "Rundle Rock."
Despite the name:
It is not part of the Rundle Group.
It is actually Sulphur Mountain Formation rock.
Frequently used as:
Flagstone.
Facing stone on buildings.
Paving stone.
Especially common in:
Canmore.
Parts of Banff.
Characterized by:
Dark coloration.
Fine grain size.
Attractive appearance when cut into slabs.
Sedimentary Structures in the Sulphur Mountain Formation
Rocks are generally very fine-grained.
Some exposures display cross-bedding.
Hummocky cross-stratification is present in some locations.
Hummocky cross-stratification is identified by:
Horizontal laminae.
Curved cross-cutting laminae.
Return to more parallel layering.
Interpreted as evidence of:
Wave activity.
Storm influence.
Shallow marine conditions.
Indicates that storms periodically affected sediment deposition.
Trace Fossils and Biotic Recovery
Trace fossils occur within some Triassic deposits.
Examples include worm burrows preserved in the Spray River Group.
These fossils are particularly significant because:
The Triassic immediately followed the end-Permian extinction.
Bioturbation was greatly reduced compared to many other periods.
Presence of burrows demonstrates:
Some organisms survived.
Ecosystems were beginning to recover.
Burrows occur on bedding planes.
Worms were moving horizontally through the sediment.
Bow Falls Exposure
Important Triassic exposure located at Bow Falls in Banff.
Opposite side of the area previously examined for Permian rocks.
Exposure consists of:
Early Triassic siltstones.
Very fine-grained sandstones.
Provides an accessible opportunity to observe:
Triassic sedimentary rocks.
Bedding planes.
Fossil traces.
Fossils occasionally found include:
Fish remains.
Ammonoid impressions.
Carbonate fossils are generally not preserved.
Fish fossils survive because phosphate material is more resistant.
Ammonoids are often preserved only as molds after shells dissolved away.
Triassic Fish Deposits
Triassic rocks are particularly important for fossil fish discoveries.
One of the most significant localities is Wapiti Lake.
Wapiti Lake is difficult to access.
Travel requires a lengthy route through northern British Columbia.
Despite the challenging access, the locality is considered spectacular for fossil preservation.
Additional fish-bearing deposits occur in the Ganoid Range.
Economic Significance of Triassic Rocks
Triassic rocks serve as hydrocarbon source rocks.
Phosphate occurs within several Triassic intervals.
Phosphate is found:
Near the Permian-Triassic boundary.
Within the upper portions of the Sulphur Mountain Formation.
Lower Triassic Depositional History
Lower clastic units represent an initial marine transgression.
Marine waters advanced across the region.
Followed by:
Shallowing conditions.
Retreat of marine environments.
Demonstrates smaller-scale sea-level fluctuations occurring within the overall long-term regression.
Halfway Formation
In NEBC and the Plaints, it is a HC source rock with phosphate marker at its base.
The lower clastic unit represents an initial transgression, followed by shallowing into nearshore environments, culminating in deposition of the Halfway formation.
An HC reservoir, comprising quartz sandstone and coquina (shell debris), and representing shallow marine bars, tidal channel deposits, and barrier islands.
Equivalent to the Llama Member in outcrop.
Represents a shallow marine depositional environment.
Environment included:
Barrier bars.
Barrier islands.
Tidal channels.
Shallow marine settings.
Dominated by:
Quartz sandstone.
Minor kokina deposits.
Interpreted as coastal environments influenced by tides and waves.
Represents a more energetic environment than the fine-grained Sulphur Mountain deposits.
Halfway Formation Depositional Model
Barrier bars formed along the coastline.
Tidal channels connected marine and restricted environments.
Barrier islands separated open marine waters from protected lagoons.
Sediments were deposited under:
Shallow marine conditions.
Active wave influence.
Tidal circulation.
Kokina deposits indicate accumulation of shell material.
Whitehorse and Charlie Lake Formations
Charlie Lake Formation is the subsurface equivalent.
Comprising clastics, dolomite with stromatolites, laminated siltstone with desiccation cracks, red dolomitic mudstone, and anhydrite.
Represents a different environment from the Halfway Formation.
Characterized by:
Evaporites.
Stromatolites.
Desiccation cracks.
Red beds.
Sand dunes in some locations.
Indicates:
Restricted conditions.
Periodic drying.
Arid climate.
Large preserved sand dunes occur near Williston Lake.
These dunes provide evidence of significant desert-like conditions during parts of the Late Triassic.
Evaporites
Gypsum occurs within these deposits.
Relationship between gypsum and anhydrite:
Removing water from gypsum produces anhydrite.
Adding water to anhydrite can convert it back to gypsum.
Evaporites form when:
Water evaporates.
Dissolved minerals become concentrated.
Minerals precipitate from solution.
Presence of gypsum and anhydrite indicates:
Strong evaporation.
Restricted marine conditions.
Arid climate.
Environmental Contrast: Halfway vs. Charlie Lake
Halfway Formation:
Shallow marine.
Barrier islands.
Barrier bars.
Tidal channels.
Quartz sandstone.
Shell debris.
Charlie Lake Formation:
Restricted conditions.
Evaporitic environments.
Stromatolites.
Desiccation cracks.
Red beds.
Sand dunes.
Strong evidence of aridity.
Baldonnel Formation
Baldonnel Formation is younger than the Charlie Lake Formation.
Represents the later stages of Triassic deposition.
Marks a return to greater biological abundance.
Carbonate deposition becomes more important.
Shell-producing organisms become much more common than they were earlier in the Triassic.
Reflects continued recovery from the end-Permian extinction.
Characterized by abundant shell debris.
Contains extensive kokina deposits.
Kokina
Kokina is a rock composed almost entirely of shell fragments.
Forms when large quantities of shells accumulate and become lithified.
In some examples:
Shells are packed so densely that little other sediment is present.
The rock is essentially compressed shell material.
Examples from the Baldonnel Formation show:
Extremely shell-rich deposits.
Thick accumulations of skeletal debris.
Strong evidence for increasing marine biodiversity.
Kokina from Pine River was shown as an example.
Demonstrates that marine ecosystems had substantially recovered compared to the Early Triassic.
Fossils:
What the invertebrate record shows is dominance of the molluscs as a phylum.
The most prominent mollusc fossils in the WCSB are scallops (such as Monotis).
Triassic Invertebrate Faunas
Invertebrates during the Triassic were dominated by mollusks.
Mollusks became one of the most successful groups following the extinction.
Fossil assemblages commonly contain large numbers of shell-bearing organisms.
Recovery of marine ecosystems is reflected in the increasing abundance of these fossils.
Monotis
Monotis is one of the most recognizable Triassic fossils.
Commonly found in Triassic deposits of Western Canada.
Belongs to a group similar to scallops.
Scallops are bivalves related to clams.
Modern scallops are capable of moving through the water by expelling water.
Monotis fossils commonly occur in enormous concentrations.
Entire rock layers can consist almost entirely of Monotis shells.
Fossils form extensive sheets and walls of shell material.
Localities such as Williston Lake contain spectacular accumulations.
Fossils are often preserved as dense masses of flattened shells.
Mystery of the Monotis Deposits
Large Monotis accumulations have generated considerable scientific interest.
Researchers have proposed numerous explanations for their formation.
Questions include:
Were the shells preserved where the organisms originally lived?
Were the shells transported after death?
What caused such large numbers to die simultaneously?
Why were so many individuals concentrated in one location?
Numerous scientific papers have investigated these questions.
The origin of these massive shell beds remains an important topic of study.
Belemnites
Belemnites are another important Triassic fossil group.
Cigar-sized and shaped internal counterweights of belemnoids.
Characterized by cigar-shaped fossils.
The preserved fossil is not the entire organism.
Instead, the fossil represents an internal structure.
Functioned as a counterweight inside the animal.
Occurred within belemnoids.
Fossils commonly appear:
Elongate.
Tapered.
Bullet-shaped or cigar-shaped.
Often preserved as isolated fossils within sedimentary rocks.
Distinguishing Belemnites from Orthocones
Belemnites are not the same as orthocones.
Orthocones were discussed previously in relation to Devonian fossils.
Orthocones
Possessed:
External shells.
Chambered interiors.
Central canals.
Growth chambers added through time.
Organism lived within the shell.
Belemnites
Lack:
Central canals.
Chambered growth structures.
External shell architecture of orthocones.
Represent only an internal counterweight.
The animal's soft tissues surrounded the belemnite structure.
Although the fossils may appear superficially similar to orthocones:
They are fundamentally different anatomically.
Belemnoids
Belemnites belonged to belemnoids.
Belemnoids resembled modern squid. They are a mollusk.
Characteristics included:
Soft-bodied anatomy.
Tentacles.
Predatory lifestyle.
Internal support structures.
The belemnite fossil occurred inside the body.
Unlike orthocones:
The animal did not live inside an external shell.
Functioned similarly to a modern squid possessing an internal support structure.
Evidence for Belemnoid Anatomy
Rare fossils preserve parts of the soft-body anatomy.
Preserved features include:
Tentacle hooks.
Body outlines.
Soft tissue is generally lost.
Hooks remain preserved because they are more resistant.
Fossils show:
Arrangement of tentacles.
General body shape.
Similarity to squid-like organisms.
These fossils confirm interpretations of belemnoids as active marine predators.
Triassic Dinosaurs
Dinosaurs appeared during the Triassic.
There is no WCSB record of them; the significant vertebrate developments were aquatic.
However, Triassic dinosaur fossils are not preserved within the Western Canada Sedimentary Basin.
Main reason:
Most preserved Western Canadian Triassic deposits are marine.
Land deposits are poorly preserved.
The fossil record is therefore heavily biased toward marine organisms.
Lack of dinosaur fossils does not mean dinosaurs were absent globally.
It reflects preservation limitations within the basin.
Triassic Vertebrates in Western Canada
Fossil vertebrates are dominated by aquatic organisms.
Fish are particularly abundant.
Western Canada preserves a diverse Triassic fish fauna.
Coelacanths
One important fish group is the coelacanths.
Possessed phosphatic plates.
Phosphate preservation is important because:
It survives more readily than carbonate material.
Fossils can remain intact even when carbonate shells dissolve.
Fossils often appear as:
Dark silhouettes.
Black impressions against lighter rock.
Preservation can resemble an undeveloped photograph.
Fine anatomical details may still be visible.
Waitia
Waitia is a coelacanth from Wapiti Lake.
Preserved using phosphatic skeletal material.
Represents one of the important Triassic fish fossils from Western Canada.
Unusual Triassic Fish Diversity
Triassic fish displayed a wide variety of body shapes.
Examples shown included:
Albertonia.
Bobasatrania.
Some species possessed:
Extremely large front fins.
Deep-bodied or diamond-shaped forms.
Demonstrates significant diversification of fish during the Triassic recovery interval.
Wapiti Lake Fossil Expeditions
Important fossil discoveries were made during expeditions in the 1980s.
Researchers accessed the region by horseback.
Work focused on exposures in the Ganoid Range.
Conditions were difficult:
Steep terrain.
Remote locations.
Physically demanding fieldwork.
Despite challenges, researchers recovered numerous important specimens.
Fossil Collection Methods
Fossils occur on bedding planes.
Paleontologists split rock layers apart to expose specimens.
Researchers developed techniques for identifying where rocks should be split.
According to the lecture:
Experienced collectors could sometimes determine splitting locations by the sound produced when tapping the rock.
Bedding planes often reveal:
Fish skeletons.
Dark phosphatic remains.
Well-preserved fossil material.
Bobasatrania
Bobasatrania is one of the best-known Triassic fish from Wapiti Lake.
Characterized by:
Distinctive body shape.
Diamond-like outline.
Specimens are displayed in the university paleontology museum.
Fossils are exceptionally preserved.
Some individuals display striking anatomical detail.
Psoricthys
Another important Triassic fish preserved in Western Canada.
Characterized by:
Long, slender body.
Elongated snout or beak-like structure.
Represents part of the diverse fish fauna that occupied Triassic marine environments.
Specimens are preserved in the university paleontology museum.
Some fossils show remarkable preservation.
One particularly famous specimen contains the skeleton of another organism inside its mouth.
The fish died while apparently attempting to consume prey.
Researchers interpret this specimen as an animal that may have died during feeding.
The fossil preserves a rare snapshot of behavior at the moment of death.
A reconstruction shows:
Psoricthys actively feeding.
Prey still lodged within its mouth.
Provides unusually direct evidence of feeding habits.
Triassic Marine Reptiles
Marine reptiles appear during the Triassic.
Among the most important are the ichthyosaurs.
Ichthyosaurs
Ichthyosaurs are preserved in Triassic rocks of the Rocky Mountains.
Fossil material has been found in areas around Jasper.
Individual bones such as ribs may occasionally be discovered in outcrop.
Complete skeletons are much rarer.
Despite the name "fish lizard," ichthyosaurs are not fish.
The lecture described them as being related to dolphins.
Possessed:
Streamlined bodies.
Powerful swimming adaptations.
Marine lifestyles.
Represent important marine vertebrate predators of Triassic oceans.
Reconstructions show:
Dolphin-like body shape.
Large eyes.
Adaptation for active swimming.
Ichthyosaurs are one of the key vertebrate groups students should remember from the Triassic.
Other Triassic Vertebrates
Additional vertebrate fossils occur in Triassic deposits.
Wapiti Lake preserves a variety of fish and marine organisms.
The vertebrate record is dominated by aquatic species because marine deposits are the primary sediments preserved in the basin.
Importance of Wapiti Lake
One of the most significant Triassic fossil localities in Western Canada.
Produced many of the fish fossils discussed in the lecture.
Importance comes from:
Excellent preservation.
Diversity of species.
Large number of collected specimens.
Much of what is known about Triassic fishes in Western Canada comes from research conducted at this locality.
Examples of Fossils Collected from Wapiti Lake
Waitia.
Albertonia.
Bobasatrania.
Psoricthys.
Various additional fish species.
Many specimens are displayed in the university paleontology museum.
Preservation of Triassic Fish
Fish fossils commonly occur on bedding planes.
Preservation is often controlled by phosphatic skeletal material.
Fossils frequently appear as:
Dark silhouettes.
Black impressions.
Distinct outlines against lighter sedimentary rock.
Splitting sedimentary layers along bedding planes often reveals complete specimens.
General Theme of the Triassic Fossil Record
Early Triassic:
Very limited fossil abundance.
Recovery immediately after the end-Permian extinction.
Middle Triassic:
Increasing biological diversity.
More evidence of marine ecosystems recovering.
Late Triassic:
Abundant shell beds.
Diverse mollusks.
Numerous fish fossils.
Marine reptiles present.
Overall pattern reflects gradual ecological recovery following the largest mass extinction in Earth's history.
Review Question
ANS: C
Lecture Conclusion
Triassic rocks of Western Canada record:
Recovery after the end-Permian mass extinction.
Falling sea levels through time.
Predominantly siliciclastic deposition.
Development of evaporitic environments.
Return of diverse marine ecosystems.
Important formations discussed:
Sulphur Mountain Formation.
Montney Formation.
Doig Formation.
Halfway Formation.
Charlie Lake Formation.
Baldonnel Formation.
Pardonet Formation.
Important fossil groups discussed:
Monotis.
Belemnites.
Coelacanths.
Albertonia.
Bobasatrania.
Psoricthys.
Ichthyosaurs.
Major recurring theme:
The Triassic of Western Canada represents a long-term recovery from the end-Permian mass extinction, progressing from sparse fossil assemblages in the Early Triassic to much richer and more diverse ecosystems by the Late Triassic.