Week 1 - Ichnofossils Flashcards
What are trace fossils?
Are the behaviours and activities of organisms left behind and are preserved. The same species can create different trace fossils.
What are the importance of trace fossils?
- Preserve the gap left by organisms that dont leave body fossils, such as those that live in low mineralisation environment
- Density and type of trace fossils can show the conditions of environment such as water depth, sediment type and oxygen levels.
What are trace fossils called?
Ichnogenera
What factors influence bioturbation intensity?
- Bottom-water Oxygen Conditions: The presence of adequate oxygen is essential for metazoan life; fully aerobic environments are characterized by diverse endofauna, well-preserved carbonate shells, and significant bioturbation.
- Substrate Consistency: The nature of the substrate, whether mud or sand, impacts burrowing behaviour, as does the firmness of the sediment.
- Water Energy and Salinity: Variations in bottom-water energy and salinity levels can impose ecological stress, which is reflected in the size, diversity, and extent of bioturbation in trace fossil assemblages.
- Rate of Sediment Deposition: High rates can smother existing benthic communities, inhibiting bioturbation.
- Geological Events: Occasional events, such as storms or turbidity currents, can drastically alter the ecological landscape of benthic environments.
What is the spectrum that illustrates oxygen availability?
- No ichnia: Maintaining primary lamination, indicative of an abiotic environment.
- Fodinichnia: Traces from non-vagile deposit feeders, such as Chondrites and Zoophycos.
- Pascichnia: Representing deposit feeders or chemosymbiotic organisms, exemplified by Scalarituba (large, segmented) and Spirophycus.
- Domichnia: Associated with well-oxygenated conditions characterized by the dominance of Skolithos.
What are the features of Thalassinoides?
-Branched, horizontal burrows.
-Often associated with crustacean activity, like thalassinid shrimp.
-Found in sandy substrates.
What are the characteristics of Ophiomorpha?
-Horizontal burrows lined with mud or faecal pellets.
-Typically formed by crustaceans in sandy substrates.
What defines Skolithos?
-Simple, vertical burrows.
-Constructed by various worm groups.
-Common in high-energy environments like shallow marine settings.
What are the features of Diplocraterion?
-Vertical U-shaped burrows with spreite.
-Indicates equilibrium structures in sedimentation.
-Viewed as paired holes on bedding planes.
What are the characteristics of Teichichnus?
-Vertical U-shaped burrows with spreite.
-No outer lining, unlike Diplocraterion.
-Indicates feeding behavior in soft sediments.
Describe Planolites.
-Simple, unlined, (usually)
unbranched horizontal burrows.
-Likely made by worms.
-Range from Cambrian to Holocene.
What is Rhizocorallium known for?
-Sub-vertical burrows with spreite.
-Formed by sediment-eating infaunal organisms.
-Often associated with Jurassic sediments.
What is Zoophycus?
-Complex, spiraling feeding traces.
-Indicates grazing behavior, often in low-oxygen abyssal zones.
-Found from the Ordovician to present.
What are the features of Cosmorhaphe?
-Grazing traces with complex spiraling patterns.
-Suggest feeding in poorly oxygenated environments.
What makes Paleodictyon unique?
-Geometric, honeycomb-like traces.
-Associated with deep marine environments by the Cenozoic.
-Origins of trace-making organism are enigmatic.
What are the characteristics of Chondrites?
-Branched, horizontal burrows.
-Common in low oxygen settings across various time periods.
-Likely formed by infaunal deposit feeders.
What are boring structures in trace fossils?
-Produced by organisms like bivalves boring into hard substrates.
-Found in rocks, wood, and sometimes on beaches.
What is spreite in trace fossils?
-Curved, layered, or backfilled structures within burrows.
-Formed by organisms adjusting their position in response to changes like sedimentation.
-Found in vertical or U-shaped burrows such as Diplocraterion, Rhizocorallium, and Teichichnus.
-Represents equilibrium structures and marks successive phases of burrow re-excavation or movement.
What are equilibrium structures in trace fossils?
-Features formed by organisms adjusting to dynamic sedimentation.
-Indicate movement to maintain equilibrium with the sediment surface.
-Examples include Diplocraterion (paired burrows with spreite) and Teichichnus (u-shaped burrows with spreite but no outer lining).
What defines the base of the Cambrian period?
The first appearance of the feeding burrow Phycodes pedum.
What behavior can Zoophycus traces indicate?
Complex spiralling feeding.
How are trace fossil structures like Skolithos formed?
They are vertical burrows that can be produced by various worm groups under similar behavioral patterns.
What can Ichnofossils show?
substrate type
energy level
sedimentation rate
food availability
oxygen levels
Why do use trace fossils?
To help build a complete picture of past environments.
Alongside the use of trace fossils what other techniques are used to reconstruct past environments?
-Geochemistry
-Body fossils
-Trace fossils
-Sedimentological logging
