Unit 4 Exam

Fossil Record

• evidence of life preserved in a geologic context

• body fossils, trace fossils (Ichnofossils)

• Fossils provide information about:

  • anatomy

  • feeding strategies

  • geographical distribution

  • ecological relationships

  • past climates and environments

Type of Fossils: Body Fossils

• examples includes:

  • bones and teeth

  • shells and exoskeletons

  • wood

• remains can represent a whole organism or just parts of an organism

• remains may be in one piece or granted/scattered

• more rarely:

  • skin, soft tissue, and organs

  • leaves and flowers

Types of preservation:

• Typical:

  • unaltered skeleton

  • per mineralization, pores become filled with silica

  • replacement with another material like quarts or pyrite

  • molds and casts. original material is dissolved and sediment fills the space

  • carbonization, preserving as carbon films

• Exceptional:

  • fossil lagerstätten:

  • konzentrat (concentration) lagerstätten: anomalously high amounts of fossil material

  • konservat (conservation) lagerstätten: unusually well-preserved fossils, including soft parts

    • stagnation deposits (anoxia, low current flow)

    • obrustion deposits (very rapid burial)

    • conservation traps (amber, for example)

Types of Fossils: Trace Fossils (Ichnofossils)

• we don’t necessarily know the identity of a trace maker

• taxonomy: Ichnogenera and Ichnospecies

• provide information about:

  • how an organism moved

  • feeding patterns

  • burrowing patterns in sediment

  • community structure

• examples:

  • footprints, trackways, and resting traces

  • burrows and tunnels

  • feeding traces

  • coprolites

Fodinichnia- Feeding burrows

• branching burrow traces of a deposit-feeding invertebrate

• e.g. Chondrites

  • precambrian- Recent

  • environmental settings: fully marine conditions perhaps indicative of low oxygen zones

Fodinchnia- feeding burrows

• burrow traces of a deposit feeing invertebrate

• e.g. Teichichnus

  • cambrian- recent

  • environmental settings: found in lower marine shore faces, intertidal settings, lagoons, deep-marine fans and abyssal plains, and brackish water settings like marine estuaries

Domichnia- Dwelling burrows

• unbranched burrow traces of a suspension-feeding invertebrate

• e.g. Skolithos

  • precambrian- recent

  • environmental settings: found in virtually every type of environment from marine to terrestrial present in high-energy marine conditions, especially in nearshore shallow Marien facies, deep marine submarine channels and canyons; continental floodplain and dune settings

Domichnia- Dwelling burrows:

• straight or gently curved burrows, horizontal to oblique bedding planes

• e.g. Planolites

  • precambrian- recent

  • environmental settings: shallow marine- deep marine deposits to continental. found in alluvial, lacustrine, and eolian settings

not only animals produce trace fossils

rhizolithi (plant root structure)

analysis of track traces

• different parts of a track can create different traces

• type of substrate, and texture of sediment is important

• can reveal details about the track maker’s anatomy and movement

dinosaur footprints and trackways

• gives clues about locomotion styles

• gives clues about dinosaur families and communities

• give clues about predation behaviors, for example maybe some dinosaurs hunted in groups

One organism can produce many traces based on their behavior

• a trace fossil may look different depending on how it was produced (for example the interaction between trace maker and sediment) and how it is viewed

traces that resulted from animal activity

e.g. deer, hog, horse

Repichnia- Locomotive traces

• e.g. Chirotherium from the Triassic

• pentadactyl footprints

• not obvious who the producer was

Adolf Seilacher

Seilacher’s interest included trace fossils, evolution of invertebrates and exceptional preservation (Lagerstätten)

Stuttgart

Tubingen

Changes in setting reflected in changes in observed traces

• Seilacher created a naming system based on using ichnotaxa to describe trace fossil types

• Cubichnia= Resting traces

• Domichnia= Dwelling traces

• Fodinichnia= Feeding traces

• Pascichnia= Grazing traces

• Repichnia= Locomotory traces

• lots of other terms have since been created

Seilacher also developed the frameworks of constructional morphology and morphodynamics

“Taphonomy” coined by Ivan Efremov in 1940

• = “The study of the laws governing the transition (in all its details) of organic remains from the biosphere into the lithosphere”

• also includes discovery, collection bias, and curation of remains

• natural sampling of biotas

• occurrence in the fossil record also depends on species diversity, morphological disparity, and Ease of preservation

• differing preservation potentials

A collection of filters

• the study of the transition from the biosphere to the lithosphere

• sources of bias:

  • biochemical

  • anatomical

  • ecological

  • geological

Sequential stages of taphonomy:

Assemblages:

• Biocenosis (life assemblage)

  • organisms have the correct orientation

  • trace fossils may be present

  • different organisms from the same community are present

  • mature and juvenile individuals may be present

• Thanatocenosis (death assemblage)

  • organisms are of similar size and/or shape

  • organisms may be from different ecological communities

• Autochthonous (In situ)

• Allochthonous (Transported)

• Single-event (census/catastrophic) assemblages:

  • unusual events like sudden anoxia, severe storms, droughts, and volcanic eruptions that kill large numbers of individuals at one time. short term, snapshot

• Attritional (time-averaged) assemblages:

  • discarded organic products (like pollen and leaves and input from normal mortality over time. Long term

Precambrian supereon

• 88% of earth history

• precambrian division:

  • Hadean eon

  • Archean eon

  • proterozoic eon

• followed by Cambrian period of Paleozoic era of Phanerozoic eon

Ancient vs Recent Rocks (there are few older rock deposits available)

• major precambrian deposits

• gray areas are Phanerozoic

• oldest rocks:

  • issue, Greenland, 3.8 billion years (Ga/By)

• approximate locations of Archean cartoons and surrounding Proterozoic regions worldwide, without sedimentary cover

Hadean eon

• ~4.6 -~4.0 billion years ago

• molten earth

• lots of extraterrestrial impacts

• primitive crust formed

• thin early atmosphere of water vapor and volcanic gases

• eventual cooling led to massive amounts of condensation and the first global liquid oceans formed

Archean eon

• ~4.0- ~2.5 billion years ago

• surface cooling

• tectonic activity began

• continents began to form

• earliest single-celled life evolved

• cyanobacteria (blue-green algae) started producing oxygen by photosynthesis

• stromatolites:

  • layered sedimentary structures

  • in shallow water

  • still around today

    • shark bay in Western Australia

Proterozoic eon

• ~2.5- ~0.54 bya

• great oxidation event

• banded iron formations (BIFs)

  • layered sedimentary rocks with alternating bands of iron oxides

    • like hematite and magnetite and iron-poor silica (chert)

  • cyclic/seasonal changes reflected in layers

• surface continued to cool

• stable supercontinents formed:

  • Columbia (right) and Rodinia (left)