Tully Monster Tullimonstrum gregarium, also known as the Tully Monster, is Illinois’s official state fossil

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Tully Monster

  • Tullimonstrum gregarium, also known as the Tully Monster, is Illinois’s official state fossil

    • Specimen from Pennsylvanian rocks, Mazon Creek Locality, Illinois

Mazon Creek Fossils

  • Approximately 300 million years ago

    • in the region of present-day Illinois,
    • sluggish rivers flowed southwestward through swamps,
    • and built large deltas that extended outward into a subtropical shallow sea
  • These rivers deposited high quantities of mud

    • that entombed many of the plants and animals living in the area
  • Rapid burial

    • and the formation of ironstone concretions
    • preserved many of the plants and animals of the area

Exceptional Preservation

  • The resulting fossils,

    • known as the Mazon Creek fossils
      • for the area in northeastern Illinois
      • where most specimens are found,
    • provide us with significant insights about the soft-part anatomy of the region's biota
  • Because of the exceptional preservation of this ancient biota,

    • Mazon Creek fossils are known throughout the world
    • and many museums have extensive collections from the area

Pennsylvanian Delta Organisms

  • During Pennsylvanian time, two major habitats existed in northeastern Illinois

    • One was a swampy forested lowland of the subaerial delta,
    • and the other was the shallow marine environment of the actively prograding delta
  • Living in the warm, shallow waters

    • of the delta front were numerous
      • cnidarians,
      • mollusks,
      • echinoderms,

Swampy Lowlands

  • The swampy lowlands surrounding the delta were home to more than 400 plant species,

    • numerous insects and spiders,
    • and other animals such as
      • scorpions and amphibians
    • In the ponds, lakes, and rivers were many
      • fish, shrimp, and ostracods
    • Almost all of the plants were
      • seedless vascular plants,
      • typical of the kinds that lived in the coal-forming swamps
      • during the Pennsylvanian Period

Tully Monster

  • One of the more interesting Mazon Creek fossils is the Tully Monster,

    • which is not only unique to Illinois,
    • but also is its official state fossil
  • Named for Francis Tully,

    • who first discovered it in 1958,
    • Tullimonstrum gregarium
    • was a small
      • up to 30 cm long
    • soft-bodied animal that lived in the warm, shallow seas
    • covering Illinois about 300 million years ago

Tully Monster

  • The Tully Monster had a relatively long proboscis

    • that contained a "claw" with small teeth in it
    • The round-to-oval shaped body was segmented
    • and contained a cross-bar,
    • whose ends were swollen,
    • and are interpreted by some to be the animal’s sense organs
    • The tail had two horizontal fins
  • It probably swam like an eel

    • with most of the undulatory movement occurring behind the two sense organs

Tully Monster

  • There presently is no consensus

    • as to what phylum the Tully Monster belongs
    • or to what animals it might be related

Late Paleozoic Paleogeography

  • The Late Paleozoic was a time of

    • evolutionary innovations,
    • continental collisions,
    • mountain building,
    • fluctuating seas levels,
    • and varied climates
  • Coals, evaporites, and tillites

    • testify to the variety of climatic conditions
    • experienced by the different continents during the Late Paleozoic

Gondwana Continental Glaciers

  • Major glacial-interglacial intervals

    • occurred throughout much of Gondwana
    • as it continued moving over the South Pole
      • during the Late Mississippian to Early Permian
  • The growth and retreat of continental glaciers

    • during this time
    • profoundly affected the world's biota
    • as well as contributing to global sea level changes

Continental Collisions

  • Collisions between continents

    • not only led to the formation of the supercontinent Pangaea
    • by the end of the Permian,
    • but resulted in mountain building
    • that strongly influenced oceanic and atmospheric circulation patterns
  • By the end of the Paleozoic,

    • widespread arid and semiarid conditions governed much of Pangaea

The Devonian Period

  • During the Silurian,

    • Laurentia and Avalonia-Baltica collided along a convergent plate boundary
    • to form the larger continent of Laurasia
  • This collision,

    • which closed the northern Iapetus Ocean,
    • is marked by the Caledonian orogeny
  • During the Devonian,

    • as the southern Iapetus Ocean narrowed
    • between Laurasia and Gondwana,
    • mountain building continued along the eastern margin of Laurasia
    • with the Acadian orogeny

Paleogeography of the World

  • For the Late Devonian Period

Paleogeography of the World

  • For the Early Carboniferous Period

Paleogeography of the World

  • For the Late Carboniferous Period

Paleogeography of the World

  • For the Late Permian Period

Reddish Fluvial Sediments

  • The erosion of the resulting highlands

    • provided vast amounts of reddish fluvial sediments
    • that covered large areas of northern Europe
      • Old Red Sandstone
    • and eastern North America
      • the Catskill Delta

Collision of Laurentia and Baltica

  • Other Devonian tectonic events include,

    • the Cordilleran Antler orogeny,
    • the Ellesmere orogeny along the northern margin of Laurentia
      • which may reflect the collision of Laurentia with Siberia
    • and the change from a passive continental margin to an active convergent plate boundary
      • in the Uralian mobile belt of eastern Baltica

Uniform Global Climate

  • The distribution of

      • reefs,
      • evaporites,
      • and red beds,
    • as well as the existence of similar floras throughout the world,
    • suggests a rather uniform global climate during the Devonian Period

The Carboniferous Period

  • During the Carboniferous Period

    • southern Gondwana moved over the South Pole,
    • resulting in extensive continental glaciation
  • The advance and retreat of these glaciers

    • produced global changes in sea level
    • that affected sedimentation pattern on the cratons
  • As Gondwana continued moving northward,

    • it first collided with Laurasia
      • during the Early Carboniferous
    • and continued suturing with it during the rest of the Carboniferous

Gondwana/Laurasia Collision

  • Because Gondwana rotated clockwise relative to Laurasia,

    • deformation of the two continents generally progressed in a northeast-to-southwest direction along
      • the Hercynian,
      • Appalachian,
      • and Ouachita mobile belts
  • The final phase of collision between Gondwana and Laurasia

    • is indicated by the Ouachita Mountains of Oklahoma
    • which were formed by thrusting
    • during the Late Carboniferous and Early Permian

Pangaea Began Taking Shape

  • Elsewhere, Siberia collided with Kazakhstania

    • and moved toward the Uralian margin of Laurasia (Baltica),
    • colliding with it during the Early Permian
  • By the end of the Carboniferous,

    • the various continental landmasses were fairly close together
    • as Pangaea began taking shape

Coal Basins in Equatorial Zone

  • The Carboniferous coal basins of

    • eastern North America,
    • western Europe,
    • and the Donets Basin of Ukraine
  • all lay in the equatorial zone,

    • where rainfall was high and temperatures were consistently warm
  • The absence of strong seasonal growth rings

    • in fossil plants from these coal basins
    • is indicative of such a climate

Fossil Plants of Siberia

  • The fossil plants found in the coals of Siberia,

    • however, show well-developed growth rings,
    • signifying seasonal growth
    • with abundant rainfall
    • and distinct seasons
    • such as occur in the temperate zones
      • at latitudes 40 degrees to 60 degrees north

Continental Ice Sheets

  • Glacial condition

    • and the movement of large continental ice sheets
    • in the high southern latitudes
    • are indicated by widespread tillites
    • and glacial striations in southern Gondwana
  • These ice sheets spread toward the equator and,

      • at their maximum growth,
    • extended well into the middle temperate latitudes

The Permian Period

  • The assembly of Pangaea

    • was essentially completed during the Permian
    • as a result of the many continental collisions
      • that began during the Carboniferous
  • Although geologists generally agree

  • no consensus exists

    • on the number or configuration of the various terranes
    • and continental blocks that composed the eastern half of Pangaea

Pangaea Surrounded

  • Regardless of the exact configuration

    • of the eastern portion of Pangaea,
    • geologists know that the supercontinent
    • was surrounded by various subduction zones
    • and moved steadily northward during the Permian
  • Furthermore, an enormous single ocean,

    • Panthalassa,
    • surrounded Pangaea and
    • spanned Earth from pole to pole

Climatic Consequences

  • The formation of a single large landmass

    • had climatic consequences for the continent
    • Terrestrial Permian sediments indicate
    • that arid and semiarid conditions were widespread over Pangaea
  • The mountain ranges produced by

    • the Hercynian, Alleghenian, and Ouachita orogenies
    • were high enough to create rain shadows
    • that blocked the moist, subtropical, easterly winds
      • much as the southern Andes Mountains do in western South America today

Mountains Influenced Climate

  • The mountains’ influence produced very dry conditions in North America and Europe,

    • as evident from the extensive
    • Permian red beds and evaporites
    • found in western North America, central Europe, and parts of Russia
  • Permian coals,

      • indicative of abundant rainfall,
    • were mostly limited to the northern temperate belts
      • latitude 40 degrees to 60 degrees north
    • while the last remnants of the Carboniferous ice sheets retreated

Late Paleozoic History of North America

  • The Late Paleozoic cratonic history of North America included periods

    • of extensive shallow-marine carbonate deposition
    • and large coal-forming swamps
    • as well as dry, evaporite-forming terrestrial conditions
  • Cratonic events largely resulted from changes in sea level because of

    • Gondwanan glaciation
    • and tectonic events related to the joining of Pangaea

Mountain Building

  • Mountain building

    • that began with the Ordovician Taconic orogeny
    • continued with the
      • Caledonian,
      • Acadian,
      • Alleghenian,
      • and Ouachita orogenies
  • These orogenies were part of the global tectonic process

    • that resulted in the formation of Pangaea

The Kaskaskia Sequence

  • The boundary between

    • the Tippecanoe sequence
    • and the overlying Kaskaskia sequence
      • Middle Devonian-Late Mississippian
    • is marked by a major unconformity
  • As the Kaskaskia Sea transgressed

    • over the low-relief landscape of the craton,
    • the majority of the basal beds deposited
      • consisted of clean, well-sorted quartz sandstones

Oriskany Sandstone

  • A good example is the Oriskany Sandstone

    • of New York and Pennsylvania
    • and its lateral equivalents
  • The Oriskany Sandstone,

    • like the basal Tippecanoe St. Peter Sandstone,
    • is an important glass sand
    • as well as a good gas-reservoir rock

Basal Kaskaskia Sandstones

  • Extent of the basal units of the Kaskaskia sequence in the eastern and north- central United States

Source Areas

  • The source areas for the basal Kaskaskia sandstones

    • were primarily the eroding highlands of the Appalachian mobile belt area,
    • exhumed Cambrian and Ordovician sandstones cropping out along the flanks of the Ozark Dome,
    • and exposures of the Canadian Shield in the Wisconsin area

Devonian Period

  • Paleogeography of North America during the Devonian Period

Sediment Sources

  • The earlier Silurian carbonate beds

      • below the Tippecanoe-Kaskaskia unconformity
    • lacked Kaskaskia-like sands
  • The absence of such sands indicates

    • that the source areas for the basal Kaskaskia
    • were submerged when the Tippecanoe sequence was deposited
  • Stratigraphic studies indicate

    • that these source areas were uplifted
    • and the Tippecanoe carbonates removed by erosion
    • prior to the Kaskaskia transgression

Kaskaskian Rocks

  • Kaskaskian basal rocks

    • elsewhere on the craton
    • consist of carbonates
    • that are frequently difficult to differentiate
    • from the underlying Tippecanoe carbonates
    • unless they are fossiliferous
  • The majority of Kaskaskian rocks are

    • carbonates, including reefs, and associated evaporite deposits
    • except for widespread Upper Devonian and Lower Mississippian black shales

Other Parts of the World

  • In many other parts of the world, such as

      • southern England,
      • Belgium,
      • Central Europe,
      • Australia,
      • and Russia,
    • the Middle and early Late Devonian epochs were times of major reef building

Reef Development in Western Canada

  • The Middle and Late Devonian-age reefs of western Canada

    • contain large reserves of petroleum
    • and have been widely studied from outcrops and in the subsurface
  • These reefs began forming

    • as the Kaskaskia Sea transgressed southward
    • into western Canada

Middle Devonian Reefs and Evaporites

  • By the end of the Middle Devonian,

    • the reefs had coalesced into a large barrier-reef system
    • that restricted the flow of oceanic water into the back-reef platform,
    • thus creating conditions for evaporite precipitation
  • In the back-reef area, up to 300 m of evaporites

    • were precipitated in much the same way as in the Michigan Basin during the Silurian

Devonian Reef Complex

  • Reconstruction of the extensive Devonian Reef complex of western Canada

Potash from Evaporites

  • More than half of the world's potash,

    • which is used in fertilizers,
    • comes from these Devonian evaporites
  • By the middle of the Late Devonian,

    • reef growth stopped in the western Canada region,
    • although nonreef carbonate deposition continued

Black Shales

  • In North America, many areas of carbonate-evaporite deposition

    • gave way to a greater proportion of shales
    • and coarser detrital rocks
      • beginning in the Middle Devonian and continuing into the Late Devonian
  • This change to detrital deposition

    • resulted from the formation of new source areas
    • brought on by the mountain-building activity
    • associated with the Acadian orogeny in North America

Increased Detrital Deposition

  • Deposition of black shales

  • is associated with the Acadian orogeny

Widespread Black Shales

  • As the Devonian Period ended,

  • These Upper Devonian-Lower Mississippian black shales are typically

    • noncalcareous,
    • thinly bedded,
    • and usually less than 10 m thick

Extent of Black Shales

  • The extent of the upper Devonian and Lower Mississippian Chattanooga Shale and its equivalent units

  • such as the Antrim Shale and the Albany Shale

New Albany Shale

  • Upper Devonian New Albany Shale,

  • Button Mold Knob Quarry, Kentucky

Dating Black Shales

  • Because most black shales lack body fossils,

    • they are difficult to date and correlate
  • However, microfossils, such as

    • conodonts
      • microscopic animals
    • acritarchs
      • microscopic algae
    • or plant spores
    • indicate that the lower beds are Late Devonian,
    • and the upper beds are Early Mississippian in age

Origin Debated

  • Although the origin of these extensive black shales is still being debated,

    • the essential features required to produced them include
      • undisturbed anaerobic bottom water,
      • a reduced supply of coarser detrital sediment,
      • and high organic productivity in the overlying oxygenated waters
  • High productivity in the surface waters leads to a shower of organic material,

    • which decomposes on the undisturbed seafloor
    • and depletes the dissolved oxygen at the sediment-water interface

Puzzling Origin

  • The wide extent in North America

    • of such apparently shallow-water black shales
    • remains puzzling
  • Nonetheless, these shales

    • are rich in uranium
    • and are an important source rock of oil and gas
    • in the Appalachian region

The Late Kaskaskia

  • Following deposition of the black shales,

    • carbonate sedimentation on the craton dominated the remainder of the Mississippian Period
  • During this time, a variety of carbonate sediments was deposited in the epeiric seas

    • as indicated by the extensive deposits of
    • crinoidal limestones
      • rich in crinoid fragments
    • oolitic limestones,
    • and various other limestones and dolostones

Mississippian Period

  • Paleogeography of North America during the Mississippian Period

Mississippian Carbonates

  • These Mississippian carbonates display

      • cross-bedding, ripple marks, and well-sorted fossil fragments,
    • all of which are indicative of a shallow-water environment
    • Analogous features can be observed on the present-day Bahama Banks
  • In addition, numerous small organic reefs

    • occurred throughout the craton during the Mississippian
    • These were all much smaller than the large barrier-reef complexes
      • that dominated the earlier Paleozoic seas

Regression of the Kaskaskia Sea

  • During the Late Mississippian regression

    • of the Kaskaskia Sea from the craton,
    • carbonate deposition was replaced
    • by vast quantities of detrital sediments
  • The resulting sandstones,

      • particularly in the Illinois Basin,
    • have been studied in great detail
    • because they are excellent petroleum reservoirs

Cratonwide Unconformity

  • Prior to the end of the Mississippian,

    • the epeiric sea had retreated
      • to the craton margin,
    • once again exposing the craton
    • to widespread weathering and erosion
  • This resulted in a craton-wide unconformity

    • at the end of the Kaskaskia Sequence

The Absaroka Sequence

  • The Absaroka sequence

    • includes rocks deposited
      • during the Pennsylvanian
      • through Early Jurassic
    • At this point, we will only discuss the Paleozoic rocks of the Absaroka sequence
  • The extensive unconformity

    • separating the Kaskaskia and Absaroka sequences
    • essentially divides the strata
    • into the North American
    • Mississippian and Pennsylvanian systems

Mississippian and Pennsylvanian Versus Carboniferous

  • The Mississippian and Pennsylvanian systems of North America

    • are equivalent to the European Lower and Upper Carboniferous systems:
      • Mississippian = Lower Carboniferous
      • Pennsylvanian = Upper Carboniferous

Absaroka Rocks

  • The rocks of the Absaroka sequence

    • are not only different from those of the Kaskaskia sequence,
    • but they are also the result of different tectonic regimes
  • The lowermost sediments of the Absaroka sequence

    • are confined to the margins of the craton

Lowermost Absaroka

  • These lowermost deposits

    • are generally thickest in the east and southeast,
      • near the emerging highlands of the Appalachian and Ouachita mobile belts,
    • and thin westward onto the craton
  • The rocks also reveal lateral changes

    • from nonmarine detrital rocks and coals in the east,
    • through transitional marine-nonmarine beds,
    • to largely marine detrital rocks and limestones farther west

Pennsylvanian Period

  • Paleogeography of North America during the Pennsylvanian Period

What Are Cyclothems?

  • A cyclical pattern of alternating marine and nonmarine strata

    • is one of the characteristic features of Pennsylvanian rocks
  • Such rhythmically repetitive sedimentary sequences are known as cyclothems

  • They result from repeated alternations

    • of marine
    • and nonmarine environments,
    • usually in areas of low relief

Delicate Interplay

  • Though seemingly simple,

  • cyclothems reflect a delicate interplay between

    • nonmarine deltaic environments
    • shallow-marine interdeltaic environments
    • and shelf environments
  • For example,

    • a typical coal-bearing cyclothem from the Illinois Basin contains
      • nonmarine units,
      • capped by a coal unit
      • and overlain by marine units

Nonmarine Units of a Cyclothem

  • The initial units represent

    • deltaic deposits
    • and fluvial deposits
  • Above them is an underclay

    • that frequently contains roots from the plants and trees
    • that comprise the overlying coal
  • The coal bed

    • results from accumulations of plant material
    • and is overlain by marine units


  • Columnar section of a complete cyclothem

Pennsylvanian Coal Bed

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