Succession in Reefs• 4 stages :

1. Pioneering or Stabilization

a. Accumulation of skeletal debris

b. Creation of a surface with some relief

Succession in Reefs

2. Colonization

a. Branching & encrusting organisms

b. Low diversity

Succession in Reefs

3. Diversification

a. Increased diversity of organisms

b. Takes the form of a massive structure

Succession in Reefs

4. Domination

a. “lamellar framestones”

b. Evidence of high water energy (rudstones)

c. Species diversity is reduced

Reef Evolution

Archaeocyathids (sponges?)

Lowly Pond Scum

Cambrian 500 my

12 bybp

Precambrian570 my

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Stromatolites

Reef Evolution

12 bybp

Loss of “ecospace”

What happens witha sea-level fall?

Precambrian570 my

Back to “pond slime”

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The Ordovician

AstrorhizaeMammelon

Stromatoporoids

Ordovician Reefs(505-438 my)

Pratt & James (1982)

Stromatoporoid

Bryozoan

Peter Sholle

EarlySilurian

Extinction

Sea-level is back up

REEF DIVERSIFICATION

The Silurian World

Equator

Chris Scotese

OCEAN

20°

20°

Silurian Time430 mybp

Dott & Prothro (1994)Scotese (1997)

Reefs

Equator

New Life in the SilurianCorals Through Time

Wider = more abundant

0

200

400

600

Crinoids

Karla Parsons-Hubbard (Oberlin College)

Beloit College Collection

Opening up;Sea-level rise

40 million years later..

Shallow, clear water

Devonian

Stromatoporoids;Rugose Corals Crinoids

StromatolitesCambrian

Ordovician500 my

430 myStromatoporoids (sponges?)

Silurian

12 bybp

390 myStromatoporoids;Tabulate Corals Crinoids

Devonian

Late Devonian

280 myPermian

Sponges

Devonian

360 myCarboniferous

A time of poor reef development Major coal swamps

Reefs made of sponges…..

The Capitan Reef Complex

Just when things were looking good…..

Sea-Level DropsSea Level Back Up

Photo by Mark EberlePhoto by Peter Sholle

Photo by Peter Sholle

280 myPermian

Sponges

Reefs disappear!!!!!!!!245 my

Triassic

Extinction

• Sea level - no• Climate change - maybe• Ocean chemistry?

Why?

Scleractinean corals

280 myPermian

Sponges

245 myTriassic

A watershed event in reef history??

20 million yr gap

Watch here…

Chris Scotese

Cretaceous

Rudists

• The cup shaped form is back…..• but it’s a mollusk this time???

Triassic --> Jurassic

Scleractineans

140 my

A broadening tropics

An open pan-equatorial seaway

No glaciers !

Open tropical seaway

Why mollusks and not corals???

• High temperatures

• “Greenhouse” climate much warmer than today

• Too warm for corals

Reefs Today

Cretaceous Reef Line

Rudist Reefs

Photo by D. Schumann (from Woods, 1999)

Drawing by John Sibbick (in Woods, 1999)

They photosynthesized??the missing article……

Cretaceous Time

Images by Mary Parrish, NMNH

The End of theCretaceous

Irridium

ExtinctionDewey McLean

Cretaceous

Rudists

65 myTertiary

Major extinction95% of species disappear

Return tosclractinean

corals

Reefs have stayed pretty much the same ever since

65 myTertiary

Rest of the Cenozoic

Cambrian “Explosion”Mostly non-reef forms

Calcification

Jaws --> BioE

Increased Calcification

M

ore

Com

ple

xF

aste

r G

row

thNo O2

Increased grazing

Sea Level

“Party Crashers”

Environment