Pilot Knob, an Extinct Cretaceous Volcanic Ecosystem

Pilot Knob, an Extinct Cretaceous
Volcanic Ecosystem
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North America Now & Then
Now
80 MYA
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Texas Now & Then
Texas – Now
Texas – 80 MYA
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Austin, TX – Now
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Austin – 80 MYA
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Pilot Knob – SEU – 80 MYA
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Central Texas Magma Zone
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Late Precambrian – 550 MYA
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Central Texas Magma Zone
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Pilot Knob Ecosystem – 80 MYA
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Fast Forward – Modern

Pilot Knob is a low rise of
basalt and tuff near Austin
International Airport with an
area of sediment build-up
to the north and north-west

The area is quarried for
limestone deposited after
the eruptions ended

Fossil clubs hunted the
area frequently
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Pilot Knob area

Quarries routinely left a
foot or so of limestone in
place to keep their
equipment from getting
mired in volcanic muds
below

In 1996 we found
something new at the
Dean Word Quarry – a
drainage ditch dug into
the volcanic clay
underneath
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1996 Drainage Ditch
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Collecting Site, 1996 – 1997

The clay (altered ash) extracted
from the drainage ditch was
dumped to the side and eroded
over time to reveal a diverse
fauna – the Pilot Knob
Ecosystem.

Unique site – preserving
specimens not found in
contemporary Austin Chalk
deposits
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Stratigraphic Sequence
Yellow “Beach” Layer
(shallowest water, bio-clastic, large
Inoceramus clams, crustaceans)
Red Layer
(shallow water, highly fossiliferous,
numerous sponges, crustaceans)
Green Layer
(deeper water, fewer fossils, many
crustaceans some ammonites,
sponges and crinoid material)
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Color/Strata Zones
Yellow layer
Green layer
Red layer
Red & Green layer
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When - Stratigraphic Ages

Pilot Knob – 80 MA

Upper Cretaceous, Upper
Austin Chalk, concurrent
with the McKowan, Dessau
and Burditt formations

Effects of the ash – great
preservation– rare sponges,
external ornamentation
preserved and even some
color pattern retention
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Ecosystem
Unique Crustacean- dominated ecosystem
~125 Different Life Forms/Traces
New & Rare Species and Range Extensions
43 BIVALVES
 39 GASTROPODS
 7 CRUSTACEANS
 7 ECHINOIDS
 5 AMMONITES
 5 WORM TUBES
 4 BURROWS

3 SPONGES
 2 CORAL
 3 SHARK
 2 FISH
 1 VERTEBRATE
 1 BRYOZOAN
 Numerous FORAMS

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Crustaceans (crabs, shrimp, etc.) Today
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Crustaceans (mud shrimp) – 80 MYA
Protocallianassa cf. mortoni
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Cretaceous Trilobite – 80 MYA
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Crustaceans (squat lobster) – 80 MYA
Galathea cretacea
juvenile - top
Galathea cretacea
Juvenile - bottom
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Crustaceans – 80 MYA
Unidentified crustaceans - left
note color patterns, top 2
Bivalves (clams, oysters, etc.) Today
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Bivalves (clams) – 80 MYA
Inoceramus sp.
Limea sp.
Liopistha elegantula
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Bivalves (clams) – 80 MYA
Crassatella (Pachythaerus) sp.
Astarte? sp.
Nucula sp.
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Bivalves (clams, etc.) – 80 MYA
Barbatia sp.
Barbatia sp.
Exogyra sp.
Acar sp.
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Bivalves (scallops) – 80 MYA
Neithea hartmani
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Bivalves (scallop-like) – 80 MYA
Camptonectes sp.
Camptonectes bensoni
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Bivalves (oysters) – 80 MYA
cf. Exogyra sp.
Pycnodonte (Phygraea) aucella
Agerostrea cf. falcata
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Gastropods
(snails)
Today
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Gastropods
cf. Falsifuses sp.
(snails) – 80 MYA
Laxispira lumbricalis
Gyrodes sp.
Solariella sp.
Oligopytcha sp.
Volutomorpha sp.
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Gastropods (snails) – 80 MYA
“Mitrid” sp.
Architectonica sp.
Euspira sp.
Scala sp.
Pseudomelania sp.
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Echinoids ( sea urchins) Today
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Echinoids ( sea urchins) – 80 MYA
Sea Urchin spine
cf. Washitaster sp.
Salenia cf. pseudowhitneyi
cf. Washitaster sp.
Sea Urchin spine
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Crinoid (sea lily) Today
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Crinoid (sea lily) – 80 MYA
“Arm”
sections
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Nautiloids Today
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Ammonites – 80 MYA
Baculites sp.
Scaphites hippocrepis
Scaphites
hippocrepis
Texasia
dentatocarinata
Texasia
dentatocarinata
Scaphites leeii
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Worm Tubes Today
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Worm Tubes 80 MYA
vrs. Serpula sp.
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Burrows – 80 MYA
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Burrows – 80 MYA
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Burrows – 80 MYA
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SpongesToday
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Rare Sponges– 80 MYA
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Rare Sponges– 80 MYA
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Sponge Borings – 80 MYA
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Horn Coral Today
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Horn Coral – 80 MYA
Parasmilia sp.
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Bryozoan – 80 MYA
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Sharks Today
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Shark Teeth – 80 MYA
Cretalamna appendiculata
Cretalamna appendiculata
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Shark Teeth – 80 MYA
Squalicorax falcatus
Hybodont fin spine
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Fish Tooth – 80 MYA
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Vertebrate Bone – 80 MYA
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Nacre – 80 MYA
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Forams – 80 MYA
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To Sum It Up…

Pilot Knob (as exposed in the Dean Word Quarry) at
some time in it’s late history (80 MYA) supported a
thriving, diverse community unlike anything in the
surrounding area. With it’s rare corals, heavy
crustacean population, exceptional preservation, new
species and range extensions it affords us an
unexpected window into a past that bears further
exploration and research. We hope someday to be able
to answer the many questions this unique site presents
us with.
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Acknowledgements
With Special thanks to:
•
Don O’Neill
•
Ed Elliott
•
John Hinte
•
Kevin Durney
•
Eric Henry
•
Chris Caran
•
Al Cherepon
•
Mark Helper
•
Rodney Feldman
•
Keith Minor
• The Dean Word Quarry
• Numerous colleagues, the Internet
and anyone I may have omitted by
mistake!
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