Transcript Document 7474601

ANGOLA: MUSEUM IN THE GROUND
Good Fossils
Ocean Currents and
Source Rocks
Dinosaur Extinction
(K-Pg Boundary)
Angolasaurus
(90 million year old
marine lizard,
also found in Texas))
Louis L. Jacobs
Roy M. Huffington Department of Earth Sciences
Southern Methodist University, Dallas, Texas
In 2005 we went to Angola because fossils of giant marine lizards (mosasaurs)
had been reported in the 1960’s. Could we find more?
Colleagues at Universidade Agostinho Neto were contacted and we briefly
visited the field.
Based on our preliminary trip, the National Geographic Society and the
Petroleum Research Fund of the American Chemical Society funded
expeditions in 2006 and 2007.
In cooperation with Universidade Agostinho Neto and ISPRA (Lubango). We
have shown that:
1.
The fossils of Angola are a “Museum in the Ground.”
2.
The geologic context of the fossils gives clues to past ocean currents and
productivity leading to petroleum source rocks.
3.
The rocks of Angola record events of worldwide interest, such as the
extinction of mosasaurs and dinosaurs, and the precise position of
ancient shores.
IEMBE (north of Luanda)
90 million years old
Drawing of original specimen, 1964
Home of
Angolasaurus
The best specimen, 2006
Discovery site of Angolasaurus in 1962
Discovery site in 2006
Ammonite in Iembe cliff
Angolasaurus before excavation
Excavation of front flipper of Angolasaurus
(note ammonite lying next to fingers)
Shark Vertebrae, Iembe, 90 Million Years
The first dinosaur,
a sauropod, found
in Angola, at Iembe.
Excavation pit for front
leg of sauropod dinosaur
Professor Jacobs (SMU)
excavating arm bone of
Angolan dinosaur
Unexcavated Turtle Skull
BENTIABA
68 Ma, 15ºS
Each red point is a good fossil.
Stratigraphic Section at
Bentiaba
Terrestrial redbeds (80 million years) at base
of Bentiaba section indicates deposition under
arid, desert conditions.
Yellow marine strata overlie the terrestrial
redbeds shown in photo at left. Black rock is
volcanic lava that flowed into the ancient sea.
Mosasaurs, plesiosaurs, turtles, pterosaurs,
and fish occur in the marine strata.
Bentiaba (68 Ma)
Plesiosaur paddle
Prognathodon kianda,
a new mosasaur from Angola !!!
Shark teeth from Bentiaba.
Shark bite marks on mosasaur rib (right).
Ray teeth from Bentiaba. MANY TOP PREDATORS,
PRODUCTIVE SEA
The abundance of top predators along the ancient coast of Angola
demonstrates that the sea was productive, just as it is now.
However, offshore productivity is now caused by the Benguela
current, which is said to be only 6 million years old, not 90-66 million
when the fossils were alive.
The explanation for ancient productivity lies in the Earth’s climatic
zones coupled with continental drift of Africa.
This allows a better understanding of when petroleum source rocks
might be generated in a given coastal area.
Cold deserts
60ºN
Figure 6-8
Westerlies
Forests
Page 107
Northeast trades
Hot deserts
ATMOSPHERIC
CIRCULATION AND
CLIMATE
30ºN
The Namibe Desert has
productive upwelling
offshore that is caused by
southeast trade winds
blowing across the
continent and pushing
Forests
water away from shore, to
Equator
be replaced by nutrient
rich water from depth.)
30ºS Southeast trades
Westerlies
60ºS
Hot deserts
Forests
Cold deserts
Africa moved northward with continental drift, changing the position of upwelling relative to the
continental margin and causing fossil localities (colored dots) to change latitude. Strongest
upwelling now lies off Namibia (shaded), but in the past, strong upwelling lay off of northern
Angola, causing the formation of petroleum source rocks there.
Desert
Temperate
Pictures of submerged
fossil logs
A 90 million year old forest (orange dot) is now fossil wood submerged from sea level rise at the
mouth of the Orange River (underwater photos in center), in the Namibe Desert. The structure
of the fossil wood (right) indicates that the forest grew originally in temperate climate, but its fossil
remains moved north through geologic time because of continental drift into the desert zone of the
Orange River Basin.
M
L
I
B
O
DRIFT OF ANGOLAN FOSSIL LOCALITIES THROUGH NAMIBE DESERT LATITUDES
(Graph of paleolatitude through time of fossil localities. Brown line at top represents Landana [L] and Malembe [M], Cabinda)
O Orange River
B Bentiaba
B Bentiaba
I Iembe
L,M
35 Million Year Old Rocks at Malembe, Cabinda
(Site of Oldest Known Subsaharan Primate)
Plant-rich organic beds of Malembe (formed in
tropical latitudes) compared to sterile beds at Cabo
Ledo, south of Luanda (formed in arid latituded).
0.0
Rotated Latitude
-10.0
-20.0
South America
-30.0
Africa
-40.0
Australia
-50.0
-60.0
-170 -160 -150
-140 -130
-120 -110 -100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
Age (170 Ma to present)
Latitudinal Drift of Africa, Australia, and South America from Jurassic to Present
0.0
-10.0
-20.0
-30.0
These graphs and the preceding photos demonstrate geologic conditions
for upwelling productivity shifting along the coast as Africa moved north
through time. The plot of latitude as a function of geologic time predicts
the age of potential source rocks in southern continents.
South Am
Africa
Stacked rocks at Bentiaba allow
the most precise determination of
ancient shoreline possible.
Landward
Seaward
Basalt at Bentiaba Demonstrates Shoreline Position
(Lava at left flowed into shallow wet sand 68 million years ago; red baked zone under lava
at right shows flow over dry land; ancient shoreline lay between the two.)
Mosasaurs and dinosaurs were supposedly
driven extinct by the impact of a large asteroid
which slammed into the sea near Mexico 66
million years ago.
The ocean wave caused by the asteroid impact
struck the Angola coast and left its mark.
The effect of asteroid impact in Angola seen at the ancient shoreline
south of Bentiaba.
WHEN DINOSAURS AND MOSASAURS WENT EXTINCT!
Our objectives are:
1. To continue this project with colleagues from Universidade
Agostinho Neto University and other Angolan institutions;
2. To train Angolan student(s) in paleontology, geochemistry,
or museum management at Southern Methodist University;
3. To obtain funding from the U.S. National Science Foundation
for laboratory and partial field costs to continue this project
for the long term.
These objectives could be facilitated from the Angolan side if
logistical in-kind support were provided (vehicles,
accommodation, translators). Help will also be needed to
identify potential students.
Thank you from
(and SMU!)
Angolasaurus