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Angola: Museum in the Ground 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 InIn 20052005 wewe wentwent toto AngolaAngola becausebecause fossilsfossils ofof giantgiant marinemarine lizardslizards (mosasaurs)(mosasaurs) hadhad beenbeen reportedreported inin thethe 1960’s.1960’s. CouldCould wewe findfind more?more? ColleaguesColleagues atat UniversidadeUniversidade Agostinho Agostinho Neto Neto were were contactedcontacted andand wewe brieflybriefly visitedvisited thethe field.field. BasedBased onon ourour preliminarypreliminary trip,trip, thethe NationalNational GeographicGeographic SocietySociety andand thethe PetroleumPetroleum ResearchResearch FundFund ofof thethe AmericanAmerican ChemicalChemical SocietySociety fundedfunded expeditionsexpeditions inin 20062006 andand 2007.2007. 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 Discovery site of Angolasaurus in 1962 Angolasaurus Discovery site in 2006 The best specimen, 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 Yellow marine strata overlie the terrestrial redbeds shown in photo at left. Black rock is Terrestrial redbeds (80 million years) at base volcanic lava that flowed into the ancient sea. of Bentiaba section indicates deposition under Mosasaurs, plesiosaurs, turtles, pterosaurs, arid, desert conditions. 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 ATMOSPHERIC Figure 6-8 CIRCULATION AND Westerlies Forests CLIMATE Northeast tradesPage 107 30ºN Hot deserts The Namibe Desert has productive upwelling offshore that is caused by southeast trade winds blowing across the Forests continent and pushing water away from shore, to Equator be replaced by nutrient rich water from depth.) 30ºS Southeast trades Hot deserts Westerlies Forests 60ºS 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 -10.0 -20.0 -30.0 South America Africa -40.0 Australia Rotated Latitude -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 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. 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 Angolasaurus (and SMU!).
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