UNIVERSITY OF SOUTH ALABAMA Last Time MAS 603: Geological Oceanography Lecture 16: Greenhouse vs. Icehouse Earths Submarine Fans Definition and morphology Transport mechanisms (density currents) Submarine fan facies/sedimentary sequences Submarine Canyons and Fans Submarine canyons: major conduits of siliciclastic sediment from the continental shelf to the abyssal plain Submarine Fans: Transport Mechanisms Mass movement is particularly important as a sediment transport mechanism on submarine fans. Submarine fans: accumulations of siliciclastic sediment from the shelf break onto the base of the continental slope Increase in water:sediment ratio http://www.dkimages.com/discover/previews/851/20117924.jpg From Walker, R.G. (1980). Facies Models. Geological Association of Canada. Submarine Fans: Transport Mechanisms On the distal fan, the flow has a high water:sediment ratio and moves as a density current. Turbidites Turbidites are formed as a result of waning flow. A classic Bouma sequence http://faculty.gg.uwyo.edu/heller/sed%20strat%20class/sedstrat%208/bouma.jpg http://serc.carleton.edu/ http://instruct.uwo.ca/earth-sci/200a-001/07turbidity.jpg 1
The Submarine Fan Model Today s s Agenda This is the best (and simplest) model we have of a submarine fan depositional facies. Greenhouse vs Icehouse Earths Paleozoic-Mesozoic Paleogeography Cenozoic Paleogeography Plio-Pleistocene climatic oscillations From Walker, R.G. (1980). Facies Models. Geological Association of Canada. 1) Snowball Earth 1) Snowball Earth 2) Icehouse Earth (continental glaciers present) 1) Snowball Earth 2) Icehouse Earth (continental glaciers present) a) Glacial stage (18 KA) b) Interglacial stage (Today) http://www.snowballearth.org/end.html http://www.snowballearth.org/end.html 2
Proterozoic Paleogeography 1) Snowball Earth Insert greenhouse 2) Icehouse Earth (continental glaciers present) 3) Greenhouse Earth Icehouse Earth Early Paleozoic Paleogeography Late Paleozoic Paleogeography Greenhouse Earth Icehouse Earth Early Mesozoic Paleogeography Middle Mesozoic Paleogeography Greenhouse Earth Greenhouse Earth 3
Late Mesozoic Paleogeography High latitudes were warm 50 F / 10 C Dinosaurs near south pole Wind belt Evaporite deposition Greenhouse Earth Most continents were isolated Seas opened: South Atlantic; Gulf of Mexico; Caribbean Sea Increased volume of mid-oceanic ridges due to rapid sea floor spreading Long period without a magnetic reversal Leading to High Sea Level Epicontinental sea ways Increased sedimentation Thick cratonic sequences 4
Mesozoic Climate Cenozoic Climate Oceans stagnated Epicontinental black muds when seas spilled over Normally thin oxygen poor zone expanded Oxygen isotopes from deep sea foraminifera suggest Late Eocene cooling This situation will change in the early Cenozoic (Late Eocene) Cenozoic Climate The temperature change is also recorded by terrestrial fossils (e.g., leaf margins) Cenozoic Icehouse Earth Paleocene-Middle Eocene: No circumpolar current Late Eocene-today: Circumpolar current Permitted development of glaciers on Antarctica Cenozoic Icehouse Earth Plio-Pleistocene Is most notable for rapid, short duration shifts in temperature and ice volume. 5
Plio-Pleistocene Is most notable for rapid, short duration shifts in temperature and ice volume. Plio-Pleistocene Glaciations started around 5 million years ago. Isthmus of Panama Emplaced 3.5 3 M years ago Started modern circulation Gulf stream carries salty Atlantic north Cools, sinks Oceanic conveyor belt High latitudes cool Milankovitch Cycles Three major changes in Earth s orbit are linked to glacial oscillations Milankovitch Cycles When taken together, the 3 cycles are capable of dropping temperatures globally Eccentricity Obliquity Precession Milankovitch Cycles The Present Icehouse Earth These cycles have been confirmed via stable isotope analysis of deep sea foraminifera (ice volume). Glacial/ stage glacial glacial glacial glacial Name of stage Holocene Wisconsinian Sangamon Illinoisan Yarmouth Kansan Aftonian Nebraskan Time frame 0-10 KA 10 75 KA 75 125 KA 125 265 KA 265 300 KA 300 435 KA 435 500 KA > 500 KA 6
The Present Icehouse Earth The Present Icehouse Earth Lowering of sea level Exposed continental shelves And permitted migrations Mammals crossed Bering Strait on land corridors Vegetation changed in response to global changes The Present Icehouse Earth Ocean circulation changed during glaciation The Present Icehouse Earth Glaciers began to retreat around 15,000 years ago Waters drained to lakes Sea level rose Tundra shifted northward Deciduous trees migrated northward Holocene Sea Level Change Transgression Lagoonal complexes transgress over coastal plain sediments Regression High sediment supply causes coast to move offshore Holocene Sea Level Change In southern Alabama, regressions caused the shoreline to shift 100 miles south. Base level of rivers dropped by 300 feet. 7
Holocene Sea Level Change Holocene Sea Level Change The Mobile River carved a canyon, the remnants of which are still exposed along the Eastern Shore Next Week SLEEP! 8