| Title: | Flip from dysoxic to oxic state of world oceans during Late Cretaceous |
| Author: | Luba F. Jansa |
| Date Submitted: | 03/21/2002 |
| Address: | Dalhousie University,
Earth Science Department
Halifax
N.S.
Canada
B3H 3J5
|
| Phone: | (902) 426 2734 |
| Email: | jansa@agc.bio.ns.ca; lubomirjansa@netscape.net |
| Co-Authors: | Chengshan Wang (Chengdu University of Technology, China), Massimo Sarti ( University of Ancona, Italy) and R.W. Scott (Univerisity of Tulsa, U.S.A.). |
| Affiliation: | Dalhousie University, Earth Sciences Department |
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| Abstract URL: | http://cis.whoi.edu/science/GG/ccod/viewAbstracts.cfm?RefNumber=19725472 |
| Author Project webpage: | http://www.iugs.org/iugs/news/igcp02.htm#463 |
| Keywords: | late cretaceus, pelagic red beds, ocean circulation, paleoclimate, equatorial seaway, paleogeography, Corg., paleoclimate, sea level changes , IGCP 463 |
| Abstract: | The Cretaceous differs from the other periods of the Mesozoic being a time of major plate tectonic, paleoceanographic, biologic and paleoclimatic changes. It is also economically important, as it contains the highest percentage of source rocks for hydrocarbon generation from the whole Phanerozoic. Most previous research has been devoted to explaining the major "anoxic" events in the early Aptian and at the Cenomanian-Turonian boundary. These events marked by positive carbon-isotope excursion have been attributed to various earth processes - such as increased volcanic activity when carbon dioxide led to global warming, changes in bioproductivity, ocean circulation and tectonics. Less attention was paid to the time between these events also characteristic by deposition of dark grey, to black shales. Deposition of such shales in the North Atlantic ocean basin was initiated during Valanginian and continued to the late Cenomanian. A major change in the character of deep sea deposits in the North Atlantic occured after deposition of the Bonarelli horizon (Cenomanian-Turonian boundary), with the dysoxic depositional environment being rapidly replaced by a highly oxic environment. This change is indicated by zeolitic red clays, lack of organic carbon and very low sedimentation rates in abyssal basins. Such deposition continued into the Paleocene in the North Atlantic, but was of shorter duration in parts of the eastern Tethys. The change to oxic ocean state is recognizeble not only in the abysal deep-sea deposits, but also on continental slopes and rises, where reddish marls, like Scaglia Rossa in Italy, or Puchovke marls in Slovakia, were deposited above the CCD. Why was there this change to a more oxic state of the world oceans? Does it indicate major changes in the bioproductivity of the oceans, ocean chemistry, oxygen, circulation, or another, unrecognized change in the Earth Systems?
To answer some of these questions the International Geologic Correlation Program approved in early 2002 the new project: IGCP #463, "Upper Cretaceous oceanic red beds: Response to ocean/climate global change." Although, several different hypothesis have been advanced to explain the major change in the oceans during the late Cretaceous and will be discussed during the Workshop, none have withstood close scrutiny. Involvement of the broad scientific comunity in IGCP # 463 might lead to an understanding of the causes of such major change in global oceans represented by the flip from dysoxic to oxic ocean in the late Cretaceous. |
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