| Title: | High stress paleoceanographic conditions during the last 700 kyr of the Maastrichtian in the eastern Tethys (Tunisia, Egypt and Israel) |
| Author: | Gerta Keller |
| Date Submitted: | 04/24/2002 |
| Address: | Geosciences Princeton University
Princeton
NJ
USA
08544
|
| Phone: | 609 258-4117 |
| Email: | gkeller@princeton.edu |
| Co-Authors: | Abramovich, S., Princeton; Adatte, T., University of Neuchâtel; Stueben, D., Berner, Z. A., Meudt, M., and Kramar, U., Univ. Karlsruhe; Hambach, U., University of Bayreuth |
| Affiliation: | Princeton University |
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| Abstract URL: | http://cis.whoi.edu/science/GG/ccod/viewAbstracts.cfm?RefNumber=19725484 |
| Author Homepage: | http://geoweb.princeton.edu/research/Paleontology/paleontology.html |
| Keywords: | Late Maastrichtian, climate changes, high-stress paleoenvironment |
| Abstract: | At Elles, Tunisia, Milankovitch-scale cycles (20 kyr precession, 40 kyr obliquity, 100 kyr eccentricity) can be recognized in high-resolution carbon-13 and oxygen-18 ratios, Sr/Ca, mineralogical and magnetic susceptibility data in hemipelagic sediments that span the last 700 kyr of the Maastrichtian. Oxygen isotope data reveal three cool periods between 65.50-65.55 Ma (21.5-23.5 m), 65.26-65.33 Ma (8-11 m) and 65.04-65.12 Ma (1.5-4 m), and three warm periods between 65.33-65.38 Ma (12-16 m), 65.12-65.26 Ma (4-8 m) and 65.00-65.04 Ma (0-1.5 m). The cool periods are characterized by small surface-to-deep temperature gradients, reflecting an intensive mixing of the water column. The carbon isotope composition of planktic foraminifera indicates a continuous decrease in surface bioproductivity. Decreasing carbon-13 isotope values (the difference between the carbon isotopes of surface and bottom dwelling foraminifera), and the carbon isotope ratios of the planktic species at the onset of gradual warming at 65.50 Ma reflect a reduction in surface productivity as a result of decreased upwelling that accompanied global warming, and possibly increased atmospheric pCO2 related to Deccan Trap volcanism. Planktic foraminifera responded to the cooling episodes with a decreased species diversity, including a decrease in globotruncanid species (intermediate dwellers), followed by continuing low diversity or a further decrease during the maximum warming. Times of high stress, are indicated by low species diversity and blooms of the opportunistic species Guembelitria at warm-cool transition intervals. During the last 100 k.y. of the Maastrichtian rapid cooling is associated with accelerated species extinctions followed by the extinction of all tropical and subtropical species at the K-T boundary.
At Qreiya in Central Egypt, significantly higher stress environmental conditions, akin to those normally experienced during the K/T transition, are indicated by faunal and stable isotopic data during the late Maastrichtian (66.8-65.4 Ma). Central Egypt experienced a breakdown of the biologically mediated surface to bottom gradient of the 13C/12C ratio, with planktic foraminiferal species diversity reduced by more than 50%, and faunal assemblages dominated (75-90%) by the opportunistic disaster species Guembelitria cretacea. This prolonged breakdown in ocean primary productivity occurred during a time of global climate cooling, but seasonally warm, wet, tropical and subtropical conditions prevailed locally. A normal carbon isotope gradient was briefly re-established during the short climate warming and rising sea level between 65.4-65.2 Ma.
At Mishor Rotem in southern Israel, late Maastrichtian high-stress conditions are also indicated by very low species richness (30-35 species) and three Guembelitria blooms (coeval Egypt and Tunisia), accompanied by seasonally wet and dry periods. Most remarkably, these climatic changes are accompanied by deposition of three red clay layers interbedded in white chalk at the base and near the middle of the Plummerita hantkeninoides zone that spans the last 300 kyr of the Maastrichtian. These red layers contain spherules and major Pd and Pt anomalies (but only minor Ir) are present in two of them. An Ir anomaly is present in the K/T boundary red layer 1.2 m upsection. The origin of the spherules and Pd and Pt anomalies, and their relationship to the environmental changes are still unclear. However, the presence of three spherule layers in coeval stratigraphic positions in Mexico suggest major volcanic and/or impact events contributed to the global climatic changes of the last 300 kyr of the Maastrichtian. |
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