HR: 16:45h
AN: OS14A-04 INVITED     [Abstracts]
TI: Tracing Tethyan Phosphogenesis From Temporal Variations of $^{44}$Ca/$^{42}$Ca and $^{143}$Nd/$^{144}$Nd Isotope Ratios in Francolites and P Accumulation
AU: * Soudry, D
EM: david.soudry@mail.gsi.gov.il
AF: Geological Survey of Israel, 30 Malkhe Israel St.,, Jerusalem, 95501 Israel
AU: Glenn, C
EM: glenn@soest.hawaii.edu
AF: Dept. of Geology and Geophysics, University of Hawaii, Honolulu, HI 96822 United States
AU: Nathan, Y
EM: y.nathan@mail.gsi.gov.il
AF: Geological Survey of Israel, 30 Malkhe Israel St.,, Jerusalem, 95501 Israel
AU: Segal, I
EM: irena.segal@mail.gsi.gov.il
AF: Geological Survey of Israel, 30 Malkhe Israel St.,, Jerusalem, 95501 Israel
AU: VonderHaar, D
EM: denys@soest.hawaii.edu
AF: Dept. of Geology and Geophysics, University of Hawaii, Honolulu, HI 96822 United States
AB: Measurements of $^{44}$Ca/$^{42}$Ca and $^{143}$Nd/$^{144}$ isotope ratios in carbonate fluorapatite (CFA) through the Cretaceous-Eocene of the Negev (Israel) and of other sites in the Tethys margins, together with quantified rates of P and Ca accumulation and bulk sedimentation, allow us to understand variations of Tethyan phosphogenesis in time and space. The data provide a $\sim$ 90 m.y. (Hauterivian-Eocene) record of the Ca and Nd isotopic composition in 72 CFA samples representing 25 time-stratigraphic phosphate levels. Similar temporal changes are displayed by $\delta$$^{44}$Ca and $\epsilon$Nd$_{T}$. $\delta$$^{44}$Ca is much lighter in the Hauterivian-Albian ($\delta$$^{44}$Ca = - 0. 19 to - 0.06 $\permil$; n = 9) than in the Campanian-Eocene ($\delta$$^{44}$Ca = + 0.29 to + 0.40 $\permil$; n = 41), whereas $\epsilon$Nd$_{T}$ increases from continental crust-like values in the Hauterivian-Albian ($\epsilon$Nd$_{T}$ = -12.8 to - 10.9; n = 8) to more radiogenic Pacific-like values ($\epsilon$Nd$_{T}$ = - 7.5 to - 6.2; n = 27) in the Campanian. Both $\delta$$^{44}$Ca and $\epsilon$Nd$_{T}$ peaks in the Campanian coincide with the peak of Tethyan phosphogenesis in the Negev, marked by a sharp rise in P accumulation rates (from $<$ 200 $\mu$mole.cm$^{-2}$ kyr$^{-1}$ in pre-Campanian times to $\sim$ 1700 $<$ 200 $\mu$mole.cm$^{-2}$ kyr$^{-1}$ in the Campanian) and by a decrease in the rates of Ca accumulation and bulk sedimentation. The coincident increases of $\delta$$^{44}$Ca, $\epsilon$Nd$_{T}$, and P accumulation in the Negev during the Campanian is interpreted as the combined effect of the Late Cretaceous global sea level rise, the development of a long-transit, westward-flowing circumglobal Tethyan current enhanced by widening of the Caribbean threshold at those times, and a favorable paleolatitude ($8\deg$ -$15\deg$) of the south Tethys shelf in the path of easterly winds. Extensive flooding of continental platforms, induced by the Late Cretaceous global sea level rise, probably reduced the influx of riverine Ca to oceans and increased carbonate deposition on shelves both causing seawater enrichment with heavy Ca. Similarly, intensification of ocean circulation, causing more incursion of Pacific water masses into the Tethys, probably also led to increase both the input of radiogenic Nd into the Tethys and the availability of dissolved P in photic waters. The much lower $\epsilon$Nd$_{T}$ values recorded in N. Africa CFA during Eocene times ($\epsilon$Nd$_{T}$ = - 10.0 to - 9.4) suggests Atlantic waters as main source of dissolved P for fuelling phosphate deposition in this area.
DE: 0330 Geochemical cycles
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting