Evolution of Tethyan phosphogenesis along the northern edges of the Arabian-African shield during the Cretaceous-Eocene as deduced from temporal variations ... [An article from: Earth Science Reviews]

by D. Soudry, C.R. Glenn, Y. Nathan, I. Segal, Vonder

List Price:	~~$14.95~~
Amazon Price:	$14.95 & eligible for FREE Super Saver Shipping on orders over $25.
Lowest New Price:	$14.95
Availablitiy:	Available for download now

Editorial Reviews
Product Description
This digital document is a journal article from Earth Science Reviews, published by Elsevier in 2006. The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser.

Description:
The evolution of Tethyan phosphogenesis during the Cretaceous-Eocene is examined to try to explain fluctuations of phosphogenesis through time, and whether or not they reflect long-term changes in ocean circulation or in continental weathering. Twenty-seven time-stratigraphic phosphate levels in various Tethyan sites, covering a time span of about 90 Myr from the Hauterivian to the Eocene, were analyzed for ^4^4Ca/^4^2Ca and ^1^4^3Nd/^1^4^4Nd in their carbonate fluorapatite (CFA) fraction. P and Ca accumulation rates and bulk sedimentation rates were quantified throughout the Cretaceous-Eocene Negev sequence to examine how changes in ^4^4Ca/^4^2Ca and ^1^4^3Nd/^1^4^4Nd are reflected in the intensity of phosphogenesis. A clear-cut change occurs in @e"N"d"("T") and @d^4^4Ca and in the rates of P and Ca accumulation and bulk sedimentation through the time analyzed. @e"N"d"("T") is much lower in the Hauterivian-Lower Cenomanian (-12.8 to -10.9) than in the Upper Cenomanian-Eocene (-7.8 to -5.9). Much lower @d^4^4Ca values occur in the Hauterivian-Turonian (-0.22 to +0.02) than in the Coniacian-Eocene (+0.23 to +0.40). P accumulation rates in the Negev steeply increase from <200 @mmol cm^-^2 k yr^-^1 in the Albian-Coniacian to ~1500 @mmol cm^-^2 k yr^-^1 in the Campanian, whereas a strong decrease is concomitantly recorded in the rates of Ca accumulation and bulk sedimentation. In addition, distinct @e"N"d"("T") values are shown by the phosphorites of the Negev (-6.7 to -6.4) and Egypt (-9.1 to -7.6) during the Campanian, and by those of the Negev (-7.8 to -6.3) and North Africa (-10.1 to -8.9) during the Maastrichtian-Eocene. The culmination of P accumulation rates in the Negev during the Campanian, occurring with a high in @e"N"d"("T") and @d^4^4Ca and a low in sedimentation rates, indicates that paleoceanographic and paleogeographical factors mostly governed phosphorite accumulation in this area. The abrupt @e"N"d"("T") rise after the Cenomanian is attributed to increased incursion of Pacific (radiogenic) water masses into the Tethys, driven by the Late Cretaceous global sea-level rise, the connection between North and South Atlantic, the global post-Santonian cooling, and the progressive widening of the Caribbean threshold, all acting in combination to significantly intensify the Tethyan circumglobal current (TCC). It also reflects a weakening of the continental Nd signal due to a reduction of exposed landmasses caused by increased flooding of continental shelves. High @d^4^4Ca values at those times also point to a decrease in weathering Ca^+^2 fluxes and expansion of carbonate sedimentation in shelves, both enriching seawater with isotopically heavy Ca^+^2. Deep ocean circulation intensified by the post-Santonian cooling of high latitudes increased P inventory in the Tethys basin, whereas the strengthened TCC and the folded shelf likely resulted in coastal and topographically-induced upwelling, supplying P-rich intermediate waters to southeastern Tethys shelves. Only in the Paleocene-Eocene, following major changes in global circulation produced by narrowing of Tethys and widening of the Atlantic, did phosphogenesis shifts its locus of high intensity to the western (Atlantic) Tethys and West African Atlantic coasts. This change in paleocirculation is expressed by distinctly differing @e"N"d"("T") in the Middle East and the North and West African phosphorites, suggesting different oceanic P sources and current systems for these two major groups of phosphorites. Our Nd isotope results further suggest a weaker TCC during the Mid-Cretaceous, becoming more intense in Late Cretaceous times. They also point to the North Pacific Ocean as major source of deep water formation for the intermediate-deep waters in the Tethys Basin during the Late Cretaceous.

Price is accurate as of the date/time indicated. Prices and product availability are subject to change. Any price displayed on the Amazon website at the time of purchase will govern the sale of this product.