Strontium Cenozoic

Graham, D.D., Bender, M.L., Williams, D.F. and Keigwin, L.D. Jr. (1982) Strontium-calcium ratios in Cenozoic planktonic foraminifera. Geochim. Cosmochim. Acta, 46, 1281-1292. 

Godderis, Y. and Francois, L.M. (1995) The Cenozoic evolution of the strontium and carbon cycles relative importance of continental erosion and mantle exchange. Chem. Geol., 126, 169-190. 

Since the Precambrian, the Sr/ Sr of seawater has fluctuated between —0.7070 and —0.7092 as the result of variations in the relative rates of input of Sr-enriched strontium from continental weathering and Sr-depleted strontium from mantle sources. Fluids in sedimentary basins containing Paleozoic strata typically have Sr/ Sr ratios in excess of seawater values that are contemporaneous or coeval with the deposi-tional age of the current host sediment. This is well illustrated by the data of Connolly et al. (1990) for the Alberta Basin, Canada. The enrichment is due to the release of strontium attending the alteration of silicates. Due to the significant increase of Sr/ Sr in seawater since the Jurassic, some formation waters in Cenozoic sedimentary basins actually have Sr/ Sr ratios lower than those of contemporaneous seawater due to the addition of strontium dissolved from older and deeper sedimentary sources... 

Overview of the Cenozoic marine strontium isotope record... 

Boron isotopes as a paleo-pH proxy and Mg/Ca as a paleo-temperamre proxy are also discussed, because information provided by these relatively new proxies has important implications for the better-established records mentioned in the preceding paragraph. The application of boron isotopes to reconstructing surface water pH provides a means of estimating past atmospheric CO2 levels. Much of the discussion of the marine strontium isotope record in the past has been linked to implicit assumptions about Cenozoic variations in atmospheric CO2 levels. New boron isotope results indicate that previous assumptions... 

The marine strontium isotope record is the proxy record most commonly used to constrain the geologic history of chemical weathering. However, in recent years it has been widely criticized as a proxy indicator of past silicate weathering rates. The osmium isotope record is analogous to the strontium record in many respects, and can help to constrain interpretations of the marine strontium isotope record. In this section the geochemical factors that influence the osmium and strontium isotope compositions of seawater are reviewed, and the structure of these two records of Cenozoic ocean chemistry is discussed. 

The most striking aspect of the Cenozoic strontium record is the nearly monotonic, and relatively rapid rise in seawater Sr/ Sr ratio during the last 40 Myr, as compared to the small... 

Figure 3 Composite marine strontium isotope record (sources Miller et al., 1991a Oslick et al., 1994 Hodell and Woodruff, 1994 Mead and Hodell, 1995 Farrell et al., 1995 Martin et al., 1999 Reilly et al., 2002). For the Early Cenozoic where data coverage is sparse the hest fit of McArthur et al. (2001) is plotted.

Os/ Os ratio remains relatively constant for the majority of this time interval, with the notable exception of the Eocene-Oligocene transition itself. During the Paleocene and Eocene (35-65 Ma), it appears that the osmium record exhibits considerably more variability than does the strontium record. Neither record shows clear evidence of systematic change to more or less radiogenic isotope compositions during this early part of the Cenozoic. 

Among the many recent papers that discuss the marine strontium isotope record, the influence of uplift and weathering of the HTP is pre-eminent as a potential cause of the increasingly radiogenic, or continental, character during the Cenozoic. Several workers argue that HTP weathering is... 

Further support for the weathering hypothesis for Late Ordovician glaciation comes from the strontium isotope record. A multimillion-year decline in the marine record of Sr/ Sr in limestones is reversed in the early Late Ordovician (Veizer et al., 1999), a likely consequence of collisional tectonics that initiated at this time and continued (as did the rise in Sr/ Sr) through the Silurian (Richter et al, 1992). The increase (from 0.7078 to 0.7088) rivals the Cenozoic rise, which has been attributed to the Himalayan uplift and associated with the progressive cooling leading to Quaternary glaciation (Raymo et al, 1988). 

The resolution of the database is considerably better for the Phanerozoic than for the Precambrian due to higher quality of samples and to much better biostratigraphic resolution, with duration of biozones from —1 Myr in the Cenozoic to —5 Myr in the early Paleozoic. The first data documenting the strontium isotopic variations in Phanerozoic seawater were published by Peterman et al. (1970), with subsequent advances by Veizer and Compston (1974) and Burke et al. (1982). 

Although weathering of siliceous minerals by CO2 (the so-called Urey reactions but see (Berner and Maasch, 1996)) contributed to the long-term flux of silica to the oceans (Berner, 1990), and potentially fostered the radiation of diatoms in the Cenozoic, by itself, orogeny cannot explain the relatively sharp increase in diatoms at the Eocene/Oligocene boundary. Indeed, the seawater strontium isotope record does not correspond with these radiations in diatoms (Raymo and Ruddiman, 1992). We must look for other contributing processes. 

Palmer, M.R., Helvad, C. Fallick, A.E. (2004) Sulphur, sulphate oxygen and strontium isotope composition of Cenozoic Turkish evaporites. Chemical Geology 209, 341-356. 

Information concerning the origin of the alkali-rich lavas of the Erebus volcanic province is derivable from the isotopic composition of strontium and the concentrations of rubidium and strontium. The first measurements of the Sr/ Sr ratios of the Cenozoic volcanic rocks in the Erebus province by Jones and Walker (1972) ranged from 0.7022 to 0.7048 with a mean of 0.70365 0.0024 (2o). These measurements demonstrated that the Cenozoic lavas are only moderately enriched in radiogenic Sr in marked contrast to the basalt flows and dolerite sills of the Eerrar Group. These results were later confirmed by Stuckless and Ericksen (1976) whose measured Sr/ Sr ratios in Figs. 16.6a, b, and c have a nnimodal distribution with a mean of 0.70332 0.00005 (2. ... 

Fig. 16.7 The ultramafic inclusions that were erupted with the Cenozoic alkali-rich lavas at Cape Crozier (CC-82) and Cape Bird (CB-64) on Ross Island and at Brandau vent (BV-5g) in the Royal Society Range define a straight line that yields a date of 1140 Ma. This date is largely based on the sample of trachyte (CC-82) which contains only 3.01 ppm of strontium and is susceptible to contanunation by radiogenic Sr. Therefore, the geological significance of the Rb-Sr date is questionable (Data from Stuckless and Ericksen (1976))...

We prefer the second alternative because the Sr/ Sr ratios of most Cenozoic lavas analyzed by Stuckless and Ericksen (1976) and by Jones and Walker (1972) provide no evidence that the magma was contaminated by strontium derived from the granitic basement rocks. The only exception is the sample of trachyte (CC-82, Fig. 16.7) which has a high Sr/ Sr ratio of 0.70501 (Stuckless and Ericksen 1976). 

Fig. 16.9 The values and initial Sr/ Sr ratios at 900 Ma of granulite inclusions in the Cenozoic volcanic rocks in the Ross Embayment and in the Transantarctic Mountains form separate clusters. These differences indicate that the inclusions originated from distinctly different crustal sources that are separated from each other by a discontinuity (Kalamarides et al. 1987). The isotope compositions of oxygen and strontium of the Kirkpatrick Basalt in the Transantarctic Mountains (Hoefs et al. 1980) define a third cluster having low values and high initial Sr/ Sr ratios. The evidence in this diagram implies that a tectonic boundary exists in the deep crust underlying the Transantarctic Mountains and the Ross Embayment. The isotopic data also rule out a connection between the granulite inclusions in the Cenozoic lavas and the Kirkpatrick Basalt of the Transantarctic Mountains (Adapted from Fig. 1 of Kalamarides and Berg (1991))...

The HIMU component typically has a high 206pb/204pb j. bo between 20.5 and 21.5 and a low Sr/ Sr ratio between 0.7025 and 0.7030 which places it in Fig. 16.42 on an extension of the hyperbolic Sr-Pb isotopic mixing line loosely defined by the Cenozoic volcanic rocks of the Hallett volcanic province. The volcanic rocks on the Balleny Islands and on Scott and Peter I islands have isotopic compositions of strontium and lead that overlap those of the Hallett volcanic province. However, the Sr/ Sr ratios of the Balleny/ Scott islands are low (0.7025-0.7030), whereas those of Peter I Island (0.7038-0.7040) are normal for oceanic island basalts. 

Isotope Compositions of Strontium of the Cenozoic Lavas of Northern Victoria Land and Adjacent Islands... 

Stott LD, McKelvey BC, Harwood DM, Webb PN (1983) A revision of the ages of Cenozoic erratics at Mount Discovery and Minna Bluff, McMurdo Sound. Antarctic J US 18(5) 36-38 Stuckless JS, Ericksen RL (1976) Strontium isotope geochemistry of the volcanic rocks and associated megacrysts and inclusions from Ross Island and vicinity, Antarctica. Contrib Mineral Petrol 58 111-126... 

Jones et al. (1967) first reported that the average 8 Sj./86Sr ratio of 15 water samples from a depth profile of Lake Vanda is 0.7149 0.0(X)1 which is identical within analytical error to the Sr/ Sr ratio of 0.7146 0.0002 of strontium in the water of the Onyx River. On the other hand, the Sr/ Sr ratios of strontium in Lake Vanda and the Onyx River differ markedly from the average Sr/ Sr ratio of the Cenozoic basalt of the McMurdo Volcanics (0.7043) and from the average Sr/ Sr ratio of two samples of seawater from the Ross Sea (0.7094). These results indicate unequivocally that the strontium at all levels in Lake Vanda and in Onyx River did not originate from marine sources or by weathering of Cenozoic basalt or volcanic ash in Wright Valley. 

Barrera E (1989) Strontium isotope ages. In Barrett PJ (ed) Antarctic Cenozoic history from the CIROS-1 Drill Hole, McMurdo Sound. DSlRBull 245 151-152. Wellington, New Zealand... 

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