Abstract We present rare earth element (REE) data of basalt and salt samples from central Germany where basaltic dykes of Tertiary age crosscut Upper Permian rock and potash salt. The glassy rims of the dykes can be considered as a natural analogue for the corrosion of nuclear waste glass in a salt repository, whereas the REE data from the salt can serve as an analogue for radionuclide migration in salt next to a leaking nuclear waste repository because the light rare earths (LREE) have a geochemical behavior similar to that of some actinides. Our basalt data demonstrate mobility and fractionation of the REE during postintrusive circulation of salt brines. The processes controlling this behavior of the REE were dissolution and reprecipitation of phosphate minerals. The salt data show that a small portion of the REE has left the basalt during postintrusive fluid circulation and migrated into the salt where a strong depletion of the LREE can be observed with increasing distance from the basalt contact. This fractionation is most probably due to precipitation of LREE-enriched accessory minerals such as apatite. In analogy to this, a similar behavior might be expected from actinides such as Am and Cm, which would in the case of a leaking salt nuclear waste repository probably be immobilized when phosphate minerals are present in the backfill material.

Abstract: Sedimentary phosphorite formation has occurred episodically over geologic time. Substantia] phosphorite deposits were formed during P-giant episodes of which the most widespread and long-lasting were the Precambrian-Cambrian and the Cretaceous-recent. The aim of this review is to reevaluate these two episodes in the light of sedimentary Sr, Nd, S, and C isotopic records. Some, although not all of these phases of phosphorite formation were accompanied by increases in seawater 87 Sr/ s6 Sr unrelated to changes in seafloor spreading, which supports a possible link between orogeny and global weathering rates, P-input, and P-giant formation. Assessing the relationship between δ 13 C and phases of widespread phosphogenesis is more complicated due to the counterbalancing effects on seawater δ 13 C of productivity/organic matter deposition and subsequent phosphogenesis/early diagenetic carbon oxidation. It is recommended that proposed links between phosphogenesis and global changes of δ 13 C or P- input continue to be reexamined on a case-to-case basis. The application of secular trends in Nd isotopic ratios to unravelling the often vital role of paleocurrents in phosphorite formation is also discussed. In addition, recent isotopic research is outlined that has led to significant improvements in stratigraphic resolution around the Precambrian-Cambrian boundary. A temporal and causal connection is put forward between metazoan evolution, that is the introduction of bioturbation, fecal pellets, biomineralization, and filter feeders, which would have helped to concentrate mineral phosphate in sediments, and widespread phosphogenesis at this time.

Abstract: Integration of biostratigraphic and Sr isotope data constrain the ages of four third-order depositional sequences within the Aurora and Onslow Embayments of the Miocene Pungo River Formation. Within the Aurora Embayment the microsphorite surface capping the Oligocene and marking the base of the Pungo River Formation is –28 Ma. The bulk of Unit A, which constitutes the Aurora Embayment Sequence (AES), is 23.2–21.6 Ma. Unit B, at 19.1–17.0 Ma, is largely contemporaneous with the Frying Pan Sequence (FPS) in Onslow Embayment. Units C and D, at 16.4–14.8 Ma, are largely contemporaneous with the Onslow Bay Sequence (OBS) in Onslow Embayment. The microsphorite surface at the contact of unit D and the Pliocene Yorktown Formation is 12.7 Ma. Within the Onslow Embayment the microsphorite at the unconformity between the Oligocene and the Miocene Pungo River Formation is 21.0–19.5 Ma. The remainder of the Frying Pan Sequence (FPS) is 20.5–16.7 Ma. Most of the Onslow Bay Sequence (OBS1–OBS3) is 15.4–14.8 Ma, with OBS4 being slightly younger. The lower units of the Bogue Banks Sequence (BBS1–BBS5) are 12.5–8.6 Ma. BBS6–BBS8 have not been constrained biostratigraphically; however, Sr ages suggest that the phosphate was reworked from pre–existing units and deposited between 8.6–7.1 Ma. Interpretation of depositional patterns in phosphate–rich sediments of North Carolina has led to the development of a sedimentological model for continental margin phosphogenesis. Sedimentation patterns in an idealized phosphogenic episode reflect various stages of sea–level change. Sea–level lowstand produces an erosional unconformity across previously deposited sediment sequences. Marine transgression is characterized by a fining–upward sequence of fine siliciclastic sediments with intermixed phosphate grain types. During early–stage transgression, a basal microsphorite crust forms and erodes to produce rip–up intraclasts that are then reworked into and dominate the lower portion of the subsequent depositional sequence. Mid–stage transgression is dominated by authigenic phosphate, including skeletal grains and fine sand–sized peloids, which form as disseminated grains below the sediment–water interface in response to the degradation of organic matter in nutrient–rich, suboxic shelf environments where there is little or no sediment winnowing or reworking. During late–stage transgression the phosphogenesis is terminated as oxygen–depleted environments migrate landward across the shelf with the formation of organic–rich dolosilts or foraminifer–rich/diatom–rich muds with little to no phosphate. The sea–level highstand is characterized by carbonate–rich sediments deposited under the influence of normal marine, open–shelf conditions. During the subsequent regression, sediments of these shallower depositional environments are often eroded and reworked to form beds of extensively reworked phosphate–rich sediments. Four episodes of phosphate sedimentation characterize the North Carolina continental margin. Three episodes (I, II, and III) are dominated by primary phosphate formation within the Miocene, whereas one episode (IV) consisting of the Pliocene–Quaternary sediments contains totally reworked phosphates derived from sediments of Episodes II and III. Episode I occurred during the Aquitanian (23.3–21.6 Ma), forms the basal sequence of the Pungo River Formation in the Aurora Embayment, and represents a mid–stage transgression that is only partially preserved. Episode II preserved all sediment facies of an entire sea–level cycle that produced the main Miocene phosphogenic event, which took place during the Burdigalian and Langhian (21.0–14.8 Ma) and extended throughout the Aurora and Onslow Embayments. Episode III was deposited in eastern Onslow Embayment during the uppermost Serravallian and Tortonian (12.7 Ma and likely continuing through 7.1 Ma). Low sea stand during the Messinian led to severe erosion and weathering of Episode III sediments, limiting their distribution and modifying their composition. Episode IV represents many sea–level events that produced Pliocene–Quaternary deposits with local and variable concentrations of reworked phosphate of many types. The four phosphate episodes recognized in North Carolina closely correspond to the Upper Cenozoic phosphorite episodes identified globally by Riggs and Sheldon (1990) .

Abstract In the central Mediterranean area, a major, second-order transgressive event spanning from the Burdigalian to the Serravallian is recorded by the widespread deposition of deeper-water facies on carbonate shelves and is matched to a large extent by changes in carbonate facies, including the sudden disappearance of corals and coral reefs and the corresponding rise in the abundance of temperate and cool-water carbonate facies. Two sections from the Maiella platform margin in the southern Apennines and the Hyblean Plateau in Sicily provide us with time series based on oxygen and carbon isotopes and detailed biostratigraphic and strontium isotope ages of unprecedented resolution to compare these facies changes to the global Neogene cooling trends and to the paleoceanographic conditions existing at the time in the Mediterranean area. An evaluation of the timing of facies change indicates that the major cooling interval in the Neogene, between 14 and 12 Ma, postdates the change from tropical to temperate carbonate facies in the Mediterranean, which began at approximately 20 Ma. Our oxygen isotope record from the Hyblean Plateau suggests relatively cool temperatures during the Serravallian (within biozones N10-N12) with progressive warming within biozone N11 (11.9–11.8 Ma). This signature is opposite to the one recorded in pelagic sections in other locations of the world and is interpreted to reflect regional conditions within the Mediterranean, as after 20 Ma, the connection to the Indian Ocean became closed or reduced to a very shallow si11, which prevented the outflow and inflow of intermediate and deeper waters. The second-order transgressive event in the central Mediterranean coincides with an increase in the δ 13 C values of skeletal carbonates. These isotope data, combined with biotic evidence, suggest increased productivity of surface waters during the transgressive event. The onset of this event predates by approximately 3 m.y. the major positive carbon isotope excursion recorded worldwide in pelagic sections (the Monterey event); its termination coincides with the end of the Monterey excursion. Our data indicate how variations in water temperatures, coupled with drastic changes in water circulation, severely affected rates of carbonate production during the deposition of a second-order sequence and had the effect of accentuating the transgressive trend within the sequences. Rates of carbonate production reached a minimum during the transgressive and early-highstand systems tracts. This low production was not linked to a decrease in the size of the carbonate-producing area along the depositional ramp but rather to changes in production rates due to environmental change. A better understanding of the response of carbonate facies to paleoceanographic changes needs to be developed, so that these changes can be used to predict sequence stratigraphic architecture in a given time slice and to better estimate the reliability of the sea-level signature preserved in carbonate sequences.