ABSTRACT A combined approach of sedimentology, carbon- and strontium-isotope chemostratigraphy, biostratigraphy, and seismic stratigraphy was used to constrain the sequence-stratigraphic correlation of the Shu’aiba reservoir at an oil field in northwest onshore Abu Dhabi. Sedimentologic and petrographic core description identified 14 reservoir and three non-reservoir lithofacies types, ranging from shallow-marine, rudist rudstone to basinal, planktonic foraminifera wackestone and shale. Carbon-isotope curves from individual wells allowed for correlation between depositional sequences and numerical ages were obtained for selected levels using strontium-isotope stratigraphy (SIS). This has helped to develop a more precise chronostratigraphy for the Hawar Member of the Kharaib Formation and the overlying Shu’aiba Formation in the studied region. The importance of suitable sample material for SIS is discussed and different results obtained from skeletal calcite and bulk rock samples are evaluated. The numerical ages derived from SIS are consistent with the results of carbon-isotope stratigraphy and proved to be particularly helpful in the identification of the Lower/Upper Aptian boundary, which is difficult to draw based on the carbon-isotope curve alone. Distinct taxa of rudist bivalves such as Offneria spp. are characteristic for Early Aptian high-energy environments, but are missing in the Late Aptian due to a pronounced extinction event affecting rudists at the Early – Late Aptian transition. The sequence stratigraphy of the studied field is discussed. The Hawar Member and the Shu’aiba Formation are interpreted in terms of seven third-order sequences. Early Aptian Hawar Sequence 1 (Hawar Member), together with Early Aptian Shu’aiba sequences 2, 3a, and 3b form the transgressive and early highstand systems tracts of the Arabian Plate Aptian Supersequence. These four sequences are seismically distinct; 3-D seismic data was used to map their areal extent over the interior platform and platform margin. Shu’aiba Sequence 2 contains the maximum flooding surface of the supersequence (MFS K80). Late Aptian Shu’aiba sequences 4a and 4b cannot be seismically separated and together represent the late highstand of the supersequence. Above the upper boundary of the supersequence, the youngest Shu’aiba Sequence 5 was deposited during a Late Aptian lowstand; it is evident in 3-D seismic data in the northern part of the field, which extends into the Bab Basin.

Abstract: Numerical ages have been derived from the 87 Sr/ 86 Sr values of well-preserved rudist shells from localities in Salento (S Italy)and Lefkas (Ionian Islands, Greece). Samples are from the platform margin (Salento) and from the toe of slope (Lefkas) of the former Apuliancarbonate platform. Rudists from both localities yielded a latest Maastrichtian age (66.4 Ma), and their rudist associations are the mostspecies-rich so far reported from the Mediterranean region so close to the Cretaceous-Paleogene (K-P) boundary. The abundance of large-size recumbent morphotypes of a taxon similar to Pseudosabinia is remarkable. Generally, the latest Maastrichtian rudist morphotypes ofthe Caribbean and of the Mediterranean region are very similar, although the faunas are highly endemic on the genus level. When comparedto the Turonian-Campanian, the increased abundance of aragonite in the shells of the dominant rudist taxa, and the higher abundance ofother originally aragonitic skeletal components, is discussed with respect to the major-ion composition of Cretaceous seawater. The nowwell-documented existence of species-rich rudist associations on both sides of the Atlantic argues for a catastrophic rather than a gradualextinction of the group.

Abstract: The trace-element content and strontium isotope ratio have been determined for twelve requienid rudists from SE France. Fromthese data the seawater ratio of eight stratigraphic intervals was determined. The biostratigraphy of the associated platform carbonates, ranging from Berriasian to Lower Aptian, was derived from shallow-water benthic organisms, including calcareous algae (Dasycladales), large foraminifera (mainly Orbitolinidae), and rudists. Isotope ratios of well preserved rudist shells were compared to secular variationsof the 87 Sr/ 86 Sr ratio of seawater as derived from belemnites and calibrated to the Boreal ammonite zonation ( McArthur et al., 2001 ).Stratigraphic mismatches between the values measured on requieniid rudists and the Boreal Sr-isotope reference curve appear to resultmainly from the fact that the reference curve is resolved rather as a band. A few larger discrepancies may be due to weaknesses in the original correlation of biostratigraphic markers and isotope values for some time intervals (e.g., upper Barremian).

Abstract The skeletal growth rates of late Cretaceous rudist bivalves have been inferred from cyclic variations of isotopic and chemical compositions which are found in sclerochronological profiles of outer shell layers. Annual shell accretion of 11 studied shells from different environmental settings was in the range of less than 10 to 54 mm. CaCO 3 production of individual rudists was calculated to range from 12 to 214 g a -1 , and estimates of annual production of rudist communities assuming dense growth fabrics range from 4.6 to 28.5 kg m -2 . These production rates are not significantly higher when compared to modern mussel or oyster beds but, in contrast to modern analogues, rudist associations were much more important for the sedimentary budget of low-latitude shallow-water depositional environments. Controlling factors for the formation of growth fabrics and carbonate production are evaluated in a case study of rudist formations from a single depositional sequence. From turbulent outer platform environments to lagoonal inner platform settings, a decrease both in carbonate production and size of shells was found among specimens of a single species. No differences in carbonate production are evident when carbonate production in siliciclastic and calcareous environments is compared. Potential feedbacks between rudists and their environment induced by vertical growth, large production of bioclastic sediment and ejected biodeposits are discussed.