ALBERT

Description: Two new species, Tubulogenerina turonica and Colomia africana, are described from the Turonian of Tanzania, and the genus Colomia is emended. The genus Tubulogenerina was originally thought to have originated in Europe in the early Eocene. Our discovery of T. turonica indicates that the roots of the genus reach back to the middle Cretaceous, and argues against a previous conclusion that it originated in temperate European regions. A tropical/subtropical site of origination would be consistent with the observation that most Tubulogenerina species inhabited warm, shallow-water environments. Tubulogenerina turonica has a relatively simple morphology, suitable as a starting point for morphological trends in the genus during the Cenozoic, thus supporting its status as a plausible ancestral species. In clay-rich middle Cretaceous sediments from Tanzania, foraminifera are exceptionally well preserved, and assemblages include a number of aragonitic taxa, including Colomia africana. This new species is distinguished from others of the genus by its aperture and toothplate structure and its dominantly biserial test without a well-developed uniserial growth stage. Morphologic similarities, however, indicate the close evolutionary relationship with other species of Colomia, so the genus is emended accordingly. Sufficient numbers of C. africana were found in multiple samples to characterize its stable carbon and oxygen isotope values relative to another aragonitic species (Epistomina chapmani) and calcitic species (Berthelina berthelini) from the same material. Results show an expected offset between calcitic and aragonitic tests that is partially explained by differential fractionation factors, but suggests vital or microhabitat effects contribute to values measured on C. africana.

Description: A major planktic foraminiferal species turnover accompanied by a dramatic reduction in shell size, a fundamental change in shell architecture, and a precipitous drop in the abundance of planktic relative to benthic species occurs across the Aptian/Albian boundary interval (AABI) at globally distributed deep-sea sections. Extinction of the large and distinctive planktic foraminifer Paraticinella eube-jaouaensis, used to denote a level at or near the Aptian/ Albian boundary, coincides with the extinctions of relatively long-ranging Aptian species of Hedbergella and Globiger-inelloides. At Deep Sea Drilling Project (DSDP) Site 511 (southern South Atlantic), which is the most complete and best preserved of the studied AABI sections, the Aptian assemblage is of low diversity and species are replaced by initially one and then two very small, smooth-surfaced, thin-walled species of Microhedbergella n. gen. The oldest species of this genus, Mi. miniglobularis n. sp., probably descended from Hedbergella praelippa n. sp. and is the nominate taxon for a new lowermost Albian interval zone and is considered ancestral to several small, gradually evolving microperforate species, including Mi. praeplanispira n. sp., Mi. pseudopla-nispira n.sp., and Mi. pseudodelrioensis n. sp., which range into the middle and upper Albian. The small hedbergellids that characterize the Mi. miniglobularis Interval Zone at Site 511 have also been identified from samples taken just above the Kilian black shale level in the Vocontian Basin of southeast France. The Albian record at Site 511 reveals a gradual increase in planktic foraminifera shell size and assemblage dominance, as well as the gradual evolution during the middle Albian of species characterized by a finely perforate, pustulose test. Taxa with this shell infrastructure are included in Muricohedbergella n. gen. A new "Ticinella yezoana" Partial Range Zone is erected at Site 511 for correlation of the middle-upper Albian at high latitudes. At Ocean Drilling Program (ODP) Site 1049 (western North Atlantic), which also yields well-preserved foraminifera across the AABI, Aptian species of Hedbergella, Globiger-inelloides, and Pseudoguembelitria blakenosensis n. gen., n. sp. are replaced by lower Albian assemblages composed only of two minute species of Microhedbergella. However, this boundary section is considered incomplete because of the absence of the Mi. miniglobularis Zone. A new upper lower Albian Ti. madecassiana Zone is defined at Site 1049 for the interval between the lowest occurrence (LO) of the nominate taxon and the LO of Ti. primula, the nominate species of the middle Albian Ti. primula Zone. The AABI at DSDP Site 545 (eastern North Atlantic) has a major unconformity spanning the uppermost Aptian through the upper Albian. A black shale sequence previously placed in the lower Albian and designated as Oceanic Anoxic Event 1b is now determined to be latest Aptian in age. The AABI at ODP Site 763 (southeast Indian Ocean) is also marked by an unconformity between the upper Aptian Pa. eubejouaensis Zone and the lower Albian Mi. rischi Zone. This site needs further study to resolve whether overlap of species from both zones is the result of downslope reworking or an exception to the pattern of abrupt species turnover observed at the other deep-sea sites. The dramatic changes in planktic foraminiferal assemblages across the AABI suggest major changes in carbonate chemistry, vertical stratification, or productivity in the surface mixed layer occurred during the last 1 myr of the Aptian. Understanding the cause or causes for these changes will require much further investigation.