Palaeoenviromental significance of Oligocene-Miocene coralline red algae ‒ a review

Coralline red algae are common in Oligocene and Miocene marine shallow-water carbonate and siliciclastic rocks and deep-water re-deposited sediments containing particles removed from the platforms. Corallines are mostly reported in reef-related carbonates but are also the main components in shallow-water heterozoan carbonates from temperate regions. The known distribution of Oligocene coralline assemblages does not suggest any palaeobiogeographical differentiation. In contrast, for the Miocene, the occurrence of taxa still living today with restricted geographic distribution supports an actualistic approach and the rough differentiation of palaeobiogeographic regions as follows: (a) a tropical region (characterised by thick Hydrolithon plants and Aethesolithon); (b) a subtropical Mediterranean (with common Spongites and Neogoniolithon species); and (c) a temperate region with shallow-water assemblages dominated by Lithophyllum. In a few examples from the northern margin of the western Tethys, the correlation of Oligocene carbonate-facies and algal assemblages indicates a dominance of Lithothamnion species in the shallower environments, while Mesophyllum is most abundant in deeper platform settings. The taxonomic composition of Miocene coralline assemblages and growth forms changed with depth, having patterns similar to those in the algal associations in present-day marine platforms. Mastophoroids and lithophylloids (Aethesolithon, Hydrolithon, Neogoniolithon, Spongites, and Lithophyllum species) characterise the shallower assemblages, whereas the melobesioids Lithothamnion and Mesophyllum and the sporolithacean Sporolithon are dominant in deeper-water settings. The common algal nodules (rhodoliths) comprised thick plants of few species in the shallowest palaeoenvironments, while in deeper platform areas they are composed of more diverse algal assemblages, with thin encrusting and protuberant-branching growth forms

Termination of the Arabian shelf sea: Stacked cyclic sedimentary patterns and timing (Oligocene/Miocene, Oman)

In the Janabah region of southeastern Oman, Oligocene/Miocene limestones of the Shuwayr, Warak and Ghubbarrah formations are widely exposed. They were deposited on an extensive shallow carbonate platform that was part of the Arabian Shelf and located on the Gulf of Aden's northeastern rift shoulder, which emerged during the Early Miocene. The uppermost part of the studied sedimentary succession developed immediately before the permanently subaerial exposure of the carbonate platform. Cyclic changes of intertidal and subtidal facies document a fluctuating relative sea level at different frequencies and a continuous decline of accommodation. Single erosive surfaces with palaeokarst cavities and caliche crusts separate larger depositional cycles. These disconformities imply relatively long episodes of subaerial exposure and are interpreted to have been formed during lowstands of third-order sea level cycles that denuded the platform. Taxonomic studies of the accompanying mollusc faunas and certain benthic foraminifers allow a correlation of the recognised subaerial disconformities with the Ru4/Ch1 to Ch4/Aq1 sequence boundaries of Hardenbol et al. [Hardenbol, J., Thierry, J., Farley, M.B., Jacquin, T., Graciansky, P.-C., Vail, P.R., 1998. Mesozoic and Cenozoic Sequence Chronostratigraphic Framework of European Basins. In: Graciansky, C.-P., Hardenbol, J., Jacquin, T., Vail, P.R. (Eds.), Mesozoic and Cenozoic Sequence Stratigraphy of European Basins. Society for Sedimentary Geology, Special Publication 60, 13­603.]. This demonstrates that the termination of the Arabian shelf sea must be back-dated from the middle Burdigalian to the early Aquitanian

Coccolithophore and benthic foraminifera distribution patterns in the Gulf of Cadiz and Western Iberian Margin during Integrated Ocean Drilling Program (IODP) Expedition 339

For the first time during an Integrated Ocean Drilling Program (IODP) Expedition (Exp. 339, Mediterranean Outflow) water samples for living coccolithophore distributions and mudline samples for coccoliths, benthic foraminifera, and geochemical analyses in the underlying surface sediments were collected. In total, 14 water samples (from 5 to 20 m water depth) and 7 mudline samples were gathered at the drill sites. Coccolithophore distributions show spatial variations in species diversity. In particular, assemblages that characterize the Western Iberian Margin differ from those in the Gulf of Cadiz, indicative of oceanographic and environmental controls on the community in the upper ocean (0–20 m depth). Comparison of the living assemblages to those in surface sediments shows differences in the presence of some species, suggesting the influence of post deposition sedimentary processes. Other factors such as the season of sampling and the limited sampling depth may also have a role in the differences recorded. Benthic foraminiferal assemblages seem to be primarily determined by source, quantity and quality of available food. Sites in the Gulf of Cadiz are bathed by Mediterranean Outflow Water (MOW) and characterized by a considerable amount of advected food particles. Elevated epibenthic foraminifera exploit this niche, while arborescent epifaunal and infaunal taxa thrive on food particles falling out of MOW. The combined data suggest different flow speeds and settling of MOW suspension load in the Gulf of Cadiz. In contrast, assemblages from the Western Iberian Margin located farthest from or outside of MOW are determined by local export productivity and mirror trophic conditions in the surface waters. Both assemblages reveal variation in the composition at intermediate and deep water depths along the southern and western Iberian Margins with distance from the Strait of Gibraltar