Tanja J. Kouwenhoven

Benthic foraminifers: proxies or problems?: A review of paleocological concepts

In this paper, we review benthic foraminiferal distribution patterns in the context of their use as proxy to reconstruct paleoenvironments, in particular against the background of relevant biological data. These data suggest that benthic foraminifera, as most microbiota, are not stenotopic to most environmental variables. A more generalist strategy seems beneficial since the low degree of specialisation prevents rapid extinction. This immediately suggests that parameters like temperature and salinity are not very important in benthic foraminiferal distribution and thus not in proxy studies. Oxygen and organic flux, on the other hand, are of great ecological importance and it is not surprising that all viable proxies today are based on relationships with these parameters. Organic flux (food) is important in deciding on abundance, but is subordinate as soon as oxygen starts to be limiting. This is the case in almost all shallow water systems with muddy substrates, sometimes down to considerable waterdepth. Microhabitat patterns are shaped through the arrangement of species along a redox gradient, whereby species distribution seems to be correlated with specific redox levels. It cannot be excluded that a relationship with specific bacterial suites also plays a role here. However, the coupling to the successive redox stages provides a means for very detailed reconstructions of oxygenation. On the other hand, organic flux reconstructions can be distorted due to the fact that the same flux levels, though with different oxygenation, are characterised by different suites of species. Therefore, assemblage characteristics are discussed as additional means to constrain organic flux reconstructions. It is concluded that species distribution with depth is mainly a function of organic flux and oxygenation. In this sense, paleobathymetry should not be based on individual marker species, but preferably on quantitative assemblage characteristics such as P/B ratios. However, more generalised schemes of assemblage successions with depth are clearly helpful. It is further concluded that benthic foraminiferal distribution, and microhabitat occupation, are regulated by the interplay of organic flux, oxygen and competition. Each of these factors is acting in a different way and leads to the complex pattern as found in living associations.

The onset of the Messinian salinity crisis in the Eastern Mediterranean (Pissouri Basin, Cyprus)

The Pissouri Basin in Cyprus contains one of the most suitable sedimentary successions with which to study the onset of the Messinian Salinity Crisis in the Eastern Mediterranean. Exposures along the new Paphos^Limassol motorway near Pissouri exhibit distinct cyclic bedding which permits the construction of a chronology based on orbital tuning. Biostratigraphic results reveal 10 planktonic foraminifera events that have been astronomically dated in other Mediterranean sections, and as such provide an excellent first-order age control. Magnetostratigraphic results are in good agreement with the biostratigraphic data and show that all magnetic chrons between C4n.1n and C3An.1n are present. The pattern of sedimentary cycles generally fits well with the insolation curve. Astronomical tuning of the succession shows that the first gypsum bed at Pissouri overlies a 40^60 kyr stromatolite-bearing transitional interval and correlates with the amplitude increase in insolation at 5.96 Ma, as in the western Mediterranean. This indicates that the onset of evaporite precipitation was synchronous right across the entire Mediterranean Basin. fl 2002 Elsevier Science B.V. All rights reserved.

Deep-water changes: the near-synchronous disappearance of a group of benthic foraminifera from the Late Miocene Mediterranean

Abstract Benthic foraminiferal and geochemical data from the Monte del Casino section in northern Italy are employed to reconstruct the sequence of events preceding the Late Miocene Mediterranean salinity crisis. We evaluate the effects of eustatic sea-level changes and tectonic events, affecting the Atlantic–Mediterranean connections. Changing benthic foraminiferal assemblages record changes in the deep-water environment, that can be explained by progressive isolation of the Mediterranean basin. The results of the analyses of stable oxygen- and carbon isotopes and redox-sensitive elements are in line with the benthic faunal trends. At 7.16 Ma, a first major step in isolation of the basin is indicated by the nearly simultaneous disappearance of a group of deeper-water benthic species usually found in middle to lower slope environments. At the same time, stable isotopes and redox-sensitive elements indicate cooling and decreasing bottom water oxygenation. After 6.8 Ma gradual development of water-mass stratification, probably accompanied by increasing bottom-water salinity, is indicated by all proxies. The cyclic pattern of homogeneous and sapropelitic sediments in the section is related to astronomical parameters, and allows a detailed correlation with Mediterranean sections at considerable geographic distances. We compared the benthic foraminiferal faunas with those from the Metochia section (Gavdos, Greece), deposited at a similar water depth (∼1000 m), to find that the benthic foraminifera at both sites indicate a similar, synchronous paleoenvironmental development. All proxies indicate that the onset of the Late Miocene Mediterranean salinity crisis dates back to the earliest Messinian. The development of the Mediterranean basin toward an evaporite trap is a result of interactions between a 400-kyr eccentricity related climatic effect superimposed upon gateway dynamics at the Atlantic–Mediterranean connections. Benthic foraminifera accurately record the steps in increasing isolation of the Mediterranean basin.

Benthic foraminifera as indicators of changing Mediterranean–Atlantic water exchange in the late Miocene

Abstract Benthic foraminifera and stable isotopes from homogeneous sediments in an Upper Miocene (Tortonian–lower Messinian) cyclic succession of homogeneous marls and sapropels from the Island of Gavdos (Greece) show significant changes in bottom-water oxygenation, presumably related to changes in the Mediterranean–Atlantic water exchange. The benthic foraminifera prove to be excellent indicators of variations in the oxygen contents of the bottom waters, even more so than the stable isotopes. Our data indicate a step-wise restriction of the Mediterranean–Atlantic water exchange resulting in increasing sluggishness of deep-water circulation. The first indication of restricted circulation is seen at 8.5 Ma, which may correspond to a severe restriction of the external zone of the Betic Strait. A second event, which had a very serious influence on the fauna in the deeper Mediterranean, occurred at 7.16 Ma. This event was presumably linked to the partial closure of the Rifian Corridor. The restricted Mediterranean–Atlantic connection also seems to have led to a gradual salinity increase and possibly to the formation of a brine in the deepest basins, thus marking the first development towards the Messinian Salinity Crisis.

Late Tortonian–early Messinian stepwise disruption of the Mediterranean–Atlantic connections: constraints from benthic foraminiferal and geochemical data

Abstract Late Miocene marine land-based sections in the Mediterranean area contain important information on the prelude to the Messinian salinity crisis (MSC). Integrated (bio-, magneto-, tephra- and cyclo-) stratigraphy allows for bed-to-bed correlations of sections throughout the Mediterranean and its borderlands, and enables correlation with extra-Mediterranean (Atlantic) sites. Benthic foraminiferal and geochemical data from five sections were compared to literature data and indicate that: (a) restriction of the Mediterranean from the Atlantic Ocean started during the late Tortonian, (b) the continuous development towards the MSC started as early as ∼7.2 Ma in the deeper parts of the basin and was enhanced by astronomical forcing and (3) the onset of the MSC must have been to a large extent related to differential vertical movements at the Betic and Rifian corridors, the Miocene connections between the Mediterranean and the Atlantic.

Benthic foraminiferal assemblages between two major extinction events: the Paleocene El Kef section, Tunisia

Abstract The development of benthic foraminiferal assemblages from the Paleocene outcrops of the El Haria Formation near El Kef, Tunisia is discussed qualitatively and quantitatively. The aim of the study is to reconstruct the paleoenvironmental evolution between the K/Pg boundary interval and the late Paleocene event, and to compare this evolution with results from other sites along the southern Tethyan margin. Eighty-four samples, covering virtually the entire Paleocene, provide a dataset that allows detailed qualitative and multivariate analysis. The benthic foraminiferal faunas indicate a complex pattern of environmental changes during the Paleocene, marked by the succession of different benthic associations. Following the K/Pg boundary event, community restoration was characterized by the gradual build-up of faunal diversity. Decreasing dominance and the entry of taxa common to normal marine, outer neritic to upper bathyal environments indicate the completion of the ecosystem restoration in Zone Plb. A highly diverse benthic foraminiferal assemblage persisted throughout the remainder of the early Paleocene into the earliest late Paleocene. At the P3a-P3b zonal transition relative sea-level lowering is evidenced by the sudden disappearance or decreasing abundance of deeper-water taxa (e.g. Anomalinoides affinis, A. susanaensis, Gavelinella beccariiformis). Neritic deposition continued into Zone P4, when trophic levels at the seafloor increased as indicated by the entry and increasing dominance of species such as Anomalinoides cf. aegyptiacus, Bulimina midwayensis, and B. strobila, which we consider to be sensitive to eutrophication. The combined effect of shallowing and the subsequent eutrophication led to the establishment of assemblages similar to late Paleocene benthic foraminiferal assemblages from Egyptian sections, some of which record the latest Paleocene extinction event. These assemblages were interpreted to be indicative of a middle neritic, highly eutrophic environment. Enhanced vertical fluxes of organic matter along the southern Tethyan margin may have resulted from intensified upwelling. This eventually led to oxygen deficiency at the seafloor. It appears that oxygen-deficient, high-productivity shelves were a common feature of the southern Tethyan margin during the latest Paleocene.

A multi-proxy record of the Latest Danian Event at Gebel Qreiya, Eastern Desert, Egypt

The Latest Danian Event (LDE) is a proposed early Palaeogene transient warming event similar to the Paleocene–Eocene Thermal Maximum, albeit of smaller magnitude. The LDE can be correlated with a carbon isotope excursion (‘CIE-DS1’) at Zumaia, Spain, and the ‘top Chron C27n event’ defined recently from ocean drilling sites in the Atlantic and Pacific, supporting a global extent. Yet, records of environmental change during the LDE (e.g. warming and sea-level fluctuations) are still rare. In this study, we focus on the micropalaeontology (calcareous nannofossils and benthic foraminifera), mineralogy and trace element geochemistry of the LDE in the Qreiya 3 section from the southern Tethyan margin in Egypt. In this section, the LDE is characterized by the occurrence of anomalous beds intercalated within upper Danian shales and marls. The event beds of the LDE are situated above an unconformity on top of a shallowing-upwards sequence deposited in a well-oxygenated outer neritic to upper bathyal marine palaeoenvironment. The lower LDE bed is barren of benthic foraminifera, but contains pyrite and fish remains, and is interpreted as an anoxic level formed during rapid relative sea-level rise. Incursion of a Neoeponides duwi (Nakkady, 1950) benthic assemblage in LDE bed II is interpreted as repopulation of the seafloor after anoxia. The sea-level cycle associated with the LDE is estimated at about 50 m maximum in the Qreiya 3 section. The environmental changes at Qreiya 3 are of supra-regional extent, since a similar sequence of events has been observed at other southern Tethyan locations. Supplementary material: A table of floral, faunal and geochemical data is available at: http://www.geolsoc.org.uk/SUP18497

Data on lithofacies, sedimentology and palaeontology of South Rifian Corridor sections (Morocco)

We provide lithological, sedimentological and micropalaeontological descriptions of 39 sections and boreholes crossing the upper Miocene deposits of the Rifian Corridor. These deposits represent the sedimentary remnants of the marine gateway that connected the Atlantic to the Mediterranean in the late Miocene. Results from these 39 sites were adopted to reconstruct the palaeogeographic evolution of the gateway presented in the associated research article (Capella et al., 2018) [1]. For each outcrop we present a synthesis of field observations, lithofacies, key sedimentological features, planktic and benthic assemblages.