Assessing pelagic palaeoenvironments using foraminiferal assemblages — A case study from the late Campanian Radotruncana calcarata Zone (Upper Cretaceous, Austrian Alps)

Abstract Two upper Campanian sections in the Austrian Alps representing the north western Tethyan biogeographic realm from either sides of the Penninic Ocean (Alpine Tethys) have been examined aiming at a high-resolution assessment of foraminiferal assemblages: the Postalm section from the Northern Calcareous Alps (southern active margin) and the Oberhehenfeld section from the Ultrahelvetics (northern passive margin). This study focuses on plankton biostratigraphy and foraminiferal palaeoecology of the Radotruncana calcarata Total Range Zone. The Postalm section displays cyclic red deposits with marls and marly limestones, while we find uniform grey marls at Oberhehenfeld. The Oberhehenfeld section from the Ultrahelvetics can be correlated stratigraphically to the Postalm section using foraminifera, calcareous nannoplankton and stable isotope stratigraphy, and provides a point of comparison from the northern margin of the Penninic Ocean. The two sections show minimal difference in faunal composition and few distinct local stratigraphic signals. Palaeoenvironmental trends from the late Campanian can be recognised relating the two sections from the Austrian Alps. The depositional water depth can be reconstructed as some 500–800 m. Plankton assemblages show a remarkable stability despite the sudden appearance and disappearance of R. calcarata, hinting at the late Campanian as a time interval of general foraminiferal stasis without significant evolutionary events. We speculate that the origin and extinction of R. calcarata are related to the prolonged evolution of ocean stratification during the Campanian from the mid-Cretaceous sluggish hothouse during a time of general slow greenhouse climate decline.


Introduction
The Campanian stage, introduced by Coquand in 1857, is the longest stage of the Late Cretaceous with a duration of more than 10 Ma (Ogg and Hinnov, 2012). Climate change is evident during this period displaying a shift from a hot greenhouse climate to more moderate temperatures (e.g., Huber et al., 2002, Hay and Floegel, 2012, Price et al., 2013. This general trend in Late Cretaceous climate history is marked by small-scale short-term palaeoenvironmental and climatic changes (e.g., Jarvis et al., 2002;Hu et al., 2012).
Durations in Earth history and related rates of change have always been a major issue for reconstructing palaeoenvironmental changes and for the understanding of fundamental processes and their application to recent global change issues. The implementation of an astronomically calibrated time scale (ATS) by Laskar et al. (1993) has, in many cases, shed light on the actual amount of time, especially in the younger part of Earth history. Thus, the ATS offers good solutions for the Cenozoic in general and a precise calibration for the Neogene (Lourens et al., 2004).
However, an accurate calibration for the Mesozoic is still largely limited to the 405 kyr orbital eccentricity cycle on a floating ATS (Laskar et al., 2004(Laskar et al., , 2011Hinnov and Ogg, 2007).
Contributing to the effort of establishing a record for this period, several studies on cyclic intervals from the Late Cretaceous and their astronomical calibration were conducted throughout the last years (Hennebert et al., 2009, Husson et al., 2011, Batenburg et al., 2012, Dinarès-Turell et al., 2013, Sprovieri et al., 2013, Locklair and Sageman, 2008. To improve biostratigraphic control, studies on Late Cretaceous foraminiferal stratigraphy provide an invaluable tool. Foraminiferal biozonation within the Campanian stage has been subject to discussion on many occasions. The reliability of certain taxa as zonal markers has been reviewed and reassessed in the last years, for instance Globotruncana ventricosa. This species is reported to be diachronous in the stratigraphic record and was in the following replaced by Contusotruncana plummerae (Petrizzo et al., 2011) as an index fossil for the mid-Campanian.

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ACCEPTED MANUSCRIPT , Hennebert et al., 2009and Odin, 2010, suggest similar durations for this interval based on various evidence), and its distinct morphology makes this species a most favourable tool in Late Cretaceous biostratigraphy. Huber et al. (2008) indicate a stratigraphic age of 76.18 to 75.71 Ma for the R. calcarata TRZ (determined by chronostratigraphic correlations based on magnetostratigraphy) (Anthonissen and Ogg, 2012). In contrast, Gardin et al. (2012) indicated a duration from 75.785 (base) to 74.190 Ma (top) based on bio-magnetochronology from the Gubbio area, Italy. Provisionally, we combined the Anthonissen and Ogg (2012) top age datum with the published cyclostratigraphic duration , ending in a most probable minimum age range from 75.71 to 76.51 Ma.
The study of Wagreich et al. (2012) in the Austrian Alps focused on the astronomically calibrated duration and the fit to a floating timescale, thus, it gave a framework to examine late Campanian foraminiferal communities in stratigraphically well defined sections. During this interval, the ongoing convergence of Eurasia and Africa, tectonically controlled active margin subsidence (Wagreich, 1993) and marine transgression caused fully marine conditions in the study area at the margins of the Penninic Ocean (Alpine-Tethys) within the north western Tethyan biogeographic realm. Cyclic pelagic sequences on the southern active and flysch -type and hemipelagic to pelagic deposits on the northern passive continental margin of the Penninic Ocean are preserved (e.g., Butt, 1981, Wagreich, 1993. This work focuses on foraminiferal communities present throughout the R. calcarata TRZ. By investigation of two outcrops in Austria -each representing opposite margins of the Penninic Ocean -a palaeoenvironmental reconstruction of foraminiferal communities during a cooling greenhouse climate (Hay and Floegel, 2012) on the brink of the late Campanian/early Maastrichtian cooling event , Friedrich et al., 2009) is possible.
The geological setting of POST is discussed in Wagreich et al. (2012). The bathyal pelagic to  (Wagreich, 1993), at the southern margin of the Penninic Ocean ("Alpine Tethys" of Stampfli et. al., 2002;Handy et al., 2010). The Gosau Group of the NCA can be separated in the Lower and the Upper Gosau Subgroup. The Lower Gosau Subgroup predominantly displays shallow water deposits of Turonian to Santonian age deposited in pull-apart basins alongside an oblique subduction zone (Wagreich, 1993). After a short phase of tectonically induced uplift of the NCA, rapid subsidence processes set in. Hemipelagic to pelagic, and in some areas turbiditic sedimentation of late Santonian/Campanian to Eocene age (Krenmayr, 1999), defines the Upper Gosau Subgroup.
POST is part of the Nierental Formation and reflects a northward deepening slope of at least 500 metres water-depth (Wagreich and Krenmayr, 2005). The deposits at this section can be defined as a Cretaceous Oceanic Red Bed (CORB), indicating well oxygenated bottom waters (Hu et al., 2005, Wagreich andKrenmayr, 2005).
OBH is located on the European continental slope, along the northern margin of the Penninic A C C E P T E D M A N U S C R I P T

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Ocean (Faupl and Wagreich, 2000). The Ultrahelvetic units have their origin within the Helvetic palaeogeographic realm. In the north, continental shelf deposits can be found. Abyssal palaeo water-depths prevail to the south.
The two sections display different sediment accumulation rates; at POST 20mm/kyr are estimated, while OBH displays only 3mm/kyr (Neuhuber et al., 2007. Figures 3 and 4 show sketches of the stratigraphical and lithological framework at POST and OBH. # Fig. 3 # Fig. 4 3. Methods and Material 3.1. Sampling The exposed R. calcarata TRZ was sampled following a biostratigraphic investigation of the two sections yielding Upper Cretaceous deposits , Neuhuber et al., 2015. As POST shows distinct cycles, samples were taken bed-by-bed, no standard distance between samples was applied. OBH displays no visible cycles; therefore a standard sample distance of 10 cm was applied.
At POST the R. calcarata interval displays a thickness of approximately 16 metres -25 samples from marls were examined. OBH exhibits a 2.4 metres thick R. calcarata Zone. 34 samples from this interval were processed for qualitative foraminiferal data.
Marl and marlstone samples were dissolved with hydrogen peroxide and the tenside Rewoquad ©.
Samples and microslides are stored in the Earth science collections at the University of Vienna, Department of Geodynamics and Sedimentology.

Qualitative data
Qualitative data (i.e. presence -absence data) were assessed at POST and OBH to unveil local biostratigraphic events and to estimate species richness in these two localities. The use of qualitative data enforces index species in ecological investigations, because index species are rare and often underrepresented in quantitative analyses because overwhelmed by abundant, not indicative species.

Preservation of microfossils
With few exceptions, the state of preservation of foraminifera from POST can be considered as moderate to poor. Most spiral and trochospiral forms (both planktic and benthic) appear with fully intact tests. Elongated forms, especially benthic taxa, frequently appear fragmented. Samples from OBH show an overall slightly better preservation.

Statistical methods
Samples from POST and OBH were clustered hierarchically using Ward's (1963) method requiring Euclidian distances. Furthermore, a Principal Components Analysis (PCA) was applied to help for defining the palaeoenvironmental characteristics of POST and OBH (Davis 1986, Harper, 1999. Principal components (PC) determined in this analysis are variables accounting for most of the variance in the dataset. A biplot sows the original axes, thus making the interpretation of palaeoenvironmental trends possible (Hammer et al, 2001).
Trends and changes in β-diversity (the diversity between samples, as well as the global β-diversity) of benthic foraminifers along POST and OBH were examined as described in Harrison et al. (1992), with Statistical analyses were conducted using the program packages R (R Development Core Team, 2015) and PAST (Hammer et al, 2001).

Taxonomic remarks
The state of preservation did not allow the definite taxonomic assignment of some individuals at species level. Thus, morphogroups for certain taxa were established.
Some double keeled globotruncanid taxa (Globotruncana arca, G. lapparenti, G. orientalis) have subsequently been merged into one group (G. arca-lapparenti-orientalis) as morphological transitions were observed and the state of preservation did not always permit an assignment to a species. In general, planktic foraminifera taxonomy follows Robaszynski and Caron (1995), Nederbragt (1991) and Premoli Silva and Verga (2004).
Benthic foraminifera were assigned to groups, predominantly following the parameters applied in A C C E P T E D M A N U S C R I P T Alegret et al. (2003) (following the works of Corliss and Chen,1988, Corliss, 1991, Nagy, 1992, based on habitat preferences and the mode of benthic life. Information on morphotypes of agglutinated foraminifera also follows Kuhnt and Kaminski (1990), Kaminski and Gradstein (2005),  and Nagy et al. (2009). As far as applicable, a classification of benthic foraminifera referring to their oxygenation preference, the "Benthic Foraminifera

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Oxygenation Index" (BFOI) (Kaiho, 1994) and general information on oxygenation preference of taxa provided in Murray (1991Murray ( , 2006  patelliformis. All of the above constantly appear throughout both sections. Globotruncanita subspinosa was frequently identified in both localities. Globotruncanella havanensis can be

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reported only from a single sample in OBH. Specimens displaying transitional forms between Contusotruncana fornicata and C. plummerae were frequently found throughout both sections.
Furthermore, OBH displays a higher abundance of biserial taxa than POST. Neither of the sections exhibits a high diversity in this group. The most abundant biserial form is Heterohelix globulosa in POST and Pseudotextularia nuttalli in OBH. Heterohelix striata frequently occurs in both sections, Heterohelix labellosa is sparsely found (Fig. 5, Fig. 6). SEM images of biostratigraphically relevant taxa are provided in Figure 7. Dentalina spp. also shows the highest taxonomic diversity with 9 species (Table 2).
Benthic foraminifera morphogroups and habitat preference Benthic foraminiferal taxa were assigned to their preferred mode of life and clustered in groups in respect of their habitat preference (Table 3).
Epifaunal calcareous or agglutinated taxa, infaunal calcareous or agglutinated taxa and calcareous or agglutinated taxa that do not depict a clear preference between in-or epifaunal habitats can be distinguished.
#Table 3 Counting species richness in reference to the preferred mode of life (habitat preference) can give information on the palaeoecological regime. Table 4 shows the absolute numbers of species per category. Figure 8 shows the relative distribution of foraminiferal species by habitat preference.
ACCEPTED MANUSCRIPT different in their composition to the former clusters, inducing the strong separation in cluster analysis ( Fig. 9). Spiroplectinella dentata dominates in Cluster f in combination with Globorotalites multiseptus, Lenticulina spp. and Cribrostomoides ssp..The latter species together with Marginulina sp. are prominent elements of Cluster g, that is dominated by Eponides beisseli and Gaudryina pyramidata.

Planktic foraminifera biostratigraphy
In both sections, the studied interval starts in the uppermost part of the G. ventricosa partial range zone (Robaszynski and Caron, 1995). This zone was first introduced by Dalbiez (1955)  The R. calcarata total range zone (TRZ) was first defined by Herm (1962). This interval was placed originally in the uppermost Campanian (e.g. Caron, 1985;Sliter, 1989 Chacón et al. (2004).
Globotruncanita elevata is present in both sections investigated in this study. POST seems to display the LO of Gta. elevata. At OBH, this taxon appears to be present throughout the R. calcarata interval. Globotruncanita stuartiformis and Gta. subspinosa, both present in either section, exhibit a constant appearance in OBH.
No specimen of Macroglobigerinelloides could be identified at POST. OBH displays 2 taxa assigned to this genus. In this time interval, members of Macroglobierinelloides usually appear in the size fractions smaller than 150 µm. The same applies principally to rugoglobigerinids, however, the latter could not be identified in either of the sections.
Other studies on the R. calcarata interval also identified G. rosetta (Salaj, 1974, Robaszyinski and Mzoughi, 2010 from Tunisia), G. aegyptiaca (Chacón et al., 2004, from Spain) and G. bulloides (e.g. Janoschek, 1968, from the Austrian Alps). These taxa could not be identified in either of the two sections examined in this study.

Benthic foraminifera and palaeoenvironment
POST and OBH yield very similar benthic foraminifera communities. Both display elements of "Deep Water Agglutinated Foraminifera" (DWAF) assemblages (Kuhnt and Kaminski, 1990) as well as elements assigning to higher productivity environments represented by lenticulinids, dentalinids and nodosariids.
are not exclusively, but frequently found in OBH, and are indicative taxa of a "Flysch-type" assemblage.
POST yields only slightly more infaunal morphotypes than morphotypes depicting an epifaunal habitat preference. At OBH the infaunal/epifaunal ratio in species counts is balanced. Thus, following Widmark and Speijer (1997), the assemblages at POST and OBH can be described as "Deep Bathyal Assemblages". POST and OBH can therefore be addressed as upper to middle slope settings of some 500 to 800 metres water depth.
In the mean, we could identify 18 different benthic foraminiferal species per sample at POST and 15 at OBH.
The benthic foraminifera Reussella szajnochae, a biostratigraphic marker for the Upper Cretaceous, has been identified in both sections. Stratigraphically indicative agglutinated species, such as Caudammina gigantea, could not be unanimously identified. For the better understanding of the palaeoecology of the two sections, it is also necessary to examine the taxa in respect to their environmental preference and ecological characteristics. Table 5 provides a listing of taxa indicative for each cluster (except for c)) determined by hierarchical clustering (see Fig. 9).

5.1.2.b. Differences in palaeoecological conditions inferred from benthic foraminifera habitats
By the distribution of agglutinated and calcareous foraminiferal species and their habitat preference we can assume certain environmental characteristics for both sections.
Calculating a PCA, the amount of benhic foraminiferal species grouped by habitat preference confirms that POST and OBH depict very similar palaeocommunities (Fig. 10a, b).
Comparing the two sections, we find a predominantly homogenous dataset at POST, while data from OBH appear more scattered.
POST: Species richness (-diversity) and the global -diversity (diversity between all samples:  global = 0.174) is lower than at OBH. Though POST is considered to be a typical CORB deposited in (highly) oxic bottom waters (Wagreich and Krenmayr, 2005;Wagreich et al., 2009), a diverse DWAF assemblage was identified. Only at the base and the top of the R. calcarata section calcareous species prevail in numbers, other parts of this section show a mixed agglutinated and calcareous benthic foraminifera community. According to the low amount of epifaunal calcareous foraminifera species and the continuously high proportion of infaunal calcareous species in this section, dysoxic conditions as a driving factor behind the migration to infaunal habitats should be taken into consideration (Koutsoukos and Hart, 1990, Jorissen et al., 1995, Van der Zwaan et al., 1999, Gooday, 2003, Murray, 2006. Furthermore, the presence of Gaudryina can be associated with dysoxic conditions (Holburn et al., 1999). Consequently, considering species indicative for the calculation of the "BFOI" (Kaiho, 1994), we sparsely find benthic species requiring oxic environments at POST. At the lowermost parts of the R. calcarata Zone and at the top, species like Cibicides or Osangularia occur together with indicators for high productivity.

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The hierarchical clustering after Ward sees the lowermost as well as the uppermost parts of the section assign to Cluster g (Fig. 10c). This cluster seems to be defined by taxa adapted to dysoxic environments. Throughout the stratigraphically older part of POST, Spiroplectammina and The fauna of the younger section part belongs to clusters e and g. Taxa like Gaudryina, Eponides, Reussella and Cribrostomoides define these clusters and seem to be indicative for a stable upper to middle slope environment. This assumption is also supported by low values for -diversity between samples from POST (see Fig. 10c).
Resuming, we can interpret POST as a bathyal, distal slope environment displaying dysoxic conditions.

OBH:
Higher species richness (-diversity) and -diversity over all section samples ( global = -diversity between succeeding samples are also more intense than at POST. Compared to POST, this section shows a higher frequency of "epifaunal to infaunal calcareous" taxa. These morphogroups are represented by species like Lenticulina or Dentalina, representing many opportunistic high-productivity taxa. Although this section depicts a higher number of benthic foraminifera species, only a mean of 15 different benthic taxa per sample could be found that is also documented in the high ß -diversities between samples. However, in addition to indicators for oxygen-depleted environments, OBH also yields some taxa

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requiring oxic conditions such as Cibicides sp. or Ramulina sp.. Groups obtained by cluster analysis show a fluctuation beween clusters a, b and d. Only samples OBH 5/30 and OBH 5/5 were assigned cluster g and e. Nothia sp.1 can, according to cluster analysis, be seen as a determining element for the clusters a and b. Cluster d shows strong influence of Gaudryina pyramidata, Eponides beisseli and Reussella szajnochae and could therefore hint to an occasionally dysoxic environment.
Considering the combined Q-and R-mode cluster analyses, it can be reasonably assumed, that samples from OBH record an instable slope environment. We find evidence for high productivity and in some samples evidence for a suboxic to dysoxic regime with high nutrient availability (also visible in the distribution and peculiarity of factor loadings inferred from the PCA, see Fig. 10c).
The presence of species requiring oxygen-saturated environments could refer to frequent faunal ingression or transport downslope from environments with better oxygen saturation. #Fig.10

The Penninic Ocean as a part of the Tethys ocean system
The foraminiferal fauna of the two sections from the northern and southern margin of the Penninic Ocean, originally a few hundred kilometres apart in north-south direction, also sheds light onto the palaeoceanography and the palaeobiogeographic evolution at the north-western Tethys.
Biogeographically, both sections clearly belong to the Tethyan pelagic realm, characterized by abundant and diverse globotruncanids. The Tethyan realm involves the whole European margin, i.e.
Connections to the Neotethys Ocean(s) to the south are, at least in the late Campanian, wide and deep enough (e.g. Handy et al., 2010) to facilitate faunal exchange from Italy and Tunisia to the Penninic Ocean. Although the Penninic Ocean in the Eastern Alps transect already started to close (subduct?) since the Aptian-Albian (Wagreich, 2001, Mandic andLukeneder, 2008), in the late Campanian sea ways were unrestricted for faunal exchange.
The benthic foraminiferal marker for the Campanian, Bolivinoides draco draco, is missing in our sections, but generally known from other Campanian sections of the NCA and the Ultrahelvetics (e.g. Oberhauser, 1965, Hradecká andLobitzer, 2003). The absence of this taxon at Post and OBH

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is not necessarily related to lacking faunal exchange, but presumably to environmental conditions (such as water depth). Overall, we can reconstruct a typical late Campanian foraminiferal fauna. This is also different from results concerning the Cenomanian-Turonian boundary interval in the Ultrahelvetics, where Gebhardt et al. (2010) speculated in terms of a restricted, "relic" biogeographic realm in the Penninic, with a semi-closed basin where global high productivity events cannot be evidenced based on foraminiferal assemblages.

Implications for sea-level
No detailed, clear-cut sea level record exists for the R. calcarata Zone. Given the two most recent and detailed sea-level curves for the Late Cretaceous, i.e. the data published by Miller et al. (2005a, b) and Haq (2014), the long-term trend is rather stable, but indicates high sea level (more than 200 m above present day sea-level according to Haq, 2014). In the short-term record, i.e. at 3 rd order cycles and sequences, Haq (2014)  Minor relative sea-level changes may be indicated by the presence of shallow water taxa in POST, i.e. Spiroplectammina spp.. However, especially in the Postalm section at the active Austroalpine margin, regional sea-level changes are possibly controlled by tectonics, but nevertheless not well expressed in our foraminiferal data. Radotruncana calcarata seems to show no relation to sea-level stands as well as no relation to palaeoclimate, as also expressed by its independent evolution in regard to Milankovitch-type climate cycles .
Despite the influence of minor sea-level changes and other palaeoecological events, i.e. as expressed by minor carbon isotope peaks Wendler, 2013) or geochemical proxy data (Neuhuber et al., 2015), or the clear-cut Milankovitch cyclicity of the sections, the foraminiferal assemblages of the calcarata Zone in the Austrian Alps show remarkable stability. It can be concluded that, although major changes and cycles (sequences) in the range of several Ma may influence foraminiferal communities, those short-term changes within the 800 kyr calcarata Zone did not significantly influence or alter the foraminiferal communities in the bathyal realm of

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water depth between 500-800 metres. There are only some subtle changes, easily overlooked, and/or challenging to interpret, i.e. the occurrence of Spiroplectammina at POST or the changes in the dominant morphogroups in benthic foraminifera.

The R. calcarata Zone as interval of palaeoenvironmental stability in the northwestern Tethyan realm ?
The late Campanian was in general identified as a time of low planktonic foraminifera turnover (Premoli Silva and Sliter, 1999). During the 806 kyr long R. calcarata interval we experience no major change in neither benthic nor planktic foraminiferal communities. This interval does not display any FO in planktic taxa except R. calcarata itself. G. elevata becomes a rare faunal element in POST, probably depicting its local LO, while it seems to be present throughout OBH.
Furthermore, no evolutionary trend or any noticeable environmentally influenced change in the composition of foraminiferal assemblages, neither planktic nor benthic, was observed. Isotopic data, assessed by Wagreich et al. (2012), give clear signals for Milankovitch cycles. Three carbon isotope excursions visible during the calcarata interval correlate well to carbon isotope data recorded by Jarvis et al. (2002).
Therefore, we interpret the R. calcarata Zone in general to show very stable conditions in terms of palaeoecology and planktonic foraminiferal evolution. We can consider a palaeoecological stasis, or at least presume a certain stability in foraminiferal communities despite the general cooling trend of the Cretaceous greenhouse.
The development of the zonal marker itself can be seen as the only major event in planktonic foraminiferal evolution, not paralleled by any other evolutionary event in planktonic foraminifera, In terms of evolution, R. calcarata cannot be considered the result of the stuartiformis-elevatasubspinosa progression, but has its origin directly in an archaeoglobigerinid ancestor (Longoria and VonFeldt, 1991), the sudden appearance and disappearance after only 806kyr seems puzzling as no

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ACCEPTED MANUSCRIPT environmental proxies regarding palaeoclimate or sea-level coincide directly neither with the appearance nor the extinction of this taxon, and no species in a line of succession of R. calcarata are known.
Here we present an alternative hypothesis for the evolution of R. calcarata, based on the principal characteristics of the Cretaceous ocean system. During the Cretaceous several factors provoked an intense stratification of the ocean's water masses, for instance Ocean Anoxic Events and (mutual) sea level highstands Watkins, 1992, Price et al., 1998;Friedrich et al., 2012). Using the difference in oxygen isotope values of benthic and planktic foraminifera, highly stratified water masses can be reconstructed for the mid-Cretaceous, whilst during the late Campanian and towards Maastrichtian the deep-water circulation seems to have increased and accordingly, we find a decrease in the difference in oxygen isotope values (e.g., Norris et al., 2001, Otto-Bliesner et al., 2002, Hasegawa et al., 2012. Evidence for stable surface and bottom water temperatures in the late Campanian is presented in Jung et al. (2013), following the investigation of Nd isotope signatures.
This period (79-74,5 Ma) is characterised by stable environmental conditions and was followed by a cooling trend in the latest Campanian (Friedrich et al., 2012). Considering the chronostratigraphic framework given by Huber et al. (2008) for the R. calcarata Zone (76.18 to 75.51 Ma), the possible impact of changes in ocean-water properties on highly specialised taxa like R. calcarata should be taken into account.
Changes in the vertical gradients and properties of the water column and the presence of regional intermediate and deep-waters (e.g. Voigt et al., 2013) could open up ecological niches for deeper dwelling planktic foraminifera. Considering the possibility of a reticulate evolutionary pattern (see Hohenegger, 2014) for this group of single keeled globotruncanids, the short stratigraphic range of R. calcarata could be caused by the opening and closing of an adaptive zone during palaeocanographic, i.e. water mass reorganisation (that also can be understood as the emergence of an ecological opportunity, permitting the further specialisation or development of a taxon) for this species, the latter causing the sudden extinction.
Developments in planktonic foraminiferal morphology, particularly the elongation of chambers or the development of tubulospines, is generally understood as a reaction to environmental change (Leckie, 1989, Hart, 1980, Hart, 1999, Coccioni et al., 2006. Adaptations in schackoinids and leupoldinids might be related to severe changes in the Cretaceous hothouse ocean dynamics, resulting in black shale events and widespread anoxia, and can therefore be seen as an adaptation to changes in oxygen availability (e.g.: Magniez-Jannin, 1998, Coccioni et al., 2006. A striking similarity in morphological traits is known from the genus Hantkenina. The gradual evolution and changes in the Hantkenina linneage follow and adapt to to climatic changes throughout the Eocene; Evidence from isotopic data suggests a shift from a planktonic deep marine habitat to an adaptation M A N U S C R I P T

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to shallow water depths close to the surface (Coxall et al., 2000). It is discussed that the development of tubulospines in hantkeninids correlates to the Eocene cooling event and that these adaptations were favourable in order to remain in the preferred position in the water column (Coxall et al., 2003, Pearson andCoxall, 2014).
The development of R. calcarata also coincides with significant changes in ocean temperatures i.e.
the late Campanian/ early Maastrichtian cooling event , Friedrich et al., 2009

Conclusion
A well resolved assessment of foraminiferal communities in the Austrian Alps during the R. Although classified as CORB, the Postalm foraminiferal assemblages do not indicate oxic bottom waters, but a dysoxic palaeoenvironment, and thus questions the strict association of CORBs with highly oxic bottom waters as published by, e.g., Hu et al. (2005).
Though qualitative data gives only insight into the presence or absence of certain taxa, we can expect the continuous presence of a taxon -within several samples of a succession -to be indicative for a common faunal element of the section examined. During the ca. 800 kyr duration of the calcarata Zone, a remarkable stability in the taxonomic composition of foraminiferal assemblages has been recognised, with only minor and local perturbations. This exemplifies a longer interval of palaeoecologic stability in foraminiferal communities in the northwestern Tethyan realm during the late Campanian. Based on these data we speculate on the evolution of R. calacarata within an opening and closing adaptive zone within changing water masses of the Late Cretaceous.    Fig. 3 and 4).     factor loadings for the first three principal components explaining 86.8 percent of variance. PC 1 mainly explains the influence of habitat group "E". The influence of infaunal agglutinated and infaunal calcareous taxa is best explained along PC1. Higher values in PC 1 can be found at POST, while OBH is rather influenced by PC 2 (predominantly defining the relation between epi-and infaunal calcareous taxa). PC 3 plays a minor role in the explanation of palaeoenvironments and predominantly explains the influence of the epifaunal calcareous, "A", and epifaunal agglutinated group, "D". c.: explains the factor loadings per samples spot, the units based on Qand R-mode cluster analysis, as well as changes in ß-diversity over the sections. Comparing the two sections, POST constantly shows a stronger influence of infaunal calcareous taxa, "C" (expressed in high loadings of PC1).  A C C E P T E D M A N U S C R I P T OBH_0b  OBH_1  OBH_1b  OBH_2  OBH_3  OBH_4  OBH_5  OBH_05/0A   OBH_6  OBH_7  OBH_8  OBH_9  OBH_10  OBH_11  OBH_12  OBH_13  OBH_14  OBH_15  OBH_16  OBH_17  OBH_18  OBH_19  OBH_20  OBH_21  OBH_22  OBH_23  OBH_24  OBH_25  OBH_26  OBH_27  OBH_28  OBH_29 OBH_30 OBH_31