Integrated analyses of multiple groups of microfossils are frequently performed to unravel the palaeoenvironmental evolution of subsurface coastal successions, where the complex interaction among several palaeoecological factors can be detected with benthic assemblages. This work investigates the palaeoenvironmental resolution potential provided by benthic foraminifera and ostracoda within a Pleistocene lagoonal succession of the Romagna coastal plain (northern Italy). Quantitative approaches and statistical techniques have been applied to both groups in order to understand the main factors that controlled the composition of assemblages and compare the palaeoecological record provided by single fossil groups.
The two faunal groups are characterized by the high dominance of
opportunistic species (
In this case, the higher abundance along the stratigraphic succession, the higher differentiation of the assemblages, and the well-defined relationship between taxa and ecological parameters determine Ostracoda as the most reliable fossil group for precise palaeoenvironmental reconstructions. Nevertheless, benthic foraminifera indicate palaeoenvironmental stress and can be used to refine the environmental interpretation in the presence of monospecific ostracod assemblages.
The use of microfossils as palaeoenvironmental proxies is quite common in geological studies since they are sensitive to a great number of ecological factors. Benthic foraminifera and Ostracoda are widely applied for stratigraphic and palaeoecological purposes since both of them have (i) an extremely wide distribution, from continental water bodies to the deep ocean; (ii) a short reproductive cycle that allows them to react quickly to environmental changes; and (iii) a hard shell that guarantees a high preservation potential in sediments (Murray, 2006; Rodriguez-Lazaro and Ruiz-Muñoz, 2012). These characteristics also make them suitable for ecological studies in modern environments, especially in the paralic realm, where benthic foraminifera and ostracoda are particularly abundant. Special attention has been reserved for lagoons because today their fragile equilibrium is endangered by a series of factors, such as anthropogenic pollution and climatic changes. Composition and structure of assemblages have been described in relation to many ecological parameters, allowing the use of recent assemblages as “modern analogues” of fossil associations.
Benthic foraminiferal assemblages are determined by multiple factors, which sometimes create stressed conditions. Benthic foraminifera have been proved to be excellent environmental bio-indicators in paralic environments, such as estuaries and lagoons (Coccioni, 2000; Frontalini et al., 2009; Armynot du Châtelet and Debenay, 2010). Under stressed conditions, these microorganisms modify the community structure and develop a series of peculiar morphological abnormalities of the test (Alve, 1991). Abundant studies have been focused on the response of benthic foraminifera to anthropogenic pollution (Yanko et al., 1994; Alve, 1995; Armynot du Châtelet and Debenay, 2010; Frontalini and Coccioni, 2011), but foraminiferal abnormalities can also occur from natural stresses, such as extreme values of salinity, nutrients, oxygen, or very rapid changes in ecological parameters (Scott and Medioli, 1980; Almogi-Labin et al., 1992; Geslin et al., 2002). High concentrations of aberrant benthic foraminifera also occur in fossil assemblages, even though only a few cases are reported in the literature and are attributed to low or oscillating salinity (Bik, 1964; Bugrova, 1975; Wang et al., 1985). As suggested by Boltovskoy et al. (1991), the presence of highly deformed assemblages in both modern and fossil environments is not related to a single factor, but it may be produced by a series of ecological parameters. Although assessing which is the main ecological factor that led to the creation of deformities is generally difficult, the relative abundance of aberrant benthic foraminifera is a good proxy for palaeoenvironmental stress (Geslin et al., 2002).
Nevertheless, benthic foraminifera could be absent in environments characterized by strong fluctuations in salinity, organic matter, and hydrodynamic conditions (Laut et al., 2016; Pint and Frenzel, 2017). Conversely, ostracoda are abundant from freshwater to hyperhaline environments and guarantee a great continuity of palaeoecological information (Rodriguez-Lazaro and Ruiz-Muñoz, 2012). Even if paralic environments with unstable environmental parameters are often characterized by oligotypic assemblages dominated by opportunistic taxa, rare species provide reliable information (Slack et al., 2000). Salinity is considered one of the major controlling factors affecting the distribution of ostracoda; therefore, this group is often applied for palaeosalinity reconstructions (Gliozzi and Mazzini, 1998; Marco-Barba et al., 2013; Amorosi et al., 2014). However, a combination of factors usually affects benthic assemblages in transitional environments, determining the degree of confinement, defined as the time of renewal for marine waters (Guélorget and Perthuisot, 1983). Ostracod assemblages can be indicative of a wide range of parameters, including the salinity and the degree of isolation from the sea, as it has been recently demonstrated by Salel et al. (2016) in the Gulf of Lion and Ebro Delta (western Mediterranean).
Both benthic foraminifera and ostracoda can provide a wide range of palaeoenvironmental information (type of substrate, salinity, organic matter content, oxygen concentration, etc.), but each group has peculiar characteristics that make it more suitable as a proxy for specific conditions. Within back-barrier sediment successions, the interaction of sediment supply, accommodation space, and eustatic oscillations produces subtle environmental changes detectable by the combined application of benthic foraminifera and ostracoda. However, palaeoenvironmental reconstructions performed on both groups are rarely applied and mostly based on qualitative or semi-quantitative approaches (e.g. Rossi et al., 2011; Trog et al., 2013), whereas quantitative analyses and statistical methods are often applied to only a single fossil group (e.g. Marco-Barba et al., 2013; Vaiani and Pennisi, 2014). Integrated analyses of multiple fossil groups are scarcely available in the literature and they are mostly restricted to the postglacial period (e.g. Cearreta et al., 2003; Amorosi et al., 2014).
The aim of this work is to compare the palaeoenvironmental resolution potential of Foraminifera and Ostracoda through multivariate analysis of fossil assemblages within a Pleistocene short sedimentary succession of the Po River coastal plain. Composition and structure of assemblages have been analysed in detail in order to investigate the ability of each group to highlight specific palaeoecological conditions within the same stratigraphic interval.
The Po River coastal plain is the easternmost part of the Po Plain (Fig. 1), a foredeep system bounded by the Alps to the north and the northern Apennines to the south, filled with Pliocene–Quaternary sediments with a maximum thickness of 7 km in the major depocenters (Pieri and Groppi, 1981; Castellarin and Vai, 1986). Geophysical investigations have evidenced that the Po basin is deformed by diffuse north-verging thrusts, but the late Quaternary sediments were deposited under relatively undisturbed conditions (Regione Emilia-Romagna and ENI–AGIP, 1998).
Detailed subsurface studies on the Po coastal plain revealed a cyclic facies architecture of transgressive–regressive (T–R) cycles formed by alternated alluvial and wedge-shaped coastal deposits (Amorosi and Colalongo, 2005). Integrated pollen analyses and radiocarbon dates performed on the three uppermost T–R cycles allowed their attribution from Marine Isotope Stage (MIS) 7 to 1 (Amorosi et al., 1999a, 2004). Specifically, thick alluvial sediments including scarce pollen of non-arboreal taxa are related to cold conditions, whereas abundant deciduous and broadleaved pollens are included within back-barrier and shallow marine deposits formed during interglacial periods (MIS 1, 5, and 7; Amorosi et al., 1999a, 2004). This suggests that T–R cycles were formed in response to glacio-eustatic fluctuations with a frequency of 100 kyr, determined by the Milankovitch eccentricity-driven cycles (Lisiecki and Raymo, 2005).
The two most recent coastal wedges show a retrogradational stacking pattern of coastal plain and littoral facies, interpreted as a landward-migrating barrier–lagoon–estuary system during the transgressive phase, followed by deltaic and coastal progradation related to high stand conditions (Amorosi et al., 2004).
Lagoonal sediments in the subsurface of the Po River coastal plain are commonly developed within back-barrier facies associations. These are generally thin (1–2 m) at the base of Holocene (MIS 1) and Eemian (MIS 5e) transgressive–regressive wedges and are truncated at the top by an erosive ravinement surface that marks the passage to transgressive barrier facies (e.g. Amorosi et al., 2004; Campo et al., 2017). In contrast, well-developed paralic successions are locally present close to the innermost palaeoshoreline position reached at the peak of the MIS 1 and 5e transgressions (Dinelli et al., 2013; Campo et al., 2017) or below the Eemian units, representing the sedimentary response to the MIS 7 sea level variation (Amorosi et al., 1999a; Vaiani and Pennisi, 2014). Specifically, below the two uppermost T–R cycles, coastal and paralic deposits attributed to MIS 7 were recognized at some locations of the Po River coastal plain at more than 140 m core depth (e.g. Fiorini and Vaiani, 2001; Bondesan et al., 2006). The age attribution is supported by the stratigraphic position and the comparison with Mediterranean pollen zones, which limit the deposition of this interval during the late Middle Pleistocene (Amorosi et al., 1999a).
Location map of core 223 S12.
The analysed succession is part of core 223 S12, drilled approximately 14 km inland from the modern shoreline near the city of Ravenna (Fig. 1) by wireline perforation, which guaranteed a continuous and undisturbed core stratigraphy, with recovery percentages higher than 90 %. This core reached a depth of 170 m and includes two paralic to shallow marine intervals formed in response to MIS 1 and 5.5 interglacials and a lagoonal interval attributed to MIS 7; these are alternated by continental deposits formed during glacial periods (Amorosi et al., 1999b, 2004). The detailed distribution of benthic foraminifera in the upper 130 m of this succession, including the MIS 1 and 5.5 interglacials, is reported in Fiorini (2004); this work is focused on the lower portion of this core, between ca. 165 and 160 m core depth, dated to the MIS 7 (Amorosi et al., 1999b), which has not been studied in detail.
Micropalaeontological analyses were performed on 19 sediment samples of ca.
150 g that were treated with a standard method as reported, for instance,
in Amorosi et al. (1999b) and in Fiorni and Vaiani (2001): (i) dried for 8 h
at 60
Identification of taxa was supported by original descriptions (Ellis and Messina, 1940). Furthermore, several reference works focusing on detailed taxonomy of Elphidiidae (Hansen and Lykke-Andersen, 1976; Hayward et al., 1997) and on the Mediterranean benthic foraminifera (e.g. Jorissen, 1988; Cimerman and Langer, 1991; Fiorini and Vaiani, 2001; Milker and Schmiedl, 2012) have been used for specific attribution of benthic foraminifera. Additional taxonomical remarks are reported in Appendix A. Due to the remarkable presence of deformed benthic foraminifera, the foraminiferal abnormality index (FAI, defined as the percentage of aberrant specimens in each sample) was calculated (Frontalini and Coccioni, 2008). Morphological abnormalities of tests were identified following Yanko et al. (1994), Geslin et al. (1998), and Coccioni (2000). Ostracod identification is also supported by works of Bonaduce et al. (1975), Breman (1975), Athersuch et al. (1989), Henderson (1990), and Mazzini et al. (1999). Photographs of specimens were obtained using a scanning electron microscope JEOL JSM 5200 at the Department of Biological, Geological and Environmental Sciences of the University of Bologna. A detailed analysis of the most common benthic foraminifera has been carried out due to their high morphological variability, and selected images are depicted in Plates 1 and 2.
Data matrices for multivariate statistical analyses were produced considering
the most abundant taxa, with a frequency
SEM
photomicrographs of some of the most common benthic foraminiferal species
found in the studied succession. Scale bar
SEM
photomicrographs of selected Elphidiidae and individuals affected by
morphological abnormalities of the test. Scale bar
A Q-mode cluster analysis, using an unweighted pair group method with
arithmetic mean algorithm (UPGMA), was performed in order to group samples
with similar fauna. To further evaluate the null hypothesis of no variability
in the faunal composition between benthic assemblages, a one-way analysis of
similarities (ANOSIM; Clarke, 1993) with 9999 permutations was carried out.
This test compares the ranks of distances within groups with ranks of
distances between groups: if the dissimilarity between groups is greater than
that within groups,
To characterize the biodiversity of assemblages, four faunal parameters were
calculated: (1) species diversity (
Multivariate statistical analyses and calculation of diversity indices were carried out using the software PAST (PAlaeontological STatistic – version 3.10 by Hammer et al., 2001) as specifically designed for palaeontological analyses.
All 16 samples included abundant ostracod valves and were counted for quantitative analysis. Due to the low abundance of benthic foraminifera at the base (163.95–163.50 m core depth) and at the top (160.85–160.55 m core depth) of the studied interval, only 11 samples were quantitatively analysed to determine the benthic foraminiferal fauna.
A total of 4756 benthic foraminifera, belonging to 36 taxa, have been counted
and identified between 163.50 and 160.95 m core depth (Table S1 in the
Supplement). The high morphological variability shown by Elphidiidae and
Species richness (
Diversity indices (species diversity, dominance, Shannon–Weaver, and Pielou's evenness indices) calculated for benthic foraminifera and ostracoda in each sample. The foraminiferal abnormality index (FAI) for benthic foraminifera is included.
Results of the one-way ANOSIM analysis based on diversity indices (Euclidean distance) and faunal composition (Bray–Curtis distance) between the two benthic foraminiferal and the three ostracod assemblages defined by Q-mode cluster analysis (Fig. 2).
Similarity percentage (SIMPER) analysis performed on benthic foraminiferal assemblages defined by Q-mode cluster analysis (Fig. 2a). Overall average dissimilarity: 25.7.
SEM
photomicrographs of the most common or peculiar ostracod taxa found in the
studied succession. Scale bar
Dendrogram classification from the Q-mode cluster analysis using the
Bray–Curtis distance on
The Q-mode cluster analysis performed on the benthic foraminifera dataset
allows us to distinguish two main groups of samples (Fig. 2a). ANOSIM analysis
confirms the presence of significant differences in species composition
between groups of samples recognized by the Q-mode cluster analysis
(
Mean values of relative abundances of selected taxa, FAI, and diversity indices for benthic foraminiferal assemblages identified using cluster analysis.
The 16 samples analysed for Ostracoda included 5013 ostracod valves from 19 taxa (Table S2). Some of the most common or peculiar taxa are reported in Plate 3.
Similarity percentage (SIMPER) analysis for ostracod assemblages defined with Q-mode cluster analysis (Fig. 2b). Overall average dissimilarity: 45.35.
The number of recorded ostracod species per sample (
Ostracoda are largely dominated by
The Q-mode cluster analysis performed on the ostracod fauna reveals the
presence of three groups of samples (Fig. 2b) with significantly different
faunal composition, as confirmed by ANOSIM (
Mean ostracod assemblages' parameters and relative frequencies of major taxa.
Stratigraphy and vertical distribution of benthic foraminifera and
ostracoda in the studied interval of core 223 S12. Curves represent the
relative frequency of major benthic foraminiferal and ostracod taxa, FAI
index, diversity indices, and the quantitative ratio between benthic
foraminifera and ostracoda (BF
The lower stratigraphic portion of core 223 S12 is composed of finely
grained, alluvial deposits completely barren in microfossils with scattered
layers of fine sand (Fig. 3; Amorosi et al., 1999b). From 163.95 to 163.50 m
core depth, ostracod assemblage 1 occurs and includes very high proportions
of noded
Both assemblages are dominated by euryhaline taxa, such as
The observed foraminiferal distribution is substantially comparable with that
present today in the Goro lagoon (Fig. 1; Coccioni, 2000), a brackish-water
area with an average depth of ca. 1.5 m, showing remarkable local and
seasonal variations in physico-chemical parameters (salinity:
11.7–31 ‰; temperature: 4.2–27.5
The concentration of abnormal individuals (FAI) is relatively high (6.58 on
average) and exceeds 1 in all samples of the assemblage, which is considered
the threshold value between stressed and unstressed populations from
literature sources (Alve, 1991; Frontalini and Coccioni, 2008). Benthic
foraminifera exposed to extreme values of salinity, oxygen deficiency, high
concentrations of nutrients, or contaminants show frequencies of deformed
tests always
Similar values of relatively low dominance (0.19 on average) and high
diversity (
The distribution of
Summarizing, the composition of foraminiferal assemblage A is indicative of
a brackish lagoon with substantially stressed conditions, possibly produced by
strong variations in salinity and oxygen. This assemblage is considered to
reflect a palaeoenvironment comparable with the recent Goro lagoon, probably
with higher organic matter and lower oxygen concentration as revealed by the
frequencies of species indicative of these conditions (such as
This assemblage shows a significantly lower number of aberrant specimens (FAI
values
The palaeoenvironmental interpretation of assemblage B is substantially comparable with that of the previous one; however, the low FAI values are indicative of unstressed conditions in a relatively stable palaeoenvironment, characterized by lower concentrations of organic matter and without oxygen depletion at the bottom.
All ostracod assemblages are dominated by
Despite the strong dominance of
The very high dominance (0.96 on average), paralleled by the low
The co-dominance of noded and un-noded
Assemblage 2 is dominated by un-noded
The increasing
Ostracod assemblage 2 is consistent with a central lagoonal basin, possibly
subject to salinity oscillations. The dramatic decrease in noded
The concentration of the euryhaline
The maximum diversity (
The composition of this assemblage is considered to reflect a lagoon highly
influenced by normal saline waters, possibly an outer lagoonal area.
Brackish-marine taxa characterize this assemblage, and the great abundance of
phytal species indicates vegetation cover at the bottom. Ostracod assemblages
with high frequencies of
Detailed micropalaeontological analyses performed on benthic foraminifera and ostracoda allow an accurate characterization of the stratigraphic interval. The two microfossil groups provide distinct information, related to specific palaeoenvironmental conditions. The main differences between the benthic foraminiferal assemblages are represented by the FAI and the number of brackish-water species related to high concentrations of nutrients. Accordingly, two assemblages have been defined: (i) a stressed assemblage, formed mainly in response to salinity oscillations accompanied by high organic matter and low oxygen concentrations at the bottom, and (ii) an unstressed assemblage that suggests oxygenated conditions in a more stable palaeoenvironment. Despite the overall lower number of species, ostracod assemblages show higher differences in the community structure and include taxa with specific environmental tolerance ranges, indicative of distinct sub-environments. In this case, the contribution of subordinate freshwater and brackish-marine taxa allowed the definition of inner, central, and outer lagoon assemblages that reflect a distinct salinity gradient.
Above the basal alluvial plain deposits, the great abundance of noded
Upward, the superposition of ostracod assemblages 2 and 3 indicates the
passage to central and outer lagoon conditions and an increasing salinity.
The development of a marine-influenced lagoon is consistent with the landward
migration of a back-barrier system driven by MIS 7 transgression, when the
sea level reached a maximum of
A drastic reduction of marine-influenced ostracod species (i.e. the onset of
assemblage 2) from 162.60 to 161.60 m core depth is indicative of lower
salinity and higher confinement, likely related to a progradation of the
lagoon during a reduced rate of sea level rise. The recorded ostracod
assemblage with extremely high concentrations (
A new phase of higher salinity, related to a higher influence of seawater, is
recorded by ostracod assemblage 3 between 161.60 and 161.10 m core depth.
The lower proportions of the opportunistic
Upward, the presence of ostracod assemblage 2 with the high dominance of
un-noded
Quantitative palaeontological analyses performed on benthic foraminifera and ostracoda from a relatively short stratigraphic interval attributed to MIS 7 allowed a detailed palaeoenvironmental reconstruction. Specifically, the quantitative approach provided information about the environmental resolution potential for each group of fossils.
The combined application of benthic foraminifera and ostracoda indicates the development of a lagoon subject to minor environmental variations, in response to the interplay of freshwater and marine water inputs. A general transgressive–regressive trend is recorded by ostracod assemblages, with the occurrence of a minor relatively regressive phase. Outer lagoonal, unstressed conditions observed by ostracoda and benthic foraminifera are related to the highest marine influence recorded in the succession.
Both fossil groups contributed to the palaeoenvironmental reconstruction;
however, the most accurate environmental resolution is commonly shown by the
Ostracoda for their (i) abundant occurrence, (ii) higher differences in the
ecological structure of assemblages, and (iii) distinct faunal composition in
terms of species with precisely defined tolerance ranges. Scarce or rare taxa
greatly contribute to the palaeoenvironmental interpretation, even if
assemblages are dominated by opportunistic species. The same characteristics
are not accomplished by benthic foraminifera, which show more similar
assemblages in this succession. In spite of the higher number of species,
they are generally not related to distinctive or quantitatively defined
environmental ranges, producing a less precise palaeoenvironmental
reconstruction. In addition, benthic foraminifera are not present in inner
lagoon deposits (probably for the low preservation potential of agglutinated
tests). However, when ostracod fauna is composed almost entirely of un-noded
Benthic foraminiferal assemblages are mainly defined by the abundance of specimens with morphological abnormalities. High concentrations of deformed benthic foraminifera are quite rare in fossil assemblages and are here considered to indicate stressed conditions, possibly produced by oxygen depletion, fluctuation of salinity, and, eventually, other factors that typically characterize transitional environments. Therefore, benthic foraminifera also give indications of palaeoenvironmental stress that are not clearly shown by ostracod assemblages.
In conclusion, it is substantially intuitive that the quantitative approach
to both (or even multiple) fossil groups should be preferred in
palaeoenvironmental studies. However, if a choice is required between
ostracoda and foraminifera within lagoonal successions, we would
prefer Ostracoda. This group allows us to obtain more detailed
palaeoenvironmental reconstructions with the recognition of sub-environments
not recorded by the benthic foraminifera. In contrast, foraminifera provide
relevant additional information (i.e. environmental stability) and, locally,
an unambiguous interpretation of peculiar ostracod assemblages (i.e.
entirely represented by un-noded
All the data analysed in this paper are available in the tables provided within the paper or in the Supplement.
Elphidiidae, Rotaliidae, and Nonionidae are some of the most common families of benthic foraminifera reported from modern and fossil coastal deposits, from arctic to tropical areas (Murray, 2006). Due to the high morphological variability among individuals of each group, the specific attribution of a taxon is sometimes difficult. Many studies were performed with the aim of clarifying the classification of these taxa from different geographical zones (e.g. Hansen and Lykke-Andersen, 1976; Hayward et al., 1997).
The contribution of recent studies that combine molecular and morphological data (e.g. Holzmann and Pawlowski, 2000; Darling et al., 2016) is a valuable resource. Previously, attribution of some taxa was controversial due to the uncertainty around formae, subspecies, or species. The genetic characterization of benthic foraminifera with similar morphological features offers solutions for this problem.
Within the studied interval, the high morphological differentiation of the
above-mentioned groups led us to a detailed taxonomic analysis, following the
classification of Loeblich and Tappan (1987). In the case of uncertain
attribution between species, varieties, or formae, the contribution of genetic
studies on benthic foraminifera has been taken into consideration, mainly for
the taxonomy of selected Elphidiidae (Darling et al., 2016). Family Subfamily Genus Plate 1, figs. 17–18 1798 1976 1978 1984 1988 1991 1993 1997 2001 2012 2013 2016
It is considered not tolerant of heavy metal pollution, preferring clean and
sandy substrates (Frontalini and Coccioni, 2008). Plate 1, figs. 19–20 1840 1976 1976 1978 2000 2013 2016
In our samples,
Family Genus Plate 1, figs. 15–16 1913 1988 1990 2000 2000 2008
Aberrant tests of
The common occurrence of deformed specimens of Family Subfamily Genus Plate 1, figs. 1–4 1839 1988 1991 1993 2000 2001 2008 2009 2012
Individuals with very large umbilical knobs can be linked to the
Deformed individuals of
This species is considered less tolerant to environmental pollution than its
counterpart Plate 1, figs. 11–14 1926 1987 1988 1991 1993 2000 2001 2004 2008 2009
Deformities recorded in
This species is known for its great tolerance of high levels of organic
matter, reduced or overwhelming salinity, and environmental pollution;
therefore, it is considered the most tolerant species of a variety of
environmental and anthropogenic stresses (Yanko et al., 1994; Geslin et al.,
1998; Almogi-Labin et al., 1992; Frontalini and Coccioni, 2008). Plate 1, figs. 5–10
Transitional individuals between Family Subfamily Genus Plate 2, figs. 1–2 1826 1846 1987 1988 1993 2005 2012 Plate 2, fig. 3 1936 1976 1987 1988 2013 2016
Results of recent genetic studies (Darling et al., 2016) performed on
benthic foraminifera with a morphology comparable to Plate 2, fig. 4 1826 1904 1976 1997 2000 2009 2013 2016
Our individuals often have a low number of sutural bridges, especially in the
first chambers, where they may be only partially developed. This species
commonly presents individuals affected by various types of deformation of the
test: abnormal protruding chambers (Plate 2, fig. 15), distorted chambers,
change in coiling direction, and also complex forms (Plate 2, fig. 14).
It characterizes oligotypic benthic foraminiferal assemblages in areas
subject to high freshwater inputs and industrial discharges (Frontalini et
al., 2009). It also shows a great tolerance for high concentrations of
nutrients and heavy metals (Coccioni, 2000; Melis and Covelli, 2013). Plate 2, figs. 6–7 1839 1930 1976 1976 1983 1987 1988 2001
Genus Plate 1, fig. 21 1922 1930 1976 1988 1990 1993 1993 2001 2005 2012 2013 Plate 1, fig. 22 1930 1953 1982 1997 2016
This species was originally considered by Cushman (1930) as a variety of
Only rare deformed specimens of this taxon have been found in our samples,
with distorted chambers (Plate 2, fig. 16).
Plate 1, fig. 23 1957 1976 1991
In our individuals, ponticuli are less evident in the last chambers, where they are often covered by pustules.
Only one specimen with an aberrant chamber shape has been found in our samples.
Plate 1, figs. 24–25
This species differs from
Only rare aberrant individuals attributed to this taxon, mainly with a
distorted chamber arrangement, are present in our assemblages. Plate 1, figs. 26–27 Subfamily Genus Plate 2, fig. 5 1881 1991 1993 2012
Both authors defined the design of the work and carried out benthic foraminiferal analyses, whereas the ostracod analyses and statistical elaborations were performed by GB. Interpretation of fossil data and preparation of the paper was contributed to by both authors.
The authors declare that they have no conflict of interest.
We are grateful to Regione Emilia-Romagna – RER – Geological, Seismic and Soil Survey for providing core material. Thanks are due to Maria Roberta Randi for the SEM assistance. We warmly thank the editor Thomas M. Cronin, Virgilio Frezza, and the anonymous reviewer for their constructive comments that greatly improved the quality of the work. Edited by: Thomas M. Cronin Reviewed by: Virgilio Frezza and one anonymous referee