Fossil Foraminiferal Assemblages Research Articles

Contemporary Salt-Marsh Foraminifera from Southern California and Implications for Reconstructing Late Holocene Sea-Level Changes

Abstract We report on the distribution of contemporary foraminifera in salt marshes in Mission Bay and Carpinteria Slough, Southern California. Combining these data with existing datasets from Seal Beach and Tijuana, we explore the potential for a regional training set to underpin quantitative reconstructions of paleoenvironmental change from foraminifera preserved in salt-marsh sediments. We demonstrate that species’ distributions are highly dependent on elevation, suggesting fossil foraminiferal assemblages here, as in many other regions, are useful depositional elevation indicators. Transfer functions provide predictions from Mission Bay cores with decimeter-scale uncertainties. Nevertheless, interpretation of marsh-surface elevation change is complicated by a complex geomorphic setting and anthropogenic impacts. An abrupt change in elevation in the mid-1700s may be related to lateral spreading of water-saturated sediments during an earthquake on the Rose Canyon fault, suggesting the potential for foraminifera to support new palaeoseismic and sea-level records for the region.

Implication of size fraction on benthic foraminiferal-based paleo-reconstructions: A case study from the Bay of Biscay (NE Atlantic)

Many paleoenvironmental studies based on benthic foraminiferal assemblages use different protocols for sample analysis. A standardized protocol has been recently established for biomonitoring applications, but for paleostudies, the influence of size fraction on benthic foraminiferal composition and biodiversity is poorly documented. We studied fossil foraminiferal assemblages along two paleorecords (BOBGEO-CS05 and SU81–44) from the Bay of Biscay covering the last ∼35 ka cal BP. We investigated diversity and community composition to compare the impact of each size fraction (63-150 μm, >150 μm, >63 μm) on environmental interpretations. Foraminiferal diversity was affected by the accumulation of small opportunistic species. In terms of faunal composition, both paleorecords displayed a different pattern depending on the size fraction selected. While in both cores, the 63-150 μm fraction blurred the signal of some rare indicator species, our results show that i) in BOBGEO-CS05, it yielded no extra ecological information compared to the large fraction whereas ii) in SU81–44, it contained small opportunistic species that were not present in the >150 μm, impacting therefore paleoenvironmental interpretations. According to these findings, we recommend: i) to focus on the large fraction for a thorough taxonomic determination and a detailed analysis of benthic assemblages, and ii) to analyse the small fraction separately after a taxonomical identification of major species and strategic selection of studied samples. Although the 125 μm size limit was not tackled in this study, we recommend to use it for the limit between the small and large fractions instead of 150 μm for harmonization with the previously published standardized protocol for living faunas.

Planktonic foraminiferal assemblages reflect warming during two recent mid-latitude marine heatwaves

Under future climate scenarios, ocean temperatures that are presently extreme and qualify as marine heatwaves (MHW) are forecasted to increase in frequency and intensity, but little is known about the impact of these events on one of the most common paleoproxies, planktonic foraminifera. Planktonic foraminifera are globally ubiquitous, shelled marine protists. Their abundances and geochemistry vary with ocean conditions and fossil specimens are commonly used to reconstruct ancient ocean conditions. Planktonic foraminiferal assemblages are known to vary globally with sea surface temperature, primary productivity, and other hydrographic conditions, but have not been studied in the context of mid-latitude MHWs. For this study, the community composition and abundance of planktonic foraminifera were quantified for 2010-2019 along the Newport Hydrographic Line, a long-term monitoring transect at 44.6°N in the Northern California Current (NCC). Samples were obtained from archived plankton tows spanning 46 to 370 km offshore during annual autumn (August – October) cruises. Two MHWs impacted the region during this timeframe: the first during 2014-2016 and a second, shorter duration MHW in 2019. During the 2014-2016 MHW, warm water subtropical and tropical foraminifera species were more prevalent than the typical polar, subpolar, and transitional species common to this region. Cold water species were abundant again after the first MHW dissipated in late 2016. During the second, shorter-duration MHW in 2019, the assemblage consisted of a warm water assemblage but did not include tropical species. The foraminiferal assemblage variability correlated with changes in temperature and salinity in the upper 100 meters and was not correlated with distance offshore or upwelling. These results suggest that fossil foraminiferal assemblages from deep sea sediment cores may provide insight into the magnitude and frequency of past MHWs.

Reproducibility and variability of earthquake subsidence estimates from saltmarshes of a Cascadia estuary

ABSTRACTWe examine fossil foraminiferal assemblages from 20 sediment cores to assess sudden relative sea‐level (RSL) changes across three mud‐over‐peat contacts at three salt marshes in northern Humboldt Bay, California (~44.8°N, −124.2°W). We use a validated foraminiferal‐based Bayesian transfer function to evaluate the variability of subsidence stratigraphy at a range of 30‐6000 m across an estuary. We use the consistency in RSL reconstructions to support estimates of coseismic subsidence from megathrust earthquakes. To assess the variability of subsidence estimates, we analyzed: nine examples of the 1700 CE earthquake (average of 0.64 ±0.14 m subsidence; range of 0.24 ± 0.27 to 1.00 ± 0.44 m), five examples of the ca. 875 cal a BP earthquake (average of 0.43 ±0.16 m; range of 0.41 ± 0.36 to 0.48 ± 0.39 m), and six examples of the ca. 1120 cal a BP earthquake (average of 0.70±0.18 m; range of 0.47 ± 0.36 to 0.80 ± 0.49 m). Our subsidence estimates suggest ~±0.3 m of within‐site (intrasite) variability, which is consistent with previous research. We also identify inconsistencies between sites (intersite) at northern Humboldt Bay greater than one‐sigma uncertainties, driven by variable foraminiferal assemblages in the mud overlying the 1700 CE subsidence contact. Therefore, we recommend at least two quantitative microfossil reconstructions across the same stratigraphic sequence from different marsh sites within an estuary to account for estimate variability and provide increased confidence in vertical coseismic deformation estimates. Our results have broad implications for quantitative, microfossil‐based reconstructions of coseismic subsidence at temperate coastlines globally.

Timing and amount of southern Cascadia earthquake subsidence over the past 1700 years at northern Humboldt Bay, California, USA

AbstractStratigraphic, lithologic, foraminiferal, and radiocarbon analyses indicate that at least four abrupt mud-over-peat contacts are recorded across three sites (Jacoby Creek, McDaniel Creek, and Mad River Slough) in northern Humboldt Bay, California, USA (∼44.8°N, −124.2°W). The stratigraphy records subsidence during past megathrust earthquakes at the southern Cascadia subduction zone ∼40 km north of the Mendocino Triple Junction. Maximum and minimum radiocarbon ages on plant macrofossils from above and below laterally extensive (>6 km) contacts suggest regional synchroneity of subsidence. The shallowest contact has radiocarbon ages that are consistent with the most recent great earthquake at Cascadia, which occurred at 250 cal yr B.P. (1700 CE). Using Bchron and OxCal software, we model ages for the three older contacts of ca. 875 cal yr B.P., ca. 1120 cal yr B.P., and ca. 1620 cal yr B.P.For each of the four earthquakes, we analyze foraminifera across representative mud-over-peat contacts selected from McDaniel Creek. Changes in fossil foraminiferal assemblages across all four contacts reveal sudden relative sea-level (RSL) rise (land subsidence) with submergence lasting from decades to centuries. To estimate subsidence during each earthquake, we reconstructed RSL rise across the contacts using the fossil foraminiferal assemblages in a Bayesian transfer function. The coseismic subsidence estimates are 0.85 ± 0.46 m for the 1700 CE earthquake, 0.42 ± 0.37 m for the ca. 875 cal yr B.P. earthquake, 0.79 ± 0.47 m for the ca. 1120 cal yr B.P. earthquake, and ≥0.93 m for the ca. 1620 cal yr B.P. earthquake. The subsidence estimate for the ca. 1620 cal yr B.P. earthquake is a minimum because the pre-subsidence paleoenvironment likely was above the upper limit of foraminiferal habitation. The subsidence estimate for the ca. 875 cal yr B.P. earthquake is less than (<50%) the subsidence estimates for other contacts and suggests that subsidence magnitude varied over the past four earthquake cycles in southern Cascadia.

Insights into the procurement and distribution of fossiliferous chert artefacts across southern Australia from the archival record

Following from previous research in Western Australia, this study explores the use of embedded microfossils—including bryozoan and foraminiferal fossil assemblages—to help identify source and distribution of fossiliferous chert artefacts from South Australian archives. Artefacts from key archaeological sites include Allen’s Cave, Koonalda Cave, Wilson’s Bluff, Ooldea and Kongarong. Preliminary analyses indicate a possible differentiation of fossiliferous chert types east and west of the Eyre Peninsula, from Otway Basin and Eucla Basin limestones, respectively. The widespread distribution and trade of fossiliferous chert is supported by ethnographic descriptions of the sources, procurement and trade as recorded by Daisy Bates, Thomas Draper Campbell and Norman Tindale. Further work combining biostratigraphy and lithology with archaeology and ethnography is needed to explore these ideas further.

Evolution of a salt marsh in the southeastern North Sea region – Anthropogenic and natural forcing

Salt-marsh sediments of the southeastern North Sea provide an archive to unravel the influences of coastal management and natural processes such as storm-tide deposition on salt-marsh development. We present a record of salt-marsh evolution during the past century from the Bay of Tümlau (northwestern Germany) based on fossil foraminiferal assemblages and sedimentological data. After diking the hinterland of the Bay of Tümlau in 1935 CE and commencing marsh management, the environment at the study site changed from a tidal flat to a salt marsh. Salt-marsh sediment accretion is influenced by recurrent dredging events, as indicated by layers rich in calcareous tidal-flat foraminifera, and redeposition of siliciclastic particles from the surrounding tidal flats during storm tides. The latter fostered the establishment of a typical salt-marsh foraminiferal fauna dominated by the agglutinating species Entzia macrescens. Storm-tide layers have a lighter sediment color and commonly a more negatively skewed grain-size distribution with variable sorting. The observed long-term coarsening of the salt-marsh sediment likely reflects the landward progression of the vertical erosional cliff and the depletion of fine-grained sediment particles in the tidal flats under the influence of sea-level rise. Supra-tidal conditions, resulting from natural protection measures and abandonment of dredging, are indicated by the occurrence of Balticammina pseudomacrescens around 2001 CE. This species is adapted to only occasional submergence during storm tides. The recent increase in elevation is accompanied by establishment of high-marsh vegetation and characterized by a present height of the marsh surface 50 cm above mean high water springs. During the past sixty years, average sediment accretion rates decreased from 18 to 11 mm yr−1 reflecting the maturing of the salt marsh. These rates clearly outpace the recent mean sea-level rise in the southern North Sea demonstrating that the regional salt marshes are still resilient to sea-level rise.

Recent benthic foraminiferal assemblages from the Celtic Sea (South Western Approaches, NE Atlantic)

The faunal composition and diversity pattern of Recent benthic foraminifera from the shelf and slope of the South Western Approaches (Celtic Sea) were assessed. The sampling stations cover a depth range from 100 to 500 m. A total number of 294 species was recorded, of which 89 were found exclusively in the living fauna and 118 only in the dead assemblage, whereas 87 species were found in both assemblages. The faunal composition revealed a distinct bisection of the living fauna on the shelf. While certain distribution patterns of living dominant species were recognized along a NE-SW trending transect towards the shelf edge, the living fauna changed within small depth intervals and geographic position on the slope. Causes for these structured slope assemblages were probably along-slope currents of varying strengths, as well as variations in topography and bottom sediments. Analyses of population densities and diversity patterns determined high densities along the shelf edge and at one slope station, as well as an increasing diversity with water depth. A comparison with literature data from the same area yields distinct differences in faunal composition on the shelf and slope. The diversity was similar on the shelf, but higher at corresponding stations on the slope. We conclude that the faunal composition was highly influenced by the time and methods of sampling. In order to obtain consistent results in regional studies, all samples should be taken in a short time interval and by using the same sampling device. In addition, we depicted the influences of environmental parameters on dead faunal assemblages and their consequences for paleoenvironmental interpretations of fossil foraminiferal assemblages.

山形県余目油田の石油地質と地球化学

Interpretation on radiolarian fossil data of Nakaseko and Sugano (1972) based on Kato and Obuse (2013) shows that oil reservoirs in the Amarume oil field, Yamagata Prefecture, belong to the lower part of the Kitamata Formation and the Kusanagi Formation. This result harmonizes with foraminiferal fossil assemblages in wells around the field.Oils produced in the field, Amarume oils, are mostly classified into light oil and slightly biodegraded. Medium oils in the southern part of the field are strongly biodegraded due to meteoric waters invaded from the south.The Amarume oils resemble oils in the Yurihara and Ayukawa fields in geochemical characteristics including relationship between API gravity and sulfur content, carbon isotope compositions of oils, light hydrocarbon compositions and biomarker maturity parameters, but are clearly distinguished from oils in the Kosei area, Akita Prefecture. Relative oil maturity among oils in the Amarume, Yurihara and Ayukawa fields varies depending on maturity parameters used. In addition to oil maturity, gas maturity and Bouguer anomaly map suggest that oil and gas generated in the center of depression near Sakata have migrated into the Amarume field.

Mg/Ca-paleothermometry in the western Mediterranean Sea on planktonic foraminifer species Globigerina bulloides: Constraints and implications

We generated a high-resolution SSTMg/Ca record for the surface-dwelling planktonic foraminifera Globigerina bulloides from the core MD99-2346 collected in the Gulf of Lion, and compared it to that obtained using modern analogue techniques applied to fossil foraminiferal assemblages (SSTMAT). The two temperature records display similar patterns during the last 28,000 years but the SSTMg/Ca estimates are several degrees warmer (∼+4°C) than SSTMAT. The temperature shift between SSTMg/Ca and SSTMAT remained relatively constant over time. This seems to exclude a bias on the Mg/Ca record associated with salinity or secondary Mg-rich calcite encrustation on the foraminiferal tests during early diagenesis. Therefore, anomalously high Mg/Ca suggests either: (1) the empirical equation for G. bulloides of Elderfield and Ganssen (2000) is incorrect; or (2) there is a specific Mediterranean genotypes of G. bulloides for which a specific Mg/Ca-temperature calibration is needed.

Coastal subsidence in Oregon, USA, during the giant Cascadia earthquake of AD 1700

Quantitative estimates of land-level change during the giant AD 1700 Cascadia earthquake along the Oregon coast are inferred from relative sea-level changes reconstructed from fossil foraminiferal assemblages preserved within the stratigraphic record. A transfer function, based upon a regional training set of modern sediment samples from Oregon estuaries, is calibrated to fossil assemblages in sequences of samples across buried peat-mud and peat-sand contacts marking the AD 1700 earthquake. Reconstructions of sample elevations with sample-specific errors estimate the amount of coastal subsidence during the earthquake at six sites along 400 km of coast. The elevation estimates are supported by lithological, carbon isotope, and faunal tidal zonation data. Coseismic subsidence at Nehalem River, Nestucca River, Salmon River, Alsea Bay, Siuslaw River and South Slough varies between 0.18 m and 0.85 m with errors between 0.18 m and 0.32 m. These subsidence estimates are more precise, consistent, and generally lower than previous semi-quantitative estimates. Following earlier comparisons of semi-quantitative subsidence estimates with elastic dislocation models of megathrust rupture during great earthquakes, our lower estimates for central and northern Oregon are consistent with modeled rates of strain accumulation and amounts of slip on the subduction megathrust, and thus, with a magnitude of 9 for the AD 1700 earthquake.

Contrasting paleoceanographic conditions off Morocco during Heinrich events (1 and 2) and the Last Glacial Maximum

Past hydrological and primary productivity regimes, on the basis of dinocyst and foraminiferal fossil assemblages as well as on stable isotopes (O, C) and alkenones, were investigated over the last 30 ka at upwelling site MD04-2805 CQ off Morocco. The results show highest upwelling intensity during Heinrich event (HE) 1, time-coeval with a distinct plateau of heavy planktonic δ 13C values, high concentrations of Pinus pollen and heterotrophic dinocysts, caused by an increased northern wind regime. In addition, we also present regional reconstructions of paleo-sea-surface temperatures (SSTs) using three different proxy tools: dinocyst and foraminiferal transfer functions as well as alkenones (U k′ 37 – SST). The reconstructed SSTs depict coherent scenarios as modulated by the typical Northern Hemisphere climatic fluctuations. Furthermore, specific occurrences of the dinocyst Spiniferites lazus and of the foraminifer Turborotalita quinqueloba are noted for HE 2, HE 1, and the Younger Dryas, whereas in the Alboran Sea and in peri-Iberian waters these cold events were accompanied by the dinocyst Bitectatodinium tepikiense and the subpolar foraminifer Neogloboquadrina pachyderma s., both implying a marked southward shift in the planktonic population in response to the migration of polar water masses. This very pronounced demarcation between the planktonic communities better seems to attest the presence of a distinct hydrological structure in proximity of the strait of Gibraltar which separated at that time African (north of Morocco) from European (southern Iberia) water masses.

Distribution of foraminifera in salt marshes along the Atlantic coast of SW Europe: Tools to reconstruct past sea-level variations

Surface sediments were sampled from the salt marshes of the Morbihan Gulf (Brittany, France), the Barbadun, Plentzia and Urdaibai estuaries (Basque Country, northern Spain), the Minho and Lima estuaries (northern Portugal) and the Sado estuary (southern Portugal), to study the vertical distribution of foraminifera and their potential use for sea-level studies along the Atlantic coasts of SW Europe. The most abundant species found in the marshes are Jadammina macrescens and Trochammina inflata, with Miliammina fusca and Arenoparrella mexicana as secondary species, but there are some important regional differences in the composition of the foraminiferal assemblages. In the Basque marshes, Haynesina germanica and Ammonia tepida are dominant species, whereas in northern Portugal the most abundant species are M. fusca, Haplophragmoides spp. and T. inflata together with J. macrescens. Local transfer functions for sea-level reconstruction were constructed from fossil foraminiferal assemblages using Partial-Least-Squares (PLS) regression for data sets with a linear distribution (Morbihan and Sado) and Weighted-Averaging-Partial-Least-Squares (WA-PLS) regression for data sets with unimodal foraminiferal distributions (Basque and Minho-Lima). The most accurate models were obtained from high marsh assemblages. The transfer function models provided errors of ca. ±0.10 m, indicating that precise reconstructions of former sea levels are possible in this area.

The application of intertidal foraminifera to reconstruct coastal subsidence during the giant Cascadia earthquake of AD 1700 in Oregon, USA

Changes in species assemblages of intertidal foraminifera can be used to estimate the amount of earthquake-related subsidence during plate-boundary earthquakes at the Cascadia subduction zone. The accuracy and precision of foraminiferal methods in paleoenvironmental reconstruction is underpinned by the relations between contemporary taxa and their environment, which are used to calibrate fossil foraminiferal assemblages in sediment sequences. A contemporary training set of surface sediment samples from five intertidal marshes along the Oregon coast was used to determine foraminiferal distributions and prevailing environmental control(s) along elevational transects. Dominant taxa include Balticammina pseudomacrescens, Trochamminita irregularis, Haplophragmoides wilberti, Trochammina inflata, Jadammina macrescens and Miliammina fusca. Unconstrained cluster analysis and detrended correspondence analysis was used to identify two elevation-dependent faunal zones: Faunal Zone I (upland, high marsh, middle marsh) dominated by Balticammina pseudomacrescens, Haplophragmoides wilberti and Trochammina inflata, and Faunal Zone II (low marsh and tidal flat) dominated by Miliammina fusca. Site-specific differences in assemblages at three marshes enabled further subdivision of Faunal Zone I. Zone Ia is based on one or more of Balticammina pseudomacrescens, Trochammina inflata, Trochamminita irregularis and Haplophragmoides sp., and Zone Ib on Jadammina macrescens, Haplophragmoides sp., Trochammina inflata and Miliammina fusca. Canonical correspondence analysis (CCA) and partial CCA of the training set from the Nehalem River marsh transect was used to infer that the zonation of foraminifera is elevation-dependent (39% of explained variance). A transfer function was developed to reconstruct sudden changes in relative sea-level during plate-boundary earthquakes in Oregon. The results indicate a robust performance of the transfer function ( r jack 2 = 0.82) with the error estimate (RMSEP jack = 0.20 m) comparable to local and regional transfer functions from other temperate marshes. To illustrate the potential of the technique, the transfer function was applied to reconstruct subsidence during the AD 1700 earthquake using at Alsea Bay, Oregon. The reconstruction (0.18 ± 0.20 m) is less than half the subsidence estimate of Nelson et al. [2008. Great-earthquake palogeoesy and tsunamis of the past 2000 years at Alsea Bay, central Oregon coast, USA. Quaternary Science Reviews, 27, 747–768] using their foraminiferal transfer function, perhaps because of differences in taxonomy and the species relationship to elevation.

New biostratigraphic data from the Cretaceous Bolinxiala Formation in Zanda, southwestern Tibet of China, and their paleogeographic and paleoceanographic implications

Planktonic foraminiferal fossil assemblages identified from the Bolinxiala Formation in Bolin, Zanda, southwestern Tibet of China, determine its age from latest Albian to Maastrichtian. The fossil contents of the Bolinxiala Formation allow its correlation with successions across a platform-to-basin transect of the Late Cretaceous Tethyan Himalaya passive margin. The ocean anoxic event at the Cenomanian–Turonian transition (OAE2) is located at the Whiteinella archaeocretacaea biozone in Zanda, but lithologically it is characterized by grey and bioturbated limestone, implying that during the OAE2 the shallow-water environments of the Tethyan Himalayan carbonate platform remained oxic. Paleogeographic reconstruction indicates that the Upper Cretaceous Oceanic Red Beds (CORBs) in southern Tibet are restricted to the slope and basinal environments but they are entirely missing in the shelf environments. This phenomenon suggests the formation of CORBs by oxidation of Fe(II)-enriched anoxic deep ocean seawater at the chemocline that separated the oxic surface ocean from anoxic deep ocean. For depositional environments above the chemocline, no CORBs would be expected. Because of the chemocline instability across different sedimentary basins, CORBs may be significantly diachronous, consistent with the occurrence of CORBs documented from global sedimentary basins.

Sediment (grain size and clay mineralogy) and organic matter quality control on living benthic foraminifera

The paleoecological interpretation of fossil foraminiferal assemblages depends on an understanding of the ecological processes operating at the present. This study investigates both the quality of organic matter (OM) by elemental analysis as well as the sediment grain size and clay mineralogy to understand their relative influence on distribution and abundance of benthic foraminifera. This study is carried out on 15 samples regularly spaced from the mudflat to the tidal marsh. The results indicate that grain size is the most limiting parameter. Living (stained) benthic foraminiferal density and species richness are both very low within coarser sediments. OM is the second limiting factor. The density of foraminifera is the lowest and the species richness is the highest with the lowest organic carbon (C org) contents and C/N < 12. Conversely, when the C org is very high and C/N > 12, the density is high and the species richness medium. A high smectite proportion within the clay-size fraction seems to favor the development of Miliammina fusca. Trochammina inflata and Jadammina macrescens are both favored by an increase of organic carbon proportion but Trochammina inflata preferentially feeds on algal-derived OM when compared with Jadammina macrescens.

Palaeoenvironmental conditions preceding the Messinian Salinity Crisis: A case study from Gavdos Island

The Messinian pre-evaporitic sedimentary succession of Gavdos Island (Metochia section) is a nearly uninterrupted succession of marine sediments, dominated by finely laminated diatomaceous marls, which are cyclically alternating with clayey diatomites and white diatomites. The qualitative and quantitative analysis of the planktonic foraminiferal fauna allowed the recognition of nine bioevents, which have been astronomically dated for the Mediterranean. The base of the diatomitic succession in Gavdos Island is dated at 6.722 Ma and the top at 6.015 Ma. The studied section contains benthic foraminiferal genera characteristic of an outer shelf to slope environment. The qualitative and quantitative analysis of this microfauna revealed three benthic foraminiferal fossil assemblages and the occurrence of allochthonous species transported into the bathyal environment by current activity. The cyclical pattern of the benthic foraminifera assemblages indicates that the studied sediments have been affected by repeated episodes of basin restriction characterized by low diversity benthic foraminifera populations, and a limited planktonic foraminifer association typified by shallow, surface-dwelling forms. This restriction was partly due to Antarctic cooling, which produced palaeo-Mediterranean sea-level oscillations during the Early Messinian, as a prelude to closure of the Atlantic connections. The relative impact of climatic versus tectonic control on sedimentation patterns within this basin is discussed.

Benthic foraminiferal evidence for the formation of the Holocene mud-belt and bathymetrical evolution in the central Adriatic Sea

Detailed analyses of modern and fossil benthic foraminiferal assemblages collected in the central Adriatic Sea are used as tools to reconstruct the environmental changes that occurred between the Last Deglaciation and the Present (last 14 Kyrs); in particular we focus on the timing and formation of the mud-belt. The modern benthic foraminiferal assemblages display a parallel zonation to the Italian coast controlled by the interaction between food/oxygen availability and water depth. Cluster analysis of 4 sediment cores separates the fossil foraminiferal assemblages in 6 groups: Cluster A is dominated by three Ammonia species; Cluster B consists of Ammonia papillosa, Nonionella turgida, Elphidium advenum and Elphidium decipiens; Cluster C is composed of two taxa, Hyalinea balthica and Trifarina angulosa; Cluster D is dominated by 5 species, Cibicides lobatulus, Buccella granulata, Reussella spinulosa, Textularia agglutinans and Elphidium crispum; Cluster E contains Bulimina spp., Gavelinopsis praegeri, Bolivina spp., Cassidulina neocarinata and Asterigerinata mamilla; and Cluster F is dominated by Bulimina marginata, Valvulineria bradyana, Globocassidulina subglobosa and Melonis padanum. The cluster analysis and contemporary distribution patterns of these taxa are used together with ecological preferences of the most frequent species to reconstruct the spatial and temporal distribution of the different biofacies in the past. This reveals information about Holocene palaeoenvironmental changes that are related to water depth fluctuations and the installment of the coast-parallel mud-belt. The benthic assemblage records the transition from a infralitoral environment (Biofacies I) to deeper marine condition (Biofacies III). After that the sea level reached about the modern level (Biofacies IV) the benthic foraminiferal community evidences the development of the mud-belt and the subsequent transformation of the ecological niches linked to the trophic evolution of the environment.

Benthic foraminifers and paleoecology of a Holocene shelly concentration, Salado Basin, Argentina

Foraminiferal fossil assemblages of the shelly concentration, which represents the type section of Cerro de la Gloria Member of Las Escobas Formation, were analyzed for the first time. Taxonomic, quantitative and taphonomical analyses were made in order to obtain paleoenvironmental (physical as well biological) information. The complexity of the internal structure of the taphocoenoses was analyzed to infer the history of the final concentration process. The shell bed of Channel 15 corresponds to a shoreface longshore bar deposited in a brackish, unstable, wave-dominate coast. Shoreface and beach (foreshore) regressive facies were recognized. Taphonomic processes have modified the paleobiocoenoses by the selective preservation of autochthonous elements and by the addition of parautochthonous fauna from relict beachs and lagoons. Thus, the taphocoenoses is a within-habitat time-averaged assemblage composed of species that inhabit shallow shelf marine environments. Discrimination of autochthonous and parautochthonous fauna was possible based on taphonomic signatures of tests. The addition of the parautochthonous elements was related with longshore currents and littoral drift, and with high-energy events, probably with storm-waves, when erosion of the Pre-Mid Holocene substrate was more intense. Thus, the contribution of parautochthonous fauna is directly related with lithology and therefore, with dynamic of the paleoenvironment: in the shoreface, autochthonous fauna dominates in clastic sands with lamination and parallel stratification, whereas parautochthonous elements dominate in shoreface shelly gravels and in the foreshore sands. In the upper part of the section (beach facies), mainly parautochthonous elements related with erosion of the Pre-Mid Holocene substrate was recognized, since the shoreface was only periodically affected by marine processes, i.e., during storms.

Geochemical evidence for non-marine depositional environment of foraminiferal fossils from the Nihewan Basin, China

From the first finding in 1970s, the findings of foraminiferal fossil assemblages in inland basins have been reported from time to time, especially in recent years. The debates on the depositional environment of foraminiferal fossils have become the hot spot of researches again in China. Based on the researches of trace element geochemistry and electron scanning microscope of shells of Quaternary foraminiferal fossils from the Xiaodukou section in the inland Nihewan basin, the original 87Sr/86Sr and other geochemical information of shells were believed to be preserved well and could be used to rebuild the geochemistry of contemporary waters where foraminifera deposited, although there existed some effects of burial diagenesis on the geochemistry of shells to a certain extent. The 87Sr/86Sr ratios of well-preserved Xiaodukou foraminiferal shells were measured, giving a range of 0.711190±25–0.712018±14, apparently higher than the value of contemporary seawater (0.709087–0.709147) and similar to that of the Sanggan River, proving that it represented the value of the ancient lacustrine water. The hyperbolic mixing models of 87Sr/86Sr-palaeosalinity and 87Sr/86Sr-Sr/Ca indicated that the contemporary waters where Xiaodukou foraminifera inhabited was an inland lake and there was no seawater input to the depositional environment.