Paralic foraminifera through time: how they have been used

Abstrac

Lithostratigraphy, biostratigraphy, and stable-isotope stratigraphy of cores from ODP Leg 105 site surveys, Labrador Sea and Baffin Bay

Trigger weight (TWC) and piston (PC) cores obtained from surveys of the three sites drilled during Ocean Drilling Program (ODP) Leg 105 were studied in detail for benthic foraminiferal assemblages, total carbonate (all sites), planktonic foraminiferal abundances (Sites 645 and 647), and stable isotopes (Sites 646 and 647). These high-resolution data provide the link between modern environmental conditions represented by the sediment in the TWC and the uppermost cores of the ODP holes. This link provides essential control data for interpretating late Pleistocene paleoceanographic records from these core holes. At Site 645 in Baffin Bay, local correlation is difficult because the area is dominated by ice-rafted deposits and by debris flows and/or turbidite sedimentation. At the two Labrador Sea sites (646 and 647), the survey cores and uppermost ODP cores can be correlated. High-resolution data from the site survey cores also provide biostratigraphic data that refine the interpretations compiled from core-catcher samples at each ODP site

Foraminifera as sea-level indicators

There are over 1000 foraminiferal species presently living in marine environments, but relatively few of these can be used as direct indicators of sea level. We detail here certain assemblages occupying marsh environments that can be used for that purpose. Marsh foraminiferal assemblages have been shown to occur worldwide within narrowly defined vertical zones some of which extend less than 10 cm in total vertical range. These assemblage zones, once known, can be relocated in paleo-marsh deposits and accurately related to paleo-sea level. The key to success of these organisms as sea-level indicators is that their primary controlling factor appears to be elevation above mean sea level. Other foraminiferal assemblages are controlled by a series of parameters (eg. salinity, temperature, dissolved O2, etc.) which often have no direct relationship with actual water depth. Under appropriate circumstances, some information concerning sea level can be derived from other foraminiferal assemblages using indirect means. For instance areas which have undergone substantial emergence often contain small basins which, prior to emergence, were marine. The marine sediments at the bottom can be identified using foraminifera and the sill elevation of the basin can then be related to some prior sea-level stand. Both these methods have imperfections, but in areas where both emergence and submergence have taken place they can be combined to obtain a relatively complete sea-level history

Morphological Variations of Benthic Foraminiferal Tests in Response to Changes in Ecological Parameters: A Review

Some of the relatively recent literature correlating morphological variation in benthic foraminifera with environmental parameters such as temperature, salinity, carbonate solubility, depth, nutrition, substrate, dissolved oxygen, illumination, pollution, water motion, trace elements, and rapid environmental fluctuation is reviewed. It appears some variables (most notably depth) are recorded more frequently, which may affect some conclusions. Although each variable is treated separately, it appears that almost no variables act independently on test morphologies. In reviewing the literature, it becomes clear that there are many individual trends, especially with shell ornamentation, but few broad ones, and that it is almost impossible, with exception of some of the larger reef-dwelling, symbiont-bearing foraminifera, to predict how any species will react to various parameters. The broad trends concern thinning or thickening of carbonate tests with changing carbonate availability, temperature, and salinity. It appears that many observations of morphological changes within species may not be recorded in the literature, perhaps because authors did not recognize the importance of small details that would be of importance at a later time

Marsh foraminifera in the Bay of Fundy: modern distribution and application to sea-level determinations

Although marsh foraminiferal zonations are comparatively well known for most of Atlantic Canada, data from the vertically expanded marsh zones in the Bay of Fundy are insufficient for marsh foraminiferal zonations that can be used to accurately determine former sea levels. In this paper we present data from two well-documented surface transects that illustrate vertical ranges of marsh foraminifera in the Bay of Fundy. Trochammina inflata characterizes the highest margin with a zone la of 20cm vertical range. Tiphotrocha comprimata together with T. inflata comprise zone lb (vertical range 75cm) while Miliammina fusca and other low marsh species characterize zone II faunas (vertical range 450cm). As in Atlantic marshes the fauna nearest the higher high water level produces the best accuracy for relocating former sea levels while low marsh (zone II) is not a good indicator. Using marsh foraminiferal zonations and the tidal amplicication curve developed in earlier work, it is now possible to accurately determine former sea levels in the Bay of Fundy, at least for the last 4000 years. RÉSUMÉ Même si L’on connait assez bien la zonation des foraminifères de marais pour la plus grande partie de la côte atlantique du Canada, le manque de données sur le dévelopment vertical des zones de marais nous empèche d'établir avec exactitude les niveaux marins passés. Dans cet article, nous présentons des données provenant de deux traverses bien documentées, qui illustrent les étendues verticales des fora-miniféres de marais dans la Baie de Fundy. Trochammlna inflata charactérise la limite supérieure par une zone la d'une étendue verticale de 20cm. Tiphotrocha comprimata ainsi que T. inflata embrassent la zone lb (étendue verticale de 75cm) cependant que Miliammina fusca et d'autres espèces de basmarais charactérisent les faunes de la zone II (fitendue verticale de 450cm). Comme dans les marais at I antiques, la faune ia plus près du plus haut niveau de marée haute procure la meilleure exactitude pour situer les niveaux marins antérieurs alors que la zone de bas-marais (zone II) n'est pas un bon indice. L'utilization des zonations de foraminifères de marais et de la courbe d'amplification de marée développée lors de travaux antérieurs permet done de déterminer avec exactitude, à tout le moins pour les derniers 4000 ans, les niveaux marins passés dans le Baie de Fundy. [Traduit par le journal

Fragile abyssal foraminifera (including new Komokiacea) from the Nares Abyssal Plain

The study of eight samples from the Nares Abyssal Plain has shown that the rhizopodan surface population of the area is dominated by forms with fragile, flexible tests. In this rarely reported component of the abyssal population we have identified 20 new species for which holotypes have been designated and figured. We have also designated five lectotypes for species previously described and introduced new terms essential for the concise description of komoki and few other abyssal foraminifera. For the rapid identification of the more complex and less known genera we have provided an identification key. -from Author

Can smaller benthic foraminifera be ignored in paleoenvironmental analyses?

Investigations of the distribution patterns have been carried out on various size fractions of faunal assemblages (eg, >63 mu m, >125 mu m, >150 mu m, >250 mu m and >300 mu m). In our study, information obtained from examination of the 63-125-mu m and the >125-mu m fractions is compared with published data based solely on the larger size fractions. We found that sieves with large openings (125 mu m, 150 mu m, 250 mu m, 300 mu m) allow a significant loss of specimens, including environmental index species, and may have created artificial 'barren zones' in sequences dominated by small-sized species. This suggests that inclusion of the 63-125-mu m fraction in foraminiferal studies may be well worth the additional time and effort required. Data from different sources certainly could be more readily compared or integrated if this procedure was more widely adopted in paleoceanographic studies. -Author

Recent Arctic shelf Foraminifera: seasonally ice covered vs. perennially ice covered areas

Benthic Foraminifera are abundant, highly diverse, and predominantly calcareous on siliceous sponge reefs of the W Axel Heiberg shelf. A total of 110 species, including 38 agglutinated taxa, were identified in 47 surface samples. Living specimens usually constitute <3%, indicating a residual fauna. An important environmental parameter is the perennial ice cover, which causes high salinity, a low sedimentation rate, and a limited food supply. The availability of niches with sufficient nutrient supply and the diverse nature of

Benthic foraminifera of the Labrador Sea and Buffin Bay

Trigger weight (TWC) and piston (PC) cores obtained from surveys of the three sites drilled during Ocean Drilling Program (ODP) Leg 105 were studied in detail for benthic foraminiferal assemblages, total carbonate (all sites), planktonic foraminiferal abundances (Sites 645 and 647), and stable isotopes (Sites 646 and 647). These high-resolution data provide the link between modern environmental conditions represented by the sediment in the TWC and the uppermost cores of the ODP holes. This link provides essential control data for interpretating late Pleistocene paleoceanographic records from these core holes. At Site 645 in Baffin Bay, local correlation is difficult because the area is dominated by ice-rafted deposits and by debris flows and/or turbidite sedimentation. At the two Labrador Sea sites (646 and 647), the survey cores and uppermost ODP cores can be correlated. High-resolution data from the site survey cores also provide biostratigraphic data that refine the interpretations compiled from core-catcher samples at each ODP site