Mervin Kontrovitz

A flume study of the movement of foraminifera tests

Abstract Assemblages of benthic foraminifera are used as indicators of paleo-environmental conditions, but if an assemblage represents post-mortem transport the reliability is limited. A repeatable method of determining such reliability was investigated by measuring the traction velocities of foraminifera in a flume with a moveable sediment substrate. Twenty-five specimens of each of twelve species were weighed and measured for various dimensions (intercepts). Volume, nominal diameter, operational sphericity, maximum projection sphericity and effective density were calculated. Each specimen was placed in a flume and the traction velocity was determined; the mean velocity was calculated for each species. Mean velocities varied from 5.1 to 18.7 cm/sec. The values for each species were compared and it was determined which were moved by velocities from the same statistical populations and which were not. If applied to assemblages, the tested specimens that were transported (sorted) would have similar velocities, but an assemblage composed of specimens representing different velocities would have remained in place, being unsorted. The method is repeatable and practical in that the specimens can be manipulated and observed easily. Only operational sphericity and weight have significant correlations with the traction velocity of foraminifera. However, with multiple regression techniques, the traction velocity for each species could be estimated with the following regression equation: X 1 = 18.4 − 11.4X 2 − 38.9X 3 where X1 is the mean traction velocity (cm/sec); X2 is the mean value of the maximum projection sphericity; X3 is the mean weight (mg) and 18.4 is the intercept of the regression plane. Thus, it may be possible to determine with flume runs if specimens in an assemblage have been transported or have remained in place. Also, estimates of traction velocities are possible without flume runs if sufficient data are obtained regarding the weight and dimensions of the specimens. The latter method may eliminate the need for flume runs.

Assessment of postmortem transportation of modern benthic foraminifera of the Washington continental shelf

A linear regression equation was used to estimate the traction velocity for each of the 31 most common benthic foraminiferal species in surface sediments of the Washington continental shelf. Using Scheffes method of multiple comparisons, the traction velocities of these species were compared individually and by groups in order to detect species that would be transported in the same statistical population. Three traction-velocity groups were recognized: 1) four species with roughly equidimensional tests and low traction velocities; 2) 19 species with elongate, inflated or coiled, moderately inflated tests and intermediate traction velocities; and 3) eight species with elongate, highly compressed or coiled, discoidal tests and high traction velocities. Depending upon the bottomcurrent velocity, one of these three traction-velocity groups might be expected to numerically dominate a current-sorted assemblage. However, each major faunal association, defined by cluster analysis in the preceding paper, is composed of mixtures from all three groups. Direct observations of bottom currents suggest that velocities at the sediment-water interface are generally too low, with directions too erratic to effectively sort species identified in this study. Hence, faunal assemblages appear to be dominated by indigenous species whose distributions reflect the oceanographic and sedimentologic factors that limited living representatives. INTRODUCTION The accuracy and reliability of foraminifer-based paleoenvironmental reconstructions depend, in part, upon the ability to distinguish in situ from allochthanous assemblages. Because microfossil assemblages are susceptible to displacement by bottom currents, recognizing the disruptive effects of postmortem transportation is especially important. Experiments that predict the behavior of foraminiferal tests as sedimentary particles can help to assess whether or not sorting by currents has modified an assemblage (Kontrovitz et al. 1978; Kontrovitz and Snyder 1981). The Washington continental shelf is an appropriate area to study the effect of bottom currents on the transportation of sedimentary particles because extensive data on the physical oceanography and geology of the region, and an adequate sample base are available. Low-level radioactive waste introduced into the Columbia River by the Hanford reactors from 1943 to 1971 stimulated interest in potential environmental effects (Pruter and Alverson 1972; Foster 1972). The study of radionuclides traced through the river and onto the shelf has contributed to the large volume of data on current patterns and sedimentary processes across this margin. The preceding paper compares distributional patterns of benthic foraminifera with large-scale patterns of sediment distribution. The objective of this paper is to assess the extent to which bottom currents have sorted assemblages so that the influence of postmortem transportation can be evaluated. METHODOLOGY Traction velocities were estimated for 31 of the 106 benthic foraminiferal species identified in this study (Appendix I). These 31 were selected because they occur in 15 or more samples or in two or more samples with a relative abundance greater than 5 percent (Appendix II). Their cumulative abundance ranges from 90.2 to 100 percent of the assemblage, with a mean of 98.2 percent (S.D. = 1.9 percent). Approximately twenty specimens of each species were individually measured to determine their long, intermediate and short dimensions. Maximum projection sphericity (MPS) was then calculated for each specimen. MPS is defined as the 3 () where S is the short dimension of the particle, and L and I are the long and intermediate dimensions, respectively. The traction velocity for each specimen was computed using the following regression equation: Y = 22.3 19.8(MPS), where Y is estimated traction velocity and 22.3 is the intercept of the y-axis (see Kontrovitz et al. 1978; Kontrovitz and Snyder 1981). Mean traction velocity was then interpreted for each species. Within-species versus between-species variation was evaluated using Scheffes method of multiple comparisons in order to group species having similar estimated traction velocities. Scheffes method results in fewer significant differences than most other methods of multiple comparison, and it is not sensitive to unequal numbers of observations among groups. Because the method is so rigorous, Scheffe (1959) recommended using the 0.10 level of significance. F-distribution tables at this level are provided by Winer (1971). The species within each group delineated by this method should be transported together (Kontrovitz et al. 1978; Kontrovitz and Snyder 1981). micropaleontology, vol. 36, no. 3, pp. 259-282, pls. 1-8, 1990 259 This content downloaded from 157.55.39.112 on Wed, 07 Sep 2016 05:24:39 UTC All use subject to http://about.jstor.org/terms S. W. Snyder, W. R. Hale, M. Kontrovitz: Postmortem transportation of modern foraminifera of the Washington continental shelf MEAN TRACTION VELOCITY (CM/SEC) RELATIONSHIPS AMONG MEAN TRACTION VELOCITIES (EACH SPECIES COMPARED TO ALL OTHER SPECIES) ADERCOTRYMA GLOMERATA A-4.56 NONION LABRADORICUS 6.01 LAGENAMMINA ATLANTICA 6.15 RECURVOIDES TURBINATUS ---6.-45GLOBOBULIMINA AURICULATA --6.48 ANGULOGERINA ANGULOSA 6.81 EGGERELLA ADVENA (AVE.) --7.09 GAUDRYINA ARENARIA 7.11 BULIMINELLA ELEGANTISSIMA 7.49 EGGERELLA ADVENA (LARGE) ---7 .58--UVIGERINA JUNCEA 7.64 NONIONELLA STELLA 7.77 PULLENIA SALISBURYI 7.89 HAPLOPHRAGMOIDES BRADYI 8 EPONIDES LEVICULUS 808 REOPHAX ARCTICA --4 BUCCELLA ANGULATA 1 TROCHAMMINA PACIFICA 8.6 EPISTOMINELLA VITREA --8.74 NONION AURICULUS ELPHIDIUM EXCAVATUM 9.02 CLAVATA FORM REOPHAX SCORPIURUS 9-37 ALVEOLOPHRAGMIUM JEFFREYSI 9.40 TEXTULARIA EARLANDI 10.47 SPIROPLECTAMMINA BIFORMIS -10.48 TROCHAMMINA SQUAMATA ---1084 BOLIVINA PACIFICA 10.94 TROCHAMMINA NITIDA 1 Q TROCHAMMINA ROTALIFORMIS 1 1. ALVEOLOPHRAGMIUM 1 1.75 COLUMBIENSE TROCHAMMINA KELLETTAE 13.27 -5

Ocular sinuses in some modern and fossil species of Echinocythereis (Ostracoda)

Ocular sinuses were studied in some Cenozoic species of the ostracode genus Echinocythereis. Internal molds indicate that the sinus is elongate and stalklike. The distal portion is expanded, with a central or offset concavity and anterior and posterior convexities. The topography is the complement of the inner surface of the eyespot. The right sinus is the larger in a carapace; it has only one major opening, the ocular pit, whereas the left sinus has an additional hole formed by the anterior hinge socket. Interspecific variation is seen in the shapes of the ocular sinuses. Such variation is useful in taxonomic applications.

Ocular Sinuses in Genera of Ostracod Family Trachyleberididae: ABSTRACT

The ocular sinuses of seven genera of ostracods (Trachyleberididae) were studied through the use of internal molds and thin and polished sections. The three-dimensional aspects of the ocular sinus in the genera Actinocythereis, Henryhowella, Malzella, Orionina, Puriana, and Radimella have not been studied before. Echinocythereis, previously studied, was included for comparison. Morphology of the sinuses varies from the low moundlike form in some specimens of Henryhowella, to the long structure in Actinocythereis. With the exception of Henryhowella, all other genera have ocular sinuses with many features in common. These properties include a stalk-like appearance marked by a distinct constriction someplace along the length of the stalk. Most of the sinus is circular in cross section except the distal portion, which is expanded and irregular in shape, presumably to accommodate the portion of the eye with the lens cell, retinal cells, and rhabdomes. The surface of the distal portion is dominated by a concavity that is the complement of the convexity of the adjoining eyespot. Adjacent to the convexity is an anterior lobe or rim and usually a higher posterior rim Channels with diameters of 2 to 6 µm probably are passageways for axons. Ontogenetic development includes an early, low, cone-shaped sinus with a central concavity. Later juveniles in most taxa have a stalk, as do adults. Despite overall similarities of the ocular sinuses, detailed examination indicates that genera and species can each be distinguished using this feature. Variations in size, shape, proportions, and secondary topography are diagnostic; thus, another character is available for taxonomic purposes. End_of_Article - Last_Page 1425------------

Morphology and Dioptrics of Some Ostracod Eyespots: ABSTRACT

On the Gulf Coast, as in other areas, ostracods have been much used in interpreting paleoenvironments. Such use may be enhanced by study of the ocular structures, including eyespots. Eyespot morphology appears to relate to light levels, which in turn are related to water depths. Thus, a new means of reconstructing water depths may be available. Eyespots from two species of Echinocythereis from modern sediments along the Gulf Coast were studied using polished sections and electron and light microscopy. The inner surface of an eyespot is undulating and has a central convex portion and posterior concavities, each with a small radius of curvature compared to the convex outer surface. Light is converged most strongly by the central area and is focused in the underlying eye space. Astigmatism occurs as light passes through the areas away from the center, in which case the focus is beyond the eye cavity in the absence of a tapetal layer. Comparison of a modern and an extinct (Eocene) species of Echinocythereis indicates similar morphology and presumably similar functioning. A potential exists for discerning modern morphology as rel ted to water depth and applying such knowledge to fossil forms and their environments. End_of_Article - Last_Page 1214------------

Diagenetic Changes to Microfossils: Experimental Study: ABSTRACT

An understanding of taphonomic processes including diagenesis would enhance the usefulness of fossils such as the Foraminifera. In this study, shells of five modern species of calcareous Foraminifera were subjected to temperatures and pressures (T-P) that simulated burial. One kilometer (0.6 mi) increments were used with a maximum simulated depth of 10 km (6 mi) in wet sediment. An increased alteration of shells occurred at each higher T-P in each sediment type (quartz, illite, or calcite). Shells in quartz were more altered than those treated in either illite or calcite. Compared to untreated shells, pores in quartz at 5 km (3 mi) were enlarged by 15%, and tiny hillocks were visible at high magnification (2,000 X). At 6 km (3.7 mi), high sharp pinnacles were formed and pores were enlarged 30 to 50%. At 7 km (4.3 mi), long narrow solution channels developed while pores were increased by 40 to 60% in diameter. The next T-P increment (8 km, 5 mi) caused even greater pore solution, whereas at 9 km (5.6 mi) sutures were obliterated and the previously formed pinnacles were removed. At the highest T-P (10 km, 6 mi), chambers and shell outlines were highly altered a d newly formed crystals appeared. There were platelets oriented perpendicular to the shell surface; often they were arranged as rosettes. Under experimental conditions, alteration features of Foraminifera shells appear diagnostic of certain T-P levels. If such features develop on shells in natural sediments they may be useful to reconstruct some conditions of diagenesis. End_of_Article - Last_Page 1466------------

Reliability of Microfossil Assemblages as Paleoenvironmental Indicators: ABSTRACT

Ostracoda and Foraminifera have been used throughout the petroleum industry as paleoenvironmental indicators even when the reliability of the assemblages cannot be demonstrated. Such reliability can be evaluated only by knowing if the fossils have been subject to transport by water currents. In this study, threshold velocities of shells were measured in a flume with a moveable sediment substrate. The velocities were different for the several genera and some species thereby providing a means of evaluating fossil assemblages. An assemblage composed of specimens with the same threshold velocities would have been transported (sorted) or represent the residual after other shells had been moved away. An assemblage with shells having different velocities would be undisturbed and would be reliable as an environmental indicator. The best predictors of threshold velocity for the small calcareous shells are several measures of shape including the maximum projection sphericity and operational sphericity. They can be used to predict (.01 level) threshold velocities and provide a reliable objective means of testing the usefulness of fossil assemblages. End_of_Article - Last_Page 1686------------