Showing papers on "Foraminifera published in 1975"

Distribution of foraminifera in surface waters of a coastal upwelling area

Abstract: BIOCOENOSES of planktonic foraminifera are usually accepted to be good indicators of different sorts of oceanic water masses1, and it is assumed that their ecological requirements have not changed drastically during the Quaternary2. Their remains have, therefore, been used for approximately the past 40 yr (ref. 3) to study, qualitatively as well as quantitatively, the palaeoclimatic record4 preserved in young, calcareous, deep-sea sediments. Despite this, however, the mechanism of the formation of death assemblages and sediment assemblages is very poorly understood, mainly because the distribution pattern of planktonic foraminiferal biocoenoses and their output of shell material is only poorly known.

Sodium, magnesium and strontium in the tests of planktonic foraminifera

Abstract: We have determined Na/Ca, Mg/Ca, Sr/Ca, AI/Ca and CI/Na atom ratios in about sixty samples of individual species of planktonic foraminifera. Na/Ca and Sr/Ca ratios are constant in different tests of one species, but Mg/Ca ratios show considerable variability. Data indicate that Na and Sr are distributed homogeneously throughout the tests, while Mg is distributed heterogeneously. Na/Ca, Mg/Ca and Sr/Ca ratios of different species from an Upper Pleistocene assemblage from the Tasman Sea covary, with shallow-living species having the highest ratios. Atom ratios of Recent North Atlantic Globigerinoides sacculifer (Brady) and G. ruber (d'Orbigny) samples do not show any clear-cut temperature dependence. It appears that at one location atom ratios increase with temperature or a temperature-related factor, and that over a broad geographical area variables other than temperature affect trace element abundance. Sodium, magnesium and strontium in the tests of planktonic foraminifera INTRODUCTION The study of the distribution of "sea salt major cations" (herein defined as Na, K, Mg, Ca and Sr) in foraminiferal calcite is of interest for a number of reasons. First, the distribution of these elements may provide an insight into biochemical processes occurring during calcification. Second, if investigations of Recent skeletal chemistry reveal that trace element abundances vary in a quantifiable way with environmental parameters, we can use skeletal chemistry as an ecological and paleoecological index. Third, the study of fossil skeletal chemistry is our prime hope for deducing past variations in the chemistry of sea water. Our interest in these problems has prompted us to undertake a comprehensive study of foraminiferal calcite chemistry; the purpose of this paper is to summarize our results to date. Our effort builds on results of a number of earlier workers. Blackmon and Todd (1959) found that benthic foraminifera had skeletons composed dominantly of high magnesian calcite, but planktonic foraminifera were composed of calcite containing less than 2 mole percent MgCO3. Emiliani (1955), Switzer and Boucot (1955), and Mayer (1932) also found that the skeletons of planktonic foraminifera were composed of calcite. Emiliani (1955) determined the TiO2, A1203, Si02, Fe203, MnO, MgO, and SrO contents of eight samples composed of single species of planktonic foraminifera. He found that the SrO content was fairly constant at a level of 0.13%, but that all other concentration values varied sympathetically in a way that could be ascribed to the presence of contaminating detritus. Krinsley (1960) analyzed ten samples for MnO, TiO2, A1203, MgO, CuO, and NiO, and concluded (contrary to the belief of Emiliani) that the shells contained on the order of 0.1 5% by weight MgO that could not be ascribed to detrital contamination. Lipps and Ribbe (1967) reinforced this conclusion with their electron microprobe work, showing that those parts of the foraminiferal tests free of detritus contained about 0.2% by weight MgO. Savin and Douglas (1973) determined the MgCO3 contents and 5018 of foraminifera and found that the tests contained between 0.1 and 0.4% by weight MgO. With the exception of Globorotalia truncatulinoides (d'Orbigny) MgO content of foraminiferal calcite increased as isotopic temperature increased. The most extensive data in the literature on planktonic foraminiferal chemistry are the analyses of Kilbourne and Sen Gupta (1973). They found that the Mg content increased linearly with habitat temperature and that solutionsusceptible species had higher Mg contents than more resistant species. Results of Savin and Douglas (1973) also agreed with this latter conclusion, leading those authors to suggest that the Mg content controlled solution susceptibility. micropaleontology, vol. 21, no. 4, pp. 448-459, october, 1975 448 This content downloaded from 157.55.39.147 on Sun, 07 Aug 2016 05:32:01 UTC All use subject to http://about.jstor.org/terms BENDER, LORENS, and WILLIAMS

Weyl's theory of glaciation supported by isotopic study of Norwegian core K 11

Abstract: Oxygen-18 analyses of pelagic and benthic foraminifera from core K 11 indicate that during the last glaciation Norwegian Sea bottom waters were warmer than in modern times and had the same physical parameters (temperature, oxygen isotope ratio, and salinity) as the North Atlantic deep water. This result indicates that the glacial Norwegian Sea was not a sink for dense surface water, as it is now, and that during glacial times North Atlantic deep water invaded the deep Norwegian basin.

Oxygen and Carbon Isotopes from Calcareous Nannofossils as Paleoceanographic Indicators

Abstract: Oxygen-18 and carbon-13 analyses of well-preserved calcareous nannofossils have been compared with those of foraminifera contained in Cenozoic cores collected in the Southern Ocean during the Deep Sea Drilling Project. The results indicate that calcareous nannofossils deposit calcium carbonate at or near equilibrium with oceanic surface waters and that they can be used as paleotemperature indicators.

Marine phosphorite formation off Peru

Abstract: Formation of contemporary phosphorite in the Peru-Chile offshore area is confirmed. Synthesis is believed to occur as a result of replacement of carbonate tests of Holocene benthonic Foraminifera in the interstitial waters of organic-rich sediments. Step-by-step phosphatization of Holocene benthic Foraminifera can be demonstrated. Four simultaneous requirements for formation of phosphorites are: (a) sediments rich in organic detritus blanketed by (b) water with low concentrations of dissolved oxygen, (c) low rates of inorganic (especially terrigenous) sedimentation and (d) low but not negligible concentrations of calcium carbonate in the sediment.

Late Cenozoic Planktonic Foraminifera and Paleoceanography at DSDP Site 284 in the Cool Subtropical South Pacific

Abstract: Population statistics of planktonic foraminiferal samples through DSDP Site 284 (late Miocene to Recent) indicate surface-water temperature variations. According to biostratigraphic correlations, the temperature variations were less intense than, but were synchronous with inferred temperature variations on the eastern side of the North Island of New Zealand. The biostratigraphy permitted dating by reference to the paleomagnetic sequences determined in New Zealand marine strata. Water temperatures were relatively warm until t = 4.7 m.y. and were significantly cooler between t = 4.7 to t = 4.3 m.y. (equivalent to Kapitean Stage of New Zealand). A brief minor warming is associated with the New Zealand MiocenePliocene boundary and is followed by a cool interval to t = 4.1 m.y. a prolonged warm interval to / = 2.6 m.y. (Opoitian Stage), and a significantly cooler episode to t = 2.15 m.y. Following this, temperatures fluctuate to an early to mid Pleistocene disconformity. The faunally determined paleotemperature changes coincide with changes in oxygen isotope composition of the water considered by Shackleton and Kennett (this volume) to indicate significant changes in ice volumes on Antarctica in the late Miocene and within the Northern Hemisphere in the late Pliocene and Pleistocene. The validity of planktonic foraminiferal paleotemperatures, placed in doubt by contradictory molluscan data in California and New Zealand, is justified by the comparative simplicity of planktonic ecologies, consistent sympathetic variations of different parameters of planktonic foraminiferal populations, and their consistent relationship to oxygen isotope data and paleoglacial history. Coiling of TV'eogloboquadrina pachyderma did not adopt its presentday pattern until early in the Pliocene and cannot be used for paleotemperature analysis of the late Miocene and early Pliocene faunas.

Oceanic micropaleontology: Progress and prospect

Abstract: The seventies were marked by explosive development of oceanic micropaleontology and drastic changes in emphasis. The main impetus for expansion came from deep-sea drilling. Global sampling made possible a global approach to paleoceanography and biostratigraphy. Scanning electron microscopy extended routine study to extremely small particles. The use of computers aided in quantifying paleoenvironmental reconstruction and in refining stratigraphic resolution. Integration of micropaleontologic information with physical and chemical oceanography has helped to make micropaleontology the mainstay of paleoceanographic research. The biogeography of planktonic foraminifera and of the paleontologically important coccoliths is now well documented. This is not yet true for radiolarians and diatoms. Much progress has been made in mapping distributions on the sea floor, in all groups, and in relating such distributions to supply, dissolution, and redeposition. Two major problems have been identified. One is the role of fecal pellets in the transfer of coccoliths and diatoms to the sea floor. The other is the relationship between preburial preservation states of microfossil assemblages and their postburial diagenesis (‘diagenetic potential’ of an assemblage). Important advances in Quaternary research include increased stratigraphic resolution, quantitative temperature determination (accuracy about 2°–3°C), and isotopic evidence for glacial-interglacial fluctuations. Changes in productivity and preservation patterns remain major questions. Pre-quaternary paleoceanography has largely been concerned with establishing biogeographic patterns through time and their correlation with changing geography due to plate tectonics. The mechanisms of cause and effect (surface currents, bottom water flow, water mass stratification, etc., versus biogeography and sedimentation patterns) remain speculative on the whole. The question of the origin of diversity and its variations through time continue to attract attention. There appears to be a positive correlation between diversity and isotopic temperature through time. Causes for major extinctions are unknown and are likely to remain so until the fundamental question of which processes control the overall productivity of the ocean is resolved. A model is developed, proposing a control of present microplankton assemblages by successive change of the limiting nutrient (silica-bionitrogen-phosphate). It is argued that a low-fertility ocean should be characterized by high silica and phosphate concentrations and that this should be recognizable in the record. Stratigraphic work has greatly benefited from DSDP results, especially when care was taken to recover long sequences. Zonations, in part preliminary, are now available for all major groups, for Cretaceous and Cenozoic sequences. Attempts to correlate some of these sequences with the less complete standard sections reveal a fundamental weakness in the concept of stratigraphic standard.

Bathymetry of the Carpathian Flysch Basin

Abstract: The environment in which the Carpathian flysch was deposited is here discussed. The views ascribing !its origin to paralic, littoral or neritic environment. Its are rejected on the basis of the sedimentary features and faunal evidence. Arguments are presented in favor of deposition from decelerating currents. This type of deposition is indicated by the sorting of mineral grains and fossils, an approximately positive correlation between the thickness and coarseness of beds and ·dimensions of erosional structures (flutes) on their soles, and a succession of structures in flysch sequences. Proximal, intermediate and distal deposition regions are characterized in each member of the succession. From the sedimentary features the conclusion is drawn that the Carpathian flysch was deposited at depths greater than the neritic zone. It is shown that the makrofauna contains 50 species of Foraminifera which in present-day seas live in waters with normal salinity. Most of these species display a marked preference for bathyal and abyssal depths. Several Foraminifera, closely related to modern deep-water species, also occur in the Carpathian flysch. The presence of calcareous Foraminifera in nearly an stratigraphic members excludes a deposition below the calcium carbonate compensation depth. Consequently, bathyal (mostly upper bathyal) depths are assigned to the Carpathian flysch basin, and changes in depths during the long deposition (uppermost Jurassic through Lower Miocene) are estimated tentatively. It has been found that the number of branched and patterned traced fossils is larger in the beds, to which greater depths are assigned on the basis of sedimentological and microfaunal evidence.

18O Changes in Foraminifera Carbonates During the Last 105 Years in the Mediterranean Sea

Abstract: The Mediterranean response to major climatic events during the Upper Pleistocene could be seen as an integration of the principal phenomena particular to oceans and of regional phenomena peculiar to the Mediterranean Sea. The magnitude of oxygen isotope changes in foraminifera tests suggests that the temperature variations between stadial and interstadial periods could not exceed I1C and that the correction factorfor isotopic changes of waters should be about twice the value usedfor the oceans,or

Holocene Carbonate Sedimentation on Northern Belize Shelf: PART 1

Abstract: The continental shelf of northern Belize is mantled by calcium carbonate sediments deposited in environments characterized as fluvial, estuarine, and normal marine. The composition, grain size, and carbonate mineralogy of these Holocene carbonate sediments were determined quantitatively by thin-section point-count analyses, sieve analyses, and X-ray diffraction techniques, respectively. Factor analysis of the accumulated data, supplemented with observations on the presence or absence of sedimentary structures, served to delineate eight facies: (1) reef facies--characterized by an abundance of coralline algae and corals welded into a wave-resistant frame; (2) Halimeda facies--characterized by abundant plates of the green alga Halimeda; (3) peneroplid-sand facies-typified by an abundance of large peneroplid Foraminifera; (4) miliolid-mud facies--distinguished by the association of many small miliolid Foraminifera with high-magnesi m calcite mud; (5) laminated miliolid-mud facies--characterized by a relatively thick sequence containing laminations of foraminiferal sand intercalated with carbonate ("lime") mud; (6) terrigenous facies--characterized by the presence of relatively large quantities of quartz sand; (7) cryptocrystalline-grain facies--distinguished by the relative abundance of cryptocrystalline calcite grains; and (8) ostracod-mud facies--characterized by the association of ostracods and scattered diatoms and charophytes with "lime" and/or terrigenous mud. The development of the coral-reef and Halimeda facies is limited to current-agitated marine waters of normal salinity, whereas the development of the other five carbonate facies is related to reduced current agitation and/or varying degrees of hyposalinity. The volume and mineralogy of the mud in each facies are controlled by current strength. They are determined by the transporting capacity of the currents in each of the depositional environments and, indirectly, by the capacity of the currents to induce the formation of mud-size particles through the abrasion of sand-size constituents.

Neogene Planktonic Foraminifera from the Central North Pacific, Leg 32, Deep Sea Drilling Project

Abstract: Three sites (Sites 305, 310, and 313) drilled during DSDP Leg 32 in the central North Pacific recovered Neogene calcareous sediments. These sites, now located between 2900 and 3500 meters water depth, lay below the lysocline throughout the time of deposition. Site 313, within a basin in the Mid-Pacific Mountains, is at a locale subject to slumping and has little biostratigraphic value. Sites 305 and 310, located on Shatsky Rise and Hess Rise, respectively, provide a valuable record of late Neogene planktonic foraminiferal and paleooceanographic events. The occurrence of calcareous and siliceous microfossils in these two sections permits the direct comparison and correlation of zonation schemes based on the two microfossil types. The positions of the Plio-Pleistocene and MioPliocene boundaries, placed at the oldest occurrence of Globorotalia truncatulinoides and G. tumida, respectively, are in good agreement with the boundaries based on other microfossil zonations. Robust, temperate-water forms of Globorotalia that make up the G. conoidea to G. inflata bioseries are consistent elements of the Pliocene and Pleistocene assemblages. The lowest appearances of G. conoidea at the Miocene/Pliocene boundary and Neogloboquadrina pachyderma in the uppermost Miocene result from improved preservation of calcareous material above those levels. The disappearance of Globoquadrina dehiscens in this area is associated with a late Miocene cooling. This species disappears earlier at the higher latitude Site 310 than at Site 305. Globorotalia puncticulata and G. crassaformis first appear at about 4.0 to 4.2 m.y. B.P. simultaneously with the radiolarian species Lamprocyclas heteroporos. This level, which approximates the first occurrence of Sphaeroidinella dehiscens in temperate latitudes of the North Pacific and has been taken as the Mio-Pliocene boundary in marine sections of the northeastern Pacific margin, is approximately 1 m.y. younger than the type MioPliocene boundary in Italy. The disappearance of keeled forms of the G. conoidea-G. inflata group (represented by G. conoidea s.l.) at approximately 2.7-2.8 m.y. B.P. is followed very shortly by the first appearance of G. inflata, which apparently migrated into the North Pacific slightly later than elsewhere. Late Neogene sediments younger than approximately 6.3 m.y. were deposited with an average rate of accumulation of 7.6 to 10.8 m/m.y., with an increased rate in late Pliocene and a 1-m.y. interval of nondeposition in the late early Pliocene. Neogene sediments older than 6.3 m.y. accumulated at a much lower average rate, resulting in a very condensed series lying unconformably on sediments of Oligocene age. Coiling changes in populations of N. pachyderma reflect surfacetemperature variations. The substantial late Miocene cooling observed in marine sections throughout the margins of the North Pacific resulted in the southward shift of the 10°C surface isotherm over Hess Rise. A sharp decrease in calcium-carbonate dissolution, reflected in both sequences by a change in dissolution facies, occurs near the Mio-Pliocene boundary and is probably correlated with the abrupt drop of the CCD at that time in equatorial regions of the Pacific. INTRODUCTION and Hess rises, respectively. These rises are broad, irregularly shaped plateaus, broken into blocks by norCalcareous Neogene sections were recovered at three mal faulting and elevated above the surrounding abyssal of the drilling sites (Table 1) during DSDP Leg 32 in the sea floor. Site 313 lies within a basin among the North Pacific. Sites 305 and 310 are located on Shatsky seamounts of the northeastern Mid-Pacific Mountains.

Cenozoic Planktonic Foraminifera from Antarctic Deep-Sea Sediments, Leg 28, DSDP

Abstract: In general, the degree of our knowledge of the stratigraphic distribution of planktonic foraminifer assemblages and their species composition is an inverse function of geographic latitude. Whereas the lower latitude faunas have been extensively studied, those of the high-latitude oceanic regions, especially around Antarctica, have remained virtually unknown. This has been due mainly to the inaccessibility of older sediments to piston coring and other sampling techniques prior to the Deep Sea Drilling program. Leg 28, the first venture of Glomar Challenger into extremely high southern latitudes, thus promised to be a unique opportunity to study the history of high-latitude planktonic foraminifers and how it has been influenced by the associated environmental parameters of low temperature and high nutrient levels and associated high phytoplankton productivity. Another aim would be to determine how long these environmental conditions have existed and if they have changed with time. The results were, unfortunately, somewhat disappointing. Foraminifers occur sporadically in the Antarctic sections cored during Leg 28; where present, they make up a minor portion of the microfossil assemblage and are of very low diversity. In addition, most assemblages show the effects of carbonate dissolution. The drill sites in the Ross Sea, which might have been expected to yield less dissolved assemblages, are mostly barren of planktonic foraminifers, apparently for paleoenvironmental reasons. Nevertheless, two general conclusions seem warranted on the basis of Leg 28 results. (1) Antarctic foraminifer assemblages have had a characteristically polar aspect since the Oligocene. That is, they are of extremely limited diversity, and some of the species present are morphologically similar to Globigerina pachyderma (Ehrenberg), which is presently the dominant species in high-latitude waters. (2) The major change in planktonic foraminifer ecology in the Antarctic area took place at or near the Eocene-Oligocene boundary. This is evidenced by the recovery of a diverse upper Eocene assemblage at Hole 267B, at 59° south latitude which is in marked contrast to the sparseness of younger faunas. This change is most likely related to the initiation of glacial conditions on Antarctica (see General Synthesis, Hayes and Frakes, this volume). Leg 28 drill sites in the Antarctic are shown in Figure 1, and site data are given in Table 1. Site 264, the first Leg 28 site, was drilled on the Naturaliste Plateau, close to port. It was primarily a test site to check the operation of the drill rig and is not included in the present report; a discussion of the planktonic foraminifers at this site can be found in the site report for Site 264 (Chapter 2), and in the report by Kennett (this volume). A distribution chart of planktonic foraminifers at this site is given in Table 2 of the present report. Distribution charts of planktonic foraminifers are given for Sites 265 and 266 in Tables 3 and 4, respectively. Occurrence data for the other sites (267-274) are given at the end of this chapter in the form of species lists. Selected species are illustrated in Plates 1 and 2.

Earliest calcareous foraminifera

Abstract: WE present here evidence that early Palaeozoic calcareous foraminifera existed and were relatively complex (multilocular and multiserial) in form but that they have been regarded formerly as calcareous algae. The early part of the invertebrate fossil record during the Cambrian period seems to show a striking contrast between the abundance of highly developed organisms such as the trilobite arthropods and the paucity of simpler forms such as the foraminiferal protozoans. Foraminifera are very small acellular animals with an important role in marine food chains1 and it is reasonable to expect them to have been a significant component of the benthic fauna throughout the Palaeozoic. Yet few foraminifera have been reported from the Lower Palaeozoic and those described from the Cambrian are mainly simple forms with unmineralised tectinous or agglutinated tests2–4. Some more complex agglutinated forms are known from the Upper Cambrian5, but the first generally recognised calcareous foraminifer is the uniserial Saccaminopsis from the late Ordovician4. Consequently, the assumptions that Lower Palaeozoic foraminifera were primitive and mainly non-calcareous have been taken as bases for inferences concerning the early evolution of the group3–4 and the paradoxical, yet apparently inescapable, conclusion has been drawn that Cambrian foraminifera are very scarce.

On the Use of Benthic Foraminifera as Sediment Tracers in a Hawaiian Bay

Abstract: Populations of foraminifera were investigated in regard to the suitability of the various species as indicators of sand transport. Of 53 species recorded in the sediments of Kahana Bay, Oahu, 16 showed distribution patterns that give evidence of the direction of sand transport within the littoral cell. IN THE COURSE of a study to map and calculate offshore sediment volume around Hawaii (Campbell et al. 1970), a detailed sampling of Kahana Bay, Oahu, was undertaken for the purpose of defining the sources of the sand as well as paths of transport within a littoral cell. A cursory examination of the microfaunas of the samples showed that foraminifera were dominant and that the foraminiferal populations varied specifically and numerically from sample to sample. Since data relevant to the physical oceanography and sedimentology ofthe bay were available, analyses of the foraminiferal populations of 53 selected samples were made to determine whether a systematic variation existed that could provide an additional means of determining the direction of sand transport. The behavior of foraminiferal tests as sediment particles has been investigated by Grabert (1971). THE ENVIRONMENT Kahana Bay, located on the northeast (windward) coast of Oahu, Hawaii (Figure 1), is a submarine extension of Kahana Valley. Abundant rainfall in the valley, more than 250 inches a year in the higher elevations (Mink, Lee, and Watson 1963), produces a discharge of 29.5 mgd by Kahana Stream (Cox and Gordon 1970). The stream usually discharges at the I Hawaii Institute of Geophysics contribution no. 637. Manuscript received 1 March 1974; revised and returned 21 June 1974. 2 University of Hawaii: Hawaii Institute of Geophysics and Department of Geology and Geophysics, Honolulu, Hawaii 96822. 3 University of Hawaii: Hawaii Institute of Geophysics and Department of Geology and Geophysics, Honolulu, Hawaii 96822. 99 eastern side of the bay; however, after unusually heavy rainfall a channel opens through the center of the beach. Along the east and west shores of the bay, the submarine topography is bounded by fringing reefs whose surfaces range from a little more than 10 feet below sea level to blocks qf coral that are exposed during low tides (Figure 2). The outer edges of the reef drop vertically 30 feet or more to a sandy area in the center of the bay that forms a channel sloping gently seaward. The channel sands are rippled uniformly to depths of at least 40 feet. A small patch reef is located in the northwestern corner of the channel. METHOD OF STUDY Sediment samples and in situ water salinity and temperature measurements were taken in Kahana Bay, Stream, and Valley from September 1970 to August 1971. Of the 136 surface sediment samples collected, only 42 (those with the suffix F, Figure 3) were collected by hand and treated with a solution of rose bengal and ethyl alcohol to preserve the living protoplasm while staining it red. The remaining deep-water samples were obtained with a van Veen grab sampler and were not stained, because they were initially collected solely for sedimentological analysis. Thus, the reported distribution of live specimens is only an approximation because some of the samples were not stained to detect those individuals, and because seasonal variation was not sampled systematically. As an independent means of determining paths of sediment transport, direct measurements of sand movement were made through a sand tracer experiment as described by 100 PACIFIC SCIENCE, Volume 29, January 1975 .," . -. .., o , o t.:-.. 5 ~t \." ':":~=S.'-A1l1l'tlOT ~~_.~. , SANO-e~ ~BI:TIKY:~~~:~~:::~~ tAT '.30.00.>00 . ""'. PACIFIC OCEAN TOP

Distribution of Holocene Benthonic Foraminifera on the Belize Shelf

Abstract: The tropical, reef-bounded continental shelf of Belize encompasses a wide variety of marine and marginal-marine environments. The distribution patterns of foraminiferal assemblages in this area reflect this environmental diversity. The distribution is strongly influenced by the effect of both the seaward barrier and the adjacent landmass on the hydrography and sedimentation of the narrow shelf. Nine foraminiferal assemblages are defined on the basis of taxonomic composition, faunal dominance, faunal diversity, and faunal density of total (living plus dead) foraminiferal populations. A high-diversity miliolid-dominant assemblage occurs throughout the stenohaline, shallow-water areas of the barrier and outer platforms-areas characterized by calcium carbonate deposition and coral-reef growth. Areas of high turbulence on the windward edge of these platforms contain a unique Archaias-Asterigerina-dominant assemblage. A low-diversity miliolid-dominant assemblage is present in the northern shelf lagoon and Chetumal Bay, which are areas of variable salinity, shallow water, partially restricted circulation, and carbonate mud deposition. A unique low-diversity miliolid assemblage dominated by Archaias occurs in a part of Chetumal Bay behind a large carbonate island. In the relatively deep southern shelf lagoon, a low-diversity Cribroelphidium-dominant assemblage occurs in two areas: (1) the landward part of the embayed Gulf of Honduras, an area influenced by high stream discharge, and (2) the lagoonal area that is adjacent to the barrier platform and is characterized by restricted circulation and mixed carbonate-terrigenous sedimentation. A high-diversity Cribroelphidium-dominant assemblage is present in deep lagoonal, stenohaline areas of uninhibited circulation. A Cribroelphidium-Quinqueloculina-dominant, mixed faunal assemblage marks the zone of influx of shoal-derived material into the lagoon. The deepest part of the continental shelf is the site of a Globocassidulina-dominant assemblage. The mainland coast of Belize is characterized by a Quinqueloculina-Cribroelphidium-dominant assemblage associated with nearshore quartzose sand and silt and a suite of marginal-marine assemblages including delta, marsh, and mainland-lagoon populations. Data on living populations provide information concerning foraminiferal ecology but do not produce consistent, mappable faunal assemblages. Marked differences between the quantitative parameters of living and total populations in some areas are thought to result from recent shifting of environmental conditions and relict faunas, faunal displacement, seasonal and/or inadequate sampling of habitats, and unknown factors perhaps reflecting seasonal reproduction or differential rates of reproduction among species.

Stratigraphy and Sedimentation in the Kutai Basin, Kalimantan

Abstract: The Kutai sedimentary basin, situated along the eastern continental margin of Kalimantan, is one of the oldest and more prolific oil producing areas in Indonesia. The drilling for hydrocarbon began in the late nineteenth century and from 1969 to date, more than 90 exploratory wells have been drilled. The early stratigraphic subdivisions of the basin were based primarily on biostratigraphic zones using larger foraminifera. Presently, biostratigraphic zonation is being refined by using smaller planktonic and benthonic foraminifera, and calcareous nanoplankton. Sedimentation during the Early Tertiary was predominantly controlled by northern and southern source areas. Tectonic uplift of the Kuching High during Late Oligocene time resulted in a major shift of the sediment source area to the west. A high sediment influx formed extensive constructive delta systems in Middle Miocene to Pliocene time, prograding from west to east. Hydrocarbon accumulations in the Kutai basin are found in progressively younger sedimentary rocks to the east and are within sandstone deposited in a delta front and delta margin depositional environment.