Planktonic Foraminiferal Faunas Research Articles

Prediction of clinical effects of some anxiolytic and hypnotic drugs by averaged photopalberal reflex : M. Tanaka, H. Isozaki and K. Inanaga (Kurume, Japan)

Paleoclimate changes are reconstructed from Late Miocene-earliest Pleistocene deep-water sediments of the Solo River section, using fluctuations in planktonic foraminiferal faunas, water depth and clastic influx. Intervals with common cold-water planktonics (Globigerina bulloides, Neogloboquadrina cf. pachyderma) are thought to reflect periods of increased upwelling, triggered by Antarctic glaciations.Correlations with well Bodjonegoro-1 (Java), DSDP Site 62-1 and Lamont Core RC 12–66 (Equatorial Pacific) using planktonic foraminiferal datum levels and paleoclimate trends suggest non-synchroneity of several commonly used datums, probably due to differences in species concepts. It also allowed dating of the climate changes with regard to the magnetostratigraphic and numerical time scales.For correlations between different faunal provinces global climate changes are an extremely useful tool, probably superior to any single faunal datum. Using this, with other evidence, the following correlations could be obtained between the five “climatostratigraphic” zones in the Solo River section and the Mediterranean and New Zealand stages (from bottom to top): 1.Zone I, samples SR 63–SR 53, cool, older than 6.0 m.y. – ±5.8 m.y., magnetostratigraphic Epoch 6 (and older?) — basal Epoch 5, planktonic zone (Upper N16?-) N17, Mediterranean stages (upper?) Tortonian—Early Messinian, New Zealand Stages Tongaporutuan—Early Kapitean, Late Miocene.2.Zone II, SR 52–SR 35, moderately warm with fluctuations, ± 5.8 m.y.–5.0 m.y., Epoch—lowermost Gilbert, upper N17 (−N18?), Late Messinian (evaporite phase), Late Kapitean, Late Miocene.3.Zone III, SR 34–SR 33, cool, 5.0–4.8 m.y., within Lower Gilbert, (N18?-) basal N19, latest Messinian (“Lago Mare” phase), latest Kapitean or earliest Opoitian, latest Miocene.4.Zone IV, SR32–SR 18, warm to very warm, 4.8–±2.7 m.y., within Lower Gilbert — within Upperg Gauss, N19 within N21, Zanclean-Piacenzian, Opoitian Pliocene.5.Zone V, SR17–SR 12, cool, ±2.7 m.y.—age of top unknown, Upper Gauss-Lower Matuyama, within N21 (−N22?), Santernian or basal Calabrian s.l., Waipipian, basal Pleistocene (Late Pliocene of workers with different Pliocene-Pleistocene boundary concepts).

Late Neogene planktonic foraminiferal biostratigraphy and climatostratigraphy of the Solo River section (Java, Indonesia)

Paleoclimate changes are reconstructed from Late Miocene-earliest Pleistocene deep-water sediments of the Solo River section, using fluctuations in planktonic foraminiferal faunas, water depth and clastic influx. Intervals with common cold-water planktonics ( Globigerina bulloides, Neogloboquadrina cf. pachyderma) are thought to reflect periods of increased upwelling, triggered by Antarctic glaciations. Correlations with well Bodjonegoro-1 (Java), DSDP Site 62-1 and Lamont Core RC 12–66 (Equatorial Pacific) using planktonic foraminiferal datum levels and paleoclimate trends suggest non-synchroneity of several commonly used datums, probably due to differences in species concepts. It also allowed dating of the climate changes with regard to the magnetostratigraphic and numerical time scales. For correlations between different faunal provinces global climate changes are an extremely useful tool, probably superior to any single faunal datum. Using this, with other evidence, the following correlations could be obtained between the five “climatostratigraphic” zones in the Solo River section and the Mediterranean and New Zealand stages (from bottom to top): 1. Zone I, samples SR 63–SR 53, cool, older than 6.0 m.y. – ±5.8 m.y., magnetostratigraphic Epoch 6 (and older?) — basal Epoch 5, planktonic zone (Upper N16?-) N17, Mediterranean stages (upper?) Tortonian—Early Messinian, New Zealand Stages Tongaporutuan—Early Kapitean, Late Miocene. 2. Zone II, SR 52–SR 35, moderately warm with fluctuations, ± 5.8 m.y.–5.0 m.y., Epoch—lowermost Gilbert, upper N17 (−N18?), Late Messinian (evaporite phase), Late Kapitean, Late Miocene. 3. Zone III, SR 34–SR 33, cool, 5.0–4.8 m.y., within Lower Gilbert, (N18?-) basal N19, latest Messinian (“Lago Mare” phase), latest Kapitean or earliest Opoitian, latest Miocene. 4. Zone IV, SR32–SR 18, warm to very warm, 4.8–±2.7 m.y., within Lower Gilbert — within Upperg Gauss, N19 within N21, Zanclean-Piacenzian, Opoitian Pliocene. 5. Zone V, SR17–SR 12, cool, ±2.7 m.y.—age of top unknown, Upper Gauss-Lower Matuyama, within N21 (−N22?), Santernian or basal Calabrian s.l., Waipipian, basal Pleistocene (Late Pliocene of workers with different Pliocene-Pleistocene boundary concepts).

Late Miocene—early Pliocene planktonic foraminiferal biostratigraphy and paleoceanography of low-latitude marine sequences

Plate reorganization and development of polar glaciation are closely associated with the changing climatic conditions of the Cenozoic. The planktonic foraminiferal fauna in three low-latitude DSDP sites (224, Ninety East Ridge; 317B, Manihiki Plateau; 366A, Sierra Leone Rise) has been examined to determine how these regions responded to the late Miocene climatic cooling that has been previously observed in high-latitude regions. It has been proposed that an expansion of Antarctic glaciation and a resultant eustatic regression are associated with this cooling, with the latter being at least partially responsible for the Messinian “salinity crisis” in the Mediterranean. Only one of the sites, 366A, shows any significant faunal change during the late Miocene and early Pliocene (approximately 8-3 Ma). During the late Miocene, there is a decrease in the abundance of species considered to be tropical-subtropical, suggesting the incursion of a cool water mass into the Sierra Leone Rise region during this time. The lack of any major faunal changes at Sites 214 and 317B indicates that the water masses of the low-latitude regions of the Indo-Pacific were relatively unaffected by this cooling in the late Miocene. The three sites also show no evidence for a change in the level of the CCD between the late Miocene and early Pliocene; however, this is most likely due to their equatorial position and shallow water depth. Higher-latitude sites from both the Atlantic and the Pacific reveal a definite shoaling of the CCD during the late Miocene.

Planktonic foraminiferal fauna associated with eastern Mediterranean Quaternary stagnations

Bradley1 predicted, before any evidence from sediment coring in the Mediterranena Sea, that changing late Quaternary climatic conditions would result in periodic stagnations of the eastern basin and with them, accumulations of organic-rich sediments. Such organic-rich layers from the eastern Mediterranean were subsequently observed in sediment cores by Kullenberg2 and later named “sapropelitic layers”3. Since these initial observations, sapropels have been reported in most studies of Quaternary sediments from the Ionian Sea4–14. As a result, there is a great deal of information available concerning the chemical15–18 and sedimentological properties13–14, faunal characteristics19 and temporal9–11 and spatial10,12 distribution of late Quaternary sapropels. In the study reported here we have attempted to characterise the planktonic foraminiferal biogeography of such late Quaternary sapropels in terms of the modern distribution of foraminefara in the Mediterranean Sea.

Comparison of radiolarian/planktonic foraminiferal paleoceanography of the subantarctic Indian Ocean

A detailed paleoceanographic history of the Subantarctic region for the last million years was determined using paleomagnetic stratigraphy, radiolarian and planktonic foraminiferal biostratigraphy, and the oxygen isotope record from stages 1 to 13 (0.5 MY) in a deep-sea core (E45-74) from the southern Indian Ocean. Changes in the abundances of Antarctissa strelkovi and Neogloboquadrina pachyderma record 12 glacial/interglacial cycles. The paleoceanographic events based on the combined results of these siliceous and calcareous indexes agree with changes in the global ice-volume record. Calcium carbonate dissolution selectively alters the planktonic foraminiferal fauna and causes test fragmentation and increased numbers of benthic foraminifera and radiolarians. Intense periods of calcium carbonate dissolution are associated principally with glacial episodes and are probably related to increased Antarctic bottom-water activity as well as changes in surface-water mass positions.

Late Mesozoic and Cenozoic movements of the Italian Peninsula: Further paleomagnetic data from the Umbrian sequence

About 210 samples of rocks of late Early Jurassic to early Tertiary age from 37 sites in the Umbrian carbonate sequence in the Northern Apennines were investigated paleomagnetically. Special attention was paid to the Scaglia Formation of Cenomanian to middle Eocene age, and three well-correlated sections were studied in detail. Accurate relative ages were determined from the well-preserved planktonic foraminiferal faunas. Paleomagnetic directions of Toarcian-Aalenian to late Aptian sites group fairly well, which implies the absence of major rotational and latitudinal movements of the sampling area during that interval. An only minor phase of movement at about Tithonian time resulted in a counterclockwise rotation over approximately 10°. Late Aptian to late Cenomanian directions indicate a southward movement over 10° of latitude; this was followed by a 30° counterclockwise rotation during Turonian, Coniacian, and Santonian time, and in addition, a northward movement over 10° of latitude during Santonian and Campanian time. Maastrichtian to early Eocene data group reasonably well but also deviate from the present local field direction; this indicates a further 25° counterclockwise rotation and an additional northward movement over more than 10° post–early Eocene time. We suggest that the data presented here from the Northern Apennines are representative for the general pattern of movements of the Italian Peninsula. These paleomagnetically deduced movements conform during at least late Early Jurassic to early Tertiary time with the movements of the African plate as established from sea-floor spreading and paleomagnetic data. At the same time, however, the paleomagnetic results indicate that this coupled motion of the Italian Peninsula and the African continent did not persist until the present: a post–early Eocene 25° counterclockwise rotation of the Italian Peninsula must have occurred relative to Africa. Our data are compared with available paleomagnetic data from the western Mediterranean area. Their relation to the structural evolution of the areas concerned is discussed.

SEA LEVEL CHANGES IN THE NEOGENE OF SOUTHERN VICTORIA

The distribution and lithology of marine sediments in southern Victoria are related to climatic events and the associated sea level changes. The most extensive transgression on the northern (onshore) margin of the southern Victorian Tertiary basins occurred late in the Early Miocene, with widespread deposition of calcareous muds and localised calcarenites with Lepidocvclina. Shallowing at approximately 14 m.y. affected all southern Victoria, initiating lithological changes in the Otway and Port Phillip Basins, and coinciding with erosion in the Gippsland Basin. Throughout the Late Miocene the grain size of sediments tended to increase and cross-bedded calcarenites became more common, consistent with shallowing deposition and sea withdrawal. By approximately 6 m.y., near the end of the Late Miocene, the sea had completely withdrawn from the onshore areas of southern Victoria.Pliocene and Pleistocene outcrops are scattered and thin, and marine beds are exclusively of nearshore and shallow deposition. For much of this period sea level was lower than at present. High levels in the Pliocene are indicated at approximately 5 m.y. and 3.5 m.y. High sea levels, associated with the rapid alternation of glacial and interglacial periods which typify the Pleistocene Epoch, were initiated late in the Pliocene, close to 2 m.y.Changes to the planktonic foraminiferal faunas parallel the sedimentological responses to sea level change. These suggest that palaeoclimatic events were the main controlling factor in Neogene sea level changes in southern Victoria, and allow differentiation of the eustatic and tectonic controls on sedimentation.

Late Quaternary paleoclimatology, stratigraphy and sapropel history in eastern Mediterranean deep-sea sediments

The Late Quaternary paleoceanographic history of the Mediterranean Sea is a complex mixture of both global and regional events. Principal component analysis and oxygen isotopic analysis of planktonic foraminifera in deep-sea sediments have been used to define detailed paleoclimatic changes and to develop a firm stratigraphy for eastern Mediterranean sediments for the past 400,000 years. The first principal component is interpreted as being temperature-dependent based on the faunal assemblages associated with this component and on its close similarity to the oxygen isotope record. Warm and cool planktonic foraminiferal assemblage groupings derived by principal component analysis agree with faunal groups previously differentiated for Late Quaternary sequences in this region. Periodic stagnations of the eastern Mediterranean basin have resulted in the deposition of numerous organicrich sapropel layers during the Late Cenozoic. These sapropel layers are marked by the complete absence of any benthonic microfossil fauna and by the presence of an abnormal planktonic foraminiferal fauna containing an unusually high percentage of the salinity-sensitive foraminifer Neogloboquadrina dutertrei. Although the deposition of sapropels appears to be synchronous throughout the eastern Mediterranean, the lack of sapropels in cores from the western Ionian Sea indicate that true stagnant phases are not basin-wide phenomena. The onset of stagnant conditions is believed to be triggered by a flushing of fresh water from the Black Sea into the eastern Mediterranean during interglacial episodes where it forms a low-salinity surface layer that prevents oxygenation of the deep portions of the eastern basin. By placing the sapropel layers within a paleoclimatic framework, it is evident that sapropel deposition occurred during both warming and cooling trends within interglacial stages 1, 5 and 7. This is in contrast to previous work which suggested that sapropel formation occurred only during the climatic transition from glacial to interglacial episodes.

Late Quaternary fluctuations of the Polar Front and Subtropical Convergence in the southeast Indian Ocean

Planktonic foraminiferal assemblages have been examined in five deep-sea cores located beneath the present position of the Subtropical Convergence Zone. Fluctuations in the positions of the Subtropical Convergence and Polar Front during the last 500,000 years are recorded by frequency changes in the total planktonic foraminiferal fauna, by coiling changes in Neogloboquadrina pachyderma and by changes in species diversity. Late Quaternary paleoceanographic events in the temperate southeast Indian Ocean can be correlated with events in the South Pacific Ocean, Atlantic Ocean and Caribbean Sea on the basis of oxygen isotope stratigraphy for the last 230,000 years, 230Th dating and the biostratigraphic displacement of Globorotalia crassaformis by Globorotalia truncatulinoides at approximately 300,000 years.

Molluscan evidence of warm sea temperatures in New Zealand during Kapitean (Late Miocene) and Waipipian (Middle Pliocene) time

Abstract Very cool sea temperatures have been suggested for the New Zealand Kapitean Stage from the evidence of planktonic Foraminiferida and for the Waipipian Stage on the basis of Foraminiferida, spores and pollen and oxygen isotopes, and the former has been used as evidence for a late Miocene glaciation. The Mollusca in rocks of these stages include several genera now living only to the north of New Zealand, and there is no molluscan evidence of lowered sea temperatures at these times. Planktonic foraminiferal faunas occurring with Kapitean molluscs vary markedly, and a 63% sinistral Globigerina pachyderma population from East Cape occurs with Amphistegina and Conus. Probably the ecology of planktonic foraminifers is not well enough known for them to be used as direct temperature indicators.

Coiling Ratios of Neogloboquadrina Pachyderma (Ehrenberg): Variations in Different Size Fractions

In surface sediments of the subantarctic and cooler subtropical areas of the southeastern Indian Ocean, coiling ratios of Neogloboquadrina pachyderma are more dextral in coarser size fractions than in finer size fractions. A sample from near lat 45°S. contained 14 percent (95 percent confidence limits 8 to 22 percent) dextral tests in the 0.124 to 0.175-mm fraction, and 67 percent (57 to 76 percent) in the size fraction >0.175 mm. The difference decreases toward the north where dextral coiling eventually becomes dominant in all size fractions, and toward the south where sinistral coiling becomes dominant in all size fractions. This phenomenon is thought to be due to the existence of at least two races or taxa in the range of forms usually classed as N. pachyderma . To these, the names N. pachyderma pachyderma (Ehrenberg) and N. pachyderma incompta (Cifelli) are applied provisionally. Whether the taxonomic interpretation is correct or not, the empirically determined differences in coiling ratios of the different size fractions provide a previously unsuspected latitude-dependent variable in planktonic foraminiferal faunas. When applied to the analysis of fossil samples, they enhance the value of coiling ratios as paleotemperature indices and can be used to detect north-south movements of ocean surface hydrologic features.

Abrupt climatic change at 90,000 yr BP: Faunal evidence from Gulf of Mexico cores

Planktonic foraminiferal studies have been carried out on 28 piston cores of late Pleistocene age from the western Gulf of Mexico, an area of high sedimentation rates. For the interval between 73 × 10 3 and 95 × 10 3 yr BP, two of these cores have sedimentation rates of 12 and 15 cm/1000 yr. Calculation of the speed of faunal changes within this interval reveals an extremely rapid paleoclimatic-paleooceanographic change at approximately 90 × 10 3 years BP. Several species including distinctly warm-sensitive forms, then disappeared from the Gulf of Mexico in less than 350 yr, leaving a depleted planktonic foraminiferal fauna greatly dominated by only three species with little apparent temperature preference. This fauna existed for 2.5 × 10 3 yr after which distinctly cooler water elements increased in abundance rapidly and formed a high frequency peak approx 83.5–85 × 10 3 years BP. This increase in cooler water elements reflects either a return to more stable environmental conditions or a lag in their migration to the Gulf of Mexico after the severe climatic cooling, rather than further cooling. The faunal event in the Gulf of Mexico correlates with an even more spectacular event recorded in the Greenland ice sheet by a drop in 18O values within a time interval of only about 100 yr (Dansgaard et al., 1971, 1972). A possibly correlative climatic event of similarly rapid nature has also been reported for speleothems from southern France (Duplessy et al., 1970). The paleoclimatic event is closely associated stratigraphically with a widespread volcanic ash layer, although it is possibly significant that the increased volcanism occurred 1000 yr after the paleoclimatic event. A rapid lowering of the lysocline occurs simultaneously with the paleoclimatic event although faunal diversity is low in the succeeding fauna despite decreased calcium carbonate solution. Both the association with volcanism and changes in the position of the lysocline may be significant in consideration of mechanisms of such rapid climatic changes. In turn, such rapid paleoclimatic-paleooceanographic changes as observed in tropical Gulf of Mexico cores, in the Greenland ice sheet and in caves of southern France must be considered in the evaluation of causal mechanisms of glacial and interglacial oscillations.

Dominance and diversity of planktonic foraminiferal faunas in Atlantic Ibero-Moroccan continental slope sediments

Influenced by temperature in biocenoses, sorting in thanatocenoses, and epigenetic and diagenetic calcium carbonate solution in taphocenoses, Pleistocene, Holocene, Portugal, Morocco

South Pacific Planktonic Foraminiferal Biogeography and Late Cenozoic Paleo-Oceanography: ABSTRACT

Distinct changes in the character of South Pacific planktonic foraminiferal faunas occur at the 2 major water-mass boundaries. The southern limits of at least 10 species occur at or near the Subtropical Convergence which marks the southern limit of subtropical water. An additional 8 species have their southern limits approximately coincident with the Antarctic Convergence, leaving only 1 species characteristic of Antarctic waters. Micropaleontologic and sedimentologic studies of South Pacific deep-sea cores have enabled partial definition of the climatic and glacial history of Antarctica and the South Pacific. Pliocene and Pleistocene cores can be divided into zones on the basis of upward sequential appearance of planktonic Foraminiferida, upward sequential disappearance of Radiolaria, and stratigraphic succession of calcareous nannofossils. A chronology of South Pacific Pliocene and Pleistocene climatic oscillations has been established, based on paleomagnetic and thorium-230 dating. Alternations of cold and warm water planktonic Foraminiferida distinguish 6 intervals of climatic warming during the last 700,000 years (Brunhes epoch) and 10 between 2.4 m.y. and 700,000 years ago (Matuyama epoch). The relative m gnitudes of climatic warmings were considerably greater during the last 500,000 years than between 2.4 m.y. and 500,000 years ago. Cooling was at times as intense during the Matuyama epoch as during the Brunhes epoch. This determination conflicts with previous paleotemperature determinations based on radiolarians which suggest somewhat warmer conditions throughout the Matuyama. Several present subtropical radiolarian species, however, apparently lost their environmental tolerance for subpolar temperatures about 0.7 m.y. ago. Climatic curves for planktonic forams and radiolarians are essentially the same for the late Pleistocene, confirming the usefulness of both groups in paleoclimatic studies. Fluctuations of certain calcareous nannofossils species closely follow radiolarian and foramin feral paleotemperature oscillations for the last 400,000 years but diverge strongly in older core sections. Abundances of the silicoflagellate genera, Dictyocha and Distephanus, clearly mark warm- and cold-water intervals respectively in late Pleistocene cores. The first appearance of ice-rafted quartz in the sub-Antarctic, about 5 m.y. ago, coincides with increases in bottom-transported quartz, suggesting a relation between increased bottom-water activity and Antarctic glaciation. Distinct changes in the radiolarian assemblages also occur at this time. Studies of land-based marine sections in New Zealand and of deep-sea cores have shown that the first major late Cenozoic cooling occurred during the late Miocene and earliest Pliocene when south-central sub-Antarctic planktonic foraminiferal faunas (approximately 55°S equivalent lat.) spread over central New Zealand. A further major cooling during the middle Pliocene spans the Gauss-Matuyama boundary (t = 2.43 m.y. ago). This cooling was followed by more fluctuating climatic conditions in the late Pliocene and early Pleistocene (lower and middle Matuyama; t = 2.43 to 1.60 m.y. ago). Evidence of possibly synchronous late Miocene cooling has also been reported in California, Italy, Japan, and the equatorial Pacific. End_of_Article - Last_Page 631------------

Ecology of the Planktonic Foraminifera Living in the Surface Layer of Drake Passage

The planktonic foraminiferal fauna was studied in 104 surface plankton samples collected by the author during the crossing in both directions of Drake Passage between Tierra del Fuego and Elephant Island off the Palmer Peninsula, Antarctica, during the months of January and February, 1969. Samples were gathered by means of a fire pump. This method is discussed and recommended for planktonic foraminiferal collection. Eight species were determined, and their horizontal distribution was established. The percentage abundance of each species, as well as the number of specimens per cubic meter of filtered water, were calculated for every station. Distribution patterns of foraminifers were compared with those obtained by previous authors and were related to the surface hydrology. Some discrepancies were found and discussed. The most simple means of separating Globigerina pachyderma from G. quinqueloba is proposed and the most simple means of locating the Antarctic Convergence by the use of foraminifers is discussed. Abnormal spinosity of foraminiferal tests is considered. Ecology of the planktonic foraminifera living in the surface layer of Drake Passage

Pleistocene paleoclimates and foraminiferal biostratigraphy in subantarctic deep-sea cores

Middle and upper Pleistocene cores from the subantarctic region of the South Pacific can be divided on the basis of the upward sequential appearance of planktonic Foraminifera into three faunal zones. Correlation of this sequence with established radiolarian zones and paleomagnetic stratigraphy are supported by radiometric dates. Alternations of cold and warm water planktonic foraminiferal faunas delimit 8 intervals of climatic warming during the last 1·2-1·3 × 10 6-yr B.P. The relative magnitude of climatic warmings were considerably greater during the last 0·5 × 10 6-yr, than between 0·5 and 1·3 × 10 6-yr B.P. when conditions were generally cooler. Conditions were only once significantly warmer than the Recent, i.e., during the interval between 0·4 and 0·5 × 10 6-yr B.P. Paleoclimatic trends for polar areas can be correlated rather closely with those of tropical areas ( Ericson and Wollin, 1968).

Foraminiferal Trends in the Quaternary of Tanner Basin, California

Climatic and oceanographic variations, two alternating planktonic foraminiferal faunas, a cold-water fauna and a warmer water or transitional fauna

Definition of the Catapsydrax stainforthi Zone in the Saucesian Stage, California

MANY attempts have been made to establish better correlations between the Miocene marine geological strata of California and those of Europe and tropical regions. The two chief difficulties have been that many of the important zonal fossils of one region are absent in other regions, and even those important faunal indices that are common to the different areas have differential ranges when compared with one another. Discovery of the Catapsydrax stainforthi planktonic foraminiferal fauna on Erben Guyot1—a guyot located about 800 miles west of San Diego—made it possible to correlate these planktonic fossils with the standard planktonic zones of tropical areas but unfortunately not with the standard California Miocene Stages of Kleinpell2.

Pliocene-Miocene Boundary in Temperate Eastern Pacific: ABSTRACT

Clockwise surface-current motion in the North Pacific deflects colder isotherms (California Current) south along the Pacific Coast of North America. This cool-water mass contains a planktonic foraminiferal fauna characterized by Globigerina pachyderma (sinistral coiling north of Lat. 45°N.), G. bulloides, G. quinqueloba, and Globigerinita uvula. A similar Globigerina bulloides fauna dominates planktonic assemblages End_Page 618------------------------------ in middle Miocene through Holocene sediments exposed along the Pacific Coast north of Lat. 28°N. Therefore, the sequence of tropical planktonic species commonly used to zone Tertiary sediments is difficult to utilize at the leading edge of the northern East Pacific. Nevertheless, variations in percentages and coiling directions of temperate and cool-water species, together with restricted occurrences of tropical species, allow paleo-oceanographic definition of that part of the stratigraphic record currently accepted as the Pliocene-Miocene boundary, specifically the interval from 13-10 × 106 yrs. ago. Bathyal upper Miocene sediments exposed north of Lat. 30°N. are characterized by a subarctic to cool-temperate planktonic fauna marked by a zone of sinistral-coiling specimens of Globigerina pachyderma. A warm-temperate to subtropical fauna characterized by Globigerina eggeri, G. conglomerata, Globorotalia inflata, G. menardi tumida, G. crassaformis, G. hirsuta, Globigerinoides ruber, G. triloba, G. conglobatus, and Sphaeroidinella dehiscens occurs in sediments deposited at Lat. 34°N. (Repetto Formation of southern California) approximately 10-9 × 106 yrs. ago. This tropical to warm-temperate facies can be traced within a wedge of bathyal marine sediments extending north from Lat. 8°N. (Charco Azul Formation of Panama) to Lat. 47°N. (Quinault Format on of Washington). North from the equator the number of subtropical and tropical species characterizing the biofacies decreases; Pulleniatina obliquiloculata is absent within the biofacies north of Lat. 25°N.; Sphaeroidinella dehiscens, Globigerina conglomerata, Globigerinoides triloba, G. conglobatus, and Globorotalia menardi tumida are not present north of Lat. 35°N. At Lat. 47°N. the biofacies is marked only by dextral-coiling specimens of Globigerina pachyderma and rare occurrences of Globorotalia crassaformis and G. hirsuta. The initial appearances of Globorotalia crassaformis, G. inflata, and Sphaeroidinella dehiscens are currently used to mark the Pliocene-Miocene boundary in tropical latitudes. Consequently, their first appearance possibly can be used as a correlative Pliocene-Miocene boundary in the temperate eastern Pacific. However, expansion of warm isotherms from the equatorial region during the early Pliocene can not be considered instantaneous. Indices of the tropical to warm-temperate biofacies appeared later at progressively higher latitudes. A choice must be made between utilization of a time-transgressive biologic datum or a radiometric datum for an epoch boundary. Given a framework of absolute dates, appearance and oscillation of planktonic foraminiferal faunas can be evaluated in terms of aleo-oceanographic parameters rather than emphasized as criteria for establishing highly controversial epoch boundaries. End_of_Article - Last_Page 619------------

Paleogeographic and Paleoecologic Analysis of Planktonic Foraminifera: ABSTRACT

Abundance studies of extinct planktonic Foraminifera are proving a fruitful method of paleogeographic and paleoecologic analysis. Population counts of species and genera in fossil faunal assemblages give approximate percentage figures for paleo-faunal studies. Comparison of population data between two or more stratigraphic sections can be used as an indication of paleo-faunal differentiation and can outline paleogeographic distribution of species. Abundance analysis based on faunal sequences appears to reveal patterns that are repeated within sections from the same faunal province. Application of this method of analysis to planktonic foraminiferal faunas from Maestrichtian and Paleocene assemblage zones in selected sections of the Atlantic, Gulf, and Mediterranean regions indicates distinct paleogeographic and paleoecologic differentiation. Broad generic distributions are evident, whereas there are more distinct geographic limitations on species in the Maestrichtian and Paleocene. There also is some indication of possible geographic subspecies variation. The most marked differentiation occurs along lines of longitude with more favorable comparisons and less marked differences along lines of latitude. A greater number of genera and species are found in low latitudes than in high latitudes in rocks of the Maestrichtian and Paleocene. Faunas from sediments deposited in shallow-water environments are characterized by a limited number of species. The species that do occur usually are the most abundant elements in the planktonic faunas found in sediments deposited in deeper-water environments. End_of_Article - Last_Page 630------------