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At least 55 records · Page 3Linked to original sources
USGS1980

Distribution of modern benthic foraminifers on the New Jersey Outer Continental Shelf

We used samples from 21 stations within a 600 km2 area of the New Jersey Outer Continental Shelf to assess the effects of a hydrodynamic environment on the distribution and redistribution of benthic foraminifers. These samples show that, although the predominant genera (Elphidium, Cibicides, and Saccammina) are the same as those reported by other investigators for this region, the environmental factors that control the generic distribution are more complex than were previously postulated. Generic distribution patterns derived from this study are correlated with the bottom topography and sediment distribution as well as the temperature, salinity, and dissolved oxygen concentrations of the bottom waters. The six predominant species observed in the samples (and their phenotypic variants) are cryophilic forms known to occur in the Virginian and Nova Scotian biogeographic provinces and in Arctic waters. Species distribution patterns also correlate well with bottom topography and hydrographic factors, but may be modified by seasonal fluctuations in test production and by redistribution of dead tests. At most stations, specimens of Elphidium subarcticum were attached to quartz grains. This phenomenon, which has not been reported before, probably is an adaptation to a high-energy environment. The distribution pattern of Elphidium subarcticum along with those of the sessile species Webbinella concava and Vasiglobulina n.sp. corroborate sedimentological evidence that the accumulation of modern sediments in the area is negligible.

New Jersey↗
USGS1981

Miocene biochronology and paleoceanography of the North Pacific

Biostratigraphic correlation based on microfossil datum levels, directly or indirectly tied to the paleomagnetic time scale, provides a high resolution time control for the Miocene in the equatorial and middle latitude North Pacific. Faunal changes and abundance fluctuations of planktic foraminiferal species combined with the oxygen Pacific. Faunal changes and abundance fluctuations of planktic foraminiferal species combined with the oxygen isotope record of foraminifers, reveal the paleoclimatic and paleoceanographic history. The planktic foraminiferal assemblage change in the early Miocene, extinction of Oligocene fauna and rise of a highly diverse Neogene fauna, appears to be related to increased water mass stratification in the world oceans presumably resulting from the establishment of circum-Antarctic circulation. An increase in the siliceous productivity in the eastern equatorial Pacific region between 20 and 18 Ma suggests that the vertical and horizontal circulation was intensified at that time. Climates cooled rapidly during the middle Miocene between 14 and 13 Ma suggesting the growth of a major east Antarctic ice sheet. Paleoclimatic conditions remained generally cool, although oscillating, during the late Miocene. In the late early to middle Miocene faunal provincialism developed between low and middle latitudes, and by late Miocene time a distinct provincialism similar to the present was established.

Marine Micropaleontology↗
USGS1981

Late Miocene biogeography and paleoclimatology of the central North Atlantic

Quantitative analyses of planktonic foraminiferal assemblages from Deep Sea Drilling Project (DSDP) Holes 334 and 410 demonstrate that subpolar and subtropical faunal provinces existed in the North Atlantic during the late Miocene. Climatic oscillations are clearly recorded in Hole 410 by variations in abundance of the Neogloboquadrina subpolar assemblage. These climatic oscillations have a period of about 1 m.y. Higher frequency oscillations with a periodicity of one to several hundred thousand years are evident from about 6.5 to 7.5 m.y. and are probably present throughout the entire late Miocene. A revised age of 7.0 m.y. is proposed for the first occurrence of the calcareous nannofossil Amaurolithus primus (the Amaurolithus datum).

Marine Micropaleontology↗
USGS1981

Miocene benthic foraminiferal isotope records: A synthesis

18 O/ 16 0 and 13 C/ 12 C ratios of Miocene benthic foraminifera from a number of Atlantic, Pacific and Indian Ocean DSDP sites (71, 77B, 206, 208, 238, 279, 289, 296, 329, 357 and 366A) have been compiled. These provide a rather detailed history of Miocene deep water especially in the Pacific Ocean. Bottom-water temperatures rose during the early Miocene and then declined rapidly during the middle Miocene. This decline was accompanied by an increase in Antarctic glaciation. Late Miocene bottom temperatures and Antarctic ice volumes are inferred to be similar to today's, but exhibited some fluctuation. The early Miocene ocean was less thermally stratified at intermediate and abyssal depths while the late Miocene deep ocean had a thermal structure generally similar to the modern ocean. Foraminiferal carbon isotope ratios at most of the sites varied quasi-sympathetically throughout the Miocene. These variations must reflect comparable variations in the mean 13 C/ 12 C of marine HCO 3 . However, the causes of such variations are not yet clear.

Marine Micropaleontology↗
USGS1982

North Pacific Late Miocene correlations using microfossils, stable isotopes, percent CaCO3, and magnetostratigraphy

A multidisciplinary approach to stratigraphy based on magnetostratigraphy, stable isotopes, percent CaCO 3 and microfossils provides a framework for paleoclimatic and paleoceanographic reconstruction of the equatorial and North Pacific. A high-resolution biochronologic time scale has been achieved through integration of diatom, radiolaria, coccolith and planktic foraminifer datum levels with direct or indirect correlations to the paleomagnetic time scale. Over 70 datum levels have been identified between 12.5 and 5 Ma from low and middle latitudes resulting in an unprecedented time control. This high-resolution biostratigraphic control combined with stable-isotopic and percent CaCO 3 analyses permits identification of regional as well as global paleoceanographic events.

Marine Micropaleontology↗
USGS1983

Bathyal ostracodes from the Florida-Hatteras slope, the Straits of Florida, and the Blake Plateau

Epibathyal ostracodes from the Florida-Hatteras slope, the Blake Plateau and the Straits of Florida were studied to determine the relationship of numerous genera and species to bottom-water environmental conditions such as dissolved oxygen and bottom-water temperatures. From a total of 100 samples, 44 samples evenly distributed between 200 and 1100 m water depth and having an average of 325 specimens were examined in detail. Using occurrence data from the adjacent continental shelf, carapace preservation, Rose Bengal staining and population data, indigenous death assemblages were distinguished from transported or reworked fossil specimens. The percent of transported specimens varied as follows: Blake Plateau less than 1%; Straits of Florida 10–60%; Florida-Hatteras slope 1–15%. Indigenous death assemblages contained between 10 and 61 species per sample, averaging 33.3 species. Krithe, Argilloecia and Pseudocythere occur in greater than 90% of the samples and usually constitute 10 to 30% of each. Trachyleberidea, Bairdoppilata, Saida, Paranesidea, Ambocythere, Bythocypris, Cytherella, Bradleya, Henryhowella , and Polycopidae occur in 45 to 80% of the samples in varying percentages. The upper depth limits of 39 taxa occur at or just below the thermocline suggesting a relationship to temperature. Australoecia, Quasibuntonia, Cytheropteron, Ruggieriella, Saida, Ambocythere, Trachyleberidea, Macrocypris, Krithe, “Thalassocythere” , and Cytherella are most common or restricted to the O 2 minimum zone. Conversely, Anchistrocheles, Bradleya, Henryhowella , and Rockallia are most common below 750 m in well oxygenated water with temperatures below 8°C. The results show that: (1) ostracodes display a narrow depth zonation controlled by dissolved oxygen and water temperature; (2) species diversity is very high for a bathyal zone; (3) ostracodes can be used to identify the source of sediment that has been transported downslope; and (4) some taxa are useful in recognizing low oxygenated water in Cenozoic deposits.

Florida↗
USGS1983

Biochronology and paleoclimatic implications of Middle Eocene to Oligocene planktic foraminiferal faunas

Planktic foraminiferal assemblages have been analyzed quantitatively in six DSDP sites in the Atlantic (Site 363), Pacific (Sites 292, 77B, 277), and Indian Ocean (Sites 219, 253) in order to determine the nature of the faunal turnover during Middle Eocene to Oligocene time. Biostratigraphic ranges of taxa and abundance distributions of dominant species are presented and illustrate striking similarities in faunal assemblages of low latitude regions in the Atlantic, Pacific and Indian oceans. A high resolution biochronology, based on dominant faunal characteristics and 55 datum events, permits correlation between all three oceans with a high degree of precision. Population studies provide a view of the global impact of the paleoclimatic and paleoceanographic changes occurring during Middle Eocene to Oligocene time. Planktic foraminiferal assemblage changes indicate a general cooling trend between Middle Eocene to Oligocene time, consistent with previously published oxygen isotope data. Major faunal changes, indicating cooling episodes, occur, however, at discrete intervals: in the Middle Eocene 44-43 Ma (P13), the Middle/Late Eocene boundary 41-40 Ma (P14/P15), the Late Eocene 39-38 Ma (P15/P16), the Eocene/Oligocene boundary 37-36 Ma (P18), and the Late Oligocene 31-29 Ma (P20/P21). With the exception of the E/0 boundary, faunal changes occur abruptly during short stratigraphic intervals, and are characterized by major species extinctions and first appearances. The Eocene/Oligocene boundary cooling is marked primarily by increasing abundances of cool water species. This suggests that the E/0 boundary cooling, which marks a major event in the oxygen isotope record affected planktic faunas less than during other cooling episodes. Planktic foraminiferal faunas indicate that the E/0 boundary event is part of a continued cooling trend which began during the Middle Eocene. Two hiatus intervals are recognized in low and high latitude sections at the Middle/Late Eocene boundary and in the Late Eocene (P15/P16). These hiatuses suggest that vigorous bottom water circulation began developing in the Middle Eocene, consistent with the onset of the faunal cooling trend, and well before the development of the psychrosphere at the E/0 boundary.

Marine Micropaleontology↗
USGS1983

Latest Oligocene through early middle Miocene diatom biostratigraphy of the eastern tropical Pacific

Study of DSDP Sites 71, 77, and 495 has allowed the development of a refined diatom biostratigraphy for the latest Oligocene through early middle Miocene of the eastern tropical Pacific which is well correlated to the low-latitude zonations for planktonic foraminifers, coccoliths, and radiolarians. Six zones and 7 subzones are proposed, and correlation with high-latitude diatoms zonations for the North Pacific, the Norwegian Sea, and the Southern Ocean is suggested by the discovery of selected diatoms in these tropical sediments which were previously thought to be restricted to high latitudes. Six new species and one new variety of diatoms which are stratigraphically useful are proposed: Actinocyclus hajosiae , n. sp., A. radionovae , n. sp., Coscinodiscus blysmos , n. sp., C. praenodulifer , n. sp., Craspedodiscus rydei , n. sp., Thalassiosira bukryi , n. sp., and Coscinodiscus lewisianus var. robustus n. var.

Marine Micropaleontology↗
USGS1984

Oxygen isotope ranking of late Eocene and Oligocene planktonic foraminifers: Implications for Oligocene sea-surface temperatures and global ice-volume

Oxygen isotope analyses of late Eocene and Oligocene planktonic foraminifers from low and middle latitude sites in the Atlantic Basin show that different species from the same samples can yield significantly different isotopic values. The range of isotopic values observed between species is greatest at low-latitudes and declines poleward. Many planktonic foraminifers exhibit a systematic isotopic ranking with respect to each other and can therefore be grouped on the basis of their isotopic ranking. The isotopic ranking of some taxa, however, appears to vary geographically and/or through time. Isotopic and paleontologic data from DSDP Site 522 indicate that commonly used isotopic temperature scales underestimate Oligocene sea surface temperatures. We suggest these temperature scales require revision to reflect the presence of Oligocene glaciation. Comparison of isotopic and paleontologic data from Sites 522, 511 and 277 suggests cold, low-salinity surface waters were present in high southern latitudes during the early Oligocene. Low-salinity, high latitude surface waters could be caused by Eocene/Oligocene paleogeography or by the production of warm saline bottom water.

Marine Micropaleontology↗
USGS1988

Neogene stratigraphy, foraminifera, diatoms, and depositional history of Maria Madre Island, Mexico: Evidence of early Neogene marine conditions in the southern Gulf of California

Foraminifera and diatoms have been analyzed from an upper Miocene through Pleistocene(?) sequence of marine sediments exposed on Maria Madre Island, largest of the Trés Marias Islands off the Pacific coast of Mexico. The Neogene stratigraphic sequence exposed on Maria Madre Island includes a mid-Miocene(?) non-marine and/or shallow marine sandstone unconformably overlain by a lower upper Miocene to uppermost Miocene upper to middle bathyal laminated and massive diatomite, mudstone, and siltstone unit. This unit is unconformably overlain by lower Pliocene middle to lower bathyal sandstones and siltstones which, in turn, are unconformably overlain by upper Pliocene through Pleistocene(?) upper bathyal to upper middle bathyal foraminiferal limestones and siltstones. These beds are unconformably capped by Pleistocene terrace deposits. Basement rocks on the island include Cretaceous granite and granodiorite, and Tertiary(?) andesites and rhyolites. The upper Miocene diatomaceous unit contains a low diversity foraminiferal fauna dominated by species of Bolivina indicating low oxygen conditions in the proto-Gulf Maria Madre basin. The diatomaceous unit grades into a mudstone that contains a latest Miocene upper to middle bathyal biofacies characterized by Baggina californica and Uvigerina hootsi along with displaced neritic taxa. An angular unconformity separates the upper Miocene middle bathyal sediments from overlying lower Pliocene siltstones and mudstones that contain a middle to lower bathyal biofacies and abundant planktonic species including Neogloboquadrina acostaensis and Pulleniatina primalis indicating an early Pliocene age. Significantly, this Pliocene unit contains common occurrences of benthic species restricted to Miocene sediments in California including Bulimina uvigerinaformis . Pliocene to Pleistocene(?) foraminiferal limestones and siltstones characterize submarine bank accumulations formed during uplift of the Trés Marias Island area, and include abundant planktonic foraminifera such as Pulleniatina obliquiloculata and Neogloboquadrina duterteri . Common benthic foraminifera in this unit are indicative of upper bathyal water depths. The Neogene depositional history recorded on Maria Madre Island involves an early late Miocene subsidence event marking formation of the Trés Marias Basin with relatively undiluted diatomaceous sediment deposited in a low oxygen setting. Subsidence and deepening of the basin continued into the early Pliocene along with rapid deposition of terrigenous clastics. Uplift of the basinal sequence began in late Pliocene time accompanied by deposition of upper Pliocene-Pleistocene foraminiferal limestones on a rising submarine bank. Continued episodic uplift of the Neogene deposits brought the island above sea level by late Pleistocene time.

Maria Madre Island↗
USGS1989

Planktonic benthonic foraminiferal ratios: Modern patterns and Tertiary applicability

The abundance of planktonic specimens in foraminiferal assemblages was determined in numerous bottom samples from inner neritic to deep oceanic depths along the Atlantic margin of the northeastern United States. The results augment previous studies in other areas that have shown a general increase in percentage of planktonic specimens in total foraminiferal bottom assemblages as water depth increases. The patterns found in this area of complex shelf bathymetry and hydrography illustrate the influence on the planktonic-benthonic percentages of water depth, distance from shore, different water mass properties and downslope movement of tests in high energy areas. The patterns found in the 661 samples from the Atlantic margin were compared with results from 795 stations in the Gulf of Mexico, Pacific Ocean and Red Sea. The relative abundance of planktonic specimens and water depth correlates positively in all open oceanic areas even though taxonomic composition and diversity of the faunas from different areas is variable. The variation of planktonic percentages in bottom samples within most depth intervals is large so that a precise depth determination cannot be made for any given value. However, an approximate upper depth limit for given percentages can be estimated for open ocean environments. A decrease in planktonic percentages is seen in the lower salinity and higher turbidity coastal waters of the Gulf of Maine. Planktonic percentages intermediate between the lower values in the less saline coastal waters and the higher values in the normal open oceanic conditions occur in the transitional area between the Gulf of Maine and the open marine Atlantic Ocean to the east. Similarly lowered values in another area of restricted oceanic circulation occur in the high salinity, clear, but nutrient-poor waters of the Gulf of Aqaba off the Red Sea. A comparison of the similarity of modern planktonic percentage values to those found in earlier Tertiary assemblages was made to confirm the usefulness of this measure in the fossil record. In some stratigraphic sections in upper Paleocene and lower Eocene strata of the eastern Gulf Coastal Plain, water depths inferred from trends and values of planktonic percentages consistently match paleobathymetry constructed from physical stratigraphic characteristics and paleogeographic relationships.

Marine Micropaleontology↗
USGS1989

Application of the Graphic Correlation method to Pliocene marine sequences

Biostratigraphy — the use of paleontological evidence to establish relative chronologies, forms the cornerstone of many sedimentary geological investigations. Several different approaches to biochronology are available. Traditional interval zones, defined on lowest and/or highest occurrences of selected taxa, are used to place bodies of rock in a relative chronological framework. Fossil datum levels, which are more numerous than zones, are often used as chronohorizons for correlation purposs. The Graphic Correlation method, like interval zonations, synthesizes information from a number of different taxa but does not assume synchrony of any one taxon. A magnetobiostratigraphic model for deep-sea Pliocene sequences has been constructed by graphic correlation of Deep Sea Drilling project cores from the North Atlantic (606), Caribbean Sea (502), South Atlantic (516), Tasman Sea (590), Equatorial Pacific (573) and North Pacific (577). All cores are hydraulic piston cores which contain abundant planktonic foraminifers, calcareous nannofossils and which record many of the magnetic reversals expected in the Pliocene. The model is based on internally consistent paleontologic data gathered by the author. This study demonstrates the advantages of graphic correlation over conventional biostratigraphic procedures. Accurate inter-regional correlations can be made between core sites without resorting to multiple microfossil zonations and without invoking synchrony of fossil events. Important results of this study are: (1) many Pliocene planktonic foraminifer and calcareous nannofossil events are diachronous by more than 0.20 m.y., (2) Globorotalia truncatulinoides first occurs in the Southwest Pacific Ocean, approximately 0.50 m.y. earlier than previously reported, (3) a previously undetected hiatus of short duration (0.38 m.y.) exists just above the Cochiti subchron at DSDP 577A.

Marine Micropaleontology↗
USGS1992

Pliocene paleoclimatic interpretation of DSDP Site 580 (NW Pacific) using diatoms

High-resolution quantitative diatom data are tabulated for the early part of the late Pliocene (3.25 to 2.08 Ma) at DSDP Site 580 in the northwestern Pacific. Sample spacing averages 11 k.y. between 3.1 and 2.8 Ma, but increases to 14 to 19 k.y. prior to 3.1 Ma and after 2.8 Ma. Q-mode factor analysis of the middle Pliocene assemblage reveals four factors which explain 92.4% of the total variance of the 47 samples studied between 3.25 and 2.55 Ma. Three of the factors are closely related to modern subarctic, transitional, and subtropical elements, while the fourth factor, which is dominated by Coscinodiscus marginatus and the extinct Pliocene species Neodenticula kamtschatica , appears to correspond to a middle Pliocene precursor of the subarctic water mass. Knowledge of the modern and generalized Pliocene paleoclimatic relationships of various diatom taxa is used to generate a paleoclimate curve (“Twt”) based on the ratio of warm-water (subtropical) to cold-water diatoms with warm-water transitional taxa ( Thalassionema nitzschioides, Thalassiosira oestrupii , and Coscinodiscus radiatus ) factored into the equation at an intermediate (0.5) value. The “Twt” ratios at more southerly DSDP Sites 579 and 578 are consistently higher (warmer) than those at Site 580 throughout the Pliocene, suggesting the validity of the ratio as a paleoclimatic index. Diatom paleoclimatic data reveal a middle Pliocene (3.1 to 3.0 Ma) warm interval at Site 580 during which paleotemperatures may have exceeded maximum Holocene values by 3°–5.5°C at least three times. This middle Pliocene warm interval is also recognized by planktic foraminifers in the North Atlantic, and it appears to correspond with generalized depleted oxygen isotope values suggesting polar warming. The diatom “Twt” curve for Site 580 compares fairly well with radiolarian and silicoflagellate paleoclimatic curves for Site 580, planktic foraminiferal sea-surface temperature estimates for the North Atlantic, and benthic oxygen isotope curves for late Pliocene, although higher resolution studies on paired samples are required to test the correspondence of these various paleoclimatic indices.

Marine Micropaleontology↗
USGS1994

Microfossil biostratigraphy of prograding Neogene platform-margin carbonates, Bahamas: Age constraints and alternatives

Benthic and planktic foraminifera and calcareous nannofossils were recovered in shallow-water carbonate rock cores from two continuous boreholes drilled 7.5 km apart on the west platform margin of the Great Bahama Bank. The microfossils define six biostratigraphic units in each hole. One unit in each hole represents a correlative condensed section. Seven foraminiferal biozones are recognized in 11 of the units between the holes: middle Miocene Globorotalia fohsi robusta Zone N12, late Miocene G. acostaensis Zone N16 and G. humerosa Zone N17, early Pliocene G. margaritae evoluta Subzone N19, late Pliocene G. exilis Subzone N21 and, tentatively, G. tosaensis tosaensis Zone N21, and early Pleistocene G. crassaformis viola Subzone N22. The twelfth unit is inferred to be of G. crassaformis viola Subzone N22 age. The oldest unit is onshore, the youngest is offshore. As presently interpreted, the nannofossil and foraminiferal zonations are partially correlative. Although the microfossils unequivocally constrain the series ages of the sediments, the incompleteness of the fossil record allows for alternative biozonal age models within the series. The Miocene and Pliocene biozones are common to both holes, but the greatest similarities between the holes are the significant mixing of middle and late Miocene, and late Miocene-early Pliocene faunas, the greatly condensed intervals at the Miocene/Pliocene boundary, and the early Pliocene influx of deep-water benthic and pelagic foraminifera. Of particular importance is the tentative recognition of late Pliocene G. tosaensis tosaensis Zone N21 in one borehole. Subsequent data not available to this phase of the study indicate that much of the zone is likely missing. Its absence will lend support to speculations of a regional unconformity in the Bahamas. The microfossils indicate that (1) several transgressions occurred from the middle Miocene to at least the earliest Pleistocene (greater than 11.5–greater than 0.46 Ma), during which banktop-derived sediments accumulating at the margin prograded the platform seaward; (2) a condensed interval on the bank top may represent a late Miocene lowstand, a period of sediment bypassing, or a lack of accommodation space; (3) the slope received thin layers of pelagic sediments in a condensed interval during the late Miocene and early Pliocene, while the bank top accommodated early Pliocene (4.2–3.4 Ma) deep-water indicators prior to a likely period of exposure (2.35 - 1.89 Ma); (4) two cycles of banktop sediment production and starvation occurred during the Pliocene; (5) the Pliocene transgression was punctuated by stillstands or low-amplitude reversals during which parts of biozones did not accumulate; and (6) the sediments containing the most complete microfossil-datum record are the thin pelagic strata that mark interruptions in the regular shedding of transgressive deposits from the platform. Sedimentation-rate patterns varied but were generally higher offshore than onshore.

Marine Micropaleontology↗
USGS1995

Deep-sea biostratigraphy of prograding platform margins (Neogene, Bahamas): Key evidence linked to depositional rhythm

New foraminiferal evidence from two boreholes on the paleoshelf and slope of western Great Bahama Bank has wide-ranging implications for understanding formation and evolution of carbonate-platform margins. The new data, abundant well-preserved planktic foraminifera, were obtained by disaggregating samples from intercalated pelagic layers and selected parts of thick hemipelagic limestone. Earlier efforts to obtain biostratigraphic ages identified six biostratigraphic units in each borehole, provided biozonal age alternatives for both holes, and resulted in different Pliocene biozones between them. The new data define six units in one hole and seven in the other, bracket the biozones present and their ages, indicate different sedimentation rates, and show that within the limits of biostratigraphic resolution the biozones are correlative between the holes. Most importantly, the revised ages show that the paleoshelf borehole probably penetrated the late Miocene rather than middle Miocene. The oldest unit is on the paleoshelf and the youngest (uppermost Pliocene) is on the slope. Between the holes, the stratigraphic interval spans the temporal interval from an inferred maximum of ~ 10.2 Ma to a minimum of ~ 1.6 Ma. Although the biozones range sequentially from the Neogloboquadrina acostaensis (N16) Zone to the basal part of the Globorotalia truncatulinoides truncatulinoides (N22) Zone ( Globorotalia crassaformis viola Subzone), absence of key species indicates that deposition was discontinuous. Numerous periods of erosion and/or nondeposition are inferred, the largest of which is a condensed section/ hiatus (~ 1.2 Myr) above the paleoslope Miocene/Pliocene boundary. In addition, the late Pliocene Globorotalia tosaensis tosaensis (N21) Zone is not recognized on the slope. Its absence is consistent with a widespread regional unconformity. Sedimentation rates and depths of series boundaries vary widely in both holes. The paleoslope Miocene/Pliocene boundary lies at ~540 m below top of the hole. The lower/upper Pliocene boundary is placed at or near 444 m. Position of the Pliocene/ Pleistocene boundary is less certain but is within the top 382 m of the hole. Its placement anywhere within this interval is a reasonable assessment considering an exceptionally high rate of sedimentation (~562 m/Myr; 168.6 m interval, based on topmost foraminiferal sample; 1.9–1.6 Ma). As expected, the lowest sedimentation rate occurs in the condensed section overlying the Miocene/Pliocene boundary (~ 5 m/Myr, 9.5 m, 5.3–4.1 Ma). The paleoshelf Miocene/Pliocene boundary lies below a hiatal condensed section (295–278 m below top of the hole) that has a greater sedimentation rate (~ 89 m/Myr, 17.7 m, 5.5–5.3 Ma) than that at the slope. The lower/upper Pliocene boundary is placed at or near a depth of 236 m, and the Pliocene/Pleistocene boundary lies within the top 113 m of the hole. Sedimentation rates on the shelf range from ~ 15 m/Myr above the condensed section (22.9 m, 5.3–3.8 Ma) to a late Pliocene high of ~ 183 m/Myr (54.9 m interval, based on the point at which the age-depth line crosses the 1.9 Myr mark between the topmost two fossiliferous samples; 2.2–1.9 Ma).

Marine Micropaleontology↗
USGS1995

Latest Quaternary foraminifers and sediment transport in Pervenets Canyon, Bering Sea

A combination of microfossil and sediment analysis has been used in an attempt to understand oceanographic processes and the late Quaternary history of the Pervenets Canyon region. The primary sedimentation process in Pervenets Canyon is downslope transport. Near the shelfbreak, there is evidence of turbidite and debris-flow activity, but at the distal end of the upper canyon and on the continental slope there is no macroscopic evidence for these processes. Analysis of the foraminiferal assemblages shows that the fauna is 97.6% from the Suborder Rotaliina and about 2.0% from the Suborder Textulariina. The Suborder Miliolina accounts for approximately 0.4% of the fauna. The Pervenets Canyon fauna is most similar to other faunas from the Bering Sea, indicating a North Pacific Ocean influence on the fauna. Foraminiferal abundance and species diversity vary widely in the samples studied. The major factors controlling these values are downslope transport of sediment, disintegration of arenaceous taxa, dissolution of calcareous taxa, and diversity limited by low-oxygen bottom waters. Downslope transport of shelf species is indicated by the presence of Elphidium clavatum and E. excavatum . Shallow-shelf and low-oxygen foraminiferal faunas are often intermixed in the samples. The distribution of these low-oxygen faunas in Core 81-65 suggests that the oxygen-minimum zone fluctuated with sea level.

Marine Micropaleontology↗
USGS1996

Middle Pliocene sea surface temperatures: A global reconstruction

Identification and analyses of Pliocene marine microfossils from 64 globally distributed stratigraphic sequences have been used to produce a middle Pliocene sea surface temperature reconstruction of the Earth. This reconstruction shows little or no change from current conditions in low latitude regions and significant warming of the ocean surface at mid and higher latitudes of both hemispheres. This pattern of warming is consistent with terrestrial records and suggests a combination of enhanced meridional ocean heat transport and enhanced greenhouse effect were responsible for the middle Pliocene warmth.

Marine Micropaleontology↗