Foraminiferal Ratios Research Articles

Foraminiferal Constraints on Very High-Resolution Seismic Stratigraphy and Late Quaternary Glacial History, New Jersey Continental Shelf

Internal stratigraphy of a Late Quaternary sediment wedge on the New Jersey outer continental shelf has been investigated using regional and 3-D seismic surveys, sediment cores and foraminiferal biofacies analysis. Results from the study help constrain Late Wisconsinan glacialldeglacial history in this area. Three major reflectors (channels, S and R) define 5 stratigraphic units: Si -modern sediments; S2-sands overlying a channelized surface (Channels reflector); S3-muds, clays and sandy muds below the channelized surface and above reflector S; S4-an unsampled unit between reflectors S and R; and S5-sands underlying reflector R, the latter surface defining the base of the sediment wedge. Multivariate quantitative analysis delineates four major faunal groups characterizing these stratigraphic units. Faunal patterns are interpreted in terms of modern foraminiferal distributions, planktoniclbenthic ratios and faunal abundance patterns. Group A dominates units S2 and S5 and is characterized by Cibicides lobatulus and Cassidulina islandica. The fauna indicates middle neritic water depths, moderate to high current energy, and moderate accumulation rates. Group B dominates unit S3 (muddy unit) and is characterized by Elphidium excavatum s.l., Buccella frigida, Fursenkoina fusiformis and miliolid spp. This fauna represents an environment with no modern analogue on the New Jersey continental shelf, reflecting middle neritic, low-energy conditions and the accumulation of predominantly muddy sediments. Group C dominates the modern sediment veneer (unit Si), and its diverse fauna is consistent with modern faunal distributions and environmental conditions. Group D consists of a low-diversity fauna dominated by Fursenkoina fusiformis and Nonionella sp., which characterizes a few samples in unit S3. Environmental conditions are probably similar to those described for faunal group B. The distribution and interpretation of these faunas, combined with preliminary C-14 AMS dates, indicate that the Quaternary history of the outer-shelf sedi-

Foraminiferal dissolution at shallow depths of the Walvis Ridge and Rio Grande Rise during the latest Cretaceous: Inferences for deep-water circulation in the South Atlantic

Abstract A high-resolution (10–20 kyr) record of variations in CaCO3 content and dissolution was established for latest Cretaceous (last 0.7 Myr) deep-sea sediments from the South Atlantic Ocean (DSDP Site 516 from the Rio Grande Rise, and sites 525 and 527 from the Walvis Ridge). The degree of fragmentation of planktonic foraminifera (DFP) was used as a measure of calcite dissolution. High negative correlations between DFP and other independent measures of carbonate dissolution (percentage of sand fraction, absolute abundance of planktonic foraminifera, and planktonic/benthic foraminiferal ratio) validate its use as a sensitive index of calcite dissolution in upper Maastrichtian deep-sea sediments. Very high DFP and a significant negative correlation between DFP and CaCO3 content suggest that Site 516 was located below the foraminiferal lysocline during the entire interval studied. Such a shallow position of the lysocline (paleodepth of Site 516 was 1.2 km) may be explained by “upwelling” of corrosive deep waters along the southern margin of the Rio Grande Rise. Sites 525 and 527 were located above the foraminiferal lysocline; however, three short periods of enhanced dissolution were recognised at Site 525 (paleodepth 1 km) and one interval of strong dissolution was identified at Site 527 (paleodepth 2.7 km). The lack of correspondence between the dissolution regimes at sites from the Walvis Ridge suggests limited deep-water communication across this physiographic barrier. Two of the dissolution maxima recognised at Site 525 correspond to carbonate maxima at Site 527. Variations in “upwelling” intensity along the Walvis Ridge, resulting in fluctuations in primary productivity in this area, may be the proximal cause of both carbonate cycles at Site 527 and dissolution cycles at Site 525. We suggest that development of the bottom Ekman layer between a hypothetical westward geostrophic current and the topographical height of the Rio Grande Rise-Walvis Ridge system may be a plausible hydrodynamical explanation for the proposed “upwelling” along the southern margin of this topographical structure.

Late Quaternary sedimentation on the Eastern Walvis Ridge, SE Atlantic (HPC 532 and four piston cores)

Five sediment cores from the Eastern Walvis Ridge have been investigated by means of a quantitative coarse fraction analysis (>40 μm. Numerous biogenous, terrigenous and authigenic particles have been distinguished. The variations in composition suggest the following conclusions: • — Core Walda KS 12 from the northern flank of the Walvis Ridge consists entirely of a slump, which contains mainly glacconite sands and biogenous opal, foraminiferal skeletons and terrigenous matter. • — The sediments in the other four cores comprise the Late Quaternary oxygen isotope stages 1—6. • — There are several levels, at the transition from warm to cold intervals, where benthos/plankton foraminiferal ratios increase from <10 up to 50–90%. Here imperforate benthonic foraminifera decrease strongly. Dissolution of planktonic foraminifera can only partly explain this finding. Lateral supply of benthos or the influence of reduced oxygen content in the bottom water might have played an additional role. • — Calcium-carbonate dissolution as revealed by the fragmentation of planktonic foraminifera shows intermediate values in coldest and warmest periods. Dissolution maxima occur at warm/cold stage boundaries. Dissolution minima have been found at the transition from cold to warm periods. • — Upwellinginfluence is reflected in varying amounts of biogenous opal. In interglacial periods the influence of upwelling is strong in all cores, with an increase in intensity to the east (core V19-259). It is explained by eddies of upwelled water which drifted westward under the influence of the westward-turning Benguela Current. In glacial periods the influence of upwelling at the core sites was very reduced. The Benguela Current problably was close to the continent and turned westward only at 17°S. Thus it did not affect the core sites. • — Climate in the near-coastal area has been arid in the latitude of 20°S throughout the investigated time slice. • — Accumulation rates reflect the position of the cores: HPC 532 and Circe Gb 211 are in the area of the sediment-filled trough which forms the Walvis Ridge Terrace. Here accumulation rates are 2 to 3 times higher in stages 2, 4 and 5 than in V19-259 and Walda KS 09, which are from the steeper flank of the Terrace outside the trough. Mean values of calcium-carbonate dissolution are similar in all cores. Lower CaCO 3 content in V19-259 and lower sand fraction percentages are explained by lateral supply of fine-grained terrigenous matter in the area of core V19-259, which probably received insoluble material from the Kuene shelf area by the N—S-flowing countercurrent.

Nannoplankton Biostratigraphy and Sedimentary Petrology of a Vertical Facies Sequence Crossing the Campanian-Maestrichtian Boundary in Central Alabama: ABSTRACT

On the basis of the occurrence of calcareous nannoplankton in Upper Cretaceous sediments, exposed in a series of road cuts near Pine Level, Alabama, the sequence is placed in the uppermost Kamptnerius magnificus zone, the Tetralithus aculeus zone, and the lower Chiastozygus initialis zone (Campanian-lower Maestrichtian). The Cusseta Sand lithology, which is considered to be of Campanian age in western Georgia and eastern Alabama, is shown to be basal Ripley or Maestrichtian at this locality, based on the occurrence of Chiastozygus initialis. This age difference suggests that the clastic wedge, building southeastward from central Georgia and represented by the Cusseta Sand in east and central Alabama, is time-transgressive as the unit progrades from east to west. Although a Demopolis Chalk lithology (calcareous clay) appears above the basal Ripley Sand (Cusseta Sand), it is not Campanian as suggested by previous workers, but is instead lower Maestrichtian. Through the use of planktonic-benthonic foraminiferal ratios, textural analyses, clay mineral ratios, and stratigraphic and biogenic structures, the following 5 sedimentary environments, in vertical sequence, were established: (1) delta-front silts and sands (regressive), (2) offshore clay (transgressive), (3) marginal-shelf sands (basal Ripley), (4) offshore clays (transgressive), and (5) barrier bar-shoal sand complex (regressive). The gradational boundaries between the various facies produced by a fluctuating strand demonstrates that there is no major break in the sedimentary record in crossing the Campanian-Maestrichtian boundary. End_of_Article - Last_Page 1899------------

Late Pleistocene Planktonic Foraminiferal Trends Off Oregon: ABSTRACT

Oscillations in radiolarian-planktonic foraminiferal ratios with increasing depth in several deep-sea sediment cores from the southern Cascadia basin and the adjoining Blanco fracture zone off Oregon are thought to be the result of climatic fluctuations. Greater production of planktonic foraminifers compared with radiolarians seems to have occurred during glacial advances of the Pleistocene, whereas radiolarians predominated during glacial retreats. At least four intervals are evident in the deep-sea sediment record of the last 50,000-70,000 years. Based on radiocarbon dates, these intervals correspond approximately with late Wisconsin glacial advances and retreats as defined for the Puget lowlands of Washington. Five species generally make up 90 per cent or more of the planktonic foraminiferal assemblage. Globigerina pachyderma and Globigerina bulloides together compose more than half of the assemblage. In grain-size fractions of less than 177 microns, Globigerina quinqueloba and Globigerinita uvula predominate. A few specimens of Globoquadrina hexagona, Globigerina digitata, and Globigerinoides ruber have been observed. The species composition of planktonic Formaminifera does not appear to reflect the change from glacial to post-glacial climates. Neither do the coiling habits of Globigerina pachyderma. This species is dominantly left-handed throughout the sections examined. Right-handed forms reach a maximum of 13 per cent and average 2.7. End_of_Article - Last_Page 464------------

Foraminiferal Ratios and Regional Environments

Simple planktonic/benthonic foraminiferal ratios, when contoured, outline parameters of ancient environments of deposition. Ratio maps of four successive subunits of Upper Cretaceous strata in east Texas, southern Arkansas, and northern Louisiana show the evolution and changes in paleocurrent systems, and when and where contemporaneous structural or topographic features of the sea floor acted as effective barriers to oceanic circulation. High-value planktonic ratios, characteristic of deep-water open-ocean environments, were also found in paleocurrent systems developed in shallow water.