Geology topics

David Bukry

Publications and source records attributed to David Bukry.

At least 55 records · Page 3Linked to original sources

USGS1986

Miocene silicoflagellates from Chatham Rise, Deep Sea Drilling Project Site 594

Miocene silicoflagellates, dominated by Mesocena, are identified and correlated from Site 594 to other Deep Sea Drilling Project sites. Relative paleotemperature values from silicoflagellates at Site 594 are very low, supporting the evidence of the associated cold-water, low-diversity Coccolith assemblages. The greatest abundances of Mesocena diodon nodosa yet recorded occur at Site 594, which is near the present Subtropical Convergence. Similarities in the ecostratigraphic records between Chatham Rise (Site 594) and the Falkland Plateau (Site 329) in the late Miocene indicate widespread events within the circum-Antarctic water mass.

Initial Reports of the D.S.D.P.↗

USGS1985

Mid-Atlantic Ridge coccolith and silicoflagellate biostratigraphy, Deep Sea Drilling Project Sites 558 and 563.

Low-latitude coccolith zonation can be used for biostratigraphy at Mid-Atlantic Ridge sites DSDP 558 (lat. 38°N) and DSDP 563 (lat. 34°N). The low-latitude zonal sequence from lower Oligocene to Holocene is interrupted by coolwater assemblages in upper middle Miocene and by hiatuses that removed the lower Pliocene and part of the upper Pliocene. A gap in the range of zonal guide fossil Discoaster druggii in the lower Miocene, also identified in other ocean basins, occurs at both DSDP 558 and 563. Coccoliths are abundant and moderately overgrown at both sites. Pentaliths occur in the Oligocene at DSDP 563 but are missing at DSDP 558, probably the result of diagenesis. New taxa of coccoliths identified include Cyclolithellai neoaprica Bukry, n. sp., and Sphenolithus calyculus Bukry, n. sp. Silicoflagellates are limited to the upper Quaternary at DSDP 558 with warm-water assemblages of the Dictyocha aculeata Zone and possibly the upper Mesocena quadrangula Zone, as indicated by the presence of Dictyocha lingii. A new silicoflagellate species, Distephanus floridus Bukry, n. sp., is described.

Initial Reports of the D.S.D.P.↗

USGS1985

Tropical Pacific silicoflagellate zonation and paleotemperature trends of the late Cenozoic

Quantitative study of late Cenozoic silicoflagellates at tropical Pacific DSDP Sites 572 and 575 shows that the greatest amplitude of fluctuation in relative paleotemperature values occurred in the late Miocene. The coolest minimum paleotemperature values (near 75 = 30) also occurred in the late Miocene. The warmest intervals (Ts = 80 to 100) occurred in the middle Miocene and late Pliocene to Quaternary. In detail, the silicoflagellate relative paleotemperature curve correlates fairly well with the eustatic sea-level curve and deep-sea hiatus sequence. The only upper Cenozoic low-latitude biostratigraphic units not identified are the Distephanus speculum haliomma Subzone and Naviculopsis quadrata Zone, owing to the absence of the nominative species, which probably had nontropical ecologic preference. Several Naviculopsis occurrence events within the Naviculopsis ponticula Zone correlate between DSDP Hole 575A and DSDP Hole 495 off Guatemala. Many local and regional biostratigraphic events are recognized. New taxa identified from DSDP Leg 85 include Dictyocha nola Bukry, n. sp., Distephanus stradneri var. grandis Bukry, n. var., Mesocena elliptica var. rhomboidea Bukry, n. van, and Naviculopsis obtusarca var. acicula Bukry, n. var.

Initial Reports of the D.S.D.P.↗

USGS1984

Paleogene paleoceanography of the Arctic Ocean is constrained by the middle or late Eocene age of USGS Core Fl-422: Evidence from silicoflagellates

Arctic Ocean Core Fl-422 has been of central importance in Arctic tectonics and paleoceanography because it provides the sole evidence for early Cenozoic marine conditions in the Arctic. The presence of several Eocene and Eocene or Oligocene guide species of silicoflagellates in samples from this core shows that it is no older than middle Eocene, and is not Paleocene as previously reported. There is no evidence of any Paleocene (54 to 65 Ma) siliceous microfossils from Core Fl-422. Paleoceanographic inferences conerning the Cretaceous-Tertiary boundary and the timing of silica deposition in the Arctic have been erroneous because of unsupported biostratigraphic correlations.

Geology↗

USGS1984

Correlation of the middle eocene Kellogg Shale of northern California

The Kellogg Shale of northern California has traditionally been considered to be late Eocene in age on the basis of benthic foraminifer, radiolarian, and diatom correlations. The 30-m-thick Kellogg section exposed west of Byron, California, however, contains middle Eocene planktonic foraminifers (Zone P12), coccoliths (Subzones CP13c and CP14a), silicoflagellates (Dictyocha hexacantha Zone), and diatoms. Quantitative studies of the silicoflagellates and diatoms show a general cooling trend through the section which is consistent with paleoclimatic trends for this part of the middle Eocene (ca. 42-45 Ma) from elsewhere in the world. Seven new silicoflagellate taxa (Corbisema angularis, C. exilis, C. hastata miranda, C. inermis ballantina, C. regina, Dictyocha byronalis, Naviculopsis americana) and one new coccolithophorid species (Helicosphaera neolophota) are described.

California↗

USGS1984

Neogene silicoflagellates from Deep Sea Drilling Project Site 543, western tropical Atlantic Ocean

The upper lower Miocene silicoflagellate assemblage in Core 19 from DSDP Hole 543 in the western Atlantic Ocean contains the greatest concentration (41%) of deflandroid Dictyochapulchella yet observed. The deflandroid morphology in Dictyocha persisted through the Eocene and Oligocene at middle and high latitude, but virtually disappeared in the late Oligocene, only to reappear as a short-lived variant of D. pulchella near the end of the early Miocene or the beginning of the middle Miocene at several low-latitude sites. Correlations with coeval tropical silicoflagellate and diatom assemblages from the tropical eastern Pacific and eastern Atlantic suggest that this deflandroid morphotype may be stratigraphically useful. A new diatom, Craspedodiscus barronii Bukry, found in Core 543-19, is described.

Initial Reports of the D.S.D.P.↗

USGS1984

Cenozoic silicoflagellates from Rockall Plateau, Deep Sea Drilling Project Leg 81

Eocene to Pliocene silicoflagellates from the Rockall Plateau are sparse to moderately abundant and include assem blages at the upper and lower boundaries of the Miocene Series. Relative paleotemperature values for silicoflagellates from the upper Miocene and lower Pliocene at DSDP Hole 552A based on quantitative data are cooler than are those from equatorial Pacific Sites 503 and 504, but show a matching warm peak at the Miocene/Pliocene boundary and a major cooling in the lower Pliocene. Five new taxa of silicoflagellates are defined from Rockall Plateau assemblages: Corbisema panda Bukry, n. sp., Dictyochapulchella var. inflata Bukry, n. van, Distephanus xenus Bukry, n. sp., Mesocena apiculata evexa Bukry, n. subsp., and Naviculopsis pacifica pansa Bukry, n. subsp.

Initial Reports of the D.S.D.P.↗

USGS1983

Upper Cenozoic silicoflagellates from offshore Ecuador, Deep Sea Drilling Project Site 504

Diverse and abundant late Miocene to Pleistocene silicoflagellates at DSDP Site 504 can be correlated by tropical biostratigraphic zones and relative paleotemperature values to eastern tropical Pacific reference site DSDP 503A farther to the west. Early Pliocene assemblages, which were poorly known until now, are present and can be correlated locally between DSDP Holes 504, 503A, and 495, using species events associated with the new Dictyocha pulchella Subzone and Dictyocha angulata Subzone. Silicoflagellate relative paleotemperature values show major warming at 4.7 to 5.0 Ma (Cores 45-48), 3.4 to 3.8 Ma (Cores 32-33), 1.5 to 1.7 Ma (Cores 12-16), and 0.5 to 0.8 Ma (Cores 3-6). Major coolings occurred at 5.0 to 5.1 Ma (Core 51), 3.9 to 4.4 Ma (Cores 38-44), and 1.0 to 1.3 Ma (Cores 8-10). The appearance of Dictyocha longa is proposed to replace the asperoid/fibuloid ratio reversal as the bottom of the Dictyocha fibula Zone, because the non-evolutionary ratio reverses several times in the upper Miocene of Hole 5O3A, and at least once in Hole 504. Three new Pliocene silicoflagellates are defined: Dictyocha concinna Bukry, n. sp., D. helix Bukry, n. sp., and D. tamarae Bukry, n. sp.

Initial Reports of the D.S.D.P.↗

USGS1982

Cenozoic silicoflagellates from offshore Guatemala, Deep Sea Drilling Project Site 495

Diverse lower Miocene to Pleistocene silicoflagellate assemblages occur at Deep Sea Drilling Project Site 495, but many samples are dominated by one or two taxa. Low-latitude zonation can be applied throughout. Cool-indicating Distephanus speculum s. ampl. is only abundant in the upper Miocene; however, relative paleotemperature values (Ts) suggest temperature extremes in the lower Miocene similar to those in the upper Miocene. The lower upper Miocene ap pears to be thinned or missing, because no Dictyocha brevispina Zone assemblages are identified. The lower Miocene assemblages of the Naviculopsis ponticula Zone are an important silicoflagellate reference because of several new taxa and associations. New taxa and recombinations described herein include: Corbisema triacantha var. nuda n. var., Dictyocha angulata n. sp., D. delicata n. comb., D. delicata var. bisecta n. var., D. longa n. sp., D. longa var.paxilla n. var., D. ornata ornata n. comb., D. ornata africana n. subsp., D. subaculeata n. comb., Distephanus crux parvus n. comb., D. crux scutulatusn. subsp., D. polyactis var. literatusn. var.,Z speculumpatulus n. subsp., Naviculopsis contraria n. sp., N. lacrima n. sp., N. lata var. obliqua n. var., N. ponticula spinosa n. subsp

Initial Reports of the D.S.D.P.↗

USGS1981

Cenozoic coccoliths from the Deep Sea Drilling Project

Coccoliths, as the dominant constituent of many Deep Sea Drilling Project cores, have provided the means of rapid and detailed biostratigraphic zonation to help guide ocean-sediment coring operations aboard D.V. Glomar Challenger. The Cenozoic has been divided into 50 to 60 zones and subzones which are most effective for middle- and low- latitude sites. Because key stratigraphic coccoliths have proved more resistant to diagenetic change than planktic foraminifers, they contributed to dating of sedimentary beds within and just above basalt, directly demonstrating the correctness of the sea-floor spreading hypothesis. An unexpected discovery of Braarudosphaera beds in the South Atlantic produced valuable speculation on the response of coccolithophorids to paleoceanographic changes. Samples from the diversity of oceanic terrains explored by early cruises of Glomar Challenger helped in the recognition of the effects of differential preservation —etching and overgrowth from species to species —and in the determination of biogeographic ranges which would affect the taxonomic, paleoecologic and biostratigraphic assignments of coccoliths. DSDP sites have provided the matrix needed to outline depth sequences based on dissolution rank, and paleotemperature sequences based on abundance along latitudinal traverses. New Hydraulic Piston Corer capabilities will make possible application of magnetic reversal stratigraphy to undisturbed cores where coccolith evolutionary transitions and datum-interval stratigraphy can be established.

Book chapter↗

USGS1981

Synthesis of silicoflagellate stratigraphy for maestrichtian to quaternary marine sediment

Cosmopolitan and low-latitude silicoflagellate distributions determined from Deep Sea Drilling Project cores are synthesized into a sequence of 23 biostratigraphic zones and subzones for tropical and subtropical ocean areas. The stratigraphic relation of major morphologic changes in silicoflagellates from all areas is summarized. Two new Neogene subzones, one new Paleogene subzone, one new species, and one new variety are defined: Dictyocha perlaevis ornata Subzone, Dictyocha neonautica Subzone, Distephanus speculum haliomma Subzone, Dictyocha neonautica Bukry, n. sp., and D. neonautica var. cocosensis Bukry, n. var.

Book chapter↗

USGS1981

Pacific Coast coccolith stratigraphy between Point Conception and Cabo Corrientes, Deep Sea Drilling Project Leg 63

DSDP Leg 63 recovered Neogene coccoliths from south of Point Conception, California (Site 467), to north of Cabo Corrientes, Mexico (Site 473), as part of a traverse exploring the sedimentary record of the California Current along the Pacific Coast. A combination of temperate and tropical zonations were used to date Leg 63 coccolith assemblages because of intergradations of warm and cool species along the transect. Variations in the abundance and the presence and absence of Discoaster species are useful in recognizing warm-cool intergradations. New taxa described in this report include Discoaster okadai n. sp., D. sanmiguelensis n. sp., Helicosphaera californiana n. sp., H. crouchii n. sp., H. gertae n. sp., and H. vedderi n. sp.

California↗

USGS1981

Silicoflagellate stratigraphy of offshore California and Baja California, Deep Sea Drilling Project, Leg 63.

Quantitative study of middle and upper Miocene silicoflagellate assemblages from Pacific Coast Sites 467 and 469 to 472 has permitted identification of warm- and temperate-water biostratigraphic zones and the formulation of a model for relative paleotemperature values (Ts) on the basis of warm- and temperate-genera abundances. Geographic and temporal trends in Ts for Pacific Coast assemblages are indicated. Three new taxa are described: Dictyocha subclinata Bukry n. sp., Mesocena diodon borderlandensis Bukry n. subsp., and M. hexalitha Bukry, n. sp. The ranges in space and time for several species, such as Dictyocha neonautica var. cocosensis and Distephanus mesophthalmus, are increased. Regionally, barred forms of Distephanus stauracanthus become predominant over ringed forms in the upper part of the middle Miocene Distephanus stauracanthus Subzone.

California↗

USGS1981