David Bukry

Uppermost Campanian-Maestrichtian strontium isotopic, biostratigraphic, and sequence stratigraphic framework of the New Jersey Coastal Plain

Firm stratigraphic correlations are needed to evaluate the global significance of unconformity bounded units (sequences). We correlate the well-developed uppermost Campanian and Maestrichtian sequences of the New Jersey Coastal Plain to the geomagnetic polarity time scale (GPTS) by integrating Sr-isotopic stratigraphy and biostratigraphy. To do this, we developed a Maestrichtian (ca. 73–65 Ma) Sr-isotopic reference section at Deep Sea Drilling Project Hole 525A in the southeastern Atlantic Ocean. Maestrichtian strata can then be dated by measuring their 87 Sr/ 86 Sr composition, calibrating to the GPTS of S. C. Cande and D. V. Kent (1993, personal commun.), and using the equation Age (Ma) = 37 326.894–52 639.89 ( 87 Sr/ 86 Sr). Sr-stratigraphic resolution for the Maestrichtian is estimated as ±1.2 to ±2 m.y. At least two unconformity-bounded units comprise the uppermost Campanian to Maestrichtian strata in New Jersey. The lower one, the Marshalltown sequence, is assigned to calcareous nannofossil Zones CC20/21 (∼NC19) and CC22b (∼NC20). It ranges in age from ∼74.1 to 69.9 Ma based on Sr-isotope age estimates. The overlying Navesink sequence is assigned to calcareous nannoplankton Zones CC25–26 (∼NC21–23); it ranges in age from 69.3 to 65 Ma based on Sr-isotope age estimates. The upper part of this sequence, the Tinton Formation, has no calcareous planktonic control; Sr-isotopes provide an age estimate of 66 ± 1.2 Ma (latest Maestrichtian). Sequence boundaries at the base and the top of the Marshalltown sequence match boundaries elsewhere in the Atlantic Coastal Plain (Owens and Gohn, 1985) and the inferred global sea-level record of Haq et al. (1987); they support eustatic changes as the mechanism controlling depositional history of this sequence. However, the latest Maestrichtian record in New Jersey does not agree with Haq et al. (1987); we attribute this to correlation and time-scale differences near the Cretaceous/Paleogene boundary. High sedimentation rates in the latest Maestrichtian of New Jersey (Shrewsbury Member of the Red Bank Formation and the Tinton Formation) suggest tectonic uplift and/or rapid progradation during deposition of the highstand systems tract.

Basement Ages and Basement Depths in the Eastern Equatorial Pacific from Deep Sea Drilling Project Legs 5, 8, 9, and 16

Recent literature contains numerous references to basement ages and basement depths determined by the Deep Sea Drilling Project. The data are derived from a variety of sources, many of them inadequately documented or preliminary, and are not uncommonly inaccurate or conflicting. In this paper we present tabulations of basement ages and depths from DSDP Legs 5, 8, 9, and 16 in the eastern equatorial Pacific, refer them to the latest biostratigraphic time scale, and document and discuss their error limits. We recommend that in future use of this type of data a similar practice be adopted and that the precise source of data, time scale used, and procedures for determining ages and errors be clearly identified in order to avoid confusion. Based on the data presented here, we also give the relations between basement age, distance from the spreading center, and basement depth. The errors inherent in the data cause these relations to be very general and to have less resolution than ascribed to them by some previous investigators.

High resolution paleoceanography of the Guaymas Basin, Gulf of California, during the past 15 000 years

Abstract Deep Sea Drilling Project Site 480 (27°54.10′N, 111°39.34′W; 655 m water depth) contains a high resolution record of paleoceanographic change of the past 15 000 years for the Guaymas Basin, a region of very high diatom productivity within the central Gulf of California. Analyses of diatoms and silicoflagellates were completed on samples spaced every 40–50 yr, whereas ICP–AES geochemical analyses were completed on alternate samples (sample spacing 80–100 yr). The Bolling–Allerod interval (14.6–12.9 ka) (note, ka refers to 1000 calendar years BP throughout this report) is characterized by an increase in biogenic silica and a decline in calcium carbonate relative to surrounding intervals, suggesting conditions somewhat similar to those of today. The Younger Dryas event (12.9–11.6 ka) is marked by a major drop in biogenic silica and an increase in calcium carbonate. Increasing relative percentage contributions of Azpeitia nodulifera and Dictyocha perlaevis (a tropical diatom and silicoflagellate, respectively) and reduced numbers of the silicoflagellate Octactis pulchra are supportive of reduced upwelling of nutrient-rich waters. Between 10.6 and 10.0 ka, calcium carbonate and A. nodulifera abruptly decline at DSDP 480, while Roperia tesselata, a diatom indicative of winter upwelling in the modern-day Gulf, increases sharply in numbers. A nearly coincident increase in the silicoflagellate Dictyocha stapedia suggests that waters above DSDP 480 were more similar to the cooler and slightly more saline waters of the northern Gulf during much of the early and middle parts of the Holocene (∼10 to 3.2 ka). At about 6.2 ka a stepwise increase in biogenic silica and the reappearance of the tropical diatom A. nodulifera marks a major change in oceanographic conditions in the Gulf. A winter shift to more northwesterly winds may have occurred at this time along with the onset of periodic northward excursions (El Nino-driven?) of the North Equatorial Countercurrent during the summer. Beginning between 2.8 and 2.4 ka, the amplitude of biogenic silica and wt% Fe, Al, and Ti (proxies of terrigenous input) increase, possibly reflecting intensification of ENSO cycles and the establishment of modern oceanographic conditions in the Gulf. Increased numbers of O. pulchra after 2.8 ka suggest enhanced spring upwelling.

Geologic history of Siletzia, a large igneous province in the Oregon and Washington Coast Range: Correlation to the geomagnetic polarity time scale and implications for a long-lived Yellowstone hotspot

Siletzia is a basaltic Paleocene and Eocene large igneous province in coastal Oregon, Washington, and southern Vancouver Island that was accreted to North America in the early Eocene. New U-Pb magmatic, detrital zircon, and 40Ar/39Ar ages constrained by detailed field mapping, global nannoplankton zones, and magnetic polarities allow correlation of the volcanics with the 2012 geologic time scale. The data show that Siletzia was rapidly erupted 56–49 Ma, during the Chron 25–22 plate reorganization in the northeast Pacific basin. Accretion was completed between 51 and 49 Ma in Oregon, based on CP11 (CP—Coccolith Paleogene zone) coccoliths in strata overlying onlapping continental sediments. Magmatism continued in the northern Oregon Coast Range until ca. 46 Ma with the emplacement of a regional sill complex during or shortly after accretion. Isotopic signatures similar to early Columbia River basalts, the great crustal thickness of Siletzia in Oregon, rapid eruption, and timing of accretion are consistent with offshore formation as an oceanic plateau. Approximately 8 m.y. after accretion, margin parallel extension of the forearc, emplacement of regional dike swarms, and renewed magmatism of the Tillamook episode peaked at 41.6 Ma (CP zone 14a; Chron 19r). We examine the origin of Siletzia and consider the possible role of a long-lived Yellowstone hotspot using the reconstruction in GPlates, an open source plate model. In most hotspot reference frames, the Yellowstone hotspot (YHS) is on or near an inferred northeast-striking Kula-Farallon and/or Resurrection-Farallon ridge between 60 and 50 Ma. In this configuration, the YHS could have provided a 56–49 Ma source on the Farallon plate for Siletzia, which accreted to North America by 50 Ma. A sister plateau, the Eocene basalt basement of the Yakutat terrane, now in Alaska, formed contemporaneously on the adjacent Kula (or Resurrection) plate and accreted to coastal British Columbia at about the same time. Following accretion of Siletzia, the leading edge of North America overrode the YHS ca. 42 Ma. The voluminous high-Ti basaltic to alkalic magmatism of the 42–35 Ma Tillamook episode and extension in the forearc may be related to the encounter with an active YHS. Clockwise rotation of western Oregon about a pole in the backarc has since moved the Tillamook center and underlying Siletzia northward ∼250 km from the probable hotspot track on North America. In the reference frames we examined, the YHS arrives in the backarc ∼5 m.y. too early to match the 17 Ma magmatic flare-up commonly attributed to the YHS. We suggest that interaction with the subducting slab may have delayed arrival of the plume beneath the backarc.

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.

Iron-Rich Basal Sediments from the Eastern Equatorial Pacific: Leg 16, Deep Sea Drilling Project

Iron-rich sediments chemically similar to those forming at present on the crest of the East Pacific Rise have been found just above basement at widely separated drill sites in the eastern equatorial Pacific, including three sites of Leg 16 of the Deep Sea Drilling Project. These sediments were probably formed when the basement was at the crest of this rise and have moved to their present location as a result of sea-floor spreading.

Interplay of Late Cenozoic Siliciclastic Supply and Carbonate Response on the Southeast Florida Platform

ABSTRACT High-resolution seismic-reflection data collected along the length of the Caloosahatchee River in southwestern Florida have been correlated to nannofossil biostratigraphy and strontium-isotope chemostratigraphy at six continuously cored boreholes. These data are interpreted to show a major Late Miocene(?) to Early Pliocene fluvial-deltaic depositional system that prograded southward across the carbonate Florida Platform, interrupting nearly continuous carbonate deposition since early in the Cretaceous. Connection of the platform top to a continental source of siliciclastics and significant paleotopography combined to focus accumulation of an immense supply of siliciclastics on the southeastern part of the Florida Platform. The remarkably thick (> 100 m), sand-rich depositional system, which is characterized by clinoformal progradation, filled in deep accommodation, while antecedent paleotopography directed deltaic progradation southward within the middle of the present-day Florida Peninsula. The deltaic depositional system may have prograded about 200 km southward to the middle and upper Florida Keys, where Late Miocene to Pliocene siliciclastics form the foundation of the Quaternary carbonate shelf and shelf margin of the Florida Keys. These far-traveled siliciclastic deposits filled accommodation on the southeastern part of the Florida Platform so that paleobathymetry was sufficiently shallow to allow Quaternary recovery of carbonate sedimentation in the area of southern peninsular Florida and the Florida Keys.

Cretaceous Arctic silicoflagellates

Cretaceous silicoflagellate assemblages from Arctic Ocean USGS Core 437 showVallacerta siderea the most abundant species; most species ofLyramula disappear halfway up the core; onlyL. burchardae, n. sp., persists into the upper sections. These occurrences are untypical of the few documented Cretaceous assemblages from other areas. A Campanian or Maestrichtian age is suggested by correlation, but the uniquely high abundance ofV. siderea and lack ofCorbisema suggests that a difference in both age and general environment could be involved. If Core 437 is latest Maestrichtian, then the evidence from this core would constrain the timing of the ocean-freshening model for the Cretaceous-Tertiary boundary extinctions.

Comparison of Miocene provincial foraminiferal stages to coccolith zones in the California Continental Borderland

Biostratigraphic ages determined by planktic coccoliths and benthic foraminifera for the same core samples from the California Continental Borderland suggest that a significant overlap exists among provincial Miocene stages of California and that some of the benthic foraminifera commonly used to recognize these stages are time-transgressive. For example, samples assigned to the middle Miocene Discoaster exilis Zone of coccoliths (∼ 14 ± 1 m.y.) are also assigned to the Relizian, Luisian, and lower Mohnian Stages on the basis of benthic foraminifera. Significantly, most past and current geologic interpretations of Cenozoic marine sequences in California rely heavily on provincial benthic foraminiferal stages and zones. Thus, the apparent overlapping of provincial stages has serious implications for geologic studies of the California Cenozoic and should be further investigated in sections onshore.

Late Cretaceous pelagic sediments, volcanic ash and biotas from near the Louisville Hotspot, Pacific Plate, paleolatitude ∼42°S

Abstract Dredging on the deep inner slope of the Tonga Trench, immediately north of the intersection between the Louisville Ridge hotspot chain and the trench, recovered some Late Cretaceous (Maestrichtian) slightly tuffaceous pelagic sediments. They are inferred to have been scraped off a recently subducted Late Cretaceous guyot of the Louisville chain. In the vicinity of the Louisville hotspot (present location 50°26′S, 139°09′W; Late Cretaceous location ∼42°S, longitude unknown) Late Cretaceous rich diatom, radiolarian, silicoflagellate, foraminiferal and coccolith biotas, accumulated on the flanks of the guyot and are described in this paper. Rich sponge faunas are not described. ?Inoceramus prisms are present. Volcanic ash is of within-plate alkalic character. Isotope ratios in bulk carbonate δ18O − 2.63 to + 0.85, δ13C + 2.98 to 3.83) are normal for Pacific Maestrichtian sediments. The local CCD may have been shallower than the regional CCD, because of high organic productivity. In some samples Late Cretaceous materials have been mixed with Neogene materials. Mixing may have taken place on the flanks of the guyot during transit across the western Pacific, or on the trench slope during or after subduction and offscraping about 0.5 Ma.