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John A. Barron

Publications and source records attributed to John A. Barron.

At least 55 records · Page 3Linked to original sources
USGS2007

Age, stratigraphy, and correlations of the late Neogene Purisima Formation, central California coast ranges

The Purisima Formation is an important upper Miocene and Pliocene stratigraphic unit in central California, cropping out from the coast at Point Reyes north of San Francisco to more extensive exposures in the Santa Cruz Mountains to the south. The fine-grained rocks in the lower parts of the Purisima Formation record a latest Miocene transgressive event, whereas the middle and upper parts of the formation consist of increasingly clastic-rich siltstones and sandstones resulting from uplift of adjacent coastal regions and the Sierra Nevada during Pliocene transgressive and regressive sea-level events. Exposures of the Purisima occur in three different, fault-bounded, structural blocks - the Santa Cruz, Pigeon Point, and Point Reyes tectonic blocks - that complicate correlations and regional age assignments. We summarize and compare published and new biostratigraphic and geochronologic data for various exposures of the Purisima Formation on the basis of mollusks, diatoms, radiometric dating, magnetostratigraphy, tephrochronology, and strontium isotope dating. On the basis of these data, we conclude that the Purisima Formation ranges in age from the latest Miocene (about 7 Ma) to the late Pliocene (about 2.6 Ma). The Purisima Formation of Santa Cruz County, exposed in the sea cliffs from Santa Cruz to Rio del Mar, is here designated a supplementary reference section because it is the most complete and well studied Purisima section in central California.

California↗
USGS2007

High-resolution climate records of the past 2,400 years from the offshore of northernmost California and central Oregon

High resolution diatom and pollen data from piston core TN062 0550 off northernmost California, and Kasten core WW7710A-26 off coastal Oregon, are compiled for the past 2,400 years. Diatom proxy data for Fall SST from both cores record warm SST's in the intervals from ca. AD 400 to 600, and from ca. AD 1050 to 1300 (later part of the Medieval Warm Period). The intervening AD 650 to 1000 interval, and the post-AD 1350 interval at both sites appear to be relatively cool. Whereas the pollen assemblage from TN062 0550 is dominated by coastal redwood, the pollen assemblage from WW7710A-26 displays alternating moist-dry cycles of alder vs. pine, as well as cycles of western hemlock (typical of the coastal forests of Oregon) vs. coastal redwood (typical of the coastal forests of northern California). Coincidence of intervals characterized by warmer diatom SST with drier pollen assemblages, and those of cooler diatom SST with moister pollen assemblages in the coastal Oregon core, recall the modern-day association of cool PDO with increased precipitation, and warm PDO with decreased precipitation, in the Pacific Northwest.

California, Oregon↗
USGS2005

Paleoceanographic history of the Guaymas Basin, Gulf of California, during the past 15,000 years based on diatoms, silicoflagellates, and biogenic sediments

High-resolution records of calcium carbonate, biogenic opal, diatoms, and silicoflagellates from western Guaymas Basin gravity core GGC55 and piston core JPC56 and eastern Guaymas Basin DSDP Site 480 reveal a complex paleoceanographic history of the central Gulf of California during the past 15,000 years. Prior to ∼ 6.2 ka, the eastern and western Guaymas Basin proxy records were remarkably similar. After conditions similar to those of today during the Bølling–Allerod, the Younger Dryas (YD) saw a major drop in diatom production, coincident with increased calcium carbonate and tropical microfossils suggestive of El Niño-like conditions. Biosiliceous productivity began increasing during the latter part of the YD, but it was only during the earliest Holocene (11.6 to 11.0 ka) that conditions similar to those of the Bølling–Allerod returned to the central Gulf. Between around 11.0 and 6.2 ka, tropical diatoms and silicoflagellates were virtually absent from the central Gulf, as relatively cooler and fresher surface waters resembling those of the modern northern Gulf were present in the central Gulf. Beginning at about 6.2 ka, tropical diatoms and silicoflagellates began increasing in the central Gulf, and coccoliths returned to western Gulf sediments. The onset of modern-day monsoon conditions in the American Southwest required the presence of warm SSTs in the northern Gulf, which probably did not occur until after about 5.4 ka, when tropical diatoms and silicoflagellates became relatively common in the central Gulf. Modern east–west contrasts, which arise from late winter–early spring coastal upwelling on the mainland side and lower diatom productivity on the western side of the Gulf, commenced between 6.2 and 5.4 ka, possibly due to a shift in the direction of late winter–early spring winds more towards the southeast, or down the axis of the Gulf. This proposed wind shift might have ultimately been due to a late Holocene strengthening of ENSO-like conditions in the eastern equatorial Pacific.

Gulf of California↗
USGS2005

Paleontology of the upper Eocene to quaternary postimpact section in the USGS-NASA Langley core, Hampton, Virginia

The USGS-NASA Langley corehole was drilled in 2000 in Hampton, Va. The core serves as a benchmark for the study of calcareous nannofossils, dinoflagellates, diatoms and silico flagellates, mollusks, ostracodes, planktonic foraminifera and bolboformids, and vertebrate remains in the upper Eocene, Oligocene, Miocene, and Pliocene sediments in southeastern Virginia. These sediments were deposited after the comet or asteroid impact that produced the Chesapeake Bay impact structure. The Chickahominy Formation was deposited rapidly in outer neritic to upper bathyal marine environments during the last 2 million years of the late Eocene. The Drummonds Corner beds are newly recognized in the Langley core. These beds appear to represent shallower water or more nearshore deposition than the underlying Chickahominy deposits. Paleontology indicates an age in the later part of the early Oligocene, with a sharp floral and faunal break between the Drummonds Corner beds and the underlying Chickahominy Formation. Late Oligocene sedimentation is represented by the Old Church Formation. The record of early and middle Miocene deposition in the Langley core is incomplete. The Calvert Formation records brief episodes of deposition in three members, which are separated by unconformities and are called the informal Newport News beds, the Plum Point Member, and the Calvert Beach Member. A second episode of rapid deposition at the Langley site is preserved as the upper Miocene St. Marys and Eastover Formations. The Eastover is overlain unconformably by the Yorktown Formation, which is both late early and early late Pliocene. The highest unit, the Tabb Formation (Pleistocene), was not studied paleontologically. Continued movement along faults and fractures of the crater and nearby region may have enhanced the contributions of older material into the various units filling the Chesapeake Bay impact crater, as suggested by the conspicuous reworking of microfossils in many of the samples from the upper Eocene and younger units in the USGS-NASA Langley core.

Virginia↗
USGS2005

Diatom biochronology for the early Miocene of the equatorial Pacific

The latest Oligocene and early Miocene diatom biostratigraphy (24.4 to 16.9 Ma) of equatorial Pacific ODP Site 199-1219 is documented and tied to paleomagnetic stratigraphy in 69 samples, allowing an average age resolution of about 100 kyrs. An updated taxonomy is provided and most of the 71 taxa are illustrated in 9 photographic plates. The equatorial Pacific diatom zonation for the latest Oligocene and early Miocene is updated: the Nitzschia maleinterpretaria Partial Range Zone is newly proposed to replace the Triceratium pileus Interval Zone and part of the Craspedodiscus elegans Partial Range Zone, and the C. elegans Zone is modified to be an interval zone. Absolute ages of 62 datum levels are estimated and compared with age estimates from elsewhere in the equatorial Pacific, as well as from the North Pacific and Southern Ocean. It is likely that many of these datum levels will be useful for correlations between the equatorial Pacific and higher latitude regions.

Stratigraphy↗
USGS2005

Scanning electron microscope studies of some early Miocene diatoms from the equatorial Pacific Ocean with descriptions of two new species, Actinocyclus jouseae Barron and Actinocyclus nigriniae Barron

Scanning electron microscope (SEM) and light microscope (LM) studies are used to propose and describe two new species, Actinocyclus jouseae Barron , sp. nov. and Actinocyclus nigriniae Barron , sp. nov. from lower Miocene sediments from equatorial Pacific ODP Site 1219. Parallel SEM and LM studies reveal that Thalassiosira bukryi Barron should be transferred to Azpeitia and suggest that Actinocyclus barronii Radionova is likely to be a variety of A. radionovae Barron

Proceedings of the California Academy of Sciences ↗
USGS2004

Oligocene and earliest Miocene diatom biostratigraphy of ODP leg 199 site 1220, equatorial Pacific

Completion of studies on material collected during Ocean Drilling Program Leg 199 at Site 1220 in the equatorial Pacific allows calibration of the ranges of >35 stratigraphically important diatoms to paleomagnetic stratigraphy for the Oligocene and earliest Miocene (~33.5–21.5 Ma). The taxonomy of these taxa is reviewed, and age estimates of their first and last occurrences are compiled. The diatom zonation for the Oligocene and earliest Miocene of the equatorial Pacific is revised and correlated with paleomagnetic stratigraphy. This biostratigraphy is likely to be applicable throughout the low-latitude regions of the world's oceans.

Proceedings of the Ocean Drilling Program: Scienti↗
USGS2003

Planktonic marine diatom record of the past 18 m.y.: Appearances and extinctions in the pacific and southern oceans

Recently published diatom biochronologies provide accurate (to 0.1 m . y .) determination of the ages of appearances and disappearances of planktonic diatoms during the past 18 m . y . in the equatorial Pacific , North Pacific , and Southern Ocean . Comparisons of these records reveal the age of evolutionary appearance and extinction of species and their region of origin. Extinct planktonic diatom species have a mean longevity of 3.4 ± 2.8 m . y . (SD, n = 53) in the equatorial Pacific , 2.5 ± 2.1 m . y . (n = 52) in the North Pacific , and 2.9 ± 2.3 m . y . (n = 38) in the Southern Ocean . The relatively large standard deviations are likely due to the inclusion of taxa that probably could be subdivided into two or more species. In the equatorial Pacific , evolutionary turnover of diatom species was relatively high between 18 .0 and 6.0 Ma compared with the period after 6.0 Ma, presumably reflecting changing oceanic circulation and evolving water masses. In the North Pacific , evolutionary turnover speaked between 10.0 and 4.5 Ma, with increasing high-latitude cooling and enhanced provincialism. In the Southern Ocean , evolutionary turnover of endemic diatoms was greatest between 5.0 and 1.6 Ma, which provides evidence for the strong provincial character of Pliocene diatom assemblages. Taken as a whole, oceanic diatom assemblages became increasingly provincial in character during the late Miocene and Pliocene, as pole-to-equator thermal gradients increased and oceanic frontal systems were strengthened.

Diatom Research↗
USGS2002

Late Miocene and early Pliocene biosiliceous sedimentation along the California margin

Biogenic opal sedimentation is compared between offshore and onshore areas of the California margin during the late middle Miocene, the late Miocene, and the early Pliocene. The records from offshore ODP Sites 1010 and 1021 have declining opal abundance, with a dramatic three-fold decline at about 11.5 Ma and a second, less pronounced drop occurring at about 7.6 Ma. Thick stratigraphic sections of diatomaceous sediments dated between 11.5 and 10.0 Ma and between 7.6 and 6.5 Ma are found onshore in California, whereas coeval intervals in offshore deep sea sites display relatively low opal percentages. This suggests that during periods of reduced strength in the California Current, diatom production declined in offshore areas while it increased in more coastal regions. The early Pliocene and early part of the late Pliocene (4.6 to ca. 2.7 Ma) are marked by the near absence of diatoms in offshore sites, while diatoms are masked by clastic components in onshore sections. Diatom production was greatly reduced along the California margin during this climatically warm period of the Pliocene at the same time that production dramatically increased in the subarctic northwest Pacific, suggesting fractionation of opal to higher latitudes.

Baja California, California↗
USGS2001

Climate variability of the Holocene, Site 1098, Palmer Deep, Antarctica

Detailed study of four Holocene sediment intervals from Ocean Drilling Program Site 1098 (Palmer Deep, Antarctic Peninsula) reveals that in situ dissolution of calcareous foraminifers in the core repository has significantly altered and in some cases eliminated calcareous foraminifers. Despite dissolution, the foraminifer and supporting diatom data show that the most open-ocean and reduced sea-ice conditions occurred in the early Holocene. The influence of Circumpolar Deep Water was greatest during the early Holocene but continued to be important throughout the Holocene. An increase in sea-ice proximal diatoms at 3500 cal. BP documents an expansion in the amount of persistent sea ice. The inferred increase in sea ice corresponds with an overall increase in magnetic susceptibility values. Benthic foraminifers are present in all samples from the Palmer Deep, including the middle Holocene pervasively laminated sediments with low magnetic susceptibility values. The consistent presence of mobile epifaunal benthic foraminifers in the laminated sediments demonstrates that the laminations do not represent anoxic conditions. The uniform composition of the agglutinated foraminifer fauna throughout the late Holocene suggests that the Palmer Deep did not experience bottom-water-mass changes associated with the alternating deposition of bioturbated or laminated sediments.

Antarctica, Antarctic Peninsula, Palmer Deep↗
USGS2001

Interglacial theme and variations: 500 k.y. of orbital forcing and associated responses from the terrestrial and marine biosphere, U.S. Pacific Northwest

Sediments collected off northern California by Ocean Drilling Program Leg 167 contain time series that show strong, orbitally driven insolation forcing of surface oceanographic conditions. Orbital forcing caused a strong response in the distribution of major terrestrial vegetation but a less predictable response for primary productivity offshore. Terrestrial vegetation responded primarily to regional sea surface temperature (SST). Coastal ocean productivity appears highest when SST is moderately high, not during peak interglacial conditions nor during insolation maxima. When individual interglacial intervals are examined closely, each has a different signature. Two of six interglacials (MIS [marine isotope stage] 5 and MIS 11) have higher SST than modern conditions, but each elicits a different response from the terrestrial and marine communities. The type of vegetation and the strength of upwelling vary between interglacials, depending on the relative strength of factors that drive the warming, including insolation, ice-cap size, and level of greenhouse gases.

California↗
USGS2001

Surface-geophysical characterization of ground-water systems of the Caloosahatchee River basin, southern Florida

The Caloosahatchee River Basin, located in southwestern Florida, includes about 1,200 square miles of land. The Caloosahatchee River receives water from Lake Okeechobee, runoff from the watershed, and seepage from the underlying ground-water systems; the river loses water through drainage to the Gulf of Mexico and withdrawals for public-water supply and agricultural and natural needs. Water-use demands in the Caloosahatchee River Basin have increased dramatically, and the Caloosahatchee could be further stressed if river water is used to accommodate restoration of the Everglades. Water managers and planners need to know how much water will be used within the river basin and how much water is contributed by Lake Okeechobee, runoff, and ground water. In this study, marine seismic-reflection and ground-penetrating radar techniques were used as a means to evaluate the potential for flow between the river and ground-water systems. Seven test coreholes were drilled to calibrate lithostratigraphic units, their stratal geometries, and estimated hydraulic conductivities to surface-geophysical profiles. A continuous marine seismic-reflection survey was conducted over the entire length of the Caloosahatchee River and extending into San Carlos Bay. Lithostratigraphic units that intersect the river bottom and their characteristic stratal geometries were identified. Results show that subhorizontal reflections assigned to the Tamiami Formation intersect the river bottom between Moore Haven and about 9 miles westward. Oblique and sigmoidal progradational reflections assigned to the upper Peace River Formation probably crop out at the floor of the river in the Ortona area between the western side of Lake Hicpochee and La Belle. These reflections image a regional-scale progradational deltaic depositional system containing quartz sands with low to moderate estimated hydraulic conductivities. In an approximate 6-mile length of the river between La Belle and Franklin Lock, deeper karstic collapse structures are postulated. These structures influence the geometries of parallel reflections that intersect the river channel. Here, reflections assigned to the Buckingham Limestone Member of the Tamiami Formation (a confining unit) and reflections assigned to the clastic zone of the sandstone aquifer likely crop out at the river bottom. Beneath these shallow reflections, relatively higher amplitude parallel reflections of the carbonate zone of the sandstone aquifer are well displayed in the seismic-reflection profiles. In San Carlos Bay, oblique progradational reflections assigned to the upper Peace River Formation are shown beneath the bay. Almost everywhere beneath the river, a diffuse ground-water flow system is in contact with the channel bottom. Ground-penetrating radar profiles of an area about 2 miles north of the depositional axis of the deltaic depositional system in the Ortona area show that progradational clinoforms imaged on seismic reflection profiles in the Caloosahatchee River are present within about 17 feet of the ground surface. Ground-penetrating radar profiles show southward dipping, oblique progradational reflections assigned to the upper Peace River Formation that are terminated at their tops by a toplapping or erosional discontinuity. These clinoformal reflections image clean quartz sand that is probably characterized by moderate hydraulic conductivity. This sand could be mapped using ground-penetrating radar methods.

Water-Resources Investigations Report↗
USGS2001

Sequence stratigraphy of a South Florida carbonate ramp and bounding siliciclastics (late Miocene-Pliocene)

In southern peninsular Florida, a late-early to early-late Pliocene carbonate ramp (Ochopee Limestone Member of the Tamiami Formation) is sandwiched between underlying marine siliciclastics of the late Miocene to early Pliocene Peace River Formation and an overlying late Pliocene unnamed sand. At least three depositional sequences (DS1, DS2, and DS3), of which two contain condensed sections, are recognized in the Peace River Formation; an additional depositional sequence (DS4) is proposed to include the Ochopee Limestone. Established chronologies and new biostratigraphic results indicate that the Tortonian and Zanclean ages bracket the Peace River Formation. Depositional sequence 1 (DS1) prograded across the present-day peninsular portion of the Florida Platform during the Tortonian age and laps out near the southern margin of the peninsula. During the latest Tortonian and Messinian ages, progradation of DS2 overstepped the southern lap out of DS1 and extended at least as far as the Florida Keys. Deposition of DS2 ended, at the latest, near the Miocene-Pliocene boundary. Siliciclastic supply was reduced during early Pliocene deposition of DS3, which is absent in southernmost peninsular Florida. This reduction in supply of siliciclastics was followed by aggradational accumulation of heterozoan temperate carbonate sediments on a widespread carbonate ramp that includes the Ochopee Limestone. The Ochopee Limestone was deposited during eustatic cycle TB3.6 and ended in the late Pliocene with basinward lap out near the southern margin of the Florida peninsula. The Ochopee Limestone ramp was buried with a late Pliocene resumption of southward influx of siliciclastics (unnamed sand and Long Key Formation) that extended south beyond the middle and upper Florida Keys.

Florida↗
USGS2000

Data report: Mid-Pliocene diatom assemblages at sites 1016, 1021, and 1022

Diatom assemblages from the middle part of the Pliocene (3.2-2.5 Ma) were investigated from Ocean Drilling Program Sites 1016, 1021, and 1022 in an effort to infer paleotemperature fluctuations off California. Diatoms are very sparse in virtually all of the samples that were examined from Sites 1016 and 1021. This is presumably because these sites were seaward (west) of the coastal zone of diatom productivity during the middle part of the Pliocene. Diatoms are relatively common in the vast majority of samples that were examined from Hole 1022A. Diatom assemblages are dominated by Chaetoceros spores (a coastal upwelling component), the cold-water (subarctic) taxa Neodenticula kamtschatica and its descendant Neodenticula koizumii, and Thalassionema nitzschioides, a temperate taxon that is typically found at the seaward edge of coastal upwelling zones. Paleotemperature interpretations, however, are not possible at this time because of the scarcity of comparative modern core-top data.

Proceedings of the Ocean Drilling Program: Scienti↗
USGS2000

Sedimentary record of the California Current system, middle Miocene to Holocene: A synthesis of Leg 167 results

During Ocean Drilling Program Leg 167, the California continental margin was drilled from about 30°N to 42°N to sample high-resolution paleoceanographic and paleoclimatic records in the California Current system. Because of typically high sedimentation rates along the margin (80 to >200 m/m.y.), drilling has proved necessary to collect late Pleistocene sedimentary records that usually are sampled by standard piston cores in other oceanic regions. Triple piston coring on Leg 167 enabled us to construct continuous submillennial paleoceanographic records to about 2 Ma. In the offshore drill sites, continuous records were constructed into the Miocene. The oldest sediments recovered on Leg 167 have an age of ~14 Ma. The California margin has an active diagenetic system driven by the degradation of organic matter. Leg 167 drilling provided a means to quantify the diagenetic processes within the deep sediment column and to study the links between sediment diagenesis and primary productivity. This synthesis chapter also documents the oceanographic variability along the California margin at all time scales, from 10 3 to 10 6 yr. Millennial-scale variability is found in Santa Barbara Basin (drilled during Leg 146) and in nearby basins drilled during Leg 167. Leg 167 cores also captured millennial-scale variability in the northern and central California margin. Orbitally forced insolation changes invoke a strong response throughout the California margin. Sea-surface temperature (SST) measured by the alkenone U k' 37 paleothermometer is highly coherent with the oxygen isotope record, being cold in glacials and much warmer in interglacials. Faunal and floral plankton assemblages vary strongly on the glacial-interglacial scale. Coastal plant communities show a glacial-interglacial variability that is most pronounced in the north, near the Cordilleran Ice Sheet. Major changes in the sediments prior to the Pleistocene mark major late Neogene oceanographic events. Opaline silica burial in the middle and upper Miocene sections have step-like drops from high opal deposition in the middle Miocene. One major drop occurs at ~11 Ma and is roughly correlative with the eastern equatorial Pacific Miocene carbonate crash. A second major drop occurs at about 8 Ma, equivalent in age to the end of the Monterey Formation. A third drop occurs slightly younger than the end of the Miocene. A lower Pliocene interval, roughly from 5 to 4.2 Ma, is low in all biogenic components. It separates the Miocene high-opal sediments from upper Pliocene high-carbonate sediments. High CaCO 3 deposition occurred all along the entire California margin in the late Pliocene, but CaCO 3 burial dropped abruptly with the beginning of Northern Hemisphere glaciation (2.6 Ma).

Baja California, California↗