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J.A. Barron

Publications and source records attributed to J.A. Barron.

27 records · Page 2Linked to original sources
USGS1986

Paleoceanographic and tectonic controls on deposition of the Monterey formation and related siliceous rocks in California

The timing of paleoceanographic and tectonic events that shaped the deposition of the Monterey Formation of California and related siliceous rocks has been determined by application of a refined biochronology. The base of the Monterey at 17.5 Ma coincides with rising global sea level and a switch in biogenous silica deposition from the Caribbean and low-latitude North Atlantic to the North Pacific. Major polar cooling, which began at 15 Ma, postdates the base of the Monterey by more than 2 Ma and cannot be invoked to cause the deposition of diatomaceous sediments occurring in the lowermost Monterey. Later polar cooling in the early late Miocene, however, apparently caused increased upwelling and deposition of purer diatomites in the upper Monterey. The top of the Monterey at about 6 Ma coincides with a major sea level drop and is commonly marked by an unconformity. Equivalent unconformities are widespread around the rim of the North Pacific and typically separate more pelagic sediments from overlying sediments with a greater terrigenous component. Above the Monterey, diatoms persist in California sediments to 4.5–4.0 m.y., where their decline coincides with increased deposition of diatoms in the Antarctic. Carbon isotope records in the Pacific and Indian Oceans record storage of 12 C in the Monterey Formation and equivalent organic-rich sediments around the rim of the North Pacific. A +1.0‰ excursion in δ 13 C beginning at 17.5 Ma coincides with rising sea level and probably reflects storage of organic material in Monterey-like marginal reservoirs. A reverse −1.0‰ shift at 6.2 Ma closely approximates the top of the Monterey and may represent erosion of these marginal reservoirs and reintroduction of stored organic carbon into the ocean—atmosphere system. Initiation of transform faulting and extension in the California margin in the latest Oligocene and early Miocene caused the subsidence of basins which later received Monterey sediments. A major tectonic event centered at 10–9 Ma, which included rotation of the Santa Barbara Basin and a change in Pacific plate motion, is recorded by an unconformity and/or interval of compressed sediments in many Monterey sections. Another change in plate motion at about 6 Ma may be expressed by the angular discordance observed in many sections across the unconformity at the top of the Monterey.

California↗
USGS1983

Paleoceanographic implications of Miocene deep-sea hiatuses

Miocene paleoceanographic evolution exhibits major changes resulting from the opening and closing of passages, the subsequent changes in oceanic circulation, and development of major Antarctic glaciation. The consequences and timing of these events can be observed in variations in the distribution of deep-sea hiatuses, sedimentation patterns, and biogeographic distribution of planktic organisms. The opening of the Drake Passage in the latest Oligocene to early Miocene (25–20 Ma) resulted in the establishment of the deep circumpolar current, which led to thermal isolation of Antarctica and increased global cooling. This development was associated with a major turnover in planktic organisms, resulting in the evolution of Neogene assemblages and the eventual extinction of Paleogene assemblages. The erosive patterns of two widespread hiatuses (PH, 23.0–22.5 Ma; and NH 1, 20–18 Ma) indicate that a deep circumequatorial circulation existed at this time, characterized by a broad band of carbonate-ooze deposition. Siliceous sedimentation was restricted to the North Atlantic and a narrow band around Antarctica. A major reorganization in deep-sea sedimentation and hiatus distribution patterns occurred near the early/middle Miocene boundary, apparently resulting from changes in oceanic circulation. Beginning at this time, deep-sea erosion occurred throughout the Caribbean (hiatus NH 2, 16–15 Ma), suggesting disruption of the deep circumequatorial circulation and northward deflection of deep currents, and/or intensification of the Gulf Stream. Sediment distribution patterns changed dramatically with the sudden appearance of siliceous-ooze deposition in the marginal and east equatorial North Pacific by 16.0 to 15.5 Ma, coincident with the decline of siliceous sedimentation in the North Atlantic. This silica switch may have been caused by the introduction of Norwegian Overflow Water into the North Atlantic acting as a barrier to outcropping of silica-rich Antarctic Bottom Water. The main aspects of the present oceanic circulation system and sediment distribution pattern were established by 13.5 to 12.5 Ma (hiatus NH 3), coincident with the establishment of a major East Antarctic ice cap. Antarctic glaciation resulted in a broadening belt of siliceous-ooze deposition around Antarctica, increased siliceous sedimentation in the marginal and east equatorial North Pacific and Indian Oceans, and further northward restriction of siliceous sediments in the North Atlantic. Periodic cool climatic events were accompanied by lower eustatic sea levels and widespread deep-sea erosion at 12 to 11 Ma (NH 4), 10 to 9 Ma (NH 5), 7.5 to 6.2 Ma (NH 6), and 5.2 to 4.7 Ma (NH 7).

Geological Society of America Bulletin↗
USGS1982

Widespread Miocene deep-sea hiatuses: Coincidence with periods of global cooling

High-resolution biostratigraphic analyses of Miocene deep-sea cores reveal eight intervals of widespread hiatuses in the world ocean at 23.0–22.5, 20.0–18.0, 16.0–15.0, 13.5–12.5, 12.0–11.0, 10.0–9.0, 7.5–6.2, and 5.2–4.7 m.y. ago. In complete sections these hiatuses correspond to intervals of cool faunal and floral assemblages, rapid enrichment of δ 18 O, and sea-level regressions. These factors suggest that Miocene deep-sea hiatuses result from an increased intensity of circulation and corrosiveness of bottom currents during periods of increased polar refrigeration.

Geology↗
USGS1980

Neogene sedimentation on the outer continental margin, southern Bering Sea

Neogene sedimentary rocks and sediments from sites on the outer continental margin in the southern Bering Sea and on the Alaska Peninsula are dominated by volcanic components that probably were eroded from an emergent Aleutian Ridge. A mainland continental source is subordinate. Most sediment in the marine environment was transported to the depositional sites by longshore currents, debris flows, and turbidity currents during times when sea level was near the outermost continental shelf. Fluctuations of sea level are ascribed both to worldwide glacio-eustatic effects and to regional vertical tectonics. Large drainage systems, such as the Yukon and Kuskokwim Rivers, had little direct influence on sedimentation along the continental slope and Unmak Plateau in the southern Bering Sea. Sediments from those drainage systems probably were transported to the floor of the Aleutian Basin, to the numerous shelf basins that underlie the outer continental shelf, and to the Arctic Ocean after passing through the Bering Strait. Environments of deposition at the sites along the outer continental margin have not changed significantly since the middle Miocene. The site on the Alaska Peninsula, however, is now emergent following shallow-marine and transitional sedimentation during the Neogene.

Alaska↗
USGS1976

Revised Miocene and Pliocene diatom biostratigraphy of Upper Newport Bay, Newport Beach, California

North Pacific diatom zones XXIII through IX of Schrader are recognizable in the middle Miocene to lower Pliocene stratigraphic section exposed around Upper Newport Bay in Newport Beach, California. Correlation with DSDP Site 173 and other stratigraphic sections in California allows the selection of diatom datums that are the most reliable for long-distance correlation. Individual diatom datums are proposed as markers for North Pacific diatom zones XXIII through IX. Correlations with DSDP Site 173 reveal a hiatus in the lower part of Core 15 that corresponds with a distinct lithologic and floral change in the core. Preliminary silicoflagellate data for the Upper Newport Bay stratigraphic section supports the diatom correlations. Correlation with calcareous nannofossil, radiolarian, and silicoflagellate zones at Upper Newport Bay and at DSDP Site 173 suggests that the boundary between North Pacific diatom zones XVII and XVI approximates the middle Miocene/upper Miocene boundary. The Miocene/Pliocene boundary is estimated to be in North Pacific diatom zone X. One new stratigraphically useful diatom species is described, Lithodesmium reynoldsii .

California↗