The North American Atlantic Outer Continental Margin Landslides Data Base: Summary and Observations: ABSTRACT

AAPG Bulletin ◽  
1990 ◽  
Vol 74 ◽  
Author(s):  
James S. Booth, Dennis W. O'Leary
Keyword(s):  
Data Base ◽  
Continental Margin ◽  
North American ◽  
The North

scholarly journals South China Sea documents the transition from wide continental rift to continental break up

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Hongdan Deng ◽  
Jianye Ren ◽  
Xiong Pang ◽  
Patrice F. Rey ◽  
Ken R. McClay ◽  
...  
Keyword(s):  
South China Sea ◽  
Continental Margin ◽  
South China ◽  
North American ◽  
Continental Rift ◽  
Continental Breakup ◽  
North American Cordillera ◽  
China Sea ◽  
The North ◽  
Continental Rifts

Abstract During extension, the continental lithosphere thins and breaks up, forming either wide or narrow rifts depending on the thermo-mechanical state of the extending lithosphere. Wide continental rifts, which can reach 1,000 km across, have been extensively studied in the North American Cordillera and in the Aegean domain. Yet, the evolutionary process from wide continental rift to continental breakup remains enigmatic due to the lack of seismically resolvable data on the distal passive margin and an absence of onshore natural exposures. Here, we show that Eocene extension across the northern margin of the South China Sea records the transition between a wide continental rift and highly extended (<15 km) continental margin. On the basis of high-resolution seismic data, we document the presence of dome structures, a corrugated and grooved detachment fault, and subdetachment deformation involving crustal-scale nappe folds and magmatic intrusions, which are coeval with supradetachment basins. The thermal and mechanical weakening of this broad continental domain allowed for the formation of metamorphic core complexes, boudinage of the upper crust and exhumation of middle/lower crust through detachment faulting. The structural architecture of the northern South China Sea continental margin is strikingly similar to the broad continental rifts in the North American Cordillera and in the Aegean domain, and reflects the transition from wide rift to continental breakup.

Environmental influence on growth history in marine benthic foraminifera

Paleobiology ◽  
2018 ◽  
Vol 44 (4) ◽  
pp. 736-757 ◽  
Author(s):  
Caitlin R. Keating-Bitonti ◽  
Jonathan L. Payne
Keyword(s):  
Continental Margin ◽  
North American ◽  
Environmental Conditions ◽  
Benthic Foraminifera ◽  
Environmental Gradients ◽  
Environmental Influence ◽  
Cell Physiology ◽  
Mean Annual Temperature ◽  
Test Volume ◽  
The North

AbstractEnergy availability influences natural selection on the ontogenetic histories of organisms. However, it remains unclear whether physiological controls on size remain constant throughout ontogeny or instead shift as organisms grow larger. Benthic foraminifera provide an opportunity to quantify and interpret the physicochemical controls on both initial (proloculus) and adult volumes across broad environmental gradients using first principles of cell physiology. Here, we measured proloculus and adult test dimensions of 129 modern rotaliid species from published images of holotype specimens, using holotype size to represent the maximum size of all species’ occurrences across the North American continental margin. We merged size data with mean annual temperature, dissolved oxygen concentration, particulate organic carbon flux, and seawater calcite saturation for 718 unique localities to quantify the relationship between physicochemical variables and among-species adult/proloculus size ratios. We find that correlation of community mean adult/proloculus size ratios with environmental parameters reflects covariation of adult test volume with environmental conditions. Among-species proloculus sizes do not covary identifiably with environmental conditions, consistent with the expectation that environmental constraints on organism size impose stronger selective pressures on adult forms due to lower surface area-to-volume ratios at larger sizes. Among-species adult/proloculus size ratios of foraminifera occurring in resource-limited environments are constrained by the limiting resource in addition to temperature. Identified limiting resources are food in oligotrophic waters and oxygen in oxygen minimum zones. Because among-species variations in adult/proloculus size ratios from the North American continental margin are primarily driven by the local environment’s influence on adult sizes, the evolution of foraminiferal sizes over the Phanerozoic may have been strongly influenced by changing oceanographic conditions. Furthermore, lack of correspondence between among-species proloculus sizes and environmental conditions suggests that offspring sizes in foraminifera are rarely limited by physiological constraints and are more susceptible to selection related to other aspects of fitness.

U–Pb geochronology of detrital zircons from a continental margin assemblage in the northern Coast Mountains, southeastern Alaska

1991 ◽  
Vol 28 (8) ◽  
pp. 1285-1300 ◽  
Author(s):  
George E. Gehrels ◽  
William C. McClelland ◽  
Scott D. Samson ◽  
P. Jonathan Patchett
Keyword(s):  
Continental Margin ◽  
North American ◽  
Detrital Zircons ◽  
Northern Coast ◽  
Coast Mountains ◽  
Metasedimentary Rocks ◽  
The North ◽  
Upper Proterozoic ◽  
Two Samples ◽  
Cordilleran Margin

Metamorphic rocks within and west of the northern Coast Mountains in southeastern Alaska consist of an Upper Proterozoic(?) to upper Paleozoic continental margin assemblage that we interpret to belong to the Yukon-Tanana terrane. U–Pb geochronologic analyses of single detrital zircon grains from four samples of quartzite suggest that the zircons were shed from source regions containing rocks of ~495 Ma, ~750 Ma, 1.05–1.40 Ga, 1.75–2.00 Ga, ~2.3 Ga, 2.5–2.7 Ga, and ~3.0 Ga. Multigrain fractions from two samples yield upper intercepts between 2.0 and 2.3 Ga, but the scarcity of single grains of similar age suggests that these fractions comprise a mixture of < 2.0 and > 2.3 Ga grains. Zircons in these rocks generally overlap in age with (i) detrital zircons in metasedimentary rocks of the Yukon–Tanana terrane in eastern Alaska and Yukon, (ii) detrital zircons in strata of the Cordilleran miogeocline, and (iii) plutonic and gneissic rocks that intrude or are overlain by miogeoclinal strata. In addition, the pre-1.7 Ga grains overlap in age with dated crystalline rocks of the western Canadian Shield. These similarities raise the possibility that metaclastic rocks in the northern Coast Mountains accumulated in proximity to western North America. The younger zircon populations were likely shed from mid-Proterozoic to early Paleozoic igneous rocks that now occur locally (but may have been widespread) along the Cordilleran margin. Recognition of a continental margin assemblage of possible North American affinity in the Coast Mountains raises the possibility that some arc-type and oceanic terranes inboard of the Coast Mountains may be large klippen that have been thrust over the North American margin.

Evidence for the Emergence of the Hercynian Front on the North American Continent

1975 ◽  
Vol 12 (8) ◽  
pp. 1474-1479 ◽  
Author(s):  
Norman Z. Cherkis ◽  
Henry S. Fleming ◽  
James V. Massingill ◽  
Robert H. Feden
Keyword(s):  
Continental Margin ◽  
North American ◽  
Fracture Zone ◽  
Magnetic Measurements ◽  
American Continent ◽  
The West ◽  
North American Continent ◽  
The North ◽  
Mid Atlantic Ridge ◽  
Marine Seismic

Recent marine seismic reflection, bathymetric and magnetic measurements made across the Charlie Gibbs Fracture Zone have clearly shown that the fracture zone extends to the east of 17 °west longitude. Projections to the west of the Mid-Atlantic Ridge extend the fracture zone to the North American Continental margin northeast of Newfoundland. Projection of the structural trends of the Hercynian Front from the European continental margin offer a remarkable linearity with the Charlie Gibbs Fracture Zone on the west. Remnants of the Hercynian Front have been identified in New Brunswick. Flemish Cap, which foundered during the initial phase of the latest opening of the Atlantic is believed to have been located on the fracture zone's southern edge, before drifting southeasterly to its present position. The alignment of the Hercynian Front with the Charlie Gibbs Fracture Zone is linked up on the North American continent and is offered as a possible clue to the pre-drift configuration of the Laurasian continent.

Syn-accretionary multistage assembly of an Early Jurassic Alaskan-type intrusion in the Canadian Cordillera: U–Pb and 40Ar/39Ar geochronology of the Turnagain ultramafic–mafic intrusive complex, Yukon–Tanana terrane

2020 ◽  
Vol 57 (5) ◽  
pp. 575-600
Author(s):  
Graham T. Nixon ◽  
J. Erik Scheel ◽  
James S. Scoates ◽  
Richard M. Friedman ◽  
Corey J. Wall ◽  
...  
Keyword(s):  
Continental Margin ◽  
North American ◽  
Ocean Basin ◽  
Early Jurassic ◽  
The North ◽  
Lithostratigraphic Units ◽  
Zircon Crystallization ◽  
Mafic Complex ◽  
Stage 1 ◽  
Host Rocks

The magmatic evolution of the Early Jurassic Turnagain Alaskan-type intrusion is inextricably linked to terrane accretionary events at the North American continental margin. We have calibrated the multistage assembly of the Turnagain ultramafic–mafic complex using high-precision air and chemical abrasion ID-TIMS U–Pb and 40Ar/39Ar geochronology. Our results are the first published geochronological calibration of zoning in an Alaskan-type intrusion. Three of four intrusive phases (Stages 1–4, oldest to youngest) were successfully dated. Cooling ages obtained on Stage 2 dunite–wehrlite include statistically identical 40Ar/39Ar plateau dates of 187.4 ± 1.5 (2σ) Ma on hornblende and 188.6 ± 1.2 Ma on phlogopite, and a concordant 206Pb/238U date of 190.3 ± 4.6 Ma on titanite. Stage 3 diorite has a 206Pb/238U zircon crystallization age of 188.11 ± 0.13 Ma. Stage 4 wehrlite and leucodiorite yield 206Pb/238U zircon crystallization ages of 185.68 ± 0.19 and 185.30 ± 0.12 Ma, respectively. The ca. 189 Ma phlogopite date represents a minimum crystallization age for Stage 2, indicating that assembly of the Turnagain intrusion spanned at least ∼4 million years from ca. 189 Ma to 185 Ma. Regional progressive contractional deformation in the Early Jurassic is constrained by the geochronological results (>189 to <185 Ma) and initially generated northeast-vergent folds in the country rocks (>189 Ma), deformed Stage 1 wehrlite–clinopyroxenite prior to emplacement of Stages 2–4, and subsequently thrust the intrusion and its host rocks onto the ancient North American continental margin (<185 Ma). Contrary to previous interpretations, new geophysical data support an allochthonous origin for the host rocks of the Turnagain intrusion. The Turnagain host succession is correlated with late Paleozoic arc-related and basinal lithostratigraphic units developed at the inboard margin of the accreted Yukon–Tanana terrane and peripheral to the Slide Mountain marginal ocean basin. The geochronological results rigorously constrain the timing and style of Early Jurassic deformation attending the initial accretion of allochthonous arc terranes in the northern Cordillera.

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