A reappraisal of seafloor spreading lineations in the Gulf of California: Implications for the transfer of Baja California to the Pacific Plate and estimates of Pacific-North America Motion

1995 ◽  
Vol 22 (24) ◽  
pp. 3545-3548 ◽  
Author(s):  
Charles DeMets
Keyword(s):  
North America ◽  
Gulf Of California ◽  
Baja California ◽  
Pacific Plate ◽  
Seafloor Spreading ◽  
The Pacific

scholarly journals MIS 5e sea-level history along the Pacific Coast of North America

2021 ◽  
Author(s):  
Daniel R. Muhs
Keyword(s):  
North America ◽  
Sea Level ◽  
Baja California ◽  
Pacific Coast ◽  
Level Indicator ◽  
Sequence Of Events ◽  
Marine Terraces ◽  
The Pacific ◽  
Mis 5E ◽  
Good Agreement

Abstract. The primary last interglacial, marine isotope substage (MIS) 5e records on the Pacific Coast of North America, from Washington (USA) to Baja California Sur (Mexico), are found in the deposits of erosional marine terraces. Warmer coasts along the southern Golfo de California host both erosional marine terraces and constructional coral reef terraces. Because the northern part of the region is tectonically active, MIS 5e terrace elevations vary considerably, from a few meters above sea level to as much as 70 m above sea level. The primary paleo-sea level indicator is the shoreline angle, the junction of the wave-cut platform with the former sea cliff, which forms very close to mean sea level. Most areas on the Pacific Coast of North America have experienced uplift since MIS 5e time, but the rate of uplift varies substantially as a function of tectonic setting. Chronology in most places is based on uranium-series ages of the solitary coral Balanophyllia elegans (erosional terraces) or the colonial corals Porites and Pocillopora (constructional reefs). In areas lacking corals, correlation to MIS 5e can sometimes be accomplished using amino acid ratios of fossil mollusks, compared to similar ratios in mollusks that also host dated corals. U-series analyses of corals that have experienced largely closed-system histories range from ~124 to ~118 ka, in good agreement with ages from MIS 5e reef terraces elsewhere in the world. There is no geomorphic, stratigraphic, or geochronology evidence for more than one high-sea stand during MIS 5e on the Pacific Coast of North America. However, in areas of low uplift rate, the outer parts of MIS 5e terraces apparently were re-occupied by the high-sea stand at ~100 ka (MIS 5c), evident from mixes of coral ages and mixes of molluscan faunas with differing thermal aspects. This sequence of events took place because glacial isostatic adjustment processes acting on North America resulted in regional high-sea stands at ~100 ka and ~80 ka that were higher than is the case in far-field regions, distant from large continental ice sheets. During MIS 5e time, sea surface temperatures (SST) off the Pacific Coast of North America were higher than is the case at present, evident from extralimital southern species of mollusks found in dated deposits. Apparently no wholesale shifts in faunal provinces took place, but in MIS 5e time, some species of bivalves and gastropods lived hundreds of kilometers north of their present northern limits, in good agreement with SST estimates derived from foraminiferal records and alkenone-based reconstructions in deep-sea cores. Because many areas of the Pacific Coast of North America have been active tectonically for much or all of the Quaternary, many earlier interglacial periods are recorded as uplifted, higher elevation terraces. In addition, from southern Oregon to northern Baja California, there are U-series-dated corals from marine terraces that formed ~80 ka, during MIS 5a. In contrast to MIS 5e, these terrace deposits host molluscan faunas that contain extralimital northern species, indicating cooler SST at the end of MIS 5. Here I present a standardized database of MIS 5e sea-level indicators along the Pacific Coast of North America and the corresponding dated samples. The database is available in Muhs (2021)  [https://doi.org/10.5281/zenodo.5557355].

scholarly journals Volcanic record of the arc-to-rift transition onshore of the Guaymas basin in the Santa Rosalía area, Gulf of California, Baja California

Geosphere ◽  
2020 ◽  
Vol 16 (4) ◽  
pp. 1012-1041
Author(s):  
Cathy Busby ◽  
Alison Graettinger ◽  
Margarita López Martínez ◽  
Sarah Medynski ◽  
Tina Niemi ◽  
...  
Keyword(s):  
Gulf Of California ◽  
Baja California ◽  
Sedimentary Basin ◽  
Volcanic Rocks ◽  
Seafloor Spreading ◽  
Geochemical Data ◽  
Normal Faults ◽  
Guaymas Basin ◽  
The North ◽  
Santa Rosalia

Abstract The Gulf of California is an archetype of continental rupture through transtensional rifting, and exploitation of a thermally weakened arc to produce a rift. Volcanic rocks of central Baja California record the transition from calcalkaline arc magmatism, due to subduction of the Farallon plate (ca. 24–12 Ma), to rift magmatism, related to the opening of the Gulf of California (<12 Ma). In addition, a suite of postsubduction rocks (<12 Ma), referred to as “bajaites,” are enriched in light rare-earth and other incompatible elements (e.g., Ba and Sr). These are further subdivided into high-magnesian andesite (with 50%–58% SiO2 and MgO >4%) and adakite (>56% SiO2 and MgO <3%). The bajaites correlate spatially with a fossil slab imaged under central Baja and are inferred to record postsubduction melting of the slab and subduction-modified mantle by asthenospheric upwelling associated with rifting or slab breakoff. We report on volcanic rocks of all three suites, which surround and underlie the Santa Rosalía sedimentary rift basin. This area represents the western margin of the Guaymas basin, the most magmatically robust segment of the Gulf of California rift, where seafloor spreading occurred in isolation for 3–4 m.y. (starting at 6 Ma) before transtensional pull-apart basins to the north and south ruptured the continental crust. Outcrops of the Santa Rosalía area thus offer the opportunity to understand the magmatic evolution of the Guaymas rift, which has been the focus of numerous oceanographic expeditions. We describe 21 distinct volcanic and hypabyssal map units in the Santa Rosalía area, using field characteristics, petrographic data, and major- and trace-element geochemical data, as well as zircon isotopic data and ten new 40Ar-39Ar ages. Lithofacies include lavas and lava domes, block-and-ash-flow tuffs, ignimbrites, and hypabyssal intrusions (plugs, dikes, and peperites). Calcalkaline volcanic rocks (13.81–10.11 Ma) pass conformably upsection, with no time gap, into volcanic rocks with rift transitional chemistry (9.69–8.84 Ma). The onset of rifting was marked by explosive eruption of silicic ignimbrite (tuff of El Morro), possibly from a caldera, similar to the onset of rifting or accelerated rifting in other parts of the Gulf of California. Epsilon Hf zircon data are consistent with a rift transitional setting for the tuff of El Morro. Arc and rift volcanic rocks were then juxtaposed by normal faults and tilted eastward toward a north-south fault that lay offshore, likely related to the north-south normal faults documented for the early history of the Guaymas basin, prior to the onset of northwest-southeast transtenional faulting. Magmatism in the Santa Rosalía area resumed with emplacement of high-magnesian andesite lavas and intrusions, at 6.06 Ma ± 0.27 Ma, coeval with the onset of seafloor spreading in the Guaymas basin at ca. 6 Ma. The 9.69–8.84 Ma rift transitional volcanic rocks underlying the Santa Rosalía sedimentary basin provide a maximum age on its basal fill. Evaporites in the Santa Rosalía sedimentary basin formed on the margin of the Guaymas basin, where thicker evaporites formed. Overlying coarse-grained clastic sedimentary fill of the Santa Rosalía basin and its stratiform Cu-Co-Zn-Mn sulfides may have accumulated rapidly, coeval with emplacement of 6.06 Ma high-magnesian andesite intrusions and the ca. 6 Ma onset of seafloor spreading in the Guaymas basin.

A new genus of cassiduloid echinoid from the lower Eocene of the Pacific coast of western North America and a new report of Cassidulus ellipticus Kew, 1920, from the lower Eocene of Baja California Sur, Mexico

1995 ◽  
Vol 69 (3) ◽  
pp. 509-515 ◽  
Author(s):  
Richard L. Squires ◽  
Robert A. Demetrion
Keyword(s):  
North America ◽  
New Genus ◽  
Baja California ◽  
Pacific Coast ◽  
Middle Part ◽  
Baja California Sur ◽  
Western North America ◽  
Lower Eocene ◽  
Shallow Marine ◽  
The Pacific

The cassiduloid echinoid Calilampas californiensis n. gen. and sp. is described from middle lower Eocene (“Capay Stage”) shallow-marine sandstones in both the middle part of the Bateque Formation, Baja California Sur, Mexico, and the lower part of the Llajas Formation, southern California. The new genus is tentatively placed in family Pliolampadidae. The cassiduloid Cassidulus ellipticus Kew, 1920, previously known only from the “Capay Stage” in California, is also present in “Capay Stage” shallow-marine sandstones of the Bateque Formation.

Serologically Differentiated Subpopulations of the Pacific Sardine, Sardinops caerulea

1964 ◽  
Vol 21 (4) ◽  
pp. 691-701 ◽  
Author(s):  
Andrew M. Vrooman
Keyword(s):  
Gulf Of California ◽  
Baja California ◽  
Frequency Of Occurrence ◽  
The Third ◽  
The Pacific ◽  
Pacific Sardine ◽  
Positive Factor ◽  
Outer Coast

Three genetically distinct subpopulations of the Pacific sardine have been differentiated by the frequency of occurrence of a C-positive blood factor. Two of these subpopulations, a northern and a southern one, live off the coast of California and the outer coast of Baja California, Mexico. The third group inhabits the Gulf of California. The C-positive factor occurred in 13.6% of the northern subpopulation, 6.0% of the southern, and 16.8% of the Gulf subpopulation.

scholarly journals New constraints on relative motion between the Pacific Plate and Baja California microplate (Mexico) from GPS measurements

2007 ◽  
Vol 170 (3) ◽  
pp. 1373-1380 ◽  
Author(s):  
C. Plattner ◽  
R. Malservisi ◽  
T. H. Dixon ◽  
P. LaFemina ◽  
G. F. Sella ◽  
...  
Keyword(s):  
Relative Motion ◽  
Baja California ◽  
Pacific Plate ◽  
Gps Measurements ◽  
The Pacific

scholarly journals Quantifying rates of “rifting while drifting” in the southern Gulf of California: The role of the southern Baja California microplate and its eastern boundary zone

Lithosphere ◽  
2020 ◽  
Vol 12 (1) ◽  
pp. 122-132
Author(s):  
Paul J. Umhoefer ◽  
C. Plattner ◽  
R. Malservisi
Keyword(s):  
Relative Motion ◽  
Gulf Of California ◽  
Baja California ◽  
Late Quaternary ◽  
Plate Boundary ◽  
Seafloor Spreading ◽  
Gravitational Potential Energy ◽  
Boundary Zone ◽  
Eastern Boundary ◽  
Topographic Relief

Abstract The southern Baja California (Mexico) microplate has been rapidly moving away from the North America plate since ca. 12 Ma. This relative motion toward the northwest developed an oblique-divergent plate boundary that formed the Gulf of California. The rift-drift hypothesis postulates that when a continent ruptures and seafloor spreading commences, rifting on the plate margins ceases, and the margins start to drift, subside, and accumulate postrift sediments, eventually becoming a passive margin. In contrast to this hypothesis, the southern part of the Baja California microplate (BCM), and in particular its actively deforming eastern boundary zone, has continued significant rifting for millions of years after seafloor spreading initiated within the southern Gulf of California at 6–2.5 Ma. This is a process we call “rifting-while-drifting.” Global positioning system (GPS)–based data collected from 1998 to 2011 show relative motion across the eastern boundary zone up to ∼2–3.2 mm/yr with respect to a stable BCM. Furthermore, the velocity directions are compatible with normal faulting across the eastern boundary zone nearly perpendicular to the trend of the plate boundary at the latitude of La Paz and therefore a highly strain partitioned domain. North of 25°N latitude up to the Loreto area, there is a domain with no strain partitioning, and northwest-directed transtensional deformation dominates. From long-term geologic and paleoseismology studies, late Quaternary faulting rates are equal to or less than the GPS-derived rates, while geologic rates older than 1–2 Ma are commonly much higher. We suggest that the “rifting-while-drifting” process may be caused by the large topographic relief across the BCM margin, which created a significant gradient in gravitational potential energy that helps in driving continued relatively slow faulting. The relief was inherited from the much faster faulting of the BCM eastern boundary zone before plate motions largely localized along the modern transform–spreading centers in the axis of the Gulf of California. The low sediment flux from the small drainages and arid climate on the southern Baja California Peninsula result in the maintenance of underfilled to starved basins, and the relatively slow late Quaternary active faulting promotes continued topographic relief over millions of years.

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