Search

Search Results

• 1. [Article] Origins of Late- Pleistocene Coastal Dune Sheets, Magdalena and Guerrero Negro, from Continental Shelf Low-stand Supply (70-20 ka), under Conditions of Southeast Littoral- and Eolian-Sand Transport, in Baja California Sur, Mexico

  Shallow morpho-stratigraphic sections (n = 11) in each of two large coastal dune sheets including the Magdalena (7000 km2) and Guerrero Negro (8000 km2) dune sheets, from the Pacific Ocean side of Baja ...

  Citation × Citation Citation Abstract Copy Title: Origins of Late- Pleistocene Coastal Dune Sheets, Magdalena and Guerrero Negro, from Continental Shelf Low-stand Supply (70-20 ka), under Conditions of Southeast Littoral- and Eolian-Sand Transport, in Baja California Sur, Mexico Author: Peterson, Curt D., Murillo-Jiminez, Janette, Stock, Errol, Price, David M., Hostetler, Steve W., Percy, David Year: 2017 Shallow morpho-stratigraphic sections (n = 11) in each of two large coastal dune sheets including the Magdalena (7000 km2) and Guerrero Negro (8000 km2) dune sheets, from the Pacific Ocean side of Baja California Sur, Mexico, have been analyzed for dune deposit age. The shallow morpho-stratigraphic sections (∼2-10 m depth) include 11 new TL and 14C ages, and paleosol chronosequences, that differentiate cemented late Pleistocene dune deposits (20.7 ± 2.1 to 99.8 ± 9.4 ka) from uncemented Holocene dune deposits (0.7 ± 0.05 to at least 3.2 ± 0.3 ka). Large linear dune ridges (5-10 m in height) in the dune sheet interiors trend southeast and are generally of late Pleistocene age (∼70-20 ka). The late Pleistocene dune deposits reflect eolian transport of marine sand across the emerged continental shelf (30-50 km southeast distance) from low-stand paleo-shorelines (-100 ± 25 m elevation), which were locally oriented nearly orthogonal to modeled deep-water wave directions (∼300° TN). During the Holocene marine transgression, onshore and alongshore wave transport delivered remobilized shelf-sand deposits to the nearshore areas of the large dune sheets, building extensive barrier islands and sand spits. Submerged back-barrier lagoons generally precluded marine sand supply to dune sheet interiors in middle to late Holocene time, though exceptions occur along some ocean and lagoon shorelines. Reactivation of the late Pleistocene dune deposits in the dune sheet interiors lead to generally thin (1-3 m thickness), but widespread, covers of Holocene dune deposits (0.41 ± 0.05 to 10.5 ± 1.6 ka). Mechanical drilling will be required to penetrate indurated subsoil caliche layers to reach basal Pleistocene dune deposits. Title: Origins of Late- Pleistocene Coastal Dune Sheets, Magdalena and Guerrero Negro, from Continental Shelf Low-stand Supply (70-20 ka), under Conditions of Southeast Littoral- and Eolian-Sand Transport, in Baja California Sur, Mexico Author: Peterson, Curt D., Murillo-Jiminez, Janette, Stock, Errol, Price, David M., Hostetler, Steve W., Percy, David Year: 2017 Shallow morpho-stratigraphic sections (n = 11) in each of two large coastal dune sheets including the Magdalena (7000 km2) and Guerrero Negro (8000 km2) dune sheets, from the Pacific Ocean side of Baja California Sur, Mexico, have been analyzed for dune deposit age. The shallow morpho-stratigraphic sections (∼2-10 m depth) include 11 new TL and 14C ages, and paleosol chronosequences, that differentiate cemented late Pleistocene dune deposits (20.7 ± 2.1 to 99.8 ± 9.4 ka) from uncemented Holocene dune deposits (0.7 ± 0.05 to at least 3.2 ± 0.3 ka). Large linear dune ridges (5-10 m in height) in the dune sheet interiors trend southeast and are generally of late Pleistocene age (∼70-20 ka). The late Pleistocene dune deposits reflect eolian transport of marine sand across the emerged continental shelf (30-50 km southeast distance) from low-stand paleo-shorelines (-100 ± 25 m elevation), which were locally oriented nearly orthogonal to modeled deep-water wave directions (∼300° TN). During the Holocene marine transgression, onshore and alongshore wave transport delivered remobilized shelf-sand deposits to the nearshore areas of the large dune sheets, building extensive barrier islands and sand spits. Submerged back-barrier lagoons generally precluded marine sand supply to dune sheet interiors in middle to late Holocene time, though exceptions occur along some ocean and lagoon shorelines. Reactivation of the late Pleistocene dune deposits in the dune sheet interiors lead to generally thin (1-3 m thickness), but widespread, covers of Holocene dune deposits (0.41 ± 0.05 to 10.5 ± 1.6 ka). Mechanical drilling will be required to penetrate indurated subsoil caliche layers to reach basal Pleistocene dune deposits. Close

• 2. [Article] Coastal Eolian Sand-Ramp Development Related to Paleo-Sea-Level Changes during the Latest Pleistocene and Holocene (21–0 ka) in San Miguel Island, California, U.S.A.

  Coastal eolian sand ramps (5–130 m elevation) on the northern slope (windward) side of the small San Miguel Island (13 km in W-E length) range in age from late Pleistocene to modern time, though a major ...

  Citation × Citation Citation Abstract Copy Title: Coastal Eolian Sand-Ramp Development Related to Paleo-Sea-Level Changes during the Latest Pleistocene and Holocene (21–0 ka) in San Miguel Island, California, U.S.A. Author: Peterson, Curt D., Erlandson, Jon M., Stock, Errol, Hostetler, Steve W., Price, David M. Year: 2017 Coastal eolian sand ramps (5–130 m elevation) on the northern slope (windward) side of the small San Miguel Island (13 km in W-E length) range in age from late Pleistocene to modern time, though a major hiatus in sand-ramp growth occurred during the early Holocene marine transgression (16–9 ka). The Holocene sand ramps (1–5 m measured thicknesses) currently lack large dune forms, thereby representing deflated erosional remnants, locally covering thicker late Pleistocene sand-ramp deposits. The ramp sand was initially supplied from the adjacent island-shelf platform, extending about 20 km north of the present coastline. The sand-ramp deposits and interbedded loess soils were 14C dated using 112 samples from 32 archaeological sites and other geologic sections. Latest Pleistocene sand ramps (66–18 ka) were derived from across-shelf eolian sand transport during marine low stands. Shoreward wave transport supplied remobilized late Pleistocene sand from the inner shelf to Holocene beaches, where dominant NW winds supplied sand to the sand ramps. The onset dates of the sand-ramp deposition in San Miguel are 7.2 ± 1.5 ka (sample n = 14). The internal strata dates in the vertically accreting sand ramps are 3.4 ± 1.7 ka (n = 34). The sand ramps in San Miguel show wide-scale termination of sand supply in the latest Holocene time. The sand-ramp top dates or burial dates are 1.7 ± 0.9 ka (n = 28). The latest Holocene sand ramps are truncated along most of the island's northern coastline, indicating recent losses of nearshore sand reserves to onshore, alongshore, and, possibly, offshore sand sinks. The truncated sand ramps in San Miguel Island and in other sand-depleted marine coastlines provide warnings about future beach erosion and/or shoreline retreat from accelerated sea-level rise accompanying predicted global warming. Title: Coastal Eolian Sand-Ramp Development Related to Paleo-Sea-Level Changes during the Latest Pleistocene and Holocene (21–0 ka) in San Miguel Island, California, U.S.A. Author: Peterson, Curt D., Erlandson, Jon M., Stock, Errol, Hostetler, Steve W., Price, David M. Year: 2017 Coastal eolian sand ramps (5–130 m elevation) on the northern slope (windward) side of the small San Miguel Island (13 km in W-E length) range in age from late Pleistocene to modern time, though a major hiatus in sand-ramp growth occurred during the early Holocene marine transgression (16–9 ka). The Holocene sand ramps (1–5 m measured thicknesses) currently lack large dune forms, thereby representing deflated erosional remnants, locally covering thicker late Pleistocene sand-ramp deposits. The ramp sand was initially supplied from the adjacent island-shelf platform, extending about 20 km north of the present coastline. The sand-ramp deposits and interbedded loess soils were 14C dated using 112 samples from 32 archaeological sites and other geologic sections. Latest Pleistocene sand ramps (66–18 ka) were derived from across-shelf eolian sand transport during marine low stands. Shoreward wave transport supplied remobilized late Pleistocene sand from the inner shelf to Holocene beaches, where dominant NW winds supplied sand to the sand ramps. The onset dates of the sand-ramp deposition in San Miguel are 7.2 ± 1.5 ka (sample n = 14). The internal strata dates in the vertically accreting sand ramps are 3.4 ± 1.7 ka (n = 34). The sand ramps in San Miguel show wide-scale termination of sand supply in the latest Holocene time. The sand-ramp top dates or burial dates are 1.7 ± 0.9 ka (n = 28). The latest Holocene sand ramps are truncated along most of the island's northern coastline, indicating recent losses of nearshore sand reserves to onshore, alongshore, and, possibly, offshore sand sinks. The truncated sand ramps in San Miguel Island and in other sand-depleted marine coastlines provide warnings about future beach erosion and/or shoreline retreat from accelerated sea-level rise accompanying predicted global warming. Close

• 3. [Article] Origins of Quaternary Coastal Dune Sheets in San Francisco and Monterey Bay, Central California Coast, U.S.A.: Reflecting Contrasts in Shelf Depocenters and Coastal Neotectonics

  The San Francisco and Monterey Bay coastal dune sheets derive from similar origins in the central California coast but differ substantially in size (respectively, ~400 and ~900 km2) and age (respectively, ...

  Citation × Citation Citation Abstract Copy Title: Origins of Quaternary Coastal Dune Sheets in San Francisco and Monterey Bay, Central California Coast, U.S.A.: Reflecting Contrasts in Shelf Depocenters and Coastal Neotectonics Author: Peterson, Curt D., Stock, Errol, Meyer, Jack, Kaijankoski, Philip, Price, David M. Year: 2015 The San Francisco and Monterey Bay coastal dune sheets derive from similar origins in the central California coast but differ substantially in size (respectively, ~400 and ~900 km2) and age (respectively, 1.0 Ma). The San Francisco dune sheet is restricted to a short alongshore interval (km) within a relatively straight coastline (150 km in length) that borders a broad shelf (~40 km in width). The Monterey Bay dune sheet is restricted to the Monterey Bay embayment (41 km alongshore length). The embayment includes a very narrow shelf (3–15 km in width), which is dissected by the Monterey Submarine Canyon. Generally low onshore topographic relief (elevation) likely enhanced inland transgression of Late Pleistocene dune fields in both the San Francisco and Monterey Bay areas. The locations of the dune sheets are directly related to sand accumulations in marine low-stand depocenters that supplied sand to the adjacent dune fields by eolian transport across the emerged inner shelves. The San Francisco shelf depocenter is apparently localized at a midshelf bight (−50 to −100 m elevation) that extends 25 km (east–west) offshore of a paleoriver mouth of a major river system, the Sacramento–San Joaquin River. The Monterey Bay shelf depocenter is bounded alongshore by major headlands and converging paleoshorelines (−30 to −90 m elevation) that effectively trapped littoral sand from small coastal drainages, primarily the Salinas River. High vertical rates of neotectonic deformation in the San Francisco dune sheet (0.4–1.0 mm y−1) limited dune sheet longevity and deposit thickness (5–35 m). Low uplift rates (~0.1 mm y−1) in the central Monterey Bay dune sheet permitted deposit accumulations of up to 250 m thickness. The differences in dune sheet extent, thickness, and age resulted from key differences in localized shelf accommodation space and coastal neotectonic vertical movements. Title: Origins of Quaternary Coastal Dune Sheets in San Francisco and Monterey Bay, Central California Coast, U.S.A.: Reflecting Contrasts in Shelf Depocenters and Coastal Neotectonics Author: Peterson, Curt D., Stock, Errol, Meyer, Jack, Kaijankoski, Philip, Price, David M. Year: 2015 The San Francisco and Monterey Bay coastal dune sheets derive from similar origins in the central California coast but differ substantially in size (respectively, ~400 and ~900 km2) and age (respectively, 1.0 Ma). The San Francisco dune sheet is restricted to a short alongshore interval (km) within a relatively straight coastline (150 km in length) that borders a broad shelf (~40 km in width). The Monterey Bay dune sheet is restricted to the Monterey Bay embayment (41 km alongshore length). The embayment includes a very narrow shelf (3–15 km in width), which is dissected by the Monterey Submarine Canyon. Generally low onshore topographic relief (elevation) likely enhanced inland transgression of Late Pleistocene dune fields in both the San Francisco and Monterey Bay areas. The locations of the dune sheets are directly related to sand accumulations in marine low-stand depocenters that supplied sand to the adjacent dune fields by eolian transport across the emerged inner shelves. The San Francisco shelf depocenter is apparently localized at a midshelf bight (−50 to −100 m elevation) that extends 25 km (east–west) offshore of a paleoriver mouth of a major river system, the Sacramento–San Joaquin River. The Monterey Bay shelf depocenter is bounded alongshore by major headlands and converging paleoshorelines (−30 to −90 m elevation) that effectively trapped littoral sand from small coastal drainages, primarily the Salinas River. High vertical rates of neotectonic deformation in the San Francisco dune sheet (0.4–1.0 mm y−1) limited dune sheet longevity and deposit thickness (5–35 m). Low uplift rates (~0.1 mm y−1) in the central Monterey Bay dune sheet permitted deposit accumulations of up to 250 m thickness. The differences in dune sheet extent, thickness, and age resulted from key differences in localized shelf accommodation space and coastal neotectonic vertical movements. Close