Marine Incursions: Marine Incursions: Implications for crustal Implications for crustal

thinning and regional strainthinning and regional strain

Kristin McDougallKristin McDougallU.S. Geological SurveyU.S. Geological Survey

Flagstaff, Arizona 86001Flagstaff, Arizona 86001kris@usgs.govkris@usgs.gov

with assistance from Ana Luisa Carreno, with assistance from Ana Luisa Carreno, Rebecca Dorsey, Arturo Martin, and Michael Rebecca Dorsey, Arturo Martin, and Michael

Oskin Oskin

QuestionsQuestions

Number of Number of incursionsincursions

AgeAge ExtentExtent EnvironmentEnvironment

Lower Colorado Lower Colorado RiverRiver

Salton TroughSalton Trough Gulf of Gulf of

CaliforniaCalifornia

LocationsLocations

Correlation Correlation lower Colorado River, Salton lower Colorado River, Salton Trough, and Gulf of CaliforniaTrough, and Gulf of California

Middle Miocene microfossilsMiddle Miocene microfossils

Range of reworked planktic foraminifers or calcareous nannofossilsRange of reworked planktic foraminifers or calcareous nannofossils

Age diagnostic Middle Miocene TaxaAge diagnostic Middle Miocene Taxa

SectionsSections1.1. Hermosillo/Hermosillo/

GuaymasGuaymas

2.2. Cerro PrietoCerro Prieto

3.3. Fish CreekFish Creek

4.4. Whitewater/Whitewater/CabazonCabazon

5.5. Laguna SaladaLaguna Salada

6.6. San FelipeSan Felipe

7.7. Tres Marias IslandsTres Marias Islands

Middle Miocene microfossilsMiddle Miocene microfossils

Range of reworked planktic foraminifers or calcareous nannofossilsRange of reworked planktic foraminifers or calcareous nannofossils

Correlation Correlation lower Colorado River, Salton lower Colorado River, Salton Trough, and Gulf of CaliforniaTrough, and Gulf of California

Gulf of Gulf of CaliforniaCalifornia

Late Miocene ~ 6-8 Late Miocene ~ 6-8 MaMa

Plio-Pleistocene <5.3 Plio-Pleistocene <5.3 MaMa

Salton Salton TroughTrough

Late Miocene ~ 6-8 MaLate Miocene ~ 6-8 Ma

Plio-Pleistocene < 5.3 MaPlio-Pleistocene < 5.3 Ma

Age of the Fish Creek Age of the Fish Creek sectionsection

Whitewater and Whitewater and Cabazon Cabazon SectionsSections

Paleoecology of the Paleoecology of the Whitewater and Cabazon Whitewater and Cabazon

sectionssections

Lower Lower ColoradColorado Rivero River

Distribution of Foraminifers in Distribution of Foraminifers in the Bouse Formationthe Bouse Formation

Cross section of LCRP wells Cross section of LCRP wells between Cibola and Parkerbetween Cibola and Parker

BiofaciesBiofacies

PaleoecologyPaleoecology

QuestionsQuestions

Number of Number of incursionsincursions

AgeAge ExtentExtent EnvironmentEnvironment

Middle Miocene incursionMiddle Miocene incursion

11-14 Ma11-14 Ma In situIn situ faunas suggest this faunas suggest this

incursion extends at least as incursion extends at least as far north as the Hermosillo far north as the Hermosillo and Guaymasand Guaymas

Reworked microfossils found Reworked microfossils found further north. further north.

The age of the sediments The age of the sediments middle Miocene faunas are middle Miocene faunas are reworked in to becomes older reworked in to becomes older to the north.to the north.

Northern limit of this incursion Northern limit of this incursion has not been determined. has not been determined.

Deposition occurred during Deposition occurred during warm climatic conditions and warm climatic conditions and high sea level.high sea level.

Late Miocene incursionLate Miocene incursion 6-7 Ma6-7 Ma Extends as far north Extends as far north

as San Gorgonio Pass, as San Gorgonio Pass, California, and as far California, and as far east as Yuma, Arizona. east as Yuma, Arizona.

Wide variety of Wide variety of environments in a environments in a warm climatic interval warm climatic interval and high sea leveland high sea level

Plio-Pleistocene incursionPlio-Pleistocene incursion Post 5.3 MaPost 5.3 Ma Extends throughout Extends throughout

most of the Salton most of the Salton Trough and lower Trough and lower Colorado River region Colorado River region as well as the current as well as the current Gulf of California.Gulf of California.

The marine section was The marine section was strongly affected by the strongly affected by the Colorado River, which Colorado River, which rapidly filled the area rapidly filled the area with fresh water and with fresh water and sediment, reducing the sediment, reducing the marine influencemarine influence

Wide variety of Wide variety of depositional depositional environmentsenvironments