Download Cenozoic California

CGcenozoic
THE CENOZOIC
I. Geologic Framework of California was established in Mesozoic
II. Uplift of land with most action (Sedimentation) in the Coast Ranges, western Transverse
Ranges and Northwestern end of Peninsular Ranges
III. Three Major categories of Cenozoic Rocks
a. volcanic rocks
b. marine sedimentary
c. nonmarine sedimentary rocks and alluvial deposits
IV. Volcanic rocks
a. all over state
b. Eocene to recent
c. basalt to rhyolite
d. most extensive area is Modoc Plateau to Cascade Mountains
e. Also extensive throughout Great Basin and Mojave Desert
V. Marine Sedimentary Rock
a. most widely in Coast Ranges, Western transverse ranges and along the coast of the
Peninsular Ranges
b. oil well drilling show also extensive underneath alluvium of Great Valley
c. Determined to be shallow, broad seaway to complex, often narrow arms of the seas
d. the narrow marine troughs subsided rapidly by faulting and folding and received many
thousands of feet of marine and continental sediments
VI. Alluvial Deposits
a. mostly Quaternary in age
b. cover wide areas--e.g Great Valley
c. Alluvial deposits and non marine sedimentary rocks, widespread in inland basins--Death Valley
and Mono Basin
VII.
Marine and non-Marine sedimentary rocks mostly clastics-Conglomerates, S.S. Mudstones; Limestones are minor; organic to chemical origin-diatomaceous shale, siliceous shale and chert (Coast Ranges)
VIII. Early Tertiary Rocks (Paleocene, Eocene and Oligocene)
a. Sierra Nevada reduced from high standing mountains to gently sloping upland
b. Great Valley received clastic sediments
c. Early Eocene seas invaded from west
d. Gravels, silts and clays-consolidated into Paleocene
Early Eocene-Capay Formation
e. Paleocene-Marine Sediments--widespread through Coast Ranges, San Joaquin Valley and
Northern Peninsular Ranges (Santa Ana Mts.)
f. Eocene
(1) Marine Shale and S.S. deposited in Basin (San Joaquin Valley)
(2) Clean White sands and clays of Ione Formation were deposited in lakes and
lagoons--in low Western foothills of the Sierra
CGcenozoic
g. Oligocene--Santa Cruz Mts, San Francisco Bay areas to Western San Joaquin Valley
Localized Seas, with seasonal climates semiarid to arid
Land laid Conglomerate, coarse sandstone to red beds (oxidized) in
Southern Coast Ranges to Transverse Ranges
a. Vasquez Formation
Volcanic Rocks, thousands of feet thick are interbedded with coarse
Non-Marine sediments in the transverse ranges
b. coarse grained sediments in Klamath, Death Valley and Mojave Desert
IX. Late Tertitary Rocks and History
a. Miocene-gradual broadening of the Seas; warm, shallow arms extended through coastal
California from NW end of Santa Ana Mts. to Pt. Arena in Northern California; a broad
embayment covered Southern San Joaquin Valley--Time and environment characterized by
distinctive group of Fossils called Vaqueros Stage
b. Late Miocene shallow seas spread throughout state. The most widespread late Tertiary Form
is middle to late Miocene Monterey Formation-abundant siliceous shales and chert beds
(1) extends from point Arena to Southern coastal California as far south as Oceanside
(2) In southern California the Monterey formation is more sandy than in the North (Santa
Monica Hills and Puente Hills)
c. Pliocene--recent sediments about 20,000 ft thick fill the Salton
trough
(1) Alluvial Fan, Flood plain, stream and lake deposits
(2) Imperial Formation--deposited in a shallow sea that came in from the Gulf of
California
Late Pliocene time shallow sea covered most of the Imperial Valley and extended across
Eastern Imperial and Riverside counties
(3) In Sierra Nevada--Extensive masses of rhyolite tuff and gravels of the Valley
Springs Formation blanketed Western Slopes and filled stream valleys--Volcanic
episode was followed in Pliocene by eruptions of Andesitic Volcanic agglomerates and
mudflows (lahars) and buried the northern Sierra Nevada under 1,500-4,000ft of debris-blanket known as Mehrten Formation
(4)Western Part of Transverse Ranges receive great thicknesses of mostly marine
Cretaceous and lower tertiary deposits continued as a trough of deposition called the
Ventura Basin--which contains more than 40,000 ft of Cenozoic sediments
(5) Seas became restricted in California in Pliocene time
(6) Los Angles Basin 15,000 ft of late Miocene and Pliocene Marine muds and
sands were deposited Foraminifera show that some sediments were deposited
in water as deep as 5,000-6,000 ft.
(7) Late Pliocene Increased Amount of gravel and coarse sand in Western
Transverse Ranges, much of Great Valley and southern Klamath Mountains
(8) Late Pliocene and early Pleistocene (evidences of strong orogenic activity)
CGcenozoic
X. Building of the Coast Ranges, Sierra Nevada, Penisular Ranges (Mountain Building Period)
a. Paleocene and Eocene epochs covered 25 million years of crustal quiet times
b. Late Eocene to early middle Miocene--seaways became restricted and parts of Coast
Ranges were elevated above sea level- moved as a wave through Coast Ranges.(folding, faulting
and uplift)
(1) later part of the early Tertiary crustal movement began in Coast Ranges--numerous
unconformitites--enormous volumes of volcanic materials
(2) Pliocene beds in many areas are unconformable deposited on Miocene Formations
c. Culmination of Coast Ranges Orogency came during late Pliocene-mid Pleistocene
(1) flat lying attitude of widespread late Pleistocene and Holocene Sediments that lie with
Angular unconformity on older formations
Best in Coast Ranges--but also extend into Transverse Ranges, L.A. Basin and
Northern Peninisular Ranges
(2) Mountain building did not effect all areas at the same time but progressed in a wave
through Coast Ranges
(a) North of San Francisco Bay Area late Pliocene Marine Merced Formation and
Sonoma Volcanics lie over wide areas with only gentle dips on older formations
(b) At same time Ventura Basin-lower Pleistocene strata folded and faulted into
Vertical position--most violent mountain building period--in middle Pleistocene
(b) folding, faulting and uplift are contemporaneous
(c) movements on San Andreas Fault largely horizontal during Quaternary; early
movements were probably vertical
(3) Faults
(a) Nacimiento-separates western coastal block of Franciscan basement rocks
from Granite block east of the Fault zone
(b) South Fork
1. separates Franciscan of Northern Coast Ranges on the west from
Mesozoic and older crystalline rocks of the Klamath Mts. on the East
2. Probably extends southward under younger formations of western
Great Valley--to form a similar boundary between coast Range
Franciscan basement of Sierra Nevada granite rocks
3. Fault is probably old and relates to late Mesozoic (Nevadan) thrusting
of Oceanic crust underneath Continental Margin
"Ophiolite"--In western mountain structures are found elongate
masses of peridotite and serpentive (sill like bodies)-contemporaneous with Late Jurassic-Cretaceous orogenic
episodes
(d) OrogenySierra Nevada, Klamath Mountains and southern Peninsular Ranges periodically uplift,
tilted westward and Faulted--very resistant
Uplift occurs at irregular intervals during the Cenozoic rejuvenated Sierra Nevada and
caused deep and extensive erosion
Thousands of ft of vertical movement (latest about 3 million years ago) continue into
present