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January 2004 - Emmons Lecture
"RECONNECTING LAKE ARCTICA TO THE ATLANTIC: GEOLOGICAL CAUSE OF PALEOCENE-EOCENE BOUNDARY EVENTS"
Malcolm C. McKenna
When two oceans become separated from
each other such that circulation is in one direction
only, their sea levels and salinities will become
different. Such was the case in the late Paleocene,
when increased proto-Icelandic lava outpourings
choked the Atlantic marine continuity with the
Norwegian/Greenland seas and beyond, and
allowed terrestrial interchange directly between
Europe and North America. Beringia was
simultaneously dry land, blocking Pacific-Arctic
University of Colorado Museum and American Museum of Natural History
An isolated Arctic Ocean (about 1% of total
oceanic volume) that was fed by rivers of the order
of magnitude of those draining into the present
Arctic Ocean would soon have exceeded
evaporation, freshened, filled the Arctic Basin to its
brim, and then would have overflowed southward.
Oceanic heat transport to the Arctic Basin would
have ceased. At first, overflow would have been
through the long Turgai Straits to Tethys in Eurasia.
However, acceleration of sea-floor
spreading in the Greenland-Scotland bridge area
beginning in geomagnetic chron 24R resulted in a
breach in the bridge, allowing rapid release
southward of brackish and fresh water. This water
would have spread out on top of and into the
Atlantic Ocean, severely affecting the marine photic
zone and its inhabitants before mixing.
With reconnection and resumption of
circulation, oceanic heat transport northward would
have resumed, helping to warm the Arctic Basin
and its waters and isolating the European terrestrial
biota from areas to the west. These changes, in
combination with slightly lowered Arctic Basin
water level, would have led to extensive methane
releases, contributing to what is now thought to
have been the root cause of an accelerated episode
of global warming that began at 55.5 Ma.
"EVOLUTION OF THE GREAT SAND DUNES, SOUTH-CENTRAL COLORADO."
Geomorphic and stratigraphic evidence
obtained in recent field studies indicate that the
sand in the Great Sand Dunes came primarily
from a lacustrine source rather than from floodplain
deposits of the Rio Grande, as previously
supposed. The source of the sand in the Great
Sand Dunes has been pondered for more than a
century, but since the 1960s, the idea that the
flood plain of the Rio Grande was the source
has been widely accepted. Closely linked to the
issue of source are questions about when and
under what conditions the sand was transported.
Although most recent publications do not assign
dates to the time of dune formation, a few infer
that the process began about 12,000 years ago
and link it to increased discharge and
sedimentation during deglaciation of the San
U.S. Geological Survey, Denver, CO
The Great Sand Dunes are a small part
(<10%) of an area of windblown sand that
blankets the east side of the San Luis Valley for
a distance of about 100 km. Stratigraphic
evidence and numerical ages show that this area
of windblown sand is the product of multiple
episodes of eolian transport that occurred
intermittently over a time span that probably
includes much, if not all, of the Pleistocene.
Accumulation of eolian sand was controlled
primarily by climatically driven fluctuations of
water-table level. During megadroughts, water
table fell and exposed areas of sandy sediment
in playas to wind erosion. These areas became
primarily by climatically driven fluctuations of
water-table level. During megadroughts, water
table fell and exposed areas of sandy sediment
in playas to wind erosion. These areas became
primary sources of new generations of dune and
sheet sand. At the same time, drought reduced
vegetation on deposits of older eolian sand
allowing wind to remobilize parts of them.
During wetter times, water table rose and
shallow lakes formed, and the sand supply on
the basin floor was replenished by inflow from
streams that originated in the surrounding
mountains and on piedmont slopes.
The distribution of the eolian sand of which
the Great Sand Dunes are a part suggests a
relationship with the closed basin part of the San
Luis Valley rather than with the Rio Grande.
This body of eolian sand is nearly coincident
with the length of the closed basin, and the
parabolic dunes north of the Great Sand Dunes
indicate a sand source and transport direction
unrelated to the Rio Grande. Also, leeside dune
belts, which typically flank riverine sand
sources, are conspicuously absent along the
leeside of the Rio Grande. Finally, the timing
suggested in previous publications for the onset
of sand transport and dune formation seems
improbable. Archeological, paleontological, and
stratigraphic data indicate that at the end of the
Pleistocene, lakes, marshes, and vegetation
occupied much more of the area between the
Rio Grande and the Great Sand Dunes than at
present. These conditions would have been
unfavorable for widespread eolian erosion and
transport of sand.
"DEBEQUE CANYON LANDSLIDE."
Jonathan L. White,
An active landslide has historically
impinged upon the Colorado River and
transportation corridors on the floor of DeBeque
Canyon, located in Mesa County, 21 miles east
of Grand Junction, Colorado. Interstate 70
passes through the toe of the landslide on the
south wall of the canyon.
Colorado Geological Survey
DeBeque Canyon was formed by the incision of the Colorado River into gently
dipping, Cretaceous Mesa Verde Group strata
on the west flank of the Piceance Basin.
Exposed on the canyon walls are cliffs of
sandstone interbedded with shales and siltstone.
The complex landslide extends from the river’s
bank to the canyon rim where large and
impressive fissures occur.
The large fissures, structural offsets, and
tilted blocks indicate landslide morphology
characterized by low-angle extensional
movements of sandstone strata at the canyon
rim and deep-seated deformations within a thick
shale stratum below. Below the cliffs of these
upper blocks, the main landslide morphology
changes to translational down-slope movements
of landslide rubble, and at the lower slope to
deep-seated rotational failures that periodically
impact the highway.
Major reactivation of the slide occurred
in April 1998 when the toe of the rotational
landslide heaved upward 14 feet and almost
closed Interstate 70. An earlier event occurred
in February 1958 when the toe heaved 24 feet.
Around 1900 much larger movements of the
landslide caused the slide toe to enter the
Colorado River and alter the river’s course.
Portions of the railroad alignment and the work
camp of Tunnel on the opposite riverbank were
subsequently washed out. This presentation will
discuss the results of an investigation of the
landslide that was done after the 1998
emergency, specifically the geology,
geomorphology, the on-going monitoring work,
and the water diversion mitigation project by
Colorado Department of Transportation.
"USING ALLUVIAL PALEOSOLS TO INTERPRET CLIMATE CHANGE AT THE
PALEOCENE-EOCENE THERMAL MAXIMUM (PETM)"
Mary J. Kraus
The Paleocene-Eocene thermal maximum (PETM)
was a short-lived (~100,000 years) spike in global
temperature that occurred approximately 55 m.y.
ago. The warming event is identified by distinct
excursions in oxygen and carbon isotope records as
well as floral and faunal extinctions and migrations.
This global warming has been attributed to the
release of methane hydrates stored in oceanic
sediments, which injected methane into the
University of Colorado at Boulder
Although there is broad agreement that
temperatures rose during the PETM, the effects of
global warming on precipitation and evaporation
patterns are less well understood and more
contradictory. Data from continental PETM records are
important for establishing a better picture of local and
regional climatic conditions during the PETM and for
thus testing and refining climate models. The analysis
of paleosols provides one approach to clarifying
precipitation and evaporation patterns during this
Paleosols were examined in the Bighorn Basin,
Wyoming, one of the few continental areas where the
PETM interval has been convincingly documented
based upon isotopic analyses of pedogenic carbonate
nodules. Paleosols within the PETM interval are
dominated by red soil colors and carbonate nodules
compared to slightly older paleosols. These features
indicate better drained conditions and suggest that
climates became drier during the PETM in the Bighorn
Basin and possibly in the region. Paleosols in the upper
part of the PETM interval show purple paleosols colors
and less abundant to absent carbonate nodules, showing
a return to more humid climatic conditions. Other
features within the PETM interval (absence of organicrich
shales with plant fossils, cut-and-fills with
paleosols) are consistent with drier conditions during
"DINOVULSION: A NEW STYLE OF AVULSION IN THE UPPER JURASSIC
Gus Gustason and Larry Jones
The low net-to-gross Salt Wash Member of the
Morrison Formation, east-central Utah, contains
exceptionally well-exposed, low-sinuosity, ribbonshaped
sand bodies of two distinct sizes enclosed by
variegated mudstones and siltstones. These sand
bodies were formed during the Jurassic by avulsion,
the relatively abrupt shift of a river to a new
EnCana Energy Resources, Inc.
paleontology, and paleoclimate suggest that river
channels, and subsequent ribbon sand bodies, were
located by a heretofore unrecognized style of
avulsion, termed dinovulsion.
Dinosaurs, well-documented inhabitants of
the Salt Wash alluvial plain, trampled channel-like
trails into the floodplain, creating conduits that
served to focus overbank flow during flooding.
During major floods, or over a period of more
numerous but less intense flooding, flow coalesced
to scour a new primary channel while sand clogged
the pre-existing channel and nearby small dinosaur
pathways. As time passed and the system aggraded,
this process repeated, and the present architecture of
isolated, very low-sinuosity sand ribbons of two
distinct size populations resulted.
April 2004 - Annual Family Night
"SEVEN SUMMITS OF THE SOLAR SYSTEM"
Joe Romig and Glen Porzak
Olympus Mons on Mars is the solar
system’s highest mountain, rising 15 miles above
the surrounding plain. What would it take to climb
such a peak and the highest summits of six other
planets? Find out by attending the 2004 Family
night presentation by Joe Romig and Glen Porzak.
Joe Romig is an astrophysicist associated with the
University of Colorado who has been a member of
the Voyager space probe science team. Glen Porzak
is a climber who has scaled the highest peaks of all
the continents on Earth. Romig will provide a
guided tour of the solar system and will serve as
Porzak’s “consultant” on certain lofty summits in
the solar system. Porzak will then describe how
these might be scaled by climbers in the 21st
century, relying on his own ascent of Mount
Everest. The talk will be illustrated with slides and
videos in the spectacular Fiske Planetarium at the
University of Colorado in Boulder. Be sure to come
early to enjoy the planetarium exhibits in the lobby.
University of Colorado, Boulder
"CHANGES IN LOESS AND DUNE DEPOSITION IN RESPONSE TO
QUATERNARY CLIMATIC FLUCTUATIONS, COLUMBIA PLATEAU,
The paired dune-loess eolian system of the
Colorado Plateau in Washington state allows the
study of dynamic interactions of dune and loess
systems. Eolian facies of the region lie in the arid to
semi-arid rain shadow of the Cascade volcanic
range, and prevailing winds that transport sediments
move southwest to the northeast. Eolian sediments
have been obtained since at least the late Quaternary
and perhaps much earlier from fine-grained
slackwater deposits (produced by glacial outburst
flooding) exposed in upwind basins. Loess
deposition appears to span much of the Quaternary.
Colorado State University, Ft. Collins, Colorado
Eolian dunes and other sandy eolian deposits
lie on the upwind perimeter of the Palouse loess.
Three mechanisms appear to control the thickness
of loess on the plateau. 1) Topographic traps:
Deeply incised valleys effectively separate saltation
from suspension processes by sequestering sand that
allows the deposition of the suspension load as thick
loess on the downwind sides of valleys.
2) Shifts in bioclimate: In the absence of
topographic traps, the sand-silt boundary freely
transgresses and regresses as a function of climate
shifts that control soil moisture and vegetation
cover density. Over time, the eolian sand has
become interstratified at the margins of deflating
basins in response to these climate shifts. The mid-
Holocene was dominated by dune activity (lesser
vegetative cover and drier surface soils leading to
more aggressive saltation processes); the present is
dominated by loess deposition. Greater vegetative
cover and/or moister soils shift saltation processes
to a more arid upwind position, with suspension fall
of dust accumulating loess on the flat.
3) Source sediment texture: Source sediment
texture controls the balance of dunes versus loess
accumulated downwind of specific basins. An
“ideal” source sediment is dominated by sand,
which limits aggregation and crusting and provides
abundant, mobile sand for saltation, while also
having significant (20–40%) silt and clay to provide
a source of fine dust that is ejected during saltation
and forms loess downwind by suspension fall. A
source sediment rich in sand but poor in silt results
in thin loess.
These three sets of controls appear to have
operated separately and in combination to create
measured variations in loess thickness. Insight into
how saltation and
suspension processes interact with each other to
control sedimentology and geomorphology of this
paired eolian system is key to better understanding
the eolian environment of the Columbia Plateau and
other eolian systems.
"MARS ROVER RESULTS, LIQUID WATER, AND THE POTENTIAL FOR LIFE ON MARS"
The Mars Opportunity rover has returned
spectacular results suggesting that there was a
substantial body of water at the Meridiani landing
site. I'll discuss these results in the context of the
history of liquid water at the surface and in the
subsurface, and then I’ll turn to the implications for
climate and for the potential that life might have
existed or might still exist on Mars. I'll also discuss
the Mars exploration program as it is planned out
over the next decade and the implications of
President Bush's recently announced new vision for
exploration by NASA.
University of Colorado, Boulder, Colorado
"A FAULT BOUNDED DEPOSITIONAL BASIN IN CENTRAL COLORADO"
Dr. Paul Myrow
The Minturn Formation of central Colorado records deposition in an active
fault-bounded basin. These strata represent braided rivers, fan deltas,
marginal marine settings, and carbonate and siliclastic shallow marine
environments. A prominent unit of subaqueously deposited interbedded sandstone
and shale has turbidite-like graded beds that contain sole marks such as
grooves, prods, and flutes. However, these beds are atypical compared to
classic Bouma turbidite sequences. Detailed process-oriented sedimentological
analysis reveals internal sedimentary structures that are consistent
with deposition under the influence of both excess weight forces and
oscillatory flow. Sedimentary structures characteristic of waves include
small- and large-scale hummocky cross-stratification and gutter casts.
There is also considerable evidence for deposition under combined flows,
including ripples with rounded crests and convex-up foresets. Individual beds thus have
characteristics of both turbidites and tempestites and were therefore deposited
in combned flows of waves and currents driven by excess-weight forces. Abundant
plant remains and deep sole marks indicate that the flows were highly charged
with plant debris. The paleogeographic context of high topographic relief adjacent
to a marine basin suggests that the flows were linked to sediment-charged flood
currents that entered the ocean and became hyperpycnal flows (i.e., oceanic floods).
These beds are unusual in that they also contain sequences of internal sedimentary
structures that record both waning and waxing flow. Such flow is also preserved by
reverse-to-normal grading patterns. These patterns may be smooth transitions from
fine to coarse to fine, or show a jump in grain size within the bed at the coarsest
division. The pattern of waxing and waning flow is interpreted as a record of the
hydrographic response to storm events, namely increasing and decreasing discharge.
The hyperpycnal flow was dynamically linked to the hydrograph and those beds with
reverse-to-normal grading record all stages of the flow, including the waxing
stage that in most density-driven flows is not preserved.
Colorado College, Colorado Springs, Colorado
"FROM BUTTES TO BOWLS: REPEATED INVERSIONS IN THE LANDSCAPE OF THE COLORADO PIEDMONT"
Vincent Matthews(1), *Matthew L. Morgan(1), Jon P. Thorson(2), Francisco Gutierrez(3) and Matthew T. Grizzell(4)
Mesas and buttes of the central Colorado Piedmont are composed of
at least two distinct rock types, which differ in their cohesiveness and ability
to withstand erosion. The lower parts are friable, Early to Middle
Paleogene sandstones of the Dawson Formation. The caprock is composed of
one or more resistant formations: Castle Rock Conglomerate, Wall Mountain
Tuff, and Larkspur Conglomerate — all of late Paleogene age. The
three resistant units were originally deposited in topographic lows.
The lower slopes of the buttes are armored with colluvium composed of fragments
of the capping units and commonly form “talus flatirons” or relict faceted slopes.
Once the caprock of a butte or mesa has been removed by erosion, the
poorly consolidated Dawson Formation quickly erodes out of the center.
This leaves the armored, lower slopes of the former butte as an erosionally-resistant,
circular ridge standing as much as 100 meters above the
surrounding topography. This process produces a topographic low where
the peak of the butte once stood.
Some buttes have prominent alluvial fans that record the main phase
of butte removal and excavation of the central part of the armored slopes.
Soil profiles and height above modern streams suggest the oldest
preserved gravel deposit is of middle Pleistocene age; the youngest alluvial fans
were deposited during the Holocene.
1 Colorado Geological Survey, Denver, CO, USA
2 Consulting Geologist, Parker, CO, USA
3 University of Zaragoza, Zaragoza, SPAIN
4 BEK/Terranext, Lakewood, CO, USA
"TABLE MOUNTAIN SHOSHONITE PORPHYRY LAVA FLOWS AND THEIR VENTS, GOLDEN, COLORADO"
During Early Paleocene time shoshonite
porphyry lava was extruded from several plugs
about 5 km north of Golden, Colorado, to form lava
flows intercalated in the upper part of the Denver
Formation. These flows now form the caps of North
and South Table Mountains. Detailed field and
petrographic studies provide insights into magma
development, linkage between vents and flows, and
the history of the lava flows.
The magna was derived from a deep crustal
source, was somewhat turbulent on its way up,
paused on its way up in a shallow-level granitehosted
chamber, and near the surface followed the
steep Golden Fault and the thick, weak, steeplydipping
Upper Cretaceous Pierre Shale. At the
surface the lava flowed out of several plug and dike
vents in a non-explosive manner, at 4 times during a
span of about 1 m.y. Potassium-rich material
acquired in the shallow-level chamber produced
distinctive textures and mineral associations in the
Lava flows 1 (the lowest) and 2 are channel
deposits derived from the Southeastern Group of
intrusives, and flows 1 lie about 150 feet below the
capping flows. Provisionally, an older felty-textured
flow, la, is distinguished from younger blockytextured
flows, lb. Flow 2, newly recognized in this
study, lies immediately beneath the capping flows.
Lava flows 3 and 4, more voluminous then the first
two, were derived from a plug vent 1-2 km farther
north-northwest and flowed south-southeast across a
broad alluvial plain. This plug is a composite body;
the Rim Phase fed flow #3 and the Core Phase flow
4. During the lapse of time between the effusion of
the four flows the composition of the shoshonite
porphyry changed subtly, having picked up more
On North Table Mountain lava flows 3 and
4 form an elongate tumulus above an underlying,
water-saturated, stream channel. On South Table
Mountain a low broad dome on lava flow 3 forced
flow 4 into channels now restricted to the west and
northeast flanks of that mesa.
The mesa-capping lava flows 3 and 4 are
broken by many small normal faults and are warped
into open synclines, probably in response to local
stresses associated with the settling of piedmont
deposits into the Denver Basin. Mid-Tertiary
deposits are inferred to have covered the upper part
of the Denver Formation and its lavas, and to have
been instrumental in changing the stream flow
direction to the east before the onset of Neogene
uplift and consequent canyon cutting across the
"SCIENCE AND SOCIETY: CULTURAL AWARENESS IN MANAGING NATURAL DISASTERS"
Natural hazards include a wide range of
earth processes that are often perceived as risky or
dangerous such as earthquakes, floods, fires,
landslides, and volcanoes. In the absence of people
and property, these natural events may go
unnoticed. As the global population grows, more
and more people and our supporting infrastructure
are being built "in harms way".
Natural disasters often bring out the best
behaviors in the global community to assist with
disaster relief efforts and post-disaster recovery.
Additionally, mitigating the threat of disasters often
brings together scientists and managers to assist
with pre-disaster planning and development
activities. Working effectively in these challenging
situations requires that we be actively aware of the
social and cultural environments in which we work.
This presentation will draw on examples
from one type of natural hazard—volcano
hazards—and show how these have been managed
and mitigated in a variety of countries including the
United States, Indonesia, the Congo.
United States Geological Survey, Denver
December 2004 - Presidental Address
"CENOZOIC HISTORY OF THE LARAMIE MOUNTAINS
IN WYOMING AND ITS RELATION TO THE PHYSIOGRAPHIC DEVELOPMENT
OF THE COLORADO FRONT RANGE"
The physiographic development of the
Colorado Front Range is difficult to unravel. Major
Late Cenozoic uplift especially affected the west
flank and southern margin of the range. After late
Cenozoic erosion, Tertiary rocks in the Front Range
are relatively few, and scattered sedimentary rocks
(mostly conglomerates) are poorly dated. Glaciers
have modified the uplands in the Front Range such
that little remains there of the original pre-
Quaternary topography. Nevertheless, the general
consensus is that there are an older rolling
topography of Cenozoic age along the eastern
flanks of the range, broad valleys below the rolling
topography, and very deep canyons cut by modern
streams into the older topography. Unfortunately,
these physiographic features in the Front Range
itself do not indicate their time of formation.
The Laramie Mountains in southeast
Wyoming is a northern extension of the Front
Range that is still covered by Cenozoic sedimentary
rocks. The highest peak in the Laramie Mountains
(Laramie Peak at an elevation of 3,130 m) is below
the limit of Pleistocene glacial ice, so no glaciation
occurred in the range. Tertiary sedimentary rocks
cover much of the range. Finally, the flanks of the
range contain physiographic features similar to
those in the Front Range. Unlike the Front Range,
these landforms can be related to Cenozoic deposits
and can therefore be dated.
The broad valleys within the Laramie
Mountains are filled with the fine-grained ash
deposits of the latest Eocene and early Oligocene
White River Formation. The White River Formation
filled valleys with high relief (maximum relief =
1,170 m). From the highest crest in the northern part
of the range, White River drainages flowed into
adjacent basins. The broad rolling surface above
these White River paleovalleys is associated with
broad sheet conglomerates of Oligocene and
Miocene age (Arikaree and Ogalalla Formations).
Locally these conglomerates extend far into the
Precambrian core of the range and represent gravels
deposited on pediments cut during the long tectonic
quiescence of the middle Cenozoic.
Modern streams have cut deep canyons in an
unusual pattern across much of the Laramie
Mountains. In the northern part of the range, almost
all of the drainages that flow west and southwest
from the topographic crest of the range are barbed
and flow east or northeast across the entire width of
the range. In the southern part of the range, where
the low-level Sherman Surface is developed, all of
the drainages flow east across the range from the
western margin of the range. Therefore, the modern
drainage divide is at the margin or even within the
adjacent Laramie and Shirley basins. This
anomalous drainage pattern reflects tilting of the
range to the east and northeast during the late
Cenozoic, after deposition of the Ogallala
Formation. Extending these landforms southward to
the Front Range, the broad valleys below the gently
rolling topography may reflect the late Eocene
surface; the rolling topography may be as young as
Miocene in age; and the deep canyons reflect late
Cenozoic uplift of the Front Range and adjacent
This talk is dedicated to Donald L. Blackstone, Jr.
(1909–2004), whose first publication was on the
development of wind gaps in the Laramie
Mountains, and whose last studies also included the
structure and Cenozoic history of the range.
University of Colorado, Boulder