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Harry Eugene Wheeler (1907-1987): A Pioneer of Sequence Stratigraphy

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Harry Eugene Wheeler (1907-1987) of the University of Washington was a pioneer of genetic stratigraphic principles that form the basis of our modern concept of sequence stratigraphy. Wheeler's papers on what he liked to refer to as "stratology" included the classification of stratigraphic units into lithostratigraphic and biostratigraphic entities, as well as cyclothems, unconformity-bounded units, and the analysis of base-level and its role in forming stratigraphic discontinuities. His work on unconformity-bounded "sequences" ultimately led the International Subcommission on Stratigraphic Classification to define them formally in 1987. The plots used to clarify the time-relationships of rock units are now referred to as "Wheeler diagrams". It is not uncommon that, in any scientific paradigm shift, many of the key pioneers are not fully recognized for their contributions at the time, being significantly ahead of prevailing concepts. It is also not uncommon that, by the time their points of view come into vogue, their contributions may have been largely forgotten with greater recognition given to those who synthesized or "popularized" their concepts. This is certainly true in the fields of seismic and sequence stratigraphy, where, despite the theoretical framework for sequence analysis formulated by Wheeler (1958a), little reference was made to Wheeler's work in the early formulation of these concepts in the 1970s and 1980s. Wheeler, schooled by Blackwelder, Mueller, and Schenck at Stanford and armed with the base-level concept of Joseph Barrell, was one of the first to recognize the concept of time stratigraphy. Due to his unorthodox view of stratigraphy, Wheeler was involved in one controversy after another and his views were deemed to be provocative. While the valuable contributions of latter practitioners and synthesizers are justifiably lauded, the works of original pioneers such as Harry Eugene Wheeler are largely underappreciated.
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Harry Eugene Wheeler (1907-1987):
A Pioneer of Sequence Stratigraphy
S. George Pemberton1, Janok P. Bhattacharya2, James A. MacEachern3andErinA.L.Pemberton
4
Ichnology Research Group, Department of Earth & Atmospheric Sciences,
University of Alberta, Edmonton, AB, Canada, T6G 2E3
email: george.pemberton@ualberta.ca
2School of Geography and Earth Sciences (SGES), McMaster University, Hamilton, ON, Canada, L8S 4L8
email: bhattaj@mcmaster.ca
3Applied Research in Ichnology and Sedimentology, Department of Earth Sciences,
Simon Fraser University, Burnaby, BC, Canada, V5A 1S6
email: jmaceach@sfu.ca
4Applied Geoscience; Sedimentology, Stratigraphy and Structure, ConocoPhillips,
600 N. Dairy Ashford, Houston, TX, USA 77079
email: erin.a.pemberton@conocophillips.com
ABSTRACT:Harry Eugene Wheeler (1907-1987) of the University of Washington was a pioneer ofgenetic stratigraphic principles that
form the basis of our modern concept of sequence stratigraphy. Wheeler’s papers on what he liked to refer to as “stratology” included the
classification of stratigraphic units into lithostratigraphic and biostratigraphic entities, as well as cyclothems, unconformity-bounded
units, and the analysis of base-level and its role in forming stratigraphic discontinuities. His work on unconformity-bounded “sequences”
ultimately led the International Subcommission on Stratigraphic Classification to define them formally in 1987. The plots used to clarify
the time-relationships of rock units are now referred to as “Wheeler diagrams”. It is not uncommon that, in any scientific paradigm shift,
many of the key pioneers are not fully recognized for their contributions at the time, being significantly ahead of prevailing concepts. It is
also not uncommon that, by the time their points of view come into vogue, their contributions may have been largely forgotten with
greater recognition given to those who synthesized or “popularized” their concepts. This is certainly true in the fields of seismic and se-
quence stratigraphy, where, despite the theoretical framework for sequence analysis formulated by Wheeler (1958a), little reference was
made to Wheeler’s work in the early formulation of these concepts in the 1970s and 1980s. Wheeler, schooled by Blackwelder, Mueller,
and Schenck at Stanford and armed with the base-level concept of Joseph Barrell, was one of the first to recognize the concept of time
stratigraphy. Due to his unorthodox view of stratigraphy, Wheeler was involved in one controversy after another and his views were
deemed to be provocative. While the valuable contributions of latter practitioners and synthesizers are justifiably lauded, the works of
original pioneers such as Harry Eugene Wheeler are largely underappreciated.
INTRODUCTION
In his excellent history of stratigraphy, Miall (2004) indicated
that Harry Eugene Wheeler (1907-1987) of the University of
Washington was one of the early pioneers of genetic stratigra-
phy (text-fig. 1). Stratigraphy, considered by many to be a rou-
tine and mundane discipline consisting mainly of the dry
cataloguing of lithostratigraphic units, has undergone a dra-
matic renaissance. With the ascendance of genetic stratigraphic
paradigms and their refinement over the past three decades,
stratigraphers have radically altered how we perceive and,
therefore, interpret the rock record. Such frameworks rely
heavily on clastic facies analysis, and as such, allow insights
derived from process sedimentology to be applied to our char-
acterization of stratigraphic bodies. One could argue that ge-
netic stratigraphic paradigms, especially those that emphasize
the processes that control and create stratigraphic patterns and
bounding surfaces, serve as the unifying theory of sedimentary
geology.
Genetic stratigraphy lies at the core of three main stratigraphic
schemes: genetic stratigraphic sequences or T-R (transgressive-
-regressive) sequences, allostratigraphy, and sequence stratigra-
phy. The recognition and assessment of the genesis and
chronostratigraphic significance of stratigraphic breaks are cru-
cial to genetic stratigraphic paradigms, but are challenging to
resolve, particularly in subsurface analysis.
Stratigraphic discontinuities reflect processes that operate out-
side the influence of individual depositional environments
(i.e., are allogenic). Such processes typically initiate or termi-
nate deposition of sedimentologically related facies succes-
sions. Interpreting the causative mechanism(s) of stratigraphic
discontinuities can be vital in resolving depositional environ-
ments of the associated deposits and in determining the allo-
genic controls on depositional systems. Linking these allogenic
mechanisms to the chronostratigraphy of depositional succes-
sions is crucial and marks a major turning point in the evolution
of stratigraphy as a science.
It is an unfortunate fact that in any paradigm shift in science,
many of the key pioneers are not properly recognized for their
contributions. At the time such visionaries undertook their
work, they were ahead – and in many instances decades ahead –
of the prevailing concepts. By the time their points of view
come into vogue, their contributions were overshadowed by
Stratigraphy, vol. 13, no. 2, pages 95–110, text-figures 1–12, 2016 95
those of workers who synthesized or popularized the concepts,
rather than invented the paradigm. We suggest that this has been
the unfortunate fate, to date, of Harry Eugene Wheeler. It is tell-
ing that Wheeler himself defined the term “sequence” to refer
specifically to unconformity-bounded stratal units (Wheeler
1958a; 1959a), and utilized the term “sequence” in a pro-
foundly modern sequence stratigraphic context (Wheeler
1958a).
Sloss et al. (1949) were the first to use the term “sequences” in a
stratigraphic context. They stated that: “Sequences should be
considered as rock units, assemblages of formations and
groups. They are simply the strata which are included between
objective, recognizable horizons, and are without specific time
significance since their limits do not coincide with time lines
and may include rocks of different ages in various areas” (Sloss
et al. 1949, p. 110). On that basis, they erected four conti-
nent-wide sequences (the Sauk, Tippecanoe, Kaskaskia, and
Absaroka). Wheeler took exception to this definition, and in his
1958a paper stated “A sequence, as the term is employed in the
present discussion, is thus defined as a preserved stratal assem-
blage which is unconformably separated from underlying and
overlying rocks.” (Wheeler 1958a, p. 1051). A year later, he
specified that a sequence “should not be envisaged as a unit be-
longing to the hierarchy or category as group, formation, or
member, for it is by definition and nature independent of them.”
(Wheeler 1959a, p. 1976).
Wheeler (1959a) then concluded that an unconformity-bounded
unit is defined as a body of rock bounded above and below by
specifically designated, significant, and demonstrable disconti-
nuities in the stratigraphic succession (angular unconformities,
disconformities, etc.), preferably of regional or interregional ex-
tent. This is shockingly similar to the definition of “sequence”
articulated nearly 20 years later by Mitchum (1977) and
Mitchum et al. (1977, p. 53), who defined a sequence as “a
stratigraphic unit composed of a relatively conformable succes-
sion of genetically related strata bounded at its top and base by
unconformities or their correlative conformities”, (without, by
the way, any reference to Wheeler); a definition that prevailed
for an additional 30 years. With the advent of additional genetic
stratigraphic frameworks, a more generic definition has been
proposed as “a succession of strata deposited during a full cycle
of change in accommodation or sediment supply” (Catuneanu et
al. 2009), a definition that nevertheless accommodates
Wheeler’s visionary concept.
Harry Wheeler was schooled by Eliot Blackwelder, Siemon
Mueller, and Hubert Schenck at Stanford University, who were
armed with the earlier “base level” concepts of Joseph Barrell.
He was a close colleague of Larry Sloss, who in turn was one of
the first to formalize the time-stratigraphic analysis of uncon-
formities. Due to his unorthodox view of stratigraphy, Wheeler
was involved in one controversy after another, with his views
deemed provocative or even heretical at the time. While we now
value and recognize the later contributions of Bill Galloway,
John Van Wagoner, Mac Jervey, Henry Posamentier, Peter Vail
and others who resurrected sequence stratigraphy, the work of
the original pioneers like Joseph Barrell, Amadeus Grabau,
Eliot Blackwelder, John Rich, and Harry Wheeler often receive
scant attention or mention. It is a sad commentary that, in the
case of Harry Wheeler, there exists only a single, 3-page memo-
rial published in a State Survey Bulletin to extol his contribu-
tions to the stratigraphic community.
HARRY EUGENE WHEELER (1907-1987)
Details on Harry Wheeler’s life were gathered from memorial
papers written by Barksdale (1982), Cheney (1987), and Illman
(1996); comments from past students (Gary Peterson, online
comments; C.V. Aiken, personal communications); comments
from colleagues (Julian Barksdale); and details given to the first
author by his daughter, Carolyn Wheeler Van Wyck.
Harry Wheeler was born on February 1, 1907, in Pipestone,
Minnesota (text-fig. 2A), the son of Mary Belle Denhart
Wheeler and Benjamin Franklin Wheeler (named after a famous
relative, apparently). The family left Minnesota soon after
Harry’s birth and his boyhood was spent in Eugene, Oregon. He
was the only son and was born late in his mother’s life; as a re-
sult, he was doted over by his parents and his two, much older
sisters (text-fig. 2B). Wheeler’s education took place during the
Great Depression and his family lost most of their accumulated
wealth during this time. He told stories about attending “speak-
easy’s” during prohibition, and said that his ability to continue
his education during the depression was a wonderful opportu-
nity, brought about with the help of his family and the fact that
jobs that might have drawn his attention were non-existent.
96
S. George Pemberton et al.: Harry Eugene Wheeler (1907–1987): A Pioneer of Sequence Stratigraphy
TEXT-FIGURE 1
Harry Eugene Wheeler 1907-1987 (photograph courtesy of Carolyn
Wheeler Van Wyck).
Harry attended the University of Oregon and graduated in 1930.
During his studies at Oregon, he served as a field assistant for
Earl Packard and Arthur F. Buddington, and there developed his
life-long love affair with fieldwork (text-fig. 3A). Harry then
went to Stanford University as a Jordan Fellow, completing his
Masters in 1932 and his PhD in 1934 (text-fig. 4A) on the
Lower Permian McCloud Limestone of northern California
(Wheeler 1934). It was at Stanford that Harry became ac-
quainted with the stratigraphic philosophy of a remarkable fac-
ulty that included Hubert G. Schenk, Siemon E. Mueller, and
Eliot Blackwelder. Stanford was a virtual factory for the gener-
ation of insightful stratigraphers, including life-long friend
Larry Sloss, Bob Weimer, George Ashley, and Charlie Stelck,
to name just a few. In 1935, Wheeler accepted the position of
Assistant Professor in the Mackay School of Mines at the Uni-
versity of Nevada in Reno. Wheeler stayed in Reno for 13 years
and worked on paleontological and stratigraphic problems in
the Paleozoic rocks of Nevada, eastern California, and northern
Arizona (text-fig. 3B). In Reno, Wheeler met his wife, Loretta
Rose Miller (text-fig. 4B) who taught in the botany department
at the University, and they were married in 1938. Loretta
quickly became a mother three times over (Eugene Anthony
Wheeler 1939, Carolyn Wheeler Van Wyck 1940, and David
Beebe Wheeler 1942), and due to the university’s nepotism
rules, was not able to go back to teaching botany. During World
War II, Wheeler served (1943-1946) in the U.S. Naval Reserve
and in 1944 moved his family to Nebraska briefly where he
taught in the V-12 program. Soon after, he moved them to
Washington, DC (text-fig. 5A and B), where he worked in the
Hydrographic Office. After the war, George E. Goodspeed re-
cruited Wheeler for the University of Washington following the
retirement of Charles E. Weaver. In 1948, Harry took up his po-
sition at the University of Washington, where he remained until
his retirement in 1976. After retirement, Wheeler remained at
the University in the position of Emeritus Professor until his
death in 1987.
Wheeler was a very genial person. That said, he was also very
confident of his findings, and his geology was out of synch with
the prevailing doctrines. His children remember him occasionally
speaking laughingly of fellow geologists who thought he was
completely nuts (in fact, his campus nick-name was “Crazy
Harry”). He spoke often of the trap of conventional thinking (the
habit of building knowledge on prevailing wisdom/assumptions)
that prevented clear thinking. His ability to take a global view in
separating data from his insight and being able to integrate it into
a fresh interpretation was what made him tick. His daughter Car-
olyn remembers that his passion for integrating knowledge was
his purpose in life. Wheeler’s unconventional thinking personi-
fied the well-known axiom attributed to Abbie Hofmann who as-
serted, “Sacred cows make the best hamburger”!
Gary L. Peterson (online blog), one of his graduate students, re-
members him as a brilliant geologist. “All in all, Harry required
patience, knowledge and perseverance in order to follow and un-
derstand him. It most certainly wasn’t easy and a lot of the stu-
dents suffered. But when you took the time and effort and tried,
Harry was one of the most interesting and inspirational geolo-
gists I’ve ever met. He had his own unique explanations for prac-
tically everything. His knowledge of stratigraphy was
overwhelming. If it was stratified, Harry knew about it and if an
idea was expressed, Harry probably had his own better idea. The
man was simply amazing. I’ve seen him back down several visit-
ing speakers to the point that they had to admit that Harry’s ex-
planation fit their data better than their own explanation. I’ve
also seen him use a speaker’s data to refute the speaker’s inter-
pretation, all of which was extremely interesting but did not en-
dear him with visiting speakers. Harry was an extremely
controversial man and strong opinions were voiced on all sides.”
Julian D. Barksdale, a colleague and close friend of Wheeler’s at
the University of Washington, also noted “Harry is a mild-man-
nered, soft-spoken person with a very rough pen; so rough in fact,
that a close friend and fellow stratigrapher has been known to
97
Stratigraphy, vol. 13, no. 2, 2016
TEXT-FIGURE 2
A. Harry Wheeler in 1908 at the age of one. B. Harry in 1913 at the age of 6 with his father Benjamin Franklin Wheeler, his sister Gretchen, and his mother
Mary B. Wheeler (photographs courtesy of Carolyn Wheeler Van Wyck).
publish what he said was a paraphrase of an old Magyar prov-
erb: “With Wheeler as a friend, who needs enemies?” Rough
but without malice…. Wheeler’s stratigraphy is not always or-
thodox, but it is provocative.” (in Cheney 1987, p. 394).
His sharp pen resulted in a number of interesting exchanges
with his fellow scientists. In 1963, he published a paper entitled
Post-Sauk and Pre-Absaroka Paleozoic Stratigraphic Patterns
in North America” The paper generated a total of six discus-
sions (Sloss 1964; R. R. Wheeler 1966; Franks 1966;
Muehlberger 1966; Hayes and Gerdemann 1966; and Moody
1966) followed by six replies from Wheeler (1964b; 1966a, b,
c, d, and e). In one of these replies Wheeler (1966d) accuses the
authors of Lysenkoism by concluding his reply with the state-
ment “In this light perhaps there is no need to reply to the
Lysenkoism expressed in the last paragraph of the Hayes-
Gerdemann discussion” (Wheeler 1966d, p.1052). Such a bold
statement would have been a telling rebuke in the mid-1960’s.
In Forbes magazine, Ferrara (2013) summed up Lysenkoism
with “Scientists who promoted Lysenkoism with faked data and
destroyed counterevidence were favored with government fund-
ing and official recognition and award. Lysenko and his follow-
ers and media acolytes responded to critics by impugning their
motives, and denouncing them as bourgeois fascists resisting
the advance of the new modern Marxism”. Likewise, in re-
sponse to a discussion of one of his papers by Weller (1958), he
concluded his reply with the statement “Regarding Weller’s
concluding words of warning against “spurious evidence in the
form of attractive generalizations,” we offer the reminder that
we did not propose most of the essential generalizations on
which this theory is based. They were presented by Weller
(1956, p. 26-27) and the few remaining essential generaliza-
tions have not yet suffered disparagement merely by his asser-
tion that they are “spurious.” (Wheeler and Murray 1958, p.
446). Other examples of his controversies with other geologists
can be found in Cheney (1987, p. 394) and include: the defining
of a number of Tertiary sequences in the Cordillera that workers
in the Pacific Northwest only began to rediscover two decades
98
S. George Pemberton et al.: Harry Eugene Wheeler (1907–1987): A Pioneer of Sequence Stratigraphy
TEXT-FIGURE 3
A. Harry doing fieldwork in Nevada, 1935. B. Harry and J. V. Galgiani in Golconda, Nevada, 1934 (photographs courtesy of Carolyn Wheeler Van
Wyck).
later; the assertion that the middle Devonian Catskill delta as
well as the Illinois and other intracratonic basins and domes
were erroneous constructs; his contention that deformation in
the Pacific Northwest was younger than commonly supposed;
and the argument that the Columbia River basalts once ex-
tended over (not below) the Cascade Range of Oregon. In each
case, his views upset the status quo and generated considerable
debate within the geological community.
As a graduate student advisor, Wheeler inspired his students
and allowed them to think for themselves. Gary L. Peterson
(online blog) noted that “Harry became my graduate school
mentor and I couldn’t have made a better choice. He was kind,
gentle, understanding, patient, always available, always a good
listener and he spent countless hours trying to unravel my tor-
tured prose. Many people used to consider Harry something of
an ogre and they wondered how I could possibly work under
such a man. Nothing could be farther from the truth. I could
freely express my ideas to Harry and we’d spend hours discuss-
ing all the ramifications. On several occasions, my explana-
tions ran directly counter to the ideas he had expressed in our
courses. As long as my approach was logical, Harry offered noth-
ing but encouragement.”
Harry’s daughter Caroline remembers that Harry was an ex-
tremely interesting conversationalist, and was passionate fore-
most about geology. His second passion was world affairs.
During the McCarthy years, his children recall Harry and Loretta
arguing about his signing the loyalty oath, which was required in
order for him to hold his job at the University of Washington. The
oath was later removed, of course, but he was always angry about
the need to sign it. He was a consummate liberal, and viewed his
position in life as being a world citizen rather than only a citizen
of the United States. In the 1950’s, he often stated that China
would be the awakening giant that would eventually turn the
world, as we know it, on its head. He dismissed the then prevalent
problems with the Soviet Union as transitory. His children recall
that Wheeler, as most geologists will do, often made derisive
statements about the geologically risky places humankind selects
to put its cities and developments - and explained why geologic
events would cause them to fail. Subsequent events, of course,
have proven the correctness of his perspective.
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Stratigraphy, vol. 13, no. 2, 2016
TEXT-FIGURE 4
A. Harry Wheeler at Stanford, 1932. B. Harry and Loretta in Reno, 1940 (photographs courtesy of Carolyn Wheeler Van Wyck).
Carolyn indicated that Harry knew how things worked. He
fixed everything and passed his knowledge (or his wiring)
down to his children. He also loved bargain hunting, and sec-
ond-hand shops were his means to buy his clothing as well as
just about everything else. Once, he found an old antique
roll-top desk while doing fieldwork in Nevada. He bought it for
$10.00 and brought it back to Seattle where he “antiqued” it
with a greenish finish. It took quite a bit of work years later for
one of his children to remove the “antiquing” and restore it to its
original antique condition. Another project was his wallpaper-
ing of Loretta’s old upright piano. The result was a rather star-
tling faux woven-mat appearance. The final outrage was his
spray paint job of a 1953 Hillman Minx automobile. He masked
out the windows and then used 13 cans of metallic green spray
paint purchased from Sears to transform it. The re-born Hillman
was suddenly transformed into a gigantic blue-bottle fly. Many
years later, when the car was on its last legs, he drove it into a
local used car lot. He sold it on the spot for $300.00 and then
took the bus home rather than risk having to drive back with it
later after arranging return transportation. Carolyn indicated
that the used car lot went out of business shortly thereafter.
During his career at the University of Washington, Wheeler de-
veloped a peripatetic style and was a Visiting Professor at Indi-
ana University (1956-1957), the University of Texas (1961),
and Southern Methodist University (1966). In 1957, he was a
guest of the French National Center for Scientific Research and,
in 1960, completed his Grand European geology tour of Europe.
Perhaps his most intriguing tour, however, came in 1963 when
he was a member of a National Academy of Science-Soviet
Academy of Science Exchange Program. Traveling extensively
in the USSR in 1963, then firmly behind the “iron curtain”,
Wheeler toured not only Moscow, but also extensive parts of
Georgia (text-fig. 6), Armenia, and the Crimea. When he re-
turned, the CIA interviewed him to find out if he had anything to
share. He didn’t. He was already angry that fellow geologists
from the Soviet Union weren’t given the same courtesy he had
been accorded when he was a visitor in their country. His Soviet
counterparts were usually forbidden by the US State Depart-
ment to come to the United States or, if allowed, their travel was
extremely restricted and heavily monitored.
Harry also served an industry consultant and worked for both
Phillips Petroleum (1948-1949) and the Gulf Oil Corporation
(1950-1958) doing various studies. He had intended to continue
writing his final book on stratigraphy after he retired, but the ad-
vance of Binswanger’s disease (much like Alzheimer’s disease
in its symptoms) robbed him of that opportunity. Harry Eugene
Wheeler passed away in Seattle, Washington, on January 26,
1987.
Anecdotal information from former University of Washington
student Carlos V. Aiken (now Professor at UT Dallas), who
overlapped with Wheeler, suggests that during Wheeler’s last
years at Washington he expressed that he was not enamored of
100
S. George Pemberton et al.: Harry Eugene Wheeler (1907–1987): A Pioneer of Sequence Stratigraphy
TEXT-FIGURE 5
A. The Wheelers in Washington, 1944. B. Harry and his children Eugene, David and Carolyn in Washington, 1944 (photographs courtesy of Carolyn
Wheeler Van Wyck).
the “new” global plate tectonic theory. We speculate that his re-
luctance to accept plate tectonic theory, unlike his colleague
Larry Sloss, may have led to the dismissal of his scientific con-
tributions by the wider academic community at that time, and
may explain why his work was ignored for so long. We would
argue that whether he accepted plate tectonics or not hardly in-
validates his approach to analyzing stratigraphic patterns; ap-
proaches that are still practiced today.
The final word should go to Harry Wheeler’s daughter Carolyn,
who summed up Harry best with Dad’s life was devoted to,
and consumed by geology. He taught in the winter and spent
his summers doing fieldwork; and on the occasions that he was
with us as we drove across the country, he was always the
teacher, explaining to us what we were seeing. We all miss
him!”
WHEELER’S STRATOLOGY
Wheeler’s colleagues stated that instead of stratigraphy,
Wheeler practiced what he referred to as “stratology”.
Stratology stressed the idea that stratigraphic analysis must in-
clude integration of observations of stratal patterns, analysis of
the time associated with unconformities, the interpretation of
these surfaces in the context of base level change, and their im-
plications with respect to regional and interregional analysis
and historical interpretations. One of his students, Gary L. Pe-
terson, recalled, “Harry had his own precise definitions and
even his own words for all sorts of stratigraphic principles and
concepts. He was constantly berating all the sacred work in the
literature and all the standard ways of doing things.”
Wheeler’s papers on stratology included: the classification of
stratigraphic units (Wheeler and Mallory 1953; Wheeler 1959a)
into lithostratigraphic (Wheeler and Mallory 1956) and
biostratigraphic (Wheeler 1958b) frameworks, as well as
cyclothems (Wheeler and Murray 1957); the analysis of uncon-
formity-bounded units, to which he applied the term “sequence”
(Wheeler 1959a); and the true nature of base-level (Wheeler
1964a). His work on unconformity-bounded units led the Interna-
tional Subcommission on Stratigraphic Classification to formally
define them in 1987. In the publication, they noted “Wheeler
(1958b; 1959a; 1959b; 1960; 1963) was probably the first to rec-
ognize unconformity-bounded units as clearly distinct from other
kinds of stratigraphic units.” (Salvador 1987, p. 233). Wheeler
was instrumental in re-introducing the concepts of Joseph Barrell
on base-level, and used them to interpret the significance of key
stratigraphic surfaces (see Romans 2007 for an excellent discus-
sion of Wheeler’s 1964a paper). Wheeler summed this up with
Constantly varying undulations of the baselevel surface relative
to the ever-changing lithosphere surface may be seen as a consis-
tent function of the ebb and flow of depositional and erosional en-
vironments in the space-time continuum.” (Wheeler 1964a, p.
607). Wheeler then took this concept and interpreted surfaces
(text-fig. 7) that can be considered to delineate the first incised
valley complex, described earlier by Wanless and Shepard
(1936).
Not all of his concepts have been adopted, however (Bhatta-
charya and Abreu 2016). His sequences, for example, were de-
fined by arbitrary vertical cutoffs. This followed earlier ideas
about the designation of lithostratigraphic units, also defined on
the basis of arbitrary cutoffs (Wheeler and Mallory 1953;
Wheeler and Mallory 1956; text-figure 8), the use of which was
criticized at the time (Fischer 1954). Wheeler and Mallory (1953,
1956) primarily were attempting to explain what they understood
to be the common, but uncodified practice of using these cutoffs
in actually defining and naming lithostratigraphic units (text-fig-
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Stratigraphy, vol. 13, no. 2, 2016
TEXT-FIGURE 6
A. Harry with his hosts in Atremi, Georgia, USSR, 1963. B. Harry at the Zion of Atemi, Atemi Valley, Georgia, in 1963 (photographs courtesy of Carolyn
Wheeler Van Wyck).
ure 8A). In other words, they regarded most lithostratigraphic
units at that time to have been defined using arbitrary cutoffs,
and they believed that it was their role to explain and codify
what was being informally practiced. In this respect, they did
not consider that they were introducing anything new or partic-
ularly radical. They indicated a need for the recognition of three
fundamentally different kinds of lithostratigraphic units: (1)
Formal lithostratigraphic units, such as groups, formations,
and members, which are traditionally designated on the basis of
their position in a vertical sequence and in places defined by ar-
bitrary cutoffs, especially where interfingering occurs (text-fig.
8A); (2) laterally varying lithofacies (text-fig, 8B); and (3) mu-
tually intertongued bodies or lithosomes, which are segregated
on the basis of their vertical and lateral position and their com-
ponent lithology (text-fig. 8C).
Bhattacharya (2011) pointed out that most formal litho-
stratigraphic units, especially those defined and named in the
1950s and 1960s and characterized by interfingering were also
defined by arbitrary vertical cutoffs, such as in the Cretaceous
clastic wedges of the Western Interior of North America
(Wheeler and Mallory 1953; 1956; text-fig. 9). Bhattacharya
(2011) went on to stress that the lithofacies concept was funda-
mentally different in Wheeler’s day (Wheeler and Mallory
1953; 1956), in that lithofacies were defined by the ratio of gen-
eral lithologies within gross stratigraphic units, which might in-
clude several formations (text-fig. 8B). This is in marked
contrast to the modern, more depositionally/paleoenviron-
mentally based lithofacies concept practiced today. The net re-
sult of the Wheeler and Mallory (1953) lithostratigraphic
approach was a proliferation of different names for the same
rocks that was ultimately confusing to all except those
geologists deeply concerned with the rules of stratigraphic no-
menclature (Bhattacharya and Abreu 2016).
Wheeler’s Stratology Terminology
Lacuna: Geochronology: A chronostratigraphic unit represent-
ing the interpreted space-time value of both non-deposition (hi-
atus) and the erosionally removed part of the subsequent
transgressive-regressive succession (Wheeler 1958a, p. 1058;
Wheeler 1964a, p. 599).
Lacuna: Stratigraphically: A period of time during which sedi-
mentation was either nil or, more likely, was removed by ero-
sion (Gignoux 1955, p. 15-16).
Total Vacuity: A missing interval or hiatus in a stratigraphic
sequence caused by both erosion and non-deposition (Wheeler
1958a, p. 1058).
Erosional Vacuity: A term used by Wheeler (1958a p. 1057),
later replaced by “degradation vacuity” (Wheeler 1964a, p. 602;
see below).
Degradation Vacuity: The space-time value of the
degradationally removed part of a transgressive-regressive
depositional sequence (i.e.., the part of a stratigraphic lacuna re-
sulting from erosional removal of previously existing rocks at
an unconformity). The term was used by Wheeler (1964a, p.
602) to replace erosional vacuity. Mitchum et al. (1977, their
figure 1) later referred to this as the erosional hiatus, but ne-
glected to acknowledge Wheeler.
102
S. George Pemberton et al.: Harry Eugene Wheeler (1907–1987): A Pioneer of Sequence Stratigraphy
TEXT-FIGURE 7
Wheeler was instrumental in re-introducing the concepts of Joseph Barrell on base-level, and used it to interpret the significance of key stratigraphic sur-
faces. Wheeler took the concept and interpreted surfaces in what can be considered the first incised valley complex described earlier by Wanless and
Shepard (1936) (after Wheeler and Murray 1957).
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Stratigraphy, vol. 13, no. 2, 2016
TEXT-FIGURE 8
Generalized stratigraphic cross-sections of rock units in the Cambrian of Tennessee, Kentucky, and Virginia, illustrating: A. Formations, which are tradi-
tionally designated on the basis of their position in vertical sequence; B. Lithofacies, which are lateral quantitative variants; and C. Mutually intertongued
bodies or lithosomes, which are segregated on the basis of both their vertical and lateral position (after Wheeler and Mallory 1956).
Hiatus: A geochronologic unit representing the space-time
value of non-deposition during a transgressive-regressive epi-
sode (Wheeler 1958a, p. 1057).
Holostrome: A term introduced by Wheeler (1958a, p. 1061)
for an intertongued chronostratigraphic unit, which restores
sediments removed by the degradational vacuity, and which
may be either depositional (comprising one or more contiguous
holostromes) or hiatal (consisting of combined, contiguous hia-
tuses).
Lithosome: A rock mass of essentially uniform or uniformly
heterogeneous lithologic character, having intertonguing rela-
tionships in all directions with adjacent masses of different lith-
ologic character (see text-figure 8C). The term was introduced
by Wheeler and Mallory (see Fischer 1954 and Wheeler and
Mallory 1954, p. 929) and defined by Wheeler and Mallory
(1956, p. 2722) as a lithostratigraphic body or vertico-laterally
segregated unit that is “mutually intertongued with one or more
bodies of differing lithic constitution” (Wheeler and Mallory
1956, p. 2722). This is somewhat closer to the modern usage of
the facies concept, albeit at a rather larger scale.
Lithostrome: A term introduced by Wheeler and Mallory
(1956, p. 2720-2722) for a sedimentary unit “consisting of one
or more beds of essentially uniform or uniformly heterogeneous
lithologic character” and representing the “three-dimensional
counterpart of a lithotope”, especially an individual tongue pro-
jecting from a lithosome.
Arbitrary Cut-Off: A concept presented as: If a rock unit ter-
minates by combined lateral and vertical gradation (or other-
wise pinches out), or if its lateral limit is one of erosion or
faulting, there are no serious problems about termination.
Moreover, no difficulties are encountered where one rock unit
pinches out between two other distinct units, …. On the other
hand, no such convenient point or line of termination is present
in the case where one rock unit bifurcates with mappable parts
passing laterally below and above an opposed terminating unit.
In this case, if each of the bifurcations is recognized as a formal
stratigraphic unit, their planes of separation from the parent
unit are not marked by lithologic distinction, and must therefore
be established arbitrarily. If this arbitrary cut-off is generally
recognized and applied as standard procedure in the prepara-
tion of both stratigraphic cross sections and geologic maps,
much of the present mistrust and disagreement among stratigra-
phers and physical geologists should be eliminated.” (Wheeler
and Mallory 1953, p. 2412).
Base-level Transit: Wheeler (1964a, c) indicated that, because
deposition and degradation always alternate due to the upward
and downward transit of base level across the lithosphere sur-
face, base level may be seen as an undulating, abstract, world-
wide surface. He termed this the Base-level Transit Cycle.
Wheeler (1964a) defined Base-level transit as: If in an ero-
sional environment at a given locality, the supply-energy ratio
increases sufficiently to induce deposition, baselevel is forced
upward across the lithosphere surface at that point at the mo-
ment deposition beings, thus initiating the first or depositional
104
S. George Pemberton et al.: Harry Eugene Wheeler (1907–1987): A Pioneer of Sequence Stratigraphy
TEXT-FIGURE 9
Lithostratigraphic subdivision within interfingering clastic wedges. (A) Intertonguing units are assigned to Formation B using arbitrary vertical cutoffs.
(B) Intertonguing units are assigned to Formation A using arbitrary vertical cutoffs. (C) Application to the Campanian Mesaverde Group strata of the
Book Cliffs, Utah. Shale tongues are assigned to the Blackhawk Formation, rather than to the Mancos Shale Formation. Modified after Wheeler and
Mallory (1953). sst = sandstone (after Bhattacharya 2011).
105
Stratigraphy, vol. 13, no. 2, 2016
TEXT-FIGURE 10
A. Generalized cross-section approximately along the Fortieth Parallel from the Pacific Coast to the Rocky Mountains showing principal sequences and
intervening unconformities from base of the Upper Mississippian (Chesterian) to the Triassic-Jurassic boundary. B. Time-stratigraphic cross-section
through the lateral extent of Sequence C in Figure A, illustrating derivation of holostrome and hiatus as primary components of regional stratigraphiccy-
cle. C. Time-stratigraphic cross-section showing holostromes and hiatuses derived from sequences shown in A (after Wheeler 1958a).
106
S. George Pemberton et al.: Harry Eugene Wheeler (1907–1987): A Pioneer of Sequence Stratigraphy
TEXT-FIGURE 11
A. Section showing physical relationships of successive unconformity-bounded sequences. B. Area-time projection of A showing lithosphere sur-
face-moment and base level transit migration patterns in time-stratigraphy (after Wheeler 1964a).
phase of a new cycle. This cyclic phase continues until the sup-
ply-energy ratio is decreased sufficiently to stop deposition and
induce erosion, at which time baselevel makes its downward
transit of the surface, thus beginning the second or hiatal cyclic
phase” (Wheeler 1964a, p. 604). Wheeler (1964b) also noted
that the major baselevel transit cycles generally differ from
what he termed “insignificant” ones by several orders of magni-
tude. This foreshadows more recent work on the order of cycles
that are recognized on modern sea-level charts.
Law of Surface Relationships: Wheeler (1964a) defined what
he called the “Law of Surface Relationships” as “Insofar as this
logic is sound, it implies the existence of the following strati-
graphic principle, which may be called the law of surface rela-
tionships: time as a stratigraphic dimension has meaning only
to the extent that any given moment in the Earth’s history may
be conceived as precisely coinciding with a corresponding
worldwide lithosphere surface and all simultaneous events ei-
ther occurring thereon or directly related thereto. At any given
moment the Earth’s lithic surface is divisable (sic) into innu-
merable areas, each of which is characterized by one or the
other of two processes—deposition and erosion. The boundary
between any two of these areas is at baselevel.” (Wheeler
1964a, p. 603).
Wheeler Diagrams
With the advent of genetic stratigraphy, interest in Wheelers’
work on stratology has been revitalized. In 1958a, Harry
Wheeler produced the most sophisticated chronostratigraphic
charts of the time (text-figs. 10 and 11), which were able to
clarify the time-relationships of rock units. He recognized that an
unconformity’s total time gap (lacuna) consists of a portion re-
flecting the removal of pre-existing strata (degradational vacuity)
and a period of sediment bypass and non-deposition (hiatus), and
understood that unconformities pass distally into correlative con-
formities (continuity) (text-figs. 11 and 12). Although not all of
Wheeler’s terminology for the various components of a
chronostratigraphic analysis has been retained (see text-fig. 11),
his general approach is now used as a standard procedure in de-
picting genetic stratigraphic relationships in time (text-fig. 12).
Sloss (1984) applied the name “Wheeler diagram” to such con-
structs, in homage to their originator. Brown and Loucks (2009)
stressed that the advantage of such a “Wheeler chart” is that it
displays strata deposited during the same time slice as equivalent
strata and reduces problems of laterally confusing litho-
stratigraphic correlations. Although it is common practice to take
a measured section, well log, or geological cross section and
place it next to a chronostratigraphic chart, such as the geological
time-scale, the only correct approach is to convert the geological
section to a Wheeler diagram, given that there is no obvious rela-
tionship between unit thickness and geological time. The conven-
tional Wheeler diagram aids in the construction of a
spatio-temporal framework of strata and is generally created
manually using outcrops, wells, or seismic data. Wheeler dia-
grams may use a relative vertical time scale, where absolute
chronometry is unknown, or they may use an absolute time scale,
where ages of units are well constrained. Mitchum et al. (1977)
and Vail et al. (1977) outlined the procedures for constructing and
107
Stratigraphy, vol. 13, no. 2, 2016
TEXT-FIGURE 12
Charts such as this have now become recognized as Wheeler diagrams and are considered a standard procedure in genetic stratigraphic characterizationsof
chronostratigraphic relationships. The diagram shows Wheeler’s“stratology” terminology that corresponds to key stratigraphic surfaces and systems tract
positions commonly employed today (modified after Bhattacharya 2011 and Zhu et al. 2012).
using Wheeler diagrams (referred to by them simply as
“chronostratigraphic charts”) to decipher magnitudes of
eustatic sea-level change based on the analysis of lap-out pat-
terns on seismic cross sections. Despite being landmark publi-
cations and the first major salvo in seismic stratigraphy, these
papers make no reference to Wheeler.
Bhattacharya (2011) and Zhu et al. (2012) have recently used
Wheeler diagrams to illustrate alternate hypotheses to test dif-
ferent time-stratigraphic relationships associated with sequence
boundaries, especially in degradational deltaic systems that are
overridden by fluvial systems. They also illustrate some of the
uncertainties that may be associated in converting a strati-
graphic cross section to a time-stratigraphic cross section. A
key problem remains – the well-known Sadler effect (Sadler
1981; Miall 2016), in which thicker and temporally longer
stratigraphic sequences appear to be deposited at ever-slower
rates. Part of this dilemma reflects the fact that sediments are
not always deposited as basin-wide layers. In many
depositional settings (e.g., rivers, deltas, continental slopes),
deposition is localized to dipping bodies (e.g. accretion beds,
clinothems) or localized channels, lobes or bars, such that they
actually record time by lateral deposition versus vertical accre-
tion, and which in many areas may experience local erosion
causing diastems. Wheeler-style analysis is a key method that
captures the time-stratigraphic record, wherein sedimentation
shifts laterally and provides a robust method for evaluating as-
sociated unconformities and more local diastems (note, the term
diastem was coined by Barrell 1917).
Qayyum et al. (2012) documented the historical development of
Wheeler diagrams. Recently, innovative work has been done on
the next generation of Wheeler diagrams by Qayyum et al.
(2012, 2014, and 2015). Automated methods using seismic data
now exist, which support the construction of 2D, as well as 3D
Wheeler diagrams. Such 3D diagrams resolve much of the
“missing record” that plague 1D and 2D records (Sadler 1981;
Miall 2016). Qayyum et al. (2012) emphasized that the dia-
grams are only complete if one utilizes the thicknesses of a se-
quence-stratigraphic unit (sequence, systems tracts) – a missing
dimension that turns a 3D Wheeler diagram into 4D.
SUMMARY
Conceptually, Harry Wheeler’s major contributions to stratigra-
phy include: 1) formalizing the concept of time stratigraphy; 2)
recognizing that hiatuses and time gaps are as important in anal-
ysis of stratigraphy as the rocks themselves; 3) depicting strati-
graphic cross-sections with time on the vertical axis, pioneering
the concept of chronostratigraphy; 4) resurrecting the
base-level concept of Powell (1875) and Barrell (1917); and 5)
defining sequences as unconformity-bounded units, and re-es-
tablishing the concepts pioneered by Blackwelder (1909).
It is an unfortunate fact that in any scientific paradigm shift,
many of the true pioneers are not fully recognized for their con-
tributions. At the times they were active, they were probably
decades ahead of the prevailing concepts and by the time that
their points of view are fully appreciated, they have been for-
gotten and later synthesizers become recognized in their stead.
This has been the unfortunate fate of Harry Eugene Wheeler.
Wheeler schooled by Eliot Blackwelder, Siemon Mueller, and
Hubert Schenck at Stanford University and armed with the base
level concept of Joseph Barrell was one of the first to recognize
the concepts of time stratigraphy and the significance of uncon-
formity-bounded units. Due to his unorthodox view of stratigra-
phy, Wheeler was involved in one controversy after another and
his views were deemed to be provocative, controversial, and
confrontational. Sequence stratigraphy was resurrected in the
late 1970’s, largely through the availability of seismic cross sec-
tions that were amenable to the analytical techniques of se-
quence stratigraphic pioneers, such as Laurence Sloss, Harry
Eugene Wheeler and their predecessors, Joseph Barrell, Eliot
Blackwelder, and Amadeus Grabau. Despite the importance of
these pioneers, we suggest that many have not received as much
attention and recognition as they deserve, and especially Harry
Eugene Wheeler, to which we devote this paper to highlight the
importance of his contributions in our field.
ACKNOWLEDGMENTS
We are indebted to Carolyn Wheeler Van Wyck, the daughter of
Harry Wheeler for supplying SGP with family photographs and
reminisces about her father. We are also grateful to Eric Cheney
of the University of Washington for supplying a field photo-
graph of Harry Wheeler. We extend our thanks to the two anon-
ymous reviewers who helped strengthen the final manuscript.
Funding for this project was from the Natural Science and Engi-
neering Research Council of Canada NSERC Discovery Grant
program for funding to SGP, JPB and JAM.
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S. George Pemberton et al.: Harry Eugene Wheeler (1907–1987): A Pioneer of Sequence Stratigraphy
... A recent summary of the life and contributions of Harry Wheeler (text- fig. 12A) can be found in Pemberton et al. (2016). Wheeler attended the University of Oregon, where he served as a field assistant for Earl Packard (1913Packard ( -1980 and Arthur F. Buddington (1890-1980. ...
... His children remember Wheeler laughing that fellow geologists thought he was completely nuts, and in fact, his campus nick-name apparently was "Crazy Harry" (cf. Pemberton et al. 2016). ...
... Despite these landmark publications being the first major salvo into seismic stratigraphy, they make no reference to Wheeler's work and regrettably termed such constructs as simply "chronostratigraphic charts". Bhattacharya and Abreu (2016) and Pemberton et al. (2016), speculated that Wheeler's refusal to accept plate tectonics and his insistence in the use of vertical cutoffs to define additional sequences at the point where the unconformity tipped-out into its correlative conformity led to an unwieldy profusion of sequences, which may also have been instrumental in his work being largely ignored in later decades. ...
Article
Few facies analysts or stratigraphers would argue against the contention that the transition to facies-driven sequence strati- graphic correlations represents one of the most important paradigm shifts in modern stratigraphy. What is less commonly appreciated is that most of the fundamental underpinnings of sequence stratigraphy were derived from a relatively small number of pioneers in the early to mid-1900s; most of them largely unknown or underappreciated by the current generation of sequence stratigraphers. Chief among these are Eliot Blackwelder, Amadeus Grabau, Joseph Barrell, John Rich, and Harry Wheeler. Blackwelder was perhaps the first to point out the presence and significance of regional unconformities in the packaging of strata in North America, which would later come to form the basis of the well-known cratonic megasequences of Larry Sloss. However, Blackwelder is best appreciated as the mentor and colleague of not only these other pioneers, but also of key workers who themselves ultimately mentored some of the most renowned sequence stratigraphers of the 1970s and 1980s. Amadeus Grabau focused his attention on expounding the law of the correlation of facies of Johannes Walther and bringing facies-driven correlations into stratigraphy; an approach at odds with the then prevailing view of lithostratigraphy as the principal physical stratigraphic framework. Grabau recognized that the rock record contains numerous temporal gaps that partition facies succes- sions, for which he defined the term “hiatus”. His Pulsation theory was used to explain the cycles of deposition and hiatal erosion/bypass, and although the mechanism is different, the net outcome of such “oscillations” is broadly similar to the effects of eustacy and tectonism that we assign to such changes today. Joseph Barrell developed the concept of base level and explored its role in controlling erosion versus deposition. Like Grabau, Barrell insisted that sedimentation was not continuous, leading to a stratigraphy that is replete with breaks of varying durations. For these he coined the term “diastems” for the small but more numerous breaks, which could be contrasted with those reflecting longer breaks which he referred to as “discontinuities”. John Rich evaluated depositional topography, for which he coined the terms clinoform, undaform and fondoform. He recognized that such depositional bodies necessarily link genetically related associations of sediment deposited from the shoreline to the basin center; what today we regard as the depositional system. The resulting architectures bounded by these surfaces form the underpinning of all systems tracts in modern sequence stratigraphy. Harry Wheeler formalized the concept of time-stratigraphy, demonstrating that temporal gaps in stratigraphy are as important in understanding the rock record as the rocks themselves. His novel approach of developing stratigraphic cross-sections with time on the vertical axis pioneered the concept of chronostratigraphy through the development of what are now referred to as Wheeler Diagrams. His resurrection of the base-level concept expounded by earlier workers was instrumental in defining sequences as unconformity-bounded units, re-establishing the concepts pio- neered by Blackwelder himself. In concert, these stratigraphic visionaries erected a stratigraphic framework focused on the understanding of the stratigraphic record as opposed to its simple lithostratigraphic mapping or biostratigraphic dating. These unsung pioneers put into place virtually all components of modern sequence stratigraphy more than two decades before its popularization in the scientific commubity.
Article
The post-Sauk Paleozoic of United States and at least southern Canada, except incompletely interpreted late Paleozoic in the Cordilleran and Ouachita regions, comprises six major discontinuity-bounded sequences. In addition to two previously defined by Sloss et al., 1949, and Sloss, 1959 (Tippecanoe and modified Absaroka), four others include: two sequences separated by the Taconic discontinuity and confined to the eastern craton and Appalachian geosyncline, but together occupying the Tippecanoe interval; and two virtually transcontinental sequences, separated by the Acadian discontinuity, and together comprising approximate "Kaskaskia" interval of Sloss et al. The discontinuities are: I, unnamed pre-Tippecanoe (pre-"Chazy-Black River"); II, Taconic, pre-Silurian (eastern America only); III, unnamed pre-"mid"-Devonian; IV, Acadian, pre-latest Devonian; and V, unnamed pre-Absaroka (about pre-Desmoines). I, II, and V have been widely recognized; III has been appreciated regionally in the Rocky Mountains and Great Plains of northern United States and southern Canada (Harker et al., 1954, and Andrichuk, 1954), but otherwise previously envisaged rather locally; and IV, long recognized in Maritime Provinces and New England, and also shown from southern Appalachians to Oklahoma (King, 1955), but otherwise previously demonstrated in many widely scattered areas. These sequences and their many interregional stratigraphic "constants," together with the intervening lacunas and their deformation-erosion differentials, demonstrate a striking historical episodicity which is unrelated to and obscured by the arbitrary time-stratigraphic subdivisions (systems, etc.) of the stratal record. Moreover, both physical and biostratigraphic patterns comprise a mutually harmonious and relatively simple order, which, by implication, tends to negate most of the previously envisaged "persistent" positive and negative intracratonic tectonic features.
Article
Practical considerations indicate a need for the recognition of three fundamentally differing kinds of lithostratigraphic units: (1) group, formation, member, et cetera, which are traditionally designated on the basis of their position in vertical sequence; (2) lithofacies, which are lateral quantitative variants; and (3) mutually intertongued bodies or lithosomes, which are segregated on the basis of both their vertical and lateral position. Past usage of these terms has been neither consistent nor always logical. Each is useful for specific purposes, and each illustrates relations not shown by the other two. The three rock-stratigraphic categories are defined, and the implications of their distinction and usage are discussed. Tongue is shown to be a lithosomal appendage. Lithotope is shown to be a non-stratigraphic, sedimentological term, and lithostrome is defined as its stratigraphic counterpart.
Article
A utilitarian "stratigraphic code" should be sufficiently flexible to permit freedom in the selection and naming of units, and should encourage the designation of stratigraphic and map units which fulfill the needs of each field of specialization, but should employ terms with uniform connotation in all fields. Cases involving designation of stratigraphic units from Cambrian to Tertiary are cited which indicate that the foregoing aims are attainable under the following conditions. 1. All stratigraphic units (lithic, biologic, or chronologic) are potentially employable as map units, and provision should be made for such application. However, only rock units, because of their objectivity, are recommended for general use as map units. 2. Geologic maps based on these various kinds of units (or their combinations) should be labeled as to type, and their units designated accordingly. Biostratigraphic units, for example, should not be called formations. 3. Rock units may effectively terminate laterally by gradation, pinch-out, faulting, transection by an intrusion, erosion, deep burial, and arbitrary cut-off (where a rock unit changes content and identity or rank without mappable lithologic contact). Recognition of the arbitrary cut-off as standard stratigraphic and mapping procedure would indicate acceptance of the following items. 4. A unit of one rank may retain its identity as parts of two or more units of greater rank. 5. Intertongued members should be assigned to one or the other of the formations involved--not alternately to each. 6. The term, tongue, should be abandoned for formal rock-unit designation. 7. Schemes of terminology employing vertically successive alternations of similar names (except in cases of structurally induced duplication) are unnecessary and needlessly compromise the law of superposition.