files

40 Pages·1996·1.67 MB·English

Vol. 6, No. 1 January 1996
INSIDE
G S A TODAY
• Presidential Address, p. 10
• GSA Bulletin Update, p. 13
• New Editors, p. 20
A Publication of the Geological Society of America
• Cordilleran Section Meeting, p. 25
Alamo Megabreccia:
Record of a Late Devonian Impact in Southern Nevada
John E. Warme, Department of Geology and Geological Engineering, Colorado School of Mines, Golden, CO 80401
Charles A. Sandberg, 395 South Lee Street, Lakewood, CO 80226-2749
ABSTRACT 116o 115o 114o
Figure l.Study area showing towns
mostT vhoel uAmlaminoo ubsr ekcncoiaw ins pourotcbraobplyp itnhge CWANOYOODNX Currant XSRIAXNMCILHE WHITE PINE CO. (lastqeuraarl edsi)s,t rDibeuvtoionnia nzo lnoceas loitfie As la(xm’so), barnedc-
c~ina4 r0sbo0ou0n tkhamteer2 nma Ncergeoavsbasrd 1eac1,c hmiaao.s Iu atn not caacivnue prraiaegnseges CCAHRNOEYETOKNX NORTH HMEATTNHX TCSRAPONRUYINOGGNH X XSIPDAESHSILL NEVADAUTAH cmia; .z Borneecc2ia, ~th6i0c kmne; szsoens:e z3o,n <e1 1–,1 ~01 m30.
thickness of ~70 m, and contains a vol-
bnauemigadinea, )noo aftf ges2ela5i,rd 0ltey+h atFkhtrm aafots3 n.rd mTieahpeneod (s beiintraeer dtclhyc a ieLa lwa oitswae ka eD ers eionvfogl-e 38o SPWRAIRNMGSX STRKNEXUOBBEN MPEEEAKKERXGOLDEN GAXTXE RGSCXORNUETSHTMFXOTNXXSWEAAMSAHNXNREOIXADRSGTRTEWHAENSGTE Pioche FtiirhngaenuFpgirgeeeburs ri2,rme eo.c eu1Ecttin easclhr rai onoergpnw ze colimonloncgeseainsmnl ittg1 oioe auAfs nn,lia ndatmasn 2eidnot.
MAIL HIKO
chaotic debrite, containing clasts as SUMMITX X NARROWS 115(cid:176) 30' 115(cid:176)
leastbAoahhxnfrlreaeaqoagc mlunmGelco i iouaseaawi sixl tel oi-et8mvswrul 0eyaisean nt l·ttgeyttte,rre5e r iarra 0 neFpdp 0sontrelt earemedrrmttiac feat,rao audlbal rtr oaynmaibotb dsmei n jd cdaea.aiac ntpwTrrtei ,brh.u nio woteIpehdnt h p Au iaicemeslctyraretepcm sobla iofyocc ftthe 37o CARWBAOSNHATEX TEMMPTINUTEHSAUNASN1MrCeXXMaO ICoTfK FiXMgMN.WO T2XSNNXW T XSXE2MTX.H IRHiHkIISILoAKHLOlSamXoDMETLSA M S3AWR CLaICNliLeCAnORtLLeMKNIMT NC ECOOX.. 38(cid:176) LINT W ORTNHINRIGTCONMGY OMTPSEALH N U T CCEGOOOLDE N M R TA GN AG TE E IRISH RHANIKGEO OKISHEAMAN RANGE318 NORTC H PAHR9 OC RE A NGEAT 3 LOL Y ITEONTE
iauzsoRmeonfpoa ndpicpwttk/ea aaoa-rclw crrt ~d sc-am6guu ta0ermeacnf rrmar ueiocenrl exsaoaes.cttf eLehs tpuhddoalp e onaca estgrpsrefu elowtnas hritetanmeafdvo dl le rbouassmhelw coddoe,ene drcartogk naldc acadwkenh b hassderolovd-iimertd eits-he.e 36o CALIFNOERVNNAIDVAA MercNuYrEy CO. 00 SI1np0dr1iina02gn0s32004X0Y3UG 5 0 R0VCA ML EACPKAiGNLliAelSoGAasmSEse XteVrseXgaCARsARANRNYOGOAWENRIZONA 37(cid:176) 30'GROOM RANGE00 H1SA0UN3M7C15MO0ICT2K0mkmPiAHRANAGATW ERSGTES. PPAHARRANSAIGNHAT G RGSRAANGELA93MV O SE.L PATHGAROOCS ARGS DELAMMAORUNTAINS
ward-propagated tsunami(s), whose
uprush and/or backwash deposited the
upper turbidite, partly above sea level.
Evidence for impact includes shocked-
quartz grains, an iridium anomaly, and
reworked conodonts, all found only
within the breccia. Because theAlamo
breccia is not known outside ofNevada,
and because the early Frasnian time of
the Alamo event is not noted for accel-
erated extinctions, being ~3 m.y. before
the Frasnian-Famennian impact(s) and
biotic crisis, the impact was probably
only of moderate size.
INTRODUCTION
The Alamo breccia, a newly
recognized carbonate megabreccia, is an
anomalous event–stratigraphic bed of
immense proportions, probably the largest
megabreccia known in surface exposures. Figure 3.View northward from the Hancock Summit area (see Fig. 2) of West Pahranagat Range,
It was emplaced in a geologic instant of showing the 55-m-thick Alamo breccia (AB) within the 600-m-thick Guilmette Formation. The
Guilmette begins at the yellow slope-forming interval (YSF in Fig. 4) in the saddle ~150 m below
thebreccia, is underlain by the Simonson Dolostone at left, and is overlain by the West Range
Megabreccia continued on p. 2 Limestone and/or Pilot Shale on dip slope at right.
IN THIS ISSUE
GSA TODAY
January
Vol. 6, No. 1 1996 Alamo Megabraccia:Record of GSAF Update .......................... 18
aLate Devonian Impact in GSA Today Science Editor ............... 20
GSA TODAY (ISSN 1052-5173) is published Southern Nevada.................... 1
New Geology Editor .................... 20
monthly by The Geological Society of America, Inc.,
with offices at 3300 Penrose Place, Boulder, Colorado. GSA On the Web....................... 7 About People.......................... 20
Mailing address: P.O. Box 9140, Boulder, CO 80301-
9140, U.S.A. Second-class postage paid at Boulder, Col- Rock Stars: Walcott..................... 8 Book Reviews.......................... 21
orado, and at additional mailing offices. Postmaster: Presidential Address .................... 10 Cordilleran Section Meeting ............ 25
Send address changes to GSA Today, Membership Ser-
vices, P.O. Box 9140, Boulder, CO 80301-9140. Bulletin Update......................... 13 In Memoriam .......................... 31
Copyright © 1996, The Geological Society of America, GSADivision Officers................... 13 Memorial Preprints..................... 31
Inc. (GSA). All rights reserved. Copyright not claimed on
content prepared wholly by U.S. Government employ- Washington Report .................... 14 Calendar .............................. 31
ees within the scope of their employment. Permission is SAGE Remarks ......................... 16 Classifieds ............................. 32
granted to individuals to photocopy freely all items
other than the science articles to further science and PEP Talk ............................... 16 Award Nominations Deadlines .......... 34
education. Individual scientists are hereby granted per-
GSA Division News ..................... 17 GeoVentures ........................... 35
mission, without royalties or further requests, to make
unlimited photocopies of the science articles for use in Northeastern Section Research Grants ... 17 GSA Meetings ......................... 39
classrooms to further education and science, and to
make up to five copies for distribution to associates in GSA Research Grant Alternates .......... 17 Coal Division Award .................... 40
the furtherance of science; permission is granted to
make more than five photocopies for other noncom-
mercial, nonprofit purposes furthering science and edu-
cation upon payment of the appropriate fee ($0.25 per
Megabreccia continued from p. 1 SUBMARINE SLIDES,
page) directly to the Copyright Clearance Center, 27
Congress Street, Salem, Massachusetts 01970, phone CARBONATE MEGABRECCIAS,
[phone] (include title and ISSN when paying). AND TSUNAMITES
Written permission is required from GSA for all other early Late Devonian time and is now
forms of capture, reproduction, and/or distribution of preserved within the Guilmette Formation Many enormous submarine debrites
any item in this journal by any means. GSA provides this
of southern Nevada. The breccia, as yet and/or turbidites, comparable in extent
and other forums for the presentation of diverse opin-
ions and positions by scientists worldwide, regardless of informally named, crops out in 11 and volume to the Alamo breccia, are
their race, citizenship, gender, religion, or political view- mountain ranges around the community known from both modern (e.g., Piper et
point. Opinions presented in this publication do not
of Alamo, Nevada (Figs. 1–3). It spans a al., 1988; Moore et al., 1994) and ancient
reflect official positions of the Society.
minimum area of 4000 km2, has an (e.g., Macdonald et al., 1993) settings.
SUBSCRIPTIONSfor 1996 calendar year: Society average thickness of ~70 m, and represents Catastrophic failure of the seaward
Members: GSA Today is provided as part of member- detachment, mobilization, and resedimen- margins of present and past carbonate
ship dues. Contact Membership Services at (800)
472-1988 or [phone] for membership informa- tation of at least 250 km3of Devonian car- platforms results in voluminous carbonate
tion. Nonmembers & Institutions: Free with paid bonate rock. megabreccias that commonly contain
subscription to both GSA Bulletin and Geology, otherwise The Alamo breccia represents an huge transported blocks (e.g., Cook and
$45 for U.S., Canada, and Mexico; $55 elsewhere. Con-
tact Subscription Services. Single copies may be extraordinary style of carbonate-platform Mullins, 1983; Hine et al., 1992). However,
ordered from Publication Sales. Claims: For nonreceipt collapse and submarine slide, now all large-scale marine mass-flow deposits
or for damaged copies, members contact Membership preserved as a single bed with the described to date, whether terrigenous
Services; all others contact Subscription Services. Claims
are honored for one year; please allow sufficient delivery characteristics of a debrite (debris-flow orcarbonate, intercalate with thinner
time for overseas copies. deposit) in the lower part that evolved resedimented beds and were interpreted
into a capping turbidite (Figs. 4, 5). It is toaccumulate in relatively deep water sea-
STAFF: Prepared from contributions from the GSA
anomalously intercalated within cyclical ward from shelf or platform edges.
staff and membership.
Executive Director: Donald M. Davidson, Jr. shallow-water carbonate-platform facies Massive shelf-edge slumping causes
Science Editor: Suzanne M. Kay ofthe Guilmette Formation (Figs. 3–6), awater-for-rock volume exchange that
Department of Geological Sciences, Cornell University,
rather than occurring in deeper water as induces an onshore tsunami. Numerous
Ithaca, NY 14853
Forum Editor: Bruce F. Molnia expected. Its huge magnitude, singular massive Quaternary underwater slumps
U.S. Geological Survey, MS 917, National Center, epiplatform occurrence, horizontal occurred adjacent to the Hawaiian Islands,
Reston,VA 22092
delamination from platform bedrock, and each potentially triggered destructive
Managing Editor: Faith Rogers
Production & Marketing Manager: James R. Clark andexotic components including shocked onshore waves (Moore et al., 1994). One
Production Editor and Coordinator: Joan E. Manly quartz, iridium, and reworked conodonts, example is suspected of causing a prehis-
Graphics Production: Joan E. Manly, Adam S. McNally
all indicate genesis from the consequences toric catastrophic tsunami that formed an
ADVERTISING of an impact of an extraterrestrial object uprush 375 m above sea level on Lanai,
Classifieds and display: contact Ann Crawford with Earth, named the Alamo event Hawaii, leaving a deposit (tsunamite) of
[phone]; fax [phone] (Warme et al., 1991; Warme, 1994). coral and other rubble in its wake (Moore
Issues of this publication are available electronically, in Discovery of the Alamo breccia and Moore, 1988). However, tsunamis
full color, from GSA as Acrobat “Portable Document coincides with current intense interest in produced by underwater landslides would
Format” (PDF) files. These can be viewed and printed
on personal computers using MSDOS or MSWindows, geologically short-lived but significant likely be dwarfed compared with those
on Macintoshes, or on Unix machines. You must use the events (e.g., Clifton, 1988) and new from oceanic extraterrestrial splashdowns;
appropriate Adobe Acrobat Reader, available for free appreciation for the possible physical the waves could be as high as the target
download from GSA and other online services. The
more powerful Adobe Exchange program, available andbiological effects of extraterrestrial water depth, conceivably 1000 m or more
from commercial software suppliers, may also be used. impacts (e.g., McLaren and Goodfellow, (Silver, l982), but few deposits from such
Download the issues of GSA Today and/or the appropri- 1990; Sharpton and Ward, 1990). This waves have been identified. Probable
ate Readers using the Uniform Resource Locator (URL):
http://www.aescon.com/geosociety/index.html. Issues preliminary report describes the breccia, impact-related slump deposits and tsuna-
of GSA Today are posted about the first of the month of discusses its genesis as a catastrophic bed, mites were described at the Cretaceous-
publication. and presents evidence that it was triggered Tertiary (K-T) boundary in cores from the
This publication is included on GSA’s annual CD-ROM and magnified by a nearby marine impact Gulf of Mexico as well as in circum-gulf
GSA Journals on Compact Disc. Call GSA Publication Sales
of moderate size. outcrops (e.g., Smit et al., 1994). An
for details.
Printed with pure soy inks on recyclable paper in the U.S.A.
Megabreccia continued on p. 3
2 GSA TODAY, January 1996
Megabreccia continued from p. 2 theconodont biofacies scheme described selective or complete dolomitization.
by Ziegler and Sandberg (1990). As shown Mostclasts are recognizable components
Eocene breccia in the subsurface under in Figures 4 and 5, platform cycles below of the Devonian carbonate platform that
Chesapeake Bay was first regarded as the the breccia contain shallow-subtidal disintegrated during the Alamo event.
tsunamite from a North Atlantic impact, biofacies and indicate water depths of 10 Quartz grains and other noncarbonate
then was reinterpreted as brecciated target m or less. Collections from fossiliferous components recovered from conodont-
rock (impactite) within the actual crater postbreccia beds at or above its top indi- sample insoluble residues represent ‹‹1%
(Poag and Aubry, 1995). Owing to the cate landward shallowing, from 60–100 m ofthe breccia volume.
numerous exposures and well-understood on the west to 10–20 m toward the east.
stratigraphic framework of the Alamo Samples from easternmost localities (zone Clasts and Matrix
breccia, it provides a useful comparison 3 in Fig. 1) were largely barren of con- The Alamo breccia contains a popula-
and basis for interpreting other less acces- odonts. Samples collected within the tion of megascopic clasts ranging in size
sible catastrophic deposits. lower part of the breccia, from both plat- from sand to blocks 80 · 500 m. Breccia
form-derived clasts and breccia matrix, “matrix” is a relative term; matrix
GEOLOGIC SETTING OF THE yielded shallow-water biofacies, as betweenclasts of given sizes is simply
ALAMO BRECCIA expected. However, samples from the smaller fragments, regardless of their
upper part contain admixed deep-water absolute scale (Fig. 8). Gravel-, sand-, and
Southern Nevada falls within the
contemporary Devonian and reworked smaller sized particles are ubiquitous
Basin and Range physiographic province,
Ordovician species, probably derived from between blocks, but become better sorted
where Paleozoic rocks are exposed along
deeper environments far to the west. and occupy progressively greater propor-
linear mountain ranges, buried deeply in
tions of the volume upward, culminating
intervening valleys (Fig. 2), deformed by
Age and Timing of Alamo Event in the well-graded top.
post-Devonian orogenies, and covered by
Conodont age determinations
Cenozoic volcanic rocks. The area of the
showthat the Alamo event is narrowly Lateral Variations: Zones 1 to 3
Alamo breccia in Figures 1 and 2 is not
bracketed within the middle part of the The Alamo breccia exhibits character-
palinspastically restored.
punctataconodont Zone of Ziegler and istic thicknesses, internal structures, and
Sandberg (1990), as shown in Figures 4 internal variability in each of the three
Stratigraphic Framework
and 5, which represents ~0.5 m.y. of early zones shown in Figures 1, 2, 4 and 6.
From Cambrian into Late Devonian
Late Devonian (Frasnian) time. The Zone 1: Foreslope or Basin Floor.
time, a westward-facing linear carbonate
punctataZone was ~3 m.y. before the Zone 1, along the west end of Tempiute
platform rimmed the west side of the
much-studied late Frasnian mass extinc- Mountain (Figs. 1 and 2), probably
North American craton, trending
tion (Sandberg et al., 1988), and has a extends much farther westward. It is 130
approximately north-south through
biochronologic date of ~13 m.y. before m thick and is composed of a thick (~100
central Nevada (e.g., Poole et al., 1992).
theend of Devonian time. Because the m) turbidite (unit A, described below)
The Alamo breccia is within the shallow-
Devonian-Carboniferous boundary has overlying a thinner debrite (unit B): the
platform facies of the Guilmette Forma-
been variously dated as 340 to 360 Ma, turbidite is generally finer grained than in
tion, except in its westernmost known
theAlamo event was between ~355 and zone 2 to the east. Maximum-sized clasts
exposure at Tempiute Mountain (Figs. 1, 370 Ma. are <5 · 15 m in two dimensions. Zone 1
2) where it is overlain by ~300 m of deeper
is interpreted as an area of platform fores-
water facies of the correlative Devils
DESCRIPTION OF ALAMO BRECCIA lope or basin floor.
GateLimestone (Fig. 4). The Guilmette
The Alamo breccia is a single bed At Tempiute Mountain, twisted and
comprises ~150 shallowing-upward
deposited during one event. Although its fractured bedrock underlies the breccia,
carbonate-platform cycles (Fig. 3)
internal structure varies significantly both laced by an array of sedimentary dikes
averaging ~5 m thick. The Alamo event
laterally and vertically, the most obvious andsills injected with carbonate breccia
slide consumed a stratigraphic interval
trends are decreasing thickness landward and rich in quartz sand grains. The overly-
~60 m thick and containing ~10 to 15
(eastward) and decreasing clast and matrix ing Alamo breccia, in contrast, is relatively
cycles. Cycle tops directly beneath the
sizes (normal grading) upward. For undeformed and weathers as a shear cliff
breccia exhibit dolomitized algal
descriptive purposes, the breccia is divided ~100 m high. The deformation is inter-
laminites, desiccation cracks, and fenestral
into lateral zones 1 to 3, from west to east preted as listric faults that moved and
fabrics that indicate upper-intertidal
(Figs. 1 and 2), and vertical units A to D, rotated during the Alamo event (Fig. 6; see
tosupratidal carbonate platform environ-
from top to base (Fig. 5). Winterer et al., 1991). Dilated fault planes
ments. Lithofacies directly above the
are filled with debris derived from fissure
breccia are more variable and demonstrate
Distribution and Lithology walls, overlying slope deposits, and the
a post–Alamo event westward-dipping
To date, the Alamo breccia is known bypassing breccia. Margins of the fissures
ramp.
at 23 localities spread across ~4000 km2 show liquefaction phenomena similar to
(Figs. 1 and 2). Thickness varies from 130 that of unit D, described below, at the
Conodont Biofacies
m in zone 1 to <1 m in parts of zone 3. baseof the Alamo breccia.
Analyses of 75 conodont samples
If70 m is taken as the average thickness, Zone 2: Seaward Platform.
from the lower part of the Guilmette
then the minimum volume of rock dis- Acrossthebroad area of zone 2, the
Formation in the study area yielded both
placed during the Alamo event is ~280 Alamobreccia averages ~60 m in thick-
paleoenvironmental information, crucial
km3. The total distribution and volume ness, contains discontinuous giant clasts
for understanding the Alamo breccia, and may be much greater; they are not fully as much as 80 · 500 m, and commonly
an exact biostratigraphic date for the bed.
documented because of sparse outcrops exhibits all four vertical units A to D
Conodont samples include 30 from the
and restricted access to the south and described below.
Alamo breccia and 45 from the Guilmette
west. Zone 3: Landward Platform. The
confining beds. The paleoecological
The Alamo breccia is almost exclu- Alamo breccia in zone 3 (<1 to ~10 m
interpretation of the lower Guilmette,
sively carbonate rock (Figs. 7–10). Its thick) may exhibit only a graded turbidite
including the interval of the Alamo
composition is limestone, except for (unit A), with <1-m-diameter clasts, or
breccia (Sandberg and Warme, 1993;
minor synsedimentary supratidal
Warme and Sandberg, 1995), employs
dolostones and local but significant Megabreccia continued on p. 4
GSA TODAY, January 1996 3
Megabreccia continued from p. 3 Vertical Units Units D and C—Detachment
The Alamo breccia is composed of Interval and Megaclasts. Units C and
may be dominantly a debrite (unit B) from one to four vertical units, A to D. D are genetically related, occur together
transitionally overlain by a thin turbidite, They are arranged from top to base as but discontinuously along the base of the
suggesting extensive turbidity-current follows (Fig. 5): unit A: upper turbidite— breccia (Fig. 5), and illustrate the mode of
bypass. The debrite contains tabular clasts present in all zones (1–3); unit B; lower epiplatform slide detachment across zone
up to 30 m long, oriented (sub)parallel to debrite—best developed in zone 2; unit C: 2. Unit D is an unusual, light-gray–weath-
bedding. Zone 3 breccia was stranded basal megaclasts, actually or nearly in ering, calcareous diamictite, <1 cm to ~3
above sea level and subaerially exposed original positions—zone 2 only; unit D: m thick, that developed ~60 m beneath
fora significant time before deposition diamictite under megaclasts—zone 2 only. the contemporary Devonian platform
ofthe next platform cycle. It may be selec-
tively eroded at the top, bleached by Section at VE
dolomitization, or karsted, in contrast A
toits confining beds. Basin StromaRtoipmoroid-coral Lagoon FluctuSahtoiorne zone
Sea level
W ALAMO BRECCIA (AB) E
Zone 1 Zone 2 MUDMOUN Slope Guilmette Formation ~100 m VE ~25
Earlyhassi Ddg SEHDEGLEF Dg SiYmeollnoswo nsl oDpoel-ofsotromneer ~5 km
AB
(80 m) B
Basin Rim Shore
Stromatoporoid-coral Fluctuation zone
punctata ? punctata Sea level
M varcus?? 3Y0 kmS F DDgsi Slope GSuiYmielmollnoeswtote ns l FoDopoerlm-ofsoatrtomionener Figure 6. Interpretation of
processes that produced the
Figure 4.Diagrammatic cross section of Alamo Alamo breccia: A: Rimmed
C
breccia (AB) within the zone 2 shallow-water Seawater replacement Devonian carbonate platform
Guilmette Formation (Dg) and equivalent zone 1 Headwall at 1:1 vertical and horizontal
dUdelpeep pDe-erw vSaoimtneiroa nnDs eMovniild sDd Golealo tvesat roLcinumes e c(sDotonsino) edis o( Dwntdi tSghu)in.b Tztohhnee eM,id- Debrisflow seaward Detachment surface: actual potential scschaaol lewex.i anBgg: g Ptelwaratoft oisoremnts. aCotf: 2fPr5laa:c1ttf uovrreemrsti-
overlain by the basal Guilmette yellow slope-form- along which failure occurred:
ing interval (YSF). Overlying cyclical carbonate Lseisdtrimic efanutaltrsy wdiitkhes and sills listric at the platform edge,
rocks and the Alamo breccia are within the early and nearly horizontal across
Frasnian punctata Zone. Beds beginning 4–10 m the platform. D: Platform fail-
above the breccia are in the Early hassi Zone. D ure: movement along listric
faults created sedimentary
pCuOnNcOtaDtOaN TZONE B ARLEACMCOIA Debrisflow seaward Tsunami dlfaoitkremersa. la Asnsudpb speidlolsrr,ot wcfrkho dmiceh tt ahrceehm peodlavte-d
BIOFACIES UNIT Reduced or vanished and slid seaward, evacuation
SHALLOW AND DEEP caused the sea surface to tilt
LATERAL ZONES
landward. E: Tsunami caused
by bedrock– sea-water
E exchange crossed the platform
MIXED SHALLOW A A Zone 1 Zone 2 Zone 3 and overtopped the headward
(WOITARHND RDOE VDWICEOEIARPNK)ED Tsunamibackwash scbloaidncekt iwnscuaaserhd, wsstehraailwned adereddb. arFi s:t uTflrsobuwindaitmei
along the periphery of the
platform (zone 3), continued
10 m across the detachment area
B (zone 2), and flowed into deep
water beyond the platform
F
(zone 1). G: The final product;
B C Zone 1 Zone 2 Zone 3 the inset shows the giant sand-
SHALLOW waves across the topof the
breccia.
~100 m VE ~25
D ~5 km
SHALLOW
Figure 5.Vertical units A to D, and conodont
biofacies paleobathymetry. Units D and C, if 50 m
present, are together: D is a zone of bedrock
fluidization; C is giant clasts preserved in the pro-
cess of tearing loose and incorporating into the
slide. Unit B is chaotic debrite, beginning at the
base of the breccia where unit C blocks were
removed. Unit A, transitional upward from unit B,
is a well-graded turbidite capping breccia every-
where. Tufted symbols represent stromatoporoids;
cones represent corals concentrated at the top.
4 GSA TODAY, January 1996
surface. The evolution of the diamictite
ispreserved in many localities, where
within a distance of 1 m, intact bedrock
changes laterally to a tight fracture-
Figure 7.Characteristics of
mosaic, a dilated fracture-mosaic, a unit D fluidization, showing
melange of isolated and rotated fragments, nearly intact bedrock (right),
and ultimately to the diamictite (Fig. 7). a mosaic of fractures (center),
Unit D is preserved only where the huge dilation (left-center and
across base), and complete
blocks of unit C are actually or nearly in
fluidization to calcareous
original position over it. Where unit C
diamictite (upper left).
blocks were lifted, fragmented, and incor-
porated into the unit B debrite, unit D was
unprotected and scoured away.
Throughout zone 2, the Alamo
breccia rests at about the same
stratigraphic level, where unit D cuts
indiscriminately along the same or Unit A—Graded Bed. Unit A is a - Upper Boundary
adjacent shallowing-upward carbonate- well-organized turbidite that transitionally Unit A usually exhibits complete
platform cycles, rarely at a bed or cycle overlies the chaotic fabric of unit B. It grading from boulder conglomerate
boundary. The massive unit C blocks, ranges from roughly graded meter-sized upward to calcareous mudstone. In zone
directly above unit D, are (sub)parallel clasts near the middle of the breccia to an 1, the very fine grained top of the breccia
tobedding and have ragged, sharp lateral exquisitely graded 5–30 m interval (100 m merges with overlying deep-water lime-
terminations, beyond which the debrite in zone 1) at the top. The sorting process stones, and in zone 3 the karsted top is
ofunit B extends to the basal plane of left zones rich in domal boulder- to cob- overlain by peritidal carbonate-platform
thebreccia (Fig. 5). ble-sized stromatoporoids and their beds. However, zone 2 is more variable.
Unit B—Chaotic Debrite. A bewil- hydraulically equivalent lithoclasts, frag- Pebble-sized clasts at the top may repre-
dering spectrum of clast sizes, shapes, and ments of tabular stromatoporoids and sent the broad crests of giant sediment
orientations characterizes unit B. The their hydraulic equivalents, and, near the waves, hundreds of meters apart (e. g.,
largest clasts are tabular, tens to hundreds top, concentrations of fragmented corals, Bretz, 1969; Moore and Moore, 1988), per-
of meters in longest dimension, and fully brachiopods, and their equivalents. haps stranded above sea level. They may
encased in unit B matrix, in contrast to Thetopmost 1 m commonly exhibits have separated parallel linear lagoonal
the unit C clasts along the base of the calcarenite cross-bed sets up to 30 cm depressions, evidenced at other localities
breccia. Smaller unit B clasts are tabular high, representing the climbing ripples by bioturbation across the upper contact.
toequidimensional (Fig. 8), and some ofBouma turbidite interval C, overlain
areintricately deformed or preserved in bya thin, finer grained, horizontally lami- EXOTIC COMPONENTS
the process of peripheral fragmentation nated Bouma interval D. At some localities Three significant exotic components
into finer grained matrix. At some locali- the upper 1 m exhibits compound grading occur within the Alamo breccia and are not
ties, multiple slabs >100 m long rode over caused by repeated scour and fill during present in overlying and underlying beds.
one another toward the top of the breccia waning runoff.
and formed logjamlike megafabrics. Beds The top of unit A also contains rare Shocked Quartz Grains
at the base of unit B are preserved in all large clasts, as much as 10 · 30 m, that Insoluble residues of conodont sam-
stages of being ripped up, injected below interrupt the graded profile. They suggest ples from the Alamo breccia concentrate
by matrix, torn away, and incorporated that the underlying debris flow still moved unusual quartz grains (Fig. 10), common
into the breccia. Figure 9 shows a as a viscous mass and that clasts from in zone 1 and progressively scarcer land-
spectacular example. below were buoyed upward and incorpo-
rated into the accumulating turbidite. Megabreccia continued on p. 6
Figure 8.Upper part of the Alamo breccia showing large clasts (beneath the Figure 9.A spectacular example of beds deformed and preserved in the pro-
person) that are transitional to the graded bed above. The small, dark clasts cess of detachment and incorporation into the Alamo breccia, West Pahrana-
are mostly whole orfragmented domal stromatoporoids. West Pahranagat gat Range. A folded package, ~20 m thick, was pried up along the base of
Range. the slide by a huge, chisel-shaped clast moving from the right. The massive
bed over the fold is 30-m-thick graded units B and A. Total breccia thickness
is 60 m.
GSA TODAY, January 1996 5
Megabreccia continued from p. 5 required to fill the space evacuated by the
debris flow. Such superwaves best account
for the exotic deep-water punctata Zone
ward. By optical petrography, these grains
conodonts, which indicate a probable
exhibit one to six sets of internal parallel
water depth of >300 m at the impact site,
lamellae and mosaic extinction, both typi-
and the reworked Ordovician conodonts
cal of shock metamorphism associated
recovered from the breccia. The waves or
with impacts (e.g., Stöffler and Langen-
associated currents may also have trans-
horst, 1994). By transmission electron
ported Ir and shocked quartz from the
microscopy (TEM), they reveal microme-
impact site. An impact could have gener-
ter-scale parallel deformation structures
ated immense runoff from water ejecta
and fractured and rotated crystal frag-
and rainfall from condensed vapor, which
ments between lamellae (Leroux et al., Figure 10.Thin section of a shocked-quartz grain swept debris off large areas of the adjacent
1995). The grains display unusual periph- showing four to six directions of shock lamellae,
craton and flowed across all three lateral
eral studding by crystals of iron oxides trains of inclusions along lamellae, and large dis-
and sulfides (Fig. 10), which may represent placive hematite crystals; the longest grain dimen- zones of the Alamo breccia.
sion is~150 µm.
diagenetic products or even impact phe-
DISCUSSION
nomena. The shocked grains were air- or
water-borne from target rock. Distinctive attributes of the Alamo
breccia separate it from all other known
senting relatively high angle listric faults,
Iridium catastrophic carbonate megabreccias. It
removed lateral support at the platform
Samples from within and above the was first recognized for its anomalous
margin. Horizontal delamination along
Alamo breccia were analyzed for Ir and epiplatform framework. Its shocked quartz
the second set allowed seaward transport
other elements that signify extraterrestrial and Ir strongly suggested an impact
of overlying beds across zone 2 (Fig. 6D).
material (Alvarez et al., 1980). Two sample trigger. Given an impact, seismic shock
(3) The resulting debris flow created a
profiles across the top of the breccia, ~100 could have induced movement on the
westward-facing, flat-floored, epiplatform
m apart in the Worthington Mountains platform-margin listric faults, causing
depression, equal in volume to the
(Figs. 1 and 2), showed similar results. lossof lateral support, and generated hori-
bedrock removed, and induced gravity-
Background Ir in the area is <10 parts per zontal epiplatform fractures, leading to
driven landward-propagated tsunami(s).
trillion (ppT). Sixteen samples spread ±0.5 platform delamination and failure. Radial
By inertia the wave(s) overstepped the
m from the breccia top showed slight Ir shock waves, similar to those accompany-
headward slide scar and flooded the
elevation, averaging 20.1 ppT, the maxi- ing thermonuclear detonations, may have
adjacent platform of zone 3 (Fig. 6E). (4)
mum being 39 ppT. Eight samples from delaminated the platform at a uniform
Backwash stranded the thin breccia across
0.5–1.5 m below the top averaged 69.4 depth below the surface (unit D) and frac-
zone 3, and dumped excess debris as a
ppT, the maximum being 139 ppT. Results tured overlying beds into approximately
seaward-thickening turbidite over the
are not available for samples from 1.5–12 equal horizontal segments (unit C blocks).
debrite of zones 2 and 1 (Fig. 6F). The
m, but six samples from 12–55 m averaged Concurrently, or alternatively, abrupt
debrite was still moving seaward, indi-
only 8.5 ppT. The Ir may have been loading and unloading of superwaves over
cated by absence of a clear debrite-tur-
diagenetically mobilized a few meters platform bedrock, and/or shear from
bidite contact and by the oversized
downward from the breccia top. Alterna- catastrophic wave uprush and backwash,
claststhat were rafted upward into the
tively, the Ir was water-borne to the site caused rapid oscillation of subsurface pore
accumulating turbidite. (5) Air- and/or
(see Displaced Conodonts below) and pressures and induced fluidization along
water-borne shocked-quartz grains, Ir-
accumulated with the thick unit A graded unit D.
bearing particles, and exotic conodonts
bed, making the anomaly very significant Several characteristics of the Alamo
were incorporated into the breccia matrix.
because of the overwhelming carbonate breccia suggest that the impact was
(6) As sea level equilibrated, the
debris that must have greatly diluted any relatively small, located near our study
breccia in zone 3 was exposed (and
accumulating Ir (and shocked quartz). area, and created waves and/or currents
eventually karsted), the shoreline was
that brought a significant volume of
nearthe slide scar, giant sandwaves
Displaced Conodonts debris onto the platform. The reworked
crossed the top and may have separated
Collections from zone 1 and from conodonts and shocked quartz grains are
linear lagoons, and water depths increased
pebbly zones of units B and A in zone 2 progressively less abundant in landward
across zone 2 into Zone 1 (Fig. 6F). The
contain rare reworked Ordovician con- samples, and may have been water-borne.
platform was temporarily converted from
odonts, probably derived from admixed The broad Ir spike 0.5–1.5 m below the
a rim to a ramp. (7) Post–Alamo event
target-rock fragments, and punctata Zone top of the breccia suggests subaqueous
deep-water limestones accumulated in
deep-water conodonts, which were accumulation simultaneous with waning-
zone 1 and outer zone 2, and shallow-
probably preserved in the matrix. Both phase deposition. Most significantly, the
water cyclic deposition eventually
represent exotic elements, likely trans- volume of the Alamo breccia appears too
resumed across inner zone 2 and zone 3.
ported from the west beyond the platform great to have come only from the shallow
The events shown in Figure 6 fail to
margin. submarine slide shown in Figure 6. Zone 3
account for the excess volume of breccia
contains significant breccia volume, but it
that was spread across zone 3, approxi-
DEPOSITIONAL HISTORY is landward of the slide; the depression
mately filled the slide area of zone 2,
across zone 2 is brim-full with breccia, but
Our scenario for the origin of the andleft a 130-m-thick deposit in zone 1.
should have been initially almost empty
Alamo breccia, shown in Figure 6, is We believe that a nearby extraterrestrial
and have temporarily accumulated deeper
consistent with our field observations impact intensified the processes dia-
water sediments; the deposit in zone 1 is
andsample data. (1) The setting for the grammed in Figure 6 and accounts for the
130 m thick, and extends westward for an
breccia is the rimmed, flat-topped, Late volume observed. Superwave uprush and
unknown distance. All these relations sug-
Devonian carbonate platform of Nevada backwash amplified the tsunami generated
gest that catastrophic waves, debris-laden
(Fig. 6, A and B). (2) Movement on two by the debris-flow–sea-water exchange,
setsof fractures (Fig. 6C) detached the enlarged the landward flood and with-
platform. Failure along the first set, repre- drawal, and transported the sediment Megabreccia continued on p. 7
6 GSA TODAY, January 1996
Megabreccia continued from p. 6 REFERENCES CITED orogen, Conterminous U.S.: Boulder, Colorado,
Alvarez, L. W., Alvarez, W., Asaro, F., and Michel, H. V., Geological Society of America, Geology of North
1980, Extraterrestrial cause for the Cretaceous/Tertiary America, v.G-3, p. 9–56.
from a nearby impact, brought the exotic
extinctions: Science, v. 208, p. 1095–1108. Sandberg, C. A., and Warme, J. E., 1993, Conodont
breccia components and required rock Bretz, J. H., 1969, The Lake Missoula floods and the dating, biofacies, and catastrophic origin of Late Devo-
volume onto the platform. channeled scabland: Journal of Geology, v.77, nian (early Frasnian) Alamo Breccia, southern Nevada:
A relatively small, local impact is also p.505–543. Geological Society of America Abstracts with Programs,
v. 25, no. 3, p. 77.
implied, because accelerated biotic Clifton, H. E., editor, 1988, Sedimentologic conse-
extinctions are not documented within quences of convulsive geologic events: Geological Sandberg, C. A., Ziegler, W., Dreesen, R., and Butler, J. L.,
Society of America Special Paper 229, 167 p. 1988, Late Frasnian mass extinction; conodont event
the punctata Zone. However, the Late stratigraphy, global changes, and possible causes, in
Devonian in general and the Frasnian- Cook, H. E., and Mullins, H. T., 1983, Basin margin Ziegler, W., ed., 1st International Senckenberg Confer-
environment, in Scholle, P. A., et al., eds., Carbonate ence and 5th European Conodont Symposium (ECOS
Famennian (F-F) boundary specifically depositional environments: American Association of V), Contribution 1: Courier Forschungsinstitut Senck-
aretimes of extinction and rapid biotic Petroleum Geologists Memoir 33, p. 539–617. enberg, v. 102, p. 263–307.
turnover perhaps unequaled in the Hine, A. C., and eight others, 1992, Megabreccia shed- Sharpton, V. L., and Ward, P. D., 1990, Global catastro-
Paleozoic (e.g., Sandberg et al., 1988; ding from modern, low-relief carbonate platforms, phes in Earth history: Geological Society of America
McLaren and Goodfellow, 1990). The Nicaraguan Rise: Geological Society of America Bulletin, Special Paper 247, 631 p.
v. 104, p. 928–943.
Alamo event occurred ~3 m.y. before the Silver, L. T., 1982, Introduction, in Silver, L. T., and
Hut, P., Alvarez, W., Elder, W. P., Hansen, T., Kauffman, Schultz, P. H., eds., Geological implications of impacts
F-F boundary, but may represent one of E. G., Keller, G., Shoemaker, E. M., and Weissman, P. R., of large asteroids and comets on the Earth: Geological
several sequential events during the Devo- 1987, Comet showers as a cause of mass extinctions: Society of America Special Paper 190, p. xii–xix.
nian (McGhee, 1994) that destabilized Nature, v.329, p. 118–126. Smit, J., Roep, Th. B., Alvarez, W., Montanari, S., and
many existing taxa and rendered them Leroux, H., Warme, J. E., and Doukhan, J. C, 1995, Claeys, P., 1994, Stratigraphy and sedimentology of KT
prone to extinction by the flux of subse- Shocked quartz in the Alamo breccia, southern Nevada: plastic beds in the Moscow Landing (Alabama) outcrop:
Evidence for a Devonian impact event: Geology, v. 23, Evidence for impact-related earthquakes and tsunamis
quent impact, volcanic, eustatic, orother p. 1003–1006. [abs.], in New developments regarding the KT event and
natural events (e.g., Hut et al., 1987). Macdonald, D. I. M., Moncrieff, A. C. M., and Butter- other catastrophes in Earth history: Lunar and Plane-
worth, P. J., 1993, Giant slide deposits from a Mesozoic tary Institute Contribution 825, p. 119–120.
CONCLUSIONS fore-arc basin, Alexander Island, Antarctica: Geology, Stöffler, D., and Langenhorst, F., 1994, Shock metamor-
v.21, p. 1047–1050. phism of quartz in nature and experiment: 1. Basic
The Alamo breccia is one of the McGhee, G. R., Jr., 1994, Comets, asteroids, and observation, experiment, and theory: Meteoritics, v. 29,
largest catastrophic megabreccias known theLate Devonian mass extinction: Palaios, v. 9, p. 155–181.
in terms of its area, thickness, volume, and p.513–515. Warme, J. E., 1994, Catastrophic Alamo Breccia, Upper
clast sizes. In 1990 the breccia was recog- Mcacl Laanrde nb,i oDl.o Jg.i,c aanl dco Gnoseoqdufeelnlocwes, oWf .g Dia.n, t1 i9m90p,a Gctes:ologi- Dmeevnotns iraeng,a rsdoiuntgh ethaset eKrTn eNveevnatd aan [da bost.h],e irn c Nateawst rdoepvheleosp-
nized within a formation that had been Annual Review of Earth and Planetary Sciences, v. 18, inEarth history: Lunar and Planetary Science Institute
well studied by previous researchers. It p.123–171. Contribution 825, p. 127–128.
commonly forms the thickest cliff within Moore, G. W., and Moore, J. G., 1988, Large-scale Warme, J. E., and Sandberg, C. A., l995, The catas-
Guilmette Formation outcrops (Fig. 3) but bedforms in boulder gravel produced by giant waves trophic Alamo breccia of southern Nevada: Record
inHawaii, in Clifton, H. E., ed., Sedimentologic conse- ofaLate Devonian extraterrestrial impact: Courier
was unnoticed or misinterpreted as reef, quences of convulsive geologic events: Geological Forchungsinstitut Senckenberg, v. 188, W. Ziegler
storm, karst, or tectonic breccias, and its Society of America Special Paper 229, p. 101–110. Commemorative Volume.
huge clasts were unwittingly measured Moore, J. G., Normark, W. R., and Holcomb, R. T., Warme, J. E., Chamberlain, A. K., and Ackman, B. W.,
and described as being in situ. 1994, Giant Hawaiian underwater landslides: Science, 1991, The Alamo Event: Devonian cataclysmic breccia
We interpret the Alamo breccia to be v.264, p. 46–47. iAnb ssotruatchtse awsittehrn P rNoegvraadmas:, Gve. o2l3o,g nicoa.l 2S,o pc.i e1t0y8 o.f America
one result of a nearby extraterrestrial Piper, D. J. W., Shor, A. N., and Clarke, J. E. H., 1988,
The 1929 “Grand Banks” earthquake, slump, and Winterer, E. L., Metzler, C. V., and Sarti, M., 1991,
impact. We have yet to understand the turbidity current, in Clifton, H. E., ed., Sedimentologic Neptunian dykes and associated breccias (Southern
details of its genesis—we seek the crater. consequences of convulsive geologic events: Geological Alps, Italy and Switzerland): Role of gravity sliding
Society of America Special Paper 229, p. 77–92. inopen and closed systems: Sedimentology, v. 38,
p.381–404.
ACKNOWLEDGMENTS Poag, C. W., and Aubry, M.-P., 1995, Upper Eocene
impactites of the U.S. east coast: Depositional origins, Ziegler, W., and Sandberg, C. A., 1990, The Late
Supported by grants from the biostratigraphic framework, and correlation: Palaios, Devonian standard conodont zonation: Courier
National Science Foundation (EAR- v.10, p. 16-43. Forschungsinstitut Senckenberg, v. 121, p. 1–115.
9106324) and UNOCAL. We thank B. W. Ptoo olaltee, sFt. DGe.v, oanndia nei gtihmt eo:t Dheervse, l1o9p9m2e, nLta toefs ta Pcroencatimnebnritaanl MAuagnuusstc1ri8p,t 1re9c9e5iv;e adc Mcepatye d1 ,S 1ep9t9e5m; breerv i2si0o,n 1 r9e9ce5i vned
Ackman, J. E. Estes-Jackson, Yarmanto,
margin, in Burchfiel, B. C., et al., eds., The Cordilleran
H.-C. Kuehner, and A. K. Chamberlain for
results of their theses research (Colorado
School of Mines) on the Guilmette Forma-
tion and the Alamo breccia; W. Alvarez,
A.K. Chamberlain, P. Claeys, H. E. Cook, GSA ON THE WEB
P. E. Gretener, D. O. Hurtubise, W. N.
Kent, J. R. Morrow, W. R. Page, W. J. Perry,
F. G. Poole, and many others for field What’s new on the GSA home pageon the WorldWide Web?
assistance and discussions; E. L. Winterer If you haven’t yetconnected to theWeb,the Uniform Resource Locator (URL) is
for interpretation of the detachment zone http://www.aescon.com/geosociety/index.html.
at the base of the breccia; J. L. Butler and
J.R. Morrow for processing conodont If you want to know more about The Publications section has a
samples; H.-C. Kuehner for separating theGSA Employment Service or about monthly table of contents and abstracts of
quartz grains; J. Skok for making thin becoming a GSA Campus Representative, articles for the GSA Bulletin and Geology.
sections; M. Attrep and the late C. Orth checkthe Membership section, which Also in this section is a guide for authors
for providing iridium analyses; H. Leroux also has information on nominating a preparing manuscripts for submission to
for TEM identifications of shocked quartz; member to fellowship and on obtaining GSA publications. GSA Today issues are
and R. R. Charpentier, P. Claeys, W. J. forms for applying to become a GSA posted here for downloading and viewing.
Perry, and E. L. Winterer for manuscript Member or Student Associate. For Congressional Contact Informa-
reviews. See the Geoscience Calendar tion, see the Administration section. n
section for a listing of meetings of general
geological interest.
GSA TODAY, January 1996 7
cutting thin sections. Cutting the rock and
then grinding it down was all hand labor,
but Walcott persisted through several
hundred sections. No trilobite legs were
known up to that time; in 1876 Walcott
Here is the second Rock Star profile (the first appeared in the November 1995 issue proved conclusively from the presence of
of GSAToday). Readers are encouraged to comment on this profile to History of Geology jointed appendages that trilobites were
Division Chair William Brice, Department of Geology and Planetary Science, University of arthropods.
Pittsburgh, Johnstown, Johnstown, PA 15904, [email protected]. To be more involved Late in 1876, Walcott became a
with the history of geology, join GSA’s active History of Geology Division. special assistant to James Hall, the state
paleontologist of New York, and the
—Robert N. Ginsburg, for the GSA History of Geology Division second most prolific paleontologist in the
world. Hall had known Walcott for years
and kept stating that he would buy
Walcott's collection. R. P. Whitfield had
From Farmer-Laborer to Famous Leader: left, and Hall was in need of an assistant,
especially to run operations during 1877
Charles D. Walcott (1850–1927)
when he went to Europe. Another volume
of the Palaeontology of New York had tobe
seen through the press, and the collections
and exhibits in the New York State
Ellis L. Yochelson A young Charles
Museum were in terrible shape. Hall was
U.S. Natural History Museum, Doolittle Wal-
autocratic and operated generally by ter-
Washington, DC 20560 cott. The back
ofthis picture, rorizing his assistants; Walcott is the only
copied from his one who did not coauthor with Hall and
In today’s vernacular, Charles D. daily pocket who continued to publish under his own
Walcott was probably a high school diary, bears the name.
date 1873. At
dropout. Without formal scientific train- Walcott was employed for little more
this time Wal-
ing, and Horatio Alger–like, he became cott was living than a year, but he remained in Albany,
anoutstanding scientist, member and on the Rust where he learned a great deal from study-
president of the National Academy of farm, east of ing Hall's collections and library; he also
Science, director of the Geological Survey, Trenton Falls, learned practical politics from lobbying
New York, and
and secretary of the Smithsonian forHall in the state legislature. By good
collecting fossils
Institution. fortune, he was hired in July 1879, as one
commercially
Walcott became interested in collect- with William of the original members of the new United
ing local fossils before he was a teenager; Rust. Photographs of Walcott are easy to date rela- States Geological Survey. Hall had written
itseemed to be the thing boys did in tively, because a few years after 1873, he grew a a letter of support for Walcott, but it was
Utica, New York. His father died when mustache. Subsequently, the amount of hair on R. P. Whitfield who obtained the position
both the top and bottom of his head was less in
hewas two. The whole family was in the for him.
each succeeding photograph.
cotton milling business, and there is no Walcott's first year was as a temporary
indication that Walcott received any geological assistant at $50 per month. He
guidance into science from any of his were so good that in 1873 they sold one worked on the Colorado Plateau and
relatives. Fortunately he met a retired collection to Louis Agassiz, the preemi- found the position of the Paleozoic-Meso-
curator from the New York State Museum nent naturalist of the day, for what would zoic boundary in the course of measuring
who had moved to Utica, and it was be $70,000 in 1995 dollars. In 1879, a section from the Cenozoic-Mesozoic
Colonel Jewett who first gave him a Alexander Agassiz, Louis's son, paid them boundary in southern Utah down to the
notion of what fossils meant. It was the modern equivalent of $80,000 for Devonian at Kanab Creek in the Grand
equally fortunate that at age twelve, another collection.
Walcott started spending summers at Walcott spent a week at the Museum
nearby Trenton Falls, New York, helping of Comparative Zoology at Harvard in
out on a farm during the Civil War. To September 1873, unpacking and arranging
thepaleontologist interested in the Middle the fossils he sold. This was his total
Ordovician, Trenton Falls is another name involvement with college, but Professor
for heaven, for the rocks are crowded with Agassiz impressed Walcott with the impor-
fossils. Every rock in the farm fields was tance of learning about the appendages of
fossiliferous. trilobites. Later, in the course of collecting
Walcott's schooling at the Utica Free at a quarry a few hundred yards from the
Academy, where there were only two or farm house, Walcott noticed fragments
three teachers, ended when he was 18, that might have been of trilobite legs and
and he may not have graduated; the hit on the notion of studying them by
records of this period are lost. He tried
working in a hardware store for a year, and
hated it. At age 20 he went to live with A trio at Rust farm, Trenton Falls, New York. The
William Rust, sometimes paying board center figure with the black beard and black hat is
and sometimes helping with the farming, the young C. D. Walcott. The dandy on the right side
which included spreading manure from of the picture is questionably identified as A. C. Peale,
a geologist with the Hayden Survey and,later, the U.S.
the cows. Rust, a farmer who also was
Geological Survey. The bearded older man is unknown,
interested in the local fossils, showed
but he could beone of theelder members of the Rust fam-
Walcott where and how to collect and ily. Smithsonian Institution Archives, Record Unit 95, Box 24,
prepare. As collectors, Walcott and Rust No. SA 187.
8 GSA TODAY, January 1996
Canyon, more than two miles of rock. His
work was so satisfactory that he was given
a permanent position as assistant geologist
and a 100% raise, to $100 a month.
Although Walcott made contributions to
paleobiology, throughout his career with
Charles Doolittle Walcott, in
the USGS his efforts were directed to
1913, posing with a pry bar in
biostratigraphy—advising field geologists
the fossil quarry he opened to
on the age of sedimentary rocks by collect from the Middle Cam-
studying fossils. brian Burgess Shale. In five sea-
If there was ever a geologist who sons, he obtained more than
deserves to be better known in America, 50,000 specimens from this
locality, by splitting slabs day
and incidentally one who had the most
after day. In 1907, Walcott
inappropriate middle name, it is Charles began a systematic study of the
Doolittle Walcott. In 15 years, he wrote a Precambrian and lower Paleo-
major monograph on Paleozoic fossils of zoic rocks of western Canada.
the est, resolved the fundamental strati- His discovery of spectacular fos-
sils in 1909 distracted him for
graphic problems of the position of the
some years from his basic pro-
"Taconic" system, confirmed the sequence
gram, but he was able to study
of trilobite zones in the Cambrian, and the Cambrian rocks and fossils
summarized the stratigraphy of the of the region and made a start
Cambrian System of North America. on the Early Ordovician. His last
In 1894, Walcott became the third field season was in 1925.
director of the U.S. Geological Survey; he
served for 13 years in this post. Toward
theend of his directorship, John Wesley
Powell had gotten crosswise with
Congress. The Congress slashed the
budget of the Geological Survey and then,
when that did not work, they slashed the
salary of Powell. When Walcott took over,
USGS then expanded into work on water bring this treasure trove back to civiliza-
it was at a lower salary than Powell had
resources, more topographic mapping, and tion. He described the fossils, both animal
received and it was to head a nearly bro-
study of the national forests. While Wal- and plant, of the incredible deposit, and
ken organization. In just a couple of years,
cott was administering all these different then continued on with the stratigraphy
Walcott had the agency back on track. The
activities, he was still an active scientist. and paleontology of the overlying beds.
He wrote on Cambrian jellyfish and Cam- Walcott had at his disposal the Smith-
brian trilobites from China, and he made sonian Miscellaneous Collections and was
significant advances in the understanding never one to waste an opportunity. He
of Precambrian life. During this interval, filled five entire volumes of that series.
Walcott also did most of the preliminary James Hall was the most prolific writer
study for U.S. Geological Survey Mono- onAmerican fossils, but if Walcott was
graph 51, Cambrian Brachiopoda, for which notsecond, I cannot imagine who
the volume of plates is as thick as the deserves that place.
volume of text. Also during this time, Besides doing research part-time
Walcott essentially ran the Carnegie Insti- while running the Smithsonian Institu-
tution of Washington (1902–1905) and tion, Walcott had other duties. After 10
deserves full credit for establishing the years as vice-president of the National
Carnegie Institution of Washington Academy of Sciences, he became president
Geophysical Laboratory. (1916–1922). Before the start ofWorld
In 1907, Walcott became the fourth WarI, G. E. Hale, the astronomer, and
secretary of the Smithsonian Institution. Walcott had formed theNational Research
He immediately began a program of field Council, and theyapplied science to
investigations, mainly in Alberta and warfare, setting apattern for the years
British Columbia, and he was in the ofWorld War II, 1941–1945.
fieldevery year until 1926. His research Quite apart from all this, Walcott
program was essentially the same as decided that research on aviation was
whenhe was at the USGS: to make known lagging in America. He steered the
the stratigraphy and paleontology of the National Advisory Committee for
pre-Trenton rocks. Aeronautics through Congress and was
Isotelus gigas (DeKay) from the Rust farm.
Thematrix is late Middle Ordovician limestone Walcott worked long and hard on the itschairman for years. NACA is no more,
ofthe Trenton Group. This beautifully preserved stratigraphy and paleontology adjacent to but it laid the foundation for the National
trilobite is representative of the quality of the fos- Banff, Alberta, though he had two signifi- Aeronautics and Space Agency. If there is
sils that Walcott and Rust sold to Louis Agassiz. On cant distractions from his field program. agreat-grandfather of the space age, it
the matrix are tool marks, an indication of some
First, he was the first geologist to attempt isthe paleontologist Charles Doolittle
of the careful preparation done; in later years, geologic investigations around Mount Walcott.n
William Rust worked for the U.S. Geological Sur-
vey as both a collector and preparator. Walcott's Robson, the highest part of the Canadian
Rust farm trilobites, which had the appendages Rockies. Second, he found the Middle For more on Walcott:
preserved, were more significant biologically than Cambrian Burgess Shale and its incredible Yochelson, E. L., 1967, Charles Doolittle Walcott,
this specimen, but they were studied by cutting biota. Walcott collected for five seasons to 1850–1927: National Academy of Sciences Biographical
thin sections and are not photogenic. Memoirs, v. 39, p. 471–540.
GSA TODAY, January 1996 9
1995 PRESIDENTIALADDRESS
If Geoscientists Went on Strike, Would Anybody Notice?
David A. Stephenson
South Pass Resources, Inc., Scottsdale, Arizona
“To retain the respect of the community
and to retain influence for good, we must
When it was obvious a year ago
be able to justify the existence of a society
that the eminently fair GSA system
devoted to investigation…. The question
ofelecting officers would ensure my
‘Cui bono?’ [to whose benefit] will be asked,
ascendancy to the presidency, I began
and the answer cannot be avoided.”
planning what my Presidential
Address should focus on as a theme. “… the Society must have more to do with
Itwas my intent to develop a scien- the outside world … if the outcome for sci-
tific debate on the concept of “con- ence is to be what it should be.”
nate water.” I planned to structure for
John J. Stevenson
you therole of ground-water flow sys-
1898 GSA Presidential Address:
tems increation of saline-water envi-
“Our Society”
ronments in deep sedimentary basins.
Ialso considered speaking about the
“science” of water-witching, using
What is striking to me about Stevenson’s words is they came
ample demonstrations that would have included audience
just 10 years after GSA was founded for the promotion of pure
participation.
science. “We must justify our existence … Cui bono… the answer
These thoughts became academic, for I was soon immersed
cannot be avoided.” Let us look quickly at what others havesaid:
in the geopolitical issues that dominated much of this year. It
became obvious that we in the geosciences have a monumental
void; one that should receive our utmost attention. In January,
“The support of the geologist depends
the outlook for a healthy community was rather dismal. There
onpublic appreciation of the value of
was much concern for the survival of a number of key activities,
hisservices.”
including the U.S. Geological Survey. There was frenzied activity
to promote the geosciences, and the outlook brightened. Charles D. Walcott
However, a postmortem on 1995 would reveal a number 1901 GSA Presidential Address:
ofunresolved issues: even though representatives of this Society “Outlook of the Geologist in America”
joined others to exert damage control in meetings with Congress
and other public representatives, the fateful hour is not the time
to educate Congress or any other portion of the public. “The spirit of the hour seems to impel
Questions remain. Can we identify the right question and me to … portray … some part of the
implement solutions so that our community does not continue obligation of the State to our science
in a crisis mode? I believe an appropriate question is: “If geoscien- and the responsibility of this science to
tists went on strike, would anyone notice?” the State.”
Unfortunately, we do not have the luxury of geologic time John M. Clarke
on our side on this issue. It would be a fair conclusion to state 1916 GSA Presidential Address:
and accept that the “public” has precious little knowledge of “The Philosophy of Geology and the
what we do, how we do it, and why we do it. I’m afraid that Order of the State”
fewwould notice were we to strike.
The void that I mentioned deserves our attention. It has to
do with our relationship to the public. It is this void that Iwish
“More clearly than ever before, is it
to emphasize, recognizing that there is not universal acceptance
necessary for us to view world affairs,
of GSA’s role relative to addressing the void. The public is not
andin them our own connections….”
particularly friendly to thesciences at this time. In fact, the
geosciences community is the recipient ofa disproportionate John C. Merriam
share of this unfriendliness. 1919 GSA Presidential Address:
Part of the problem is that we hold a time-honored belief “Earth Sciences as the
that the search for geologic understanding deserves a high-prior- Background of History”
ity position relative to political attractiveness. We haven’t paid a
whole lot of attention to a politician’s viewpoint. We have not
paid much attention to a premise that we are citizens with a
“Those who have a knowledge of geol-
special responsibility to the public.
ogy have a vast educational advantage
How am I using this word “public”? Hopefully, not as “a
over those who have none.”
public nuisance,” butmore as “conducted in public” or “tomake
public” (to cause to become generally known). “As geology becomes rounded out, …
It was decided to look to history for what other GSA presi- it will have surpassing value in the
dents have said. A surprising number of the 106 previous presi- education of mankind.”
dents have implored this Society to be involved with the public. R. A. F. Penrose, Jr.
The first to do so was John Stevenson, president #10. 1930 GSA Presidential Address:
“Geology as an Agent in Human Welfare”
10 GSA TODAY, January 1996