Stratigraphic investigations of carbon isotope anomalies and
Neoproterozoic ice ages in Death Valley, California
Frank A. Corsetti†
Department of Earth Sciences, University of Southern California, Los Angeles, California, 90089-0740, USA
Alan J. Kaufman‡
Department of Geology, University of Maryland, College Park, Maryland 20742-4211, USA
ABSTRACT
INTRODUCTION
An unusual richness of biogeochemical
events is recorded in Neoproterozoic–
Cambrian strata of the Death Valley region, California, United States. Eight negative carbon isotope (d13C) excursions are
found in carbonate units between 1.08 Ga
and the Precambrian/Cambrian boundary;
four of these excursions occur in carbonates
that contain textural features similar to
those found globally in postglacial ‘‘cap
carbonates’’ (including one or more of the
following: laminite with rollup structures,
apparent ‘‘tube rocks,’’ seafloor precipitates, and sheet-crack cements). However,
only two of these units, the Sourdough limestone member of the Kingston Peak Formation and the Noonday Dolomite, rest directly upon glacial strata. The basal Beck
Spring Dolomite and the Rainstorm Member of the Johnnie Formation each contain
negative excursions and cap-carbonate–like
lithofacies, but do not rest on known glacial
deposits. If the negative d13C excursions are
assumed to record depositional processes,
two equally interesting hypotheses are possible: (1) The Death Valley succession records four glacial pulses in Neoproterozoic
time, but glacial units are not preserved at
two stratigraphic levels. (2) Alternatively,
other global oceanographic processes can
cause negative excursions and cap-carbonate–
like facies in addition to, or independent of,
glaciation.
The dawn of the Phanerozoic is one of the
most fascinating times in the development of
the biosphere (Cloud, 1988; Knoll and Walter,
1992; Lipps and Signor, 1992). With the advent
of new analytical techniques (isotopic and molecular, for example), incredible fossil discoveries (e.g., metazoan embryos, Xiao et al.,
1998), and a broadened interest in early animal
evolution, the Neoproterozoic has become a focal point for integrated geobiological studies.
The Neoproterozoic is characterized by climate
extremes that may be unrivaled in the Phanerozoic (e.g., snowball Earth) (Kirschvink, 1992;
Hoffman et al., 1998b). Speculations with regard to the effects of this severe climatic deterioration on life (recorded in the geologic record as low-latitude glacial diamictites, extreme
perturbations in the biogeochemical cycles of
carbon and sulfur, and unusually textured carbonate seafloor cements) have been proposed
(Harland and Rudwick, 1964; Kirschvink,
1992; Kaufman et al., 1997b; Hoffman et al.,
1998b; Knoll and Carroll, 1999). These speculations are based, however, on chronostratigraphic frameworks that are limited in biostratigraphic resolution and radiometric age
constraints, as well as omissions in stratigraphic records characteristic of continental-margin
successions.
In carbonate-dominated strata, temporal
variations in carbon, sulfur, and strontium isotope compositions of well-preserved samples
hold great promise for regional correlation.
Global correlation is more problematic insofar
as siliciclastic strata dominate many key successions, thus impeding the construction of
continuous isotope trends regardless of the degree of preservation. The large number of
publications purporting a composite ‘‘Neoproterozoic reference section’’ is testament to the
Keywords: chemostratigraphy, Death Valley, Earth history, glaciation, Neoproterozoic, stratigraphy, carbon isotopes.
E-mail: [email protected].
E-mail: [email protected].
†
‡
GSA Bulletin; August 2003; v. 115; no. 8; p. 916–932; 11 figures; 1 table; Data Repository item 2003105.
916
For permission to copy, contact [email protected]
q 2003 Geological Society of America
general acceptance of isotope stratigraphy as
a critical tool in this ancient interval. Unfortunately, it is also a manifestation of the ambiguity inherent in constructing global paradigms from local systems. This is the
‘‘pre-Cambrian correlation problem’’ in sum:
the absence of rigorous biostratigraphic control or high-resolution radiometric age dates,
the eccentricities of each sedimentary basin
may be given global significance with few independent tests to evaluate the purported significance. Excellent preservation (e.g., lack of
metamorphism, structural simplicity, and good
exposure) is not a guarantee of stratigraphic
completeness. Thus, researchers working on
variably segmented and preserved stratigraphic successions around the world disagree on
something as basic as the number of glaciations in Neoproterozoic time (e.g., Kaufman
et al., 1997b; Hoffman et al., 1998b; Saylor et
al., 1998; Kennedy et al., 1998; Crowell,
1999; Knoll, 2000; Brasier et al., 2000; Walter
et al., 2000).
The Death Valley area of eastern California/
western Nevada, United States, contains a
thick, intensely studied stratigraphic package
spanning from late Mesoproterozoic through
middle Paleozoic time (Cloud, 1973). The
area is well known for its structural complexity and long tectonic history; the succession is
replete with stratigraphic breaks of unknown
duration. Few radiometric dates are available
and, except for stromatolites and rare microfossils, the Proterozoic sedimentary rocks are
poorly fossiliferous. Accepting these caveats,
Death Valley strata nonetheless provide an opportunity to study the extreme climatic perturbations recorded in Neoproterozoic time.
The regional sequence stratigraphy is well
documented, and the physical succession of
strata is relatively unambiguous. If one works
around the moderately intricate structural re-
DEATH VALLEY NEOPROTEROZOIC CHEMOSTRATIGRAPHY
lationships in the area, it is possible to walk
though the entire package, from late Mesoproterozoic through Ordovician strata (see volumes edited by Cooper et al. [1982] and Cooper and Stevens [1991]). Notably, glacial
diamictites (Miller, 1982, 1983, 1985, 1987;
Prave, 1999) are found at several stratigraphic
horizons and are overlain by texturally and
isotopically unique ‘‘cap carbonates’’ (Corsetti, 1998; Prave, 1999; Corsetti and Hagadorn,
2000; Corsetti et al., 2000). In this paper, we
present a basin-scale integrated stratigraphy,
supported by high-resolution isotopic analysis
of thick carbonates in multiple equivalent sections along and across the ancient depositional
system. It is important to note, however, that
in certain portions the succession is predominantly siliciclastic. The isotopic records are
therefore discontinuous through some stratigraphic intervals. Although the clear trends
defined by closely spaced samples are testament to the excellent preservation of depositional carbon isotope (d13C) variations, sample
alteration is addressed by the use of petrographic, cathodoluminescent, and/or geochemical screens (see Kaufman and Knoll
[1995] for a discussion of the methods). The
relative sequence of environmental and climatic events preserved in Death Valley will
be used to test predictions from other Neoproterozoic basins worldwide.
Geologic Background
The Death Valley section consists of (in ascending order) the Pahrump Group (the Crystal Spring Formation and Beck Spring Dolomite, and the Kingston Peak Formation), the
Noonday Dolomite, the Johnnie Formation,
the Stirling Quartzite, and the Wood Canyon
Formation (which contains the Precambrian/
Cambrian boundary) (Stewart, 1966, 1970;
Wright et al., 1974a; Corsetti and Hagadorn,
2000) (figs. 1A, 1B). The Death Valley section
is locally .6 km thick, but averages ;4.5 km
(Stewart, 1966, 1970; Wright et al., 1974a).
Crystal Spring Formation
The Crystal Spring Formation, the basal
member of the Pahrump Group, is a mixed
siliciclastic-carbonate succession that ranges
in thickness from ;450 to 1200 m (Roberts,
1982). The Crystal Spring rests on 1.7 Ga
metamorphic basement intruded by 1.4 Ga
granitoid rocks (Labotka, 1978). Diabase sills
dated at ca. 1.087 Ga intruded the lower part
of the formation (Heaman and Grotzinger,
1992). In some areas, the intrusions reacted
with the carbonate rocks and formed the distinctive talc deposits that are apparent around
the Death Valley area (Wright and Troxel,
1965). An angular unconformity has been recognized within the formation above the diabase (Mbuyi and Prave, 1992, 1993). Carbonates below and above this intrusion contain
stromatolites of limited biostratigraphic utility
(Awramik et al., 2000). Our study focuses on
the ‘‘upper units’’ (Wright et al., 1974a; Roberts, 1982), consisting of a coarsening-upward
sequence of shale-siltstone-quartzite with minor carbonate near the base and at the top
(;150 m).
Beck Spring Dolomite
The basal Beck Spring Dolomite records a
flooding event, as the underlying coarsegrained siliciclastic and carbonate rocks of the
upper Crystal Spring Formation are overlain
by very finely laminated carbonates of the
Beck Spring Dolomite; some have considered
this contact conformable (Marian, 1979),
whereas others have considered it a disconformable sequence boundary (Mbuyi and
Prave, 1992, 1993). The lower 200 m contains
finely laminated dolostone that displays abundant soft-sediment deformation, rollup structures (Fig. 2A), breccias, and some megabreccias, interpreted as slope deposits. The middle
100 m contains oolitic packstones, grainstones, and stromatolites, and the remaining
Beck Spring Dolomite contains mostly cherty
grainstone with some stromatolites. The oolitic units commonly contain ‘‘giant ooids’’
characteristic of late Precambrian time (Fig.
2B). The formation represents typical shoaling
and progradational carbonate-platform sedimentation; deeper-water sedimentation is recorded in the lower part, and shallow subtidal
to peritidal parasequence sets constitute the
upper part. A deep karst surface is present at
the top of the main body of the Beck Spring
Dolomite, and several beds of thin carbonates
in shale are present between the main body of
the Beck Spring Dolomite and the overlying
siliciclastic-dominated Kingston Peak Formation. We follow recent convention and denote
these the ‘‘transition beds’’ (e.g., Link et al.,
1993). However, the karst may suggest a more
significant break at this stratigraphic position;
thus, the transition beds may not be depositionally intermediate.
The age of the Beck Spring Dolomite is unknown, but certainly postdates 1.08 Ga. The
vase-shaped microfossil Melanocyrillium
(Horodyski, 1987) is found in the transition
beds. It is not known whether Melanocyrillium or other vase-shaped microfossils have
correlative potential; similar taxa do occur in
the Chuar Group in the Grand Canyon area
beneath an ash dated at 742 6 6 Ma (Porter
and Knoll, 2000; Karlstrom et al., 2000; Dehler et al., 2001). If this regional correlation
holds, it would constrain the Beck Spring Dolomite to be older than ca. 742 Ma (but younger than 1.08 Ga). However, vase-shaped microfossils have been interpreted to represent
testate amoebae (Porter and Knoll, 2000), an
extant group, and thus the correlation is
tenuous.
Kingston Peak Formation
The Kingston Peak Formation is a heterolithic unit containing turbidites, shallowmarine and possibly fluvial sandstones, siltstones, conglomerate, dropstones (Fig. 2C),
diamictite, ironstone, organic-carbon–rich
laminated carbonates, and volcanic rocks
(Troxel, 1982b; Miller, 1982, 1983, 1985). Facies change rapidly across the basin, indicating deposition in an actively extending tectonic environment (Wright and Troxel, 1966;
Miller, 1985). The correlations proposed by
Prave (1999) and the informal terminology
proposed by Miller (1982) form the framework within which we interpret the Kingston
Peak Formation as a whole to contain two glacially derived intervals each overlain by carbonates. The lower diamictites of the Surprise
member (including an iron-rich dropstoneladen mudstone facies) are overlain by the
finely laminated Sourdough limestone member. The upper-basement and quartzite-clast
diamictites of the Wildrose member are overlain by the Noonday Dolomite. At Goler
Wash, we have observed an iron-rich dropstoneladen facies above the basement-clast diamictite immediately beneath the Noonday Dolomite contact, as well. Other thin carbonates
are known from the Kingston Peak Formation:
A thin, microfossiliferous, wavy-laminated
and oncolite-bearing unit is known from within or capping the lower diamictites in the
Kingston Range (Pierce and Cloud, 1979;
Troxel et al., 1987; Awramik et al., 2000). We
interpret this unit as a probable onshore equivalent to the Sourdough limestone member. An
unnamed limestone unit located stratigraphically above the Sourdough limestone member
and below the Noonday Dolomite in the Panamint Range area contains shallow-water carbonate lithofacies, including oncolites. Other
workers may have mistaken this unit for the
Noonday Dolomite (see Prave, 1999).
Despite the presence of a moderately diverse microfossil assemblage of nondiagnostic
Proterozoic age (Pierce and Awramik, 1994),
no independent age constraints are currently
available for the Kingston Peak Formation.
However, the presence of diamictite, volcanic
rocks, ironstone, and evidence for syndeposi-
Geological Society of America Bulletin, August 2003
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CORSETTI and KAUFMAN
tional normal faulting (e.g., Miller, 1985) led
some workers to correlate the Kingston Peak
Formation with the rift-related Rapitan Group
in northwest Canada (ca. 750 Ma) (Stewart
and Poole, 1974; Stewart and Suczek, 1977).
Prave (1999) suggested that the lower part of
the formation may correlate to these units, but
that the upper part may be much younger (ca.
600 Ma) (Walker et al., 1986). This interpretation would imply that .100 m.y. of time
would be represented by the relatively thin
stratigraphic package between the Sourdough
limestone member and the Noonday Dolomite
(an alternative view is presented subsequently
herein). The relationship between the Kingston Peak Formation and overlying strata is
complex: An angular unconformity is present
in many areas (Wright and Troxel, 1966;
Christie-Blick and Levy, 1989), whereas the
contact appears genuinely conformable in other areas (Prave, 1999; Corsetti et al., 2000).
Noonday Dolomite
The Noonday Dolomite exhibits a myriad
of unusual carbonate textures that are common
in carbonates that cap Neoproterozoic glacial
diamictites worldwide. At the base, ubiquitous
isopachous cements line horizontal sheet
cracks and ‘‘pseudostromatactis’’ vugs (Fig.
3). The lower part of the formation has been
interpreted to contain large domes (up to
;200 m in diameter) interpreted as megastromatolites (Wright et al., 1974b, 1978; Cloud
et al., 1974; Williams et al., 1974a, 1974b)
that approach the shelf margin; basinal facies
are found to the west in the equivalent Ibex
Formation and include megabreccias, carbonate turbidites, and laminites (Troxel, 1982a).
Tubular (or apparently tubular) structures of
probable biologic affinity (Marenco et al.,
2001), several centimeters in diameter and up
to 100 cm in length, are found to be subvertical within the domes (Cloud et al., 1974;
Wright et al., 1978) and in other areas without
purported domal buildups (Corsetti et al.,
2000) (Fig. 3). These same structures have
since been interpreted to represent gas escape
structures from methane cold seeps (Kennedy
et al., 2001b). In addition, crystal ‘‘bushes’’
are also recognized on the extreme flanks of
the domes from the middle part of the lower
Noonday Dolomite. They are poorly pre-
Figure 1. (A) Stratigraphic column for the
Death Valley Succession (after Stewart
[1970], Wright et al. [1974a], and Awramik
et al. [2000]). (B) Key to lithologic symbols
used throughout.
M
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Geological Society of America Bulletin, August 2003
DEATH VALLEY NEOPROTEROZOIC CHEMOSTRATIGRAPHY
ted structure interpreted as a possible
calcimicrobe) was consistent with a Riphean
age (ca. 900–700 Ma). Previous chemostratigraphic studies have alternately correlated the
Noonday Dolomite with Sturtian (ca. 700 Ma;
Corsetti, 1998; Corsetti et al., 2000) and Varangian deposits (ca. 600 Ma; Prave, 1999),
respectively.
Figure 1. (Continued.)
served, and their affinity is not known, but the
external morphology is not unlike a calcareous
algae (cf. Epiphyton) rather than abiotic crystal fans. Sandy dolomite dominates the upper
part of the Noonday Dolomite at most localities (Stewart, 1970). The lower and upper
parts of the Noonday Dolomite are separated
by a notable sequence boundary with at least
tens of meters of local relief (Summa et al.,
1991, 1993a, 1993b; Summa, 1993) and possibly as much as 100 m of relief. The contact
between the Noonday Dolomite and the overlying Johnnie Formation has been considered
conformable (Stewart, 1970; Benmore, 1978;
Christie-Blick and Levy, 1989). However,
Summa (1993) demonstrated the presence of
karst at the top of the Noonday and hypothesized a significant stratigraphic break of unknown duration.
The age of the Noonday Dolomite is uncertain, although Wright et al. (1978) suggested that the presence of Dzhelindia (a clot-
Johnnie Formation
The Johnnie Formation contains mixed
siliciclastic-carbonate lithofacies interpreted
to represent shallow-marine deposition with
minor fluvial influence (Stewart, 1970; Benmore, 1978; Summa et al., 1991, 1993a,
1993b; Summa, 1993). Stromatolites are
abundant in the carbonate units (Benmore,
1978). Several regionally persistent shallowingupward sequences truncated by fluvial quartzites and/or karstic carbonates are present within the Johnnie Formation, separated by
paraconformities of unknown temporal magnitude (Summa, 1993). A regionally extensive
marker bed, the Johnnie oolite, occurs in the
upper part of the formation (Rainstorm Member, e.g., Stewart, 1966, 1970) (Fig. 4). Summa (1993) and Summa et al. (1994) suggested
the presence of a major sequence boundary at
the base of the laterally persistent oolite marker bed. Although no incised valleys are known
from this stratigraphic level, the clear juxtaposition of deeper-water facies (below storm
wave base) beneath the shallow-water, crossbedded oolite suggests a depositional hiatus.
On the craton, karst has been recognized at
the base of the oolite (C. Fedo, 2001, personal
Figure 2. (A) Rollup structures from the basal Beck Spring Dolomite, Alexander Hills section (see location in Fig. 6). (B) Giant ooids
characteristic of the Beck Spring Dolomite. These occur as clasts in the overlying Kingston Peak Formation and the Rainstorm Member
of the Johnnie Formation. (C) Large dropstone of Beck Spring Dolomite within the iron-rich turbidites of the Kingston Peak Formation,
Sperry Wash, eastern Death Valley.
Geological Society of America Bulletin, August 2003
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CORSETTI and KAUFMAN
Figure 3. (A) Vertical tubular structures in the upper part of the Lower Noonday Dolomite
(Winters Pass Hills section). (B) Cement-filled vug (cf. ‘‘sheet-crack cement’’), Noonday
Dolomite, southern Nopah Range section 1. See locations in Figure 6.
commun.). The post-oolite Rainstorm Member
contains a sequence of interference-ripple
cross-laminated quartzite, siltstone, and shale
with local preservation of thick carbonates.
The carbonates are distinctively pink, continue
for .50 m in some exposures, and contain
intraclastic or peloidal grainstones punctuated
by beds characterized by calcite pseudomorphs of small aragonite crystal fans that apparently grew on the ancient seafloor (Fig. 4).
In addition to several smaller-magnitude sequence boundaries, a major incision surface
cuts into the upper part of the Johnnie Formation (Summa et al., 1991, 1993a, 1993b,
1994; Summa, 1993) (Fig. 4). The surface removes the Johnnie oolite at certain localities
along section (implying up to 150 m of erosional relief) (Summa, 1993; Levy et al.,
1994; Charlton et al., 1997). Incised-valley fill
consists of subangular blocks of varied lithology in a sandstone or mudstone matrix and
Figure 4. (A) The Johnnie oolite and pink, postoolite Rainstorm Member carbonate beds (southern Nopah Range section 2). (B) Distinctive Beck Spring Dolomite giant oolite clast within the incised-valley fill, Rainstorm Member of the Johnnie Formation (southern
Nopah Range section 1). (C) Seafloor precipitates, Rainstorm Member, Johnnie Formation. (D) Clast of distinctive lower Johnnie
Formation stromatolites, now upside down, in incised-valley fill (same as B).
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Geological Society of America Bulletin, August 2003
DEATH VALLEY NEOPROTEROZOIC CHEMOSTRATIGRAPHY
Figure 5. Generalized tectonic setting for the Neoproterozoic Death Valley succession
(modified from Awramik et al., 2000). The pre–Kingston Peak units are commonly preserved in down-dropped basins in response to the rifting of the North American craton
in Neoproterozoic time.
includes large clasts of the Johnnie oolite,
lower Johnnie Formation stromatolites, and
Beck Spring Dolomite (Fig. 4). It is notable
that readily identifiable clasts of lower Johnnie
and Beck Spring lithotypes are found within
the incised-valley fill in the Nopah Range, potentially indicating many kilometers of regional uplift and erosion during or near upper
Johnnie time (cf. Summa, 1993) (see subsequent discussion). The remaining Johnnie Formation consists of featureless dark green mudstones (Moore, 1974; Charlton et al., 1997)
that become progressively sandy up section to
the contact with the overlying Stirling Quartzite. A finely laminated micritic limestone is
also found within this interval.
The occurrence of the stromatolite Boxonia
is consistent with a ‘‘Vendian’’ age for the
Johnnie Formation (Cloud and Semikhatov,
1969). The stratigraphic position of the purported Boxonia has, however, not been confirmed, as it is found as clasts in the incisedvalley fill. Christie-Blick and Levy (1989) and
Abolins et al. (2000) tentatively correlated the
large incision to sea-level drawdown associated with ‘‘Marinoan’’ age glaciation on the
basis of sequence stratigraphic correlation
with units in Utah (see discussion in Corsetti
et al., 2000), rather than regional uplift (e.g.,
Summa, 1993). If correct, preincision beds are
likely to be older than 580 Ma, the age of
postincision volcanic rocks of the Brown’s
Hole Formation, Utah (Christie-Blick and
Levy, 1989). Unfortunately, there is no independent chronostratigraphic evidence to support this correlation.
Stirling Quartzite
The Stirling Quartzite is predominantly
composed of coarse-grained siliciclastic rocks,
with minor carbonate layers, interpreted to
represent continental braidplain to marginalmarine paleoenvironments (Fedo and Cooper,
2001). Carbonates are noted in the middle of
the Stirling in possibly lagoon-like facies and
in the D member (of Stewart, 1966, 1970)
found in more offshore localities. Problematic
calcareous fossils have been reported from the
D (Langille, 1974) and C members and have
been related to Cloudina (cf. Hagadorn et al.,
2000), suggesting a ‘‘latest Proterozoic’’ age.
The available data would suggest an age
younger than 580 Ma but older than 544 Ma
(the Precambrian/Cambrian boundary, see
next section) (Corsetti and Hagadorn, 2000).
Wood Canyon Formation
The Wood Canyon Formation is formally
subdivided into the predominantly marine
Lower Member, the conglomeratic, continental braidplain-dominated Middle Member, and
the mixed siliciclastic-carbonate marine Upper
Member (Stewart, 1966, 1970; Diehl, 1979;
Fedo and Cooper, 1990, 2001; Fedo and Prave,
1991). The Lower Wood Canyon Formation,
of primary interest here, can be divided into
three siliciclastic-carbonate shoaling-upward
parasequences (Prave et al., 1991; Corsetti and
Kaufman, 1994; Horodyski et al., 1994; Corsetti and Hagadorn, 2000). Ediacaran fossils,
including Ernietta (Horodyski, 1991) and
Swartpuntia (Hagadorn and Waggoner, 2000),
have been reported from the siliciclastic beds
above the contact between the Stirling Quartzite and Lower Wood Canyon Formation. Treptichnus pedum, the fossil used to correlate the
Precambrian/Cambrian boundary, occurs several tens of meters above the Ediacaran fossils
in the siltstones of the third parasequence, between the second and third carbonate units
(Horodyski et al., 1994; Runnegar et al., 1995;
Hagadorn, 1998; Hagadorn and Waggoner,
1998; Corsetti and Hagadorn, 2000). A mildly
diverse Early Cambrian fauna—including olenellid trilobites, archaeocyaths, hyoliths, and
inarticulate brachiopods—are known from the
Upper Wood Canyon Formation (Stewart,
1970; Fritz, 1975, 1993; Mount et al., 1991).
Tectonic Setting
In the most general sense, pretrilobite strata
in the southern Great Basin are thought to
have been deposited in response to the Neoproterozoic rifting of western North America
and the formation of a passive margin (Stewart, 1970; Stewart and Poole, 1974; Stewart
and Suczek, 1977; Bond, 1997) (Fig. 5). Geologic evidence for rifting is found in the Kingston Peak Formation, including volcanic units
deposited in extensional basins, tentatively
correlated to other well-known rift-related sequences in North America (e.g., the ca. 750
Ma Rapitan Group in northwestern Canada)
(Stewart and Poole, 1974; Miller, 1987; Fedo
and Cooper, 2001). Thermal-subsidence modeling, however, would predict a much younger
age for the onset of thermal subsidence, between 625 and 540 Ma (Armin and Mayer,
1983; Bond et al., 1985; Levy and ChristieBlick, 1991; Bond, 1997). This potentially
long offset in rift age vs. the onset of thermal
subsidence, coupled to the lack of radiometric
constraints, has spawned a host of possible
tectonic interpretations (Stewart and Poole,
1974; Levy and Christie-Blick, 1991; Prave,
1999; Corsetti et al., 2000; Fedo and Cooper,
2001). At this point, the controversy will only
be resolved with improved age constraints.
The tectonic setting of the pre–Kingston
Peak units (the Crystal Spring Formation and
the Beck Spring Dolomite) is more poorly understood. It is likely that the Crystal Spring
Formation and Beck Spring Dolomite were
part of an extensive cratonal cover sequence
and were preserved in grabens as a result of
Geological Society of America Bulletin, August 2003
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CORSETTI and KAUFMAN
block faulting during extension and deposition
of the Kingston Peak strata (Stewart, 1970;
Heaman and Grotzinger, 1992). Previous
workers considered the Pahrump Group to
have been deposited in an ‘‘aulacogen’’ on the
basis of presumed facies patterns and a
trough-like paleogeography (e.g., Wright et
al., 1974a). However, palinspastic reconstruction of the region (e.g., Levy and ChristieBlick, 1989) demonstrated that the trough
shape of the basin may be due to later tectonic
juxtaposition. In addition, Heaman and Grotzinger (1992) argued that the so-called aulacogen was simply too long lived (from pre–
1080 Ma to as young as 600 Ma) to be
geologically reasonable. Recognition of an
intra–Crystal Spring Formation unconformity
(Mbuyi and Prave, 1993) and the deep karst
at the top of the Beck Spring Dolomite highlight the discontinuous nature of Pahrump
Group sedimentary preservation. Further work
is required to decipher the detailed tectonic
history of the pre–Kingston Peak units.
CHEMOSTRATIGRAPHY OF THE
DEATH VALLEY SUCCESSION
Several key sections from the Death Valley
area were chosen for geochemical analysis on
the basis of their structural simplicity and
completeness, as well as supporting sequence
and biostratigraphic data (Fig. 6; Table 1). The
entire succession can be traversed at the combined southern Nopah Range sections (Nopah
Range 1 and Nopah Range 2) plus Alexander
Hills section as well as at the Kingston Range
section. A high-resolution chemostratigraphic
profile was generated for the Beck Spring Dolomite at the Alexander Hills section. The isotopic data are available.1
Where noted, we have combined our data
with that of Corsetti and Kaufman (1994),
Prave (1999), and Corsetti and Hagadorn
(2000). Other geochemical data are available
for different parts of the succession (Tucker,
1986; Zempolich, 1989; Strauss and Moore,
1992; Kenny and Knauth, 1992, 2001). However, few of the papers covering these other
data contain the detailed stratigraphic information needed to plot the samples with temporal meaning. Thus, these data are acknowledged but not included here, although they
broadly fit the trends outlined herein.
1
GSA Data Repository item 2003105, stratigraphic and isotopic data from carbonates in Neoproterozoic to Cambrian strata of Death Valley, California, USA, is available on the Web at http://
www.geosociety.org/pubs/ft2003.htm. Requests
may also be sent to [email protected].
922
Figure 6. Locality map for the chemostratigraphic profiles discussed in the text (outcrop
area of Neoproterozoic–Cambrian strata after Stewart, 1970). AH—Alexander Hills; BC—
Boundary Canyon; Death Valley National Park; CP—Chicago Pass, northern Nopah
Range; GW—Goler Wash; Panamint Range; KR—Kingston Range; NR—southern Nopah
Range; TM—Tucki Mountain, Panamint Range, Death Valley National Park; SSp—
Saratoga Springs, southern Death Valley, Death Valley National Park; WP—Winters Pass
Hills; SSh—Salt Spring Hills; PC—Pleasant Canyon.
TABLE 1. KEY SECTIONS FROM THE DEATH VALLEY AREA
Key section and abbreviation in figures
Alexander Hills (AH)
Southern Nopah Range (NR1)
Southern Nopah Range (NR2)
Northern Nopah Range (at Chicago Pass [CP])
Winters Pass Hills (WP)
Kingston Range (KR)
Saratoga Springs area (SSp)
Boundary Canyon area (BC)
Panamint Mountains (Tucki Mountain) (TM)
Panamint Mountains (Goler Wash) (GW)
Formations included
Two sections including Crystal Spring Formation, Beck
Spring Dolomite, Kingston Peak Formation
Noonday Dolomite, Johnnie Formation, and Stirling
Quartzite
Rainstorm Member of the Johnnie Formation
Stirling Quartzite and Lower Wood Canyon Formation
Noonday Dolomite and Johnnie Formation
Crystal Spring Formation, Beck Spring Dolomite, Kingston
Peak Formation
Crystal Spring Formation and Beck Spring Dolomite
Stirling Quartzite and Lower Wood Canyon Formation
Kingston Peak Formation
Kingston Peak Formation
Sample Preservation
Samples from the Great Basin sections were
treated in the manner outlined in Kaufman and
Knoll (1995) to evaluate postdepositional alteration; this approach included analysis of the
petrographic fabrics and cathodoluminescence
prior to microdrilling (to avoid the ambiguities
inherent in whole-rock analysis) of nonluminescent micrites, microspar, and ooids from
polished sections. Elemental and oxygen isotope analyses have regularly been used to
evaluate degrees of meteoric alteration of
Phanerozoic marine carbonates (Veizer, 1983a,
1983b; Popp et al., 1986) and later adopted
for Neoproterozoic samples (Kaufman et al.,
1991). However, given that strong environmental gradients (i.e., anoxic oceans, extreme
cold, and extensive sea ice) characterized
Neoproterozoic glacial cycles, the enrichment
of Mn (and Fe) and strong depletion of 18O in
some cap-carbonate lithofacies may faithfully
be recording primary seawater compositions.
In general, the geochemical analyses should
be used as guidelines, recognizing that unique
primary events might otherwise be interpreted
as diagenetic variants.
A number of samples were processed for
coexisting organic carbon as well as carbonate
carbon isotopes (see footnote 1). The generally constant fractionation (Knoll et al., 1986;
Hayes et al., 1999) between carbonate and or-
Geological Society of America Bulletin, August 2003
DEATH VALLEY NEOPROTEROZOIC CHEMOSTRATIGRAPHY
ganic carbon pairs provides an additional level
of confidence that primary seawater variations
are preserved. However, in the organic-carbon–
rich carbonates at the base of the Beck Spring
Dolomite and in the Sourdough limestone
member cap carbonate, as well as in organiccarbon–poor crystal-fan beds of the Rainstorm
Member of the Johnnie Formation, carbon isotope fractionation is strongly attenuated; the
d13C values of organic carbon are increased by
up to 15‰ relative to beds above and below.
The 13C enrichment is presumed to reflect
nearly original depositional conditions, as no
evidence for postdepositional alteration of
these particular stratigraphic intervals is
present.
Much of the section contains dolomite and
thus does not reliably retain the strontium isotope composition of ancient seawater. Thus,
the 87Sr/86Sr was not routinely processed for the
Death Valley succession. Given the smooth
d13C trends defined by our high-resolution sampling of petrographically screened carbonates,
it is most likely that near-primary d13C variations are preserved, although environmental
variance of a few per mil across the depositional basin are expected (Kaufman et al.,
1991) and stratal omissions at unconformities
complicate the construction of composite
curves in any basin (Kaufman et al., 2000). A
comparison of geologic and isotopic features
characteristic of each formation is provided
(Fig. 7).
Integrated Stratigraphy
Crystal Spring Formation
Compared to all other formations in the
Death Valley succession, the least is known of
the basin architecture and chemical stratigraphy of the siliciclastic-dominated Crystal
Spring Formation. The 10‰ variability in
d13C compositions (ranging between 25.1‰
and 15.1‰) of the intercalated thin carbonate
beds (Alexander Hills, Kingston Range, Saratoga Springs area sections) may be a function
of several factors, including primary temporal
changes, diagenetic or metamorphic resetting,
hiatus, or environmental variance (cf. Kaufman et al., 2000). The intrusion of the Mesoproterozoic diabase, low sample density,
and likelihood of sub–Beck Spring erosion
makes interpretation of temporal variations in
this unit, which requires greater study,
problematic.
Beck Spring Formation
The Beck Spring Dolomite was sampled at
the Kingston Range, Saratoga Springs area,
and Alexander Hills sections (Fig. 8). Three
additional sections of the basal Beck Spring
Dolomite were collected along strike at the
Alexander Hills section to confirm lateral continuity of the isotopic signatures, and organiccarbon isotopes were processed for the Kingston Range and Saratoga Springs area sections
to confirm the veracity of the carbonate d13C
record. Except in rare cases, there is good
agreement between the carbonate-carbon and
organic-carbon pairs. The section at Saratoga
Springs area is notable in that it contains some
limestone, whereas the other sections are entirely dolostone. In addition, the form of the
isotopic curve for the Saratoga Springs area
mimics that of the other sections studied, but
is offset ;2‰ more negative. For all sections,
carbonate isotope values are negative or near
zero in the initial 10 m and rise to as high as
15.8‰ within the ;100-m-thick basal Beck
Spring Dolomite interval of deeper-water laminites, chip breccia of laminite, rollup structures, and resedimented carbonates. The greater variance in d13C in this interval (relative to
upper Beck Spring Dolomite beds) may be
due to sedimentary mixing, because many of
the beds contain transported material. The
d13C values remain similar through the next
interval (;50 m), which is dominated by
shallow-water deposits capped by giant ooids.
Above this horizon, d13C values shift to
;13‰ and remain consistently positive for
;100 m through a series of meter-scale subtidal to peritidal shallowing-upward cycles.
Toward the top of this cycle stack, d13C values
again shift in a positive direction to ;14‰
(at the Alexander Hills section, a prominent
exposure surface marks the jump to values indicating 13C enrichment). At all localities, the
uppermost Beck Spring Dolomite is marked
by a negative excursion recorded in both carbonate carbon and coexisting organic carbon.
At the Kingston Range section, this excursion
occurs over 100 m (and reaches a nadir of
26‰); at the Saratoga Springs area section,
the event is telescoped down to 50 m (and
reaches as low as 24‰); and at the Alexander
Hills section, the excursion is recorded in a
mere 20 m (and reaches 21‰). The latter two
sections appear truncated by sub–Kingston
Peak erosion. The data presented in Prave
(1999) from the Alexander Hills are a close
match to our high-resolution analyses presented from the same range.
Kingston Peak Formation
The Kingston Peak Formation is predominantly siliciclastic; no regionally persistent
carbonates are currently known from the formation although locally developed carbonate
facies are recognized (Fig. 9). The thin, basal
Kingston Peak Formation carbonates—
interbedded with mudstones within the first
20 m above the contact with the Beck Spring
Dolomite in the Kingston Range and Alexander Hills sections—record predominantly
positive d13C values. Those recorded at the
Kingston Range section are between 12.0‰
and 13.1‰ (Fig. 8), i.e., slightly more positive than the Alexander Hills samples, and cooccur with vase-shaped and other microfossils
(Horodyski and Mankiewicz, 1990). At the
Kingston Range locality, a thin, locally persistent fossiliferous and oncoid-rich carbonate
(Pierce et al., 1977; Pierce and Cloud, 1979;
Awramik et al., 2000) is found ;200 m above
the transition beds; this carbonate possibly
caps the lower diamictites. From the base to
the top, this unit records a strong positive d13C
trend from 24.1 to 11.1‰. In the Panamint
Range to the west, the organic-carbon–rich,
finely laminated Sourdough limestone member caps the lower Kingston Peak Formation
diamictite succession and records d13C values
from 22.4‰ to 21.6‰ in Goler Wash and
23.1‰ and 22.9‰ in Pleasant Canyon.
Prave (1999) presented additional data from
Redlands Canyon in the same region that demonstrates a continuation of the isotopic trend to
values as high as 12‰ (strikingly similar to
the oncolite layer in Kingston Range). In the
northern part of the Panamint Range at Tucki
Mountain, the shallow-water carbonates of the
unnamed limestone record d13C values between
14.7‰ and 15.3‰, confirming the data presented by Prave (1999).
Noonday Dolomite
The Noonday Dolomite was sampled in the
Nopah Range 1 and Winters Pass Hills sections (Fig. 9). The microbially laminated lower Noonday Dolomite records consistently
negative d13C values (;23‰) in association
with sheet-crack cement fabrics, crystal
‘‘bushes,’’ and enigmatic tubes (Cloud et al.,
1974). A 1‰–2‰ positive step in values is
noted across a significant sequence boundary
(as recognized by Summa, 1993) in sandy dolostones of the upper Noonday Dolomite.
Johnnie Formation
The Johnnie Formation was sampled in the
Nopah Range, Winters Pass Hills, and Alexander Hills sections, and our chemostratigraphic framework has been integrated with
the detailed sequence stratigraphic analysis
provided by Summa (1993) (Fig. 10). The
Winters Pass Hills section is thinner than the
two Nopah Range sections and represents a
more ‘‘cratonal’’ expression of the Johnnie
Formation. Two sections were measured in the
Geological Society of America Bulletin, August 2003
923
Figure 7. Summary of the key lithologic, paleontologic, and chemostratigraphic features of the Neoproterozoic Death Valley succession. Abbreviations: dol.—dolostone;
ls.—limestone; ppt.—precipitate.
CORSETTI and KAUFMAN
924
Geological Society of America Bulletin, August 2003
DEATH VALLEY NEOPROTEROZOIC CHEMOSTRATIGRAPHY
Figure 8. Chemostratigraphy of the Beck Spring Dolomite and preglacial Kingston Peak Formation (localities noted in text and Fig. 6).
Where sampled, the basal 20 m records a negative to positive d13C anomaly (repeated at several sections along strike); vsm—vaseshaped microfossil (cf. Melanocyrillium).
Figure 9. Chemostratigraphy of the glacial to postglacial Kingston Peak Formation and Noonday Dolomite (localities noted in text and
Fig. 6). Data from Prave (1999) plotted for comparison. SDL—Sourdough limestone member; UNL—unnamed limestone; KPonc—Thin
oncolite bed in the Kingston Range.
Nopah Range: the section designated Nopah
Range 2 contains the Johnnie oolite and Rainstorm Member carbonates, whereas a subsequent incision has removed these units from
the Nopah Range 1 section. The d13C values
measured in thin dolomites in the lower and
middle parts of the Johnnie Formation (many
of them stromatolitic) remain negative
(;23.5‰)—continuing the isotopic trend
from the underlying Noonday beds—over a
thickness of 200–300 m and across several
significant sequence boundaries (Stewart,
1966, 1970). Above this interval, stromatolitic
carbonates record a trend toward positive d13C
values, reaching a perigee of near 13.5‰ near
the contact with the Rainstorm Member.
Where not removed by incision, the Johnnie
oolite, deposited during a flooding event atop
a major sequence boundary (Summa, 1993),
records a strong negative d13C trend that declines up section from 23.7‰ to 27.1‰.
Pink limestones several meters above the oolite (separated by green interference-ripple
cross-laminated siltstones) display crude
Geological Society of America Bulletin, August 2003
925
CORSETTI and KAUFMAN
Figure 10. Chemostratigraphy of the Johnnie Formation (localities noted in text and Fig.
6). Note that the incised valley has removed the Rainstorm Member carbonates along
strike. JO—Johnnie oolite.
crystal fans and crystal layers, interpreted as
former-aragonite seafloor cements (Fig. 4C).
Over 100 m within the Nopah Range 2 section, these highly negative d13C values decrease monotonically from 29.0‰ to
210.4‰. In the Winters Pass Hills section,
the post-oolite carbonate beds are clastic and
peloidal and trend from 29.1‰ to a nadir of
211.5‰; values return to ;29‰ at the Johnnie/Stirling contact.
In the Nopah Range 1 section, the Johnnie
oolite and Rainstorm Member carbonates have
been removed by incision and replaced by
several beds of conglomerate and breccia interpreted as debris-flow deposits associated
with incised-valley fill (Summa, 1993). Several clasts within the incised-valley fill are
identifiable from underlying lithofacies (Beck
Spring Dolomite giant ooids, Johnnie oolite,
and lower Johnnie Formation stromatolites)
and carry the isotopic fingerprint of their
source. Above the debris flows, a monotonous
sequence of featureless green and dark green
shale extends up to the contact with the conglomerates of the overlying Stirling Quartzite.
One thin carbonate unit, consisting of very
finely laminated dark limestone, is present in
926
this interval and records d13C values between
12.6‰ and 12.9‰.
Stirling Quartzite
The Stirling Quartzite in Death Valley is
predominantly nonmarine and contains few
carbonate beds. The unit thickens to the west
and records episodic marine incursions (Stewart, 1970). In the Nopah Range 1 section as
well as in the Salt Spring Hills section (not
plotted), the thin, possibly lagoonal, carbonates found throughout the middle part of the
Stirling Quartzite record entirely negative d13C
values, but these become less negative up section (see footnote 1). The d18O values of the
middle Stirling Quartzite carbonates are highly depleted and suggest likely alteration. Farther to the west, marine carbonates in the
overlying D member continue the positive
trend, from 20.9‰ to 11.6‰ in the Boundary Canyon area and 10.1‰ to 11.6‰ at
Bare Mountain (see footnote 1 and Corsetti
and Hagadorn, 2000, respectively).
Wood Canyon Formation
Three prominent carbonate units are commonly exposed in the Lower Wood Canyon
Formation (but the exact number varies from
section to section) (Stewart, 1970; Diehl,
1979; Corsetti and Hagadorn, 2000). In the
Boundary Canyon section, the lowest carbonates in the Lower Wood Canyon record isotopic values similar to those of the D member
of the Stirling (10.5‰) followed by a negative excursion (to an isotopic nadir of 24.4‰)
(see footnote 1 and Corsetti and Hagadorn,
2000). The d13C values of the uppermost carbonate return to mildly positive numbers
(;12.4‰). Treptichnus pedum is found below the last carbonate unit in the Boundary
Canyon section in association with negative
d13C values, and arthropod scratch marks (cf.
Monomorphichnus) are found above (Corsetti
and Hagadorn, 2000). In the northern Nopah
Range section at Chicago Pass, the lower two
carbonate units record negative d13C values,
whereas the upper carbonate records a positive
d13C excursion. Treptichnus pedum is found in
association with negative d13C values between
the second and third carbonate units, as in the
Boundary Canyon area (Horodyski et al.,
1994; Corsetti and Hagadorn, 2000; Hagadorn
and Waggoner, 2000). Similar trends are noted
in the equivalent White-Inyo facies to the
northwest (Corsetti and Kaufman, 1994; Corsetti and Hagadorn, 2000).
The stratigraphic trends defined by wellpreserved, closely spaced samples of Death
Valley carbonates—duplicated at multiple
sections—are accepted in this study to broadly reflect primary changes in ancient seawater.
Furthermore, we recognize seven negative
d13C anomalies in a single stratigraphic succession constrained between the basal Beck
Spring Dolomite (post–1.08 Ga) and the Precambrian/Cambrian boundary (Figs. 7, 11).
Because negative d13C anomalies are known
to be associated with postglacial ‘‘cap’’ carbonates, the logical progression is to classify
each of these potential geochemical events as
primary or secondary and as glacial or nonglacial in origin. In the next section we outline
the criteria used to evaluate the nature of each
geochemical anomaly.
ATTRIBUTES OF NEOPROTEROZOIC
CAP CARBONATES
The current state of Neoproterozoic correlation was outlined by Knoll (2000), who realized the ambiguities inherent in data sets
from various continents. His task was difficult; lacking a high-resolution biostratigraphic
framework and abundant reliable radiometric
constraints, the subdivision of Neoproterozoic
time—compared to more recent time intervals—
is much more at the whim of personal bias and
Geological Society of America Bulletin, August 2003
DEATH VALLEY NEOPROTEROZOIC CHEMOSTRATIGRAPHY
(Kennedy, 1996; Hoffman et al., 1998a). Recognition of known variations in sea level as
recorded in the physical sedimentary record is
thus central to our understanding of isotopic
changes in the Neoproterozoic ocean.
Stratigraphic Shape and Duration of the
Negative d13C Anomaly
Figure 11. Chemostratigraphic summary for the Death Valley succession. Seven negative
anomalies are noted from the Beck Spring Dolomite to the Lower Wood Canyon Formation (four are associated with cap-carbonate–like features, and two actually rest upon
glacial strata). The detailed analysis is found in Figure 7. Note that the two lower caplike units contain ‘‘Sturtian-like’’ features, and the two upper cap-like units contain ‘‘Marinoan-like’’ features, as defined by Kennedy et al. (1998).
basinal eccentricity. It is not surprising, then,
that researchers sometimes have viewed the
Neoproterozoic stratigraphic phenomena in
their basin as a global model. The debate regarding the number of glaciations in Neoproterozoic time is a prime example of regional
biases taking the global stage. One group,
working primarily in Namibia, Svalbard, and
Canada, sees more than two glaciations in the
way they have interpreted their data, and they
have made global correlations based on this
paradigm (e.g., Kaufman et al., 1997b; Knoll,
2000). Others, working predominantly in Australia (e.g., Kennedy et al., 1998; Walter et al.,
2000), see only two glaciations and use this
finding as the global archetype (but see Corkeron and George, 2001). Given the focused
interest in the evolutionary and climatic
events recorded in Neoproterozoic strata, this
is the expected situation and will only be resolved with further study.
In particular, Kennedy et al. (1998) have
proposed a testable model that would suggest
the presence of only two glacial-unit plus capcarbonate couplets in Neoproterozoic time. By
using PAUP (Phylogenetic Analysis Using
Parsimony), a parsimony-based approach
commonly used in cladistic phylogenetic analysis (coupled with the fact that no single sec-
tion unambiguously contained more than two
glacial-unit plus cap-carbonate successions),
they hypothesized that Neoproterozoic cap
carbonates fell into two groups (or ‘‘clades’’).
An older group displayed characteristics that
included an organic-carbon–rich laminated
cap carbonate with a negative d13C anomaly
that returned to positive values over a short
vertical stratigraphic interval. A younger
group recorded very unusual seafloor precipitates and/or tube rock, with sheet cements and
a negative d13C anomaly that continued over
a significant stratigraphic thickness. The older
group was correlated with the Sturtian interval
(ca. 700–750 Ma) and the younger with the
Varangian or Marinoan ice age (ca. 600 Ma).
We can summarize these observations into
four key areas, as described in the following
sections.
Sequence Architecture
Although postglacial rebound might obscure the absolute magnitude of sea-level
change, all known cap carbonates are deposited on underlying glacial strata or a correlative hiatus. The cap carbonates are therefore
deposited on a transgressive surface and appear to fill available accommodation space
The d13C composition of the oceans between ca. 750 Ma and ca. 590 Ma was, for
the most part, highly positive (some d13C values exceed 112‰) except for short negative
spikes presumed to be associated with the glaciations (e.g., Kaufman et al., 1997a). We consider any primary negative d13C values found
in a stratigraphic succession deposited during
this time interval (such as the Death Valley
succession) to be ‘‘anomalous.’’ Note that a
spike will have an initial positive-to-negative
trend followed by a negative-to-positive trend.
The shape of the negative d13C anomaly recorded in the strata, however, is a function of
the direction of secular change as well as the
timing and rate of sediment accumulation and
thus may be highly variable. It is possible that
only the rising limb of a spike may be recorded in the rock record. Taken at face value, this
limb might be considered a ‘‘positive excursion,’’ because the d13C values start out negative and end up positive. However, recall that
Neoproterozoic time is characterized by highly positive d13C values only briefly punctuated
by negative values. Thus, we consider any
negative d13C values to record a negative excursion, regardless of the actual shape or direction of the anomaly recorded in the stratigraphic succession. Despite these controls,
Kennedy et al. (1998) proposed that specific
d13C trends might be a diagnostic feature of
cap carbonates. In some caps the d13C values
are ;0‰ or slightly negative immediately
above diamictites and then fall to more negative values before ultimately returning to
positive ones. In other organic-carbon–rich
examples, the first preserved carbonate is
strongly negative and trends toward positive
d13C values over a relatively short stratigraphic thickness. This variation suggests the possibility that cap-carbonate accumulation was
initiated at different times across the basin and
that these deposits are time-transgressive. In
organic-carbon–poor cap carbonates, the d13C
values appear to start negative and continue to
fall over a significantly larger stratigraphic
thickness.
The Presence of Unique Carbonate Facies
and Fabrics
The preponderance of cap carbonates are
composed of thin (meters to tens of meters),
Geological Society of America Bulletin, August 2003
927
CORSETTI and KAUFMAN
finely laminated, allodapic dolostone. However, unusual carbonate textures are not uncommon and may be characteristic of the two
cap clades discussed at the beginning of this
section. Rollup structures, indicative of sediment cohesiveness and organic-carbon–rich
laminite, characterize one group, and sheetcrack cements, pseudo–teepee structures, tube
rocks, and seafloor precipitates characterize
the other. In addition, we suggest that signs of
unusually high seawater alkalinity will be
most notable as discrete episodes in predominantly siliciclastic successions (e.g., the lonesome Johnnie oolite).
The Presence of Underlying Diamictite
This observation is the litmus test of the
Kennedy et al. (1998) subdivision, as they do
not consider any units that do not sit atop
diamictites or unconformities that can be
clearly correlated with glacial episodes (cf.
Saylor et al., 1998).
CHARACTERIZATION OF
NEOPROTEROZOIC
BIOGEOCHEMICAL ANOMALIES IN
DEATH VALLEY
Knauth, 1992). It is notable, however, that the
organic-carbon d13C values generally co-vary
with those of carbonate carbon, suggesting
that this negative excursion records an oceanographic rather than diagenetic process (Kaufman et al., 1997b). In addition, the negative
excursion (recorded in samples microdrilled
from nondiagenetic phases) starts nearly 100
m beneath the karstic surface (Halverson et
al., 2002).
Sourdough Limestone Member
The deep-water Sourdough limestone member is in depositional contact with the glacial
diamictites and coarse siliciclastic rocks of the
lower part of the Kingston Peak Formation
(Tucker, 1986) and thus constitutes a flooding
surface. The Sourdough limestone member records a negative d13C excursion and a return
to more positive d13C values over a short
stratigraphic interval. The limestone consists
of a finely laminated organic-carbon–rich carbonate with possible rollup structures (Tucker,
1986). All of these features would suggest that
the Sourdough limestone member is a cap carbonate (Prave, 1999).
Wildrose member diamictite in some areas
and rests unconformably on the eroded remnants of various units of the underlying Pahrump Group and basement rocks in other areas. Thus, the Noonday Dolomite was
deposited on a major flooding surface. These
features, when combined, suggest that the
Noonday Dolomite is a cap carbonate (Corsetti, 1998; Prave, 1999; Corsetti et al., 2000).
The lower part of the overlying Johnnie
Formation, separated from the upper Noonday
Dolomite by a significant sequence boundary,
records negative d13C values, as well. This
succession is predominantly siliciclastic, lending a discontinuous nature to the chemostratigraphic profile. Thus, it is not possible to
assess the completeness of the isotopic record
through this interval. However, it is interesting
to note that the negative d13C values persist
from the basal Noonday Dolomite through the
lower part of the Johnnie Formation across a
major sequence boundary and several minor
sequence boundaries (Summa, 1993). Thus,
the biogeochemical event may not be constrained to a single depositional sequence, and
‘‘recovery’’ to more ‘‘normal’’ positive d13C
values in post-Noonday time may have been
protracted.
Kingston Peak Oncolite Bed
Basal Beck Spring Dolomite
The Rainstorm Member
The basal Beck Spring Dolomite was deposited on the irregularly eroded uppermost
Crystal Spring Formation (a sequence boundary, Mbuyi and Prave, 1993) and records at
least 100 m of deeper-water facies that shoal
to shallow depths, thus satisfying the floodingsurface criteria. These beds contain organiccarbon–rich laminite and rollup structures
(Fig. 2A). Carbon isotope analyses reveal a
slight negative excursion that returns to positive values of .10–15 m from the base of the
formation. Although the basal Beck Spring
Dolomite does not rest on a known glacial deposit, it does sit above an unusual ferruginous
sandstone interval in the upper Crystal Spring
Formation at some localities.
Upper Beck Spring Dolomite
The carbonates recording the 10‰ negative
excursion at the top of the Beck Spring Dolomite were deposited during a sea-level highstand and were eroded and affected by karst
processes prior to Kingston Peak Formation
deposition (Kenny and Knauth, 2001). These
carbonates do not contain unusual carbonate
fabrics. The negative d13C excursion occurs in
association with the karst, which has been interpreted as a diagenetic artifact (Kenny and
928
This ;3 m bed sits atop diamictite of the
Kingston Peak Formation. The negative
anomaly at the base of the unit occurs in finely
laminated carbonate. The d13C values return to
positive numbers within the overlying fossiliferous, oncolitic part of the unit (Awramik et
al., 2000). The contact between the finely laminated lower part and the oncolitic part is
sharp and possibly erosional. Note that we
have sampled this unit stratigraphically at two
sections along strike; thus, our data differ
from previously published data (Kennedy et
al., 2001a), which involved grab samples from
the uppermost bed and not a stratigraphic isotopic profile. Thus, the unit does contain some
cap-carbonate characteristics (including the
‘‘litmus test’’ of an underlying glacial deposit), although it appears to be sandwiched between two identical diamictite units.
The Noonday Dolomite
The Noonday Dolomite records a negative
excursion that remains negative over a significant stratigraphic interval and includes
unique tubular structures and cement fabrics
nearly identical to those found in the Maieberg Formation, Otavi Group, Namibia (Hoffman et al., 1998b, 1998a). The Noonday Dolomite rests in depositional contact on the
The Johnnie oolite and the pink carbonates
of the Rainstorm Member of the Johnnie Formation record an intensely negative excursion
during a flooding event above the base-ofoolite sequence boundary, but below a major
incision surface. No glacial strata are currently
known from directly below the Johnnie oolite.
The oolite itself represents unusual carbonate
precipitation, as it is the only carbonate bed
in a predominantly siliciclastic succession and
is extraordinarily laterally persistent. The pink
limestones above the oolite display small crystal fans, in addition to a peloidal or clasticcarbonate texture in some sections (Fig. 4).
These features, when combined, suggest that
the oolite-precipitate carbonate is similar to
cap-carbonate lithofacies, although these units
do not rest on a known glacial deposit. We
further note that these features are present below the incision that has been considered by
others (e.g., Christie-Blick and Levy, 1989;
Charlton et al., 1997; Abolins et al., 2000) to
represent glacially driven sea-level drawdown
during Marinoan glaciation. If this is so, it is
possible that the Rainstorm Member carbonates record a preglacial negative trend in d13C
as seen in other sections around the world
(Hoffman et al., 1998b; McKirdy et al., 2001),
but the presence of unusual carbonate fabrics
Geological Society of America Bulletin, August 2003
DEATH VALLEY NEOPROTEROZOIC CHEMOSTRATIGRAPHY
(e.g., crystal fans) is atypical in this stratigraphic position.
The origin of the highly negative d13C values (;210‰) is difficult to explain as a primary phenomenon without some sustained additional source of isotopically light carbon to
the depositional basin. Similar events are recognized in broadly equivalent successions in
Australia (Calver, 2000; McKirdy et al.,
2001), Oman (Burns and Matter, 1993), and
the Lesser Himalayas of India (Kaufman et al.,
2000). Calver (2000) has explained these as
the result of water-column stratification in a
restricted basin, but this interpretation is inconsistent with the clearly open- and shallowmarine conditions recorded in the Johnnie
Formation. Additional sources of 13C-depleted
carbon are currently being considered (Kaufman and Corsetti, 2001); the thick stratigraphic interval bearing the negative anomaly
would seem to preclude a catastrophic methane release.
Stirling Quartzite
The thin lagoonal carbonates with negative
d13C compositions in the middle part of the
Stirling Quartzite also record highly depleted
d18O values and probably do not reliably record original seawater compositions. They do
occur on a flooding surface, but they do not
contain other cap-carbonate features. Thus,
there is no evidence that they represent a capcarbonate lithofacies. In addition, they do contain poorly preserved Cloudina (Hagadorn
and Waggoner, 2000), one of the first weakly
mineralized fossils, and thus postdate the interval commonly considered to contain glacial
deposits.
Lower Wood Canyon
The negative anomaly in the Lower Wood
Canyon Formation clearly brackets the Precambrian/Cambrian boundary and represents
the boundary excursion seen in many sections
around the world (e.g., Corsetti, 1998; Corsetti
and Hagadorn, 2000).
DISCUSSION AND IMPLICATIONS
These comparisons suggest that the Death
Valley succession records four biogeochemical events represented by carbonate d13C
anomalies and carbonate textures analogous to
those in Neoproterozoic cap carbonates; only
two, however, are known to lie above recognized glacial deposits (Fig. 11). Each of these
cap-like carbonates was deposited during a
flooding event; thus, we cannot rule out the
possibility that glacial strata have simply not
been preserved along these hiatal surfaces.
The situation is similar for the Maieberg cap
carbonate from the Otavi Group in northern
Namibia, which rests unconformably on the
underlying Ombaatjie Formation platform carbonates in proximal settings and on thick glacial diamictites of the Ghaub Formation in
basinward settings (Hoffman et al., 1998a,
1998b). In the platform setting, the Ghaub glaciation is represented (except in rare instances)
by a disconformity. Therefore, although we
can confirm the occurrence of four negative
excursions in strata with cap-carbonate–like
features, we cannot rule out the existence of
at least four glaciations in Neoproterozoic
time.
Alternatively, some other, nonglacial process may control the occurrence of negative
d13C anomalies and cap-carbonate–like lithofacies. For example, Grotzinger and Knoll
(1995) and Knoll et al. (1996) hypothesized
that intense ocean stratification, with concomitant buildup of alkalinity via sulfate reduction
and d13C depletion in anoxic deep waters,
might be responsible for the observable features. It is unclear, however, whether enough
alkalinity could be delivered from (presumably) one overturn event to precipitate such
widespread cap carbonates. In this scenario,
cap carbonates and d13C anomalies need not
be unquestionably linked to glaciation.
The two older ‘‘events’’ preserved in Death
Valley record features similar to Sturtian-style
cap carbonates (the basal Beck Spring Dolomite and the Sourdough limestone member of
the Kingston Peak Formation), whereas the
two younger ones record features similar to
Marinoan-style (or Varangian) cap carbonates
(the Noonday Dolomite and the Rainstorm
Member of the Johnnie Formation) as defined
by Kennedy et al. (1998). PAUP analysis can
be used to highlight the similarity (or difference) between character sets, but it cannot be
used to imply temporal information as has
been inappropriately done in this debate.
Thus, an equally parsimonious way to interpret the data would be to call upon some, or
all, of the sister groups (the individual cap carbonates) to represent separate events. Hypothetically, this interpretation could mean the
possibility of many separate Sturtian-style
events and many separate Marinoan-style
events (a chemostratigrapher’s nightmare). We
think that our data support the existence of
at least two Sturtian-style events and two
Marinoan-style events in one continuous section, thus demonstrating the pitfall in using
PAUP analysis to bring temporal information
to this debate. Although we can comment on
the number of cap-carbonate–like units in
Neoproterozoic time, the Death Valley succession is too poorly dated to resolve the timing
of these events, and the terms ‘‘Sturtian-style’’
and ‘‘Marinoan-style’’ simply are used for
comparison, not to imply age control.
Although certain carbonate lithofacies,
commonly interpreted to have formed in deeper water (e.g., Kennedy, 1996), characterize
Neoproterozoic cap carbonates worldwide (as
already discussed), they are not unique to
these units, and other lithofacies and geochemical indicators appear possible. For example, the Johnnie oolite fits several of the
cap-carbonate criteria but does not represent a
traditional cap-carbonate lithofacies. The 2–3m-thick oolite unit can be traced continuously
over 16,000 km2 in the Great Basin and is also
similarly widespread in the Neoproterozoic
succession in Caborca, Mexico (Stewart,
1970; Stewart et al., 1984). It is an extraordinarily widespread carbonate unit within a
predominantly siliciclastic succession and
may represent a unique cap-carbonate lithofacies in which the biogeochemical anomaly
is manifested in shallow-water, agitated environments. Shallow-water facies have been described from the Egan Formation, Kimberley
region, Western Australia, known to cap glacial units and record negative d13C values
(Corkeron and George, 2001). It is interesting
to note that these units are thought to record
a post-Marinoan glacial episode (Grey and
Corkeron, 1998), thus adding to the known
number of Neoproterozoic glaciations in Australia. Shallow-water cap-carbonate facies are
also known from Mauritania (Deynoux et al.,
1976).
The basal Beck Spring Dolomite, the Sourdough limestone member, and the crystal-fan
beds of the Rainstorm Member of the Johnnie
Formation all record strongly enriched 13C
compositions of organic carbon relative to the
d13C values in carbonate beds above and below
(e.g., the Dd13C, or d13Ccarbonate 2 d13Corganic, is
reduced). The process responsible for these
low Dd13C values is unknown. However, in the
modern ocean, the introduction of micronutrients (e.g., iron) causes a reduction in d13C of
corresponding organic matter; as growth rates
increase in response to the influx of nutrients,
carbon becomes limiting and biogenic isotopic
discrimination (commonly ;20‰–30‰) decreases (Bidigare et al., 1997, 1999). Neoproterozoic postglacial oceans are predicted to
contain an abundance of dissolved iron and
other nutrients; the reduced Dd13C may reflect
this prediction (Kaufman et al., 1997a; Hayes
et al., 1999).
Geological Society of America Bulletin, August 2003
929
CORSETTI and KAUFMAN
CONCLUSION
The correlation of Neoproterozoic strata is
difficult, and therefore the ability to determine
the tempo of evolutionary events recorded in
Neoproterozoic strata is restricted. We acknowledge that the Death Valley succession
may not be as well preserved, dated, or structurally simple as other Neoproterozoic sections around the world. But as originally recognized by Cloud (1973), the Death Valley
section, arguably one of the most accessible
and intensely studied in the world, does contain many of the key geologic features that
characterize Neoproterozoic time. This study
confirms the presence of multiple negative
d13C excursions throughout the Neoproterozoic. Two of these are associated with known
glacial deposits, but at least two others are associated with cap-carbonate lithofacies lacking the underlying diamictite. This circumstance indicates either that more than two
glaciations occurred in Neoproterozoic time or
that negative excursions and cap-carbonate
lithofacies are the result of other oceanographic perturbations, which may be independent of
glacial phenomena.
ACKNOWLEDGMENTS
We thank the following individuals for stimulating
discussions over the years and for freely sharing information with us regarding the much-studied Death
Valley succession: Jack Stewart, John Crowell, Stan
Awramik, David Pierce, Russell Shapiro, Whitey Hagadorn, Ben Waggoner, John Grotzinger, John Cooper, Chris Fedo, Tony Prave, Cathy Summa, Andy
Knoll, Paul Link, Lauren Wright, Bennie Troxel, Jeff
Mount, Donna Hunt, Pedro Marenco, David Bottjer,
Mary Droser, Soren Jensen, Jim Gehling, Bruce Runnegar, Pete Palmer, Marilyn Vogel, Paul Knauth, Rob
Ripperdan, Steve Rowland, Paul Hoffman, Pippa
Halverson, and Carol Dehler. In particular, we thank
John Grotzinger for introducing one of us (Kaufman)
to the succession and showing us the crystal bushes
in the Noonday Dolomite and Chris Fedo for providing some Stirling carbonate samples. Reviews by David Bottjer, Whitey Hagadorn, Paul Hoffman, Karlis
Muehlenbachs, and an anonymous reviewer improved the manuscript. Funding during the latter
phase of this project was provided to AJK through
NSF grant EAR-0126378 and NASA-Exobiology
grant NAG512337.
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