Spring 2021 Volume 43, Number 1 - New Mexico Bureau of Geology and Mineral Resources / A Research Division of New Mexico Tech
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Spring 2021
Volume 43, Number 1
New Mexico Bureau of Geology and Mineral Resources / A Research Division of New Mexico Tech
Spring 2021
Volume 43, Number 1 A publication of the
New Mexico Bureau of Geology and Mineral Resources
A Research Division of the
New Mexico Institute of Mining and Technology
Science and Service
ISSN 0196-948X
New Mexico Bureau of Geology and
Mineral Resources
Contents Director and State Geologist
Dr. Nelia W. Dunbar
Late Pennsylvanian Calcareous Paleosols from Central New Mexico: Implications Geologic Editor: Bruce Allen
for Paleoclimate Production Editor: Belinda Harrison
Tanner, Lawrence H. and Lucas, Spencer G. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3–9
EDITORIAL BOARD
Dan Koning, NMBGMR
New Mexico Graduate Student Abstracts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10–16 Barry S. Kues, UNM
Jennifer Lindine, NMHU
Gary S. Morgan, NMMNHS
New Mexico Institute of Mining and Technology
President
Dr. Stephen G. Wells
BOARD OF REGENTS
Ex-Officio
Michelle Lujan Grisham
Governor of New Mexico
Stephanie Rogriguez
Acting Cabinet Secretary of Higher Education
Appointed
Deborah Peacock
President, 2018–2022, Corrales
Jerry Armijo
Secretary-Treasurer, 2015–2026, Socorro
Dr. David Lepre
2021–2026, Placitas
Dr. Yolanda Jones King
2018–2024, Moriarty
Veronica Espinoza, student member
2021–2022, Sunland Park
New Mexico Geology is an online publication available
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Editorial Matter: Articles submitted for publication
should follow the guidelines at
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NMGguidelines.html
Cover Address inquiries to Bruce Allen, Geologic Editor,
New Mexico Bureau of Geology and Mineral Resources,
801 Leroy Place, Socorro, NM 87801. For telephone
Located about 5 miles northeast of Socorro, the Ojo de Amado is a spring that feeds a pool that is inquiries call 575-835-5177 or send an email to
an important source of water for local wildlife. “Ojo” literally means “eye” in Spanish, but the word NMBG-NMGeology@nmt.edu
is used dialectically in New Mexico to refer to a spring. The Ojo de Amado is also known to locals geoinfo.nmt.edu/publications/periodicals/nmg
as Bursum Springs, one of several geographic features in the state named after Holm Bursum (1867–
1953), a longtime resident of Socorro and an important political figure of the New Mexico Territory
who ultimately served in the U. S. Senate from 1921 to 1925. The steeply dipping strata around the
Ojo de Amado are Upper Pennsylvanian clastic and carbonate rocks of the Atrasado Formation. They
are faulted up just east of the local eastern edge of the Rio Grande rift and along the western flank of
the Cerros de Amado, a set of rugged hills developed in Upper Paleozoic strata.
—Photograph by Spencer G. Lucas.
Late Pennsylvanian Calcareous Paleosols from Central
New Mexico: Implications for Paleoclimate
Spencer G. Lucas, New Mexico Museum of Natural History and Science, Albuquerque, NM 87104, spencer.lucas@state.nm.us
Lawrence H. Tanner, Department of Biological Sciences, Le Moyne College, Syracuse, NY 13214, tannerlh@lemoyne.edu
Abstract Introduction Lucas, 2013). Gypsum beds are rare,
with one well documented example in
We document calcareous paleosols from Upper What have been called “climate-sensi- early Late Pennsylvanian (Missourian)
Pennsylvanian (lower Virgilian) strata of the tive lithologies” are rock types specific strata (Rejas, 1965; Lucas et al., 2009;
Burrego Member of the Atrasado Formation
to a particular climate, the best known Falcon-Lang et al., 2011). Paleosols
in the Cerros de Amado of Socorro County, of Pennyslvanian age, especially cli-
New Mexico. The Burrego paleosols are an being coal (wet), gypsum (dry) and cal-
careous paleosols (seasonally wet/dry). mate-sensitive calcareous paleosols,
excellent example of a scarce, climate-sensitive
lithology in the Pennsylvanian strata of New Such rock types play a prominent role have only been documented from two
Mexico. These paleosols contain mostly in the interpretation of past climates, late Paleozoic basins in northern New
stage II to III carbonate horizons, and their
constrain climate models and are crit- Mexico (Tabor et al., 2008; Tanner and
overall morphology suggests deposition and Lucas, 2017, 2018). Here, we add to
pedogenesis under subhumid, seasonally dry ical to paleogeographic reconstructions
(e.g., Boucot et al., 2013; Cao et al., this sparse record of climate-sensitive
conditions. This conclusion is consistent with
paleobotanical and other data that indicate 2019). However, the distribution of rocks in the New Mexican Pennsylva-
such climate conditions were widespread on climate-sensitive lithologies remains nian strata a succession of calcareous
Late Pennsylvanian Pangea. The mean value
unevenly and incompletely docu- paleosols in lower Virgilian strata of
of the oxygen-isotope ratios from Burrego Socorro County (Fig. 1).
paleosol carbonates compares well with the mented, particularly in older geological
values from Virgilian paleosols of the San time periods.
Juan, the eastern Midland and Chama basins Indeed, in the Pennsylvanian Stratigraphic context
of New Mexico-Texas, suggesting similar con- sedimentary rocks of New Mexico, rel-
ditions of temperature and paleoprecipitation.
atively few such rocks have been doc- The calcareous paleosols documented
Application of the diffusion-reaction model to
the mean carbon-isotope composition of the umented. Thus, coal beds are few and here are in the Burrego Member of
carbonate suggests a paleo-pCO2 of approx- mostly thin, localized and confined to the Atrasado Formation, strata that
imately 400 ppmV, which is also consistent early Middle Pennsylvanian (Atokan) encompass the Missourian-Virgilian
with estimates from correlative carbon- strata (e.g., Armstrong et al., 1979; boundary, in the Cerros de Amado of
ate deposits that formed farther east in
Kues and Giles, 2004; Krainer and Socorro County (Figs. 1-2). Thompson
Late Pennsylvanian Pangea.
Figure 1. Three late Paleozoic basins in New Mexico that have documented calcareous paleosols of Late Pennsylvanian-early Permian age. Relevant publica-
tions are A = Tanner and Lucas (2018); B= Tabor et al. (2008); C = Tanner and Lucas (2017); D = Mack (2003) and references cited therein; E = Tabor et al.
(2008); F = this paper.
Spring 2021, Volume 43, Number 1 3 New Mexico Geology
(1942) presented the first detailed litho- into the Cerros de Amado region east section described here, though very
stratigraphy and biostratigraphy of the of Socorro (also see Kottlowski, 1960). close to one of the sections Lucas et
Middle-Upper Pennsylvanian strata that He used Burrego Member much as did al. (2009) published (their Minas de
crop out in central and southern New Thompson (1942), as a slope form- Chupadera section) was not studied by
Mexico. In this monograph, Thompson ing, mixed clastic-carbonate interval them. We discovered this section during
(1942) named six formation-rank units between two prominent limestone units, fieldwork in 2018.
in the northern Oscura Mountains of the Council Spring Member (below) In the Cerros de Amado, the
Socorro County that Lucas and Krainer and Story Member (above). Burrego Member is 13–55 m thick
(2009) reduced in rank to members of Lucas et al. (2009), Barrick et and consists mostly of slope-forming
the Atrasado Formation, including the al. (2013) and Krainer et al. (2017) mudstone and shale interbedded with
Burrego Member. published stratigraphic sections of the arkosic/micaceous sandstone and
Rejas (1965), in an unpublished Burrego Member and adjacent strata limestone (Rejas, 1965; Lucas et al.,
master’s thesis, brought much of Thomp- at several locations in the Cerros de 2009; Barrick et al., 2013; Krainer
son’s (1942) stratigraphic nomenclature Amado and vicinity. However, the et al., 2017). Most limestone beds in
the Burrego Member are evidently of
marine origin, as they contain marine
macrofossils, including algae, crinoids,
molluscs and brachiopods. Conodont
and fusulinid biostratigraphy indicates
the Borrego paleosols are close in age
to the Missourian–Virgilian boundary,
and we consider them here to be of
early Virgilian age (Lucas et al., 2009;
Barrick et al., 2013).
Material and methods
We used standard field methods with a
1.5-m staff, tape measure and Brunton
pocket transit to measure the thickness
of strata in the stratigraphic section
discussed here, which is located in the
SE ¼ sec. 26, T2S, R1E (UTM coordi-
nates are in the caption to Figure 2),
(Fig. 2). Samples were collected for
petrographic and isotopic analysis.
To confirm the pedogenic origin of
the carbonate, standard 30 μm petro-
graphic thin sections were examined
for pedogenic fabrics and textures and
for evidence of diagenetic effects.
Carbonate aliquots for isotopic
analysis were obtained by selectively
drilling micritic calcite in lapped slabs
corresponding to prepared thin sections
with an ultrafine engraving tool while
viewing under a binocular microscope.
The samples were analyzed for δ18O
and δ13C by the Duke Environmental
Stable Isotope Laboratory (Nicholas
School of the Environment, Duke Uni-
versity, Durham, North Carolina) using
standard operating procedures (see
Tanner and Lucas, 2018, for details).
Figure 2. Stratigraphic section of the Burrego Member of the Atrasado Formation near Minas de We calculated paleo-pCO2 using
Chupadera in Socorro County (base of section at UTM 333433, 3775122 and top at 333299, 3775300,
zone 13, datum NAD 83; inset map of New Mexico shows location of section in Socorro County). On
the mean δ13C value from 8 samples
left, lithostratigraphy of the measured section with the calcareous paleosols in the section labeled A–E. and the diffusion-reaction model of
On right, field photographs of the calcareous paleosols A–E. Cerling (1991, 1999). But, as we did
Spring 2021, Volume 43, Number 1 4 New Mexico Geology
not obtain organic matter from the section. These are marked by repetition sparse fossils of marine gastropods,
samples for determination of δ13Com, of specific types of B horizons (Bt, Btk capped by a 0.2 to 0.3-m-thick dark
we applied values from the literature or Bk) without an intervening A hori- to light limestone bed that is nodular,
for formations of similar age and zon, suggesting an erosional episode and the weathered surface has vertical
geographic proximity (within 2 degrees (Kraus and Hasiotis, 2006). channels up to 2.5 cm wide and 10 cm
latitude), primarily from the published The stratigraphic section we long that are filled with smaller calcare-
data supplements to Montañez et al. measured encompasses ~ 40 m of most ous nodules. We infer that these record
(2007, 2016). of the Burrego Member and its upper root channels formed during subaerial
contact with the overlying Story Mem- exposure and pedogenesis of the marine
ber (Fig. 2). Most of this stratigraphic carbonate. The top of the unit is a 0.1
Outcrop description section is mudrock, about 82% of the m mudstone/limestone breccia consist-
thickness of the strata measured. Minor ing of limestone blocks up to 4 cm in a
Where the paleosols in the section dis- lithologies are sandstone/conglomerate red mudstone matrix with root traces
play sufficiently distinctive pedogenic (11% of the section) and limestone and small calcareous nodules. This unit
features to allow classification, we apply (7% of the section). represents a calcic Argillisol formed on
the terminology of Mack et al. (1993) The section (Fig. 2) begins with red- the reworked limestone surface.
in assigning names of paleosol orders, bed mudstone overlain by a thin-bed- Unit 14 is 2.9 m of dark brown,
modified by adjectives describing the ded, ripple-laminated, very-fine grained fine-grained mudstone with a crumb
most prominent subordinate charac- sandstone that is 0.5 m thick (units fabric, but the outstanding feature of
teristic. The most common paleosol 2–3). This sandstone has a platy fabric the unit is the presence of numerous
types we found in the measured section and contains some discrete calcareous rhizoliths. These are calcareous masses
are calcic Argillisols and Calcisols to nodules and scarce root traces that that weather out of the outcrop face,
argillic Calcisols. The calcic Argillisol increase in abundance upward and mostly vertically oriented and irregular
denotes a paleosol horizon in which has a bioturbated/pedoturbated top. (noncylindrical) in shape. The masses
the defining characteristic is a clay-rich The top 0.1 m is a well-developed are up to 1.0 m long, 0.1 m in diameter
B horizon that is visibly enriched in carbonate horizon (Stage II of Gile et and have no internal structure. Most
CaCO3 in the form of nodules, i.e., a al., 1966) with carbonate nodules 1 to of these features have a rough, knobby
Btk horizon. In any paleosol profile 2 cm in diameter, drab root traces and appearance because they consist of
with multiple defining characteristics, rhizoliths up to 5 cm long. We consider vertically stacked, calcareous oblate
such as illuviated clays and pedogenic unit 2 a truncated Calcisol that is spheroids of varying diameters. Many
carbonate, whether they occur in the relatively immature, given the lack of of them taper downward, and some
same horizon or in separate horizons, coalescing nodules, consisting only of exhibit branching, supporting their
a subjective judgement was made to C and Bk horizons. It is overlain by 0.3 interpretation as rhizoliths. The unit
determine which feature is dominant m of red mudstone (unit 4) followed also contains subhorizontal arcuate
and which is subordinate. Thus, there by a 0.3-m-thick bed of coarse- soil fractures and irregular (botryoidal)
may be a fine distinction between a grained, arkosic sandstone capped calcareous masses up to 0.1 m wide.
calcic Argillisol and an argillic Calcisol. by a 0.1-m-thick limestone-pebble Unit 14 lacks any horizonation, so it
In profiles where development of the conglomerate (units 5–6). Some of the is interpreted to represent a single B
calcareous B horizons (Bk, or Btk if limestone pebbles in this conglomerate horizon containing calcareous nodules
argillic and calcic) is stronger than the contain marine macrofossils, including and vertic fractures. We classify this
argillic (Bt) horizons, we assign the des- brachiopods and gastropods. The unit as a calcic Vertisol that formed
ignation Calcisol or argillic Calcisol, as overlying unit 7 is 11.3 m thick and is a through an extended interval of con-
appropriate. In addition to Argillisols red mudstone slope with its upper half tinuous sedimentation (aggradation)
and Calcisols, and variations thereof, covered by mostly colluvium. The lower during pedogenesis, in other words, a
we recognize calcic Vertisols, paleosols half of this unit has numerous carbonate cumulative paleosol. The outcrop does
with prominent vertic fractures and nodules isolated in the mudstone, but not contain the top of the unit, and no
calcareous features in the B horizon. lacks distinct horizonation. Therefore, A-horizon is preserved.
Many mudstone beds of varying thick- we consider this unit a calcic Protosol. The overlying 5.4 m of red mud-
ness display pedogenic features, such Above unit 7 is a nodular and stone (unit 15) has clay-lined root traces
as calcareous nodules, drab colors and bioturbated limestone (unit 8) rich and numerous carbonate nodules that
root traces, but lack distinct horizona- in marine macrofossils, including increase upward to form a coalesced
tion. We term these units Protosols, and echinoids, gastropods and nautiloids. (Stage III to IV) layer 0.6 m thick that
where they contain calcareous nodules A 1.2-m-thick, very coarse-grained, is exposed over a lateral extent of 5 m.
we label them calcic Protosols. Most arkosic sandstone bed (unit 9) above We regard this unit as the Btk horizon
paleosol profiles in the section are has limestone rip-ups at its base and of an argillic Calcisol. The unit is
truncated in that they lack a discernible displays somewhat indistinct, tabular truncated above abruptly by a massive,
eluviated upper (A) horizon and display bedding. The overlying interval of 0.5-m-thick sandstone ledge (unit
evidence of sediment removal. We also limestone (units 10–13) begins with a 16). The sandstone is overlain by 1.7
recognize compound profiles in the 0.2-m-thick bed of lime mudstone with m of red mudstone with drab-brown
Spring 2021, Volume 43, Number 1 5 New Mexico Geology
mottling at the top (unit 17). The mud- Outcrop interpretation argillic Calcisols and Calcisols with
stone contains numerous rhizoliths well-developed (Stage III to Stage IV
and calcareous nodules that increase in As noted above, the Burrego Member sensu Gile et al., 1966; Machette, 1985)
abundance vertically to form two hori- is a lithosome that includes a mixture carbonate horizons hosted in argillic
zons, each approximately 0.3 m thick, of sediments of marine and nonmarine red beds. Examination of petrographic
of carbonate nodules up to 8 cm in origin, and the section we studied is thin sections indicates that pedogenic
diameter, which coalesce to form Stage representative of that. Thus, limestone carbonate in the section consists of
II to III pedogenic carbonate horizons. beds in the section with marine inver- micritic calcite with displacive textures
Nodules decrease in abundance in the tebrate fossils (units 8, 12 and 18) are and fabrics, including circumgranular
upper 0.4 m of the overlying mudstone obviously of marine origin, whereas the cracking, that demonstrate a lack
interval of unit 17. The transitional other strata are of nonmarine origin. of diagenetic replacement (Fig. 3).
nature of the underlying and overlying The relatively thick intervals of Samples generally were selected from
mudstone intervals of unit 17 suggests red mudstone that host the calcare- below the coalesced carbonate horizon
that this unit represents a calcareous ous paleosols we studied are readily to maximize depth below the original
paleosol, specifically a compound interpreted as nonmarine deposits of soil surface.
argillic Calcisol with Btk (Stage II) and alluvial floodplains that have under-
Bk (Stage III) carbonate horizons. gone variable amounts of pedogenesis.
The overlying bed of limestone Sandstones in the section are likely of
Paleosol analysis
(unit 18) is a 1.3 m thick, thickly bed- fluvial origin, and limestone clasts in
ded, cherty bioclastic wackestone with the conglomerate low in the section Four paleosols were sampled for isoto-
abundant crinoidal debris. Above that (unit 6) contain marine invertebrate pic analysis (labelled A, C, D and E in
is a covered slope 2.1 m thick overlain fossils, which suggests proximity to Figure 2). In ascending order these are:
by a very coarse grained, micaceous, marine carbonate beds. Thus, we (1) a thin Calcisol with Stage II calcar-
trough crossbedded sandstone (unit interpret the section as mostly repre- eous paleosol developed in a blocky,
20) that is 1.7 m thick. The uppermost senting floodplain deposition close to very-fine grained sandstone containing
part of the Burrego Member is a 6.1 m the shoreline and sea, interrupted by calcareous rhizoliths (station A); sta-
thick slope, mostly covered, but where marine incursions. tion B is a nodular carbonate formed
bedrock is exposed on this slope it is red The section we studied includes on a marine limestone and was not
mudstone (unit 21). The base of the over- meter-scale profiles of simple and sampled due to the likelihood of
lying Story Member is a medium-bedded, cumulative paleosols, including calcic incorporation of marine carbonate; (2)
cherty wackestone with fossils of algae, Argillisols, argillic Calcisols, Calcisols station C is a calcic Vertisol exposure,
crinoids and brachiopods. and calcic Vertisols. Most samples for 2.9-m thick, notable for the abundance
isotopic analysis were selected from of calcite-cemented rhizoliths up to 1
meter in vertical length in a mudstone
matrix with blocky ped fabric; (3) sta-
tion D is a Calcisol with a prominent
Stage III nodular horizon; and (4) sta-
tion E is a calcic Argillisol containing
two nodular horizons exhibiting Stage
II and Stage III morphology, likely
representing stages in formation of a
cumulative soil.
Petrography reveals the presence
of typical alpha-type fabrics in the car-
bonate nodules sampled in the section,
such as grain coronas and corroded
floating grains that indicate that these
nodules represent the accumulation of
carbonate in the B horizon of paleosols
(Fig. 3; Alonso-Zarza and Wright,
2010). Thus, we are confident that
these carbonates formed within soils
developed on alluvial muds.
Isotopic analysis of eight carbonate
samples from the Burrego Member are
tightly clustered and yielded δ13Ccarb
Figure 3. Petrographic features of Burrego Member calcic paleosols. A) Spar-filled voids and shrinkage values ranging from -6.4 ‰ to -5.6 ‰
fractures (sf). B) Mudstone clast surrounded by circumgranular crack (cc). C) Mudstone matrix with with a mean of -6.0 + 0.1 ‰ (VPDB)
displacive micrite (dm). D) Mudstone clast surrounded by sparry grain halo (gh). (Table 1). The isotopic composition of
Spring 2021, Volume 43, Number 1 6 New Mexico Geologytwo samples from rhizoliths at Station from the Virgilian paleosols of the 2005). Thus, paleosol morphology
C (-6.0 ‰, -5.6 ‰ (VPDB)) is the same Chama Basin of northern New Mexico supports the isotopic analyses in
as measured in samples of carbonate (Tanner and Lucas, 2018), suggesting suggesting sediment deposition and
nodules, suggesting micritization of the similar conditions of temperature and soil formation under widely varying
root casts in the deep (>50 cm depth) paleoprecipitation. moisture conditions.
soil environment and therefore repre- Overall, the morphology of the
sentative of the isotopic composition paleosols in the Burrego Member sug- Table 1. Isotopic analyses of Burrego
of soil respired CO2. Values of δ18O gests deposition and pedogenesis under calcareous paleosol samples. Values
have a wider spread, ranging from -5.7 subhumid, seasonally dry conditions. in units ‰ VPDB.
to -1.8 ‰, with a mean value of -3.4 The calcareous paleosol horizons vary
+ 0.5‰ (VPDB). The greater range Unit δ18O δ13C
in maturity from Stage II to IV, and
for δ18O likely records pedogenic both cumulate and composite paleosol
carbonate precipitation under a range profiles are present, suggesting higher Station A -3.8 -5.8
of temperature and/or precipitation rates of sedimentation during some
conditions. The composition of the car- intervals, alternating with slow sedi- Station C-1 -3.5 -5.6
bonate is determined by a combination mentation during others (e.g., Deutz
of factors in the diffusion model: plant et al., 2002; Monger et al., 2009). In Station C-2 -4.0 -6.0
respiration rate, isotopic composition particular, the “mega-rhizolith” horizon
of the plant organic matter (OM), at Station C appears to be a single, Station D-1 -2.6 -6.2
atmospheric isotope composition and undifferentiated B horizon with an
pCO2. The isotopic composition of the exposed thickness of 2.9 m. This attests Station D-2A -4.0 -6.1
plant OM tells us about the vegetation, to continuous aggradation of the sur-
but only in the most general sense (C3 face contemporaneous with pedogenic
vs C4), and nothing is known about Station D-2B -5.7 -6.4
processes, particularly root turbation.
any possibly unique isotopic aspects of The interplay of sedimentation and
Pennsylvanian plant OM. biological activity with pedogenesis Station E-1 -1.8 5.9
The lack of δ13Com measurements suggests meteoric precipitation at the
in this study makes application of the higher end of the range for which calcar- Station E-2 -2.1 -5.6
diffusion-reaction model of Cerling eous paleosol formation is considered
(1991; 1999) somewhat problematic. possible (Birkeland, 1999; Retallack,
However, the datasets of Montañez
et al. (2007, 2016) provide useful Ma
measurements of δ13Com that allow 299 series N AM "global"
us to at least make an approximation stage stage
of paleo-pCO2. Temperature of soil
carbonate formation, the isotopic
composition of atmospheric CO2 and
Gzhelian
Virgilian
the contribution of soil-respired CO2
Late Pennsylvanian
(the S(z) term) are also required for
Burrego
application of the model. We assumed Member
Burrego
values based on (but not identical to) Member
paleosols
δ13 C
those of Montañez et al. (2007, 2016), paleosols
pCO2
using values δ13Com = -21.0 ‰, δ13Ca 304
= -2.5 ‰ (composition of atmospheric
Kasimovian
Missourian
CO2), T = 25oC and S(z) = 3000 ppmV.
The S(z) value reflects the fact that
carbonate precipitation mainly occurs
during the drier months when plant
productivity is decreased (Breecker,
2013). The Borrego carbonates yielded 307
Middle
a mean δ13Ccarb of -6.0 ‰. Using the
Desm.
Penn.
Mosc.
values cited above we obtained a
paleo-pCO2 for the early Virgilian of ~
400 ppmV. This estimate accords well δ13 C
-12 -10 -8 -6 -4 -2
with values presented by Montañez et pCO 2
al. (2016) for the late Missourian, and 300 600 900 1200 1500
the early Virgilian (Fig. 4). The mean Figure 4. Compilation of Late Pennsylvanian δ13Ccarb data from Montañez et al. (2016), the pCO2 curve
δ18O value of -3.4 + 0.5 ‰ (VPDB) of Chen et al. (2018) calculated from the Montañez et al. data, δ13Ccarb values obtained in this study, and
obtained compares well with the values the calculated pCO2 value from the Burrego Member.
Spring 2021, Volume 43, Number 1 7 New Mexico GeologyDiscussion Climate models, paleosol data and References
paleobotany converge to identify a
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Boucot, A.J., Chen, X., Scotes, C.R. and Morley,
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orogeny. Around the fringes and on the from habitats with seasonal moisture Concepts in Sedimentology and Paleontology,
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deposition took place in some locations the fossil assemblages and evidently Breecker, D.O., 2013, Quantifying and under-
during the Pennsylvanian, such as the grew in close proximity. These floras standing the uncertainty of atmospheric
section described here, and by early indicate climates that varied from CO2 concentrations determined from calcic
subhumid to semiarid and arid paleosols: Geochemistry, Geophysics, Geosys-
Permian time fluvial deposits (largely tems, v. 14, p. 3210–3220.
siliciclastic red beds) were filling the (DiMichele et al., 2017).
Brotherton, J.L., Chowdhury, N.U.M.K., and
formerly marine basins. The Burrego paleosols formed in a
Sweet, D.E., 2020, Synthesis of late Paleozoic
Calcareous paleosols are compara- subhumid climate under seasonally dry
sedimentation in central and eastern New
tively common in lower Permian strata conditions. The pCO2 value of ~ 400 Mexico: Implications for timing of ancestral
in New Mexico (particularly in the ppm we calculate is within the range of Rocky Mountains deformation: SEPM
Abo Formation: Mack, 2003 and refer- values given by Montañez et al. (2016, Special Publication 113. doi: 10.102110/
ences cited therein), but a few Virgilian fig. 2) across the Missourian–Virgilian sepmsp.113.03.
calcareous paleosols are the only Penn- boundary. Thus, the Burrego paleosols Cao, W., Williams, S., Flament, M., Sahirovic, S,
sylvanian examples that have been doc- indicate a climate within the range of Scotese, C. and Müller, R.D., 2019, Palaeolat-
umented prior to the Burrego Member what were thought to be the climates itudinal distribution of lithologic indicators
of equatorial Pangea during the Late of climate in a palaeogeographic framework:
record documented here. Thus, Tabor Geological Magazine, v. 156, p. 331–354.
et al. (2008) briefly discussed a few late Pennsylvanian—subhumid and season-
Cerling, T.E., 1991, Carbon dioxide in the atmo-
Virgilian calcareous paleosols in the ally dry. The Burrego paleosols thus
sphere: evidence from Cenozoic and Mesozoic
Rowe–Mora basin (Taos trough) and add an important data point of climate
paleosols: American Journal of Science, v. 291,
in the Bursum Formation of southern sensitive lithologies from what was far p. 377–400.
New Mexico, and Tanner and Lucas western, tropical Pangea during the Cerling, T.E., 1999, Stable carbon isotopes in
(2018) documented similar late Vir- Late Pennsylvanian. palaeosol carbonates; in Thiry, M. and Simon-
gilian paleosols in part of the Paradox Coinçon, R., eds., Palaeoweathering, palae-
basin (Fig. 1). These workers concluded Acknowledgments osurfaces and related continental deposits:
International Association of Sedimentologists,
that the Virgilian paleosols indicate
Special Publication 27, p. 43–60.
highly variable climate ranging from The comments of the reviewers, D. O. Chen, J., Montañez, I.P., Qi, Y., Shen, S., and
subhumid to semiarid with extremes Breecker and H. C. Monger, and the Wang, X., 2018, Strontium and carbon
in seasonal precipitation, which is editor, B. D. Allen, improved the con- isotopic evidence for decoupling of pCO2
consistent with our interpretation of tent and clarity of the manuscript. from continental weathering at the apex of
the Burrego paleosols. the late Paleozoic glaciation: Geology, v. 46,
New Mexico was located near the p. 395–398.
western end of the Pangean tropical
belt during the Late Pennsylvanian.
Spring 2021, Volume 43, Number 1 8 New Mexico GeologyDeutz, P., Montañez, I.P. and Monger, H.C., Kues B.S., and Giles K.A., 2004, The late Paleo- Tabor, N.J. and Poulsen, C.J., 2008, Palaeocli- 2002, Morphology and stable and radiogenic zoic Ancestral Rocky Mountains system in mate across the Late Pennsylvanian–early isotope composition of pedogenic carbonates New Mexico; in Mack G.H., and Giles, K.A., Permian tropical palaeolatitudes: a review in late Quaternary relict soils, New Mexico, eds., The Geology of New Mexico, A Geologic of climate indicators, their distribution, and USA: an integrated record of pedogenic over- History: New Mexico Geological Society, relation to palaeophysiographic climate printing: Journal of Sedimentary Research, v. Special Publication 11, p. 95–136. factors: Palaeogeography, Palaeoclimatology, 72, p.809–822. Lucas, S.G. and Krainer, K., 2009, Pennsylvanian Palaeoecology, v. 268, p. 293–310. Dickinson, W.R., and Lawton, T.F., 2003, stratigraphy in the northern Oscura Moun- Tabor, N.J., Montañez, I.P., Scotese, C.R., Sequential intercontinental suturing as the tains, Socorro County, New Mexico: New Poulsen, C.J. and Mack, G.H., 2008, Paleosol ultimate control of Pennsylvanian Ancestral Mexico Geological Society, Guidebook 60, p. archives of environmental and climatic history Rocky Mountains deformation: Geology, v. 153–166. in paleotropical western Pangea during the 31, p. 609–612. Lucas, S.G., Krainer, K., and Barrick, J.E., 2009, latest Pennsylvanian through Early Permian: DiMichele, W.D., Cecil, C.B., Chaney, D.S., Elrick, Pennsylvanian stratigraphy and conodont bio- Geological Society of America, Special Paper S.D., Lucas, S.G., Lupia, R., Nelson, W.J. and stratigraphy in the Cerros de Amado, Socorro 441, p. 291–303. Tabor, N.J., 2011, Pennsylvanian-Permian County, New Mexico: New Mexico Geologi- Tanner, L.H., and Lucas, S.G., 2017, Paleosols vegetational changes in tropical Euramerica; cal Society, Guidebook 60, p. 183–212. of the Upper Paleozoic Sangre de Cristo For- in Harper, J.A., ed., Geology of the Pennsyl- Machette, M.N., 1985, Calcic soils of the south- mation, north-central New Mexico: Record vanian-Permian in the Dunkard basin: 76th western United States: Geological Society of of early Permian palaeoclimate in tropical Annual Field Conference of Pennsylvania America, Special Paper 203, p. 1–21. Pangea: Journal of Palaeogeography, v. 6, p. Geologists Guidebook, Washington, PA, p. Mack, G.H., 2003, Lower Permian terrestrial 144–162. 60–102. palaeoclimate indicators in New Mexico and Tanner, L.H., and Lucas, S.G., 2018, Pedogenic DiMichele, W.A., Chaney, D.S., Lucas, S.G., their comparison to palaeoclimate models: record of climate change across the Pennsyl- Nelson, W.J., Elrick, S.D., Falcon-Lang, H.J. New Mexico Geological Society, Guidebook vanian–Permian boundary in red-bed strata and Kerp, H., 2017, Middle and Late Penn- 54, p. 231–240. of the Cutler Group, northern New Mexico, sylvanian fossil floras from Socorro County, Mack, G.H., James, W.C., and Monger, H.C., USA: Sedimentary Geology, v. 373, p. 98–110. New Mexico, U.S.A: New Mexico Museum 1993, Classification of paleosols: Geological Thompson, M.L., 1942, Pennsylvanian System in of Natural History and Science, Bulletin 77, Society of America Bulletin, v. 105, p. 129–136. New Mexico: New Mexico School of Mines, p. 25–99. Monger, H.C., Cole, D.R., Buck, B.J. and State Bureau of Mines and Mineral Resources, Falcon-Lang, H.J., Jud, N.A., Nelson, W.J., Gallegos, R.A., 2009, Scale and the isotopic Bulletin 17, 92 p. DiMichele, W.A., Chaney, D.S. and Lucas, record of C4 plants in pedogenic carbonate: S.G., 2011, Pennsylvanian coniferopsid forests from the biome to the rhizosphere: Ecology, v. in sabkha facies reveal the nature of seasonal 90, p.1498–1511. tropical biome: Geology, v. 39, p. 371–374. Montañez, I.P., Tabor, N.J., Niemeier, D., DiMi- Gile, L.H., Peterson, F.F., and Grossman, R.B., chele, W.A., Frank, T.D., Fielding , C.R., and 1966, Morphological and genetic sequences Isbell, J.L., 2007, CO2-forced climate and of accumulation in desert soils: Soil Science, v. vegetation instability during late Paleozoic 100, p. 347–360. deglaciation: Science, v. 315, p. 87–91. Kluth, C.F. and Coney, P.J., 1981, Plate tectonics Montañez, I.P., McElwain, J.C., Poulsen, C.J., of the Ancestral Rocky Mountains: Geology, White, J.D., DiMichele, W.A., Wilson, J.P., v. 9, p. 10–15. Griggs, G., and Hren, M.T., 2016, Climate Kottlowski, F.E., 1960, Summary of Pennsylva- pCO2 and terrestrial carbon cycle linkages nian sections in southwestern New Mexico during Late Palaeozoic glacial-interglacial and southeastern Arizona: New Mexico cycles: Nature Geoscience, v. 9, p. 824–831. Bureau of Mines and Mineral Resources, Parrish, J.T., 1993, Climate of the superconti- Bulletin 66, 187 p. nent Pangaea: Journal of Geology, v. 101, p. Krainer, K., and Lucas, S.G., 2013,The Penn- 215–33. sylvanian Sandia Formation in northern and Rejas, A., 1965, Geology of the Cerros de Amado central New Mexico: New Mexico Museum area, Socorro County, New Mexico: [M.S. of Natural History and Science, Bulletin 59, thesis]: New Mexico Institute of Mining and p. 77–100. Technology, Socorro, 128 p. Krainer, K., Vachard, D., Lucas S.G., and Ernst, Retallack, G.J., 2005, Pedogenic carbonate prox- A., 2017, Microfacies and sedimentary ies for amount and seasonality of precipitation petrography of Pennsylvanian limestones and in paleosols: Geology, v. 33, p. 333–336. sandstones of the Cerros de Amado Area, east Tabor, N.J., and Montañez, I.P., 2004, of Socorro (New Mexico, USA): New Mexico Permo-Pennsylvanian alluvial paleosols Museum of Natural History and Science, (north-central Texas): High-resolution proxy Bulletin 77, p. 159–198. records of the evolution of early Pangean Kraus, M.J. and Hasiotis, S.T., 2006, Significance paleoclimate: Sedimentology, v. 51, p. of different modes of rhizolith preservation to 851–884. interpreting paleoenvironmental and paleo- hydrologic settings: examples from Paleogene paleosols, Bighorn Basin, Wyoming, U.S.A.: Journal of Sedimentary Research, v. 76, p. 633–646. Spring 2021, Volume 43, Number 1 9 New Mexico Geology
New Mexico Graduate Student Abstracts
New Mexico Geology recognizes the important research of graduate students working in M.S. and Ph.D. programs.
The following abstracts are from M.S. theses and Ph.D. dissertations completed in the last 12 months that pertain to the
geology of New Mexico and neighboring states.
New Mexico Institute of shelf to basin sandy turbidites and carbonate
mass-transport deposits sourced from the north
as the Nitt Monzonite. The Nitt Monzonite is
pervasively potassically and phyllically altered
Mining and Technology and northeastern shelf margins during Leonard- with local late-stage vein-controlled propylitic
ian time (275 Ma). Compositional heterogeneity alteration assemblages. Carbonate-phyllic alter-
TWO-STAGE LANDSLIDE EMPLACEMENT within this unit is poorly understood but strongly ation observed in the Nitt Monzonite consists
ON THE ALLUVIAL APRON OF AN impacts the spatial and temporal distribution of of sericite + carbonate + quartz + chlorite ±
EOCENE STRATOVOLCANO reservoir forming elements. Substantial research pyrite. This alteration style is atypical of the
Chirigos, Michael G., M.S. has focused on the Bone Spring Formation, but classic quartz-sericite-pyrite (QSP) type phyllic
little work has been undertaken to understand alteration of porphyry copper deposits.
The Sawtooth Mountains, western New Mex- the depositional controls on intramember min- The Nitt Monzonite exhibits an inherently
ico, comprise erosionally isolated klippen of eralogy and compositional heterogeneity of the low permeability (initial development of a graben associated with of 81.9 ka, the calculated intra-dome eruptive vanadium and arsenic are released under
collapse of the Magdalena caldera during the frequency is 1 eruption event per 5.5 ka for when oxidizing, alkaline conditions. Groundwater
mid-Tertiary. This study infers that, although Valles caldera enters periods of sustained dome leaching experiments showed appreciable release
not exposed at present erosion levels, a magma emplacement. Volume estimations, along with of uranium and vanadium, but not arsenic. The
intruded the fault zone associated with the published volumes of the youngest eruptions, third study investigates the leachability of redis-
graben and generated a magmatic hydrothermal indicate that the post-caldera dome and vent tributed-type ores from the Westwater Canyon
fluid which interacted with indigenous carbonate complexes range in volume from 0.8 km3 to Member, and primary-type ores of the Jackpile
strata in the subsurface. The dissolution of car- 14.1 km3 and have both increased and decreased Sandstone and Brushy Basin members. Here,
bonate resulted in modification of the magmatic throughout post-caldera evolution. In contrast, leaching tests using alkaline lixiviants and ambient
fluid which rose to upper structural levels and eruptive flux following caldera collapse has sys- groundwater showed that gangue mineralogy and
reacted with the Nitt Monzonite, producing the tematically increased between each post-caldera the non-mineral hosts of uranium produce leach-
carbonate phyllic alteration. This process may volcanic complex from 0.09 to 2.56 km3/ka ing trends entirely discordant to those of stoichio-
be related to underlying calcsilicate alteration in during post-caldera evolution. Using new ages of metric minerals previously identified as important
the subsurface rock units, with the potential for the caldera-forming ignimbrite, a syn-resurgent components in these deposits (meta-tyuyamunite,
accompanying base metal mineralization. lava, and the oldest post-resurgent ring-fracture meta-autunite, uraninite).
eruption, the resurgence durations at Valles
QUANTIFYING THE TIMESCALES OF caldera are constrained to be between 74.4 ± RAINFALL-RUNOFF RELATIONSHIPS IN
ERUPTIONS AND RESURGENCE FOL- 3.3 ka and 41.8 ± 6.7 ka. The average magmatic THE ARROYO DE LOS PINOS, SOCORRO,
LOWING CALDERA COLLAPSE: 40AR/39AR flux during resurgence is between 0.52 and 0.92 NEW MEXICO
DATING AND VOLUME ESTIMATIONS OF km3/ka, which is similar to pluton-filling rates, Richards, Madeline A., Ph.D.
POST-CALDERA VOLCANISM AT VALLES suggesting that resurgence is partially explained
CALDERA, NORTHERN NEW MEXICO by a significant decrease in magmatic flux follow- The Arroyo de los Pinos is an ephemeral tribu-
Nasholds, Morgan Wade Maynard, Ph.D. ing the large fluxes that sustain caldera-forming tary to the Rio Grande located in central New
magma bodies. Establishing an accurate timing Mexico, draining an area of 32 km2. In 2018 the
Despite recognition as one of the greatest of rapid events during post-caldera evolution is US Bureau of Reclamation funded a sediment
volcanic hazards in the southwestern United possible due to the combination of dating only transport study at the confluence of the arroyo
States, many aspects of the post-caldera history sanidine grains without melt inclusion-hosted and the Rio Grande, with the goal of monitoring
of Valles caldera are poorly constrained. This excess 40Ar and the ability of ARGUS VI mass sediment influx to the mainstream channel
study provides 49 new high-precision 40Ar/39Ar spectrometer to identify problematic grains that in order to better inform sediment transport
sanidine ages and surface volume estimations to skew the weighted mean ages. The eruptive fre- models. To supplement this study and to enable
reveal insights into lifespans of dome emplace- quency during dome activity and increasing flux generalization to other ephemeral tributaries,
ment as well as resurgence. Caldera collapse has important implications should Valles caldera more information was needed on up-basin flow
and deposition of the Tshirege Member of the enter a new phase of volcanic activity. Likewise, generating processes. This thesis focuses on these
Bandelier Tuff at 1231.6 ± 1.0 ka was followed developing similar comprehensive age and efforts to characterize the runoff generating
by emplacement of 34 volcanic units erupted volume datasets is necessary to assess hazards at mechanisms.
from vents on the resurgent dome and along the other Quaternary volcanic systems. A network of eighteen pressure transducers
caldera-ring fracture. New ages indicate vent and and five rain gauges were installed throughout
dome complexes that followed collapse were IMPLICATIONS OF CRYPTIC, NONSTOI- the arroyo’s watershed in various subbasin trib-
emplaced during polygenetic and monogenetic CHIOMETRIC URANIUM MINERAL- utaries. Pressure transducers monitored water
eruptive events. The Deer Canyon rhyolite IZATION ON THE FORMATION AND stage data, and these were converted to discharge
eruptions began immediately following caldera LEACHABILITY OF SANDSTONE-HOSTED hydrographs for each flow event. The runoff
formation and lasted until 1220.5 ± 3.6 ka for a URANIUM ORES, GRANTS DISTRICT, events monitored this way were all small, close
total lifespan of 11.4 ka. Similarly, the Redondo NEW MEXICO to the threshold of runoff generation, and did
Creek Member erupted between 1199.0 ± 5.9 Pearce, Alexandra Rose, Ph.D. not fully activate the channel network. Tipping
ka and 1186.3 ± 2.9 ka for a lifespan of 12.7 bucket rain gauges monitored rainfall. Data
ka. Cerro del Medio, the oldest post-resurgent This dissertation consists of three studies exam- collected from this network show that rainfall
dome, is also the longest-lived ring-fracture ining sandstone-hosted uranium ores from the intensity, subbasin lithology and antecedent soil
complex, erupting seven units in 25.2 ka between Grants uranium district in northwestern New moisture conditions are the primary factors that
1157.2 ± 3.1 and 1132.0 ± 4.7 ka. Following Mexico. The first investigates the mineralogy control runoff initiation, while total rainfall
Cerro del Medio, Cerros del Abrigo erupted at of primary-type uranium ores from the Jackpile depth and lithology are the main controls on run-
least twice between 1009.8 ± 1.7 and 997.0 ± Sandstone and Brushy Basin members of the off ratio, and subbasin area is the main control
1.6 ka. These longer-lived dome complexes are Jurassic Morrison Formation. These ores are on lag time.
located within structurally-complex zones of the characterized by cryptic mineral and mineraloid Prior to transducer installation, a particularly
caldera suggesting the dense network of faults mixtures, and uranium hosted by “uraniferous large flood on 7/26/2018 left behind high-water
promote magma transport to the surface, pro- organic matter.” The host organic matter and the marks at several locations throughout the water-
ducing long-lived eruptions. Conversely, the six uranium mineralization is interpreted as having shed. These high-watermarks were surveyed and
dome and vent complexes that erupted between been fixed within the sediments during multistage used as a proxy for maximum flood stage at
804.7 ± 1.9 ka and 68.7 ± 1.0 ka have shorter groundwater mixing episodes involving one each location. Peak stage comparisons show that
eruptive lifespans than the early post-caldera or more brines and humic acid-bearing fluid(s) maximum infiltration occurs in the lower third of
eruptions. Three of the complexes—San Antonio that resulted in humate flocculation. The second the watershed that is dominated by alluvial cover
Mountain, South Mountain, and the East Fork study evaluates the environmental geochemistry and where the channel develops a multi-threaded
Member—are polygenetic with lifespans between of ores of the Jackpile Sandstone sampled from planform. Results from a relative gravity survey
5.2 and 5.5 ka. The Cerro Santa Rosa 2, Cerro the St. Anthony Mine in Cibola County, NM. conducted in 2018 confirm that maximum
San Luis, and Cerro Seco domes are either mono- The site, slated for remediation, was assessed infiltration occurs in the lower elevations of the
genetic or polygenetic with lifespans less than by its responsible party using a geochemical watershed, where the channel is multi-threaded
the associated age uncertainties.The mapped model which used the uranylsilicate mineral and flows over alluvium.
post-caldera units are grouped into a total of 15 uranophane to determine alternate abatement
eruptive events, bracketed by measurable intra- standards for uranium in groundwater. In our
and inter-dome repose periods. Combined with examination, we did not find uranophane. Batch
the total duration of dome and vent lifespans leaching tests showed that significant uranium,
Spring 2021, Volume 43, Number 1 11 New Mexico GeologyPENNSYLVANIAN-PERMIAN EVOLUTION gene and Quaternary Puysegur Subduction Zone arc zircons (92–223 Ma). Isolated, secondary
OF THE DARWIN BASIN OF EASTERN of New Zealand. The formation of a subduction Cambrian peak ages occur at the 2.0 Ma strati-
CALIFORNIA: BASIN DEVELOPMENT zone on the southwestern margin of Laurentia graphic horizon in the Mesilla basin and 3.1 Ma
IN THE BACK-ARC OF THE INCIPIENT would end the transmission of transpressional stratigraphic horizon in the Socorro basin and
CORDILLERAN SUBDUCTION ZONE. stress from the California-Coahuila Transform overlap in age with Cambrian intrusions that
Vaughn, Lochlan Wright, Ph.D. Fault that drove Ancestral Rocky Mountains have been reported from parts of New Mexico
uplift. Our timeline for the onset of Cordilleran and southern Colorado (519–516 Ma). All strati-
The Pennsylvanian-Permian Darwin Basin of Subduction is independently supported by detailed graphic horizons record contributions derived
Eastern California records the abrupt onset of studies of ARM basins which indicate that the slip from Precambrian basement sources that were
large-magnitude subsidence of the southwestern on high-angle faults that drove ARM uplift ended being exhumed during Oligocene–Miocene rifting.
margin of Laurentia. The basin formed in the at the Pennsylvanian-Permian boundary. Mixing models were determined from the Rio
late Pennsylvanian but continuously expanded Grande rift corridor in southern Colorado and
during the early Permian as subsidence and
extensional faulting allowed calciclastic base-of- New Mexico State throughout New Mexico and used with detrital
zircon provenance trends to better understand
slope apron depositional systems to retrograde University the timing and nature of drainage development.
on to the subsided slope and shelf. Areal expan- Inputs for mixing models required grouping
sion of the Darwin Basin propagated east and source areas into three primary provinces that
PROVENANCE AND SEDIMENT MIXING
southeast through time and is marked by the first included detritus from (1) late Cenozoic volcanic
TRENDS OF THE PLIO–PLEISTOCENE
deposition of deep-water facies in areas that had fields primarily associated with the San Juan
ANCESTRAL RIO GRANDE FLUVIAL
been carbonate shelves since the Ordovician. A and Mogollon Datil volcanic fields, (2) recycled
SYSTEM, RIO GRANDE RIFT, NEW MEXICO
nearly identical stratigraphic and structural evo- Mesozoic strata (reflecting previously determined
Parker Ridl, Shay, M.S.
lution is present in the Pennsylvanian-Permian Mesozoic eolianite provenance signatures); and
of southern California, indicating that the driver (3) recycled Paleozoic and Precambrian basement
of subsidence in the Darwin Basin was able to Pliocene–Pleistocene strata that record axial-flu- that crop out along the Rio Grande rift flanks.
affect a large swath of the southwestern margin vial sedimentation of the ancestral Rio Grande The earliest phase of drainage development
of Laurentia at once. Furthermore, subsidence in fluvial system crop out in New Mexico and (~5.0–4.5 Ma) in northern New Mexico was
the Pennsylvanian-Permian of California coin- southern Colorado, and they preserve the history characterized by elevated detrital contributions
cides with a significant change in deformation of drainage evolution and late-stage exhumation from recycled Mesozoic stratigraphy likely
style of Ancestral Rocky Mountains basins and of the Rio Grande rift. Presented here are new derived from the Colorado Plateau, whereas
uplifts, suggesting that the driver of subsidence U-Pb detrital zircon data (N=8 samples; n=2382 basins in central and southern New Mexico were
in California may have affected tectonics across analyses) from the Camp Rice and Palomas receiving detritus largely from rift flanks (i.e.,
southwestern Laurentia. Speculative basin formations collected at two to three stratigraphic Paleozoic and Precambrian sources) and late
evolution models invoke tectonism associated intervals in the Socorro, Hatch-Rincon, Jornada Cenozoic volcanic-field sources. The late Pliocene
with the Late Paleozoic continent-truncating del Muerto, and Mesilla basins. U-Pb ages were (3.1–2.6 Ma) phase of drainage development in
California-Coahuila transform fault as the then integrated with similar, previous studies northern New Mexico was marked by a relative
principal driver of subsidence in the Darwin from age-equivalent strata that are exposed in decrease in detrital contributions from recycled
Basin and southern California. However, the southern Colorado and northern New Mexico to Mesozoic strata. The model shows nearly equal
onset of large-magnitude subsidence in southern develop sedimentary mixing models for the entire detrital contributions from recycled Mesozoic
and eastern California is spatially and tempo- Rio Grande rift corridor in this region. strata, rift flank, and volcanic field sources at the
rally associated with the first appearance of New U-Pb detrital zircon data from the central 3.1–2.6 Ma stratigraphic horizon in central and
magmatism and volcaniclastic sedimentation in and southern portion of the Rio Grande fluvial southern New Mexico. The Pleistocene (2.0–1.6
the Late Paleozoic of the southwestern U.S. The system record peak ages at 34, 167, 519, 1442, Ma) phase of drainage development records a
geochemistry of these early to middle Permian and 1686 Ma, suggesting that the ancestral Rio shift in provenance in the southern rift basins
igneous rocks, which include plutons and lavas Grande was receiving detritus from late Ceno- and models suggest decreased contributions
in southern California and newly identified tuffs zoic volcanic fields (e.g., San Juan and Mogollon from late Cenozoic volcanic field and rift flank
in eastern California, demonstrates that these Datil volcanic fields), recycled Mesozoic stra- sources, and increased contributions from recy-
rocks formed in a continental subduction zone. tigraphy (Mesozoic eolianites), and Proterozoic cled Mesozoic stratigraphy.
The presence of continental arc-derived igneous basement provinces (e.g., A-Type granitoids and Provenance data and mixing trends that
rocks in the early Permian of California is inter- the Mazatzal and Yavapai provinces). Although demonstrate increased detrital contributions
preted to indicate that the onset of Cordilleran peak ages across the southern Rio Grande rift from recycled Mesozoic strata of the Colorado
Subduction occurred earlier than has previously are similar across all basins and stratigraphic Plateau support a model of headward erosion
been recognized. horizons in this study, there are distinct spatial of the Rio Puerco into the Jemez Lineament and
We present 15 new measured sections, facies and temporal, up-section changes in provenance southwestern margin of the Colorado Plateau
analysis, clast and point counts, and new cono- recorded across the southern Rio Grande fluvial during the Plio–Pleistocene. Headward erosion
dont biostratigraphy that document the Pennsyl- system in central and southern New Mexico. and possibly minor exhumation along the west-
vanian-Permian evolution of the Darwin Basin. Basal strata (~5.0–4.5 Ma) record the largest ern margin of the rift resulted in increased detrital
We also report on whole-rock geochemistry and contributions of detritus derived from the San contributions from the oldest and deepest parts
XRD analysis of five previously unknown tuffs Juan and Mogollon Datil volcanic fields (34–29 of caldera sources between the Pliocene and late
identified in the Darwin Basin. We propose that Ma) and lesser occurrences of recycled Cordille- Pliocene. These same caldera source areas were
subsidence in the Darwin Basin and southern ran arc zircons derived from recycled Mesozoic less of a source for the system by the Pleistocene.
California was caused by extension and dynamic stratigraphy from the Colorado Plateau. The
topography above the incipient Cordilleran Sub- late Pliocene phase (3.1–2.6 Ma) marks similar ERUPTIVE VOLUME AND EXPLOSION
duction Zone. We further suggest that the first contributions of detritus derived from late Ceno- ENERGY ESTIMATES FROM KILBOURNE
appearance of this subsidence dates the onset of zoic volcanic fields and marks the emergence of HOLE MAAR, SOUTH-CENTRAL
subduction, which appears to have begun shortly peaks that overlap with recycled Cordilleran arc NEW MEXICO
before the Pennsylvanian-Permian boundary. Arc sources (217–82 Ma). Pleistocene (2.0–1.6 Ma) Vitarelli, Daniela C., M.S
magmatism may have begun as early as 290 Ma, stratigraphic horizons show a relative decrease
but was likely low-volume and confined to small of zircons that overlap in age with the San Juan
portions of the southwestern plate margin during and Mogollon Datil volcanic field sources and an Maar-diatremes are a common type of mono-
the Permian, as is the case for the nascent Neo- increase in contributions of recycled Cordilleran genetic volcano defined by ascending magma
Spring 2021, Volume 43, Number 1 12 New Mexico GeologyYou can also read
