New GSA Bulletin Articles Published Online Ahead of Print in October
Boulder, Colo., USA: The Geological Society of America regularly publishes
articles online ahead of print. GSA Bulletin topics studied this
month include the nature and dynamics of China and Tibet; lithologic
controls on microfracturing from legacy underground nuclear explosions; and
late Cenozoic deepening of Yosemite Valley, USA. You can find these
articles at
https://bulletin.geoscienceworld.org/content/early/recent
.
Rifted margin with localized detachment and polyphase magmatism: A new
model of the northern South China Sea
Shihao Hao; Lianfu Mei; Xiong Pang; Laurent Gernigon; Douglas Paton ...
Abstract:
Continental passive margins are commonly classified into volcanic (or
magma-rich) and non-volcanic (or magma-poor) types based on the magmatic
budget. It is difficult, however, to use either of these models to define
the northern margin of the South China Sea (SCS). Based on 2-D/3-D
time/depth-migrated seismic data and borehole data from the Pearl River
Mouth Basin in the northern SCS, we examine the detachment fault systems
and syn-rift magmatism in the Baiyun and Liwan Sags. The detachment fault
systems and related tilted blocks of the northern SCS established in the
Baiyun and Liwan Sags in previous studies may be mainly constrained to the
Baiyun Sag. The Liwan Sag, however, acts as a “sag-type” basin accompanied
by magmatic domes. Radiometric age of igneous samples from wells, coupled
with multi-horizon onlapping terminations within syn-rift layers, reveal
four-phase rift-related magmatism in the northern SCS. The crustal thinning
in the Baiyun Sag is controlled by a detachment fault, but in the Liwan
Sag, it is mainly controlled by a preferential thinning of the lower crust.
High thermal conditions and intense syn-rift magmatism weakened the lower
crust, which contributes to the depth-dependent thinning in the Liwan Sag.
View article:
https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B36264.1/618540/Rifted-margin-with-localized-detachment-and
Formation of authigenic carbonates contributed by sulfate- and
metal-driven anaerobic oxidation of methane in the northern Okinawa
Trough, East China Sea
Lei Liu; Hongxiang Guan; Lanfang Xu; Zhilei Sun; Nengyou Wu
Abstract:
Authigenic carbonates of the northern Okinawa Trough have been shown to be
contributed by both sulfate- and Fe-driven anaerobic oxidation of methane
(SD-AOM and Fe-AOM, respectively); however, the microorganisms involved
remain poorly constrained. To better understand the types and roles of
microorganisms in specific biological methane oxidation processes,
authigenic carbonates collected from the northern Okinawa Trough at water
depths between ∼540 m and 700 m were studied using petrographic,
mineralogical, elemental, and lipid biomarker analyses. The carbonate
minerals were primarily aragonite, high-magnesium calcite, low-magnesium
calcite, or dolomite. The extremely low δ13C values of bulk
carbonates (−59.2‰), molecular fossils of anaerobic methane oxidizing
archaea (ANME; −131‰), and sulfate-reducing bacteria (SRB; −77‰) indicated
that the authigenic carbonates formed as products of AOM. Biogenic methane
was confirmed to be the main carbon source for all carbonates, whereas
bio-degraded oil and hydrothermal input complemented carbon sources, as
revealed by the occurrence of unresolved complex mixture, strongly enriched
As and Sb, and their correlations with Fe/Al. Combined with enriched δ 18O values (as high as +5‰), the methane fluids were suggested
to derive from the dissociation of gas hydrates. ANME-2 and a mixture of
ANME-1 and ANME-2 were identified for the two calcitic carbonates,
respectively, as revealed by their specific biomarker patterns. The
relatively higher contents of 13C-depeleted isoprenoids and
SRB−related fatty acids, strong Mo enrichment, and biological debris in
both calcite- and aragonite-dominated carbonates reflect precipitation
driven by SD-AOM in a shallow sulfate-methane transition. For other seep
carbonates, low amounts of 13C-depeleted isoprenoids and the
near absence of crocetane suggest dominance of the ANME-1 assemblage. The
extremely low amounts and non-13C-depleted iso-/ anteiso-C15:0 fatty acids (−27‰) in the
dolomite-containing carbonates indicate the decoupling of ANME and SRB.
These carbonates were most likely formed below or at the bottom of the
sulfate-methane transition and included contributions from Fe-AOM, as
indicated by the low Mo content, occurrence of dolomite and siderite, and
decreased δ56Fe values with increasing Fe/Al ratios.
View article:
https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B36400.1/618541/Formation-of-authigenic-carbonates-contributed-by
Quantitative and geomorphologic parameterization of megaclasts within
mass-transport complexes, offshore Taranaki Basin, New Zealand
Wei Li; Yan Li; Kamaldeen O.L Omosanya; Tiago M. Alves; Song Jing ...
Abstract:
Mass-transport complexes (MTCs) in sedimentary basins reflect the
gravitational transport of sediments from the shelf edge to the abyssal
plain. Megaclasts, large sedimentary blocks of hundreds of meters long
within MTCs, can record kinematic and sedimentary information deemed
essential to understanding source-to-sink systems. Yet, deformation
structures in such megaclasts remain poorly understood. This study uses
high-quality, three-dimensional (3-D) seismic reflection data from the
deep-water Taranaki Basin offshore New Zealand to analyze the morphological
character of 123 megaclasts and propose a new classification scheme based
on their morphometric properties. The megaclasts are up to 400 m tall, 1900
m long, and 1200 m wide. In the study area, they are high- to
moderate-amplitude features owing to their different lithologies and
continuous-to-contorted seismic facies. The megaclasts can be classified as
undeformed, rotated, deformed, and highly deformed based on their internal
deformational styles. Two different kinds of morphological depressions
observed on their basal shear zones further indicate whether the megaclasts
are transported or formed in situ. Our study demonstrates that quantitative
parameterization of the megaclasts provides important information about
their deformational processes and a more complete understanding of
megaclast emplacement along continental margins.
View article:
https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B36446.1/618542/Quantitative-and-geomorphologic-parameterization
Cambrian−Ordovician magmatic flare-up in NE Gondwana: A silicic large
igneous province?
Wei Dan; J. Brendan Murphy; Gong-Jian Tang; Xiu-Zheng Zhang; William M.
White ...
Abstract:
The origin of the Cambrian−Ordovician tectono-magmatic events affecting NE
Gondwana and the adjacent peri-Gondwanan terranes (e.g., Himalaya, Lhasa,
Southern Qiangtang, Baoshan, Tengchong, Sibumasu, Helmand, and Karakorum)
is controversial. Although its volume is poorly constrained, we propose
that an extensive belt of granitic rocks that formed in various pulses
between ca. 510 Ma and 460 Ma may represent the remains of a potential
silicic large igneous province (LIP), which is referred to here as the
Pinghe silicic LIP, with an areal extent of ∼2.5 Mkm2. The
putative Pinghe silicic LIP is composed predominantly of S-type granites
with subordinate A-type granites and minor intraplate mafic rocks. The
recognition of this belt of granitic rocks aids in the refinement of
tectonic reconstructions of Gondwana and of models for the rifting of
terranes from its northern margin. The Pinghe silicic LIP broadly coincides
with the adjacent 511 Ma Kalkarindji LIP in northern Australia, and the
plume or mantle upwelling that triggered the Kalkarindji LIP may have been
responsible for driving crustal melting that generated the granitic rocks,
in a manner analogous to the Karoo−Chon Aike association.
View article:
https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B36331.1/618507/Cambrian-Ordovician-magmatic-flare-up-in-NE
Growth of the southern Tian Shan-Pamir and its impact on central Asian
climate
Fabiana Richter; Jozi Pearson; Marius Vilkas; Richard V. Heermance; Carmala
N. Garzione ...
Abstract:
Uplift and amalgamation of the high-elevation (>3000 m) Tian Shan and
Pamir ranges in Central Asia restricts westerly atmospheric flow and
thereby limits moisture delivery to the leeward Taklimakan Desert in the
Tarim Basin (<1500 m), the second largest modern sand dune desert on
Earth. Although some research suggests that the hyper-arid conditions
observed today in the Tarim Basin developed by ca. 25 Ma, stratigraphic
evidence suggests the first erg system did not appear until 12.2 Ma. To
address this controversy and to understand the tectonic influences on
climate in Central Asia, we studied a continuous, 3800-m-thick
stratigraphic section deposited from 15.1 to 0.9 Ma now exposed within the
western Kepintagh fold-and-thrust belt in the southern Tian Shan foreland.
We present new detrital zircon data (n = 839), new carbonate oxygen (δ 18Oc) and carbon (δ13Cc) stable
isotope compositions (n = 368), structural modeling, and stratigraphic
observations, and combine these data with recently published
magnetostratigraphy and regional studies to reconstruct the history of
deposition, deformation, and climate change in the northwestern Tarim
Basin. We find that basins along the southern (this study) and northern
(i.e., Ili Basin) margins of the Tian Shan were likely receiving similar
westerly precipitation by 15 Ma (δ18Oc = ∼−8‰) and
had similar lacustrine-playa environments at ca. 13.5 Ma, despite
differences in sedimentary provenance. At ca. 12 Ma, an erg desert formed
adjacent to the southern Tian Shan in the northwestern Tarim Basin,
coincident with a mid- to late Miocene phase of deformation and exhumation
within both the Pamir and southern Tian Shan. Desertification at ca. 12 Ma
was marked by a negative δ18Oc excursion from −7.8 ±
0.4‰ to −8.7 ± 0.7‰ in the southern Tian Shan foreland (this study), coeval
with a negative δ18Oc excursion (∼−11 to −13‰) in the
Tajik Basin, west of the Pamir. These data suggest that only after ca. 12
Ma did the Pamir-Tian Shan create a high-elevation barrier that effectively
blocked westerly moisture, forming a rain shadow in the northwestern Tarim
Basin. After 7 Ma, the southern Tian Shan foreland migrated southward as
this region experienced widespread deformation. In our study area, rapid
shortening and deformation above two frontal foreland faults initiated
between 6.0 and 3.5 Ma resulted in positive δ13Cc
excursions to values close to 0‰, which is interpreted to reflect
exhumation in the Tian Shan and recycling of Paleozoic carbonates.
Shortening led to isolation of the study site as a piggy-back basin by 3.5
Ma, when the sediment provenance was limited to the exhumed Paleozoic
basement rocks of the Kepintagh fold belt. The abrupt sedimentologic and
isotopic changes observed in the southern Tian Shan foreland appear to be
decoupled from late Cenozoic global climate change and can be explained
entirely by local tectonics. This study highlights how tectonics may
overprint the more regional and global climate signals in active tectonic
settings.
View article:
https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B36471.1/618334/Growth-of-the-southern-Tian-Shan-Pamir-and-its
Lithologic controls on microfracturing from legacy underground nuclear
explosions
Erika M. Swanson; Jennifer E. Wilson; Aviva J. Sussman
Abstract:
Detection and verification of underground nuclear explosions (UNEs) can be
improved with a better understanding of the nature and extent of
explosion-induced damage in rock and the effect of this damage on
radionuclide migration. Much of the previous work in this area has focused
on centimeter- to meter-scale manifestations of damage, but to predict the
effect of damage on permeability for radionuclide migration, observations
at smaller scales are needed to determine deformation mechanisms. Based on
studies of tectonic deformation in tuff, we expected that the heterogeneous
tuff layers would manifest explosion-induced damage differently, with
welded tuffs showing more fractures and nonwelded tuffs showing more
deformation bands. In comparing post-UNE samples with lithologically
matched pre-UNE equivalents, we observed damage in multiple lithologies of
tuff through quantitative microfracture densities. We find that the texture
(e.g., from deposition, welding, alteration, etc.) affects fracture
densities, with stronger units fracturing more than weaker units. While we
see no evidence of expected deformation bands in the nonwelded tuffs, we do
observe, as expected, much larger microfracture densities at close range
(<50 m) to the explosive source. We also observe a subtle increase in
microfracture densities in post-UNE samples, relative to pre-UNE
equivalents, in all lithologies and depths. The fractures that are
interpreted to be UNE-induced are primarily transgranular and
grain-boundary microfractures, with intragranular microfracture densities
being largely similar to those of pre-UNE samples. This work has
implications for models of explosion-induced damage and how that damage may
affect flow pathways in the subsurface.
View article:
https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B36466.1/618335/Lithologic-controls-on-microfracturing-from-legacy
Cretaceous−Cenozoic cooling history of the Qiangtang terrane and
implications for Central Tibet formation
Wenjun Bi; Yalin Li; Peter J.J. Kamp; Ganqing Xu; Jiawei Zhang ...
Abstract:
Reconstructing the growth process of the Qiangtang terrane in space and
time is crucial for understanding the geological evolution of Central
Tibet. However, its growth process and dynamic mechanism remain unclear.
Here, we present new fission track data obtained along a N-S transect near
the Puruo Kangri Mountain in the central zone of the Northern Qiangtang
terrane. The completely reset apatite fission track ages of detrital
samples range from 65.1 to 89.6 Ma, which show a northward younging trend.
The thermal history modeling results indicate that this region underwent
northward-propagating exhumation during the Late Cretaceous (ca. 92−65 Ma).
Our data, combined with previously reported low-temperature
thermochronology data for the Qiangtang terrane, suggest that the Qiangtang
terrane experienced three main stages of cooling: ca. 120−65, ca. 55−35,
and <25−0 Ma. The first stage (ca. 120−65 Ma) displays an
outward-propagating cooling pattern from the Central Qiangtang terrane,
which was related to the crustal shortening and thickening driven by the
Lhasa-Qiangtang collision. The low exhumation rate, flat lavas, and
paleoaltimetry studies imply that the central and southern zones of the
Northern Qiangtang terrane and Central Qiangtang terrane may form plateau
landscape by 65−55 Ma. The second stage (ca. 55−35 Ma) of cooling is mainly
documented in the Southern Qiangtang terrane, and the northern zone of the
Northern Qiangtang terrane. This cooling event was caused by the crustal
deformation and shortening driven by intracontinental subduction related to
ongoing convergence of the Indian and Asian plates. Subsequently, both the
transition to low erosion rates (<0.05 mm/yr) and paleoaltimetry data
indicate that the Qiangtang terrane became a primitive plateau by ca. 35
Ma. The final stage (<25−0 Ma) of cooling was linked to the E-W
extension in the Qiangtang terrane.
View article:
https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B36313.1/618336/Cretaceous-Cenozoic-cooling-history-of-the
New insights into deep carbon recycling and formation of
nepheline-bearing alkaline rocks from Sr-Nd-Mg isotope compositions
Weiliang Kong; Zhaochong Zhang; Dongyang Zhang; Changhong Wang; M. Santosh
...
Abstract:
Magnesium isotopes are widely used to trace recycled carbonates in the
mantle source. We recently recognized extremely light Mg isotope values (δ 26Mg = −0.50 to −0.62‰) in nepheline syenites in the Tarim large
igneous province (TLIP), NW China. To evaluate the significance of the
light Mg isotopes, we conducted petrological, mineral chemical, zircon U-Pb
ages, and geochemical and isotopes (Sr-Nd-Mg) analyses on the nepheline
syenite to understand its petrogenesis. Laser ablation−inductively coupled
plasma−mass spectrometry zircon U-Pb dating yields an age of 272.5 ± 1.4 Ma
for the nepheline syenite. Petrographic and geochemical studies show that
the nepheline syenite and nephelinite in the TLIP display similar mineral
assemblages, clinopyroxene Sr isotope compositions and bulk-rock Sr and Nd
isotope compositions (87Sr/86Sr(i) =
0.70364−0.70399, εNd(t) = +3.51 to +4.49 versus 87Sr/ 86Sr(i) = 0.70348−0.70371, εNd(t) = +3.28
to +3.88 for nepheline syenite and nephelinite, respectively), indicating
they are possibly co-magmatic. Rhyolite-MELTS modeling shows that the
nepheline syenite formed from nephelinite by fractional crystallization of
spinel, olivine, clinopyroxene, apatite, and biotite. In combination with
information from previous studies, we correlated the extremely light
magnesium isotopes of nepheline syenite to “genetic genes” of nephelinite
(δ26Mg = −0.35 to −0.55‰) which were produced by the reaction
between peridotite and carbonated silicate melt derived from the carbonated
eclogite. We invoke a three-stage model for the genesis of the nepheline
syenite in the TLIP. Initially, the subduction of oceanic crust delivered
the sedimentary carbonate rocks into the deep mantle and formed carbonated
eclogite. The carbonated silicate melt derived by the melting of the
carbonated eclogite reacted with ambient peridotite to form primary
nephelinitic magma. Finally, fractional crystallization of nephelinitic
melt during ascent produced the nepheline syenite. Our study provides
insights into the implication of light magnesium isotopes for deep carbon
recycling in the origin of alkaline rocks.
View article:
https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B36555.1/618247/New-insights-into-deep-carbon-recycling-and
East Antarctic Ice Sheet variability during the middle Miocene Climate
Transition captured in drill cores from the Friis Hills, Transantarctic
Mountains
Hannah Chorley; Richard Levy; Tim Naish; Adam Lewis; Stephen Cox ...
Abstract:
This study describes 16 well-dated, terrestrial glacial sedimentary cycles
deposited during astronomically paced climate cycles from the termination
of the Miocene Climatic Optimum (MCO) through the middle Miocene Climate
Transition (MMCT) (15.1−13.8 Ma) in the Friis Hills, Transantarctic
Mountains, Antarctica. Three locations were continuously cored (79%
recovery) to a maximum depth of 50.48 m through a succession of interbedded
till sheets and fossil-bearing, fluvio-lacustrine sediments. A composite
chronostratigraphic framework is presented for the cores based on the
previous mapping, a seismic refraction survey that defines basin geometry,
and a new, integrated age model based on paleomagnetic stratigraphy that is
constrained by radioisotopic 40Ar/39Ar numeric ages
on two newly identified silicic tephra. The paleoecologic and
sedimentologic characteristics of organic-rich lithologies are relatively
consistent up-section, which implies that successively younger interglacial
deposits during the MMCT represented broadly similar environmental and
climatic conditions. During these interglacials, the Friis Hills hinterland
was likely ice-free. Major disconformities in the section suggest a
transition to colder climates, and after ca. 14.6 Ma, thicker, more
extensive and erosive ice cover occurred across the Friis Hills during
glacial episodes. Diamictites in the upper three cycles suggest that
climate cooled and became drier after ca. 14.2 Ma. However, cyclical
retreat of the ice and a return to warm climate conditions during
interglacials continued through ca. 13.9 Ma. These direct records reflect a
highly variable East Antarctic Ice Sheet margin but show that the ice
margin became progressively more extensive during successive glacial
intervals, which is consistent with a cooling trend toward more glacial
values in the far-field benthic foraminifera δ18O proxy ice
volume and temperature record. Age constraints show that
glacial-interglacial variability at the terrestrial margin of the East
Antarctic Ice Sheet was primarily paced by astronomical precession (∼23
k.y.) through the onset of the MMCT (15−14.7 Ma). Precession-driven cycles
are modulated by short-period (∼100 k.y.) eccentricity cycles. Intervals of
maximum eccentricity (high seasonality) coincide with sedimentary cycles
comprising thin diamictites and relatively thick interglacial sandstone and
mudstone units. Intervals of minimum eccentricity (low seasonality)
coincide with sedimentary cycles comprising thick diamictites and
relatively thin interglacial sedimentary deposits. Major disconformities in
the Friis Hills succession that span more than ∼100 k.y. reflect episodes
of expansion of erosive ice across, and well beyond, the Transantarctic
Mountains and coincide with nodes in eccentricity (∼400 k.y.). These
relationships suggest that during relatively warm intervals in the middle
Miocene, the East Antarctic Ice Sheet expanded and contracted over 100 k.y.
cycles, while its margins continued to fluctuate at higher (∼23 k.y.)
frequency. After 14.5 Ma, obliquity is the dominant frequency in δ 18O records, marking a period during which large regions of the
Antarctic Ice Sheet grounded in marine environments.
View article:
https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B36531.1/618248/East-Antarctic-Ice-Sheet-variability-during-the
Geological architecture and history of the Antigua volcano and
carbonate platform: Was there an Oligo−Miocene lull in Lesser Antilles
arc magmatism?
Leny Montheil; Mélody Philippon; Jean-Jacques Cornée; Marcelle
BouDagher-Fadel; Douwe J.J. van Hinsbergen ...
Abstract:
Since the acceptance of plate tectonics, the presence of calc-alkaline
magmatic rocks has been recognized as evidence of subduction. But under
specific geodynamic circumstances, subduction may occur without generating
magmas. Here, we investigate the Cenozoic northern Lesser Antilles arc
where, from sparsely exposed magmatic records, Eocene−Oligocene and
Pliocene magmatic flare-ups and a Miocene lull were postulated.
Nevertheless, most of the arc is submarine, so it is challenging to discern
lulls and flare-ups from sampling bias. We review the magmatic evidence
exposed onshore in the Lesser Antilles and investigate in detail the island
of Antigua, which exposes an Eocene to Miocene volcanic sequence and
platform carbonate series that coincide with the postulated lull. By
combining lithostratigraphic analysis, structural mapping, 40Ar/ 39Ar geochronology, and biostratigraphy, we refine the magmatic
history of the island and date the arrest of extensive arc magmatism at 35
Ma, with minor activity until 27 Ma. No magmatic products are interleaved
with the platform sequence until the latest Oligocene, which confirms a
lull in northern Lesser Antilles arc magmatism that may have lasted ca. 20
Ma. Flare-up of magmatic activity contributed to crustal thickening and
land emersion, whereas magmatic lulls and related thermal cooling induced
subsidence/submersion. Thus, we propose that the paleo-(bio)-geographical
evolution of the eastern Caribbean region has been partly controlled by
magmatic activity. Fault kinematic analysis, along with anisotropy of
magnetic susceptibility, suggest that, at the island scale, magmatic arrest
is not associated with a change in stress field during the Oligocene. We
speculate that slab flattening triggered by progressive curvature played a
role in the temporal shutdown of the northern Lesser Antilles arc.
View article:
https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B36465.1/618249/Geological-architecture-and-history-of-the-Antigua
Late Cenozoic deepening of Yosemite Valley, USA
Kurt M. Cuffey; Alka Tripathy-Lang; Matthew Fox; Greg M. Stock; David L.
Shuster
Abstract:
Although Yosemite Valley, USA, catalyzed the modern environmental movement
and fueled foundational debates in geomorphology, a century of
investigation has failed to definitively determine when it formed. The
non-depositional nature of the landscape and homogeneous bedrock have
prevented direct geological assessments. Indirect assumptions about the age
of downcutting have ranged from pre-Eocene to Pleistocene. Clarity on this
issue would not only satisfy public interest but also provide a new
constraint for contentious debates about the Cenozoic tectonic and
geomorphologic history of the Sierra Nevada in California. Here we use
thermochronometric analysis of radiogenic helium in apatite crystals,
coupled with numerical models of crustal temperatures beneath evolving
topography, to demonstrate significant late Cenozoic deepening of Tenaya
Canyon, Yosemite’s northeastern branch. Approximately 40%−90% of the
current relief has developed since 10 Ma and most likely since 5 Ma. This
coincides with renewed regional tectonism, which is a long-hypothesized but
much debated driver of Sierran canyon development. Pleistocene glaciation
caused spatially variable incision and valley widening in Yosemite Valley,
whereas little contemporaneous erosion occurred in the adjacent upper
Tuolumne watershed. Such variations probably arise from glacial erosion’s
dependence on opographic focusing of ice discharge into zones of rapid
flow, and on the abundance of pre-existing fractures in the substrate. All
available data, including those from our study, are consistent with a
moderately high and slowly eroding mid-Cenozoic Sierra Nevada followed by
significant late Cenozoic incision of some, but not all, west-side canyons.
A likely driver of this event was range-crest uplift accompanied by
fault-induced beheading of some major drainages, although other mechanisms
such as drainage reorganization following volcanic deposition are
plausible.
View article:
https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B36497.1/618250/Late-Cenozoic-deepening-of-Yosemite-Valley-USA
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