Big Bend Research Articles

New insights into the kinematics of fault-propagation folding from analogue models monitored using particle image velocimetry

This study aimed to understand the 2D kinematic processes associated with the development of fault-propagation folds in contractional systems. Analogue models were used to analyse the influence of, and the interplay among, various parameters, including: (1) the analogue material (quartz sand v. glass microspheres); (2) the mechanical stratigraphy (anisotropic models v. models with two different analogue-packs); and (3) the initial thickness of the analogue-pack. Each model was analysed using particle image velocimetry to quantify the spatial and temporal patterns of the strain rates during progressive deformation. The results showed that fault-propagation folding combines different kinematic mechanisms, such as flexural slip and basal thickening. Ramp initiation can occur in different ways: from the detachment, within the deformed layers or via a combination of these processes, as observed in outcrops of the Jaca–Pamplona Basin (southern Pyrenees) and the Big Bend National Park (western Texas, USA).

A late Pleistocene nest cave of Gymnogyps californianus (California Condor) in Texas: New radiocarbon and stable isotope analyses

ABSTRACT Fossil remains of Gymnogyps californianus (California Condor) from Mule Ears Peak Cave, Big Bend National Park, Texas, recovered in the 1930s were reexamined to determine a precise age for nesting condors in this region. Bones of at least 6 prefledged chicks account for most (15, or 65%) of the 23 skeletal elements from this cave and a new osteology collection of known-age condor chicks at the U.S. National Museum, Division of Birds, now allows accurate estimate of the age of death of these fossil condor chicks based on their bone development and porosity. Current and previous radiocarbon dates on juvenile and adult bones, respectively, indicate the presence of condors at this site beginning at ~15,000 calendar years before present (cal yrs BP), with definite nesting occurring at ~13,000 cal yrs BP. Stable isotope analysis (δ13C and δ15N) of bone collagen on 2 bones of adult condors reflects a diet similar to other fossil condors previously analyzed from the inland western U.S. The δ13C values in the Mule Ears Peak condors indicate a diet of megafauna that subsisted on C4 plants in a desert grassland ecosystem. These results support the hypothesis that condors were extirpated from the inland west with the loss of megafauna at the end of the Pleistocene. Further, Big Bend National Park with its vast open space and cliffs and canyons for nesting condors should be considered as an additional release site for captive-reared condors as part of the current Condor Recovery Program.

Carbon isotope chemostratigraphy of the Yucca Formation from the Solitario, Big Bend Ranch State Park, Texas

Introduction: The Yucca Formation is a Lower Cretaceous sedimentary unit present in West Texas. Based on its relative stratigraphic position in the Cretaceous succession of West Texas, it is expected that the Yucca Formation is of Albian and/or Aptian age. It is also expected that the carbon isotope excursions associated with OAE 1a and OAE 1b should be identified in the Yucca Formation. The goals of this project are to 1. construct a carbon isotope chemostratigraphic record of the Yucca Formation, and 2. correlate the Yucca Formation with strata of similar age using chemostratigraphy.Methods: 163 samples were collected from Big Bend Ranch State Park (BBRSP) to determine the δ13C value of bulk sedimentary organic matter.Results: C-isotope values range from −27.02‰ to −18.42‰.Discussion: Carbon isotope excursions (CIEs) that are associated with the Aptian-Albian Boundary are identified as well as CIEs associated with Oceanic Anoxic Events (1a and 1b). This allows us to conclude that the Aptian-Albian boundary is recorded within the Yucca Formation strata at about 71 m above the base of the section exposed in the Lower Shutup of the Solitario in Big Bend Ranch State Park. Regional correlation of the Yucca Formation to other chemostratigraphic records from other Cretaceous strata suggests that the Yucca Formation in BBRSP is time equivalent to the Sligo, Pine Island, James, Bexar, and a portion of the lower Glen Rose Formation on the Comanche Platform and to a portion of the lower Glen Rose Formation in Big Bend National Park.

Stratigraphy and depositional history of the Aguja Formation (Upper Cretaceous, Campanian) of West Texas, southwestern USA

Abstract Although the Aguja Formation (West Texas, southwestern USA) and its fossil vertebrate fauna have been known for over a century, its basic stratigraphic requisites (type area and type section) have not been formally documented. The formation is herein subdivided into a series of formal members, and a lectostratotype section is proposed. Lithostratigraphic and biostratigraphic subdivisions are documented and integrated with geochronologic data to provide an age model for the formation. Four terrestrial vertebrate biozones are proposed. There are at least four major depositional intervals represented in the Aguja and intertonguing Pen Formations. An initial progradational deltaic succession is recorded by the La Basa Sandstone and lower part of the Abajo Shale Members of the Aguja Formation. A second phase of deposition resulted in a retrogradational shoreface succession that includes the upper part of the Abajo Shale, overlying Rattlesnake Mountain Sandstone Member, and lower part of the McKinney Springs Tongue of the Pen Formation, up to a skeletal phosphate bed interpreted to represent the maximum flooding surface. The third phase of deposition comprises a progradational deltaic succession that includes the upper part of the McKinney Springs Tongue, Terlingua Creek Sandstone Member of the Aguja Formation, and lower part of the Alto Shale Member of the Aguja Formation. This third succession records eastward migration of the strandline and withdrawal of the Western Interior Seaway from the Big Bend region. The fourth phase of deposition comprises a series of aggradational fluvial channel and floodplain successions that form the upper part of the Alto Shale Member and is coincident with redirection of stream flow to the southeast. This interval is much thicker in the central part of the Big Bend region, thins to the southwest and northeast, and likely records initial subsidence in the Laramide Tornillo Basin. The upper part of this succession was also contemporaneous with a series of basaltic pyroclastic eruptions, the westernmost expression of the Balcones igneous province. A dramatic constriction in the southern entrance to the Western Interior Seaway through the Gulf of Mexico occurred during this final phase in deposition of the Aguja Formation and corresponds to a shift of stream flow southeastward and to an outbreak of local pyroclastic eruptions. Regional uplift associated with this episode of magmatism is likely responsible for closing the southern aperture of the Western Interior Seaway.

Seismotectonics of the San Andreas Fault System in the San Gorgonio Pass region: A synthesis

In the San Gorgonio Pass region of Southern California, USA, the San Andreas fault exhibits greater geometric complexity than anywhere else along its length, with multiple nonparallel fault strands that branch and join both laterally and at depth (Fig. 1). These structures are associated with regional contraction within the San Gorgonio Pass region due to the nearby Big Bend of the San Andreas fault. The complexity of past and present faulting in this region has led Jon Matti, Doug Yule, and others to call this the “San Gorgonio knot.” Due to its complexity, this part of the San Andreas fault system may serve as both a barrier and an initiation point for devastating earthquakes. Research to understand and unravel the San Gorgonio knot has important implications for seismic hazard in southern California. The first author of this manuscript, Doug Yule, investigated slip rates and earthquake records in this enigmatic region from the mid-1990s until his death in 2022 (Fig. 2). During the 2010s, many researchers, including co-authors Cooke and Oglesby, were inspired by Doug Yule’s work in this area. Together, the three authors coordinated a five-year research effort to investigate active faulting within the San Gorgonio Pass, involving many researchers in the Southern California Earthquake Center (SCEC) community with support from SCEC, their various organizations, and institutions. Many of the results of this effort are compiled in this Geosphere thematic issue, with 11 papers that span earthquake geology, geomorphology, geodesy, potential field geophysics, crustal deformation models, and dynamic rupture models. Here, we highlight findings from these studies and honor the role that Doug played in bringing together earthquake scientists from a variety of disciplines to better understand the rupture potential through the complex faults of the San Gorgonio Pass. Much of this science can be organized around a few key questions.

New Gastropods from the Gulf of Mexico (Northwestern Florida, the Yucatan Peninsula, and the Flower Garden Reefs of Texas)

Three new species of gastropods are described from the Gulf of Mexico. These include: Fasciolaria ixchel n.sp. (Fasciolariidae) from near Isla Mujeres on the eastern side of the Yucatan Peninsula of Mexico; Jaspidiconus forticostatus n.sp. (Conidae) from the Big Bend area of northwestern Florida; and Jaspidiconus hortusensis n.sp. (Conidae) from the West Flower Garden Reef southeast of Galveston, Texas. The eastern Yucatan fasciolariid is the newest member of a previously-overlooked complex that contains four closely-related Fasciolaria s.s. species that are endemic to the Gulf of Mexico. The two new cones are members of a complex containing ten species of Jaspidiconus that are now known to be inhabit shallow water areas around the Gulf of Mexico.

Long-Term Trends in the Plant Community in Three Habitats in the Big Bend of Texas

Long-Term Trends in the Plant Community in Three Habitats in the Big Bend of Texas

Lineagona, a new millipede genus (Diplopoda, Chordeumatida, Cleidogonidae) from Texas, USA, and Nuevo Len, Mxico.

Lineagona n. gen., is established for two species from either side of the Rio Grande River in Texas and Mxico. Lineagona culmenicola n. sp., is from the vicinity of Monterrey, Nueva Leon, Mxico, and L. chisosi (Loomis, 1963) n. comb. ex Cleidogona Cook, in Cook & Collins 1895 is from Big Bend National Park, Texas, USA. A key to the genera of Cleidogonidae is provided and gonopod terminology in Cleidogonidae is updated.

The Establishment of Big Bend National Park and U.S.—Mexico Transborder Governance

The Establishment of Big Bend National Park and U.S.—Mexico Transborder Governance

Extensive and Continuing Loss of Seagrasses in Florida's Big Bend (USA).

Florida's Big Bend in the northeastern Gulf of Mexico contains the second-largest contiguous seagrass meadow in the continental United States, providing numerous ecosystem functions and services, including carbon cycling and storage. We present 21 years of mapping data and 13 years of annual in-water monitoring that reveal extensive declines in area, species frequency of occurrence (FO), and percent cover of seagrass. Seagrass area declined by 15% to 85,170 ha in 2022. Subregions in the southern Big Bend experienced extensive seagrass losses of 90-100%. North of the Steinhatchee River, the Northern Big Bend contained 85% of the total seagrass area and experienced losses of only 8.4%. The FO of seagrass and bare quadrats exhibited similar trends to areal coverage. The lowest FO along with complete loss of species was observed near the mouth of the Suwannee River. At a distance from the Suwannee River, FO also declined, but no species were lost. In the remainder of the Big Bend, FO remained stable except for short-term reductions in 2013-2014, which were likely related to anomalously high runoff from rainfall and tropical storm activity. Mean percent cover, however, declined throughout Big Bend, reaching minimal levels in 2014, with little to no recovery through 2019. The persistence of low percent cover may increase vulnerability of beds to continuing areal losses, but the persistence of seagrass species at a distance from the Suwannee River mouth may allow recovery if environmental conditions improve.

Your journey to Prada Marfa, McDonald Observatory and Santa Elena Canyon: Probes for a hot planet, dark skies and cool gaze

This article takes readers on a brief journey through the remote regions of far west Texas, site of the Greater Big Bend International Dark Sky Reserve, the largest dark sky reserve in the world. Spanning 15,000 square miles, the reserve is home to The University of Texas at Austin McDonald Observatory and Big Bend National Park, along with many other natural areas and art installations. This article uses Prada Marfa, McDonald Observatory and Santa Elena Canyon as probes for a hot planet under dark skies, while also deploying a cool gaze into the Milky Way. In so doing, cool media takes on a profound new meaning for our shared destiny on a tiny planet, getting ever hotter as it hurtles through the vast universe.

Formation of Billowed Structures Along Margins of Basaltic Intrusions: Insights from Big Bend National Park, Texas and 71 Gulch, Idaho

Billowed margins of basaltic intrusions provide opportunity to study the conditions of non-explosive magma-pore water interactions and how magma propagates and interacts with unconsolidated sediment in the subsurface. Basaltic intrusions exhibiting billowed structures that formed at different paleodepths in Big Bend National Park, Texas (200–500 m) and 71 Gulch, Idaho (≤24 m) have been examined and reconstructed in three dimensions (3D) using structure for motion (SfM) techniques. To characterize billowed structure diversity, a classification system was developed utilizing 21 high-resolution 3D models of outcrops from both locations. Seven structure types are recognized: linear, sinuous, teardrop, bulbous, circular, transitional, and overprinted. Relative abundances of each structure type are similar between both localities. All structures identified were recognized along dikes, apart from one sill. Each site hosts ≥3 structure types, no one structure type is dependent on another, and the dimensions of structure types are similar at both localities with insignificant variation in mean wavelength and amplitude of crests and troughs (≤6 cm), suggesting that depth of intrusion is not a major influence in the occurrence of different structure types. Aligned plagioclase laths and stretched vesicles along margins are evidence that billow formation occurred while margins were fluid, deformable, and flowing. These observations indicate billowed structures likely form during the initial stages of intrusion while the margins are experiencing Kelvin-Helmholtz instabilities during cooling. As billowed intrusions from varying paleodepths at the two localities both occur near phreatomagmatic diatreme structures, changes in the rate or flux of magma intrusion or local heterogeneities in the host sediment and/or pore fluid content may be more responsible for explosive vs. non-explosive interactions rather than simple arrival of magma.

The Mojave Section of the San Andreas Fault (California), 2: Pleistocene Records of Near‐Field Transpression Illuminate the Atypical Evolution of the Restraining “Big Bend”

AbstractWith an obliquity of ∼30° relative to plate motion direction, the ∼300‐km‐long Big Bend of the San Andreas Fault is one of the world's largest restraining bends. The 5–6 Ma (∼160 km of total displacement) longevity of this mechanically inefficient structure and the lack of evidence for associated widespread uplift both challenge existing models of transpression and bend evolution. We focus on the structurally simplest section of the Big Bend (the Mojave section of the San Andreas: MSAF) to characterize the pattern of near‐field (<5 km from the San Andreas trace) uplift over two different timescales. The topography of vertically deformed alluvial surfaces is used to demonstrate that near‐field uplift along the least oblique segment of the MSAF has been significant over the last ∼40 ka (∼1–2 mm/yr), and driven by slip on two oppositely dipping blind reverse faults. Topographic and structural analyses of the MSAF near‐field are conducted at the scale of the entire fault to show that, at least on the NE side of the MSAF, these blind structures coincide with the front of a fault‐parallel bedrock ridge with clear characteristics of a young transpressive ridge. Structural, sedimentary, and geomorphic arguments converge to suggest that these blind structures were activated ∼315 ka ago and record a Mid‐Pleistocene kinematic reorganization of the MSAF fault‐zone. This reorganization is tentatively interpreted as a shift in the mode of accommodation of the transpressive component of plate motion, in turn driven by the strike‐slip advection of crustal strength gradients along the Big Bend.

Elucidating the Role of Hydrocarbons in Cinnabar (HgS) Ore Formation: A Model for Hg Mineralization in the Terlingua Mining District, Big Bend National Park, SW Texas

Abstract The genetic relationship between organic-rich source rocks and Hg deposits remains the subject of debate. This paper evaluates the role of organic-rich source rocks in cinnabar ore formation in the Terlingua mining district, Texas, which was deposited at relatively shallow depths in Cretaceous sedimentary rocks spatially related to intrusive alkali igneous rocks. The mineralization formed at ~45 bar and ~200°C. The aqueous ore-forming fluid had a pH of ~5 to 7 and was H2S saturated. Cinnabar was deposited as a result of H2S oxidation through mixing and cooling with local meteoric water. Both Hg0(org) and Hg0(aq) species were likely important in cinnabar ore formation. However, recent studies on the solubility of Hg0 in hydrocarbons show that at cinnabar saturation, Hg0 is more than an order of magnitude more soluble in hydrocarbons (Hg0(org) = 163 mg/kg) than Hg0 in water (Hg0(aq) = 10.8 mg/kg). Despite their proximity in some deposits, conditions of ore formation of the rare Hg oxychloride and sulfate minerals are not compatible with conditions under which most cinnabar ores formed, requiring fO2 conditions orders of magnitude more oxidizing, a relatively high chloride ion activity (>10–1), and alkaline conditions, with pH > 10. Mass dependent fractionation versus mass independent fractionation of Hg isotope data from Hg-bearing minerals in Terlingua support a genetic link to the source of Hg being the organic-rich marls and tuffaceous black shales of the Lower Eagle Ford Formation. This source rock is chronostratigraphically equivalent to the Lower Cretaceous oceanic anoxic event (OAE-2), which defines the Cenomanian-Turonian boundary. OAE-2 represents the culmination of a global anoxic ocean event at ~94.1 Ma, believed to be a consequence of volcanic activity associated with a large igneous province. Mercury was sequestered by the organic-rich source rocks of the Lower Eagle Ford Formation and associated coeval ash and tuffs. Tabular igneous bodies that intruded and uplifted the local stratigraphy formed the Terlingua monocline and provided a source of heat for hydrothermal activity and maturation of organic matter. The subsequent generation and migration of liquid hydrocarbons and formation brines from the Lower Eagle Ford Formation transported Hg0(org) updip toward the hinge line of the Terlingua monocline where mixing with oxygenated meteoric water and subsequent oxidation of H2S produced the cinnabar-rich ores.

Observed trends in scavenging by common bottlenose dolphins (Tursiops truncatus truncatus) in for‐hire fisheries in the eastern U.S. Gulf of Mexico

AbstractInteractions between bottlenose dolphin and recreational rod and reel fisheries are a complex issue for resource managers in the United States, which may impact anglers' catch and lead to dangerous situations for scavenging or depredating dolphins. To examine this issue, we analyzed data collected by observers on for‐hire fishing vessels off the eastern U.S. Gulf Coast from 2009 to 2020. A generalized additive model indicated number of anglers, number of discarded fish, proximity to shore, prior scavenging events, type of released fish, and area fished were all significant predictors of scavenging by dolphins. The Florida panhandle had the highest odds of scavenging, while scavenging in the Big Bend and Tampa Bay has increased through time. The Florida panhandle is a well‐known area for illegal feeding of dolphins, suggesting human behavior may be influencing fisheries interactions. Model outputs indicate that dolphins are primarily cuing on fishing activity rather than number of discards, but are more likely to scavenge discards from the family Lutjanidae (snappers), which comprised 40% of observed discards but 80% of scavenging events. This study highlights factors influencing the frequency of dolphin scavenging events, guiding managers and scientists on additional studies and mitigation measures needed to address this issue.

Integrating assemblage structure and habitat mapping data into the design of a multispecies reef fish survey

AbstractObjectiveSince 2010, three spatially disjunct reef fish video surveys have provided fishery‐independent data critical to the assessment and management of reef fishes in the Gulf of Mexico. Although analytical approaches have recently been developed to integrate data from these surveys into a single measure of relative abundance and size composition, a more parsimonious approach would be to integrate survey efforts under a single Gulf‐wide survey design. Accordingly, we conducted a retrospective analysis of historical video‐ and habitat‐mapping data to develop a novel stratified random sampling design for conducting surveys of natural and artificial reef habitats.MethodsWe conducted a series of classification and regression tree analyses to delineate both spatial and habitat strata, and conducted simulations to assess the performance of an optimized survey design.ResultSpatially, classification and regression tree results identified three depth strata (10–25 m, >25–50 m, >50–180 m) and three regional strata (north‐central Gulf, Big Bend, southwest Florida) in the eastern Gulf. For both natural and artificial reefs, habitat strata were delineated based on a combination of relative relief (low, medium, high) and size of the individual reef feature, although reef scale differed markedly between natural (<100 m2, 100–1000 m2, >1000 m2) and artificial habitats (<25 m2, 25–100 m2, >100 m2). To optimize effort among sampling strata, effort was allocated proportionally based on a combination of habitat availability and managed‐species richness for each stratum. Simulation results indicated that relative median biases were <10% and relative median absolute deviations <30% on estimates of abundance for most species examined on natural reefs under the optimal design, except Greater Amberjack Seriola dumerili. These measures of bias and imprecision were similar or higher for most species simulated using simple random and stratified random survey designs. Estimated relative median bias and relative median absolute deviations were notably higher for artificial reef surveys.ConclusionBased on these results, survey efforts were integrated as the Gulf Fishery Independent Survey of Habitat and Ecosystem Resources (G‐FISHER) in 2020.

Fine-scale intraspecific niche partitioning in a highly mobile, marine megafauna species: implications for ecology and conservation.

A species may partition its realized ecological niche along bionomic and scenopoetic axes due to intraspecific competition for limited resources. How partitioning manifests depends on resource needs and availability by and for the partitioning groups. Here we demonstrate the utility of analysing short- and long-term stable carbon and nitrogen isotope ratios from imperiled marine megafauna to characterize realized niche partitioning in these species. We captured 113 loggerhead sea turtles (Caretta caretta) at a high-use area in the eastern Big Bend, Florida, between 2016 and 2022, comprising 53 subadults, 10 adult males and 50 adult females. We calculated trophic niche metrics using established and novel methods, and constructed Bayesian ellipses and hulls, to characterize loggerhead isotopic niches. These analyses indicated that loggerheads partition their realized ecological niche by lifestage, potentially along both bionomic (e.g. trophic) and/or scenopoetic (e.g. habitat, latitude or longitude) axes, and display different characteristics of resource use within their niches. Analysis of stable isotopes from tissues with different turnover rates enabled this first characterization of intraspecific niche partitioning between and within neritic lifestages in loggerhead turtles, which has direct implications for ongoing research and conservation efforts for this and other imperiled marine species.

Big Bend National Park: Mexico, the United States, and a Borderland Ecosystem. By Michael Welsh

Formed by one river and an already humongous 800,000 acre park, part of the rugged ecosystem spread across two countries with their shifting priorities and fluctuating relationships in a remote and arid landscape, the greater Big Bend area, long dreamt for united recognition and management. We write this review as longtime NPS employees, one a historian, and the other a landscape architect who acquired park knowledge as he worked on Sierra Club service trips for eighteen years, removing fences and planting vegetation to counter overgrazing. Each chapter details different eras and the vacillating prospects for a truly binational park in Michael Welsh’s traditional political history based on his several administrative histories. We recommend this book for people interested in the complexities of park management who are already acquainted with this park and for people interested in the many-decade efforts to establish a binational park/protected area over the larger area bisected by the Rio Grande/Rio Bravo.

Crustal Architecture Across Southern California and Its Implications on San Andreas Fault Development

AbstractIn this study, we perform a 2‐frequency sequential receiver function stacking investigation in Southern California. The resulting Moho depths exhibit similar patterns to previous studies while the crystalline crustal Vp/Vs values show more regional variations. Most Vp/Vs variations can be explained by compositional differences. We observe a dichotomy in Moho depth, Vp/Vs, and crustal strain rates between the Peninsular Ranges and Southern San Andreas Fault system. Comparisons between strain rates, Vp/Vs, and temperature suggest that crustal compositional variations may have played a more critical role in influencing the crustal strain rate variations in the Peninsular Ranges and Southern San Andreas than temperature. The structural and compositional variations provide a new insight into the causes of the migration of the Southern San Andreas Fault system and the formation of the “Big Bend.”

The remarkably enzyme-rich venom of the Big Bend Scorpion (Diplocentrus whitei)

Scorpion venoms have long been studied for their peptide discovery potential, with modern high-throughput venom-characterization techniques paving the way for the discovery of thousands of novel putative toxins. Research into these toxins has provided insight into the pathology and treatment of human diseases, even resulting in the development of one compound with Food and Drug Administration (FDA) approval. Although most of this research has focused on the toxins of scorpion species considered medically significant to humans, the venom of harmless scorpion species possess toxins that are homologous to those from medically significant species, indicating that harmless scorpion venoms may also serve as valuable sources of novel peptide variants. Furthermore, as harmless scorpions represent a vast majority of scorpion species diversity, and therefore venom toxin diversity, venoms from these species likely contain entirely new toxin classes. We sequenced the venom-gland transcriptome and venom proteome of two male Big Bend scorpions (Diplocentrus whitei), providing the first high-throughput venom characterization for a member of this genus. We identified a total of 82 toxins in the venom of D. whitei, 25 of which were identified in both the transcriptome and proteome, and 57 of which were only identified in the transcriptome. Furthermore, we identified a unique, enzyme-rich venom dominated by serine proteases and the first arylsulfatase B toxins identified in scorpions.