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A paleotopographic record of Taiwan shows ~2 km of surface uplift since ~1.3–1.5 Ma. 

We present the first paleotopographic reconstruction of Taiwan by measuring the hydrogen isotope composition of leaf waxes (δ²H_nC29) preserved in 3-Ma and younger sediments of the southern Coastal Range. Plant leaf waxes record the δ²H of precipitation during formation, which is related to elevation. Leaf waxes produced across the orogen are transported and deposited in adjacent sedimentary basins, providing deep-time records of the source elevation of detrital organic matter. δ²H_nC29exported from the southern Taiwan orogen decreased by more than 40‰ since ~1.3–1.5 Ma, indicating an increase of >2 kilometers in the organic source elevation. The increase in organic source elevation is best explained by rapid surface uplift of the southern Central Range at around ~1.3–1.5 Ma and indicates that this part of the orogen was characterized by maximum elevations of at least 3 km at this time. Further increase in organic source elevation from ~0.85 to ~0.3 Ma indicates continued topographic growth to modern elevations.

 

The Sierra San Francisco (SSF) is a Neogene volcanic range along the topographic crest of the Baja California peninsula in northern Baja California Sur, Mexico. The SSF is ~55 km long (NW-SE) and ~30 km wide and its highest peaks exceed 1500 m elevation. The SSF has a long history of volcanism and has been eroded by deep, rugged, radially-draining canyons. The development of SSF topography is intimately associated with the volcanic evolution of the range. The SSF is a large and complex dacitic adakite dome complex largely built of a thick, up to 800 m, stratigraphic succession of dacitic tuff breccias with minor interbedded basaltic andesite lavas. These deposits overlie rare exposures of aeolian sandstone of unknown age. The tuff breccias represent block-and-ash-flows and lahars generated from steep-sided peleean dacite and andesite domes, with three radiometric dates of 11-10 Ma. This intermediate sequence is unconformably capped by widespread bajaite mafic lavas, 5.5-4.5 Ma. SSF topography evolved dramatically since the late Miocene: 1) From 11-10 Ma, adakite domes erupted across the central SSF, locally along NNW faults. Thick sequences of bedded tuff breccias accumulated around the domes and are radially inclined away from source domes. The duration of this volcanism is unknown. 2) From 10-5 Ma, deep erosion of the pyroclastic strata formed a range-wide radial drainage network, with channel depths of up to 130 m or more. 3) From 5.5-4.5 Ma, voluminous bajaite lavas from cinder cones and dike vents flooded the top of the range and flowed down the radial drainages with flow distances up to 12 km. Vents are strongly aligned along steep NNW normal faults. 4) After 4.5 Ma, erosion removed interfluves of tuff breccia not armored by younger mafic lavas. Today, the long, steep-sided, lava-capped ridges are inverted topographically. At Santa Martha, an area in the central SSF with the highest concentration of domes, hydrothermal alteration of the volcanic deposits during and after the dome volcanism caused severe material weakening and slope failure within the volcanic center. The area is now a distinctive erosional basin, partly filled with clay-rich landslide deposits. Comparable volcanic history and topographic development are likely to have occurred in a dome field of similar age and size at Santa Agueda, 60 km SE of Santa Martha. 

The processes and deposits of tide‐dominated river deltas and estuaries are well‐understood, but the sedimentary dynamics of tide‐dominated straits and seaways are relatively little studied. Although recent depositional models have started to fill this gap, many aspects of tidal strait sedimentation such as interaction with strait‐margin alluvial fans and marginal marine systems remain poorly understood. This paper presents a study of the late Miocene basal carbonate member of the Bouse Formation exposed along the lower Colorado River, where prior studies have suggested a tidal influence on deposition. This study explores the applicability of tidal strait models in a continental oblique‐rift setting, and tests hypotheses for depositional processes and environments through detailed analysis of sedimentary facies, cross‐bedding architecture and palaeocurrent data. Mixed carbonate–siliciclastic facies on the west margin of the southern Blythe Basin record sedimentation in alluvial fans and fan‐fringing tidal flats at the retreating margin of a transgressive tidal strait. Pre‐Bouse normal faults established a narrow, tectonically confined basin architecture that led to amplification of tidal currents. Basin‐margin deposits pass laterally and up‐section into high‐energy cross‐bedded grainstone facies that record southward migration of compound dunes in the dune‐bedded strait zone of a shallow (ca25 m) tidal strait. These findings provide the basis for recognition of strait‐margin facies in other settings where complex facies associations result from along‐strike variations in palaeobathymetry and current velocity. The results support a tidal origin for the southern Bouse Formation and provide new evidence for post‐Miocene uplift of the lower Colorado River Valley and adjacent areas.

 

Mixed carbonate–siliciclastic deposits provide unique insights into hydrodynamic processes that control sedimentation in tidal systems. This study presents sedimentological and ichnological data from the upper Miocene to lower Pliocene Bouse Formation, which accumulated during regional transgression at the margin of a tidal strait near the north end of the ancestral Gulf of California. The basal carbonate member of the Bouse Formation records deposition in a tide‐influenced, compositionally mixed carbonate–siliciclastic system dominated by salt marsh, tidal flat and channel environments. The basal carbonate member is an overall deepening up succession of facies associations comprising: Facies Association 1 – siliciclastic‐rich heterolithic facies, lime mudstone with desiccation cracks, and plant debris rich carbonate silt interpreted as siliciclastic‐rich tidal flats; Facies Association 2 – well‐sorted gravels, siliciclastic‐rich sandy strata, lime mudstone with desiccation cracks, and sandy microbial micrite interpreted as tidal‐channel deposits; Facies Association 3 – carbonate‐rich heterolithic lime mudstone to well‐sorted, cross‐bedded bioclastic grainstone interpreted as intertidal to shallow subtidal deposits; and Facies Association 4 – lime mudstone interpreted as shallow to deep subtidal low‐energy deposits that record the end of tidal conditions in the basin. Trace fossils include marine formsGyrolithes,TeichichnusandThalassinoides,and non‐diagnostic formsArenicolites,Cochlichnus,Conichnus,Lockeia,Planolites,SkolithosandTreptichnus(known from marine, brackish and freshwater environments). The diminutive size of trace fossils reflects brackish conditions created by mixing of freshwater and seawater. This study provides evidence for a late Miocene to early Pliocene humid climate in south‐western North America, in stark contrast to the modern hyperarid climate. Factors that controlled the relative percentage of mixed carbonate and siliciclastic sediment include siliciclastic input from local rivers,in situcarbonate production, current energy, degree of tidal mixing and relative sea level. Pronounced facies variability at bedform, outcrop and basin scale documented in this study appears to be an important characteristic of mixed carbonate–siliciclastic deposits in tidal depositional systems.

 

To review the histories of the Colorado River and North American monsoon system to ascertain their effects on the genetic divergence of desert‐adapted animals.

Lower Colorado River region, including Mojave and Sonoran deserts, United States.

We synthesized recent geological literature to summarize initiation phases of lower Colorado River evolution, their discrepancies, and potential for post‐vicariance dispersal of animals across the river. We simulated data under geological models and performed a meta‐analysis of published and unpublished genetic data including population diversity metrics, relatedness and historical migration rates to assess alternative divergence hypotheses.

The two models for arrival of the Colorado River into the Gulf of California impose east‐west divergence ages of 5.3 and 4.8 Ma, respectively. We found quantifiable river‐associated differentiation in the lower Colorado River region in reptiles, arachnids and mammals relative to flying insects. However, topological statistics, historical migration rates and cross‐river extralimital populations suggest that the river should be considered a leaky barrier that filters, rather than prevents, gene flow. Most markers violated neutrality tests. Differential adaptation to monsoon‐based precipitation differences may contribute to divergence between Mojave and Sonoran populations and should be tested.

Rivers are dynamic features that can both limit and facilitate gene flow through time, the impacts of which are mitigated by species‐specific life history and dispersal traits. The Southwest is a geo‐climatically complex region with the potential to produce pseudocongruent patterns of genetic divergence, offering a good setting to evaluate intermediate levels of geological‐biological (geobiological) complexity.