Magmatism, migrating topography, and the transition from Sevier shortening to Basin and Range extension, western United States

ABSTRACT The paleogeographic evolution of the western U.S. Great Basin from the Late Cretaceous to the Cenozoic is critical to understanding how the North American Cordillera at this latitude transitioned from Mesozoic shortening to Cenozoic extension. According to a widely applied model, Cenozoic extension was driven by collapse of elevated crust supported by crustal thicknesses that were potentially double the present ~30–35 km. This model is difficult to reconcile with more recent estimates of moderate regional extension (≤50%) and the discovery that most high-angle, Basin and Range faults slipped rapidly ca. 17 Ma, tens of millions of years after crustal thickening occurred. Here, we integrated new and existing geochronology and geologic mapping in the Elko area of northeast Nevada, one of the few places in the Great Basin with substantial exposures of Paleogene strata. We improved the age control for strata that have been targeted for studies of regional paleoelevation and paleoclimate across this critical time span. In addition, a regional compilation of the ages of material within a network of middle Cenozoic paleodrainages that developed across the Great Basin shows that the age of basal paleovalley fill decreases southward roughly synchronous with voluminous ignimbrite flareup volcanism that swept south across the region ca. 45–20 Ma. Integrating these data sets with the regional record of faulting, sedimentation, erosion, and magmatism, we suggest that volcanism was accompanied by an elevation increase that disrupted drainage systems and shifted the continental divide east into central Nevada from its Late Cretaceous location along the Sierra Nevada arc. The north-south Eocene–Oligocene drainage divide defined by mapping of paleovalleys may thus have evolved as a dynamic feature that propagated southward with magmatism. Despite some local faulting, the northern Great Basin became a vast, elevated volcanic tableland that persisted until dissection by Basin and Range faulting that began ca. 21–17 Ma. Based on this more detailed geologic framework, it is unlikely that Basin and Range extension was driven by Cretaceous crustal overthickening; rather, preexisting crustal structure was just one of several factors that that led to Basin and Range faulting after ca. 17 Ma—in addition to thermal weakening of the crust associated with Cenozoic magmatism, thermally supported elevation, and changing boundary conditions. Because these causal factors evolved long after crustal thickening ended, during final removal and fragmentation of the shallowly subducting Farallon slab, they are compatible with normal-thickness (~45–50 km) crust beneath the Great Basin prior to extension and do not require development of a strongly elevated, Altiplano-like region during Mesozoic shortening.

Morphological and molecular evidence confirms a new species, Riccia subcrinita YouL.Xiang & R.L.Zhu) and Riccia junghuhniana Nees & Lindenb. (Ricciaceae, Marchantiophyta) new to China

Riccia is the largest genus of complex thalloid liverworts (Marchantiopsida) with over 250 species currently accepted. Our recent investigation of Chinese liverworts found two interesting Riccia species, R. junghuhniana and Riccia subcrinita sp. nov. Riccia junghuhniana is currently known from Australia and Indonesia, while Riccia subcrinita is known only from China. Riccia subcrinita is similar to R. crinita, but differs in having smaller spores (56–71 µm in diameter), and spore distal surface and proximal surface alveoli without thick borders. The sequences of rbcL, rps4, and trnL-F, detailed descriptions, and illustrations of the Chinese specimens are provided. The range extension of R. junghuhniana suggests that more taxa of Riccia may have a wider distribution. The discovery of R. junghuhniana and the new species also suggests that a more intensive survey of Riccia diversity in China is necessary.

Kerevata Belokobylskij (Hymenoptera: Braconidae: Rogadinae) is no longer a Papua New Guinean endemic with descriptions of three new species from the Indomalayan Region

The rogadine genus Kerevata Belokobylskij is newly reported from the Indomalayan region. We describe and illustrate three new species, two from India (K. kethai sp. nov. and K. orientalia sp. nov.) and one from Vietnam (K. longi sp. nov.) and provide an illustrated key to the extant species of the genus along with the photographic illustration of the type species of K. pacifica Belokobylskij. Range extension and morphological characters of Kerevata are discussed.

First records and range extension of Bristle-spined Porcupine, Chaetomys subspinosus (Olfers, 1818) (Rodentia, Erethizontidae), in Minas Gerais state, Brazil

We report from three localities four new records of the threatened Brazilian Atlantic Forest endemic Chaetomys subspinosus (Olfers, 1818). These are the first records of this porcupine species from the state of Minas Gerais, and these new data extend the distribution of this species by approximately 220 km to the southwest. As C. subspinosus was observed in areas of transitional vegetation, this species may be found in a much broader spectrum of habitat types than previously thought. We recommend further surveys focusing on documenting this species.

An investigation into the spatiotemporal patterns of the Nymphalid butterfly Vagrans egista sinha (Kollar, [1844])

Vagrans egista sinha (Kollar, [1844]), the Himalayan Vagrant is a subspecies of Nymphalid (Brush-footed) butterflies spread across Asia, whose western limit is in the north-west India. Observations of this subspecies have considerably increased over the past half-a-decade, with a spike in new sightings to the west of their previously known range. This has been considered as a range extension. The current study reports new records of this species from Bilaspur District, Himachal Pradesh, India (which are the first records for the district), through systematic and opportunistic sampling. This raises the question of whether the purported range extension towards the west could instead be a range shift or vagrancy, and whether there is any shift in elevational ranges in the populations across their known range. Questions pertaining to spatial differences in elevational ranges and seasonal variation, across their range, also piqued our curiosity. Using data from academic sources (such as published literature and museum collections), supplemented by data from public participation in scientific research and personal observations, these research questions are addressed. The accuracy of results when using citizen science data is also explored using the same dataset, focused on the impact of method of extraction of coordinates, and elevation derived from it under different scenarios. It was discovered that there has not been a range shift (either longitudinal or latitudinal) and observations do not suggest vagrancy but a case of range extension. Other results indicated that there was no climb of population to higher elevations, no spatial differences in elevational ranges in the populations, or seasonal variation in activities across their range. It was also discovered that the method of data collection by, and extraction from, citizen science databases, can influence the accuracy of the results. Some problems involved in collecting data are discussed, and remedial solutions are suggested.