White Rock Canyon Research Articles

Additional species for the Jemez Mountains, New Mexico, U.S.A.

In this paper, we note 161 species and varieties of plants in the Jemez Mountains verified through voucher specimens. These species were not previously listed in the most detailed previous floristic study in this area Floristic Studies in North Central New Mexico, U.S.A. the Tusas Mountains and the Jemez Mountains by Reif et. al. (2009). Most of these specimens are housed in the Jemez Mountain Herbarium (JMH) at the Los Alamos, New Mexico Nature Center. Others are housed in the herbarium at the Museum of Southwestern Biology at the University of New Mexico (UNM), and a few elsewhere as noted (SEINet).
 If this number is added to the total for the Jemez Mountains from Reif’s work, the new total for the Jemez Mountains is 1,504 taxa. These additions include seven new state records, as well as several species not expected in the Jemez Mountains environment and altitude range. Of special interest are the flora of the San Pedro Parks Wilderness in the northwest part of the range, White Rock Canyon along the Rio Grande, and the desert shrublands west of San Ysidro at the extreme southwest part of the Jemez Mountains. For completeness, we include species escaped from cultivation but apparently well established in the wild, and a list of species that have not recurred where they were collected. Finally, there are comments on aspects of Reif et al. (2009).

An integrated trilobite and conodont biostratigraphy across the base of the Laurentian Whiterockian Series (lower Middle Ordovician) at its stratotype, Whiterock Canyon Narrows, Nevada

AbstractThe outcrop at Whiterock Canyon Narrows, Nevada, is the stratotype for the Middle Ordovician Whiterockian Series in Laurentia. Contrasts in the distribution of trilobites and conodonts between two parallel sections at the stratotype demonstrate the presence of an unconformity separating Ibexian faunas (the historic trilobite Zone J, the more recent restricted “Pseudocybele nasuta” trilobite Zone, theReutterodus andinusconodont Zone) from overlying Whiterockian faunas (Zone L, thePsephosthenaspis pseudobathyurustrilobite Zone, theOrthidiellabrachiopod Zone, theTripodus combsiconodont Zone). The unconformity represents the erosional loss of a minimum of 10 m of shale and bedded limestone within the upper Ninemile Formation. In comparison to more continuous section in the Ibex region, Utah, the equivalent to the thinPsephosthenaspis microspinosatrilobite Zone and, possibly, the uppermost interval of the underlying “P.nasuta” Zone are missing.Illaenus welchinew species is described from the Whiterockian faunas of the upper Ninemile and Antelope Valley formations.

Trilobites from the base of the type Whiterockian (Middle Ordovician) in Nevada

No trilobite species, and very few genera, pass from the Lower (Ibexian) into the Middle Ordovician (Whiterockian), which is a turning point in Laurentian trilobite history. Trilobites from three sections exposing the base of the Whiterock Series (basal Middle Ordovician) in Nevada are described and illustrated. They are attributable to different, and generally more open-shelf, biofacies from the Bathyurid biofacies trilobites described from the Ibex area, Utah, by Fortey and Droser (1996), but include species in common, which allow correlation into the Ibexian type section. At Little Rawhide Mountain the basal Middle Ordovician is developed in Olenid biofacies, described for the first time in western North America from rocks of this age. Correlation based on species-level similarity shows that the “spike” that has been used to define the type base of the Whiterockian (and hence the Middle Ordovician) at Whiterock Canyon is at a level younger than the base of the Whiterockian assumed in recent discussions of its international correlation. The type Whiterock base correlates with thePsephosthenaspis glabriortrilobite Subzone at Ibex, well above the major change in trilobite faunas at the base of thePsephosthenaspisZone (P. microspinosaSubzone). In all study sections there is an abrupt change of facies after trilobite Zone J, possibly associated with regression. Four new species are described:Cloacaspis tesselata, Harpillaenus rossi, Acidiphorus?lineotuberculatus, andBenthamaspis serus.

Late Pleistocene landslide-dammed lakes along the Rio Grande, White Rock Canyon, New Mexico

Massive slump complexes composed of Pliocene basaltic rocks and underlying Miocene and Pliocene sediments flank the Rio Grande along 16 km of northern White Rock Canyon, New Mexico. The toe area of at least one slump complex was active in the late Pleistocene, damming the Rio Grande at least four times during the period from 18 to 12 {sup 14}C ka and impounding lakes that extended 10-20 km upriver. Stratigraphic relationships and radiocarbon age constraints indicate that three separate lakes formed between 13.7 and 12.4 {sup 14}C ka. The age and dimensions of the ca. 12.4 ka lake are best constrained; it had an estimated maximum depth of {approx}30 m, a length of {approx}13 km, a surface area of {approx}2.7 km{sup 2}, and an initial volume of {approx}2.5 x 10{sup 7} m{sup 3}. The youngest landslide-dammed lakes formed during a period of significantly wetter regional climate, strongly suggesting that climate changes were responsible for reactivation of the slump complexes. We are not certain about the exact triggering mechanisms for these landslides, but they probably involved removal of lateral support due to erosion of the slope base by the Rio Grande during periods of exceptionally high flood discharge or rapid incision;more » increased pore pressures associated with higher water tables; higher seepage forces at sites of ground-water discharge; or some combination of these processes. Seismic shaking could also have contributed to triggering of some of the landslides, particularly if aided by wet antecedent conditions. 54 refs., 19 figs., 3 tabs.« less

Lacustrine chronology links late Pleistocene climate change and mass movements in northern New Mexico

Well-dated lacustrine deposits in northern White Rock Canyon, New Mexico, record damming of the Rio Grande by at least four separate failures of a slump complex between about 17.5 and 12.4 ka ({sup 14}C), linking mass movements to a period of rapid climate change in the western United States. Failure of metastable slumps probably resulted from removal of lateral support during down-cutting and erosion by the Rio Grande and from a decrease in resisting forces due to increased pore pressures. Our chronology suggests that the lake that formed between 17.5 and 15.0 ka may record effects of both glacial melt and pluvial activity (mainly enhanced rainfall); the youngest lake (neary 12.4 ka) may record pluvial runoff; and the intermediate lakes (13.7 to 13.1 ka) may record pluvial and minor melt-water activity. We have not found lacustrine deposits younger than about 12.4 ka. The record of geomorphic response along the Rio Grande suggests that late Pleistocene climatic changes may have triggered similar mass movements elsewhere in the southwest. 27 refs., 4 figs.

Stratotype of Ordovician Whiterock Series

Here the authors reaffirm and document fossil ranges at the stratotype section for the base of the Whiterock Series in Whiterock Canyon, northern Monitor Range, Nevada, and designate a reference section at Meiklejohn Peak, Bare Mountain quadrangle, Nevada. In both sections, stratigraphic ranges of conodonts indicate that the boundary between the Whiterock and the underlying Ibex Series lies between Oepikodus evae below and Tripodus laevis above. This level is correlated with the inception of the Isograptus victoriae graptolite lineage. Coeval brachiopod and trilobite faunas are summarized and their ranges graphically illustrated. The base of the Whiterock Series seems to be coincident with the start of the Taconic Orogeny. During the Whiterock other tectonically controlled events preceded the Tippecanoe Sequence in North America.

Paleomagnetic and structural evidence for middle Tertiary counterclockwise block rotation in the Dixie Valley region, west-central Nevada

Paleomagnetic data from late Oligocene to early Miocene ash-flow tuffs at four localities in the northern Dixie Valley region, west-central Nevada, indicate that parts of the crust have rotated counterclockwise by at least 25/sup 0/ and perhaps significantly more in late Cenozoic time. Field relations in White Rock Canyon, Stillwater Range, suggest that rotation (1) was accommodated by right-lateral slip on northwest-trending faults, (2) spanned ash-flow tuff emplacement, and (3) probably ceased before eruption of overlying middle Miocene basalts. Accurate estimates of Cenozoic extension, as well as evaluation of earlier Mesozoic structures, must include the strain partitioned into rotation in the area.