Rock Ridge Research Articles

An inland population of the common ringtail possum (Pseudocheirus peregrinus) at Black Rock Ridge, New South Wales: a preliminary ecological assessment

The common ringtail possum (Pseudocheirus peregrinus) is considered abundant throughout its distribution in eastern Australia but appears to be declining at a regional level in inland New South Wales. Previous studies of the common ringtail possum in south-eastern Australia have focussed on coastal populations and little is known about the ecology of inland populations. In south-western Australia studies of the closely related western ringtail possum (Pseudocherius occidentalis) have found that coastal populations differ from inland populations, particularly in their nesting behaviour. In this preliminary study of an inland population of the common ringtail possum at Black Rock Ridge in central west New South Wales population density has been estimated and the habitat and nesting preference assessed. Up to one ringtail per hectare and 4.5 ringtails per spotlight hour were recorded. Tree hollows appeared to be the preferred nest site, with possums seen entering hollows during spotlighting and no dreys being located. Threats to common ringtail possums at Black Rock Ridge include the isolation of the remnant ridge vegetation within an extensively cleared landscape and the associated change in fire regimes. Within this landscape there has been an extensive reduction in available habitat, and an overall lack of habitat connectivity has placed ringtail possums at an increased risk of predation.

Tropical paradox: a multi-scale analysis of the invasion paradox within Miami Rock Ridge tropical hardwood hammocks

The invasion paradox describes the scale dependence of native-exotic richness relationships (NERRs), where NERRs are negative at neighborhood scales and positive at landscape scales. However, a lack of tropical surveys and past failures to isolate potential confounding variables contribute to significant gaps in our understanding of the processes producing these patterns. We surveyed the vascular flora of 13 tropical hardwood hammocks for community characteristics (e.g., native and exotic species richness, vegetative cover) with a hierarchical sampling design. Using model selection, we determined which variables best predicted patterns of exotic species richness at each spatial scale of consideration. We found that native and exotic species richness were positively correlated at neighborhood scales, but negatively correlated at landscape scales. The latter result stands in stark opposition to the patterns published in the literature thus far. We found that natural disturbance history (as approximated by vegetative cover) was positively correlated with exotic species richness at intermediate and landscape scales only. Overall, hammock identity was the most important factor driving exotic species richness patterns at all spatial scales. Hammocks with highly-disturbed hydrologies, brought about by water management, had fewer native species and more exotic species than hammocks with more natural hydrological conditions. Our results are among the first from examination of subtropical communities, and may support the hypothesis that tropical and subtropical communities are subject to more intense biotic interactions. However, given our unique sampling design, our results do not reject the hypothesis that environmental heterogeneity drives the relationship between native and exotic species richness patterns.

Efficacy of electrical resistivity tomography technique in mapping shallow subsurface anomaly

Electrical Resistivity Tomography is a versatile, fast and cost effective technique for mapping the shallow subsurface anomaly. It covers a wide spectrum of resistivity ranging from <1 Ohm.m to several thousands of Ohm.m. In this paper applications and utility of two-dimensional Electrical Resistivity Tomography (ERT) technique are discussed to look into huge data density coverage, different signal strengths of data from subsurface and their implications in resolving the aquifer zones, related geological structures etc. of the substratum ranging from alluvium to tectonically disturbed hard rock ridge region of the country. The major advantages and flexibility of ERT over conventional resistivity methods are also discussed.

Sedimentary cover and late Cenozoic history of the Okushiri Ridge (Sea of Japan)

A complex (petrographic, micropaleontological, and X-ray diffraction) investigation of the sedimentary cover on the northwestern slope of the Okushiri Ridge in the Sea of Japan revealed that its basal layers are of Oligocene age and composed of terrigenous silty-clayey sediments, which were deposited in coastalmarine environments with calm hydrodynamics and low sedimentation rates. The relative sea-level rise combined with regional tectonic processes at the early-middle Miocene transition resulted in widening and deepening of sea basins and accumulation of a thick diatomaceous-clayey sequence of middle-upper Miocene sediments. Tectonic activation in the Pliocene was responsible for development of the ridge and exhumation of rocks formerly occurring at depth of 500–1000 m.

Pleistocene Carbonate Stratigraphy of South Florida: Evidence for High-Frequency Sea-Level Cyclicity

Pleistocene carbonates of south Florida and islands of the Florida Keys are currently divided into five marine sequences designated, from oldest to youngest, the Q1–Q5 units. The units include a mosaic of freshwater and shallow marine deposits that accumulated on the Florida platform during high sea-level stands. The units are separated by regional-scale subaerial-exposure surfaces that formed during glacioeustatic lowstands. Analyses of cores recovered at Grossman Ridge Rock Reef and Joe Ree Rock Reef in the Florida Everglades reveal additional subaerial-exposure surfaces that are used to delineate subdivisions within units Q1 (Q1a–Q1b), Q2 (Q2a–Q2d), and Q4 (Q4a–Q4b). Units Q1–Q5 preserve evidence of at least 10 separate sea-level highstands, rather than 5 as indicated by previous studies. Compilation of available uranium-series dates on corals recovered from the Florida Keys indicates that the Q4 unit accreted during sea-level maxima associated with marine oxygen-isotope Stage 9 (Q4a) and isotope Stage 7 (Q4b). The Q5 unit formed during isotope Stage 5. No reliable dates are available for units Q1–Q3. We infer that unit Q3 was formed during the extended sea-level highstand of isotope Stage 11 and that units Q2 and Q1 predate isotope Stage 11.

Cryptoendolithic cyanobacteria from calcite marble rock ridges, Taylor Valley, Antarctica

Cryptoendolithic cyanobacteria from calcite marble rock ridges, Taylor Valley, Antarctica

Habitat characteristics of juvenile cowcod, Sebastes levis (Scorpaenidae), in Southern California

We characterized habitat requirements of juvenile cowcod, Sebastes levis, using information from surveys conducted aboard the manned research submersible Delta. We conducted 303 dive surveys on rocky banks and outcrops in water depths between 28 and 365 m in southern and central California, covering 483 km (963,940 m2) of seafloor. We counted 549,263 fishes from at least 134 species; 216 individuals were juvenile cowcod, S. levis, of 45 cm or less in total length (TL). Juvenile cowcod occupied depths between 52 and 330 m and demonstrated ontogenetic shifts in their habitat associations. Small fish (5–20 cm TL) lived primarily among cobbles or cobbles and small boulders. As fish grew, they moved into high-relief rock habitats, including boulder fields and rock ridges. Small cowcods were found with pygmy, Sebastes wilsoni, and swordspine, Sebastes ensifer, rockfishes. Larger juveniles often associated with juvenile bocaccio, Sebastes paucispinis, juvenile widow rockfish, Sebastes entomelas, and squarespot rockfish, Sebastes hopkinsi. Our study resulted in a characterization of seafloor habitats on a small spatial scale that is relevant to juvenile cowcod nursery areas, which is important when considering effective management strategies for this overfished species.

Habitat-based submersible assessment of macro-invertebrate and groundfish assemblages at Heceta Bank, Oregon, from 1988 to 1990

Exploitation of groundfish off the U.S. Pacific coast reached maximum levels during the 1990s, resulting in severe declines in at least nine species of groundfish. From 1988 to 1990, we used the 2-man submersible Delta to make 42 dives and run replicate visual belt transects at six stations ranging from 67–360 m in depth at Heceta Bank on the outer continental shelf of Oregon. We identified four major habitats and associated benthic macroinvertebrate and groundfish assemblages: (1) shallow rock ridges and large boulders (< 100 m deep) dominated by basket stars, juvenile rockfishes, yelloweye rockfish, and lingcod; (2) mid-depth small boulder-cobbles (100–150 m) dominated by crinoids, brittle stars, rosethorn, pygmy/Puget sound, and canary rockfishes; (3) deep cobble (150–200 m) dominated by crinoids, brittle stars and various small rockfish species, and (4) deep mud slope (> 200 m) dominated by fragile urchins, sea cucumbers, shortspine thornyhead, and flatfishes. Although substantial interannual variation in groundfish abundance among seafloor types was evident in the 12 most abundant and/or commercially important fish taxa sampled, high variance resulted in statistically significant differences among years only in juvenile rockfishes. These data provide a baseline for future comparisons exploring long-term change this continental-shelf ecosystem.

Morphology, structure and evolution of California Continental Borderland restraining bends

Abstract Exceptional examples of restraining and releasing bend structures along major strike-slip fault zones are found in the California continental Borderland. Erosion in the deep sea is diminished, thereby preserving the morphology of active oblique fault deformation. Long-lived deposition of turbidites and other marine sediments preserve a high-resolution geological record of fault zone deformation and regional tectonic evolution. Two large restraining bends with varied structural styles are compared to derive a typical morphology of Borderland restraining bends. A 60-km-long, 15° left bend in the dextral San Clemente Fault creates two primary deformation zones. The southeastern uplift involves ‘soft’ turbidite sediments and is expressed as a broad asymmetrical ridge with right-stepping en echelon anticlines and local pull-apart basins at minor releasing stepovers along the fault. The northwest uplift involves more rigid sedimentary and possibly igneous or metamorphic basement rocks creating a steep-sided, narrow and more symmetrical pop-up. The restraining bend terminates in a releasing stepover basin at the NW end, but curves gently into a transtensional releasing bend to the SE. Seismic stratigraphy indicates that the uplift and transpression along this bend occurred within Quaternary times. The 80-km-long, 30–40° left bend in the San Diego Trough–Catalina fault zone creates a large pop-up structure that emerges to form Santa Catalina Island. This ridge of igneous and metamorphic basement rocks has steep flanks and a classic ‘rhomboid’ shape. For both major restraining bends, and most others in the Borderland, the uplift is asymmetrical, with the principal displacement zone lying along one flank of the pop-up. Faults within the pop-up structure are very steep dipping and subvertical for the principal displacement zone. In most cases, a Miocene basin has been structurally inverted by the transpression. Development of major restraining bends offshore of southern California appears to result from reactivation of major transform faults associated with Mid-Miocene oblique rifting during the evolution of the Pacific–North America plate boundary. Seismicity offshore of southern California demonstrates that deformation along these major strike-slip fault systems continues today.

The vegetation and flora of Platt Park, Southbury, Connecticut

Abstract Platt Park is a 43.3-hectare (107-acre) natural area situated in the Southwest Hills Eco-region of Southbury, in New Haven County, Connecticut. Characterized by Triassic sandstone and trap rock ridges, the area offers a diversity of habitats for plant life. This investigation of the vegetation types of Platt Park provides information relevant to the preservation and management of natural areas and critical habitats. Abundance data derived from 263 quadrats were analyzed by the computer program TWINSPAN, circumscribing seven cover types. These cover types are: the Wolffia spp. Cover Type, the Bromus inermis Cover Type, the Juniperus virginiana–Carex pensylvanica Cover Type, the Acer saccharum–Ostrya virginiana Cover Type, the A. saccharum–Berberis thunbergii–Lindera benzoin Cover Type, and the Tsuga canadensis Cover Type. A Shrubland–Woodland Cover Type was also represented, comprising mainly introduced and cultivated species. Each cover type and its corresponding habitat are discussed in the cont...

Patterns of body size and habitat use in a lizard assemblage

:We quantified differences in the distribution and behaviours of three territorial species of phrynosomatine lizard (Urosaurus ornatus, Uta stansburiana, and Sceloporus undulatus) between two habitats on the elevated mesas of western Colorado. Community lizard density was greater on rock ridges dissecting pinyon-juniper woodland than in the surrounding flat, open areas. The frequency of community-level interactions, or behaviours directed towards another lizard of any species, was also greater in the rock compared to the flatland habitat for S. undulatus. Snout-vent length frequency distributions of all three species differed between habitats, with larger lizards residing in the rock habitat. For each species, the distribution of hatchling lizards between habitats was opposite to that expected based on the distribution of conspecific adult females, with the majority of adult females residing in the rock habitat and the majority of hatchlings in the flatland. Indices of juvenile recruitment (number of hatchlings per adult female) in the flatland habitat approximated average clutch size for U. ornatus and U. stansburiana despite known high rates of juvenile mortality in these species. We suggest that ontogenetic habitat shifts may explain the observed age and size distributions of species between habitats. Hatchlings may disperse from rock to flatland to avoid aggression and predation from adult lizards in the rock habitat and return when they have attained larger body size and thus face reduced predation risk, being presumably more able to compete within social hierarchies.

Genovesa Submarine Ridge: A manifestation of plume‐ridge interaction in the northern Galápagos Islands

Despite its circular coastline and calderas, Genovesa Island, located between the central Galapagos Platform and the Galapagos Spreading Center, is crosscut by both eruptive and noneruptive fissures trending NE‐SW. The 075° bearing of the fissures parallels that of Genovesa Ridge, a 55 km long volcanic rift zone that is the most prominent submarine rift in the Galapagos and constitutes the majority of the volume of the Genovesa magmatic complex. Genovesa Ridge was the focus of detailed multibeam and side‐scan sonar surveys during the Revelle/Drift04 cruise in 2001. The ridge consists of three left stepping en echelon segments; the abundances of lava flows, volcanic terraces, and eruptive cones are all consistent with constructive volcanic processes. The nonlinear arrangement of eruptive vents and the ridge's en echelon structure indicate that it did not form over a single dike. Major and trace element compositions of Genovesa Ridge glasses are modeled by fractional crystallization along the same liquid line of descent as the island lavas, but some of the glasses exhibit higher Mg # than material sampled from the island. Most of the submarine and the subaerial lavas have accumulated plagioclase. Incompatible trace element abundances of dredged Genovesa Ridge rocks are lower than the island's lavas, but ratios of the elements are similar in the two settings, which suggests that the island and ridge lavas are derived from nearly identical mantle sources. Glass inclusions in plagioclase phenocrysts from the ridge are compositionally diverse, with both higher and lower MgO than the matrix glass, indicative of homogenization at shallow levels. The structural and geochemical observations are best reconciled if Genovesa Ridge did not form in response to injection of magma laterally from a hot spot‐supplied central volcano, like Kilauea's Puna Ridge. Instead, Genovesa Ridge and its western extension are the result of passive upwelling directed by far‐field tectonic stresses that are generated by tension across the 91°W transform. The proximity of the plume causes magmatism in the extensional zones where it would not ordinarily occur.

Subglacial environment inferred from bedrock-coating siltskins, Mendenhall Glacier, Alaska, U.S.A.

AbstractRetreat of Mendenhall Glacier nearJuneau, Alaska, U.S.A., has exposed a bedrock ridge spotted with “siltskins”, patchy coatings of calcite-cemented clay-to sandsized lithic grains. Coatings 0.5–20 mm thick occur in two distinct morphologies. Thin, striated siltskins coat mainly stoss faces. Thicker, corrugated siltskins on lee faces consist of parallel micro-ridges elongated downslope. Thin-section analysis shows that siltskins consist of a basal, calcite-rich layer overlain by microlaminated layers of calcite-cemented lithic grains. Scanning electron microscope (SEM) energy-dispersive spectrometer (EDS) analysis of laminae and surfaces shows laterally persistent Ca/Si differences. Isotopic values for δO18 and δO13 ranged from −19.52‰ to −12.74‰ and −6.18‰ to −3.44‰, respectively, consistent with deposition from subglacial waters of varying isotopic composition and with derivation of carbon from inorganic sources. Corrugated siltskins are complex depositional features modified by erosional processes. Parallel micro-ridges spaced 1–10 mm apparently formed as sediment-rich water dripped down lee-slope rock faces. Ice–rock separation, flow energy and the transported sediment controlled the layering and depositional forms. Siltskins probably formed when a subglacial cavity system was active on the rock ridge and provide clues about how microscale hydrologic processes interact with larger-scale subglacial systems.

Regional Quaternary submarine geomorphology in the Florida Keys

High-quality seismic reflection profiles fill a major gap in geophysical data along the south Florida shelf, allowing updated interpretations of the history of the Quaternary coral reef system. Incorporation of the new and existing data sets provides the basis for detailed color maps of the Pleistocene surface and thickness of overlying Holocene accretions. The maps cover the Florida Keys to a margin-wide upper-slope terrace (30 to 40 m deep) and extend from The Elbow Reef (north Key Largo) to Rebecca Shoal (Gulf of Mexico). The data indicate that Pleistocene bedrock is several meters deeper to the southwest than to the north east, yet in general, Holocene sediments are ∼3 to 4 m thick shelf-wide. The Pleistocene map demonstrates the significance of a westward-dipping bedrock surface to Holocene flooding history and coral reef evolution. Seismic facies show evidence for two possible Holocene stillstands. Aerial photographs provide information on the seabed surface, much of which is below seismic resolution. The photographs define a prominent, regional nearshore rock ledge that extends ∼2.5 km seaward from the keys9 shoreline. They show that bands of rock ridges exist along the outer shelf and on the upper-slope terrace. The photographs also reveal four tracts of outlier reefs on the terrace, one more than had been documented seismically. Seismic and photographic data indicate the tracts are >200 km long, nearly four times longer than previously thought. New interpretations provide insights into a youngest possible terrace age (ca. 175 ka?) and the likelihood that precise ages of oxygen isotope substage 5e ooid tidal-bar and coral reef components may differ. The tidal-bar/reef complex forms the Florida Keys.

Analysis of shearing of a rock ridge

A rock ridge carrying a major roadway through a quarry in the greater Chicago, IL area sheared along sub-vertical regional joints causing significant distress of the roadway as a result of apparently limited adjacent quarry excavation of a glory hole. The large-scale movement rendered the road unusable. This paper presents a detailed analysis of factors contributing to this response. Post-event field observations of ridge movement revealed that lateral displacements were concentrated along a horizontal thin shaley seam below the bottom of the quarry. These observations show that the sheared ridge slid along the shaley seam and moved as a single block. Three-dimensional numerical analyses of the ridge and the quarry construction activities show that as the quarry was deepened, a buildup of large horizontal stresses occurred in the rock base above the shaley seam. The excavation of the glory hole through this rock base lead to arching and an increase in longitudinal stresses and a reduction in lateral confining stresses along the ridge. The analyses show how the unique combination of large horizontal stresses, the horizontal shaley seam, and stress redistribution due to glory hole construction lead to large shear displacements along the persistent sub-vertical regional joints.

Yucca Mountain pro and con [nuclear waste storage

It's just a lonely ridge of volcanic rock in Nevada, but it's generating more controversy than an indicted CEO. It's where the US Department of Energy wants to build a permanent underground repository for high-level nuclear waste. This paper discusses the arguments for and against Yucca Mountain.

The Snelston Ridge: evidence for a concealed ridge of mineralized Dinantian rocks to the south of the Derbyshire Dome

SUMMARY Little is known of the southern continuation of the Lower Carboniferous (Dinantian) rocks of the Derbyshire Dome where they lie concealed beneath Triassic rocks at the margin of the Needwood Basin. Evidence from regional Bouguer gravity anomaly surveys pointed to the existence of a ridge of shallow Dinantian rocks, here called the Snelston Ridge, largely concealed by Triassic strata apart from two small inliers. The NNW–SSE trending ridge was proved by a borehole which intersected (Dinantian) Widmerpool Formation rocks at a depth of 61 m. Evidence from a seismic reflection profile indicates that the ridge, at least at Birchwoodpark (Snelston), is probably an asymmetrical, fault-controlled anticline. There is, however, no evidence for any significant changes in the thickness of Dinantian rocks hereabouts. The base metal potential of the Snelston Ridge was investigated using detailed geophysical and geochemical surveys and drilling. A borehole on the top of the mineralized mudmound that forms the Limestone Hill Inlier proved minor replacement galena–sphalerite–baryte mineralization with up to 10% Pb over an intersection of about 11 m. Two boreholes on the flanks of the feature revealed little sign of mineralization, indicating that it is restricted to the exposed dolomitized summit of the mudmound.

Magnetic anomalies at the Puna Ridge, a submarine extension of Kilauea Volcano: Implications for lava deposition

High‐resolution magnetic data collected along the axis and the south flank of the Puna Ridge, the submarine extension of the East Rift Zone of Kilauea Volcano, Hawaii, aid in the interpretation of magmatic processes. Crustal magnetization varies along the crest of the Puna Ridge. Three prominent magnetization highs are located between the depths of 1500 and 2500 m. Each of the magnetization highs is associated with distinct volcanic features: a flow field on top of fissured terrain, a lava plateau, and a staircase of lava terraces. The crustal magnetization highs can be explained by the presence of these volcanic features, taking into account water depth and the size of the volcanic features and making simple assumptions about the rock magnetization. No measurements of rock magnetization have been made on Puna Ridge samples. We assume two values: 50 and 10 A/m, based on values from mid‐ocean ridge basalts and the estimated ages of Puna Ridge rocks [Clague et al., 1995]. The two shallowest magnetization highs are adjacent to a landslide scarp. Lava flows overtop the scarp suggesting that a dike has been emplaced and eruptions have occurred since the landslide formed. A possible scenario is that the collapse of the flank led to dike intrusion and eruption at this location because of a reduction in the horizontal stress within the edifice. Our observations suggest that flows are starting to fill in the gap caused by the landslide to rebuild this section of the north flank.

Structure of Réunion Island (Indian Ocean) inferred from the interpretation of gravity anomalies

Réunion is a volcanic edifice whose origin is related to a hot spot in the Indian Ocean. Only 3% of its volume is emergent. Many geological and geophysical studies were carried out on Réunion Island during the 1980's but few of them allow study of the internal structure of the edifice. Several gravity surveys have been carried out on the island since 1976 and we have compiled the available data set. The lack of data on the western side of the island led us to conduct a regional survey in 1993 to obtain a more homogeneous distribution of the stations. Computation of Bouguer anomalies for different correction densities accounts for the variable density of the rocks constituting the edifice and provides a distribution of gravity anomalies interpreted as dense bodies of intrusive rocks inside the edifice. Two very large intrusive complexes can be unambiguously recognised: one beneath Piton des Neiges and one beneath the Grand Brûlé area. Both have been penetrated by geothermal exploration drill holes and the first is also known from outcrop observations. 2.5D simple models were constructed to reveal the geometry and extent of the buried intrusives. They are deeply rooted, extending several kilometres below sea level, and extensive (20–25 km long and 10–13 km wide for the Piton des Neiges complex, 12–15 km long and some kilometres wide for the Grand Brûlé complex). The development of such complexes implies that the activity of the two volcanic centres was long lasting and remained stable while the volcanoes were growing. The Grand Brûlé complex has been interpreted as relics of an old volcano named Alizés Volcano. The interpretation of the gravity maps suggests the presence of a ridge of dense rocks to the North of the axis joining the centres of Piton des Neiges and Piton de la Fournaise volcanoes. By analogy with the other structures, 2.5D models show that this structure would culminate between 0 and 1 km below sea level and be 15 km wide. This complex induces a maximum anomaly in Takamaka Valley and we thus propose to name it Takamaka Volcano. No geological evidence of the nature of these dense rocks is available but the ridge coincides with structures revealed by magnetic and seismic data. Interpretation of the Bouguer anomaly maps suggests that the inner gravity structure of Piton de la Fournaise is not characterised by the presence of a voluminous dense body but probably by more restricted concentrations of dense rocks. Some structures can be recognised: along the present NE and SE rift zones and in the previous central part of Piton de la Fournaise to the West of the present summit. The recent eastward migration of the centre of activity of Piton de la Fournaise accounts for the lack of a large positive anomaly beneath the active craters.

Rock art and rock markings

This paper examines a range of features commonly found at rock art sites, that have conventionally been considered components of rock art, but which (as briefly outlined elsewhere [Rosenfeld 1993 :76-7, l997:29 l]) should be considered as a distinct cultural category. These features include the fingerflutings, abraded lines and pits of the caves along the southern margin of the continent, battered rock ridges that are common, for instance, in the Laura area, pitted rocks in several regions of subtropical Australia, incised grooves that are widespread throughout Central Australia, as well as hand stencils, hand prints and other stencils or prints.