Quartzite Boulders Research Articles

An Actualistic Experimental Study of Giant Quartzite Core Reduction Strategies: Implications for Large Flake Blank Production and Handaxe Manufacture at Amanzi Springs, South Africa

ABSTRACT The later Acheulian assemblages (ca. 534–< 390 ka) from Amanzi Springs in South Africa show a preferential selection for large flake blanks when undertaking large cutting tool manufacture. However, due to the small number of giant cores from the site, we have limited insight into the technical preparation of quartzite raw material packages for large flake production. Here, we present an actualistic experimental study to better understand these procedures at the site and to gain perspective on how knappers may have reduced quartzite boulders of differing internal qualities. Our results highlight the influence of raw material constraints and how the overall morphology of quartzite boulders in turn impacts giant core reduction sequences and large flake blank morphologies. Finally, the experimental study exemplifies the need for high levels of knapping expertise to deal with tough, heterogeneous quartzite varieties.

Morphosedimentological features of the sea floor in the outer sector of the Bahia Blanca estuary, Argentina

The purpose of this paper is to analyze the morphology of the Quaternary relict features and bedforms that characterize the outer zone of an extensive mesomareal system, which is part of the Bahía Blanca estuary (Argentina), and to estimate the prevailing hydro-sedimentological conditions on the continental shelf adjacent to the estuary. Surveys with a multibeam bathymetric system, side-scan sonar and a high-resolution seismic system (3.5 kHz) were carried out and bottom sediment samples were collected. In general, the seafloor presents a varied configuration, marked by changes in its physiography. The Quaternary relict features are composed of two terraces (12–14 m and 18–22 m deep), with steeply sloping escarpments, that are oriented approximately parallel to the current coastline. Associated with these terraces, wide abrasion platforms develop with irregular and plateau-like structures up to 4 m high, together with large rocky blocks up to 6 m in diameter. Here, the predominant sediment corresponds to a gravel-sized material composed of quartzite boulders, siltstone fragments of up to 7 cm, and biogenic remains with different degrees of fragmentation. These sedimentological data, together with the bathymetric and seismostratigraphic information, indicate that the terraces and abrasion platforms are ancient shorelines that originated in an environment with high wave energy, corresponding to periods of stabilization of sea level rise during the final stage of the last postglacial transgression (late Pleistocene-Early Holocene). On the other hand, asymmetric dunes of different sizes (0.5 m < height < 5 m, 5 m < wavelength < 200 m), sand ribbons (length > 300 m) and comet marks originated in equilibrium with the present-day hydro-sedimentological conditions. The availability of sandy material mobilized as bedload is the determining factor for the generation of the varied bedforms. Thus, sand ribbons and comet marks are generated especially in the northern sector of the area, with mobile sediment thicknesses ≤ 0.5 m. With larger thicknesses the formation of dunes occurs. Their size and asymmetry show an intense transport of sand as bedload towards the continental shelf, the southern sector of the area being the main route of the sediment that leaves the estuary. This sediment is the supply source of the sandy shoals that are part of the great ebb delta developed on the continental shelf in the external area of the Bahía Blanca estuary.

Bouldery deposits along the Kherlen fault, Central Khentey, Mongolia: implications for paleoseismology

The assumed Jargalant rockslide is located in Khentey Upland of Mongolia, an area undergoing active tectonic deformation and seismogenic activity but where geomorphic research that connects rock slope failure and long-term paleoseismic events has yet to be conducted. We present the first reconnaissance study on this topic, which demonstrates the possibility of cosmogenic 10Be dating of landslide-induced bouldery deposits to date the timing of the assumed seismic events. We performed integrated geomorphic analysis (geomorphic mapping, topographic profile analysis, and surface trenching) and 10Be surface exposure dating (boulder and bedrock scar) to document the recurrence interval of the assumed paleoseismic events by determining the recurrence of rock slope failures in Jargalant River valley. We identified four geomorphic surfaces and units identified based on their morphology, the distribution of quartzite boulders, and their ages. The geomorphic units are as follows: (1) outburst flood fan (S1), (2) remnant landslide-dam deposit (S2), (3) surviving rockslide body (S3), and landslide scar (S4). Bedrock quartzite outcrops only in the assumed headscarp, while most of the upland is composed of schist. The average 10Be age of quartzite boulders of S1 to S3 is 283.4, 138.8, and 48.4 ka, respectively, and that of the landslide scar (inner and outer edge) are 44.5 and 193.5 ka. Based on the morphology, depositional characteristics, quartzite provenance, and separated and clustered 10Be exposure age, we hypothesize that at least three catastrophic rock slope failures could occur at 283 ka, 138 ka, and 48 ka, likely being triggered by earthquakes associated with active Kherlen fault.

Salt dissolution tectonism and microbial origin of drainage-line silcrete in the Lower Cretaceous Athabasca Oil Sands, foreland Alberta Basin

Abstract The Beaver River Sandstone is a 10 s cm to 1.7 m thick silicified interval emplaced enigmatically within unconsolidated fluvial sand beds of the Lower Cretaceous McMurray Formation, the principle host rock of the Athabasca Oil Sands in northeastern Alberta. The silicified interval was partially eroded into during the Late Pleistocene as glacial meltwaters enlarged and deepened the Athabasca River Valley. The silcrete consists of a 10 s km long linear trend of discontinuous caprocks that sourced the innumerable quartzite boulders along the floor of the Athabasca River Valley. Siliceous cementation was concurrent with Aptian deposition of the McMurray Formation. The silicified bed extends along the disconformity between the lower and middle intervals of the McMurray Formation. The silicification at the end of lower McMurray deposition was spatiotemporally linked to regional dissolution of halite-anhydrite beds in Devonian Prairie Evaporite substrate, 200 m below. A sulphate-rich brine migrated up-section into the uppermost sand beds of the lower interval accumulated along topographic lows of the ancestral Athabasca River Valley, a segment of the regional Assiniboia Paleovalley. Near surface redox of the seep occurred by sulphate reducing microorganisms sourced from groundwater emanating from widespread peat mires. Strongly acidic groundwater resulted in corrosion of the quartz sand grains and silica saturated groundwater in the shallow subsurface. A pH shift occurred at onset of the middle interval, triggering silica cementation as the acidic seep mixed with meteoric-charged oxygenated groundwater along topographic lows of the river valley. Microbial filaments of unknown taxonomic affinity, now silicified, are the first recognized in the McMurray Formation oil sands. These microfossils consist of silicified hollow branching sheaths covered with nanoscale bulbous protuberances that preserve stepped transition textures of hydrated silica into quartz crystallites. They are evidence of partial microbial controls on the sulphate redox process resulting in this unusual type of silcrete.

Scottish landform examples 45: Sgriob na Caillich: a landslide-sourced medial moraine on the Isle of Jura

ABSTRACTMedial moraines deposited by former glaciers and ice sheets are rare in Scotland. The most prominent example is the Sgriob na Caillich moraine, which consists of two to four parallel belts of angular quartzite boulders that extend northwestwards for over 3.5 km from the SW flank of Beinn an Oir on the Isle of Jura. The boulder belts extend to within 300 m of the present coastline, where they are truncated by a low bluff and raised marine terrace. The source of the moraine coincides with bedrock gullies and cliffs that represent the scars of former rock-slope failure(s), indicating that the moraine debris was sourced by one or more rockfalls or rockslides onto the ice surface after Beinn an Oir had emerged from the thinning ice cover as a nunatak. Exposure dating of boulders on the moraine indicate that it formed at 16.6 ± 0.8 ka, consistent with the timing of ice-sheet retreat in this sector. The alignment of the moraine indicates ice-margin retreat to the SE; as regional ice-sheet retreat across the adjacent offshore shelf was to the NE, this anomaly implies that a residual icefield became stranded on Jura during ice-sheet retreat.

Prospectando rochas fluviais e artefatos do Paleolítico Médio Africano descobertos ao longo do Rio Cunene, fronteira entre Angola e Namíbia

Vestígios líticos do Paleolítico Médio Africano (PMA) preservados em corredores ribeirinhos como o perene Rio Cunene atesta a presença de atividades pré-históricas ao longo da atual divisa entre Angola e Namíbia. Próximo à Serra Cafema, mais de 30 vestígios líticos preservados em um contexto a céu aberto (plein-air) incluem lascas de quartzito, núcleos e pontas com alguma abrasão e polimento nos gumes, incluindo as primeiras pontas Levallois encontradas nesta região da África. Uma vez que a arqueologia desta região é pobremente conhecida, estas coleções culturais permitem correlações iniciais e fornecem uma base para reconstrução da proveniência, da procura e da produção de artefatos durante o PMA. Para avaliar as potenciais áreas-fonte de matéria-prima nesta região, métodos de contagem de seixos e avaliações composicionais foram conduzidos nos vestígios e no aluvião Quaternário (Qal) do terraço do rio. A fonte primária em potencial mais próxima de quartzito está em afloramentos rochosos localizados dentro de 2 km de distância do sítio, mas áreas-fonte confirmadas não foram identificadas especificamente. Uma hipótese emergente é que o Qal no terraço do Rio Cunene era uma fonte preferida para coleta de quartzito enquanto matéria prima pelos grupos móveis de caçadores-coletores durante o PMA após 225 mil anos atrás.

Enhanced development of lacustrine microbialites on gravity flow deposits, Great Salt Lake, Utah, USA

The Great Salt Lake, Utah, USA is a shallow, hypersaline, intracontinental lake hosting extensive microbial deposits. At a large spatial scale, the distribution of these deposits is driven by environmental and geodynamical factors (i.e. water-level fluctuations and a fault-related framework). A detailed mapping of the Buffalo Point area, in the north-western part of Antelope Island, indicates the presence of an anomalous concentration of microbial deposits dated ca. 5.8ka BP and distributed along a lobe-shaped geometry. This uncommon microbial deposit geometry results from an extensive colonization of a conglomerate substrate exhibiting an accumulation of m-sized rounded Cambrian quartzite boulders. We suggest that this conglomerate substrate provides a stable nucleation point that promotes the development and preservation of the lobe-shaped microbial deposits. Microbial deposits may also have protected the conglomerate substrate from erosional processes and thereby increased the preservation potential of the lobe-shaped structure. Based on the characteristics of the conglomerate (e.g. grain size, texture) and its location (i.e. 200m beyond the average shoreline), this lobe-shaped structure likely results from subaqueous debris or a hyperconcentrated density flow that transports sedimentary material from the Buffalo Point slopes downward to the shore. We estimate the age of the conglomerate deposition to be between 21 and 12ka BP. The initiation of the flow may have been triggered by various mechanisms, but the existence of a major active normal fault in the vicinity of these deposits suggests that an earthquake could have destabilized the accumulated sediments and resulted in conglomerate emplacement. The catastrophic 15ka BP Bonneville Flood, which led to a drop in the lake level (approximately 110m), may also provide an explanation for the initiation of the flow.

Chapter 51 The glaciogenic Jequitaí Formation, southeastern Brazil

Abstract Glaciogenic deposits of the Jequitaí Formation (Fm.) are well exposed along the margins of the Serra do Cabral on the São Francisco Craton, southeastern Brazil. The Jequitaí Formation is thin (0–150 m thick), lenticular and overlies the Espinhaço Supergroup on a discrete unconformity. Sandstones show subglacial erosional structures such as grooved and striated pavements oriented ENE–WSW. The Jequitaí Fm. consists of massive and stratified diamictites with granules, pebbles and boulders of gneiss, granite, quartzite and carbonate. At the base, the diamictites are massive, whereas the upper part contains many alternating beds of clast-rich and -poor diamictites. They also contain discontinuous, fine-grained sandstones and a few laminated siltstone–mudstone intercalations. This diamictite association indicates glaciomarine sedimentation. The Jequitaí Fm. covers the São Francisco cratonic domain and its equivalent extends eastward over the Araçuaí fold belt where it is part of the metasedimentary Macaúbas Group, a thick Neoproterozoic unit with metadiamictites, quartzites and schists. The diamictite–turbidite association of the Macaúbas Group was deposited on the border of the Pan-African–Brasiliano rift as gravity flows.

Borings in Quartzite Surf Boulders from the Upper Cambrian Basal Deadwood Formation, Black Hills of South Dakota

Shallow, semi-spherical borings occur in clusters with densities of 1–3.5/cm2 in quartzite boulders and in vein quartz from the localized basal conglomerate of the Cambrian-Ordovician Deadwood Formation in the east-central Black Hills of South Dakota. Some borings are superimposed on primary but enigmatic semi-circular structures, 2.5–5 cm in diameter, which are soft-sediment trace fossils formed prior to lithification. The macroborings are the first to be recorded from quartzite and vein quartz. Host boulders were eroded from near vertically dipping Paleoproterozoic quartzites from several different stratigraphic units. The thin boulder conglomerate grades were abruptly changed to sandstone through a layer ≤2 m thick in the Marjuman transgression (regionally correlated to the Cedarina dakotaensis trilobite zone). This transgression occurred prior to the start of the globally recognized Upper Cambrian Paibian Stage. Physically similar rocky-shore settings are widely known from quartzite islands of Cambrian age in Wisconsin, Middle Ordovician age on Ontario's Manitoulin Island, Ordovician-Silurian age in Manitoba, and Devonian age in western Australia. Erosion of quartzite surf boulders of equal or larger size occurred in all those regions, but the Black Hills of South Dakota is the only region where borings in quartzite are documented.

A HIGH-LATITUDE EPILITHOZOAN FAUNA ON QUARTZITE CLASTS AND THE PROBLEM OF COBBLE TRANSPORT ACROSS A COASTAL PLAIN: MIDDLE TURONIAN KASKAPAU FORMATION, BRITISH COLUMBIA, CANADA

Abstract The Middle Turonian Kaskapau Formation in the Rocky Mountain Foothills of northeastern British Columbia comprises up to 950 m of shallow marine sandstones cyclically interstratified with marine mudstones and minor lagoonal deposits. Transgressive surfaces are commonly mantled by thin pebble lags. A transgressive pebble lag exposed in Quality Creek near Tumbler Ridge town site includes rare, well-rounded quartzite cobbles and a quartzite boulder, which were deposited at a paleolatitude of about 67°N. Encrusting organisms are unevenly distributed over five of the largest clasts. Disciniscid brachiopods are abundant on one cobble but are otherwise rare. A conical-shelled lingulate brachiopod with concentric growth lamellae occurs sparsely, and a weakly ribbed lingulate brachiopod is represented by one shell. Serpulid worm tubes, encrusting bryozoans, and possible basal attachments of corals are also present. Attached foraminifera are abundant and distributed over several clasts. Generic diversity an...

Cosmogenic nuclide ages for Last Glacial Maximum moraine at Schnells Ridge, Southwest Tasmania

Moraines on Schnells Ridge, southwest Tasmania, have been dated using in situ 10Be. An age of 19,400 ± 600 yr is indicated for the well-preserved innermost moraine from consistent measurements on four large quartzite boulders. This corresponds closely with exposure ages reported by T.T. Barrows et al. (2002, Quaternary Science Reviews 21, 159–173) for Last Glacial Maximum glacial features farther north in Tasmania and southeast Australia. In contrast, ages between 39,000 and 141,000 yr were obtained from a series of boulders on a more extensive outer moraine, indicating that this has had a more complex history.

Digital Analysis of Lichen Cover: A Technique for Use in Lichenometry and Licnenology

Image analysis software was used to obtain various measures of thalli in crustose lichen communities. Lichens growing on flat-faced quartzite boulders in two glacier forefields were photographed and the images were transferred to a computer. Barren rock was digitally removed using Adobe Photoshop and Idrisi geographic information system (GIS) software was used to measure thallus size, perimeter, compactness, and total lichenized area. Replicate analyses show that the technique produces reproducible results that allow a user to distinguish very small differences in lichen coverage and obtain other quantitative measures of a lichen population. The technique is suitable for use with smooth, evenly illuminated surfaces where there are clear color differences between the various lichens and the substrate is a uniform color. Excellent results can be obtained using a 35 mm film camera, inexpensive flash units, a film or print scanner and DOS based versions of Idrisi that permit batch processing of images. The technique can be used to examine lichen colonization patterns and explore new approaches in lichenometric dating.

The provenance of Devonian sandstones from Shetland: a Sm-Nd and trace element study

Synopsis A Sm-Nd isotope and trace element study has been performed on a selection of four whole rock samples of Devonian sediments, two impure/banded quartzite boulders and two unfoliated granite/granophyre boulders from a Devonian conglomerate. Included in the study are also three samples of Caledonian metasediments (from the Whiteness, Clift Hills and Yell Sound Divisions) and one Archaean tonalite gneiss (the Wilgi Geos Group) from Shetland. The Devonian sediments and the granite boulders have relatively low Nd model ages of 1.0 to 1.1 and 1.3 to 1.5 Ga, respectively, which suggests the presence of Caledonian juvenile material in both of these rock types. The Proterozoic metasediments have Nd model ages in the range 1.8 to 2.5 Ga, while the tonalitic gneiss has a high Nd model age of 2.9 Ga. The Caledonian metasediments form two compositionally contrasting groups where the Yell Sound and Clift Hills Divisions and the two impure quartzite boulders all have relatively low time-corrected 143 Nd/ 144 Nd ratios and low Nb-and Sr-contents relative to the Whiteness Division. These two groups of Caledonian metasediments together with representative Caledonian ophiolite rocks define a compositional field of time-corrected 143 Nd/ 144 Nd ratios and Nb and Sr contents, within which plot the compositions of the Devonian sediments and the granite/granophyre boulders. Cr is generally immobile at surface and low-grade metamorphic conditions, but is less suitable as a provenance indicator due to the wide variations in the Cr-content in Caledonian juvenile rocks.

ENIGMATIC FOSSIL ENCRUSTING AN UPPER ORDOVICIAN ROCKY SHORE ON HUDSON BAY, CANADA, IS A CORAL

An enigmatic encruster from the Upper Ordovician rocky shore exposed near Churchill, Manitoba, was recently described by Johnson et al. (1998). The specimen was found attached to a quartzite boulder enclosed in carbonate matrix. The matlike, calcareous fossil consists of densely packed, vertical, cylindrical columns with upward-radiating structures issuing from their centers. It was identified as a new genus and species, Storeacolumnella hudsonensis, of uncertain taxonomic affinity but with possible characteristics of sponges and calcareous green algae. In particular, the radiating structures within columns were compared with spicules of a sclerosponge and with the siphon system of siphonous green algae.

Enigmatic fossil encrusting an Upper Ordovician rocky shore on Hudson Bay, Canada, is a coral

An enigmatic encruster from the Upper Ordovician rocky shore exposed near Churchill, Manitoba, was recently described by Johnson et al. (1998). The specimen was found attached to a quartzite boulder enclosed in carbonate matrix. The matlike, calcareous fossil consists of densely packed, vertical, cylindrical columns with upward-radiating structures issuing from their centers. It was identified as a new genus and species, Storeacolumnella hudsonensis, of uncertain taxonomic affinity but with possible characteristics of sponges and calcareous green algae. In particular, the radiating structures within columns were compared with spicules of a sclerosponge and with the siphon system of siphonous green algae.

Cosmogenic dating ranging from 20 to 700 ka of a series of alluvial fan surfaces affected by the El Tigre fault, Argentina

It is crucial to date continental landforms to quantify processes involved in terrestrial surface evolution, especially in regions affected by active tectonics. Andean quaternary alluvial fan surfaces affected by the El Tigre strike-slip fault have been studied using combined geomorphic and 10 Be exposure age approaches. Field observations and SPOT (French acronym for “Satellite for Observation of the Earth”) image analysis enable the identification of six alluvial fan units. Measurements of in situ–produced cosmogenic 10 Be concentrations in quartzite boulders exposed on the top of fan surfaces show that the depositional periods ended during successive major interglacial stages. The calculated minimum exposure ages date the abandonments of the alluvial fan surface from 41 000 ± 8500 yr for the youngest to 670 000 ± 140 000 yr for the oldest unit. When linked to the measured maximum cumulative right-lateral displacement of stream channels, the exposure ages yield a horizontal slip rate of about 1 mm/yr on the El Tigre fault. This study shows that for arid regions, where fan surface erosion is minimal, in situ–produced 10 Be can be used to constrain the age of stratigraphically separate alluvial fan surfaces. These fan surface exposure ages can be further used to calculate slip rates on active faults and infer depositional periods correlative with climatic events.

Notes on Some Early Geological Investigations in Kansas

Just a little more than 250 years ago, a Frenchman passed up the Kaw (Kansas) River Valley and made note of the granite and quartzite boulders for what may have been the first recorded notes on the geology of Kansas. Most of the early records were sporadic and not systematically taken. Early expeditions were mainly military; later ones were railroad surveys. Scientists, if on the expeditions, were natural scientists and not geologists, so descriptions usually were of topography, agriculture suitability, transportation feasibility, climate, botany, and other natural phenomena, but seldom of the geology. Documents of these early expeditions, including those of expeditions of Lewis and Clark (1804-6), Pike (1805-7), Long (1819-20), Fremont (1843-45), Emory (1846-47), Stansbury (1849), Marcy (1852), and Beckwith (1853-54) were in a narrative form - long on generalities but short on detail. Thus by the mid-19th century, the geology of Kansas was known only in a general way.The ‘Great American Desert’ was a place to cross, not to stay. The influx of gold seekers and those wanting to exploit the land changed everything and information on the geology became important. To fill the void, ‘guides’ by a variety of self-styled experts on the history, geography, climate, mineral resources, soils, etc., were issued as aids to the emigrants. The guides, usually published by the author, were interesting and popular but included little scientific information. In 1852, David Dale Owen was commissioned a "United States Geologist" and made observations in northeastern Kansas as part of a larger survey. Other geological observations were made by members of early federal government-sponsored territorial surveys of the West. The fossils collected on these surveys and by collectors were described by paleontologists - most reports described the different, new, or spectacular finds. In 1864 the State commissioned the first geological survey headed by B. F. Mudge; the second survey was created in 1865 with G. C. Swallow as State Geologist. Thus the State government assumed responsibility for the surveying - mostly with the idea of making an inventory of economic resources and promoting development of the young state. During the period from creation of the second geological survey in 1865 to the third in 1895, the Kansas Academy of Science Transactions served as one of the leading outlets for information on Kansas geology. The systematic and regular recording of the geology of Kansas commenced in 1895 with creation of the third (and present) State Geological Survey in Lawrence with Erasmus (Daddy) Haworth appointed State Geologist.

The lower Devonian Kowmung volcaniclastics: A deep‐water succession of mass‐flow origin, northeastern Lachlan Fold Belt, N.S.W.

Abstract The Lower to ?Middle Devonian Kowmung Volcaniclastics form the upper part of a succession of Upper Siluran to mid‐Devonian flyschoid rocks in the Yerranderie area of N.S.W., and contain two major facies associations. (1) A mudstone facies association represents the ambient, background sedimentation, comprising predominantly buff mudstone that is host to an assemblage of coarser‐grained sediments, including graded‐bedded to massive siltstone, sandstone, conglomerate, allodapic limestone, and large allochthonous limestone blocks and associated limestone breccia. Bouma sequences are common, sole structures occur and maximum bed thickness is about 3 m. (2) A volcaniclastic facies association intrudes and interrupts the accumulation of the ambient mudstone facies association, and contains massive to partly graded, quartzofeldspathic siltstone, sandstone, breccia and conglomerate. Sedimentation units in the volcaniclastic facies association are up to 120 m thick. The two facies associations interfinger. Stratigraphically, the base of the Kowmung Volcaniclastics is taken as the first sedimentation unit of the volcaniclastic facies association. The mudstone facies association below this level is part of the Siluro‐Devonian Taralga Group. Both facies associations were deposited in relatively deep‐water. The dominant transport process in both associations was mass‐flow, involving granular mass‐flows (turbidity currents, grain flows), debris flows and avalanches. Massive mudstone is hemipelagic in origin. The volcaniclastic facies association probably represents a submarine volcanic apron around the emergent, volcanic Bindook Complex. Grossly, the succession coarsens upwards, and there is evidence of several sources of sediment, rather than a single point at the head of a submarine fan. Provenance is diverse. In the mudstone facies association, framework grains in sandstone are microlitic volcanic‐rock fragments with a mafic to intermediate volcanic source. Clasts in conglomerate and breccia are consistent with derivation from the regionally extensive, quartzose Ordovician flyschoid successions. Clasts of ?penecontemporaneous limestone also occur. The volcaniclastic facies association was probably derived largely from the nearby, coeval Bindook Complex, which consists of silicic ash‐flow and ash‐fall tuff, lava, associated sediment and granitoids. Detritus was either derived directly from volcanic eruptions or was worked in fringing littoral and fluvial environments prior to redeposition by mass‐flow. Quartzite boulders mixed with volcanic clasts in the conglomerate suggest that Ordovician quartzarenite was also exposed around the volcanic complex. Tentative provenance correlations have been made between the different rock units in the Kowmung Volcaniclastics and their possible sources in the northern part of the Bindook Complex.

The character and interpretation of some pediment mantles

Some pediment mantles provide crucial evidence concerning the processes responsible for the shaping of the cut bedrock surfaces, or pediments, upon which they rest. On the western side of the Flinders Ranges, the mantles on the dissected Brachina pediments consist of 2–3 m of limestone and quartzite boulders and cobbles set in a silt matrix. The cobbles are derived from the uplands to the east and have been transported by rivers. Comparisons with contemporary stream channels suggest deposition by divaricating streams emerging from the uplands on to the desert plains. No palaeosol intervenes between the mantle above and the cut bedrock surface below, and the latter is ascribed to planation by laterally migrating distributary streams. Similar deposits occur, and similar interpretations can be applied, to several other dissected pediments located at the upland margins, and to some within the Ranges. But the most prominent old valley floors, or pediment remnants, in intermontane situations are capped and preserved by coarse angular blocks of quartzite. Many of the remnants are quite steeply inclined (up to 7°) compared to the 3°–4° that is normal for the pediments proper. The cappings are interpreted as slump deposits laid down either on the toes of slopes or on the heads of pediments; they are related to scarps that have since retreated (partly through slumping). But on granite pediments (e.g. on Eyre Peninsula, in northern Queensland; and on dacite and rhyolite in the Gawler Ranges) the fine textured mantles are thin, and mineralogically indicate nothing but derivation from the underlying bedrock; there is no unequivocal evidence of downslope transport. Yet, after rains, there is evidence of rillwash and sheetwash; surely these pediment surfaces are surfaces of transportation like those of the Flinders Ranges. The crucial upper layer of sediment that may provide clues to the processes active appears to have been eroded away, possibly as a consequence of European settlement and land use.

Cambrian Tropical Storm Waves in Wisconsin

Sizes and shapes of quartzite boulders in Cambrian strata surrounding ancient islands at Baraboo, Wisconsin, allow estimation of the magnitude of Cambrian ocean waves using results from wave tank and flume experiments, as well as observations of very coarse stream gravel. Breakers at least 7 to 8 m high were required to tumble and move the largest well-rounded boulders (1.5 m diam) interstratified with Cambrian sandstone. Storm generation of waves of such magnitude is consistent with independent paleomagnetic evidence that suggests that Wisconsin lay near the equator 500 m.y. ago, at which latitude intense tropical storms would be expected.