Water-laid Deposits Research Articles

Epiclastic deposits associated with large-scale landslides and the formation of erosive calderas in oceanic islands: The example of the La Palma Island (Canary Archipelago)

The growth and evolution of the La Palma Island has frequently been punctuated by high magnitude mass-wasting events triggered by gravitational collapses of volcanic edifices and by the erosion of the Caldera de Taburiente. These episodes are evidenced by voluminous debris accumulations in the submarine vicinity of the island and the presence of six very-coarse epiclastic units in the geological record of the island. In this paper we study these epiclastic units in order to characterize their stratigraphic architecture and facies associations, and the mechanisms involved in the transport and emplacement of the material associated with large failures and the erosion of volcanic edifices. Emphasis is also placed on characterising the temporal sequence of processes that have occurred on the island and discussing the origin of the Caldera de Taburiente.Three of the units described — La Cumbrecita Breccias and Megabreccias, La Pared de la Caldera Breccias and Conglomerates and La Viña Breccias – are overlying the detachment surfaces of the Santa Cruz de La Palma, Playa de la Veta and Cumbre Nueva landslides, respectively. They mainly represent the products of debris avalanches and debris flows with subordinate stream-flows filling the scars of the landslides. Unit 4, Las Angustias Breccias and Conglomerates, is interpreted as debris-flow or lahar deposits generated by landslides during the growth of the Bejenado Volcano. The uppermost units, the Tazacorte Conglomerates and El Riachuelo Conglomerates, represent water-laid deposits related to the excavation and erosion of the Caldera de Taburiente, and the incision of a valley between the Bejenado Volcano and the Cumbre Nueva scarp, respectively.Our results provide new and valuable data about cyclic events of construction–destruction of volcanic edifices worldwide, and their related processes and deposits.

High-resolution stratigraphy and depositional model of wind- and water-laid deposits in the ordovician Guaritas rift (Southernmost Brazil)

The upper portion of the Pedra Pintada Alloformation includes about 100 m of mostly eolian deposits. This paper emphasizes the vertical succession and lateral association of sedimentary facies, based on analysis of outcrop data and aerial photographs, as well as the hierarchy and origin of bounding surfaces. It aims to propose a high-resolution stratigraphic and depositional model that may be useful to exploitation of eolian reservoirs. The succession has been preserved due to basin subsidence, and is described in terms of four facies associations that constitute three dominantly eolian units. These units are sharply bounded by major flooding surfaces (super surfaces) that, in turn, are overlain by 1 to 2 m thick, dominantly water-laid facies (lacustrine, fluvial, deltaic and eolian). Both their internal organization and boundaries were controlled by changes in the base level rise rate. The basal Eolian Unit is composed of crescentic eolian dunes and damp interdune deposits ascribed to a wet eolian system. On the other hand, eolian units II and III, also characterized by crescentic eolian dunes (simple and compound) deposits, were related to dry eolian systems, since they comprise dry (eventually wet) interdune facies. Eolian Unit III is truncated by basinwide unconformity, which is then overlain by the ephemeral fluvial deposits (Varzinha Alloformation). This second type of super surface is related to climate-induced wind erosion (deflation) down to the water table level (regional Stokes surface) followed by fluvial incision linked to tectonic activity.

Clues from Fe Isotope Variations on the Origin of Early Archean BIFs from Greenland

Archean rocks may provide a record of early Earth environments. However, such rocks have often been metamorphosed by high pressure and temperature, which can overprint the signatures of their original formation. Here, we show that the early Archean banded rocks from Isua, Akilia, and Innersuartuut, Greenland, are enriched in heavy iron isotopes by 0.1 to 0.5 per mil per atomic mass unit relative to igneous rocks worldwide. The observed enrichments are compatible with the transport, oxidation, and subsequent precipitation of ferrous iron emanating from hydrothermal vents and thus suggest that the original rocks were banded iron formations (BIFs). These variations therefore support a sedimentary origin for the Akilia banded rocks, which represent one of the oldest known occurrences of water-laid deposits on Earth.

Late‐Pleistocene avifaunas from Cape Wanbrow, Otago, South Island, New Zealand

Fossil avifaunas from the Hillgrove Formation at Boatmans Harbour, Ruby Gully, and Old Rifle Butts, all on Cape Wanbrow, Oamaru, north‐east Otago, are listed. The marine beach sands and gravels at Old Rifle Butts that form the lowest part of the Hillgrove Formation and overlie the palaeo‐wave platform were deposited during the last interglacial ∼130–110 kyr BP (Oxygen Isotope Stage 5). There are a few small avifaunas (totalling 11 spp.) from these beach sediments (J41/f8710, f8214, f8227). The colluvial, valley‐fill deposits in Ruby Gully and at its mouth are the youngest in the sequence. Radiocarbon dating indicates their emplacement between 27 and 34 kyr BP, or the later part of Oxygen Isotope Stage 3. If these ages are representative of the true age of the samples and not the limitations of radiocarbon technology, they indicate that these deposits in Ruby Gully are much younger than the beach deposits. Radiocarbon ages on a pitfall fauna from a small cave 3–4 m above the base of the Hillgrove Formation indicate that the cave fauna has a similar age as that in Ruby Gully. The dune and interdune waterlaid deposits at Old Rifle Butts (>2 m above the wave platform) may date from an unknown time between 100 and 35 kyr BP or be coeval with those in Ruby Gully. Fifty‐three species of bird (32 land and freshwater taxa) are represented in the combined avifaunas making this the richest Pleistocene avifauna known from New Zealand. All bird taxa are known from Late Holocene avifaunas in the eastern South Island. Key taxa (Pachyornis elephantopus, Emeus crassus, Euryapteryx geranoides, Coturnix, Chenonetta, Cnemiornis, Harpagornis, Fulica, Porphyrio, Gallinula) indicate that the habitat was mainly grassland and shrubland. Tuatara, indeterminate skinks, and seals are also present.

A Luminescence Dating Study of Open-Air Palaeolithic Sites in Western Epirus, Greece

We report results of a preliminary luminescence dating study of middle to late Pleistocene red beds and early Holocene dune deposits from prehistoric sites in northwest Greece. The wide range in age estimates contradicts the impression that all the red sediments of the region are as old as the Pliocene or early Pleistocene and that artefacts found in them are late intrusions and hence worthless in a stratigraphic context. Our data provide support for a recently proposed chronological framework of the Palaeolithic in the region. TL-IRSL comparisons confirm the IRSL as a more appropriate means for dating water-laid deposits, while both methods appear to be equally useful for aeolian sediments. The study cautions that the effect of various laboratory procedures used to obtain TL or IRSL dates in a context of complex depositional histories precludes a simple prima facie interpretation of the ages. A proper evaluation of luminescence dates requires a full account of the laboratory procedures employed and an understanding of the depositional history of the sediments.

Luminescence dating of fine-grain Holocene sediments from a coastal setting

Abstract A detailed study of a core of Holocene age from a site (Adventurers’ Land, F21) in the Fenlands, UK, based on the measurement of infra-red-stimulated luminescence (IRSL) with silt-sized fractions of water-laid deposits has yielded a sequence of 24 luminescence ages. An additive dose procedure was applied to evaluate the palaeodose, and the annual dose was assessed on the basis of radioactivity and elemental analyses of samples taken from the core. The proportions by weight of the mineral fraction of water and organic material within the sediments ranged from c. 20 to 170% for the former and between c. 10 and 25% for the latter. Overall, the sequence of IRSL age evaluations is consistent with the calibrated radiocarbon ages obtained for three intercalated organic horizons within the core. Although the luminescence ages for F21A do not possess a resolution that would enable rates of sedimentation between the organic sediments to be determined with confidence, the general trend of the luminescence ages with depth suggests a chronological resolution of the order of 1 ka or better.

Sand-drift surfaces: A neglected type of bounding surface

Sand-drift surfaces are sharp, generally erosional surfaces separating waterlaid deposits from overlying eolian sand-sheet deposits. They form in many modern playa-lake, ephemeral-stream, and alluvial-fan environments, but have rarely been reported from ancient sequences. Sand-drift surfaces are an important type of bounding surface, one which marks the transition from subaqueous to eolian depositional processes, thereby providing valuable information for environmental reconstructions, architectural element analysis, and short- and long term climate changes. Because of their nature, sand-drift surfaces cannot be described by existing bounding-surface classifications. To overcome some of the classification problems, we suggest a simple nonhierarchical terminology.

Relationships between major structures, salic volcanism and sedimentation in the Kenya Rift from the equator northwards to Lake Turkana

Summary At the equator, the Kenya (Gregory) Rift Valley is a half-graben, faulted on the eastern side. It passes northwards into a deep graben with a double western margin, and then into what is essentially a downwarped depression. The deep graben sector (0°15′–1°00′N) is virtually devoid of late Miocene-Quaternary trachytic central volcanoes: their counterparts in areas of strong faulting are salic flood lavas. Moreover, the scarcity of pyroclastics in early-late Miocene ‘plateau’ phonolite sequences of the deep graben suggests that the thick tabular lava units are some distance from source. The phonolites exposed on the western side of the rift (Kamasia-Uasin Gishu) probably came from eruptive centres beyond the deep graben, whereas on the eastern side (Laikipia) a substantial part of the sequence could well belong to a lava shield on the plateau. In contrast to intra-volcanic pyroclastic sediments that occur predominantly N of latitude 1°N, the formations in the Kamasia region consist of waterlaid deposits intercalated with tabular lava flows. This spectacular development of waterlaid sediments is attributable to the absence of major eruptive centres and the existence of tectonic-geomorphic sediment traps in the deep graben sector of the rift.

Uranium and other trace element geochemistry of the Hopi Buttes volcanic province, northeastern Arizona

Over 200 diatremes occur in the Hopi Buttes volcanic province on the southwestern flank of the Black Mesa basin in northeastern Arizona. The diatremes are funnel-shaped vents with maar craters at the surface. They were formed by phreatomagmatic eruptions along existing northwest-southeast fractures during mid-Pliocene time. Anomalous concentrations of uranium occur in at least 20 of the diatremes. The diatremes and dikes which feed them are composed of lamprophyres, monchiquite, and limburgite. Tuff breccias and agglomerates rimming the vents consist of sedimentary and igneous fragments in a limburgite matrix. The maars contain waterlaid deposits of interlayered tuff, claystone, and marl. The lamprophyres are enriched in light rare earth elements and may have been derived from a slight partial melting of the upper mantle. Average uranium values are: tuff breccias, 10.54 ppm; tuffs, 23.95 ppm; limestones, 58.23 ppm. The average Th/U ratio in the lamprophyres is 2.02. The lack of correlation between U and Hf or Th indicates that uranium traveled in mobile phases and was segregated from many elements in the lamprophyres. Localization of uranium in maar-type diatremes may have occurred as fluids percolated up through fractures in the vents and mixed with ground and surface waters.

Geologic evidence for age of deposits at Hueyatlaco archeological site, Vasequillo, Mexico

Direct tracing of beds during excavation in May 1973, confirmed that the artifact-bearing layers at Hueyatlaco underlie 10 m of fine-grained, water-laid deposits that constitute part of the wide-spread Valsequillo gravels. Dissection of these deposits by the adjacent Río Atoyac has reached a depth of 50 m. The stratigraphic section at Hueyatlaco includes four distinctive tephra units. The oldest one occupies a small channel in a series of cut-and-fill stream deposits that have yielded bifacial tools. It lies more than a meter above flat-lying, fine-grained beds from which edge-retouched tools have been recovered. The three other tephra units occur higher in the section. Fission-track ages on zircon phenocrysts from two of the younger tephra layers (370,000 ± 200,000 and 600,000 ± 340,000 yr, 2σ) agree with concordant uranium-series dates for a camel pelvis that was found associated with bifacial tools at Hueyatlaco (245,000 ± 40,000 yr by 230Th and > 180,000 yr by 231Pa). These dates are compatible with the depth of burial and subsequent dissection of the Hueyatlaco deposits, as well as with the degree of hydration of volcanic glass shards and with the extent of etching of heavy-mineral phenocrysts from within the tephra layers. These findings suggest to us that further search for archaeological remains in deposits as old as those at Hueyatlaco would be warranted.

Whitianga group sediments of the Table Mountain area, Coromandel peninsula

Abstract A lower to mid-Pliocene sequence of rhyolitic Whitianga Group sediments is described and one new formation erected. The Wainora Formation includes basal rudites overlain by finer epiclastic lake sediments containing leaf and freshwater mussel impressions. It has a maximum thickness of 35 m and is inferred to have been deposited in two lakes on the dissected surface of the Beesons Island Volcanics' andesites. Conformable on the Wainora Formation are thicker (450 m maximum exposed thickness) and more extensive water-deposited and subaerially-deposited pyroclastic sediments and rarer ignimbrites of the undifferentiated Coroglen Subgroup. Many of these water-laid deposits are inferred to be the result of hot pyroclastic flows entering a valley system having lacustrine, fluviatile, and flood-plain environments. The paleogeography and eruptive history of the Whitianga Group in the Table Mountain area are inferred.

Textural and mineralogical significance of the Granitic Xenoliths from the Central Volcanic Region, North Island, New Zealand

Abstract Granitic boulders have been found at four localities in the central North Island: Mt Tarawera, Huka, Atiamuri, and Hinuera. They occur closely associated with the acid volcanic suite, in pumice breccias and associated water-laid deposits. Two distinct types of boulders are recognised, the true granodiorites of Tarawera and Huka, and those characteristically containing extensive graphic intergrowths, found at Atiamuri and Hinuera. Both types are characterised by a “high temperature” mineralogy, and are regarded as co-magmatic with the acid volcanic rocks of the region, and not part of the basement. The granodiorites are characterised by subhedral to euhedral zoned plagioclase, subhedral to euhedral embayed quartz, subhedral to interstitial sanidine, and the presence of biotite, hornblende, hypersthene, and magnetite. The granodiorites are considered to be representative of the magma from which they crystallised, but the second type show evidence of progressive potassium enrichment and are consider...

THE CLAY MINERALS IN SOME BRITISH COLUMBIA SUBSOILS

X-ray diffraction analysis was used to identify the clay minerals present in fourteen subsoil samples that were selected to represent some more important clay-bearing deposits in British Columbia. The clay mineralogy of the subsoils varied considerably but montmorillonitic clay minerals tended to predominate in the water-laid deposits of the south and illite in the soil parent materials of the Interior Plains region of the northeastern part of the Province.

Some Structural Differences Between Wind-Laid and Water-Laid Deposits on the West Shore of Lake Michigan

ABSTRACT A study was made of beach deposits along the west shore of Lake Michigan for the purpose of determining differences between the wind-laid and water-laid deposits. The bedding is more irregular in the wind-laid than in water-laid material and the lenses vary more in thickness. In individual dunes, sections perpendicular to wind direction show an arching effect in the bedding planes which increases upward. Also the presence of horizontal layers of pebbles indicates water-laid material.