Relict Soils Research Articles

Interpretation of soil features produced by ancient and modern processes in degraded landscapes. VII. Water duration

Rising saline groundwater and fresh perched water have increased over 120 years (modern processes) in the Mediterranean region (>600 mm per annum) of the Mt Lofty Ranges, South Australia. This was caused by replacement of native vegetation with pastures which use less water. Relationships between morphological features (mainly soil colour) and field measurements (e.g. watertable duration, salinity, and sodicity) were studied to 3 m at 12 sites down a representative toposequence of red-yellow-grey duplex soils (Palexeralfs-Natraqualfs), which are common from crest to flat in these catchments. Three soil systems were identified from groupings of soil features: (i) brown/grey topsoil system (e.g. A and E horizons), (ii) red subsoil system (e.g. Bt), and (iii) yellow/white subsoil system (e.g. Btng or Cg). A water duration index was developed to quantify water duration in the brown/grey topsoil system from perched water levels measured in 12 dipwells installed to 0.5 m. Nested piezometers were used to determine if unsaturated zones occurred within the subsoil systems. Measured water duration and levels were compared with the presence pr absence of inferred redoximorphic features. Most features in the brown/grey topsoil system and the red and yellow/white subsoil systems reflected differences in water duration. A conceptual model was constructed to match successive changes in hydrology with differences in soil morphology and thus distinguish between modern and relict (late Mesozoic) soil features that developed under past and present hydrological conditions.

Stream-terrace genesis: implications for soil development

Genesis of three distinct types of stream terraces can be understood through application of the concepts of tectonically induced downcutting, base level of erosion, complex response, threshold of critical power, diachronous and synchronous response times, and static and dynamic equilibrium. Climatic and tectonic stream terraces are major terraces below which flights of minor complex-response degradation terraces can form. These three types of terraces can be summarized by describing a downcutting-aggradation-renewed downcutting sequence for streams with gravell bedload. By tectonically induced downcutting, streams degrade to achieve and maintain a dynamic equilibrium longitudinal profile at the base level of erosion. Lateral erosion bevels bedrock beneath active channels to create major straths that are the fundamental tectonic stream-terrace landform. Aggradation events record brief reversals of long-term tectonically induced downcutting because they raise active channels. They may be considered as major (the result of climatic perturbations) or minor (the result of complex-response model types of perturbations). Climatically controlled aggradation followed by degradation leaves an aggradation surface; this type of fill-terrace tread is the fundamental climatic stream-terrace landform. Aggradation surfaces may be buried by subsequent episodes of deposition unless intervening tectonically induced downcutting is sufficient for younger aggradation surfaces to form below older surfaces. Raising of the active channel by either tectonic uplift or by climatically induced aggradation provides the vertical space for degradation terraces to form; first in alluvial fill and then in underlying bedrock along tectonically active streams. These are complex-response terraces because they result from interactions of dependent variables within a given fluvial system. Pauses in degradation to a new base level of erosion, and/or minor episodes of backfilling, lead to formation of complex-response fill-cut and strath, or of fill terraces. Fill-cut terraces are formed in alluvium; they are complex-response terraces because they are higher than the base level of erosion. Good exposures and dating are needed to distinguish static equilibrium complex-response minor strath terraces from dynamic equilibrium tectonic (major) straths. Strath terraces may be regarded as complex-response terraces where degradation rates between times terrace-tread formation exceed the long-term uplift rate for the reach based on ages and positions of tectonic terraces. Late Quaternary global climatic changes control aggradation events and even the times of cutting of major (tectonic) straths, because the base level of erosion can not be attained during times of climatically driven aggradation-degradation events. Most terrace soils form on treads of climatic and complex-response terraces. Aggradation surfaces may provide an ideal flight of terraces on which to study a soils chronosequence. Each aggradation event is recorded by a single relict soil where tectonically induced downcutting is sufficient to provide clear altitudinal separation of the terrace treads. Multiple paleosols are typical of tectonically stable regions where younger aggradation events spread alluvium over treads of older climatic terraces. Pedons on a climatic terrace in a small fluvial system commonly are roughly synchronous - variations of soil properties that can be attributed to temporal differences will be minor compared to altitudinally controlled climatic factors. Climatic terraces of adjacent watersheds also should be roughly synchronous (correlatable) - variations of soil properties that can be attributed to temporal differences will be minor compared to lithologic and climatic factors between different watersheds. Such generalizations may not apply to basins with sufficient relief that geomorphic responses to climatic changes occur at different and overlapping times, and to large rivers whose widely separated reaches are characterized by different response times to climatic perturbations. Soils on climatic terraces of distant watershedswill not be synchronous if their respective aggradation events occur during full-glacial times and interglacial times. Soils on some complex-response terraces may be diachronous within a given fluvial system, and typically are diachronous between watersheds.

The Santa Rita fault zone: Evidence for large magnitude earthquakes with very long recurrence intervals, basin and range province of southeastern Arizona

A discontinuous zone of subdued, west-facing fault scarps offset Quaternary alluvium along 58 km of the western piedmont of the Santa Rita Mountains, south of Tucson, Arizona. Scarps trend NE to N-S and are 1 to 6 km basinward from the deeply embayed mountain front. Scarp heights range from 1 to 7 m, and maximum scarp slope angles range from 3° to 9.5°. A 6-m-deep trench excavated in middle Pleistocene and younger deposits exposed a high-angle fault zone with about 3.5 m of total displacement. Estimated ages of faulted and unfaulted surfaces, extent of degradation of piedmont scarps, and stratigraphic relations exposed in the trench suggest an age of about 100 ka for the most recent surface-rupture event. Units having well-developed relict soils of late Pleistocene age and older are faulted, whereas units having weakly to moderately developed soils, of latest Pleistocene and Holocene age, are not offset. Morphologic fault scarp analyses suggest an age of 60 to 100 ka. Earthquake magnitude estimates derived using minimum and maximum seismic source moment calculations range from 6.4 to 7.3 One or more earlier surface-rupture events are implied by significantly high scarp heights on mid-Pleistocene than on late Pleistocene surfaces. Scarp heights on middle and early (?) Pleistocene surfaces are similar, restricting faulting to post-middle Pleistocene time (<200 to 300 ka). Stratigraphic relationships observed in the trench also suggest two fault-displacement events. Tectonic landform analysis of the mountain front-piedmont area implies several m.y. of inactivity along the range-bounding fault system prior to these late Quaternary displacements. Extremely long recurrent intervals between displacement events and reactivation of faulting after an interval of tectonic quiescence are typical of late Quaternary fault behavior in southeastern Arizona.

Cenozoic paleosols San Diego area, California

Ancient weathering profiles provide mute evidence of the major climatic regimes that operated in the southern California area during the Cenozoic Era. A tropical climate during part of the Paleocene and Early Eocene caused severe weathering of Jurassic andesitic rocks, Cretaceous granitic rocks and Late Cretaceous and Early Eocene terrigenous rocks. Erosional remnants of this paleosol exist as buried soils up to 30 meters thick and as exhumed soils on some modern hills. The main weathering horizon is overwhelmingly composed of kaolinite with residual quartz grains and minor amounts of iron oxides. This tropical climate was in effect at 35° to 40° north latitude. Late Eocene sedimentary rocks were deposited under a semi-arid climate with 50 to 60 cm of annual rainfall that was concentrated during one season. This interpretation is based on: 1) the dominance of conglomerate and immature sandstone in the Upper Eocene section compared to the relative scarcity of claystone, 2) the immaturity of the clay mineral suite which is dominated by smectite and vermiculite, 3) the presence of fractured clasts presumably split by growth and differential expansion of salts, 4) the multiple caliche beds that individually are up to one meter thick, and 5) the paleohydrology of the fluvial deposits which transported rhyolite gravels over 300 km distance from an eastern bedrock source about 4,000 m high in a river of 1.3 sinuosity with 100 year flood discharges up to 30,000 m 3/sec. The extensive marine terraces in San Diego are mantled by relict soils that record composite weathering characteristics from glacial and interglacial climates from Late Pliocene to present. Maximal development of the paleosol includes an ironstone concretion layer (B ir horizon) above an illuvial clay layer (B t horizon) which rests on an iron- and silicacemented hardpan (C m horizon).

Cenozoic paleosols San Diego area, California

Ancient weathering profiles provide mute evidence of the major climatic regimes that operated in the southern California area during the Cenozoic Era. A tropical climate during part of the Paleocene and Early Eocene caused severe weathering of Jurassic andesitic rocks, Cretaceous granitic rocks and Late Cretaceous and Early Eocene terrigenous rocks. Erosional remnants of this paleosol exist as buried soils up to 30 meters thick and as exhumed soils on some modern hills. The main weathering horizon is overwhelmingly composed of kaolinite with residual quartz grains and minor amounts of iron oxides. This tropical climate was in effect at 35° to 40° north latitude. Late Eocene sedimentary rocks were deposited under a semi-arid climate with 50 to 60 cm of annual rainfall that was concentrated during one season. This interpretation is based on: 1) the dominance of conglomerate and immature sandstone in the Upper Eocene section compared to the relative scarcity of claystone, 2) the immaturity of the clay mineral suite which is dominated by smectite and vermiculite, 3) the presence of fractured clasts presumably split by growth and differential expansion of salts, 4) the multiple caliche beds that individually are up to one meter thick, and 5) the paleohydrology of the fluvial deposits which transported rhyolite gravels over 300 km distance from an eastern bedrock source about 4,000 m high in a river of 1.3 sinuosity with 100 year flood discharges up to 30,000 m 3/sec. The extensive marine terraces in San Diego are mantled by relict soils that record composite weathering characteristics from glacial and interglacial climates from Late Pliocene to present. Maximal development of the paleosol includes an ironstone concretion layer (B ir horizon) above an illuvial clay layer (B t horizon) which rests on an iron- and silicacemented hardpan (C m horizon).

Properties and History of an Exhumed Tertiary Oxisol in California

AbstractThe Ione Formation occurs as isolated exposures along the western foothills of the Sierra Nevada. Presence of an intensely weathered soil profile (an Oxisol) on remnants of the Eocene Ione Formation is direct pedologic evidence for a tropical climate during or subsequent to that time. This is the first detailed description of an exhumed Oxisol in the continental United States. The pedon described here has a thin Al horizon, a red and yellow ironstone horizon over a thick oxic horizon. Below the oxic horizon is a thick deposit of kaolinite clay. The oxic horizon has 11.4% F2O3, 0.04% organic C, 10.9 meq/100 g clay CEC (Cation Exchange Capacity), 3.5 meq/100 g clay KCl extractable Al, and a pH in H2O of 3.3. Kaolinite is the only clay mineral present. This relict soil pedon does not meet criteria below the order level in Soil Taxonomy because of moisture regime limitations. Data such as these illustrate the usefulness of pedology in the study of Tertiary paleoclimatology.

Some applications of paleopedology in Japan

Paleosols in Japan consist of buried soils and relict soils. The former occur primarily in tephra deposit, whereas the latter occupy old land surfaces in various parts of the country. The buried soils affect construction of highways and urban development. The relict soils pose problems in forestry. The paleosols formed in tephra and buried by subsequent volcanic eruptions are chiefly Andosols with their low bulk densities, low solid ratios, high specific surfaces and high water losses. These characteristics are responsible for poor engineering performance of the paleosols and tephras. These have been especially troublesome in the Kanto plain near tokyo and around the Ashitaka Volcano. Some buried soils in tephra, as for example those in the San'in district, are exceptions to the general rule and have desirable properties for construction. Those tephras have clay fractions low in allophane and high in layer-silicate minerals. The buried soils have provided approximate ages of human artifacts through radiocarbon dating of humic horizons. Conversely, identification of artifacts found in buried soils has helped to bracket their ages. Paleosols that are relicts are chiefly members of a Red-Yellow group, many of which seem to be Udults (Ultisols). The soils apparently began forming in warmer past periods but still persist on the land surface. Such soils are strongly acid and very low in plant nutrients, with resulting low productivity when used for forestry or farming. Moreover, such soils are readily subject to erosion because of their landscape positions and poor plant cover.

Utilization for agriculture and forestry of Graulehme, Tertiary paleosols in central Europe

The Graulehme (grey loams) are relict soils or paleosols formed during the Tertiary or earlier but persisting locally on land surfaces. Thus, for example, the Permotriassic peneplain of the Rhinish Massif in Germany was mantled by deep soils during most of the Tertiary, but these were largely removed during a period of uplift and dissection in the Late Tertiary and the Pleistocene. Graulehme remained on the parts of the massif that lagged behind in the general uplift and therefore suffered little erosion. These paleosols now occupy the flat and low-lying positions in the landscape. Other components of the soil pattern are Rankers, acid brown earths and Rotlehme, the last also being paleosois but of limited extent. The Graulehme are high in silt and clay, plastic, virtually impermeable and low in base saturation and plant nutrients. Consequently, the soils are not suitable for cultivation generally. Exceptions are local bodies of the paleosols where materials from acid brown earths have been mixed with or mantle the Graulehme. The paleosols are suitable for pasture without drainage but require lime, complete fertilizer and modern management. The Graulehme are also suitable for forestry. Spruce is the best adapted species, but beech and oak can also be grown.

Kaolinite and Other Clay Minerals in Arctic Ocean Sediments

ABSTRACT Estimates of clay mineral assemblages in deep-sea cores indicate widespread occurrence of kaolinite throughout the Amerasian half of the Arctic Ocean. Illite is the dominant clay mineral but the kaolinite/chlorite ratio of nearly 1.0 is twice that reported in North Atlantic and North Pacific sediments. Kaolinite averages 26% and is present throughout the lengths of all cores, some of which penetrate 2.8-3.0 m.y. old sediment. The widespread accumulations of kaolinite under conditions apparently unfavorable to its formation has special paleoclimatic significance because it has been used as an indicator of low latitude weathering. The kaolinite in Arctic Ocean sediments is apparently derived from shales and relict soils of northern Alaska and Canada.

THE GENESIS OF SOME BASALTIC SOILS IN NEW SOUTH WALES

SummaryField and laboratory investigations of 182 soil samples and their underlying basalts in the Inverell area indicated that not all of the red soils in the area are relicts of Tertiary laterization as was previously thought. The soils on basalt were divided morphologically and mineralogically into shallow (black, brown/ chocolate, and red) and deep (krasnozems and lateritic soils) profiles. The mineralogy of the sand fractions of the shallow soils, which were similar in all respects except colour and location, suggests that they are young soils as the heavy minerals in the sand fractions are dominantly pyroxene, olivine, and the black opaque minerals which weather quite rapidly. The shallow black and brown/chocolate soils occupy whole slopes under grassland vegetation or grassland with trees, while the shallow red soils are restricted to steeper well‐drained slopes and crests where trees tended to dominate grass. In similar areas throughout the New England region red soils are found on basalt in areas receiving 75 cm or less average annual rainfall, although previous workers have assumed that red soils develop from basalt at present only in areas receiving more than 140 cm average annual rainfall. The deeper soils, which were characterized by a lower pH, occupied upper or upper and middle slopes. The dominance of the resistant altered opaque minerals in these soils suggests that they are relict soils. The krasnozems showed little horizon differentiation apart from a slight darkening of the upper 8–10 cm. The lateritic soils had marked horizons, with laterite overlying mottled and pallid zones, the whole sequence being deeper than the krasnozems. The lateritic soils contained a high percentage of heavy minerals in the sand fractions in contrast to all the shallow profiles. Only one period of laterization is indicated in the area, although the laterite levels were not always accordant.

Die Aussagekraft vorzeitlicher Bodenbildungen als Klima- und Zeitindices

Abstract. The value of fossil and relict soils as indicators of past climates or periods differs greatly. It is rather high when we want to reconstruct former climates, of which we can often find out the general type and partly also the approximate amount of temperature and precipitation. On the other hand reliable statements on the time which fossil soils take for their development are largely confined to relative data, which we can only get under very favourable circumstances. Absolute estimates of time can always be done only approximately. These results, however, are only useful, if the state of development of the fossil soils under discussion can be determined with sufficient reliability. Beyond all factors which influence the exactness of our statements we must keep in mind the principle, that fossil climates can only be reconstructed out of climax soils, whereas the estimation of the duration of soil development is only possible with immature soils.