Subaerial Denudation Research Articles

Karst terrain in the western upper Galilee, Israel: Speleogenesis, hydrogeology and human preference of Manot Cave

A karst survey of the western upper Galilee in Israel shows that karst has been a dominant geomorphic factor throughout the Cenozoic. We discuss the geomorphic character of Manot Cave on the background of other karst features of the region, in order to decipher the preferences of the humans who favored this cave over others. Tens of caves distributed over the study area demonstrate that phreatic and hypogene isolated voids and conduit segments are more abundant than vadose shafts, sinking stream caves and spring caves, although all these types are present. Most caves belong to old stages of landform development, prior to Plio-Pleistocene uplift and stream entrenchment. Manot Cave is a relict chamber cave, which corresponds to a plaeo-water table and the erosion plain above it. Subaerial denudation and slope processes have opened the cave to the surface during the mid-late Pleistocene. Manot Cave is compared with other caves in the region, demonstrating its unique character. It may have been selected due to the small entrance facing to the SW, and the large inner chamber which could be used for non-domestic purposes. This suggests a possible role of a unique behavioral and cultural suite of characters which influenced hominin preferences. The cave was used by hominins and animals until being closed again by colluvium and possibly collapse, ∼30 ka. Clastic, chemical, archaeozoological and anthropogenic accumulations reflect the various stages of cave development and gradual sealing of the entrance.

Cenozoic landforms and post-orogenic landscape evolution of the Balkanide orogen: Evidence for alternatives to the tectonic denudation narrative in southern Bulgaria

Continental denudation is the mass transfer of rock from source areas to sedimentary depocentres, and is typically the result of Earth surface processes. However, a process known as tectonic denudation is also understood to expose deep-seated rocks in short periods of geological time by displacing large masses of continental crust along shallow-angle faults, and without requiring major contributions from surface erosion. Some parts of the world, such as the Basin and Range in the USA or the Aegean province in Europe, have been showcased for their Cenozoic tectonic denudation features, commonly described as metamorphic core-complexes or as supradetachment faults. Based on 22 new apatite fission-track (AFT) and 21 helium (AHe) cooling ages among rock samples collected widely from plateau summits and their adjacent valley floors, and elaborating on inconsistencies between the regional stratigraphic, topographic and denudational records, this study frames a revised perspective on the prevailing tectonic denudation narrative for southern Bulgaria. We conclude that conspicuous landforms in this region, such as erosion surfaces on basement-cored mountain ranges, are not primarily the result of Paleogene to Neogene core-complex formation. They result instead from “ordinary” erosion-driven, subaerial denudation. Rock cooling, each time suggesting at least 2km of crustal denudation, has exposed shallow Paleogene granitic plutons and documents a 3-stage wave of erosional denudation which progressed from north to south during the Middle Eocene, Oligocene, Early to Middle Miocene, and Late Miocene. Denudation initially prevailed during the Paleogene under a syn-orogenic compressional regime involving piggyback extensional basins (Phase 1), but subsequently migrated southward in response to post-orogenic upper-plate extension driven by trench rollback of the Hellenic subduction slab (Phase 2). Rare insight given by the denudation pattern indicates that trench rollback progressed at a mean velocity of 3 to 4km/Ma. The Neogene horst-and-graben mosaic that defines the modern landscape (Phase 3) has completely overprinted the earlier fabrics of Phases 1 and 2, and has been the prime focus of tectonic geomorphologists working in the region. The new narrative proposed here for linking the geodynamic evolution of SE Europe with surface landform assemblages raises issues in favour of better documenting the regional sedimentary record of existing Paleogene basins, which constitute a poorly documented missing link to the thermochronological evidence presented here.

Denudation rates of carbonate pinnacles in Japanese karst areas: Estimates from cosmogenic 36Cl in calcite

This study attempted to quantify long-term subaerial denudation of bare carbonate rock surfaces by using in situ-produced cosmogenic 36 Cl in calcite. Carbonate samples were collected from the topmost 5 cm of exposed pinnacles at several non-glaciated karst areas in subtropical to subarctic regions in Japan. Concentrations of natural Cl and 36 Cl in calcite were determined by accelerator mass spectrometry with isotope dilution with 35 Cl-enriched carrier spike. The nuclide concentrations were of the order of 10 5 –10 6 atom g −1 , and converted to total denudation rates averaged over a 10 5 yr-timescale of chemical and physical processes acting on the karst surfaces. The denudation rates were 20–60 mm kyr −1 , being lowest in the central part of Japan. This tendency indicates the alternation of relative importance of chemical (dissolution) and physical (frost shattering) processes in denudation, depending on site-specific factors such as mean temperature, annual precipitation, and freeze–thawing intensity.

The Mid-Cimmerian tectonic event (Bajocian) in the Alborz Mountains, Northern Iran: evidence of the break-up unconformity of the South Caspian Basin

Abstract The Mid-Cimmerian tectonic event of Bajocian age can be documented all across the Iran Plate (Alborz Mountains of northern Iran, NE Iran, east-central Iran) and the southern Koppeh Dagh (northeastern Iran). In the Alborz area, the tectonic event consisted of two main pulses. A distinct unconformity (near the Lower–Upper Bajocian boundary) at or near the base of the Dansirit Formation is the sedimentary expression of rapid basin shallowing due to uplift and erosion. Another unconformity is developed in the early Upper Bajocian, close to or at the top of the Dansirit Formation. Locally, it is expressed as an angular unconformity due to block rotation and is overlain by a thin transgressive conglomerate followed by silty marls of the deep-marine Upper Bajocian–Callovian Dalichai Formation. This upper unconformity signals a rapid subsidence pulse. On the Tabas Block of east-central Iran, a single unconformity can be documented that is time-equivalent to those bounding the Dansirit Formation (i.e. ‘mid-Bajocian’). Local folding gives direct evidence of compressional tectonics, and conglomerates indicate subaerial denudation of older Mesozoic or Palaeozoic strata. After a stratigraphic gap, transgressive sediments of ?Late Bajocian–Bathonian age follow, suggesting a fusion of the lower and upper Mid-Cimmerian unconformities in east-central Iran. Along the southern margin of the Koppeh Dagh Mountains (NE Iran), a Late Bajocian subsidence pulse initiated the opening of the strongly subsiding Kashafrud Basin, an eastwards extension of the South Caspian Basin. In all of these areas, one phase of uplift and erosion took place followed by a pronounced pulse of subsidence running counter to trends of the eustatic sea-level curve. Thus, what is generally understood as the Mid-Cimmerian tectonic event is now thought to consist of a tectonic phase, confined to the Bajocian. This phase is explained as the expression of the onset of sea-floor spreading within the South Caspian Basin situated to the north of the present-day Alborz Mountains. This strongly subsiding basin developed close to the Palaeotethys suture during the Toarcian–Aalenian and went through a change from the rifting- to the spreading-stage during the Bajocian. The Mid-Cimmerian event therefore reflects the break-up unconformity of the South Caspian Basin.

The Rise and Fall of the Davisian Cycle of Erosion: Prelude, Fugue, Coda, and Sequel

The Cycle of Erosion formulated by the American geographer William Morris Davis in the 1880s remained the dominant paradigm in geomorphology well into the 20th century, before it waned in response to improved understanding of Earth's crustal and surface behavior. The Davisian model sought to explain landforms in terms of structure, process, and stage. Following initial rapid tectonic uplift, landforms were presumed to evolve on a quiescent crust through stages of youth, maturity, and old age, to culminate in a peneplain. A new cycle would be initiated by landform rejuvenation in response to a changing base level of erosion. This model was a reflection of its time, of the cycle mania of the 19th century, which in turn was founded on Hutton's limitless "succession of worlds" and dissatisfaction with earlier notions of landscape origins constrained by limited Earth time. Davis's model was derived from ideas regarding orogenic cycles favored by Dana and Le Conte, and of prolonged subaerial denudation toward base-level observed by Powell and Dutton. The model's supremacy was challenged from time to time, notably by the Pencks (father and son) and by alternative cyclic denudation models that invoked pediplanation and etchplanation rather than peneplanation. The relevance of the Davisian model declined after 1940 in response to a growing awareness of Earth's crustal mobility, changing climates and geomorphic processes, and refined dating of geologic time. The subsequent quantitative revolution in geomorphology, with its emphasis on measurement of form and process aided by rapidly improving technologies, and based in part on lingering antecedents, sounded the death knell for the Davisian model but also triggered something of a theoretical hiatus. In recent years, resurrection of the concept of isostasy, defined by Dutton but ignored by Davis, has led to the formulation of a more realistic but more complex model, briefly introduced here, in which landforms may be viewed as responses to more-or-less continuous interaction between tectonic activity, subaerial denudation, and isostatic adjustment.

Quantification of late Cenozoic erosion and denudation in the Sognefjord drainage basin, western Norway

The total late Cenozoic erosion and denudation in the Sognefjord drainage basin, western Norway, has been calculated to about 5400 km3 by subtracting the present topography from a reconstructed preglacial (paléic) surface. This volume corresponds to a mean erosion and denudation of 440 m in the Sognefjord drainage basin. The total volume of subaerial denudation and fluvial activity amounts to about 400 km3. The remaining volume of about 5000 km3 yields a mean glacial erosion of about 400 m in the Sognefjord drainage basin. Assuming glacial erosion in a period of 1 million years during the past 2.57 million years, the average rate of glacial erosion in the Sognefjord drainage basin was about 40cm 1000 yr-1 (0.4mm yr-1).

Effect of regional topography and hydrology on the lacustrine isotopic record of Miocene paleoclimate in the Rocky Mountains

Oxygen isotopic compositions of upper Miocene (9.2 m.y.) lacustrine limestone from northwestern Wyoming range from −21.5 to −35.2% (PDB) and are the lightest yet reported for a non-marine carbonate sequence. These values require that lake water was greatly depleted in 18O relative to modern meteoric precipitation and indicate that most inflow was sourced as meltwater from glaciers in the adjacent Gros Ventre range. Assessment of climatic factors influencing the isotopic composition of global meteoric water indicates either that nearly all of Miocene precipitaaion in the southern Rocky Mountains was derived from large lake systems in the Snake River Plain and northern Great Basin to the west, or that Gros Ventre catchment elevations were up to 2300 m higher than at present. Because erosion rates in modern alpine regions suggest that subaerial denudation could only account for up to 1200 m of post-Miocene elevation reduction, any additional lowering must reflect the influence of post-Laramide epeirogeny during Basin and Range extentional tectonism. Lacustrine isotopic data therefore provide boundary conditions on the timing and magnitude of changes in late Cenozoic paleoclimate, topography, hydrology, and tectonism in the western Wyoming portion of the Rocky Mountains.

THE JURASSIC FACIES IN THE LEVANT

The Triassic‐Liassic contact in the Levant is a distinct sedimentary break expressed by lateritic palaeosols (Mishhor) or volcanics (Asher).A marine platform carbonate regime began in the Pliensbachian (Ardon‐Nirim) and continued in the Toarcian (Qeren‐Nirim). It was interrupted by Toarcian‐Aalenian clastics in the Negev, adjacent Sinai and along a belt crossing Central Israel into South Anti‐Lebanon (Inmar‐Rosh Pinna). In Northern Israel, Lebanon and North Anti‐Lebanon it persisted without interruption through the Oxfordian (Haifa or Kesroaune).Bajocian lithofacies vary from being mixed in the Negev (Daya), to largely marly in Sinai (Maghara), and to monotonous Bajocian‐Oxfordian platform‐carbonates (Haifa) in the north. Bajocian‐Bathonian lithofacies in the Coastal Plain consist of Haifa carbonates, interwedged by oolitic shoals (Sederot) and spiculites (Barnea). Paralic clastics dominate the early Bathonian in the south (Safa‐Sherif), followed by middle‐late Bathonian micrites and marls (Kehailia/Karmon). The latter characteristic body of shales continues to the Callovian, and in the Coastal Plain separates the Bathonian carbonates from the early Callovian calcarenites (Brur).Callovian‐Oxfordian platform micrites are interwedged by marls and biostromes in the Negev (Zohar‐Beersheba) but may consist of bioherms (Nir'Am) in the Coastal Plain. A complete or partial hiatus of the middle‐late Callovian coincides with the extension of the transgressive onlap of early Oxfordian shales (Kidod) from North Sinai to South Anti‐Lebanon, crossing the Coastal Plain and Central Israel.Kimmeridgian oolites, shales and occasionally sands (Halutza) terminate the Jurassic cycle, ending in a regional uplift followed by subaerial denudation or submarine canyons (Gevar‐Am).The palaeotectonic setting of the Jurassic in Israel and adjacent Sinai, prior to Infra‐Cretaceous truncation, consists of the Negev High which extends to the coastal plain area (Beersheba nose), separating the North Sinai Maghara Basin from the Central Israel‐Hermon trough, the latter being disturbed by Lartet's (1869) Neogene‐Quaternary wrench movement of over 100 km sinistral displacement. A rather shallow platform in the north includes Galilee, Lebanon and North Anti‐Lebanon.The clastics of the Liassic‐Bathonian part of the sequence are connected with the wearing‐down of the Arabian Massif in the south and SE. Yet the thickening of the early Oxfordian shales in the offshore wells points to derivation from some landmass in the west, now hidden beneath the Mediterranean.

Messinian badlands on the southeastern margin of the Mediterranean Sea

Substantial subaerial denudation of the North African continental margin took place during the Late Miocene salinity crisis. The Nile drainage was deeply entrenched as far as 1200 km inland, upto the Aswan cataract. Beneath the modern birdfoot delta the thalwegs of ancient Messinian river valleys lie as much as 2.5 km below present sea level. The relief between the top of the incised Late Miocene coastal plain and the axis of excavated channels exceeds 1.2 km. In the subsurface of the lower reaches of the modern Nile Cone a network of bifurcating entrenched channels descends to 4.6 km below sea level to become covered by the southern limit of the Messinian Evaporite Formation. A paleodrainage system is also present beneath the Levantine margin. Seismic reflection profiles document an extremely rough and steeply gullied morphology which is analogous to the badlands of South Dakota. In addition, reflection profiles reveal uniform and gentle seaward gradients of the preerosion (Jurassic to Late Miocene) and posterosion (Pliocene and Quaternary) sedimentary successions beneath the coastal plain and continental shelf. The closely comformable nature of all these depositional surfaces strongly indicates that the badland topography does not owe its origin to an epiorogenic uplift and tilting of the continental edge, but, instead, to a lowering of base level brought about by an unprecedented eustatic drop in water level within isolated Mediterranean basins. Calculations which consider the progressive isostatic loading of both the onshore and offshore sedimentary prism indicate a fall of the base level of at least 3.5 km. This accounts for the observed depth in the Levantine Basin at which Messinian-age shallow-water evaporites lap against the contemporaneous North African subaerial erosional surface.

Stratigraphy of the Volcanic Ash Deposits in the Vicinity of Lake Nojiri, Nagano Prefecture

The volcanic ash deposits distributed in the vicinity of Lake Nojiri can be classified into three units; the Older, the Middle and the Younger volcanic ash. The nearly 10 meters thick Older volcanic ash consists of brown to reddish scoria beds. Characteristically the about 0.6-1.5 meters thick beds of hornblende andesite pumice occur in the lower and upper parts of the Older volcanic ash. These beds are good guides.The Older volcanic ash interfingers with the main part of the Toyono formation which was deposited in the middle Pleistosene lacustrine basin to which the writers adapted the name “the Toyono Lake”. The surface of the Hanami plane I, from 900 to 1000 meters above sea-level, may be accepted as the deposition surface of the Older volcanic ash. This was subjected to up-warping followed with subaerial denudation and the formation of the Hanami plane II, from 700-800 meters above sea-level, around Lake Nojiri. Although the Hanami plane I' about 600-800 meters above sea-level, is separated by the flexure scarp from the Hanami plane I, it is thought that it is a correlative of the latter.The nearly 2 meters thick Middle volcanic ash is distributed only on the Hanami planes and is superposed upon the Older volcanic ash with little unconformity. A bed of yellowish, pebble size hornblende pumice occurs at its basal part. It attains about 1 meter in thickness and an excellent stratigraphic marker.The Younger volcanic ash covers several planes in different hights is classified into three parts, each of which is separated by an unconformity, and designated as I, II and III in upwards sequence. From the horizon II of the Younger volcanic ash, during the excavation of the bottom of Lake Nojiri, the remains of Paleoloxodon namadicus naumanni and Megaceros (Shimomegaceroides) yabei were collected, and the 14C dates from 16.150±520 to 21.600±900 B.P. years are obtained from two drift woods found together with elephant teeth and bones remains.

Paleozoic Stratigraphy of Four Corners Region, Utah, Colorado, Arizona, New Mexico: ABSTRACT

The sedimentary rocks of region can be organized into (1) units containing similar fauna, (2) units of equal time span, or (3) units of similar lithology. Locally all three unit types may be nearly identical within sedimentary sequence, but regionally their bounding planes intersect at appreciable angles. Methods (1) and (2) depend upon paleontological criteria. A major fraction of rocks in the field (and most well cuttings) yields no diagnostic fossils; of fossils recovered, taxonomy and range are, more often than not, moot questions. Methods (1) and (2) are subject therefore to fair measure of personal interpretation. Organization of sedimentary rocks on the basis of lithology is concrete. This virtue is recognized in the U.S.G.S. definition of formation as a mappable lithologic unit. Facies change introduces complexities, but these can frequently be resolved into operational units by diligent effort. The organizational system in this paper is lithologic. Cambrian sediments of the Four Corners region can be divided into: (1) transgressive phase composed of basal sand (Tapeats-Ignacio) followed and overlain in turn by marine shales (Bright Angel-Ophir) and carbonates (Muav-Hartman-Bowman-Lynch), and (2) thinner regressive phase composed of retreatal sandstones and dolomites. Time lines cross lithology; hence, at the close of Lower Cambrian time Tapeats sandstone was being deposited in the west Grand Canyon-San Rafael swell region, Bright Angel-Ophir shales in the St. George-Cedar City belt, and carbonates in Nevada. By Upper Cambrian time Tapeats-Ignacio facies had advanced to the Four Corners-San Juan mountain area; Bright Angel facies had been overlapped by carbonates. Latest Cambrian witnessed rapid marine retreat and clastic offlap. Ordovician and Silurian rocks have not been identified on the Four Corners region. Subaerial denudation during Ordovician, Silurian, and Lower to Middle Devonian time developed at least locally mature topography on Cambrian sediments. Marine invasion of the Upper Devonian End_Page 950------------------------------ differed from that of the Cambrian in that Devonian seas advanced upon carbonate terrane, except (1) where valley cutting exposed Tapeats, and (2) in the easterly reaches of Cambrian deposition where Cambrian carbonates never covered the Ignacio conglomeratic sandstone and arkose. The lower part of the Upper Devonian is therefore dolomite contaminated with sands and shales except (1) in valleys where clean sandstone lenses are present in Devonian dolomites, and (2) in the eastern reaches of Devonian deposition where it overlapped exposed Tapeats-Ignacio to lie locally on pre-Cambrian. Brief marine withdrawal gave rise to thin gray-green clay zone at the top of the Devonian over which Mississippian carbonate-depositing seas advanced. Distribution of the clean carbonate Madison in the Four Corners region is similar to Devonian. Cambrian-Devonian-Mississippian distribution patterns were replaced in Pennsylvanian time by new tectonic trends. Crustal mobility supplanted earlier Paleozoic stability. Permo-Pennsylvanian sedimentation exhibits great variation in thickness and lithology. Dominant tectonic elements in the region were the Uncompahgre-San Luis uplift, Zuni-Defiance uplift, Paradox basin, and intervening shelf areas. Excessive rate of crustal subsidence in the Paradox basin produced an evaporite lens nearly mile thick while normal limestones were deposited on surrounding shelves. Contemporaneous moderate uplift of the Uncompahgre element caused delivery of Paradox basin-marginal arkosic flysch. Climactic uplift in later Pennsylvanian and Permian time spread thick Cutler arkosic fanglomerate and mix d clastic apron over the central Four Corners region. On its periphery the semiterrigenous Abo-Supai-Hermit-Queantoweap redbed terrane accumulated. Diminishing Permian redbed deposition was augmented and followed by invasion of light-colored, largely aeolian sands and local bolson evaporites, the Toroweap-White Rim-De Chelly-Coconino-Yeso sequence. Marine Kaibab-San Andres deposition on the western, southwestern and southern margins of the Four Corners region ended Paleozoic stratigraphic history. Subsurface stratigraphy of the Four Corners region displays wealth of possible petroleum exploration frontiers. A few of the most promising include: (1) Devonian channel sands of the Sage Plain-Farmington area, (2) linear Mississippian limestone-dolomite facies change belts flanking the Monument upwarp, (3) Paradox basin-marginal bioherms and associated dolomites, (4) Kaibab limestone and local sand lenses in the Castle Valley-Kaiparowitz region. Emphasis in this region should be strongly stratigraphic, preference going to noses developed on interesting stratigraphy rather than to closures in neutral rocks. End_of_Article - Last_Page 951------------

Geology of the Western Parts of Isawa and Nishi-Iwai-gun, Iwate Prefecture

This area which occupies a part of the backbone ranges between Iwate and Akita Prefecture consists largely of marine Lower and Middle Miocene, terrestrial Upper Miocene and Lower Pliocene sediments. These are underlain by the Permian sediments and granodiorite, moreover overlain by the Recent volcanics. The Cenozoic sediments of this area are sub-divided as shown in the text. In the eastern part of this area, the Orose, Mizuyama, and Ohira formations make a centroclinal fold with low angles. These formations are also broken by a system of radial faults conversing to the center of the area and make some minor folds with the N-S trend along the western most part. In the central part of the area, the Maekawa and Orose formations make a system of asymmetrieal folds with axes forming broad arcs with their concave sides facing towards the east and with dip angles of 10-20° along every western wing and of 15-30° along every eastern wing. The western part of the area consists of the Oidegawa and Isawagawa formations besides the subjacent pre-Tertiary rocks. An anticlinal structure traverses along the middle portion of this part, and the Maekawa and Oidegawa formations dip at angles varying from 20° to 40° towards the east along the eastern wing, and the Iwaigawa formation and the pre-Tertiary rocks are exposed along the crest of the anticline. The Maekawa and Oidegawa formations which build the western wing of the anticline dip westwards at angles of 30°. After deformation of the Permian sediments, intrusion of granodiorite and subsequent prolonged subaerial denudation, the first intense extrusion of basic lava and its pyroclastics of Neogene age took place in this area. This volcanism was followed by the first marine transgression of the Neogene and it was at this time that the initial phase of the Tertiary geosyncline in North Japan was born. The Lower Miocene Isawagawa formation is a product of such a condition. The subsequent intense volcanic activity of acidic lava and its pyroclastics occurred during progression of the aforestated marine transgression. Thus, the middle Miocene Oidegawa formation of shallow water origin were formed. When these volcanisms became weakened and marine transgression progressed further, the siliceous shale besides conglomerates of the Maekawa formation deposited. The aforesaid conditions were followed by marine regression in this area which resulted in the deposition of coarse-grained pyroclastic sediments of the Orose formation. Before the sea was completely withdrawn from this area, gradual uplift along the western borderland occurred. Thus, following complete regression, the Orose was well as the subjacent formations became exposed above sea-level. The dacite and its tuffs of the Mizuyama formation were deposited in a depressed basin fomed in the Upper Miocene in this area. With the opening of the Pliocene, the lowland of this area was invaded by a new marine transgression. This transgression is responsible for the building of the Ohira formation. After the deposition of the Ohira formation, this area was uplifted and all of the Neogene formations stated above were subject to a subaerial denudation until Recent date. Some volcanic cones, sub as Yakeishi-dake, etc., were formed in the late Pleistocene, and the several river terraces and fans were constructed along the eastern margin of this area almost simultaneously with the neo-volcanisms or somewhat later.

Problems of a Peneplain

The writer reviews certain problems regarding peneplains, and concludes as follows. 1. The so-called peneplains are divided into two kinds according to the manner and position of their origin: one is a peneplain which is concerne with the base-level of the sea and is formed on land of subaerial origin, the other a peneplane formed under sea level by marine agencies. 2. A peneplain is one stage between an old stage (a subdued mountain stage) and a peneplane. 3. Two types of peneplains have hitherto been considered, one de MARTONNE's type, which is mainly the result of subaerial denudation and the other CHAMBERLIN's type, mainly the result of the lateral erosion of rivers. 4. Martonne's type may be regarded as the normal one, and Chamberlin's type as the abnormal, so far as Japanese climates concerned. 5. A thorough study of peneplanation requires a study of weathering soil layers. 6. The nature of a weathering soil layer may be taken as one of the indicators in ascertaining the difference between a subdued mountain and a peneplain. 7. The views hitherto held with respect to the land form of a peneplain have been various. Most of them, however, have been very ideal and imaginal, lacking in positive evidences, so that the writer of this article summarizes the methods of positive evidences which have already been adopted. 8. More consideration and testing than have been formerly done are required to show how groups of almost the same height of summits and spurs have been formed. 9. One of the so-called up-lifted peneplains, which is assumed from the projected profile method, may have to do with its rock structure.

Major John Wesley Powell, 1834–1902

THE centenary occurs on March 24 of the birth of Major John Wesley Powell, the distinguished American explorer, geologist and ethnologist. Born at Mount Morris, New York, of English parents who had emigrated to the United States in 1830, Powell was educated at Illinois and Oberlin College. He served in the army during the Civil War, losing an arm at the battle of Shiloh, and ifr 1865 became professor of geology in the Illinois/Wesleyan University at Bloomington. Two years later he began a series of hazardous and important expeditions to the Rocky Mountains and the Green and Colorado Rivers, which led to a Government geographical and geological survey of the Rockies. Powell served on this for several years and his reports, together with those of F. V. Hay den and G. M. Wheeler, were embodied by Clarence King in the United States Geological Survey bulletins. In 1879 Powell was made director of the United States Bureau of Ethnology, and in 1881, on the resignation of King, he became also director of the Geological Survey. He held the latter post for thirteen years, but retained the former until his death at Haven, Maine, on September 23, 1902. Powell was one of those pioneer geologists of the Far West, who as von Zittel said, “by their vivid portrayal of the work of subaerial denudation roused the intellectual life of the middle of the century to new conceptions on a grand scale”.

II. The coraIlian rocks of Oxford, Berks and North Wilts

The rocks described in this paper strike roughly E. N. E.-W. S. W., from Wheatley, near Oxford, to the neighbourhood of Wootton Bassett and Tockenham in Wiltshire, a distance of about forty miles. They are mapped on the Old Series 1-inch Geological Survey Maps, sheets 13 and 34, and those portions east of Kingston Bagpuize also on the New Series 1-inch Oxford Special Sheet. The extreme south-westerly portions have also been recently re-mapped by the Survey on the new Marlborough sheet. This strip of rocks, of which the average breadth is about two and a half miles, varying from five miles to nothing, has resisted subaerial denudation to a greater extent than the Oxford and Kimeridge Clays below and above it. In consequence it forms a conspicuous ridge, roughly parallel to the Chalk escarpment, dividing the Vale of the White Horse (in its broadest sense) into the valley of the Isis on the north and the valley of the Ock on the south. Near Wootton Bassett is the water-parting between the Bristol Avon and the Thames, of which the Isis is the upper portion, above Abingdon, the point of confluence with the Ock. All the formations within this area have an apparent dip to the north-east.

Changes of Relative Levels of Land and Sea

AMONG the different kinds of evidence showing that changes in the relative levels of sea and land are going on all over the globe, the forms assumed by coast-lines are now recognised by geologists as being the most convincing and satisfactory. Sea-erosion, acting only along shore-lines, and sub-aerial denudation, operating over the whole landsurfaces, result in features of such clearly differentiated character that no unbiassed observer can fail to recognise their great significance and value. When we find long, narrow, deep, and winding inlets from the sea into the land (“fiords,” etc.), it is obvious that such features could not result from the cutting back of the coast-line by the sea, but that they are old river-channels that have been drowned by the sinking of the land. On the other hand, sea-beaches, with caves, fan-taluses, and other signs of shore work, occurring at various heights above the present sea-level, speak, quite as unmistakably, of elevation having taken place.

A Possible Limiting Effect of Ground-Water upon Eolian Erosion

Previous articleNext article FreeA Possible Limiting Effect of Ground-Water upon Eolian ErosionJoseph E. PogueJoseph E. Pogue Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The Journal of Geology Volume 19, Number 3Apr. - May, 1911 Article DOIhttps://doi.org/10.1086/621844 Views: 19Total views on this site PDF download Crossref reports no articles citing this article.

XXIX. The Economic and Petrographic Geology of the New Red Sandstones of the South and West of Scotland

I. Introduction. There are in the South and West of Scotland eight separate areas of some considerable extent occupied by red sandstones of post-Carboniferous date. Six of these areas have been economically developed. That they are younger than the Coal Measure sandstones is certain, but they have been variously regarded as of Permian or Triassic age. Whatever their age may be, their characteristics are very similar, and they will here be referred to as “New Red Sandstones.” The various districts may be separately distinguished as—(1) Arran, (2) Mauchline Basin, (3) Thornhill Basin, (4) Dumfries Basin, (5) Annan Basin, (6) Lochmaben and Corncockle Moor, (7) Moffat, (8) Ballantrae. They consist of bright brick-red, red, or orange-red sandstones, with abundant false bedding, associated with more or less volcanic material at their base. They will be referred to in the order given. There seems good reason to believe that they were originally all connected, their subsequent isolation being due to subaerial denudation. Goodchild ( Trans. Geol. Soc. of Glasgow , vol. xi., part i., page 96—“Desert Conditions in Britain”) considers that the new red rocks, and even the younger Jurassic rocks, formerly covered nearly the whole of Britain; and Sir A. Geikie (“Scenery of Scotland”) mentions the discovery of fossils belonging to the Avicula contorta zone of the Rhaetic group as indicating that the Arran sandstones and marls belong to the Triassic period. He further says that these strata no doubt at one time extended over a much wider area of This 250-word extract was created in the absence of an abstract

Solifluction, a Component of Subaërial Denudation

According to the theory of river development, as it has been worked out in its full modern form by a number of eminent American morphologists, the occurrence of narrow v-shaped valleys in a region indicates that the region in question has passed only the very first stages of the cycle of erosion. This type of valleys, considered by older European geologists as the most important feature of river-action, is, according to the modern American school, only an immature stage in the development of river valleys. In the course of time the blocks of land left between the principal valleys will be dissected by secondary streamlets, the valleys will be broadened, and their slopes will get more and more gentle. At last, if the subaerial denudation has time enough to fulfil its work under unaltered conditions, the hills are wholly consumed, the region is base-leveled, and the land once deeply dissected is turned into a slightly undulating plain with broad and shallow, faintly insected river valleys. Not till then has the process reached the final stage of its cycle, the "peneplain." This theory of subaerial denudation is based upon the premise that river-erosion works all over the areas, and not only linearly, as was supposed by an older school of geologists. This assumption looks at first somewhat startling. Evidently the main stream and the principal tributaries of a river form only a branching system of erosive lines. Only when the innumerable rivulets and feeders, all the transient small waters washing hillsides and slopes at rainfalls and snow-meltings, are taken into consideration, does the erosive system present a network so close that it can be said to cover all the area.

I.—The Kishon and Jordan Valleys

That broad trench through the Palestine Highlands, an ancient highway and battlefield of nations—the plain of Esdraelon or the valley of Megiddo, together with the plain of Acre—has for long presented to me a difficult problem in Physical Geology, for it seemed inexplicable by subaerial denudation under existing conditions. Its floor varies roughly from five to eight miles in breadth; running approximately from south-east to north-west, it is bounded on the more western side by the limestone mountains of Samaria and on the more eastern by those of Galilee. The former descend from the ridge of Carmel (1,742 feet at highest) with a fairly steep escarpment, which becomes a little less regular as we follow it to the bastion-mass of Mount Gilboa; the latter correspond in their general outlines with those of the eastern portion of Samaria, but the advance of a lower spur towards the south-west divides the plain of Esdraelon from that of Acre, by a kind of strait in which, so far as I could see, there is but little level ground on either side of the Kishon. This spur, however, of the northern hills, hardly does more than interrupt the floor of the Kishon valley, for above it the great trench is continued between two hill masses, much of these ranging from thirteen to sixteen hundred feet above sea-level. Beyond the strait the upper basin (plain of Esdraelon) quickly broadens out, extending towards the south-east for about fifteen or sixteen miles, where it is divided into two arms by Jebel Duhy (Little Hermon) (1,690 feet), which is thus isolated from Tabor (1,846 feet) on the north, and from Gilboa (1,698 feet) on the south; a broad, rather shallow, grassy valley descending from the last-named mass to lose itself in the plain.