Structural Geomorphology Research Articles

Structural geology and geomorphology of the Oued Maala region, central Tunisia

Structural geology and geomorphology of the Oued Maala region, central Tunisia

Structural geomorphology of a fast-spreading rise crest: The East Pacific Rise near 3�25?S

A deeply-towed instrument package was used in a detailed survey of the crest of the East Pacific Rise (EPR) near 3°25′S, where the Pacific and Nazca plates are separating at 152 mm/yr. A single 90 km-long traverse of the rise crest extends near-bottom observations onto the rise flanks. A ridge at the spreading axis is defined by its steep regional slopes, probably caused by rapid crustal contraction as the spreading magma chamber freezes, rather than by outward-facing fault scarps. It can be divided into a marginal horst-and-graben zone with low (<50 m), symmetric fault blocks, and a 2 km-wide elongate axial shield volcano that is unfaulted except for a narrow crestal rift zone. This has a summit graben (10–35 m deep) probably formed by caldera collapse, and narrow pillow basalt walls built over vent fissures. Small, low (<50 m) volcanic peaks occur on the shield volcano and the horst-and-graben zone, and some may have been built away from the spreading axis. Major plate-building lava flows issue from the crestal rift zone and flow an average of 500 m down the sides of the volcano. The marginal horst-and-graben zone results from tensional faulting of a thin crust of lava, and evolves by progressive shearing on inclined fault planes. Crustal extension continues at least as far as 20 km from the axis, and the large, long fault blocks formed in thicker crust beyond the subaxial magma chamber develop into abyssal hills. Pelagic sedimentation, at a maximum rate of 22 m/106 years, gradually infills open fissures and smooths the small-scale roughness of the fault blocks. Off-axis volcanism has also resulted in smoother crust, and built seamounts. Comparison of the EPR at 3°25′S with the Famous Rift and Galapagos Rift reveals a similarity in the processes and small-scale landforms at fast, medium and slow-spreading ridges. There are significant differences in the medium-scale landforms, probably because plate-boundary volcanic and tectonic processes act on crust of very different strength, thickness, and age.

J. Tricart 1974. Structural Geomorphology. Translated from French by S. H. Beaver &amp; E. Derbyshire. xiii + 305 pp., 112 figs. Longman, London. Price £4.75.

J. Tricart 1974. Structural Geomorphology. Translated from French by S. H. Beaver &amp; E. Derbyshire. xiii + 305 pp., 112 figs. Longman, London. Price £4.75.

Crust of the Earth

Structural Geomorphology. By J. Tricart. Translated by S. H. Beaver and E. Derbyshire. Pp. xiii+305. (Geographies for Advanced Study.) (Longman: London, April 1974.) £4.75.

Structural Geomorphology Investigations in the Northern Ustyurt in Connection with Oil and Gas Prospecting

AbstractStructural-geomorphic techniques are tested in the northern part of the Ustyurt plateau (Lat. 46°N Long. 56°E) between the Caspian Sea and the Aral Sea in an attempt to identify local uplifts that may be potentially oil or gas bearing. The techniques include a structural-geomorphic photo interpretation, morphometric analysis of topographic maps and field mapping. Specific relationships between structure and surface relief are established in the three basic regions of the study area: the plateau, the escarpment zone and the foreland plain. In the plateau, surface relief generally directly reflects buried structures. In the plain, crustal movements are evident in the impact of abrasion and deposition processes that took place during transgressions of the nearby Caspian Sea. In the escarpment zone, both direct and inverse relationships are established between scarp promontories and embayments, on the one hand, and the plateau structure, on the other hand. Aside from some local uplifts, the investigat...

MORPHOTECTONICS AND THE GEOMORPHOLOGICAL SCIENCES WITH SPECIAL REFERENCE TO AUSTRALIA

The apparent decline of Davisian geomorphology is less than might appear from the literature, as genetic geomorphology has found increasing application in photogeology and is widely used in all geological reconnaissance. Structural geomophology has grown slowly but is now an established technique whereby one of the Davisian trilogy—structure—may be inferred from geomorphological observations. Morpho-tectonics involves a study of external form of major topographic units as well as of their internal structure and permits tectonic inferences relative to areas as large as continents. Both structural geomorphology and morphotectonics add considerably to the techniques available for the study of cratons, and in Australia the results indicate long-continued activity along ancient lines of weakness and considerable evidence for greater mobility of the cratonic units than is normally attributed to them. Lineaments and blocks are prominent and many of the geological basins are framed by lineaments. There are similarities with the neotectonic characteristics of the Russian platform, especially in the reflection of ancient structures in younger and the evidence for recent movements which may be of a continuing nature. This is one point in which the Davisian trilogy is deficient; but genetic geomorphology has afforded a sound basis for understanding when its principles have been rigidly applied.

Aerial Photographs and Structural Geomorphology

The intensive use of vertical aerial photographs to aid geological exploration during the last two decades has revealed serious weakness in some of the traditional concepts of American geomorphology. A new realization is now widely held, not by geomorphologists but by "photogeologists," namely, that tectonic elements of the crust (such as dipping strata, faults, joints, fold axes, flexures) can be found with aerial photographs in almost every square mile of the continental surfaces through their geomorphic expression. This has long been known of the deformed "mountain regions"; it is nearly as true of the so-called "plains" and "plateaus," even where tectonic elements are deeply buried by relatively undeformed, homoclinal strata. The writer attempts to present a usable revision of geomorphic concepts mainly through two basic principles: (1) the concept of essentially universal superposition of drainage in "flatland" regions, as well as in most tectonic systems, and (2) the concept of an almost universal tectonic influence on most continental drainage. Exceptions to the control of principles 1 and 2 are some, but not all, of the streams on deltas, volcanoes, lava flows, dune plains, and elsewhere. Elevated dissected bedrock benches of erosional origin are employed in explaining the usual process of stream adjustment to tectonic anomalies. The Pawhuska peneplain of central and southwestern central United States is briefly described. A distinction is made between tectonically influenced and tectonically adjusted drainage.