Vertical Block Movements Research Articles

T-t Evolution of the Early Proterozoic Rocks in the Northern Ladoga Region from the Data on U-Pb, Rb-Sr and Sm-Nd Systems in Minerals

This paper presents the results of a study of isotopic systems in minerals and rocks in southern margin of the epi-Archean Karelian craton in the zone of its junction with the Svecofennian mobile belt. U-Pb, Sm-Nd and Rb-Sr mineral ages of metamorphic rocks allowed reconstructing a T-t trend during ~1.88–1.61 Ga, which reflects a wide-ranging cooling history of metamorphic rocks from the peak values of about 650–700 °C at 1.88–1.79 Ga (U-Pb age of monazites and apparent oldest Sm-Nd age of amphiboles) to 300–400 °C at 1.61 Ga (model Rb-Sr age of biotites) in zones of low- and medium-temperature metamorphism. The specificity of removal of deep-seated rocks to the present-day erosion surface and the reconstructed T-t trend comply with the development of thrust-nappe structures during the exhumation of the Svecofennids. It is also assumed that differential vertical block movements played a significant role during the post-orogenic extensional collapse and neorifting.

Transition from the Hajir Formation to the Muaydin Formation: A facies change coinciding with extensional, syndepositional faulting (Ediacaran, Jabal Akhdar Dome, Central Oman Mountains)

In the core of the Jabal Akhdar Dome, an irregular horst composed of carbonates of the Hajir Formation is bounded by syndepositional extensional faults on either side. The western, SSW-dipping fault is an extensional growth fault associated with rollover anticline and syncline within syndepositional siliciclastic strata of the Muaydin Formation. Syndepositional extension is indicated by increasing thickness of the involved strata of the Muaydin Formation towards the fault. The eastern, ESE-dipping fault, exhibits a larger displacement than the western fault. Both the western and the eastern fault are blanketed by postdeformational Muaydin deposits. Taking into account that the strike of both faults differs significantly (see above), we suggest that the eastern fault represents the main fault of a relay ramp system whereas the western one is the fault of a breached relay ramp with a dip angle of 65°. Compaction is able to explain some particular stratal patterns of the Muaydin Formation. The eastern fault may provide insights as to possible similar Ediacaran movements along the NNE-striking Proto-Semail Gap (i.e. the Proterozoic Semail Gap). Ediacaran vertical block movements at the latter may explain why the Muaydin Formation is present in the Jabal Akhdar Dome in the west but absent in the easterly located Saih Hatat Dome. The tectonic setting is characterized by WNW-ESE-oriented extension. Immediately west of the irregular horst we found a seemingly complete stratigraphic transition from the Hajir Formation to the Muaydin Formation. On top of this structure is a minor stratigraphic hiatus at the contact between both formations. Although the observed features are all outcrop-scale phenomena, we suggest that they provide insights into the general Ediacaran tectonic and depositional setting. This setting is characterized by complete and incomplete stratigraphies and by syndepositional extension which may be held responsible for the abrupt change from carbonate to siliciclastic facies as well as common slumps in the lower part of the Muaydin Formation.

Active Deformations Extracted from Drainage Geomorphology: A Case Study from Southern Sonbhadra District, Central India

Since the Precambrian time the Narmada-Son Lineament (NSL) is a zone of weakness and both the northern and southern portions of Narmada-Son Lineament experienced vertical block movements. It is established by the earlier workers that NSL is a sub-crustal feature which is responsible for the deposition and folding of the Vindhyans (Meso-Neoproterozoic) and Gondwanas (Permo-Carboniferous-lower Cretaceous). Recent tectonic activity in the Narmada-Son region is evidenced by high heat flow thermal activity, sulphur springs and seismically the Narmada-Son Lineament region is known to be a significantly disturbed zone. The present study area is the part of Narmada-Son Lineament zone. The drainage geomorphology of the area between Kanahar and Rihand rivers (tributaries of the tectonically controlled Son river) around Renukoot area have been studied aiming to understand active tectonics of the region, integrating detailed analysis of landforms and drainages. Various geomorphic features present in the study area such as incision of valley, aligned drainage, aligned valleys, linear valleys, offset channels, offset ridges and fault scarps demonstrate that the area is undergoing active deformation.

Deep electrical structure over the igneous arc of the Indo Burman Orogen in Sagaing province, Myanmar from magnetotelluric studies

Magnetotelluric studies over the igneous arc of the Indo Burman range in the Sagaing province of Myanmar have delineated the high resistivity Indian plate subducting westwards beneath the Burmese block to depths of 30km and beyond. The thick moderately resistive (20–100Ωm) layer overlying the subducting Indian plate may be due to the low resistivity sediments. The entire region is covered with prominent sedimentary layer with a conductance varying between 20 and 3000S showing a general increase from the east to west, suggesting that their thickness increases toward the west. The large unsystematic variations in the conductance are indicative of the widely varying depositional environments and also possible vertical block movements during the course of their deposition. A west dipping low resistivity zone to the east of Burmese block seems to demarcate its eastern limit, suggesting the possibility of a hitherto unknown deep seated fault, which is also supported by the several earthquake foci located over this zone. The nature of the crustal movements over this fault is not immediately apparent. Possibility exists that the Sagaing fault is an en echelon fault and the present feature observed here is a part of this en echelon fault. The possibility of channel flows of the weakened rocks in the deep crust observed in the vicinity of the eastern Himalayan syntaxis may also cause such low resistivity zones.

Crustal Evolution and Tectonics of the Archean Bundelkhand Craton, Central India

Abstract Magnetotelluric studies over the Bundelkhand craton indicates a high resistivity sub-structure, typically observed in the Archean-Proterozoic regions. The geoelectric section shows a single high resistivity layer in the northern part of the craton, extending from surface to a depth of about 60 km and a three layered resistivity structure overlying a conductive bottom in its southern part. The geological studies reported earlier have delineated an EW trending zone of ultramafic rocks, called the Bundelkhand tectonic zone (BTZ), which marks the divide between the two electrical resistivity patterns. The geoelectric structure is broadly indicative of a northward dipping tectonic fabric in this region which conforms to the Himalayan subduction, to the immediate north of this craton. However this observation cannot explain the findings from geochemical, isotope analysis and geological studies, suggesting possible vertical block movements in the region, which are also indicated in the Bouguer gravity studies. The geoelectric structure beneath the Vindhyan group to the south shows low resistivities even up to 60 km, suggesting that the Bundelkhand craton which is characterized by high resistivity rocks, does not extend to the south beneath the Vindhyans, as was believed by the earlier researchers. A low resistivity body with an extremely high conductance of about 100,000 Siemens is delineated at the mid crustal depths beneath the exposed Bijawars south of Bundelkhand craton. The causative factors behind this low resistivity are not immediately apparent, but some possibilities are discussed here.

Basement-involved tectonics in North Fossa Magna, central Japan: The significance of the northern Itoigawa-Shizuoka Tectonic Line

The Toyama Trough and Fossa Magna basin are major transverse tectonic depressions located between northeast Japan (NEJ) and southwest Japan (SWJ). Itoigawa-Shizuoka Tectonic Line (ISTL), the western margin of Fossa Magna is a boundary between two tectonic provinces along the inner side of NEJ and SWJ. Abrupt lateral variations in thickness of the Middle to Upper Miocene strata are quite significant among these provinces in the North Fossa Magna. The development of the thrust/fold belt is attributed not only to horizontal compression but also to vertical block movements as basement-involved tectonics. In response to the Pliocene and later compression regime, the old fault-block boundaries were reactivated and produced differential block movement such as the tilting of the Central Upheaval Zone and uplifting of the Nishikubiki Belt. One possible model for the deeper geologic structure is presented that high-angled block faults on the surface among tectonic provinces originate in vertical weak zones in the deep seismogenic zone under the sedimentary layer. The folded Neogene system comprises the present-day thrust-fault province of the North Fossa Magna and the stress regime of strikeslip faulting occupies the basement, as inferred from focal mechanism solutions for small events. In order to account for the apparent discrepancy, a duplex stress field is possible for the active tectonics in the region.

Geoelectric structure of the Dharwar Craton from magnetotelluric studies: Archean suture identified along the Chitradurga-Gadag schist belt

SUMMARY Broad-band magnetotelluric data were collected at 50 stations over a 400 km long, approximately east‐west profile over the granite‐greenstone terrain of Dharwar, southern India. The tensor decomposed data were interpreted using a 2-D inversion scheme. The geoelectric model is suggestive of a suture along the Chitradurga‐Gadag schist belt, formed by the thrusting of the West Dharwar Craton beneath its eastern counterpart, with an easterly dip of 20‐30 ◦ . The thrust proposed here pre-dates the formation of these schists, which occurred during the Late Archean (2600 Ma). The accretionary wedge of the thrust and the depressed part of the West Dharwar Craton may have controlled the emplacement of the Chitradurga‐Gadag and Shimoga‐Dharwar schists. The subsequent weathering, the several episodes of tectonic activity witnessed during the Precambrian and the vertical block movements caused during the passage of the Indian Plate over the Reunion hotspot may have modified the crust, leading to the present-day geological configuration. Despite its age and several tectonothermal episodes, the signature of this thrust is adequately preserved in the Dharwar Craton. Several similarities with younger sutures, as is evident from the observed relics of the oceanic rocks present along the Chitradurga schist belt, suggest that the tectonic processes leading to this Archean event may have had a close resemblance to those witnessed in recent times. Magnetotelluric studies also image a zone of low resistivity at a depth of 40 km beneath the west Dharwar Craton. This seems to be a regional feature, extending to the north over a distance of at least 250 km beneath the Deccan volcanics. The low heat flow values and the high density associated with this feature make partial melting an unlikely explanation for the low resistivity. The grain boundary graphites and the sulphides deposited in the form of pyrites may have caused the low resistivity in the lithospheric mantle of the West Dharwar Craton, although the fluids generated and trapped in the mantle during the passage of the Indian Plate over the Reunion hotspot in the waning phase of its outburst could also be a possibility. The asthenosphere is delineated at a depth of about 100 km beneath the East Dharwar Craton.

O SUPERGRUPO ESPINHAÇO DA SERRA DO ESPINHAÇO MERIDIONAL (MINAS GERAIS): O RIFTE, A BACIA E O ORÓGENO

The Serra do Espinhaço is a mountain chain built up mainly of quartzitic rocks of the EspinhaçoSupergroup. It extends from the central part of Minas Gerais to the north of Bahia, a length of 1200 km in a NSdirection. The southern part of the Serra do Espinhaço (SdEM), which is 300 km long, extends fromQuadrilátero Ferrífero to Olhos d’Água (Fig. 1), and during its initial rifting phase of development wasseparated from the northern part by a NE-trending sinistral transfer fault system (Fig. 2).The Guinda Group contains the synrift sedimentary and volcanic rocks of the SdEM (Tab. 1 and 2). Therifting processes were thermally controlled and started at 1750 Ma. The rifting evolved in 3 distinct phases:the first phase was marked by sedimentation of the Bandeirinha Formation (fluvio-eolian environments) withstrong extensional activity that caused block tilting of the units of this formation and the exhumation of a corecomplex in the median-central part of the SdEM; during the second rifting phase the fluvial sediments of theSão João da Chapada Formation were deposited, following minor thermal subsidence of the rift; anasthenospheric plume upwelling below the continental crust along the central part of the rift (Fig. 3) causedthe third phase of rifting by intensive vertical block movements, generating half-grabens that propagated tothe east. The fluvial and lacustrine sediments of the Sopa-Brumadinho Formation (Fig 4) mark this third phaseof rifting. During the eastward propagation of the extensional tectonics (Fig. 5), the half-grabens wereprogressively filled up by eolian sediments of the Galho do Miguel Formation.The crustal extension culminated in mantle-uncovering at the axial zone of the rift (Fig. 3), generally withserpentinization, and a marine basin was formed. Thick piles of clastic sediments and banded iron formationswere deposited in the neritic and bathyal/abyssal zones, and at the same time the alluvial sediments (fandeltas) of the Sopa-Brumadinho Formation prograded out into the coastal parts of the basin (Fig. 6).Because of the strong thermal subsidence of the basin, the locus of deposition of the marine coastalsediments was at least 80 km westward (Fig. 7), this being indicated by the occurrence of the ConselheiroMata Group (Tab. 1) in the western part of the SdEM. The thermal subsidence of the basin marks the start ofthe Espinhaço passive continental margin and the end of rift-forming processes.Tectonic inversion started at about 1.5 Ga with eastward subduction of oceanic crust, and this precededthe continental collision that built up the SdEM. The units of the Espinhaço Supergroup in the western andcentral parts of the orogen were folded in N-S trending open folds during the initial phase of the tectonicinversion. The deformation related to the subsequent collision was strongly partitioned, consequent both onthe plate indentation and on transcurrent/strike-slip fault movements (Fig. 8, 9 and 10).In the proximal collision zone (eastern edge of the SdEM), a thrust belt developed, and in the southcentralpart of the SdEM and the eastern region of the Quadrilátero Ferrífero the thrust sheets propagatedonto the western domain of the orogen, destroying either partially or totally the previous folding system (Fig.9 and 11).The wandering of the São Francisco craton through high latitudes at about 1.05 Ga caused a mountainglaciation in its higher parts, as indicated by the meta-tillites of the Macaúbas Group and equivalent units.Around 2.5% of the SdEM surface is formed of basaltic rocks derived from basic magmatism ( 906 Ma)that preceded the fragmentation of the continental mass that had been amalgamated by the end ofMesoproterozoic time. This continental fragmentation formed the Neoproterozoic basins of the westernAfrican continent and caused extensive subsidence of São Francisco craton. A large epicontinental basinwas developed there, now indicated by units of Bambuí Group (Fig. 1).The orogenesis of the West Congolian belt ( 750-500 Ma) caused a strong reactivation of the EspinhaçoSystem, with the units of the Macaúbas and Bambuí groups being overthrusted by sequences of the EspinhaçoSupergroup (Fig. 9 and 11). The westward subduction of the oceanic plate of the West Congolian basin underthe southeastern edge of the São Francisco craton (Fig. 12) is indicated by the size and frequency of graniticplutons in the eastern parts of the Araçuaí belt and SdEM, as well as by thermal event of Brasiliano age thatis recorded in metamorphic and granitic rocks over the whole eastern part of this craton.

Sedimentologic evidence for repeated pre-Cenozoic vertical movements along the northeast margin of the Nubian Craton

The northeast margin of the Nubian Craton, comprising the Eastern Desert, the Gulf of Suez and Southwest Sinai, contains sedimentary units ranging in age from early Palaeozoic to Tertiary. Below the extensive Late Cretaceous marine transgressive units, older rocks, especially those of the Palaeozoic and early Mesozoic, have limited spatial distribution. The entire sequence is present, however, with major breaks, along the northeastern flank of the Red Sea basement high, in the subsurface Gulf of Suez and in southwest Sinai. The Eastern Desert Platform, on the other hand, is mantled by Cretaceous and younger sediments suggesting that the area was a topographic high until about the end of Jurassic, or that the area suffered post-Palaeozoic uplifting. The Palaeo-Mesozoic sequences in the Gulf of Suez lowlands and adjoining areas attest at least four episodes of marine incursions during (1) Early Palaeozoic (Cambro-Silurian?), (2) Early Carboniferous, (3) Middle Jurassic and (4) Late Cretaceous. Except for the Jurassic transgression, each episode was interrupted by a brief but rapid fluvial progradation. Such brief and rapid progradational interruptions of the major transgressive episodes were probably caused by vertical block movements. The early Palaeozoic and Late Cretaceous progradations show northerly to northwesterly dispersal suggesting northeast to easterly trending vertical movements, whereas the Early Carboniferous progradation was in a general easterly direction indicating approximately N-S trending block movements. Sporadic occurrence of Middle Jurassic sediments in isolated fault blocks below extensive Cretaceous units in the northern Gulf of Suez outcrops, their abrupt thickness change in the subsurface of north central gulf and the occurrence of fault controlled basic dikes and sills within these rocks point to a Late Jurassic-Early Cretaceous extensional episode and resultant block movements in the area. A minor episode of Early Cretaceous local block movement in the Gulf of Suez area is indicated by the occurrence of an unique polymictic conglomerate containing angular pebbles of chert, banded iron formation, jasper and metavolcanic rocks at the base of the lower Cretaceous Malha Formation in the southwest Sinai and northern Gulf of Suez outcrops. Source rocks for this conglomerate occur in the Precambrian basement southwest of Quseir and in western Saudi Arabia. Recurrent pre-Tertiary block movements parallel to the Miocene Suez-Aqaba rifts and associated fault blocks suggest control of the pre-Miocene structural elements in the development of the latest rift system in the area. Careful lineament analyses of the Precambrian basement and fringing sedimentary cover may be helpful in locating and dating some of the pre-Miocene crustal fracture zones in the area.

Subsurface Geology of Tertiary Rocks of Northeastern District of Western Desert, Egypt: ABSTRACT

The lithofacies analysis of the Tertiary rocks reveals two ancient subbasins at the north and southeast of the northeastern district, Western Desert. The southeastern subbasin seems deeper than the northern one as it received relatively thicker Paleocene and early and middle Eocene rocks. The lithofacies of the Paleocene and early and middle Eocene sections are mainly calcareous. The clastic ratio ranges from 0.05 to 1. Shale predominates in the late Eocene rocks. The clastic ratio is more than one everywhere. The Paleocene rocks seem to have accumulated in a lagoonal environment of epineritic depths. Semi-restriction of water circulation at the southeastern subbasin was caused by an elongated ridge, separating the two subbasins. The Paleocene rocks of the northern subbas n indicate accumulation on an unstable shelf, i.e., slow deposition in a rapidly subsiding basin or at least slow deposition in an overall carbonate aerobic environment. Widening of the northern subbasin occurred during the early Eocene. The Paleocene environmental conditions seem to have prevailed during the early and middle Eocene. During the late Eocene, rocks of shallow-water and current-agitated environments accumulated. The lower clastic layers of the Oligocene, having a sand/shale ratio less than one, indicate a clastic shoreline environment-lagoonal subenvironment. The sediments of such an environment are brought down by rivers and reworked by waves and currents. The Oligocene clastics are overlain by a basaltic sheet at the eastern part of the district. The depocenter of the nor hern middle Miocene subbasin lies farther north. The sand/shale ratio increases to the south, being more than one. The middle Miocene lithofacies indicate rock accumulation in a contemporaneously subsiding basin under lagoonal or delta-front conditions at the southern part of the district. Marine stagnant-bottom-water conditions prevailed during the accumulation of the middle Miocene rocks at the northern parts. The Pliocene shoreline shifted farther northward. The Pliocene rocks seem to have accumulated in lagoons, where the inflow exceeded evaporation and alternating periods of exposure and flooding by either fresh or saline water of poor circulation prevailed. The tectonic instability of the district was initiated by volcancity during the late Oligocene. This volcanic activity was acc mpanied by uplifting, folding, and faulting of Oligocene and older rocks. The uplifting of the southern part was accompanied with subsidence of the northern one. The subsidence was associated with vertical block movements of the basement rocks. Basaltic magma climbed along faults. The folds are of the brachyanticlinal type, affected by faulting forming a median horst block. This block remained high for a great period of time. The axes of folding are parallel to the fault trends due to their association with the vertical block movements of the basement. The northern flanks of the folds are relatively steeply dipping. The middle Miocene and Pliocene rocks are not affected by faulting. The source lands of those sediments are deduced as nearby low elevated lands affected by the same tectonic events that affected the depositional basin itself during different epochs. End_of_Article - Last_Page 456------------

“Fundy Cataclastic Zone,” New Brunswick: Evidence for Post-Acadian Penetrative Deformation

Research Article| September 01, 1973 “Fundy Cataclastic Zone,” New Brunswick: Evidence for Post-Acadian Penetrative Deformation A. A. RUITENBERG; A. A. RUITENBERG 1Department of Natural Resources, Mineral Development Branch, New Brunswick, Canada2Present address: Mineral Development Branch, P. O. Box 1519, Sussex, New Brunswick, Canada. Search for other works by this author on: GSW Google Scholar D. V. VENUGOPAL; D. V. VENUGOPAL 1Department of Natural Resources, Mineral Development Branch, New Brunswick, Canada2Present address: Mineral Development Branch, P. O. Box 1519, Sussex, New Brunswick, Canada. Search for other works by this author on: GSW Google Scholar P. S. GILES P. S. GILES 1Department of Natural Resources, Mineral Development Branch, New Brunswick, Canada2Present address: Mineral Development Branch, P. O. Box 1519, Sussex, New Brunswick, Canada. Search for other works by this author on: GSW Google Scholar Author and Article Information A. A. RUITENBERG 1Department of Natural Resources, Mineral Development Branch, New Brunswick, Canada2Present address: Mineral Development Branch, P. O. Box 1519, Sussex, New Brunswick, Canada. D. V. VENUGOPAL 1Department of Natural Resources, Mineral Development Branch, New Brunswick, Canada2Present address: Mineral Development Branch, P. O. Box 1519, Sussex, New Brunswick, Canada. P. S. GILES 1Department of Natural Resources, Mineral Development Branch, New Brunswick, Canada2Present address: Mineral Development Branch, P. O. Box 1519, Sussex, New Brunswick, Canada. Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1973) 84 (9): 3029–3044. https://doi.org/10.1130/0016-7606(1973)84<3029:FCZNBE>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation A. A. RUITENBERG, D. V. VENUGOPAL, P. S. GILES; “Fundy Cataclastic Zone,” New Brunswick: Evidence for Post-Acadian Penetrative Deformation. GSA Bulletin 1973;; 84 (9): 3029–3044. doi: https://doi.org/10.1130/0016-7606(1973)84<3029:FCZNBE>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Rocks ranging in age from late Precambrian to early Carboniferous, and (or) Late Devonian, have been deformed by intense cataclasis in a broad upwarped belt which extends for a distance of 140 km along the Bay of Fundy in southern New Brunswick. This upwarped belt is denned by a penetrative cleavage (S1), which is generally roughly parallel to bedding (S0) in sedimentary rocks, although cross-cutting relationships have been observed. Most rock and mineral fragments in these deformed rocks have been crushed, flattened, stretched, and (or) pulled apart in several directions parallel to S1. In a few localities, S1 is roughly parallel to axial surfaces of mesoscopic folds (F1), but there is no evidence for regional F1 folds. S1 surfaces have been folded, throughout almost the entire area, by a second group of folds (F2) and a third group of folds (F3) mainly in the northeastern part of the belt. These structures have, in numerous localities, been truncated by high-angle reverse or normal dip-slip faults and locally by low-angle thrusts.The S1 fabric probably resulted from up-warping or bending (under a lithostatic load) which was produced by vertical movements of basement blocks underlying deformed layers. Mesoscopic F1 folds are believed to have formed along the margins of uplifted blocks. F2 folds appear to have resulted mainly from gravity sliding along slopes produced by continued upwarping. F3 folds were produced by slip roughly parallel to S1.The structure of the “Fundy cataclastic zone” differs greatly from the Acadian (Middle Devonian) deformed belt, which is characterized by upright, close to isoclinal folds produced by northwest-to-southeast shortening. The vertical block movements, to which we attribute the cataclastic deformation, probably occurred during a period of readjustment following the Acadian orogeny. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Structural Pattern of Egypt and Its Interpretation

Most of the structural elements of Egypt could be fitted into a pattern that appears to have been originated by compressive stresses that acted mainly from N. 10° W. and S. 10° E. During the Precambrian these stresses already were active and they produced shears which were expressed as right- and left-lateral strike-slip faults at the Gulfs of Suez and Aqaba, the Red Sea, and most of the Nile Valley in Egypt. These same stresses, after slightly shifting westward, produced the North Sinai folds. Theoretically, the original forces could have produced nearly east-west thrust faults. However, faults that trend in this direction (other than those associated with major folds) are either gravity or strike-slip faults. It is contended that the walls of the ancient thrus s were peneplaned before the deposition of younger sediments. Later displacements along the same faults were either downdip (gravity) or parallel with their strikes (strike-slip). Several uparching movements, of which the most important occurred during the Paleogene, caused stretching and consequent downfaulting of grabens mostly along the ancient lines of weakness produced by shearing. Differential vertical block movements of adjacent strips of the basement resulted in folding and faulting in the overlying sediments. Supratenuous folds have been formed whenever block movements were contemporaneous with sedimentation. The bearing on the occurrence of petroleum of the integrated structural pattern presented here is discussed.