Folded Structure : Created by Puja Basu Chowdhury Folded Structure By
Puja Basu Chowdhury
Folding : Created by Puja Basu Chowdhury Folding Definition – Folds are wavy undulations, which are developed in country rocks whenever the region is subjected to severe compressional pressure. The resulting wave like form is made up of a series of alternate crests and trough. Folds in rock beds may vary in size between wide limits. In case of exceptional large folds, the consecutive crest and troughs may be hundreds of miles apart. The small folds on the other hand, may have several crests and troughs within a span of a few inches only. The stretch of the rock beds lying between any crest and the adjacent trough on either side is described as the limb of the fold.
Slide 3 : Created by Puja Basu Chowdhury In fig I (a), processing from left to right, A to S , S to A` and A` to S` are the successive limbs of a series of fold. Any two successive limbs together constitute one individual unit fold. Thus in fig I (a), the two continuous limbs AS and SA` constitute one unit of fold which is concave upwards.
Similarly, the two adjacent limbs SA` and A`S` together form another unit of fold which is convex upwards. Thus, any two consecutive folds, as a rule must have one limb common to both of them.
In any individual unit of fold, whether concave or convex upwards, it is always possible to imagine a plane or surface which divides the fold into two halves as symmetrically as possible. Such an imaginary plane of symmetry of any fold is described as the axial plane [fig I (b) i , ii , iii ] .
Depending upon the nature of the fold its axial plane may be vertical or inclined or it may even be a curved surface. In any fold, the line of intersection of the axial plane with the upper or lower surface of the constituent beds are known as the axis. In all single folds the axis are generally horizontal.
Types of Folds : Created by Puja Basu Chowdhury Types of Folds From the point of view of there structure, geometry and appearance in space, a number of different types of folds have so far been recognized:-
Anticline
Syncline
Symmetrical
Asymmetrical
Overturned fold
Isoclinal fold
Recumbent fold or nappe
Monoclinal fold
Structural Terraces
Fan fold
Chevron fold
Open fold
Closed fold
Geo-syncline
Geo-antisyncline
Synclinorium and Anticlinorium
Drag fold
Plunging fold
Dome
Basin
Slide 5 : Created by Puja Basu Chowdhury ANTICLINE - An anticline is a fold which is generally convex upwards. In case of such folds, the limbs commonly slope away from the axial plane. In most of the anticlines progressively older belts occur towards the centre of curvature of the fold. Example-
The Weald-Artois Anticline is a geological structure running between the regions of the Weald in southern England and Artois in north eastern France.
The Virgin Anticline Reservoir, which takes its name from the nearby Virgin River , United States.
Anticline near Bcharre, Lebanon.
Slide 6 : Created by Puja Basu Chowdhury SYNCLINE – A syncline on the other hand is a fold which is generally concave upwards. The limbs in syncline commonly slope towards the axial plane. In most of the synclines progressively younger beds occur towards the centre of curvature of the fold. Syncline and anticline occur in succession in any folded region. Examples-
A notable syncline is Wyoming's Powder River Basin (USA).
Syncline, Torres del Paine National Park, Chile
Synclinal folds in bedrock, near Saint-Godard-de-Lejeune, Canada.
Slide 7 : Created by Puja Basu Chowdhury SYMMETRICAL - A fold, whether anticline or syncline, is described as Symmetrical when its axial plane is vertical and thus both the limbs have same amount of dip. It results from equal amount of compressional forces acting from both the sides. Example-
An example of symmetrical folding in the layered rocks of the Perry Mountain Formation (USA). ASYMMETRICAL - However, if the forces are unequal asymmetrical folds developed. The limbs of anticline or syncline generally slope away from or towards each other, having dip in opposite direction. Example –
Kaza, Himachal Pradesh, India.
An asymmetrical fold in sedimentary strata along the main road from Jerusalem to the Dead Sea.
Slide 8 : Created by Puja Basu Chowdhury OVERTURNED FOLD - If in any fold both the limbs dip towards the same direction, it is called an Overturned Fold. In such fold one limb occurs in normal position whereas the other appears to have been rotated or completely overturned from its usual position. Example-
Hanklit reveals an overturned fold of Fur Fm. (Paleocene) bedrock, surrounded by glacial gravel, and resting on till with faulting of fold core (left) and extreme stretching of fold nose.
Overturned fold of the lower Ravenscrag Fm, in the southwestern part of Saskatchewan province, Canada.
An overturned fold in the thinly interbedded greywacke sandstone and slate (distal turbidite) succession of the Booley Bay Formation (Cambrian) at Bella Vista Bay, Hook Head in County Wexford , Ireland.
Slide 9 : Created by Puja Basu Chowdhury ISOCLINAL FOLD - If in any fold, the amount of overturning be such that both the limbs have the same amount of dip in the same direction, the structure is called an Isoclinal fold. Example-
Isoclinal fold of Caledonian age in a marble-gneiss succession, Generalfjella Formation (Meso-proterozoic), located in Sigurdfjellet near Haakon VII Land, Northern Spitsbergen, Norway.
Isoclinal folds and bondage of Caledonian age in a marble-gneiss succession, General-fjella Formation (Mesoprotero-zoic), located in Hornbækpollen near Liefdefjorden, Northern Spitsbergen, Norway.
Soil-creep fold in tempura on side of volcanic cone, Eifel region, western Germany. Extreme, near isoclinal, folding is seen on the side of this extinct volcano.
Slide 10 : Created by Puja Basu Chowdhury RECUMBENT FOLD or NAPPE - When a fold is so much overturned that its axial plane is horizontal or nearly so, it is described as a Recumbent fold. A nappe is a large sheet like body of rock that has been moved far from its original position. Nappes form during continental plate collisions, when folds are sheared so much that they fold back over on themselves and break apart. The resulting structure is a large-scale recumbent fold. Example-
The Donara nappe at the metamorphic core of the Himalaya and Karakoram.
The Austro-alpine nappes of the eastern Alps consist of a series of three thrust faulted nappe stacks which overlie the three older Penninic nappes in this very complex system in the Eastern Alps.
Recumbent fold, Royal Palms State Beach, San Pedro, California.
Recumbent, east-verging Caledonian fold in Ordovician limestone located in Tsjebysjovfjellet near Hornsund South, Svalbard Island, Norway.
Slide 11 : Created by Puja Basu Chowdhury MONOCLINAL - In horizontal or gently sloping beds, slight and another localized change in there usual altitude leads to the formation of Monoclinal structure. In monoclines the beds are relatively flat but appears to have been bent locally to exhibit higher dips. Example-
Monoclinal fold in the Wittenberg Subgroup, Ceres, South Africa.
The Waterpocket Fold defines Capitol Reef National Park, western North America. A nearly 100-mile long warp in the Earth's crust, the Waterpocket Fold is a classic monocline: a regional fold with one very steep side in an area of otherwise nearly horizontal layers. A monocline is a "step-up" in the rock layers.
A classic monocline near Mexican Hat, Utah. (USA) Mesozoic strata are bowed down along the fold. they are horizontal on the plateau at left and in the foreground but dip 45 degrees or more along the fold.
Slide 12 : Created by Puja Basu Chowdhury STRUCTUREAL TERRACES - In structural terraces, however, the dipping beds become horizontal at a particular spot and then continue to follow there original dip. FAN FOLD - If in any fold, both the limbs are overturned, they assumed the shape of a fan and this called Fan Fold.
Slide 13 : Created by Puja Basu Chowdhury CHEVRON FOLD - The crests and troughs of a fold are generally rounded. Occasionally, however, sharp angular crests and troughs do occur in some folds and are described as Chevron Folds. Example-
Developed in Carboniferous sandstones and shales, Saundersfoot, Pembrokeshire in South West Wales, UK This is the Lady's Cave fold - a famous structure.
Chevron fold in limestone, Kaikoura peninsula, NZ
Chevron fold, Las Pozas, Mexico.
Slide 14 : Created by Puja Basu Chowdhury OPEN FOLD - In an open fold, no flowage occur and constituent beds have the same thickness everywhere within the fold. Example-
Mosaic Canyon, Death Valley (USA). The dashed line follows foliation around a tight fold hinge; the entire fold is folded around the more open fold on the right.
The Raplee Anticline in southeastern Utah, USA is an example of a large-scale, open fold. The originally flat-lying rocks have been deformed, and exposed by stream and river incision.
Slide 15 : Created by Puja Basu Chowdhury CLOSED FOLD - In a tight or closed fold the relatively mobile beds thin out at the limbs and thickens out of the crests and troughs due to plastic flow of constituent materials. Example-
The part of the Zagros Mountains along the southwest coast of Iran by the Persian Gulf. These mountains consist mainly of elongate folds which arch upwards as anticlines and downwards as synclines. The anticlines here make up distinct landforms as high hills with central ridges that taper at either end (a condition referred to as a closed fold).
Jiang Jia Long cave in China is developed in limestone of the lower Triassic age Jia Ling Jiang Formation. Notice the tight fold in the ceiling.
Slide 16 : Created by Puja Basu Chowdhury GEOSYNCLINE - A Geosyncline is a very large, shallow depression which accommodates a considerable thickness of sediments due to subsidence of flow content with sedimentation. These are commonly occupied by shallow seas and are sites for future complex mountains. Example-
Massive limestone's at Carrickalinga Head , south of Adelaide (Australia) on the Fleurieu Peninsula overlooking the Gulf of St. Vincent. Tilting of geosyncline rocks shows sedimentary layering.
In the Geosyncline region of central Pennsylvania, (USA) the mountains are made of ancient seafloor sediment that has been pushed together and then raised up. The rippling sinuous mountains are typical of geosyncline formations around the world.
Slide 17 : Created by Puja Basu Chowdhury GEOANTICLINE - A geoanticline is an area from which sediments are derived and deposited in the geosyncline. SYNCLINORIUM & ANTICLINORIUM - A large syncline with secondary folds of smaller size developed on geosyncline is known as Synclinorium while an anticline of similar nature is called an Anticlinorium. Example-
The Late Jurassic to Early Cretaceous Purcell Anticlinorium in British Columbia (Canada).
The Blue Ridge Anticlinorium of northern Virginia in the Appalachians (USA).
Slide 18 : Created by Puja Basu Chowdhury DRAG FOLD - When a comparatively weak bed lies between strong beds, any sliding motion in the stronger beds leads to the development of minor asymmetric fold known as Drag Folds within the weaker folds. Example-
Footwall cutoff with development of a small drag fold, tertiary turbidite sequence of accretionary prism of SW Japan.
Drag fold along Grand Canyon, Arizona. The drag has occurred along a faulted part of the East Kaibab Monocline. A portion of Nankoweap Mesa is at the right
Drag folds created by movement along the fault. Hudson Highlands, I-84, eastern New York.
Slide 19 : Created by Puja Basu Chowdhury PLUNGING FOLD - If the folds are so oriented in space that there axis no longer remain horizontal and slops towards the same direction, the folds are said to be Plunging. Folds too often plunge in two opposite directions and are then described as Doubly Plunging Fold. Example-
Tight closure in a steeply plunging fold, Bloubergstrand, Cape Town, South Africa.
Sheep Mountain - a doubly plunging anticline (NW WY). "V" s are pointing the direction of the plunges. Erosion due to the Gros Ventre River along the south flank resulted in a spectacular landslide in 1925
Slide 20 : Created by Puja Basu Chowdhury DOME - An anticlinal uplift with central symmetrical dipping is known as Dome. Domes are generally formed from one main deformation event, or via diapirism from underlying magmatic intrusions or movement of upwardly mobile, mechanically ductile, material such as rock salt (salt dome) and shale (shale diapir). Example-
The Richat Structure is a huge depression in the country of Mauritania. It was originally thought to be the impact of a meteorite. Now it is thought to be a symmetrical uplift (circular anticline or dome) that has been exposed to erosion.
The granite domes and cliffs of the Llano Uplift, such as Enchanted Rock are popular with climbers, picnickers, and hikers.
Slide 21 : Created by Puja Basu Chowdhury BASIN - A synclinal depression with central reversal dip is known as Basin. Example-
Rainbow Basin Syncline near Barstow, California.
Western Hamersley Basin, Western Australia.
Economic Significance : Created by Puja Basu Chowdhury Economic Significance Doubly-plunging or faulted anticlines, culminations, and structural domes are favored locations for oil and natural gas drilling; the low density of petroleum causes it to buoyantly migrate upward to the highest parts of the fold, until stopped by a low-permeability barrier such as an impermeable stratum or fault zone. Examples of low-permeability seals that contain the hydrocarbons, oil and gas, in the ground include shale, limestone, sandstone, and even salt domes. The actual type of stratum does not matter as long as it has low-permeability.
Periclines are important focal points for pooling of hot, metal-laden formational brines, which can form manto ore deposits, Irish-type lead-zinc deposits and uranium deposits, amongst others.
Culminations in folded strata which are cut by shears and faults are favoured loci for deposition of saddle-reef style lode gold deposits.
Questions.......? : Created by Puja Basu Chowdhury Questions.......?
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Slide 26 : Created by Puja Basu Chowdhury The Virgin Anticline Reservoir
Slide 27 : Created by Puja Basu Chowdhury Anticline near Bcharre, Lebanon.
Slide 28 : Created by Puja Basu Chowdhury Powder River Basin
Slide 29 : Created by Puja Basu Chowdhury Syncline, Torres del Paine National Park, Chile
Slide 30 : Created by Puja Basu Chowdhury Synclinal folds in bedrock, near Saint-Godard-de-Lejeune, Canada.
Slide 31 : Created by Puja Basu Chowdhury Perry Mountain Formation, Coos Canyon, Byron, Maine
Slide 32 : Created by Puja Basu Chowdhury Asymmetric fold, Kaza, Himachal Pradesh, India.
Slide 33 : Created by Puja Basu Chowdhury An asymmetrical fold in sedimentary strata along the main road from Jerusalem to the Dead Sea.
Slide 34 : Created by Puja Basu Chowdhury Hanklit reveals an overturned fold of Fur Fm , Mors, Denmark
Slide 35 : Created by Puja Basu Chowdhury Overturned fold of the lower Ravenscrag Fm
Slide 36 : Created by Puja Basu Chowdhury Booley Bay Formation (Cambrian) at Bella Vista Bay, Hook Head.
Slide 37 : Created by Puja Basu Chowdhury Isoclinal fold of Caledonian age in a marble-gneiss succession, Generalfjella Formation (Meso-proterozoic),
Slide 38 : Created by Puja Basu Chowdhury Isoclinal folds and bondage of Caledonian age in a marble-gneiss succession, General-fjella Formation (Mesoprotero-zoic)
Slide 39 : Created by Puja Basu Chowdhury Extreme, near isoclinal, folding is seen on the side of this extinct volcano
Slide 40 : Created by Puja Basu Chowdhury the Donara nappe
Slide 41 : Created by Puja Basu Chowdhury Austroalpine nappes
Slide 42 : Created by Puja Basu Chowdhury Recumbent fold, Royal Palms State Beach
Slide 43 : Created by Puja Basu Chowdhury Recumbent, east-verging Caledonian fold in Ordovician limestone
Slide 44 : Created by Puja Basu Chowdhury Monoclinal fold in the Wittenberg Subgroup, Ceres
Slide 45 : Created by Puja Basu Chowdhury The Waterpocket Fold defines Capitol Reef National Park.
Slide 46 : Created by Puja Basu Chowdhury A classic monocline near Mexican Hat, Utah
Slide 47 : Created by Puja Basu Chowdhury Developed in Carboniferous sandstones and shales, Saundersfoot, Pembrokeshire in South West Wales, UK
Slide 48 : Created by Puja Basu Chowdhury Chevron fold, Las Pozas, Mexico.
Slide 49 : Created by Puja Basu Chowdhury Chevron fold in limestone, Kaikoura peninsula, NZ
Slide 50 : Created by Puja Basu Chowdhury Mosaic Canyon, Death Valley, USA.
Slide 51 : Created by Puja Basu Chowdhury The Raplee Anticline in southeastern Utah.
Slide 52 : Created by Puja Basu Chowdhury The full Landsat scene covers part of the Zagros Mountains along the southwest coast of Iran by the Persian Gulf.
Slide 53 : Created by Puja Basu Chowdhury Jiang Jia Long cave, Ging Muguan village, Chongqing province, China
Slide 54 : Created by Puja Basu Chowdhury Carrickalinga Head
Slide 55 : Created by Puja Basu Chowdhury A Landsat MSS synthetic color photo of the Geosyncline region of central Pennsylvania, USA.
Slide 56 : Created by Puja Basu Chowdhury Footwall cutoff with development of a small drag fold, in SW Japan
Slide 57 : Created by Puja Basu Chowdhury Drag fold along Grand Canyon, Arizona.
Slide 58 : Created by Puja Basu Chowdhury Drag folds created by movement along the fault. Hudson Highlands, I-84, eastern New York.
Slide 59 : Created by Puja Basu Chowdhury Tight closure in a steeply plunging fold, Bloubergstrand, Cape Town, South Africa.
Slide 60 : Created by Puja Basu Chowdhury Sheep Mountain, Alaska, USA.
Slide 61 : Created by Puja Basu Chowdhury Richat Structure
Slide 62 : Created by Puja Basu Chowdhury The granite domes and cliffs of the Llano Uplift, Texas.
Slide 63 : Created by Puja Basu Chowdhury Rainbow Basin Syncline near Barstow, California
Slide 64 : Created by Puja Basu Chowdhury Western Hamersley Basin, Western Australia