Clastic Dikes Research Articles

Soft-Sediment Faults in the Tesnus Formation and their Relationship to Paleoslope

ABSTRACT The Tesnus Formation in the Marathon region, Texas, consists of interbedded sandstone turbidites and shales of a late geosynclinal filling phase. Deposition was on an unstable slope as indicated by the occurrence of deformational features of pre-consolidation origin including rolled sandstone bodies (several meters long), sandstone dikes (up to 2 cm wide and 1.5 m long), diapiric structures, and numerous normal faults of small displacement. Throw on these micro-faults is less than 2 cm and averages 0.5 cm. The displacement is seen only on the undersides of sandstones and cannot be traced through the beds in which they occur. The faults intersect the base of beds at an average angle of 55 degrees from the base, whereas fractures of post-consolidation origin are nearly all oriented normal to the base. The measured intersections of 100 faults with the base of beds shows that their mean orientation is 97 degrees to the direction of paleoslope as indicated by flute casts. The standard deviation is 15 degrees. Hence, the faults tend to parallel paleoslope contours. Of hundreds of faults examined, more than 95 percent were downthrown down the paleoslope. Each fault has a fault zone less than one millimeter wide. Petrographic evidence for a soft-sediment origin includes the following: (1) boundaries between fault zones and country rock are not sharp; (2) fractured grains are absent in the fault zones; and (3) healed fractures of post-consolidation origin always cut the fault zones. Soft-sediment faults have been found useful for providing current directions for sole markings such as groove casts which normally give only orientation. If used carefully, soft-sediment faults can also provide paleoslope information where sole markings are absent.

Structure of Miocene Rocks in Sierra Madre, Northeastern Santa Barbara County, California: ABSTRACT

Folds in Miocene rocks of the central Sierra Madre commonly are northwest-trending, curvilinear, concentric, and symmetrical; asymmetry and overturning occur in the vicinity of reverse faults. Fold hinges undulate across the area and in places bifurcate or merge. Disharmonic folds and sandstone dikes occur locally in the Monterey Shale. Faults are of three types: (1) along the northeastern edge of the range is a distributive fault zone consisting of parallel, longitudinal, reverse-slip faults which join both westward and downward and which have a subsurface distributive component that is now obscured by more recent deposits on the northeast; (2) southwest of the reverse-slip faults is a group of parallel, longitudinal, normal-separation faults; and (3) the remaining faults are mostly small, diagonal faults of different types; many are hinged at one or both ends and have slips or separations that indicate contemporaneous folding and faulting. Folding began during late Miocene or Pliocene while Miocene sediment was still unconsolidated and water laden. Diagonal faulting, intrusion of sandstone dikes, and possibly disharmonic folding accompanied early deformation. Asymmetrical and overturned folds formed later and large reverse-slip faults developed along their hinges. Normal-separation faults possibly formed last as lag faults. Northeast-southwest shortening of the area averages about 22%. End_of_Article - Last_Page 433------------

Igneous Activity, Metamorphism, and Heart Mountain Faulting at White Mountain, Northwestern Wyoming: Reply

The spire of brown volcanic rock at White Mountain, long regarded as a filled volcanic conduit associated with eruption of the Eocene Wapiti Formation, is actually an erosional remnant of volcaniclastic sedimentary rocks of the Eocene Cathedral Cliffs Formation that has been transported 10 to 15 mi southeastward as part of a Heart Mountain detachment fault block. Prevolcanic Paleozoic carbonate rocks, which comprise the western part of this block, are metamorphosed and strongly folded, in contrast to the rocks of other Heart Mountain fault blocks. This metamorphism ends abruptly downward at the Heart Mountain fault plane. Rounded fragments of metamorphosed carbonate rock in Heart Mountain fault breccia and in related clastic dikes show that the metamorphism occurred before the faulting, presumably as a result of the Cathedral Cliffs igneous activity. Igneous rock fragments in the Heart Mountain fault breccia at White Mountain seem to have been derived from allochthonous sills and dikes that predate the Heart Mountain fault. Therefore these fragments are not evidence for volcanic activity during Heart Mountain faulting, nor for introduction of volcanic gases along the fault plane as suggested by Hughes (1970a). A fault plate would have to be large and coherent to be buoyed up by volcanic gas or other fluids. The present widespread distribution of the remnants of the upper plate indicates that the upper plate broke up to form a number of fault blocks very soon after the Heart Mountain faulting began.

Tectonic Dewatering and Strain in the Michigamme Slate, Michigan

Cleavage in graywacke, siltstone, and pelite of the Michigamme Slate appears to have been produced by tectonic dewatering. Clastic dikes, from paper-thin dikelets to zones 10 m wide, are intruded parallel to cleavage in many outcrops. In other places, liquefication and mobilization have homogenized the sediments into massive, structureless rocks. The planar cleavage which pervades all rock types is produced by pelitic folia formed during tectonic dewatering. Ellipsoidal concretions with the same ductility as the host siltstone indicate large plane strains. Maximum shortening is perpendicular to cleavage with greater than threefold extension in the cleavage. Lengths parallel to fold axes are essentially unchanged, but stratigraphic thicknesses may be grossly exaggerated by deformation. Tectonic dewatering of the Michigamme Slate may have occurred after tectonic dewatering of the underlying Siamo Slate.

Igneous Activity, Metamorphism, and Heart Mountain Faulting at White Mountain, Northwestern Wyoming

The spire of brown volcanic rock at White Mountain, long regarded as a filled volcanic conduit associated with eruption of the Eocene Wapiti Formation, is actually an erosional remnant of volcaniclastic sedimentary rocks of the Eocene Cathedral Cliffs Formation that has been transported 10 to 15 mi southeastward as part of a Heart Mountain detachment fault block. Prevolcanic Paleozoic carbonate rocks, which comprise the western part of this block, are metamorphosed and strongly folded, in contrast to the rocks of other Heart Mountain fault blocks. This metamorphism ends abruptly downward at the Heart Mountain fault plane. Rounded fragments of metamorphosed carbonate rock in Heart Mountain fault breccia and in related clastic dikes show that the metamorphism occurred before the faulting, presumably as a result of the Cathedral Cliffs igneous activity. Igneous rock fragments in the Heart Mountain fault breccia at White Mountain seem to have been derived from allochthonous sills and dikes that predate the Heart Mountain fault. Therefore these fragments are not evidence for volcanic activity during Heart Mountain faulting, nor for introduction of volcanic gases along the fault plane as suggested by Hughes (1970a). A fault plate would have to be large and coherent to be buoyed up by volcanic gas or other fluids. The present widespread distribution of the remnants of the upper plate indicates that the upper plate broke up to form a number of fault blocks very soon after the Heart Mountain faulting began.

Note on sandstone dykes at Minchinbury, N.S.W

Note on sandstone dykes at Minchinbury, N.S.W

Clastic Dikes Associated with Soil Horizons in the North and South Carolina Coastal Plain

A large number of clastic dikes occur in many areas of the North and South Carolina Coastal Plain. The dikes begin within the B soil horizon, and none have been observed cutting the A horizon. Most dikes are less than 6 in. in width and taper downward, usually about 5 ft, but dikes 22 ft in downward extension have been observed. Horizontally, they have been traced for a maximum distance of 75 ft. The dikes are not confined to any one formation or rock of a particular age, and they are composed of sandy mud, which is often thoroughly iron stained. The rock they cut is well drained clayey or muddy sand. The clay minerals found in the dike and adjacent country rock are kaolinite, dioctahedral vermiculite, and traces of clay mica. Within the dike is a consistent dioctahedral vermiculite/kaolinite ratio with depth; outside the dike the ratio decreases with depth. The clastic dikes may be oriented parallel to hillslopes and some are associated with collapse structures. We conclude that the clastic dikes in the Carolina Coastal Plain were formed through filling of fractures by soil material developed in the upper B horizon. Most fractures probably developed in weathered rock as a result of slump or hillside creep.

Sandstone Dikes and Sills in the Moreno Shale, Panoche Hills, California

Over 350 sandstone dikes and sills intrude the eastward-dipping Moreno Shale along the east flank of the Panoche Hills. The intrusions vary in width from several inches to 23 ft. Many crop out for several hundred yards and several extend continuously for 0.5 mi. The dikes and sills are composed of very well-sorted, fine-grained, poorly indurated sandstone. The intruding sand was derived primarily from thick unconsolidated sand beds in the lower part of the Moreno and was injected upward as a water-charged, low-viscosity slurry into three principal sets of fractures. The sills intruded shear planes produced by flexural-slip folding. Two sets of dikes fill a system of conjugate shear fractures. The intrusions appear to be very late in the structural history and possibly are post-Miocene in age.

Classification and Interpretation of Disturbed Bedding Types in Jackfork Flysch Rocks (Upper Mississippian), Ouachita Mountains, Arkansas

ABSTRACT The Jackfork Group in the Ouachita Mountains of Arkansas is an Upper Mississippian flysch succession that displays readily distinguishable lithofacies. The frontal Ouachitas contain a preponderance of disturbed beds which are interbedded with turbidite sandstones. These disturbed and disrupted beds developed at the foot of a northern unstable slope, the resultant bedding dependent upon the type of material involved, its state of consolidation, and the distance moved. Information gathered concerning the progressive changes from one type of sedimentary structure to another gives a qualitative measure of downslope distance. Muds which undergo submarine deformation upon a sloping sea floor first become flowage shales which change to blocky mudstones with continued failure. Failure of plas ic muds and cohesive sandstone progressively form contorted, chaotic, and rubble bedding. Deformation of muds and sands form slurried bedding and breccias. Movement of flowing, creeping, or sliding clean sand may have occurred but is not considered to be a type of disruptive bedding. The deformation of mobilized, liquefied sand under some sediment cover produced load structures, sandstone dikes, and intrastratal flow structure. The Ouachita trough possibly consisted of an offsetting series of unstable shale slopes deepening southward to a gentle, west-dipping abyssal plain. The muds and channel sands upon the slope frequently slumped southwards, sometimes flowing out over the abyssal floor at right angles to basinal turbidites flowing westward down the trough axis. Belts where disturbed bedding comprises the greatest percentage of the entire section define the unstable margins of the flysch trough while the highest sand-shale ratios parallel the axis of the trough.

Contemporaneous faulting and clastic intrusions in the Quirke Lake Group, Elliot Lake, Ontario

Contemporaneous faults and clastic intrusions near Elliot Lake are common within the Espanola Formation of the Quirke Lake Group. Contemporaneous faults formed in response to differential vertical displacements which controlled regional paleocurrents and basin slope. The normal faults within the sedimentary succession probably channeled the intrusive material of the clastic dikes. Four types of clastic dikes occur in the Espanola Formation: internally sorted conglomerate dikes; internally unsorted conglomerate dikes; thin sand- and siltstone dikes; and discordant sandstone masses with scattered quartz pebbles. Emplacement of the conglomerate masses into the Espanola Formation may represent a sub-permafrost phenomenon, provided the glacial origin for the boulder conglomerates within the Huronian succession is accepted.

Premetamorphic Down-to-Basin Faulting, Folding, and Tectonic Dewatering, Rangeley Area, Western Maine

The Rangeley area of western Maine is underlain by a thick sequence of dominantly eugeosynclinal metasedimentary rocks of Ordovician, Silurian, and Devonian age. The dominant structural pattern of these rocks is defined by tight, upright, northeast-trending passive flow folds and by three major normal faults along which younger rocks on the southeast are down-faulted against older rocks on the northwest. Each normal fault, together with a major syncline and a complementary anticline farther southeast, defines a geometrically related fault-fold unit. In best-exposed units, displacement along the faults increases in the direction of plunge of the synclines and of increasing structural relief in the syncline-anticline pairs. A genetic relation between normal faulting and folding is inferred. The dominant fault-fold pattern represents the oldest recognized deformation in the area. Slaty or phyllitic cleavage of this deformation is typically subparallel to the axial surfaces of folds, but locally crosses the faults and the axial surfaces of tight folds at low angles. Metamorphosed clastic dikes along the cleavage suggest that cleavage formation was in part a diagenetic dewatering process. This process probably graded, however, into low-grade metamorphism at depth. It was quickly followed by emplacement of large plutons, local superposed passive slip and flexural slip folding, and by two recognized events of greenschist and amphibolite facies metamorphism. Porphyroblasts of these events have grown across slip cleavages as well as older phyllitic cleavage, and metamorphic zones cross the dominant fault-fold pattern. Deformation, as well as sedimentation, is considered to have been controlled by the ancestral Merrimack synclinorium—a strongly linear two-sided trough that persisted at least from Late Ordovician through Early Devonian time. The fault-fold pattern is inferred to have evolved over a long period of time, as follows: (1) Rapid deposition of 15,000 to 20,000 ft of nearly-impermeable clastic sediments in Late Ordovician and Early Silurian time on the southeast-dipping slope of the sedimentary trough; mass weakened in depth by excess fluid pressure. (2) Continuing sedimentation, down-to-basin creep with associated slump faulting and folding, probably beginning in Middle Silurian time; faults flattened basinward in depth along lower boundary of zone of excess fluid pressure. (3) Horizontal compression developed parallel to slide direction as mass piled against material in the trough; incipient slaty cleavage developed normal to compression, improving vertical permeability. (4) Pore fluids expelled vertically, permitting the slumping mass to compact horizontally, and fold with at least 25 percent shortening. The process culminated in Early Devonian time, during and after deposition of the youngest exposed rocks in the area.

The Origin of Slaty Cleavage: Evidence from Precambrian Rocks in Colorado

Research Article| February 01, 1970 The Origin of Slaty Cleavage: Evidence from Precambrian Rocks in Colorado WILLIAM A BRADDOCK WILLIAM A BRADDOCK Department of Geology, University of Colorado, Boulder, Colorado 80302 Search for other works by this author on: GSW Google Scholar Author and Article Information WILLIAM A BRADDOCK Department of Geology, University of Colorado, Boulder, Colorado 80302 Publisher: Geological Society of America Received: 09 Jul 1969 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1970, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1970) 81 (2): 589–600. https://doi.org/10.1130/0016-7606(1970)81[589:TOOSCE]2.0.CO;2 Article history Received: 09 Jul 1969 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation WILLIAM A BRADDOCK; The Origin of Slaty Cleavage: Evidence from Precambrian Rocks in Colorado. GSA Bulletin 1970;; 81 (2): 589–600. doi: https://doi.org/10.1130/0016-7606(1970)81[589:TOOSCE]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 Mesoscopic and microscopic features of Precambrian metascdimentary rocks in the northeastern Front Range, Colorado, indicate that the formation of slafy cleavage involved extensive intergranular movement in the form of laminar intrusion of sedimentary material across bedding and the formation of clastic dikes. The formation of cleavage is believed to have occurred prior to metamorphism and to have been facilitated by high pore-fluid pressure. 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.

Origin of Clastic Dikes in the Fountain and Casper Formations (Pennsylvanian) Southeastern Wyoming

Origin of Clastic Dikes in the Fountain and Casper Formations (Pennsylvanian) Southeastern Wyoming

Sedimentary features and penecontemporaneous slumping in the Waitemata Group, Whangaparaoa Peninsula, North Auckland, New Zealand

Abstract Rocks belonging to a turbidite facies of the Lower Miocene Waitemata Group are exposed extensively about Whangaparaoa Peninsula. Interbedded with this sequence are a number of thick, distinctive, volcaniclastic grits believed to have been emplaced by submarine lahars. These sediments accumulated towards the axial parts of a marine basin within a continental borderland. The turbidites were deposited by predominantly south-east - flowing currents. Directions of weak bottom (traction) currents were more variable. Deformation and contortion of strata occur on a grand scale and are attributed to the penecontemporaneous slumping of poorly consolidated sediments in response to tilting of the sea floor. Injection of clastic dikes accompanied later stages of movement in slumped sequences. Evidence suggests that one great slump sheet extends over a distance of at least 10 miles from near Red Beach in the west to Whangaparaoa Head and possibly Tiritiri Matangi in the east.

Intrusive Sandstone Dykes in the Siamo Slate near Negaunee, Michigan

Sandstone dykes up to 15cm wide and more than 3 m long transect the bedding and are parallel to the cleavage in the Siamo Slate of the Marquette synclinorium. These clastic dykes are common in slates of very low metamorphic grade east of Negaunee, and are composed of fine-grained sandstones commonly containing a higher proportion of iron-rich carbonate than the host rocks. The cleavage in both the slates and the interbedded sandstones is produced by parallel orientation of thin pelitic foliae. Individual cleavage foliae can be traced from one pelitic layer, through a sandy lamination and into the next pelitic layer. Microstructures in disrupted sandy laminations indicate that the sandstone dykes formed penecontemporaneously with the cleavage. Both the cleavage foliae and sandstone dykes are interpreted as having formed by intrusion accompanying tectonic dewatering of the Siamo Slate during late diagenesis or very low-grade metamorphism.

Soft-Sediment Faults as Indicators of Paleoslope Orientation: ABSTRACT

The Tesnus Formation in the Marathon region, Texas, consists of interbedded sandstone turbidite and shale of a late geosynclinal filling phase. Deposition was on an unstable slope as indicated by the occurrence of deformational features of preconsolidation origin including rolled sandstone bodies (tens of feet long), sandstone dikes (up to 1 in. wide and 5 ft long), diapiric structures, and numerous normal faults of small displacement. Throw on these microfaults is less than 1 in. and averages 0.25 in. The displacement is seen only on the undersides of sandstone beds and cannot be traced through the beds in which they occur. The faults intersect the base of beds at an average angle of 55° from the base, whereas most fractures of postconsolidation origin are oriented normal to the base. The measured intersections with the base of beds of 100 faults show that their mean orientation is 97° to the direction of paleoslope as indicated by flute casts. The standard deviation is 15°. Hence, the faults generally parallel paleoslope contours. Of hundreds of faults examined, more than 95% were downthrown down the paleoslope. Each individual fault has a fault zone less than 1 mm wide. Petrographic evidence for a soft-sediment origin includes (1) boundaries between fault zones and country rock are not sharp, (2) fractured grains are not present in the fault zones, and (3) all healed fractures of postconsolidation origin cut the fault zones. Soft-sediment faults have been found useful for providing current directions for sole markings, such as groove casts, which normally give only orientation. If used carefully, the faults also can provide paleoslope information where sole markings are absent. End_of_Article - Last_Page 746------------

Flow structures in sandstone dikes

A large swarm of sandstone dikes (about 150) crops out in the northwestern part of Sacramento Valley, California. Most dikes are massive medium-grained sandstones and have no readily apparent internal structures; some, however, contain a wide variety of structures, some of which strongly resemble certain common primary sedimentary structures. In many dikes tabular grains have a preferred orientation of planar elements parallel with the dike walls; in some dikes this fabric gives the dike rock a well-developed cleavage parallel with their contacts. Some dikes are layered parallel to their margins; individual layers are well-defined and vary in grain size. Some layers are graded perpendicular to the dike walls; others have structures somewhat resembling cross-bedding. On the boundaries between certain layers are a variety of structures somewhat resembling flute casts, groove casts, and ripple marks. Although difficult to account for individually, the internal structures are interpreted as flow structures produced when water-charged sediment was forcefully injected into tension cracks as they opened. Most linear structures are oriented vertically or nearly so within the dikes, but they do not indicate whether intrusion was from above or below.

The Triassic rocks of the west-central section of the Vale of Glamorgan: With particular reference to the ‘Boulder’ Breccias at Ogmore-by-Sea

The main Triassic exposures of this area are of limestone breccias derived mainly from the sub-aerial erosion of the underlying Carboniferous Limestone under dry savannah conditions. An outlier of exceedingly coarse boulder breccia at Bwlch y Ballring, near Ogmore-by-Sea, is interpreted as a fossil fan deposit, occupying an ancient wadi, previously regarded as a product of the collapse of the roof of a large cavern. Large-scale quarrying of the Carboniferous Limestone in the Ewenny and St. Brides areas has exposed several pipe infillings or Neptunian dykes of red-brown calcareous clays, considered to be of Upper Triassic age and containing reptilian or early mammalian remains, locally on a prolific scale.

Genesis of Clastic Dikes and Planeless Faults in the Miocene Deposits of the Sendai District:Studies on Faults at the Boundary of Sedimentary Basins (2)

Genesis of Clastic Dikes and Planeless Faults in the Miocene Deposits of the Sendai District:Studies on Faults at the Boundary of Sedimentary Basins (2)

Volcanic Breccias of the Tokatoka district, Northland

Abstract Breccias from 40 localities in the Tokatoka district, Northland, are either clastic dikes or tuff-breccias of the Navajo type. The tuff-breccias form dikes and plugs which cut Cretaceous to Eocene argillaceous limestones and are themselves commonly intruded by basalt dikes. The tuff-breccias are composed dominantly of fragmented basalt similar to that of the associated basalt dikes, and minor sedimentary and andesitic debris. The Tokatoka examples are compared with a schematic section through a Navajo tuff-breccia pipe.