*Structural GeologyGLY 4400 Lecture 03Primary Sedimentary Structures

*Petrified Forest

*Grand Canyon BeddingPhoto shows the many different layers, which are emphasized by different resistance to erosionVertical cliff faces are produced by sandstone and limestone (cliff-formers)Sloping surfaces are shale beds

*Primary Structures Within BedsProvide information concerning:Depositional environmentsYounging directionCurrent direction

*Bouma SequenceTurbidity depositsFigure 2.2 in text

*Graded BeddingGraded bedding means a deposit becomes finer higher in the sequenceMost graded beds are the product of turbidity flows, clouds of sediment that move downslope under water

*True Origin of FlyschFlysch sequences are recognized as as turbidites deposited in deep trenchs, associated with convergent plate boundaries (ocean-continent or ocean-ocean)Trenches have steep slopes, so turbidites flows are common

*Cross-beddingFigure 2-3a in text

*Cross-bed FormationFormed by movement from the windward (upstream) face of a dune, ripple mark, or delta deposit, to the leeward (downstream) sideCurrent velocity on the leeward side is lower, so sediment settles out

*Cross-beddingCross-beds occur within a thicker master bedCross beds are oblique to the boundary surfaces of the master bed Cross-beddingZion National Park, UtahPhoto Duncan Heron

*Surface MarkingsRain, desiccation, current traction, and movement of organisms provide an indication of facing directionThese markings are often called right-side-up indicatorsThings like mudcracks, ripple marks, raindrop impressions, salt crystal casts, etc. fall in this category

*Mudcracks

*Aeolian Ripple MarksAeolian (wind) ripples at White Sands, New Mexico (Photo Yamato Sato)

*Fossilized Ripple MarksParallel ripple marks preserved on a slab of sandstone The rocks contain the fossilized remains of marine animals - these ripples were formed in shallow sea water by gentle currents

Capitol Reef National Park, Utah

*Raindrop Impressions

*Salt Crystal CastsWhen deposition occurs in the ocean, especially if the water is quite saline, salt crystals may precipitate and settle on the sediment

*Sand Volcano PhotoSand boil or sand volcano measuring 2 m (6.6 ft) in length erupted in median of Interstate Highway 80 west of the Bay Bridge toll plaza when ground shaking transformed loose water-saturated deposit of subsurface sand into a sand-water slurry (liquefaction) in the Oct. 17, 1989, Loma Prieta earthquakeVented sand contains marine-shell fragments Credit: J.C. Tinsley, U.S. Geological Survey

*Clastic DikeFigure 2-7 in textVery coarse clasts in the center of the dike, which cuts sharply through the Proterozoic sandstonesSudbury, Ontario

*Disrupted BeddingDisrupted turbidite beds, with a hammer (left center) for scaleCantabria, SpainFigure 2-8 in text

*Load CastsEifel, GermanyThe stakes are support for grape vines, in a wine-growing regionFigure 2-6 in text

*ContactsSurfaces between geologic units Color differences highlight the contact between layers

*Types of ContactDepositional contacts Fault contacts Intrusive contacts

*Depositional Contact TypesConformableUnconformable examples of types of unconformities are shown on the next four slides

*Angular UnconformityStrata above and below the contact have a different attitudeThe angular discordance of the beds makes recognition of these unconformities in the field very simple

*Buttress Unconformity PictureA buttress unconformity (contact at red arrow) is one in which the younger, overlying rocks are cut by the contact

*Disconformity Rocks above and below the contact surface are parallel, but there is a measurable age difference between the underlying and overlying sequencesDisconformities represent periods of nondeposition or active erosion, without tectonic deformationThis is by far the hardest type of unconformity to recognize in the field

*Disconformity RecognitionFigure 2.12c in textFossil evidence

*Disconformity RecognitionFigure 2.12a in textChannel Scouring

*Disconformity RecognitionFigure 2.12d in textPaleosol formation

*Disconformity RecognitionFigure 2.12b in textBasal ConglomeratePicture from Blue Ridge Tertiary Deposit near Clints Well on the Mogollon Rim

*Disconformity PhotoDifficult to identify, unless there are big differences in rock type (like in this photo) or you know the ages of every layer

*Nonconformity DiagramNonconformities are characterized by an erosional surface which truncates igneous or metamorphic rocks

*Nonconformity PictureThis is the unconformity at the base of the Grand Canyon

*Differential CompactionDifferential compaction may occur within a horizontal layerParts of the layer compact more than others, producing lateral variations in thickness, called pinch-and-swell structures. Pinch and swell couples in the Wallace Formation north of Plains, Montana - Light gray quartzite beds with thin black argillite interlayers

*Pitted PebbleFigure 2.13 in text

*StyoliteFigure 2.14 in textNote penknife for scale

*Liesegang Band PhotoIron oxide Liesegang Bands (rust color) precipitate when oxygenated ground water moving through fracture permeates granite containing chemically reducing porewater

*Slump FoldingFigure 2.15 in text

*Salt Structure TerminologySalt structures which are symmetrical in plan view are called salt domes or salt pillowsIf the are elongated, they are called salt anticlinesIf the salt pierces the overlying layer, it becomes a salt diapir

*Fracturing by SaltA normal-fault array above a salt dome in TexasFigure 2.19 in text

*Normal FaultsDuring slumping, the landward side of the basin is stretchedTensional forces create normal faults

*Listric FaultsThe dip of the faults decreases with depth, and the faults are called listric faultsSalt rises beneath the faults, taking advantage of the zone of weakness, and creating structures, known as salt rollers, which resemble waves

*Photo: 86-2-30 David L. Warburton*Photo: 24-4 David L. Warburton

*Image: GC_Grol.jpg*Source: http://dekalb.dc.peachnet.edu/~pgore/geology/geo101/sedrx.htm#Carbs

*Photo: http://www.ori.u-tokyo.ac.jp/ori/17E.html*Image: http://pubs.usgs.gov/gip/deserts/eolian/*Photo Source: http://www.eos.duke.edu/geo41/win2.htm

*If sediment is allowed to dry out, it may shrink, causing mudcracks to developMudcracks are always widest at the top

Cinema Expeditions Geologic Images on CD-ROM

Photo rocks\sediments\mudcrack\0464013_.jpg

*Ripple marks are created by currents passing over already deposited sediments Certain types of ripple marks are useful in determining which side was up during deposition

bottom photo #WSands02.jpg

*Source: http://dspace.dial.pipex.com/justdesign/lith35.html

*On fine sediment, the impact of a raindrop may create an impression that is preserved when the sediment lithifiesRaindrop impressions are always on the top side of the rock

Cinema Expeditions Geologic Images on CD-ROM

Photo rocks\sediments\features\RAINDROP\0464023_.jpg

*Crystals leave an impression in the sedimentThey may later redissolve, but the impression remains

Picture: The Sundance Sea that covered a major portion of western Wyoming 167 million years ago. These crystals were photographed on the Flitner Ranch in Wyoming.

Photo: http://www.geo-sciences.com/FRDT.htm

*http://science.nasa.gov/newhome/headlines/mgm_images/msad01jan98_2f.htm*http://www.srs.fs.usda.gov/4201/LOGOS/contact_zone_sandhills_web.jpg*Image: http://www.earth.rochester.edu/structure/matty/photos/201FT/angular_unconformity.*Image: http://www.uoregon.edu/~millerm/butuncon1.html

*Image: http://earthnet.bio.ns.ca/english/glossary/d/disconformity.html

Original Source:adapted from The Last Billion Years [a book in preparation by the Atlantic Geoscience Society at the Geological Survey of Canada (Atlantic)] *Image: http://www.psiaz.com/Schur/azpaleo/clintswell.html

*Image: http://www.ldeo.columbia.edu/dees/ees/ies2/stratigraphy2/sld008.html*Diagram: http://www.gpc.peachnet.edu/~pgore/geology/historical_lab/relativedating.htm (Pamela Gore)*Image: http://www.ldeo.columbia.edu/dees/ees/ies2/stratigraphy2/sld004.html*Image: http://www.trgs.org/BeltIV/Assets/figs_pics/plate10_c.jpg*Image: http://coastal.er.usgs.gov/barton/mirrorlake/*Upper Image: http://www.dgi.com/earthvision/images/diapir2b_p450.gif

Lower Image: Text, figure 2-18*Source: http://earth.leeds.ac.uk/faults/normal/listric.htm