I. Geologic time Relative dating A. Relative Dating - One unit is older than the other 1. Law of Superposition 2. Law of crosscutting relationships - The crosscutting unit is younger 3. Law of faunal succession - Each fauna or flora is succeeded by a different species through time a) - Fossil - The preserved remains, impressions or casts of plants and animals b) - Index fossil - Fossil that has a distinct morphology, wide ranging, the species was present for a short period of time. 110 m.y. 180 m.y. A i:i:i:i:i:i:i:i: 111 111 i i ^^a^ ^ m.y. -_r-i=-iE-: S Shale |£HHS ^no-ISO jfSfj 3 m.y. ^ehz- 'htititi ii i iiiii 180 m.y. -^r^k «. - If half life is 57 million years then the rock is 57 million years x 2 = 114 million years old © 2001 Brooks/Cole Publishing/ITP What Materials Can Be Dated? • Most radiometric dates are obtained from igneous rocks • As magma cools and crystallizes, radioactive parent atoms separate from daughter atoms - Parent and daughter fit differently into the crystal structure of certain minerals • Geologists can use the crystals containing the parent atoms to date the time of crystallization TABLE 1 -3 Some of the More Useful Nuclides for Radioisotopic Dating Parent Nuclide" Half-Lifet Daughter Nuclide Source Materials Carbon-14 5730 years Nitrogen-14 Organic matter Uranium-238 4.5 billion years Lead-296 Zircon, uraninite, pitchblende Uranium-235 704 million years Lead-207 Thorium-232 14 billion years Lead-208 Rubidium-87 48.8 billion years Strontium-8 7 Potassium mica, potassium feldspar, biotite, glauconite, whole metamorphic or igneous rock Potassium-40 1251 million years (1.251 billion years) Argon-40 (and calcium-40)* Muscovite, biotite, hornblende, whole volcanic rock, glauconite, and potassium feldspar** 'Nuclide is a convenient term for any particular atom (recognized by its particular combination of neutrons and protons). +Half-life data from Steiger, R. H., and Jäger, E. 1977. Subcommission on geochronology: Convention on the use of decay constants in geo- and cosmochronology. Earth and Planetary Science Letters 36:359-362. *Although potassium-40 decays to argon-40 and calcium-40, only argon is used in the dating method because most minerals contain considerable calcium-40, even before decay has begun. Relative dating Stratigraphic record can be subdivided according to a variety of criteria including lithology (lithostratigraphy), fossils (biostratigraphy, ecostratigraphy), seismic profiles (sequence stratigraphy), magnetic polarity (magnetostratigraphy), event deposits (event stratigraphy). Types of Rock units 1. Chronostratigraphic units (time-rock units) - all strata in the world deposited during a given time interval (example: Upper Devonian Series) 2. Biostratigraphic units - stratigraphic units of rocks defined by their fossil content 3. Lithostratigraphic units - stratigraphic units (usually spatio-temporally restricted, three dimensional rock bodies) defined by lithology and/or physical and chemical characteristics of rocks (Group, Formation, Member, Tongue, Bed) (Event Stratigraphic Units - Units based on short-term events that had widespread depositional effects, that is,events that produced an isochronous event deposit; useful in regional (basin-wide) stratigraphic correlations) 4. Magnetostratigraphic units (polarity time units) - stratigraphic units based on magnetic reversals of the Earth's poles 5. Sequences (Sequence Stratigraphy) - basin wide stratigraphic sequences that are separated by regional unconformities or their correlative conformities TabSe 1 Summary of Categories and Unit-Terms in Strati graphic Classification* Strati graphic Categories Principal Stratigraphic Unit-terms Lrthostratigraphic Formal ion Member Bed{s). Flowfs) UnwnfQrmLty-bcwjndBd Synthem Bioslraligraphic Biozones: Range zones Inlerval 2gnes Lineage zones Assemblage zones Abundance zones Olher kinds or brozanes Magnatastratigraphic polarity Polafity zone Oilier (informal) siraligraphic calegpries (rnineralogic, stable isotope, environmental, seismic, etc.) -zone (with appropriate prefix) Equivalent Geochronologic Units C hrono&tratig raphlc Eonothem Erafosm System Series Stags Subside (Ch ranozone} Eon Era Period Epoch Age Subage (or Age) (Chron) ' if additional tanks are needed, prefixes Sub and Super may be used with unit'terms when appropriate, although restraint is recommended to avoid complicating the nomenclature unnecessarily. 1. Lithostratigraphy a. description of unit properties (e.g. color, texture, particle shape, stratification, lithology) b. named after dominant grain size fraction c. hierarchy of lithostratigraphic units (1) group: consists of 2 or more formations (2) formation: a main unit that has considerable lateral extent (3) member: a named unit within a formation; names are geographical d. lithostratigraphic units of Wisconsin (WGNHS handout) Formální (tj. nomenklatoricky pevné a hierarchicky uspořádané podle Zásad české stratigrafické klasifikace 1997) litostratigrafické jednotky ve zvrstvených sledech jsou souvrství - základní pojmenovaná jednotka zahrnující soubor hornin s typickými litologicko-faciálními znaky a zaujímající určitou stratigrafickou pozici (např. macošské souvrství), člen (vrstvy) - nižší pojmenovaná jednotka než souvrství, jejíž litologicko-faciální znaky ji odlišují od ostatních částí souvrství (např. josefovské vápence), vrstva - nejnižší jednotka sedimentárních hornin deskovitého tvaru vymezená vrstevními plochami. U hornin výlevných tvoří její analogon lávový proud nebo výlev. Souvrství jsou někdy spojována do jednotek vysokého ranku označovaných jako skupiny. Ty představují vnitřně složité soubory více souvrství nebo též soubory obtížně vnitřně členitelné omezené většinou výraznými hranicemi (např. vrbenská skupina). Jednotky nižší než souvrství hrají roli především při sestavování místních litostratigrafických škál (např. dílčí části pánví). Biostratigraphic Zones Biozones - the most fundamental biostratigraphic units. A zone is a body of rock whose lower and upper boundaries are based on the ranges of one or more taxa (usually species or phena) (see this Figure for graphic examples of the major types of biostratigraphic zones) Last appearance Taxon Range Zone First appearance Partial Range Zone i i Interval between two first appearances Interval between two Figure 17.3 last appearances Diagram illustrating the principaf kinds of interval zones as defined by the North American Stratigraphic Code (1 983) and the International StratiaraDhic Guide (19941. Index Fossils Guide Fossils (other terms used: Zone Fossil, Index Fossil) A good index fossil must be: 1. Independent of environment 2. Fast to evolve 3. Geographically widespread 4. Abundant 5. Readily preserved 6. Easily recognised Examples: Graptolites, Ammonites, Foraminiferans, Pollen, Nannoplankton Correlation of strata using fossils • Identical fossils mean strata are same age Universityof Geology 101 Environmental Geology Lecture 4 Slide 12 Connecticut Ray Joe sten Chronostratigraphy Lithostratigraphy - only local lithostratigraphic units. To compare the strata of the same age deposited in different regions biostratigraphy is used. Its use enables to determine chronostratigraphic units (time-rock units) - all strata in the world deposited during a given time interval (example: Upper Devonian Series) číselné datování litostratigrafie skupina souvrství člen (vrstvy) vrstva Obr. 5. Vztahy stratigiafických metod a vznik Mezinárodní stratigrafické stupnice (upraveno podle Hollanda 1992). Ze shrnutí nejrůznějších dat z profilů (místní stupnice) a jejich korelací se vynořuje syntéza významných etap vývoje zemské kůry ve formě chronostratigrafických jednotek a Globální stratigrafické standardní stupnice. Tyto jednotky jsou založené na horninách vznikajících během určitého intervalu geologické historie a jejich hranice jsou odvislé od vybraných konkrétních bodů na spodních hranicích stratotypových profilů. Slouží k sjednocování a řazení událostí a jevů v historii planety a představují členění této historie podle mezinárodně dohodnuté hierarchie. Základní jednotkou je stupeň, který v dnešní etapě stratigrafického poznání má většinou jen regionální platnost a proto korelace stupňů v celosvětovém měřítku skýtají těžkosti. Jeho rozsah je dán stratotypy spodní a svrchní hranice (mají mít co nejvýraznější a na velké vzdálenosti sledovatelnou charakteristiku), jeho jméno většinou geografickým názvem typické oblasti (např. givet, baden). Vyšší jednotkou je oddělení, jehož hranice jsou definovány spodní hranicí jeho nejstaršího stupně a horní hranicí nejmladšího stupně. Jeho znaky přesahují většinou již hranice oblastí a mají interregionální ráz. Názvy jsou dány pozicí uvnitř útvaru (např. spodní, střední, svrchní devon) nebo vzácněji geografickým jménem. Oddělení skládají vyšší jednotku - útvar. Útvary mají většinou již značný časový rozsah, celosvětovou platnost a jsou odrazem celosvětově sledovatelných evolučních kroků. Jejich hranice jsou analogicky dány hranicemi nejstarší a nejmladší nižší jednotky. Jejich názvy jsou v literatuře tradovány mnohdy již od úsvitu geologie a vyjadřují vztahy etnografické (např. silur), geografické (např. perm), litologické (křída), či pozici ve stratigrafickém sledu (např. kvartér). Jednotkou vyšší je eratem, který vymezuje velmi významné etapy života na naší planetě (např. paleozoikum) a nejvyšší pak eonotem odrážející nejvýznamnější kroky historie Země (např. fanerozoikum). Spodní hranice mezinárodních stratotypů (vybraných typických, co nejúplnějších a chráněných profilů) je definována jedinečným (standardním) bodem v profilu (tzv. „golden spike"), který zaujímá jistou konkrétní polohu v geologické historii vyjádřenou např. stupněm vývoje organického světa, radiometrickým stářím, polaritou etc. Príklad : Chronostrati grafické jednotky Geochronologické jednotky Oblastné litostratiqra-tické jednotky Rýdzo biostratiqrafidké jednotky fontrozoikum e o n o t * m eon fnezozoikum e t a t e rr> era jura útvar perioda Skupina S ú v r ^ t v i e has odděleni* epocha rôzne druhy toark st upen věk Cien biostratigratických zón Hildoceras bitrons chronozóna chron Isubzóna) vr*tva (horizont) ( biohonzont) Obr. 23a, Prehľad hlavných stratigrafických jednotiek. Chronostratigrafické a geochronologické jednotky si vzájomne zodpovedajú a ich obsah je presne stanovený. Oblastné litostratigrafické a biostratigrafické jednotky sú nezávislé od iných stupníc a hierarchické usporiadanie je relatívne 31 Chronostratigrafie zkoumá a řadí horninové jednotky na základě jejich radiometrického i relativního stáří. Je tedy také vztažena k horninovým jednotkám narozdíl od geochronologie, která vymezuje etapy ve vývoji Země v "absolutním" čase Mass Extinctions Punctuate Geologic Record soon 600 500 400 300 200 100 0 Millions of years ago • Mass extinctions mark the end of Paleozoic and Mesozoic Eras, Ordovician, Devonian, &Triassic Periods Univeratyof Geology 101 Environmental Geology Lecture 4 Slide 16 Connecticut Ray Joe sten F. Paleomagnetism 1. Movement of magnetic pole 2. Chron: major and complete reversal; last about 1,000,000 years •last major reversal 780,000 YBP •Brunhes - normal •Matuyama - reversed 3. Subchron: shorter-lived reversals within a chron 4. Allows correlation of isolated stratigraphic sections over broad regions Sequence Stratigraphy Metoda sekvenční stratigrafle. Vychází z myšlenky, že kolísání hladiny světového >ceámi (eustatické pohyby) v geologické historii zanecháva v sedimentech zemské kůry :áznaim který může být využit i pro globální celosvětové korelace. Zvyšování a následný Během jednoho cyklu dochází k uložení nejméně jednoho tělesa sedimentů označovaného jako sekvence Any package of sedimentary strata bounded above and below by an unconformity (of any kind) is a sequence. Sequence stratigraphy makes sequences the fundamental units of the rock record, and hence emphasizes periods of deposition and nondeposition (closely related to episodes of rising and falling sea level) as the essential information. Sequence stratigraphy grew out of seismic stratigraphy; unconformities are easily distinguished in seismic records, but lithology is often unknown. The second and often co-incident step in the interpretation of well logs and cores is the use of parasequence stacking patterns (the vertical occurrence of repeated cycles of coarsening or fining upwards sediment) of to identify the lowstand system tracts (LST), transgressive system tracts (TST) and highstand system tracts (HST) that are enveloped by the mfs, TS and SB. These parasequence cyclic stacking patterns are commonly identified on the basis of variations in grain size and when these fine upwards are indicated by triangles whose apex is up while those that coarsen upwards are indicated by inverted triangles whose apex is down. The repeated stacking patterns for LST cycles are: - •Cyclic fill of incised depressions that tend to fine upward. •Cyclic sand to shale bodies of basin floor fans that tend to fine and thin upward. •Cyclic sand to shale bodies of shelf margin clinoforms that tend to coarsen and thicken upward. The repeated stacking patterns for TST cycles are: - •Regressive cyclic shale to sand bodies of that tend to coarsen and thin upward. Correlations based on Lithology - Lithostratigraphio Sequence Stratigraphic Interpretation of sedimentary strata as products of "relative sea level change" Correlations based on Bounding Surfaces - Aliostratigraphic mis (Maximum Flooding surface) TS (Transgressive Surface) SB (Sequence Boundary) LST Lowstand System Tract TST Transgressive System Tract HST Highstand System Tract Relative sea level is the depth of water relative to the local land surface. Relative sea level can change due to local vertical tectonic motions or due to eustatic sea level variations (i.e. global changes in the volume of ocean water or of the ocean basins). In both sequence and traditional stratigraphy, the critical events that determine the locations of environments and unconformities are transgressions and regressions. A transgression is a landward shift in the coastline, and hence a landward shift in all marginal marine environments. A regression is a seaward shift in the coastline. SeiSmiC StratigraPhy Interpreting how the Earth's sedimentary layers have formed, is difficult. Cores taken on land and from the ocean are not only expensive to retrieve, but represent a small percentage of the Earth's surface. Methods using seismic waves developed in the 1960's help to observe the crust's layers in detail. Seismic stratigraphy is when energy waves are used to bounce off the different layers of the Earth. These layers provide us with data that a seismic stratigrapher can then interpret. For example, in the seismic profile below we show the results of waves bouncing off the different layers and then recorded on the surface of the Earth. These "wavy" images can then be used to reconstruct the area in rock units, as shown in the interpretation of the seismic profile. These advances have allowed geologists to map more area than ever before. Prior to these advances, only outcrops and geologists walking and recording on their maps could be used. Chemostratigraphy . Oxygen Isotopes 1. 3 Oxygen Isotopes; 16O and 18O most common 2. Fractionation a. 16O lighter so evaporates preferentially; 18O heavier so condenses preferentially b. ratio at which these isotopes enter chemical compounds is temperature dependent c. most widely used proxy for: •changes in global ice sheet volume •changes in global temperatures 3. Measurement a. measure how much 18O/16O ratio deviates from isotope proportions found in modern oceans b. 518O %o is zero for standard marine ocean water 4. During Glacials: •16O preferentially evaporated from oceans • 16O deposited on ice sheets & concentrated there • ice sheets relatively depleted in 18O so 818O is negative • 18O concentrated in seawater; ice age oceans have 518O values of about +5 •marine shells also enriched in 18O during glacials 5H. Other Dating Methods 1. Dendrochronology 2. Lacustrine Sediments - varvites 3. Lichenometry INSIDE THE TREE Tree ring width Variability of tree ring width and climatic conditions Seasonal patterns: Early wood Large, thick-walled cells Late wood Small, densely-packed, thin-walled cells Together = an annual growth ring Mean width of rings dependant on: tree species tree age availability of stored food climate (precipitation, temperature, humidity, sunshine, windspeed, humidity) Trees as filters and sources of palaeoclimatic data Lichenometry ^ Most used to date glacial deposits in tundra environments ^ Also used to date lake-level, sea-level, glacial outwash, trim-lines, rockfalls, talus stabilization, former extent of permanent snow cover ^ Assumes constant growth rate of lichen so that the largest diameter lichen will be the oldest Liehen Dates Species Diameter Age Location Aleetoria minuseula 160mm 500-600 yrs Baffin Island Rhizoearpon geographieum 280mm 9,500 +/-1500 yrs Baffin Island Rhizoearpon alpieola 480mm 9,000 yrs Swedish Lapland Ecostratigraphy is the stratigraphy of ecosystems, a powerful tool for high-resolution cyclic and sequential stratigraphy, based on biostratigraphy. It is founded on the application of ecological knowledge to the reconstruction of past ecosystems and their succession, in relation to global external forcing agents such as sea level oscillations, climate changes, etc. The ecostratigraphic techniques used in this study (mainly palynocycles and ecologs) have provided regional chronostratigraphic correlation frames from 2nd order cycles (3 to 50 million years duration) to periodic cycles within the Milankovitch band (around 100,000-year period), for Paleocene, Eocene, Oligocene, and Miocene stratigraphic sequences. Facies Facies - The set of characteristics of a body of rock that represents a particular processes. Sedimentary Facies Stratigraphic units distinguished by lithologic, structural and organic characteristics reflecting the processes of the depositional environment. example facies description beach Sandstone, white, fine grained, rounded, well sorted, slightly muddy at base (<5% mud), laminated at top, burrowed, at base, 15'6" thick Lithofacies - the set of lithological characteristics of a body of rock that represents a particular depositional environment or can be interpreted in terms of depositional processes Biofacies - the set of biological characteristics of a body of rock that represents a particular depositional environment and ecosystem or can be interpreted in terms of depositional and biological processes (Biofacies and Biozones are not synonimous terms!) Ichnofacies - facies delineated on the basis of trace fossils Taphofacies - facies delinated on the basis of preservational charecteristics of fossils A = Sandstone facies (beach environment) B = Shale facies (offshore marine environment) C = Limestone facies (far from sources of terrigenous input) Each depositional environment grades laterally into other environments. We call this facies change when dealing with the rock record •Walther's Law •Facies that are adjacent laterally •will be superimposed vertically Sedimentary Environments Glacier Lake Continental shelf Glacjal Continental slope Organic reefs Deep-sea Kanti n e n t □ I n e Přechodné Mořské subaerické (terestrické) subakválne deltové ogunarne rezi du alne eolické glaciál ne vulkanicko - terestrické Kuvíatilné Lim nické kaspibraki cké bra ki cke hypersalínne euxibrakické T spec. pr i pod : rífové [ b i ohermné ) T p e Lagi cké špec. případ: euxínske ! anaeróbne) Pulil£ÍĽ- ■- - _ I fiiťiiM.i^i^: I f. 11 p I L-: ■ r i ■_ i riflí- t*-^ Iniidľ U-.iIíi ■ I '! .'.'i ii! ^[SuĽdii.LúrLi.l- nam m i.^.^mi fii MXHI ni Li '.I .".'I ľll WJUU ,: I ľ+.i.ľii-'in Kadil TEXTURE (SIZE). FIGURE 3-10 Idealized gradation of coarser ncarshorc sediments to finer offshore deposits. Particle size in clastic sedimentary rocks reflects the ENERGY of the depositional environment. E.g. (above) Nearshore - waves crashing on beaches -> fairly high energy -> coarse textured deposits (pebbles/sand); offshore -> progressively lower energy environments -> progressively finer textured deposits - medium sand - fine sand - silt/mud - clay - carbonates (beyond land-derived sedimentation in shallow tropical oceans). Land of low relief a) Quartz sandstone - predominantly quartz grains ("clean sandstone"). Long transportation (quartz survives long transportation because it is relatively hard). Distant from mountainous regions, tectonically stable. Often form at coastlines, in deserts, on higher energy coastal plains and river floodplains (e.g. Padre Island). Quartz grains make up 90%+ of rock and the grains are well rounded. Cross beds and ripples are common. CARBONATES: Most common = limestone (calcium carbonate). Formed by abundant marine organisms and the precipitation of calcium carbonate from sea water. Warm, clear, shallow tropical oceans - particularly common in platform areas. TEXTURE (SIZE). FIGURE 3-10 Idealized gradation of coarser ncarshorc sediments to finer offshore deposits. Particle size in clastic sedimentary rocks reflects the ENERGY of the depositional environment. E.g. (above) Nearshore - waves crashing on beaches -> fairly high energy -> coarse textured deposits (pebbles/sand); offshore -> progressively lower energy environments -> progressively finer textured deposits - medium sand - fine sand - silt/mud - clay - carbonates (beyond land-derived sedimentation in shallow tropical oceans). b) Arkose - terrestrial; derived from granitic highlands, contain > 25% feldspar grains (implies fairly short transportation, because feldspar is relatively soft and erodes over long distances). Commonly pink-red color. c) Graywacke - mixture of sand, clay and rock fragments ("dirty sandstone"). Indicates tectonic activity, rapid erosion/sediment accumulation, short transportation. Often deposited as turbidites (submarine landslide deposits). Matrix is usually 30%. Beds are often graded (sorted by size - coarse at the base, finer at the top). SHALES: Form in similar environments to sandstones, only deposited under lower energy conditions (i.e. "quieter" locations) -> finer particles (clay, silt). Shallow marine, marshes, lakes, lower energy coastal plains and floodplains. Finely layered, often fissile. Common fossils. Terms for Marine (i.e. Ocean) Environments and some characteristic sediment facies Turbidity currents ■Suspension of water, sand, and mud that moves downslope (often very rapidly) due to its greater density than that of the surrounding water (often triggered by earthquakes) 'Speed of turbidity currents first appreciated in 1920 — breaking of phone lines in the Atlantic; also gave indication of distance traveled by a single deposit A:; Turt:i y curranl Blowa. Settle ttHlfJWMJ by smaller A $ratf ed bad ©1993 Wadsworth Publishing Company/ITP CÔNE BATHYAL deep sea ten) plaine abyssale (décantation) CLASSICAL TURBIDITE G'O'-i Boumo {(962) Divisions IntetpfeToTton Pente Pelagic Mdirrventation V r Mot*iv* or graded Turb*dtt( fine" grained, low denvly lurbidify current deposition Upper porollef laminoe 1 Ripples, wavy or convoluted laminae LOwer parT of Lower Flow Regime \ Rone parol lei lorn i no e upper Flow Regime Plane Bed 1 ■ ■ **. - • ■ * j 1 o ■I 2 & o Massive, graded ? Upper flow Reqime Rapid deposition and Quick bed P) DISTRIBUTION OF DEEP-SEA SEDIMENTS sedimentaci vápnitých nebo křeimtýck bahen je karbonátová kompenzační hloubka (CCD). > stupeň nasycení 0.5 0.6 0.8 1.0 1.5 2.0 3.0 4.0 5.0 7.Q Obr. 21. Křivky závislosti nasycení mořské vody vzhledem k aragonitu a kalcitu na hloubce mořské vody pro současný Atlantik. Vlnovkou jsou vyznačeny kompenzační hloubka aragomtu (ACD) a kalcitu (CCD), lyzoklina je hloubková úroveň, ve které rychle vzrůstá rychlost rozpouštění kalcitu ale ve které se ještě vyskytuji pelagické karbonáty. Upraveno podle Broecker (1974). subtropical oceanic upwelling convergence divergence area Distribution of modern sediment facies in the crmleit of depth :ind ute tin fertility, based on sediment pa 11 ems in I lie eastern central Pacific. Numbers are typical sedimentation rates in mm/1000 yrs •Marine •- Continental Shelf - Continental Slope - Continental Rise •Turbidite Deposits Facies changes due to rising sea level - Water Getting Deeper River Comparison of sediments deposited