Historical Geology: Historical geology is the use of the principles of geology to reconstruct and understand the history of the Earth. It focuses on geologic processes that change the Earth's surface and subsurface. Historical Geology is the study of changes to Earth and life in time and space. Study of the evolution of Earth, its environments, and its life through time combines many subdisciplines of geology •Sedimentology •Stratigraphy •Structural Geology •Plate Tectonics & Paleogeography •Paleobiogeography •Paleontology •Geochemistry Some of the topics covered: •Paleoenviroment analysis: interpreting ancient environmental conditions from the rock record (e.g.: river & lake systems, deltas, lagoons, deep marine, etc.) •Geologic Time: how to determine numerical and relative dates in time •The principles of organic evolution •The Geologic Column: its construction and its operation •Orogenesis: the rise (and fall) of mountain ranges • http://facstaff.gpc.edu/~pgore/geology/geo102.htm •1669 Nicolaus Steno Stratigraphy - principle of superposition - principle of original horizontality •Abraham Werner (1750-1817) neptunism - primitive rocks - transition rocks - alluvium •James Hutton (1726-1797) "Father of geology" •plutonism uniformitarianism "Theory of the Earth" 1785 - Cyclical view of earth's history Profound changes can be the result of small changes over long periods of time. • History of Geologic Thought Founders of Historical Geology Abraham Gottlieb Werner 1749-1817 Most influential geologist of the late 18th century Studied at the Freiburg Mining Academy Taught mineralogy at Freiburg. Developed the “Neptunian” classification of rocks All rocks of the crust were deposited or precipitated from sea water A universal ocean once covered the Earth Followers called “Neptunists” abraham_werner Founders of Historical Geology James Hutton 1726-1797 Father of Modern Geology Edinburgh physician & geologist? Opponent to Neptunism Believed fire was the answer. Recognized change on the Earth’s surface (Surficial processes were active) Developed cyclic view of Earth “No vestige of a beginning, no prospect of an end”. hutton Laid foundation for uniformitarianism “The past history of our globe must be explained by what can be seen to be happening now”. By observing geologic processes in operation around him, Hutton could infer the origin of features observed in rocks. “Present is the key to the past”. Archibald Geike 1835-1924 Founders of Historical Geology Theory of the Earth" 1785 img007 Cuvier (1769-1832) catastrophism Showed that fossil animals found in different stratigraphic intervals in Paris Basin had undergone extinction (did not believe that new species arose) Recurrent catastrophic events causing widespread extinction and resulting in sharp boundaries between fossil layers. Founders of Historical Geology smith William Smith 1769-1839 English surveyor and mining engineer Created the first geologic map Understood sequences of rock, applied soils, lithology, and fossils First to recognize that rocks could be identified by their fossil assemblages First to “correlate” rocks of the same age but different lithology smithmap Founders of Historical Geology William Smith 1769-1839 Correlation led to Principle of Faunal Succession If we know the position of each rock layer in a sequence, we know their relative age. Then, if we look a the fossils in the layers, we can determine the relative ages of them. This sequence will occur again and again in the geologic record on a widespread geographic scale. Can then be used to provide relative age of the rocks. layer_sequence2 Smith determined that the life forms of each age in Earth history were unique for given intervals Fossils could then be used to determine the chronology of the rocks Smith saw it, knew it was right, but didn’t know WHY img012 Charles Lyell (1830) "Principles of Geology" The same processes we see today also acted in the past. principle of cross-cutting relationships Primary, Secondary, Tertiary, Recent. darwin geosyn0 James Hall , James Dwight Dana In the late 19th century, geologists interpreted the structure of mountain ranges this way. They reasoned that the sedimentary rocks had to accumulate in basins, and since the two belts of rock were so different, there was likely a barrier between them. The uplifted deep crustal rocks found in the cores of many mountain ranges seemed to support the idea of a ridge. The two belts of sedimentary rock were envisioned as accumulating in great troughs, formed by folding of the entire crust. These crustal warps were called geosynclines. The intervening ridge was termed a geanticline. The deep-water, volcanic belt, with its great accumulations of rocks, was called the eugeosyncline (eu = Greek "real", i.e. the "real" geosyncline, and the shallow-water belt was called the miogeosyncline (mio = Greek "somewhat", i.e. the "sort of" geosyncline. Geosynclinal Model - Dana, Hall, end of 19th century Marcel Bertrand described nappes in 1884, Hans Schardt proved their existence in 1893, Maurice Lugeon expanded and popularized the notion in 1902. marcelbertrandfot Marcel Bertrand Wegeners's findings were published in 1915 in his book Die Entstehung der Kontinente und Ozeane (The origin of the continents and oceans). His ideas were not widely accepted as critics thought that the evidence were not strong enough, that the underlying cause of the drift was not explained and that the drift was impossible. Wegener gif wegener 1960s Plate Tectonics In 1962, Harry Hess proposed the hypothesis that midocean ridges represent narrow zones where ocean crust forms. Plate Tectonics theory--late 1960’s. •Based on new understanding of lithosphere and asthenosphere. •Tied sea-floor spreading together with Wegener’s idea of continental drift. •Lithosphere made of rigid tectonic plates that move over the asthenosphere. Spreading centers Mantle material moves upward, carrying heat. Heat causes expansion and rising of sea floor. Volcanism occurs (also earthquakes) Convection in the mantle drives the system Large scale thermal convection in the mantle. Convection cells. Roughly circular. Mantle heat probably due to radioactive decay If the rising part of a convection cell is beneath a continent, it will cause it to RIFT apart. Also causes seafloor to rift apart at mid-ocean ridge. Continents move alont with ocean crust, and do not plow through it. earths_crust_8x6 Wilson Cycle: Hypothesis by J. Tuzo Wilson in the 1970s that includes a cycle of continental fragmentation, opening and subsequent closing of ocean basins and plate convergence (reassembly of the continent). Slide12 The asteroid impact theory was first proposed by Louis and Walter Alvarez in 1980. They discovered high concentrations of iridium - an element rarely found on Earth but found in abundance in extraterrestrial bodies such as asteroids and meteorites - in a thin layer of clay from Italy. The iridium was found at the Cretaceous-Tertiary (K/T) boundary, the layer of geological deposits dated at 65 million years when the dinosaurs became extinct. alvarez •K/T boundary site in Italy • •2.5-cm-thick clay layer shows high concentration of iridium Cretaceous-Tertiary Boundary WICHG31529a In 1980 Walter and Luis Alvarez and their colleagues Frank Asaro and Helen Michel published an historic paper suggesting that an asteroid about 10 kilometers (6 miles) in diameter struck the earth sixty-five million years ago at the end of the Cretaceous. The resulting impact should have left a crater at least 160 kilometers (100 miles) in diameter. If the impact site were in the ocean, huge tsunami ("tidal waves") would rise several kilometers in height, sweeping hundreds of kilometers across the continents, sweeping away everything in their path. As hot material ejected from the impact rained back down, huge fires would start up all over the world. Dust thrown up by the impact would have spread out covering the entire world in darkness. Temperatures would have dropped precipitously. Plants would have failed to receive enough sunlight to allow photosynthesis to continue. After the plants died, plant-eating animals dependent on them would die, as would meat-eating animals once their plant-eating prey were gone. Conditions in the oceans would not be much better as massive acid rain buildup poisoned the water and destroyed shell-bearing creatures, disrupting the entire food chain. About 70% of all species died out at the end of the Cretaceous. This included the dinosaurs which had dominated the landscape for over 160 million years. asteroid_impact Asteroid impact This theory is that an asteroid 4-9miles in diameter hit the Earth.　 Since the asteroid scattered awful amount of dust and debris in the atmosphere, the dust and debris blocked the most of the sunlight, and the temperature lowed down globally. The low temperature caused the mass extinction. DDHORZ K-TCLOSE KTHIT chicxulub Chicxulub impact-graphchixculubs impact-yucatan impact-ct2 mimbral tectites qtz-chic A 0.32 mm shocked quartz grain from intracrater breccia sample Y6 N14 of the Chicxulub crater. The drill hole Yucatán-6 was located ~50 km from the crater's center and penetrated ~500 metres of impact melt and breccias at its base. The melt and breccia units contain clear evidence of production by impact, including mineral grains showing evidence of shock metamorphism. In the mineral quartz the passage of a strong shock wave can cause dislocation of the grain's crystal structure along preferred crystallographic orientations. This quartz grain shows at least 8 sets of planar deformation features when rotated; two strong sets (and part of a third set) of shock lamellae are visible in this orientation. The lamellae are decorated with inclusions. Impact is the only natural process known to produce shock waves of sufficient strength to cause deformation of this type. Basic geological terms 1. Boundaries - Contacts - Contacts separate different rock types a) Conformable -No rocks or interpreted time is missing -b) Unconformable - unconformity - Rocks and or interpreted time is missing at the contact (1) Angular Unconformity fig. 8.5 - Angular discordance of bedding (2) Disconformity Fig. 8.4 - Irregular erosional surface - Nonirregular erosional surface Konkordance je takzvané souhlasné uložení vrstev či vrstveních celků. Vrstvy tedy jsou uloženy paralelně - jedná se o normální uložení mladších vrstev na starší bez přerušení sedimentace (jen se mohli změnit sedimentační podmínky, které způsobili změnu charakteru sedimentu). Tedy vztah mezi paralelně uloženými vrstvami či souvrstvími vzniklými bez přerušení sedimentace můžeme nazvat jako konkordantní. 3 Úhlová diskordance http://www.geology.cz/aplikace/fotoarchiv/fotoarchiv.php?jev=13 Diskordance je naopak takzvané nesouhlasné uložení vrstev. Vyjadřuje vztah dvou jednotek, mezi jejichž uložením nastalo období bez sedimentace nebo období erozní činnosti. Jedná se tedy o projev přerušení sedimentace. Můžeme vymezit různé typy diskordancí: 1 Skrytá diskordance Diskordance s výrazně erodovaným podložím 2 angular_unconformity_diagram_b_8x6 img009 Transgression -Shift of depositional base level landward -Movement of shoreline in a landward direction -Regression -Movement of shoreline in a seaward direction -Shift of depositional base level seaward Transgres_Regres Slide 1 •Regression (offlap sequence) •Transgression (onlap sequence •Transgressive sequence •Deeper water facies overlie shallow water facies. A "deepening upward" sequence. •Regressive sequence •Shallow water facies overlie deeper water facies. A "shallowing upward" sequence. regressn transgn Sea-level change Relative sea-level change includes a global component (eustasy) that is uniform worldwide and can be measured relative to a fixed datum (e.g., the center of the Earth), and regional to local components (isostasy, tectonism) that are spatially variable Eustasy involves changes in ocean-basin volume, as well as changes in ocean-water volume (amplitudes ~101–102 m) Tectono-eustasy (time scales of 10–100 Myr) Glacio-eustasy (time scales of 10–100 kyr) 21-12 Slide 1 Slide 1 •Eustatic Sea Level Changes •- Climate (ice ages) •Changes in Sea Level •Tectonic (development of mid-ocean ridges) •Figure 3.14, p. 50 Lambeck22 Slide 1 •Local Sea Level Changes •- Uplift - Subsidence Basic stratigraphic principles 1.The principle of superposition - in a vertical sequence of sedimentary or volcanic rocks, a higher rock unit is younger than a lower one. "Down" is older, "up" is younger. 2.The principle of original horizontality - rock layers were originally deposited close to horizontal. 3.The principle of cross-cutting relationships - a structure that cuts another is younger than the structure that is cut. 4.The principle of inclusion - a structure that is included in another is older than the including structure. 5.The principle of "uniformitarianism" - processes operating in the past were constrained by the same "laws of physics" as operate today. 6.The principle of faunistic succession 7.The Walter law THE PRINCIPLE OF SUPERPOSITION •In a sequence of strata, any stratum is younger than the sequence of strata on which it rests, and is older than the strata that rest upon it. "...at the time when any given stratum was being formed, all the matter resting upon it was fluid, and, therefore, at the time when the lower stratum was being formed, none of the upper strata existed." Steno, 1669. • PRINCIPLE OF INITIAL HORIZONTALITY •Strata are deposited horizontally and then deformed to various attitudes later. "Strata either perpendicular to the horizon or inclined to the horizon were at one time parallel to the horizon." Steno, 1669. • PRINCIPLE OF CROSS CUTTING RELATIONSHIPS * Things that cross-cut layers probably postdate them. "If a body or discontinuity cuts across a stratum, it must have formed after that stratum." Steno, 1669 •Principle of Superposition •Principle of Original Horizontality • •Principle of Cross-cutting Relationships The crosscutting unit is younger The Principle of Faunal Succession was later added by William Smith in the late 1700's who observed and studied fossils embedded in rock layers. This principle states that the oldest fossils in a series of sedimentary rock layers will be found in the lowest layer (layer A). Progressively younger fossils occur in higher layers (layer B). This is the same concept as superposition, but it helped geologists realize that you can look at the age of these layers and assign relative dates. This parallels evolution. Younger organisms replace older organisms as the older ones become extinct. img006 Walther's Law - Facies Successions Facies situated in conformable vertical successions of strata are also situated in laterally adjacent environments Transgres_Regres Walther’s Law The vertical progression of facies will be the same as the corresponding lateral facies changes PRINCIPLE OF UNIFORMITARIANISM based onrealizing that "The Present is the key to the Past."a. To understand past, study processes at work today.b. Origin of rocks understood by how rocks form now.c. Geologic processes are uniform through Earth history, with only a few minor exceptions.d. Rates that processes work are NOT uniform. PRINCIPLE OF ACTUALISM--a more general statement saying: "The laws of nature are constant thru time."1. Scientific experiments always give same results.2. Actualism is a fundamental concept of all science; itwas generalized from geological Uniformitarianism. Principle of uniformitarism (actualism) Chemical parameters 1)Different salinity of the oceans – Precambriam 2)Composition of the atmosphere 3)Different sediments (some U deposits, banded iron formations) 4) Evolution of bilogical systems 1)Hadaikum – no life 2)Absence of floral cover 3)Changes in environmental requirements 4) Changes in erosion 1) Different intensity of geological processes – orogenic cycles, climatic oscillations Different astronomical parameters – slower the rotation of Earth Differencies in the past LENGTH OF THE DAY Narrative: The length of day and number of days per year is slowly changing. Tidal friction on Earth of lunar and solar tides slows it down. Also, the moon is slowly retreating from the Earth. Rate: rotation - slows by 1.7 milliseconds/year moon retreat - 5 cm/year Geophysical calculations of slowing are validated by evidence from fossils - which record daily bands and lunar cycles. (primarily the frequency and magnitude of tides) -Stromatolites -Corals -Bivalves 900 million years B.C. -- day: 18 hours; 440 days/year 150 million years B.C. -- day: 23.5 hours; 370 days/year (late Jurassic) Modern -- day: 24 hours; 365.25 days/year Circadian rhythm in higher animals does not adjust to a period of less than 17-19 hours per day. Therefore, records the time of emergence of metazoans. • • • Basic geological terms 1. Boundaries - Contacts - Contacts separate different rock types a) Conformable -No rocks or interpreted time is missing -b) Unconformable - unconformity - Rocks and or interpreted time is missing at the contact (1) Angular Unconformity fig. 8.5 - Angular discordance of bedding (2) Disconformity Fig. 8.4 - Irregular erosional surface - Nonirregular erosional surface (3) Nonconformity -Sed. rocks overlie older, massive igneous and/or metamorphic rocks 4) Paraconformity - are characterized by a surface of nondeposition separating two parallel units of sedimentary rock (4) Diasthem – minor depositional break without erosion Angular Unconformity Nonconformity - sed. rocks overlie older, massive igneous and/or metamorphic rocks Disconformity - unconformity in this case is directly recognizable as a surface resulting from erosion of underlying beds. The rocks above and below a disconformity are parallel in this case . angular_unconformity_diagram_b_8x6 img009 PARACONFORMITIES Paraconformities are characterized by a surface of nondeposition separating two parallel units of sedimentary rock, which is virtually indistinguishable from a sharp conformable contact; there is no obvious evidence of erosion. An examination of the fossils shows that there is a considerable time gap represented by the surface. Paraconformity 47-4 Diastem • A diastem is a relatively short interruption in sedimentation, with little or no erosion before deposition is resumed. • The time involved in a diastem may be days or years (e.g. the time between floods on a flood plain). • In a sedimentary succession a diastem may be a bedding plane or may not be visible at all. Subsidence - The earth's surface sinks due to sediment or tectonic loading Transgression -Shift of depositional base level landward -Movement of shoreline in a landward direction -Regression -Movement of shoreline in a seaward direction -Shift of depositional base level seaward •Transgressive sequence •Deeper water facies overlie shallow water facies. A "deepening upward" sequence. •Regressive sequence •Shallow water facies overlie deeper water facies. A "shallowing upward" sequence. regressn transgn Slide 1 •Regression (offlap sequence) •Transgression (onlap sequence Slide 1 Slide 1 •Eustatic Sea Level Changes •- Climate (ice ages) •Changes in Sea Level •Tectonic (development of mid-ocean ridges) •Figure 3.14, p. 50 21-12 Slide 1 •Local Sea Level Changes •- Uplift - Subsidence