Geologi Fisik (Stratigrafi, Paleontologi & Umur Geologi) Oleh : Irvani Referensi : Thomson, G. R. and Turk, J. 1991. Modern Physical Geology. Saunder College Publishing, USA. Lutgens, F. K., Tarbuck, E. J. and Tasa, D. 2012. Essentials of Geology, 11th Edition, Pearson Prentice Hall, New Jersey. Freeman, T. 2004. Environmental Geology Laboratory. John Wiley & Sons, Inc., USA. Monroe, J. S. and Wicander, R. 2009. The Changing Earth: Exploring Geology and Evolution. 5th Edition. Pre-Press PMG, USA. Carlson, D. H., Plummer, C. C. and Hammersley, L. 2011. Physical Geology : Earth Revealed. 9th Edition. McGraw-Hill, New York. Bates, R.L. and Jackson, J.A., 1987. Glossary Geology. 3th Edition. American Geological Institute Elexandria, Virginia. Williams, L. 2004. Earth Science Demystified. McGraw-Hill, New York. Frisch, W., Meschede, M. And Blakey, R., 2011. Plate Tectonics : Continental Drift and Mountain Building. Springer-Verlag Berlin Heidelberg. German. DLL 1
Materi : - Pendahuluan (P.1) - Sejarah, Struktur & Komposisi Bumi (P.2) - Proses-Proses Geologi & Tektonik Lempeng (P.3-4) - Pengenalan Unsur, Mineral & Batuan (P.5-8) : - Unsur & Mineral - Batuan Beku - Batuan Sedimen - Batuan Metamorf - Prinsip Stratigrafi, Paleontologi & Umur Geologi (P.9) - Pengenalan Struktur Geologi (P.10-11) - Pengenalan Hidrogeologi & Geomorfologi (P.12) - Pengenalan Kebencanaan Geologi (P.13) - Pengenalan Peta, Kompas, Navigasi dan Peralatan Geologi (P.14) - Kuliah Lapangan (Situasional) 2
I. PRINSIP STRATIGRAFI Danish anatomist Nicolas Steno (1638 1686) : 1. principle of superposition 2. principle of original horizontality 3. principle of lateral continuity The Scottish geologist James Hutton (1726 1797) : - Principle of cross-cutting relationships. - Inclusions Carlson, et al. 2011 3
Law of Superposition The law simply states that in an underformed sequence of sedimentary rocks, each bed is older than the one above it and younger than the one below. OR In an undisturbed succession of sedimentary rock layers, the oldest layer is at the bottom and the youngest layer is at the top. Principle of Original Horizontality It means that layers of sediment are generally deposited in a horizontal position. Sediment is deposited in essentially horizontal layers 4
Principle of lateral continuity States that sediment extends laterally in all directions until it thins and pinches out or terminates against the edge of the depositional basin Principle of Cross-Cutting Relationships An igneous intrusion or fault must be younger than the rocks it intrudes or displaces 5
Inclusions Inclusions are pieces of one rock unit that are contained within another. OR Inclusions, or fragments of one rock contained within a layer of another, are older than the rock layer itself. Unconformities Layers of rock that have been deposited essentially without interruption, we call them conformable. The deposition of sediment has been interrupted again and again. All such breaks in the rock record are termed unconformities. Four types of unconformable contacts (unconformities) are recognized: (1) angular unconformity, (2) disconformity, (3) paraconformity, and (4) nonconformity. Boggs (2006) 6
Schematic representation of four basic kinds of unconformities. Arrows indicate the unconformity surface. For the purpose of illustration, the youngest strata below the unconformity surface in each diagram is shown to have a (hypothetical) age of 1 00 million years and the oldest strata above the unconformity surface an age of 50 million years, indicating a hiatus in each case of 50 million years. Boggs (2006) Angular unconformity : It consists of tilted or folded sedimentary rocks that are overlain by younger, more flatlying strata. An angular unconformity indicates that during the pause in deposition, a period of deformation (folding or tilting) and erosion occurred. Angular unconformity is an erosional surface on tilted or folded strata over which younger strata were deposited. 7
8
Disconformities are more common but usually far less conspicuous because the strata on either side are essentially parallel. Disconformity is a surface of erosion or nondeposition separating younger from older rocks, both of which are parallel with one another 9
Nonconformity : Here the break separates older metamorphic or intrusive igneous rocks from younger sedimentary strata. An erosional surface cut into metamorphic or igneous rocks is covered by sedimentary rocks. 10
11
12
II. Paleontology The scientific study of fossils - Fossils: Evidence of Past Life The remains of relatively recent organisms may not have been altered at all. Such objects as teeth, bones, and shells are common examples. A type of fossilization called carbonization is particularly effective in preserving leaves and delicate animal forms. 13
Examples of such trace fossils include: 1. Tracks-animal footprints made in soft sediment that was later lithified. 2. Burrows-tubes in sediment, wood, or rock made by an animal. These holes may later become filled with mineral matter and preserved. Some of the oldest-known fossils are believed to be worm burrows. 3. Coprolites-fossil dung and stomach contents that can provide useful information pertaining to food habits of organisms. 4. Gastroliths-highly polished stomach stones that were used in the grinding of food by some extinct reptiles. 14
Fossils and Correlation Fossil organisms succeed one another in a definite and determinable order, and therefore any time period can be recognized by its fossil content. This has come to be known as the principle of fossil succession. Once fossils were recognized as time indicators, they became the most useful means of correlating rocks of similar age in different regions. Geologists pay particular attention to certain fossils called index fossils. 15
Dating with Radioactivity For example, we know that Earth is about 4.6 billion years old and that the dinosaurs became extinct about 65 million years ago. Three common types of radioactive decay : 1. Alpha particles (particles) may be emitted from the nucleus. An alpha particle is composed of 2 protons and 2 neutrons. Consequently, the emission of an alpha particle means that the mass number of the isotope is reduced by 4 and the atomic number is decreased by 2. 2. When a beta particle (particle) or electron is given off from a nucleus, the mass number remains unchanged because electrons have practically no mass. However, because the electron has come from a neutron (remember, a neutron is a combination of a proton and an electron), the nucleus contains one more proton than before. Therefore, the atomic number increases by 1. 3. Sometimes an electron is captured by the nucleus. The electron combines with a proton and forms an additional neutron. As in the last example, the mass number remains unchanged. However, as the nucleus now contains one less proton, the atomic number decreases by 1. 16
17
Radiometric Dating 18
19
POTASSIUM-ARGON. Although the halflife of potassium-40 is 1.3 billion years, analytical techniques make possible the detection of tiny amounts of its stable daughter product, argon-40, in some rocks that are younger than 100,000 years. Another important reason for its frequent use is that potassium is an abundant constituent of many common minerals, particularly micas and feldspars. 20
Dating with Carbon-14 Carbon-14 is the radioactive isotope of carbon. The process is often called radiocarbon dating. Because the half-life of carbon-14 is only 5730 years, it can be used for dating events from the historic past as well as those from very recent geologic history. In some cases carbon-14 can be used to date events as far back as 70,000 years. It is important to emphasize that carbon-14 is only useful in dating organic materials, such as wood, charcoal, bones, flesh, and even cloth made of cotton fibers. 21
Using Tree Rings to Date and Study the Recent Past 22
23
Terima Kasih 24