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0 B N{ 5GUC .l 62% = Gieological Time AR pring 2022 GEL 109 Angular unconformity —an angular uniformity is similar to a disconformity, but now the sedimentary erosional surface has been tilted or folded before the younger strata are deposited on top. This results in titled layers, with deposition of straight younger layers on top of them. Nonconformity — a nonconformity involves an erosional surface that has been worn into metamorphic or igneous rocks. Much younger sedimentary layers then cover this erosional surface, leaving a time gap. Sedimentary layers can be found directly overlying much older igneous or metamorphic rock when layers have been eroded away. Geological Time In order to date the relative (comparative) age of a series of rock layers, it is very helpful to know the geological age of some of the rock layers, for example by using radioactive dating or index fossils. The largest blocks of geological time are called eras, which typically encompass hundreds of millions of years. The geological eras since 540 million years ago are the most useful, since they contain fossils. Our current era since about 65mya when the dinosaurs became extinct to present is the Cenozoic. The “age of the dinosaurs” was the Mesozoic, from about 250mya to 65mya, and the era before that was the Paleozoic (for “ancient life”) from about 540 mya to 250 mya. Eras are then broken into geological periods, blocks of time that typically encompass tens of millions of years. For example, you live in the Tertiary period of the Cenozoic, while Tyrannosaurus rex lived in the Cretaceous period of the Mesozoic. Periods can further be broken down into epochs and ages. Procedure: We will be trying to determine the relative age of 13 different rock layers shown in a cross- sectional diagram on the following page. Start by identifying the types of rock below as igneous, sedi y or phic. Use what you have learned previously in the course. Type of Rock Information - Table 1 Rock Type on Rock Type — Igneous, Sedi Diagram S Ss (a, band c) sandstone Sedimenary Cg conglomerate Sedimendrary [Sh(aandb) [shale | Sedienentacy Qa {w Nent+aryd siltstone Dedimentary | andesite | diorite granite | schist | Lm (a and b) Spring 2022 GEL 109 Age Information Table 2 — we have age information for some of the layers. Complete either the period or approximate age range information on the table depending on which is missing, using the geological time scale. Put the ages on each component of the diagram on the following page, to help you order the events. Note the epoch column on the geologic time scale showing L for lower (youngest), M for middle and E for early (oldest) to help you narrow down ages. | Period | Approximatéfir* Fossils in Ssa are lower Eocene Paleogene | epoch (Ypresian) Fossils in Lmb are middle Carboniferous Pennsylvanian epoch Fossils in Ssc are lower Ordovician | Ordovician period Zircon in granite (Gr) is ~600Ma diacaran 620 Ma - 542Ma | Zircon in Diorite (Di)is~260Ma___ | {Jex mian 260 Ma - 254Ma | Biotite in Andesite (V) is ~450 Ma o¢ dovician 455 Ma - 446Ma | Zircon in the conglomerate (Cg) is | 620 Ma - 542Ma } ~600 Ma | Ediacoran Cross Section Diagram