Examples of Teaching with Visualizations
May 9, Independent dating techniques have established that the H. naledi fossils are the later parts of the Pleistocene in Africa, and indicate a much younger age of a single species of an ancient human-relative discovered in Africa. . with fine sand containing small-scale ripple cross laminations and rodent. The geologic cross section below, illustrates a series of rock layers as they the relative ages we use the four fundamental principles of relative age dating that. Base your answers to questions 1 and 2 on the cross sections of three rock outcrops, A, B, and C. . The large cone-shaped mountain on Earth's Which statement correctly describes the relative ages of rocks A and C and gives the best supporting evidence from the .. accurately dating the age of a rock is the isotope's.
Recognizing and mapping faults using lidar and field data part of Structural Geology: Activities In this activity, students create a geologic map and cross-section of the Fish Springs cinder cone and surrounding area in the Owens Valley, CA, using a high-resolution DEM developed from airborne lidar data as a Teaching the Methods of Geoscience: Activities This activity requires students to explore a range of datasets that help substantiate Plate Tectonic Theory.
How Many Is A Million? Visualizations with Teaching Notes Roger Steinberg, Department of Natural Sciences, Del Mar College Description To help students visualize the immensity of geologic time, or even the immensity of just one million years, I have created a very large Examples In this series of visualizations and accompanying activities, students visualize the distribution and magnitude of earthquakes and explore their distribution at plate boundaries.
Earthquakes are visualized on a 3D This, along with the increased recognition of the utility of fossils in interpreting rock successions, made it possible to begin addressing the question of the meaning of time in Earth history. Determining the relationships of fossils with rock strata The hypothesis of fossil succession in the work of Georges Cuvier During this period of confrontation between the proponents of Neptunism and uniformitarianism, there emerged evidence resulting from a lengthy and detailed study of the fossiliferous strata of the Paris Basin that rock successions were not necessarily complete records of past geologic events.
In fact, significant breaks frequently occur in the superpositional record. These breaks affect not only the lithologic character of the succession but also the character of the fossils found in the various strata. Indeed, they seemed to represent extinct forms, which, when viewed in the context of the succession of strata with which they were associated, constituted part of a record of biological succession punctuated by numerous extinctions.
These, in turn, were followed by a seeming renewal of more advanced but related forms and were separated from each other by breaks in the associated rock record.
Cross sections of folded and dipping beds
Whatever the actual cause, Cuvier felt that the evidence provided by the record of faunal succession in the Paris Basin could be interpreted by invoking recurring catastrophic geologic events, which in turn contributed to recurring massive faunal extinction, followed at a later time by biological renewal.
In the course of evaluating various natural rock outcroppings, quarries, canals, and mines during the early s, Smith increasingly utilized the fossil content as well as the lithologic character of various rock strata to identify the successional position of different rocks, and he made use of this information to effect a correlation among various localities he had studied.
The consistency of the relationships that Smith observed eventually led him to conclude that there is indeed faunal succession and that there appears to be a consistent progression of forms from more primitive to more advanced.
As a result of this observation, Smith was able to begin what was to amount to a monumental effort at synthesizing all that was then known of the rock successions outcropping throughout parts of Great Britain. With this, it now became possible to assume within a reasonable degree of certainty that correlation could be made between and among widely separated areas. Smith, WilliamWilliam Smith, engraving, The application of the ideas of Lyell, Smith, Hutton, and others led to the recognition of lithologic and paleontologic successions of similar character from widely scattered areas.
It also gave rise to the realization that many of these similar sequences could be correlated. Not convinced that catastrophes caused massive and widespread disruption of the biota, Lamarck preferred to think of organisms and their distribution in time and space as responding to the distribution of favourable habitats.
If not, they became extinct. Moreover, his view that organisms respond to the conditions of their environment had important implications for the uniformitarian approach to interpreting Earth history. The concepts of facies, stages, and zones Facies During the latter half of the 18th and early 19th centuries, most of the research on the distribution of rock strata and their fossil content treated lithologic boundaries as events in time representing limits to strata that contain unique lithology and perhaps a unique fossil fauna, all of which are the result of unique geologic processes acting over a relatively brief period of time.
Hutton recognized early on, however, that some variations occur in the sediments and fossils of a given stratigraphic unit and that such variations might be related to differences in depositional environments. He noted that processes such as erosion in the mountains of Scotland, transportation of sand and gravels in streams flowing from these mountains, and the deposition of these sediments could all be observed to be occurring concurrently.
At a given time then, these diverse processes were all taking place at separate locations. As a consequence, different environments produce different sedimentary products and may harbour different organisms.
This aspect of differing lithologic type or environmental or biological condition came to be known as facies. Shark The significance of the facies concept for the analysis of geologic history became fully apparent with the findings of the Swiss geologist Amanz Gressly. While conducting survey work in the Jura Mountains inGressly observed that rocks from a given position in a local stratigraphic succession frequently changed character as he traced them laterally.
He attributed this lateral variation to lateral changes in the depositional environments responsible for producing the strata in question. Having no term to apply to the observed changes, he adopted the word facies. While Gressly employed the term specifically in the context of lithologic character, it is applied more broadly today.
As now used, the facies concept has come to encompass other types of variation that may be encountered as one moves laterally e. Lithologic facies, biological facies, and even environmental facies can be used to describe sequences of rocks of the same or different age having a particularly unique character.
Stages and zones The extensive review of the marine invertebrate fauna of the Paris Basin by Deshayes and Lyell not only made possible the formalization of the term Tertiary but also had a more far-reaching effect. The thousands of marine invertebrate fossils studied by Deshayes enabled Lyell to develop a number of subdivisions of the Tertiary of the Paris Basin based on the quantification of molluskan species count and duration.
Lyell noted that of the various assemblages of marine mollusks found, those from rocks at the top of the succession contained a large number of species that were still extant in modern environments. We also discuss implications of this cross-sectional reconstruction for the timing and style of extension in the northeastern Great Basin and its importance to mineralization processes and mineral exploration at Spruce Mountain. It is significant that this belt of rocks is also within a zone of metamorphic core complexes that characterizes the eastern fringe of the hinterland of the Mesozoic Sevier fold and thrust belt Fig.
Cordilleran metamorphic core complexes, which are exposures of formerly deeply buried mid-crustal and lower crustal metamorphic-plutonic rocks, are the iconic landforms of extended crust Crittenden et al.
In proximity of Spruce Mountain, crustal thickening events, perhaps Late Jurassic to Late Cretaceous in age, are recorded by thrust faults and regional metamorphic rocks exposed in the Ruby Mountains—East Humboldt Range to the northwest, in the Wood Hills to the north, and in the Pequop Mountains to the northeast Thorman, ; Howard, ; Snoke and Miller, ; Hudec, ; Camilleri and Chamberlain, Thermobarometry and thermochronology data from the East Humboldt Range and the Wood Hills suggest that a decompression event may have occurred there as early as the Late Cretaceous, which may reflect the onset of crustal extension in northeastern Nevada Hodges et al.
However, work has also underscored the importance of middle Miocene extension in the region e. Spruce Mountain exposes Ordovician to Permian miogeoclinal sedimentary rocks Fig.
Lower Paleozoic rocks exposed at the deepest structural levels may have reached greenschist facies metamorphic grade Camilleri and Chamberlain, Throughout most of the district, the Paleozoic rocks dip to the east at moderate to steep angles, but in some fault blocks in the northern part of the district, Paleozoic rocks dip consistently westward Fig.
Cenozoic volcanic and sedimentary rocks unconformably overlie Paleozoic rocks at Spruce Mountain. A southeast-dipping Cenozoic dacite tuff crops out near Cole Creek on the eastern side of the district and overlies Permian and upper Pennsylvanian rocks Fig. Sedimentary rocks that crop out in the southwestern corner of the district Fig. Although intrusive rocks constitute only a small fraction of the surface exposures at Spruce Mountain, a variety of intrusive rocks have been observed in the district Fig.
Prior to this study, there were no radiometric ages on intrusive rocks from Spruce Mountain.
However, in nearby ranges, most igneous rocks range from Jurassic through late Eocene in age e. Six samples that represent many of the igneous rocks known at Spruce Mountain were selected for U-Pb zircon geochronology Baril, and are described in Appendix 1. Igneous rocks with a fine-grained groundmass are assigned volcanic rock names whether extrusive or shallow intrusivewhereas coarser grained porphyritic and equigranular rocks are given plutonic rock names. Hypabyssal rocks may have either a volcanic or plutonic name, depending on grain size.
Sample locations are listed in Table 1 and plotted in Figure 3A.
Geochronology | Earth science | thebluetones.info
Table 1 also lists the stratigraphic hosts of each sample; this bears on the possible depth of emplacement of the intrusions, as well as the alteration-mineralization characteristics of each sample, which are relevant to evaluating the age of alteration mineralization. Analytical methods and reporting procedures are described in Appendix 2and results are summarized in Table 1.
Late Eocene Rhyolite An east-west—trending dike or band of dikes of late Eocene rhyolite porphyry and quartz-rich breccias cuts across the northern side of Spruce Mountain, crossing the range at a pass near the Kille mine Figs. Seedorff, personal data; Baril, This sample is potassically altered and cut by quartz veins with minor molybdenite Figs. Henry,written commun. Samples from the vicinity of the Standard mine on the western side of the district Figs. Undated Intrusive Rocks In addition to the intrusive rocks dated as part of this study, several other occurrences of undated igneous rocks have been reported at Spruce Mountain.
A lamprophyre dike of unknown age was observed in the underground workings of the Black Forest mine Fig. Small, altered dikes also crop out on Banner Hill Fig. Our geochronologic data and mapping indicate that the porphyry moldybdenum deposit formed in the late Eocene, ca.
Skarn and carbonate replacement deposits were first discovered in the Spruce Mountain district inand there was at least small production from these ores for most years between and Hill, ; Schrader, ; Smith, ; LaPointe et al.
The district historically has been mined for lead and silver, with subordinate zinc, copper, and gold, from small underground mines, including the Ada H, Banner Hill, Black Forest, Keystone, Kille, Monarch, Paramount, and Standard Fig. The principal hypogene ore minerals are argentiferous galena, tetrahedrite, sphalerite, chalcopyrite, pyrite, arsenopyrite, and minor bornite Schrader, Scheelite occurs at the Atlantic prospect, which is a few hundred meters west of the Black Forest mine Stager and Tingley, Supergene phases include cerussite, anglesite, malachite, and chrysocolla along with lesser amounts of wulfenite, calamine, and smithsonite.
Oxidation extends to depths of 70 m or more, and most of the production was from supergene-enriched carbonate ores that contain higher silver contents than sulfide ores LaPointe et al.
A map of alteration-mineralization products is shown in Figure 3Bwhich complements the companion geologic map Fig. As shown on these maps, a belt of skarn, quartz-rich breccias, and local hornfels is discontinuously exposed at the surface along the east-west—trending band of silicic porphyry dikes, but hornfels is absent and skarn is mostly supplanted by jasperoid and carbonate replacement and fissure vein deposits in calcareous rocks at the eastern end of the band Hope, ; LaPointe et al.
At the surface, the porphyry dikes are variably altered but have rare quartz-molybdenite veinlets with associated potassic alteration and locally exhibit quartz-sericite-pyrite alteration. In contrast, the skarns consist principally of garnet, pyroxene, actinolite, and fluorite Granger et al. Seedorff, personal data; LaPointe et al. Skarn is localized around the porphyry dikes.
Copper and local tungsten are mostly restricted to skarn; zinc grades generally decrease toward porphyry dikes Schrader, Lead and silver grades are highest in fissure fillings, commonly in marble or limestone LaPointe et al.
Both skarn and altered igneous rocks are enriched in tin, tungsten, and fluorine E. Seedorff, personal data; Tingley, ab. Complete results are not publicly available, although published cross sections showing selected results suggest that a well-mineralized area occurs near the Kille mine American CuMo Mining Corporation, in the footwall of a steeply dipping normal fault probably the West fault; Fig.
In recent years, this part of the district has been controlled by Mosquito Gold Mines Limited, now known as American CuMo Mining Corporation; this company reports molybdenum intercepts copper grades not reported from 5 of the historic drill holes that are — m in length American CuMo Mining Corporation, The average grades in each of the 5 intercepts range from 0.
A length-weighted average of these intercepts, which might be a rough estimate of the average grade of the resource, is 0. Molybdenum is preferentially localized in porphyry dikes, whereas copper is concentrated in adjacent skarns American CuMo Mining Corporation, and appears to be best developed in Pennsylvanian Ely Limestone. Lead, zinc, and silver preferentially occur in carbonate replacement deposits and fissure veins in limestones and other calcareous and dolomitic rocks, especially of Pennsylvanian—early Permian age.
Descriptions of underground exposures e. Likewise, porphyry-related skarn mineralization at least locally occurs adjacent to dikes and along faults Schrader,and brecciated quartz veins occur within the Prospect fault Figs.
There are several textural varieties of porphyritic rhyolite and rhyolite porphyry at Spruce Mountain. Analogies with porphyry molybdenum deposits elsewhere in the world e. Although some crosscutting relationships between faults and rhyolite intrusions are known Table 2other relationships remain to be determined. The spatial and genetic relationship between various rhyolite porphyry dikes and porphyry-related mineralization also is only weakly constrained see Table 2. Therefore, it is not possible to determine whether porphyry-related mineralization was genetically related to intrusions as old as