Some of these questions must be answered by consulting your textbook which correlates with the video series. Consult: "Physical Geology -Earth Revealed" by Carlson, Plummer and McGeary; published by McGraw Hill, New York City, NY
Quiz #3 Review
You may want to review chapters 8 (time and geology), 12 (weathering and soils), 13 (mass wasting), 14 (sediments and sedimentary rocks), 15 (metamorphism), 16 (streams) and the relevant videos that go along with these chapters.
We discussed absolute and relative time. Absolute time uses radioactive decay to give an actual date. C14 is an isotope which is used be archeologists; however, because of it's short half life and because carbon is a component of organic tissue (not rock usually), it has only limited use in Geology, U235 is more commonly used to date certain rocks. As the parent decays, the daughter product (lead in the case of U235) increases.
Relative time uses the basic laws of geology such as law of supperposition, original horizontality, cross-cutting relationships to obtain an order to past geological events. Sedimentary Rock A is older than Sedimentary Rock B because it is beneath Rock B. I handed out a sheet that had a variety of cross-section sketches and showed how dikes, contact metamorphism, unconformities and inclusions could all be used to obtain relative ages of rock units.
By the way, a rock unit that has certain characteristics that is geographically widespread is called a "formation". We learned a bit of Long Island Geology when I sketched the formations of rock (actually unlithified sediment) which, in some cases can be traced to outcrops of clay or sand in New Jersey. The Magothy Formation and Raritan Formation are examples of such Long Island/New Jersey formations. These are Cretaceous in age (the last geological period of the Mesozoic era).
Sometimes sandstone and conglomerate cemented with hematite can be found eroded out of the Cretaceous material, its not all just sand and clay but there are some beds where the sediment has been lithified (turned into rock). Sometimes ancient tropical wood and leaf imprints can be found in this material but, for the most part it is hidden under Glacial Till and Outwash.
Remember the Eras: Pre Cambrian, Paleozoic, Mesozoic and Cenozoic and the Periods: C, O, S, D, M, P, P, T, J, C, T, Q. The Paleozoic begins with the Cambrian explosion and seas suddenly teamed with multicellular invertebrates, many with hard shells that could be fossilized and preserved (mostly in sedimentary rock). There were major extinctions at the end of the Permian and at the end of the Cretaceous. The dinosaurs went extinct at the end of the Cretaceous. Iridium, a rare element seen in asteroids (in space) is suspiciously enriching a thin deposit of clay that closes the Mesozoic Era (T, J, C are the 3 periods of the Mesozoic).
It's interesting to note that the formations below the glacial material on the surface of Long Island are Cretaceous in age. Since the Glacial sands and gravels are Quaternary (pleistocene epoch) there is a major unconformity between the 60 million year old Magothy and the 60,000 yr. Ice Age deposits. Missing beneath LI is the entire Tertiary which is found along the Atlantic Coastal Plain from New Jersey south to Florida.
We were able to search through Tertiary (miocene epoch) material about 20 million yrs of age and deposited along the east coast of what is now the US in a warm, tropical shallow sea. From the fossils found, we see an aquatic community of diverse sharks, corals, sting rays and crocodiles.
I got a little carried away and told you about the glacial till (unsorted sediment- various sizes) which was bulldozed by the massive continental glacier from the north and left here making up the Harbor Hill Moraine on the north shore and the Ronkonkoma Moraine which extends along the middle of LI to Montauk. The two forks of LI are there two moraines. The lighter sands and gravels washed out from the moraines to the south where we find outwash (many farms are located on outwash from the Harbor Hill, the central pine barrens is located especially on the outwash from the Ronkonkoma Moraine.
Mass Wasting is a process we can see on Long Island. We dont experience rock slides (off Long Island especially where rock has been blasted to make level road beds in building the interstate) and we dont experience mudflows (when volcanic activity melts the ice on top which then mixes with layers of ash on the slopes of the volcano). The flows can move for miles at 20-30 mph and have a consistancy of wet cement. We do experience Slumping. At Montauk and along the north shore the moraines are eroded by ocean/sound waves. This destabilizes the mass of sediment and slump blocks move downslope to be washed away at the base of the bluffs by waves. While problematic for the preservation of the Montauk Lighthouse and bluff-top homes, the erosion here provides the sand that maintains the beaches. When the bluffs are stabilized by gabions (wire cages filled with rocks), massive rock or sea walls, the amount of sediment to the beach is lessened, sometimes so much that the beaches begin to disappear. In order to have sand deposited as beaches you have to allow sand to erode.
We viewed mass wasting along the California coastline and hills of Southern California where "it never rains- it pours" and where human activity has accelerated mass wasting (gravity movement of rock/sediment downslope). The slowest mass wasting process is creep which happens on very low slopes.
Weathering happens "in place" and erosion implies transportation. Rock must be weathered before it can be eroded. Weathering cant happen to rock until it comes to the surface where it is exposed to "weather".
There is mechanical weathering which is simply rock broken up into smaller pieces and then there is chemical weathering where the rock is actually altered so that certain minerals change into other minerals or chemical forms. Chemical weathering can take place when CO2 and H2O in the air forms carbonic acid. Carbonic Acid makes rain naturally acid (5 on the pH scale). Such rain will slowly dissolve limestone, marble and more reactive mineral components of other rock. Sometimes industrial pollutants such as SO2 can also form acids that make rain even more acidic (acid rain). Acid rain can be harmful to farm productivity and the health of forest and aquatic ecosystems. Oxygen in the air can react with iron minerals in rock to cause the rock to rust (basalt may appear rusty brown on the outside- and then you crack it open to see the unweathered black color). Oxidation of iron-containing minerals can cause rock to crumble and can also produce new minerals in the process such as hematite and limonite. The hematite can be carried in groundwater and exentually, under certain conditions, cement sand grains together into sandstone. H2O, the universal solvent can work it's wonder dissoving minerals in rock. Some minerals become dissolved, some recrystalize into new forms, some like mica and feldspar can change into a different class of minerals called the clays.
Quartz as a component of rock, is hard and resists weathering. As other minerals weather away, quartz falls away as grains of sand. Most of what we see on the surface of LI and making up our beaches is quartz, it is so durable.
Mechanical weathering can include frost or ice wedging, exfoliation (common in granite masses), and even the roots of trees and actions of animals. There isn't any chemical alteration of the rock in this mechanical or physical weathering process. The big pieces simply break into smaller.
Soil takes time to form from the process of weathering. The text tells you about soil horizon A containing organic material (humus) and most fertile for plant life including food production, soil horizon C is below the top soil and subsoils and is in contact with the basement rock the soil if the soil was formed in place. Long Island soils are formed from glacial material deficient in carbonate rock therefore it is a acidic soil. For most food crops (and lawn grasses), it requires the application of crushed limestone in order to reduce the soil acidity (and raise the pH to a more neutral 7). Our pine barrens vegetation is interesting and unusual in that the plants do well in Long Island acidic soils.
I spoke about the greenhouse effect and the possibility of accelerated warming due to CO2 added into our atmosphere by burning fossil fuels and how this may cause sea level to rise as the glaciers covering Greenland and Antarctica to melt. During the Pleistocene Ice Age sea level was 350 feet lower than it is today- if all the present glacial ice were to melt, sea level would be about 150 feet higher than it is today, which means that thousand of Long Islanders would flock to Suffolk's Eastern Campus as one of the few points on LI which would escape being submersed!
The migration north of agriculture belts (such as the US Corn Belt or Wheat Belt) would probably not be possible because- to the north, the Canadian Shield has little soil covering since most was scraped off and transported to the south. This alone could cause catastrophic famine. But then, we are just speculating.
Whether you are inclined or not to react to greenhouse warming speculation (and I do not want to tell you my opinion- do your own research, look for facts, get the information you need to become informed) there have been and are problems with soil loss and degredation. The video we viewed showed footage of the depression era "dust bowl". You should know what natural causes along with human impact caused this massive loss of top soil and how the US Soil Conservation Service policies prevent future disasters like that. We also spoke of salinization of US soils in the arid southwest due to poor irrigation practices. I didn't mention "desertification", how farmland in many parts of the world where soil conservation practices are non existing, is becoming desert (in many ways like an extended "dust bowl" event.
I could go on and on about soil.
Oh yes, sedimentary rock. Lithification of sediments turn the loose stuff into rock, how? Compaction, consolidation and cementation of grains is the general way we think lithification happens. Know those sediments and the rocks they can form. Clastic rocks like sandstone are formed from sediment. Carbonate rocks like limestone are formed usually from marine life (shelled animals, calcareous algae, corals) and tends to contain fossils or indications of past life. Evaporite rocks such as rock salt and rock gypsum are formed where a body of water is subjected to long term evaporation. Looking at the sedimentary rock and applying the law of unifority can allow us to interpret the environment of deposition. Large scale cross bedded sandstone may indicate deposition as great dunes. Black shale with carbonized fern imprints may indicate deposition in a swamp.
Metamorphism can cause one kind of rock to change. Sometimes the change is subtle like in contact metamorphism which might take place along the base of a lava flow or it may be major with an entire new rock texture and new minerals forming in the process. Regional metamorphism is major. It happens when two plates collide. Heat, pressure and stress cause rocks to partially melt and flow, new minerals form and segregate into bands of light and dark, sometime they fold under stress. High grade metamorphism happens where there are the greatest stresses, as we move away from the plate contact, the grade of metamorphism is reduced. Garnets will form and grow in the process of metamorphism. Schistocity happens when platy minerals form (like mica, talk and chlorite) form in response to a particular direction of stress. Foliation includes schistocity- it simply means that there is a lining up due to metamorphic stress. Gneiss, schist, slate are foliated metamorphic rocks. Quartzite (was sandstone), marble (was limestone) are non foliated.
Streams: headwaters, mouth, tributaries, watershed (drainage basin), base level, load/capacity relationship, gradient, sand bars and bank cuts, meanders, oxbows, levees and divides. Lots of terminology involving rivers. Youthful rivers (Load < Capacity) have a high gradient, fast velocity, falls and rapids, erosional and downcutting. Mature rivers (Load = Capacity) are out of the mountains and out on the foothills, lower gradient and velocity, side-cutting, erosion = deposition, begins to meander, river bars (inner bend) and cut banks (outer bend). Old rivers (Load > Capacity) are depositional, they are sluggish (except when velocity increases due to added discharge such as snow melt) and meander across their flat floodplain. When they overflow their banks sediments are spread out over the flood plain (muddy silts and clays, organic material). The overflow can also cause a natural levee to form. Society tends to build artificial levees to prevent overflow (flooding the flood plain) because foolish people have built communities in the flood plain of major rivers. Meanders and oxbow lakes (cut off meanders) are characteristic of the flood plains of old rivers.
I mentioned that intermittant streams, seen as a dashed blue line on a topographic map, are occassionally dangerous if they fill with water from a torrential desert rainstorm. Perennial streams are sometimes fed by groundwater and springs which keeps them always flowing.
On the board in class I sketched a simple hydrologic cycle consisting of precipitation, runoff and evaporation. During a single rain event a great amount of erosion can happen due to sheet erosion even before the rain runoff gets to a stream channel. Making sure that soil surfaces are always covered by vegetation can minimize this.
We discussed groundwater in relation to caves, karst topography and I drew speleothems such as stalctites, stalagmites, columns and flowstone. Zone of aeration and zone of saturation and the water table separates them...a sink or sinkhole at the surface indicates caverns below which may be flooded. The material included on the exam will not cover Long Island Groundwater .
Is there more? You bet- but my fingers are tired.