GEOLOGY 435 FIELD EXERCISE 2, SPRING SKETCHING, DESCRIBING, AND MAPPING EXPOSURES OBJECTIVES:

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1 OBJECTIVES: GEOLOGY 435 FIELD EXERCISE 2, SPRING SKETCHING, DESCRIBING, AND MAPPING EXPOSURES To develop and refine your field skills in: 1. observation and rock and sediment description 2. sketching and describing outcrops 3. locating yourself and in measuring attitudes, fold axes, and lineations 4. simple geologic mapping LOCATION: The field area encompasses coastal bluffs between the mouth of Redwood Creek and the rocky point approximately 1500 ft north of the mouth - see attached topographic map and oblique air photos. The area is part of Redwood National and State Parks; please do not use rock hammers or collect samples. Although the beach is wide, you should be aware of the waves and tide. We will be starting out at a rising tide (-0.8 ft). High tide Sat. Apr. 9 is just about 2:00 PM (~ 6.3 ft) EQUIPMENT NEEDED: Brunton compass Hand lens Colored pencils, 2H or 3h pencils, eraser, sharpener MATERIALS ACCOMPANYING EXERCISE: Oblique 2005 color airphotos of mapping area (2) Topographic map, 1:2400 scale, created from LiDAR image by Nick Graehl, modified by Andre Lehre Composite airphoto and map 1:2400 scale BACKGROUND: Bedrock exposed in the bluffs north of the mouth of Redwood Creek is Redwood Creek schist. This unit, correlative with the South Fork Mountain schist, is part of the Franciscan Assemblage. The Redwood Creek schist is typically a light-green to dark grey phyllite or fine-grained schist consisting largely of quartz, chlorite, white mica, and albite (Harden et. al 82; Cashman et. al ( 86, 95). The schist is commonly metamorphosed mudstone and metagreywacke, but locally includes metabasalt and metamorphosed tuff. 1. Preliminary walk-through We will start by walking together through the study area so that you all become familiar with the rocks and structures. We ll start at the south end of the bluffs and walk north up the beach as a group. I ll point out particular exposures that merit careful study. When we reach the prominent outcrop at the north end of the mapping area, you can begin your descriptions and measurements, and work your way south toward the vehicles. We should all be back at the vehicles by 2:30 PM. 2. Field measurement of attitudes and mapping and description of the bedrock exposed along the beach north of the mouth of Redwood Creek. You will start where we end our walk up the beach. Work back down the beach toward the mouth, keeping track of your location on the oblique airphotos, composite map/photo and the topographic map. a. Measurement of bedrock attitudes: At the two exposures I indicate, and also wherever you find an exposure that reveals geologic structure: 1. Locate your position on the airphoto and map. Number your locations sequentially in the notebook beginning with 1 at the north. Mark your numbered positions on the oblique airphoto(s) and the vertical airphoto. 2. At each location examine the bedrock and measure any of the following you can recognize: Strike and dip of bedding and/or foliation Strike and dip of faults, jointing, cleavage, or planar veins filling joints Trend and plunge of lineations or fold axes 3. Record orientation measurements neatly in a table in your notebook. 4. Plot representative foliation and lineation measurements for each station on the topographic map at the correct locations, using the appropriate symbols from Compton (p )

2 b. Bedrock description and sketch at the two outcrops I indicate: 1. make a careful lithologic description of the bedrock. Descriptions should be clear, concise, and informative. Lithologic descriptions should include: overall color and appearance degree of weathering -- how hard is the rock, is it friable, what does it break down to if it's pretty weathered? particle/grain size texture (foliated, non-foliated ) mineralogy -- what minerals can you see in it, if any? any sedimentary features observable: grain size, rounding, sorting, stratification (well-laminated? massive?) type of rock -- give it a name! 2. describe of the outcrop and its structural features such that a person who has never seen the outcrop could read it and understand what you saw Outcrop descriptions should include (but are not limited to): attitude (strike & dip) of bedding and/or foliation how obvious is bedding? how strongly developed is foliation? is there more than one direction of foliation? how are foliation and bedding related (e.g. parallel, crossing at 90, or what?) is there any folding? how does it relate to foliation? is there more than one set of folding? what is the attitude (trend & plunge) of any fold axes how fractured is the rock? is it massive? are there any joints? are they closely or widely spaced (give dimensions)? is there more than one joint direction? what is the attitude of the joints? are there vein-fillings of joints? if so, what is their orientation (strike & dip)? are they folded or faulted? how continuous are they? 3. make a simple annotated/labeled geologic sketch of the outcrop showing the features you measured/observed c. Geologic outcrop map (on the topographic base map) -- to be made as you work your way down the beach: There are two geologic units that I want you to map: 1) outcrops of Redwood Creek schist (KJfr), and 2) cones of talus (Qtal). 1. Locating yourself: At each outcrop or feature to be mapped, carefully locate yourself by inspection of topography, and by using the oblique and composite airphotos. 2. Outcrop mapping: On your composite topographic map/photo, draw the boundaries of the schist outcrops in the bluffs and large blocks on the beach. You can use the vertical and oblique airphotos to help you. You can use pacing to help measure horizontal dimensions. Vertical extent will have to estimated either by eye, or by the combination of pacing a distance normal to the bluff and then taking a vertical angle with the Brunton. On your map lightly color these green. 2. Talus mapping: On the composite topographic map/photo, draw the boundaries of the cones of bare talus and slope debris. Lightly color these yellow. Do not map vegetated slopes as talus. 3. Landslide scarps: If you recognize any landslides, draw in the boundaries of their head and side scarps using the symbol below:

3 WHAT YOU WILL NEED TO TURN IN Due date: All materials are due no later than 5PM on Friday, April Field notes: A clear, readable photocopy of your field notes and sketches. This should be the original notes, not recopied ones. 2. Observation locations: Oblique airphoto(s) with station locations correctly shown and neatly numbered and keyed to notebook. 3. Field map: The map you prepared in the field on the topographic map base. 4. Geologic map: Transfer your data from the field map/photo to the office copy of the map. This geologic map should show: 1) all attitudes correctly plotted and inked at sites where they were measured; and 2) outcrop and talus boundaries neatly plotted and inked. Label schist outcrops KJfr and lightly color these green. Label the talus cones and slope debris Qtal and color them yellow. Show any lanslide scarps using the symbol above. Use Compton to be sure you are using correct symbols (i.e., for bedding, foliation, jointing, cleavage, lineations, fold axes) Note: use a very fine pen for inking. 5. Lithologic and outcrop descriptions For each one of the two outcrops, turn in a) a typed, clearly written lithologic description (see b1 above) and b) a clearly written outcrop description (see b2 above). These should be single-spaced and should be a maximum of 2 pages for each outcrop. (That is, no more than 4 pages for the whole works.) I expect that you will use good English and complete but concise sentences. 6. Evaluation sheet on last page of this lab REFERENCES Harden, D.R, H.M. Kelsey, S.D., Morrison, and T.A. Stephens, Geologic map of the Redwood Creek drainage basin, Humboldt County, California: US Geological Survey Water-Resources Investigations Open -File Report Cashman, S.M., Cashman, P.H., and Longshore, J.D., 1986, Deformation history and regional tectonic significance of the Redwood Creek schist, northwestern California: Geological Society of America Bulletin, v. 97, p Cashman, S.M., H.M. Kelsey, and D.R. Harden, Geology of the Redwood Creek Basin, Humboldt County, California: US Geological Survey Professional Paper 1454-B, p. B1-B13.

4 EVALUATION OF REDWOOD CR MOUTH MAPPING EXERCISE Name: Notebook: organization, neatness & readability (10) Points Notebook: completeness & relevant detail, descriptions (10) Airphotos: observation station locations: (10) Map: contact accuracy : (10) Map: detail & coverage: (10) Map: attitudes: (10) Map: presentation, neatness: (10) Rock unit and outcrop descriptions (30) Total

GEOLOGY 470 FIELD EXERCISE 3, SPRING SKETCHING, DESCRIBING, AND MAPPING EXPOSURES

GEOLOGY 470 FIELD EXERCISE 3, SPRING 2009 -- SKETCHING, DESCRIBING, AND MAPPING EXPOSURES 1 OBJECTIVES: To develop and refine your field skills in: 1. observation and rock and sediment description 2. sketching