GEOL 152 - Lab 9

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Lab 9: Stratigraphy — Telling Time from Rock Part I Constructing a Correlation Chart The stratigraphic occurrence of several different types of fossils is available from the five sections you will be correlating. The first is a group of microfossils called Foraminifera. These organisms are closely related to amoeba (foraminifera can be thought of as mocbas'wnh‘shclls). Some species live as plankton, consuming single-celled algac and other microorganisms in oceanic surface waters. Others live as bemthos (on the sea floor), consuming organic detritus in the sediment. The chart on the next page provides the names and stratigraphic ranges of foraminfera you will need to carry out this activity. Examine the large-scale models of foraminifera. Draw and label two distinct types of foraminifera in order to help you remember what they look like. (12 points/6 cach). firo(l(,l.«(a.u« H‘ . o T - TJurassi ¢ g uf’[’"“ €ocene

Lab 9: Stratigraphy ~ Telling Time from Rock 6.) In each of the five sections, use the biostratigraphic ranges of each of the macrofossil bluge pencil. species to delineate biostratigraphic zones. Indicate the contacts between zones using a 7.) Using a blue pencil, draw correlation lines connecting the macrofossil biostratigraphic intervals, 8.) Finally, using a pormal, grav pencil, correlate lithologies between adjacent sections. Keep the following in mind: a. Lithostratigrahic correlations cannot cross unconformities (red lines), but they can cross the boundaries of biostratigraphic zones (blue lines). from the decp ocean). b. Lithologic beds can pinch out between sections. Sandstones will tend to pinch out castward (away from land) and mudrocks will tend to pinch out westward (away 9.) Color in the sandstones yellow and the mudrocks green (these are the conventional color choices used by stratigraphers). This will help you see the sedimentary architecture of the stratigraphic succession. : ion i 1.) What intervals of geologic time plain exposed? were times of major sea level fall that left much of the coastal M A €Ly ene s MaA Miocewne 2.) What intervals of geologic time were times of high relative sea level that flooded much of the coastal plain? ( ) \NC (veta ous 10 a\kvl &k 3.) Why does the unconformity formed during the pre-middle Eocene disappear between wells OT-30 and OT-7? ( o £

Lab 9: Stratigraphy - Telling Time from Rock 4) Which unconformitis appear o be angular unconformities? (Number the unconformitics starting with the oldest or use geologic time periods to label them) Part 11. Wheeler Diagram. ) ) Sedimentary rocks accumulate through time, but they do not record time continuously or al a constant rate. The result is that different columns recording the same duration can have very different thickness (as should be evident from your cross-section). To understand the B relationship between distinct events in geologic history and quantify actual rates of change, it 1S necessary 1o convert from the rock thicknesses depicted in a stmignghic cross-section to ime. i hi f the lab i ship b lationship DEIWEOEN S 1 ST thickness and time. In the lower Iefiofwnaos-section.thacisafiamewo«k for 2 Wheeler diagram, a chart indicating what kind of rock was being deposited at what time at cach location (these are sometimes called rock fime diagrams). The x-axis represents distance (just like the cross- section) and includes all five of the stratigraphic columns that you have correlated. However, unlike the cross-section, the y-axis represents time rather than thickness. For your convenience, intervals of the geologic time scale have been marked at their correct ages. 1.) With a blue pencil, mark the boundaries of foraminiferal biostratigraphic zones along the right-hand margin of the time-rock chart. 2.) For each of the five columns, mark the beginning and end of intervals during which rock was deposited and is preserved. 3.) Using the allostratigraphic correlations from the correlation chart as a guide, tie the five columns together on the Wheeler diagram (i.c., which rock intervals at a given section connect to which ones in the adjacent sections). Remember that although unconformities have no thickness in rock, they represent durations of time, so they will be intervals on this diagram that can change duration from column to column. Color unpreserved time corresponding to unconformities light gray. 4.) Using your cross-section as a guide, draw in the macrofossil biostratigraphic zone boundaries using a blue pencil. 5.) Using your cross-section as a guide, draw in and color the distribution of carbonates in time (use orange).