Geol 5, Lab #6: Sea-floor Spreading and Plate Tectonics (Access is reserved to SMC students only)

Verificaton of Sea-Floor Spreading

question 1, page 58

DSDP hole 105: Brotzenia, Lenticulina, Bairdia, Saccocoma
DSDP hole 10: Globotruncana forn., Globigerina, Globotruncana maya
DSDP hole 11: Orbulina, Uvigerina, Globigerina, Globorotalia
DSDP hole 137: Globotruncana maya, Lenticulina, Hedbergella

question 2 part A, page 58
Always indicate ages from older to younger, with either relative or numerical methods.

DSDP hole 105: Middle Oxfordian to Top Kimmeridgian
DSDP hole 10: base Campanian to Middle Maastrichtian
DSDP hole 11: Lower Miocene to Middle Miocene
DSDP hole 137: (for this question, you were asked not to consider Globotruncana maya) Middle Albian to Middle Cenomanian

question 2 part A, page 58

DSDP hole 105: 158 my to 152 my ago
DSDP hole 10: 84 my to 72 my ago
DSDP hole 11: 21 my to 15 my ago
DSDP hole 137: 106 my to 95 my ago

question 3, page 58

DSDP hole 105: 156 my
DSDP hole 10: 81 my
DSDP hole 11: 18 my
DSDP hole 137: 99 my

question 4, page 58
Ages measured through magnetic reversals are still related to radiometric dating of the oceanic crust. As a consequence, the age measurement error would fall in the range described in the question. Dating with fossils actually allows for a refinement of said measurement

question 5, page 58
Just label the isochrones and play with the figure if you want. There are no answers you need to provide for this question

question 6, page 58
Distance from DSDP Hole 11 to the Ridge: 8 mm. Scale is 1 mm = 20 km, so 160 km
Age (time) is 18 million years
Rate is 160 km / 18 my, or 0.89 cm/yr

question 7, page 58
DSDP hole 105 is at 156 my ago. DSP hole 10 is at 81 my ago. The difference is 75 my (time)
Distance between the two is 55 on the map. Scale is 1 mm = 20 km, so 1100 km
Rate is 1100 km / 75 my, or 1.47 cm/yr

question 8, page 58
The distance is 120 mm. Scale is 1 mm = 20 km, so 2400 km
At a rate of 1.47 cm/yr, the age of the crust at the 2000-m depth line is approximately 163 million years

question 9, page 58
Because coarse terrigenous sediment, such as sand, cannot be transported to the middle ocean, except for extraordinary situations (Sahara desert sands have been found in isolate spots at the ocean bottom, following strong wind storms, but they are an exception, not the rule). The only terrigenous sediment found at greta depth is clay, which would only show up as a sediment when chalk or chert are not present. Otherwise it would be diluted into them.

question 10, page 58
Yes, such a find would invalidate the hypothesis