Morgan HenryHomework 3

Layer 1: This layer is limestone, which is a sedimentary rock made mostly of calcium carbonate in the form of mineral calcite. It typically forms in warm marine envionments and is created by shell debris. Layer one is the oldest layer in Danforthia based on the law of superposition.

Layer 2: This layer is made of shale, which is a fine-grained sedimentary rock that forms when silt and mud are compacted. It is laminated, or made up of many smaller layers and splits easily along these. Layer 2 is second oldest in Danforthia.

Layer 3: Layer 3 is Danforthias next oldest layer, and is made of sandstone. Sandstone is made of sand grains od rock and organic material that have been bound together.

Layer 4: Layer 4 is made of shale and is the next oldest layer.

Layer 5: This layer is also made of sandstone.

Layer 6: Layer 6 is made of shale.

Layer 7: Layer 7 is the youngest layer, based on the law of superposition and is made of sandstone.

W: The layer between layers 4 and 5 is a basalt sill. A sill is a sheet intrusion that forms between layers of rock like those found in Danforthia. Basalt s fine-grained igneous rock made of plagioclase and pyroxene minerals and underlies a majority of Earths surfaces. This type of rock is formed in oceanic divergent boundaries, oceanic hotspots, of mantle plumes and hotspots found underneath continents.

X: This is a basalt dike. The dike cuts across layers of rock. It is extrusive, one form of igneous rock formation, which means that it was formed from magma that erupted to the surface and then cooled. The dike seems to be the most recent geological formation in Danforthia, as it is unaffected by any of the folding or fault alterations that affect the other rock layers.

Fault Y: This fault has fractured the layers in Danforthia. Its a normal fault in which the hanging wall goes down and the footwall goes up.

X: This is a Granite Pluton, which is a body of granite that was formed by an eruption of magma into the surrounding rock layers. The granite pluton is more recent than any of the surrounding layers of rock based on the cross cutting relationshipthe mass of granite cute through the other rock formations with the exception of fault Y and basalt dike Z which are both more recent than the pluton formation. You can see where it has displaced parts of layer 5, representing sandstone inclusions within the granite. Granite plutons are associated with volcanic areas, continental shields, and orogenic belts.

Fold A: This fold is an anticline that has older rock layers near the center of the fold. This seems to be a mostly symmetrical fold. Surface erosion has eroded parts of layer 5 and exposed the basalt sill. You can see the effects of the folds: the principle of horizontality tells us that the layers of rock were originally horizontal, but the folding that has occurred has caused them to bend.

Fold B: This fold is a syncline, with the younger rock layers closer to the center of the fold. This is a somewhat asymmetrical fold. Surface erosion has left the land mostly flat.

Summary:

Danforthia has a limestone base with various layers of shale and sandstone. Between shale layer 4 and sandstone layer 5, a basalt sill has formed. These layers have been folded by an asymmetrical syncline and a symmetrical anticline. These folds were formed due to some sort of permanent deformation, and are consistent with folding patterns due to compression. A granite pluton has erupted from beneath the surface, crosscutting the previously formed layers of rock. A normal fault has then cut across the layers and the pluton, shifting the hanging wall down and the footwall up. Finally, a basalt dike has vertically crosscut all previous formations in the landform.