JAC - 05-3 HW - Sedimentary rocks - guided inquiry (1)

.docx

School

University of North Dakota *

*We aren’t endorsed by this school

Course

101

Subject

Geology

Date

Dec 6, 2023

Type

docx

Pages

Uploaded by CommodoreFalconPerson959

1 Guided Inquiry: Sedimentary Rock Photos All photos are found at http://www.marlimillerphoto.com/Sed.html Go to that website for larger photos - you will want them to answer the questions below. The fifteen numbered questions refer to the 15 numbered photographs. SOME OF THESE QUESTIONS ARE VERY DIFFICULT WITH NO ABSOLUTELY CORRECT ANSWER. SO, JUSTIFY/EXPLAIN YOUR ANSWERS WHEN APPROPRIATE. 1. Look closely at the photo and you will see that the rock contains clasts of many different sizes. (a) What kind of rock is this(name it)? (b) The caption says that the original sediment was deposited in an alluvial fan . What does that mean? This rock is a tilted conglomerate, and being deposited in an alluvial fan means that it was deposited from material that was transported by flowing water and then deposited in a triangular fan shape, possibly at the base of a mountain. 2. This view shows sediment (it has not been lithified and turned into a rock yet) in a mudflow deposit. (a) What is a mudflow deposit ? How do such deposits form? (b) What kind of rock will this sediment become if it is lithified? A mudflow deposit is a poorly sorted mixture of silt, boulders, organic materials and other debris, and is a deposit that is collected when mud mixes with water and flows like a fluid down a slope. As the mudflow flows, it will leave behind deposits of mud, and when these deposits do eventually lithify, they can form mudstone, or shale. 3. The caption (or the photo) is upside down. Somebody goofed. This is sandstone above conglomerate. There is a sharp line that separates the two kinds or rocks. Why? How? How did sediment of two completely different sorts get deposited like this in distinct and adjacent beds? These two different kinds of sediments could have been deposited by a flow of water, that first started with a fast current and then slowed down over time. When the water was moving fast, large particles of rock would have been deposited, and then lithified to form a conglomerate, and then as the current slowed, only the fine material was carried and then deposited, and then lithified to form sandstone.

4. This photo is labeled a channel deposit . (a) What does that mean and (b) why does the rock contain both large (cobbles) and small (sand sized) clasts? A channel deposit is a deposit that was moved by a channel of water, such as a stream or river, and is typically made up of sand and gravel. This rock contains both large cobbles and small clasts, because its possible the water wasn’t moving very quickly, and so neither the cobbles or smaller clasts moved very far before being deposited. It is also possible that the channel deposit occurred at a delta. At a delta, large and small clasts may be deposited at the same time and lead to the different sized clasts in the rock. 5. The sediment that later became the rock seen (sandstone and shale) was deposited horizontally in a turbidite . Later it was tilted. (a) What is a turbidite and (b) why do turbidites often contain alternating layers of sand (that later become sandstone) and mud (that later become shale)? A turbidite is sediment that originates in an underwater canyon, as it gets disturbed, it creates dense slurries that flush down underwater canyons in a large gravity induced event. As the sediment flows to the base of the canyon, it gets deposited in sheet like layers. This flush transports coarser sediment to the ocean floor, and then the sediment settles based on density, with the heavier sediments settling first, such as sand, and the less dense sediments such as mud settling later, leading to the formation of different layers. 6. This photo shows eolian crossbeds in Utah. (a) What does eolian mean? (b) And how do eolian crossbeds form? Eolian refers to a deposit of windblown sediments, such as fine dust and sand. Eolian crossbeds form from wind that blows the sand and fine dust particles switching directions, leading to layers that may form at angles depending on which direction the wind was blowing when the sediment was deposited. 7. This outcrop shows ripple marks in a sandstone. (a) How do ripple marks form? There are two kinds: eolian and fluvial. They (sort of) form the same way. Explain both. Ripple marks are created as sediment grains pile up on top of a plane bed and are determined by flow type. Eolian ripple marks can occur when wind blows sediments such as sand into wave like or ripple like forms, such as sand dunes. Fluvial ripple marks are formed in much the same way, however they occur underwater, when the water currents flow and form fine sediment deposits such as sand into wave like or ripple like patterns. 8. This photo shows mudcracks in a kind of limestone called dolomite . How do mudcracks form? Mudcracks form from clay rich sediment that is submerged underwater and then dries out. As the clay’s crystalline structure fills with water, the grains of sediment will swell, and as they lose water, they shrink back up leaving behind deep polygonal cracks that taper to the surface.

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help