Sedimentary Rocks Identification Assignment. For Part 2 of this assignment, you

Question

Sedimentary Rocks Identification Assignment.

For Part 2 of this assignment, you need to compare the environments listed in table 2 and the descriptions and rock names you listed in Part 1.

Note: I have already done Part 1 of this assignment and provided Part 1 Sedimentary Rocks Table and the environments listed in table 2 below. The lines that need to be filled in is provided below also.

Part 1 Sedimentary Rocks Table:

Table 2:

Lines that need to be filled in/out for each sedimentary rock sample that is provided in Part 1 Sedimentary Rocks Table:

Rock Nam e Other ROCK SAMPLE ROCK TYPE | COMPOSITION | TEXTURES Grain Size Shape, ect) Observations Mostly quartz Mostly sand Quartz grains (weatheredmm) from other rocks) Clastic Presence of (1/16 mm-2 Sandstone some dark mineral/rock fragment. Clastic Shale Mostly rock Mostly clay and mineral(K1/256 mm) fragments (weathered from other rocks) Splits easily fissile Biogenic Mostly shells Poorly Commonly marine environment. Coquina consolidated mass of shells & shell fragments or shell fragments may or may not be visible with the naked eye) and/or very fine- grained calcite (mud); effervesces in acid Scratches glass; conchoidal fracture Chemical Mostl Microcrystalline Chert varieties of quartz (chalcedony, flint, opal etc Clastic Mostly rock Mostly gravel Conglomerate Rounded and mineral(2mm) fragments (weathered from part can be minerals or

Explanation / Answer

G : Possible environments could be Beach clastic environment and Shallow sea clastic environments. In the beach environments if there is any source of clastic materials Quartz Sandstone could form. The continuous swash-backwash effects near the shoreline makes the grains rounded and well sorted because the clay materials are removed by high energy of currents effecting perpendicular to the beach. Also the longshore currents carry sediments parallel to the beach transports sand grains to long distance. In Shallow sea environments, the effect of waves makes the environment high energy which transport sand grains to the strand plains and barrier bars and the mud is removed by the high energy currents. Quartz is the most resistant mineral so it remains and other materials get breakdown. Along with Quartz, some other materials like heavy minerals generally dark in colour also present due to high resistance.

H : Shale is a sedimentary rock contains mostly clay size particles and clay minerals having paralle arrangement which forms the fissile planes. Generally forms in quite environment, so the possible environments are Deep sea clastic environment and Lake clastic environments. In Deep water regions the water depth is so much that wave or tide action are not effective and the energy condition is very low. So the low energy currents can only carry fine grained sediments in suspension. They don't have sufficient energy to carry the sand. Generally known as pelagic clay minerlas falls on the suface and due to overburden pressure from succesive sediments gets arranged in parallel to each other and forms lamination. Same is the case with Lake clastic environments generally seen in large lake bodies. The energy condition is quite. Material falling from the nearby slopes, only the clays are transported to inner parts and form shale bodies. Shale could also form in River environments, Delta environments but in very less amount where the energy condition is low like in river floodplains.

I : Coquina is an interesting rock forms in Biogenic Reef environment. These are mostly limestones i.e made up of calcium carbonate in chemical composition. They form in the famous carbonate reefs made by the secretion of chemicals form making shells by the various organism. They are generally made by bounding of the shelly materials. Some of the organisms make these type of carbonate barriers in reef. They could be fine grained or coarse grained depending on the type of organisms making the shells (microscopic organisms like foraminifera, calcareous or macroscopic organisms like bivalves). They form by stacking of shells one above the another and bounded by carbonate mud which acts as the cementing material.

J : Chert is a fine grained rock mostly made up of fine grained varieties of quartz and mostly composed of siliceous material. These are generally form in Deep sea chemical environment. Fine grained varieties of quartz like flint, opal etc. Some of the materials could be amorphous. Two sources of silica are present in deep sea are present , first they are secreted to make the shells of microscopic organisms like radiolaria and diatoms and after these organisms die, their shells fall to deeper parts forming siliceous oozes because other sediments are very less there. Another source is hydrothermal fine grained amorphous deposits which form in the white smoker chimneys.

K : Conglomerate is a rock which should have atleast 30% of gravel size or larger than gravel size material along with other finer grain materials as matrix. These are formed in extremely high energy environments. Primarily forms in River clastic environments and Glacier environments but may also form in Beach and Lake clastic environments. In River at high altitude where the river falls from a steep slope to relatively gentler slope like in alluvial fans gravel sized materials are deposited. Also in other parts of river, conglomerate is formed when river breaks the rock bodies beneath it and lifts up the gravel size grain. Glacier transport all size of grains simultaneously without any sorting effect because it acts much like solid, so wherever it deposits it sediments all size of unsorted sediments gets deposited forming conglomerate or most likely breccia. In the outwash plains where the glacier is melting, it deposits it sediment sorting wise and conglomerate at the most near area to glacier and finer grains form st far places.

L : Rock gypsum is mostly composed of Gysum mineral having calcium sulphate as composition. It is an evaporite deposit forms when the brine water is evaporated and when saturation point is reached gypsum precipitates. Generally forms in Lake chemical environment where evaporation rate is more than precipitaion generally in desert areas or sabkhas. Due to the evaporation of the water in the lake, the gypsum forms a layer on the lake surface.

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