Recall that seafloor spreading comes about when the hot molten material rises from the crack along the mid-ocean ridge and cools as it spreads and hardens. Pillow lava forms at mid-ocean ridges when the molten material erupts underwater and hardens right away. …

What is pillow lava and how is it formed?

Pillow basalt is a volcanic igneous rock that forms when lava of basaltic compositionis erupted underwater. The rapid cooling of the lava by cold water on all sides forms the pillow-shaped bodies, which can then break open and extrude more of the hot lava from inside.

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What does pillow lava mean?

Pillow lavas are bulbous, spherical, or tubular lobes of lava. They form during eruptions with relatively low effusion rates. Slow extrusion gives enough time for a thick crust to form on all sides of a pillow lobe, and prevents individual pillows from coalescing into a sheet.

Where can you find pillow lava?

Pillow lavas form when hot lava flows into water and cools rapidly, creating long tubes and bulbous pillow-shaped mounds of rock. Pillow lavas are found not only in the ocean but also under glaciers that overlie volcanoes. They are a classic geological indicator that the area you are standing in was once under water.

Is a pillow a structure?

The pillows are close-fitting, the concavities of one matching the convexities of another. The spaces between the pillows are few and are filled either with material of the same composition as the pillows, with clastic sediments, or with scoriaceous material.


What causes convolute bedding?

Convolute bedding forms when complex folding and crumpling of beds or laminations occur. This type of deformation is found in fine or silty sands, and is usually confined to one rock layer. This deformation is caused from sand being deposited onto mud, which is less dense.

What is pillow structure?

Definition and description Ball-and-pillow structure is a soft-sediment deformation structure comprising rounded masses of clastic sediment (pseudonodules, q.v.) set in similar or finer grained matrix, that are vertically stacked within one horizon (Figure B2(A), (B)).

How are flute casts formed?

Flute casts form by erosive scour. The most common geologic phenomena that produce flute casts are turbidity currents (underwater sediment slides). Sedimentary rocks representing deposition by ancient turbidity currents are called turbidites. Many turbidite successions have well preserved flute casts.


How do load casts form?

Load casts form on the underside of the overlying denser layer (sands, coarse sands, or gravels), which is superimposed on a less-dense hydroplastic layer (muds, silts or finer sands). The casts take on the form of slight bulges, swellings, deep or rounded sacks, knobby excrescences or highly irregular protuberances.

What is a gutter cast?

gutter cast An elongate cast found on the base of a bed and formed by the infilling of a gutter structure. The gutter is a linear to sinuous, U-shaped depression, up to 10 cm wide and of similar depth to its width, formed by fluid scour from helical vortices travelling parallel to the flow direction.

How are graded beds formed?

Graded beds form when a steep pile of sediment on the sea floor (or lake floor) suddenly slumps into a canyon or off a steep edge. Such mixed sediment-water flows are termed turbidity currents, because the flow makes the water cloudy (turbid). These are tilted layers of lake bed sediments exposed in Death Valley, CA.

What causes reverse grading?

Inverse grading in turbidites is conventionally ascribed to dispersive pressure caused by mutual collisions among grains within a traction carpet or grain flow. If coarser size fractions are available, they will arrive later than the head, permitting the development of inverse grading.

What is the difference between cross bedding and graded bedding?

What is the difference between cross-bedding and graded bedding? Cross-bedding occurs when sediments are layered at an angle inclined to the horizontal, whereas graded bedding occurs when larger sediments are deposited at the bottom of the layer, gradually changing to fine sediments at the top.

What does graded bedding mean?

Graded bedding simply identifies strata that grade upward from coarse-textured clastic sediment at their base to finer-textured materials at the top (Figure 3). The stratification may be sharply marked so that one layer is set off visibly from those above and beneath it.

How do graded beds form quizlet?

A graded bed may be deposited by a TURBIDITY CURRENT which is a turbulently flowing mass of sediment-laden water that is heavier than clear water and therefore flows down-slope along the bottom of the sea or a lake. List the detrital sediment particles in order of decreasing grain size.

What do mud cracks and ripple marks indicate about the geologic past?

What do mud cracks and ripple marks indicate about the geologic past? Mud cracks indicate that the sediment was deposited in an area that was alternately wet and dry, whereas ripple marks indicate that the sediment was deposited by directional currents in water or air.

How are ripples preserved?

Sediments, Reservoirs, and Deposits Ripple marks are caused by water flowing over loose sediment which creates bed forms by moving sediment with the flow. Ripples are commonly preserved in sedimentary rocks and asymmetric ripples indicate flow direction, with the steep slope on the downcurrent direction.

How do current ripples form?

How are unidirectional ripples formed? Above threshold of movement on artificially smoothed bed unidirectional flow ripples are formed at relatively low flow strengths. They may also form from initial bed irregularities on bed surface. Unidirectional flow ripples are sometimes also called “current ripples”.

Which is the most abundant chemical sedimentary rock?

limestone

Which rock type is associated with a high energy environment?

Conglomerate rock

Which is the most abundant chemical sedimentary rock quizlet?

Limestone is the third most abundant sedimentary rock and the most abundant chemical rock. Which sedimentary rock is usually composed mostly of quartz? Sandstone is usually dominated by quartz because this is the mineral in igneous rocks that is most resistant to weathering.

What are the two most abundant minerals in detrital sedimentary rock?

The most abundant detrital minerals in sediments are quartz and clays. Quartz is an abundant mineral in many rocks.

Which are two most common minerals in detrital rocks quizlet?

Clay minerals and quartz are the primary minerals found in detrital sedimentary rocks. Clays are the product of weathering of silicate minerals, mostly feldspars. Quartz is abundant in igneous rocks such as granite, and is very durable and resistant to weathering.

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What are the most common minerals found in mature sedimentary rocks?

Common Sedimentary Minerals Thus, of the eight common igneous minerals, only quartz, K-feldspar, and muscovite are commonly seen in sedimentary rocks. These minerals are joined in sedimentary rocks by clay minerals, calcite, dolomite, gypsum, and halite. The clay minerals form during mineral weathering.