📚 Sedimentary Rock Formation | 沉积岩的形成
Sedimentary rocks cover much of the land and ocean floor. They form from loose materials called sediments, which are pressed and glued together over millions of years. These rocks often contain layers and fossils, making them important records of Earth’s history.
沉积岩覆盖了大部分陆地和海底。它们由称为沉积物的松散物质经过数百万年的压实和胶结而形成。这些岩石通常含有层理和化石，因此是地球历史的重要记录。
1. What Is a Sedimentary Rock? | 什么是沉积岩？
A sedimentary rock is a type of rock that forms when small pieces of material called sediment are pressed and stuck together over a long time. Sediment can be made of rock fragments, mineral grains, bits of shell, or even remains of living things.
沉积岩是一种岩石，当称为沉积物的小块物质经过长时间被压紧并粘合在一起时形成。沉积物可以由岩石碎屑、矿物颗粒、贝壳碎片甚至生物遗骸组成。
Sedimentary rocks often build up in layers, called beds or strata. Each layer represents a period of deposition, so the oldest layers are usually at the bottom and the youngest layers are at the top.
沉积岩通常呈层状堆积，这些层称为地层。每一层代表一段沉积时期，因此最古老的岩层通常在底部，最年轻的岩层在顶部。
2. Weathering: Breaking Rocks Apart | 风化作用：岩石的破碎
Weathering is the first step in making sedimentary rocks. It breaks down existing rocks into smaller fragments without moving them far. Weathering can be physical, chemical, or biological.
风化是形成沉积岩的第一步。它在不把岩石搬远的情况下将原有岩石破碎成较小的碎块。风化可以是物理风化、化学风化或生物风化。
Physical weathering includes freeze-thaw action, where water enters cracks, freezes, expands, and splits the rock. Chemical weathering happens when rainwater or acids react with minerals and dissolve or change them. Biological weathering is caused by living things, such as plant roots growing into cracks.
物理风化包括冻融作用，即水进入裂缝后结冰膨胀，使岩石劈裂。化学风化发生在雨水或酸与矿物反应并使其溶解或改变时。生物风化由生物引起，例如植物根系长入裂缝。
3. Erosion and Transport | 侵蚀与搬运
Erosion is the process that picks up and carries away the weathered rock fragments. Moving water, wind, and ice are the main agents of erosion. Rivers are especially important because they carry sediment from mountains to the sea.
侵蚀是拾起并带走风化岩石碎块的过程。流动的水、风和冰是侵蚀的主要营力。河流尤其重要，因为它们把沉积物从山区搬运到海洋。
During transport, rock fragments collide with each other and become smaller, smoother, and more rounded. Heavier or larger grains settle out first when the water or wind slows down, while finer particles travel further.
在搬运过程中，岩石碎块相互碰撞，变得更小、更光滑、更圆。当水流或风速减慢时，较重或较大的颗粒先沉积下来，而较细的颗粒会被搬运得更远。
4. Deposition: Settling Down | 沉积：沉淀下来
Deposition happens when the transporting agent loses energy, so the sediment drops to the ground or settles to the bottom of a river, lake, or sea. Over time, many layers of sediment build up in the same place.
当搬运营力能量减弱时，沉积物就会下落或沉降到河流、湖泊或海洋底部，这就是沉积作用。经过一段时间，同一地点会堆积许多层沉积物。
The sediments are often sorted by size during deposition. Sand may be deposited near the shore, while mud and clay settle in calmer, deeper water. This sorting helps form distinct layers.
沉积过程中，沉积物通常会按颗粒大小分选。沙子可能沉积在近岸处，而泥和黏土则在更平静、更深的水中沉降。这种分选有助于形成清晰的层理。
5. Compaction: Squeezing Layers | 压实作用：挤压成层
As more and more sediment piles on top, the weight of the upper layers presses down on the lower layers. This process is called compaction. It squeezes the grains closer together and pushes out water from the spaces between them.
随着越来越多的沉积物堆积在上方，上层沉积物的重量向下挤压下层。这个过程称为压实作用。它把颗粒挤压得更紧密，并把颗粒之间空隙中的水分排出。
Compaction is most effective when the sediment contains a lot of water, such as mud or clay. The tiny flat grains of clay line up in parallel, which can give shale its thin layers.
当沉积物含有大量水分（如泥或黏土）时，压实作用最为明显。黏土细小的扁平颗粒会平行排列，这使得页岩具有薄层结构。
6. Cementation: Gluing Grains Together | 胶结作用：把颗粒粘在一起
Cementation is the next step. Water carrying dissolved minerals flows through the pore spaces between the compacted grains. When the water evaporates or conditions change, these minerals crystallise and act like glue, binding the grains together.
胶结作用是下一步。含有溶解矿物质的水流经压实颗粒之间的孔隙。当水分蒸发或条件改变时，这些矿物质结晶并像胶水一样把颗粒粘合在一起。
Common natural cements include silica, calcite (calcium carbonate), and iron oxide. Calcite cement is common in sandstone and limestone. Iron oxide cement often gives rocks a red, orange, or brown colour.
常见的天然胶结物包括二氧化硅、方解石（碳酸钙）和氧化铁。方解石胶结物在砂岩和石灰岩中很常见。氧化铁胶结物常使岩石呈红色、橙色或棕色。
7. Types of Sedimentary Rocks | 沉积岩的类型
Sedimentary rocks are grouped by the size and type of their grains. Common examples include sandstone, shale, limestone, and conglomerate.
沉积岩根据颗粒的大小和类型分类。常见的例子包括砂岩、页岩、石灰岩和砾岩。
Sandstone is made mainly from sand-sized grains. Shale forms from compacted clay and mud. Limestone is often made from calcium carbonate, including shells and coral fragments. Conglomerate contains large rounded pebbles mixed with finer material.
砂岩主要由沙粒大小的颗粒组成。页岩由压实的黏土和泥形成。石灰岩通常由碳酸钙组成，包括贝壳和珊瑚碎块。砾岩含有大的圆形卵石与较细物质混合。
Each type of sedimentary rock gives clues about the environment where it formed. For example, sandstone often forms on beaches or in deserts, while shale forms in calm lakes or deep seas.
每种沉积岩都能为其形成环境提供线索。例如，砂岩常形成于海滩或沙漠，而页岩则形成于平静的湖泊或深海。
8. Fossils and Sedimentary Rocks | 化石与沉积岩
Sedimentary rocks are the main type of rock that contains fossils. A fossil is the preserved remains or trace of a living thing from long ago. Fossils form when organisms are buried quickly by sediment before they can fully decay.
沉积岩是含有化石的主要岩石类型。化石是远古生物的遗骸或遗迹被保存下来的产物。当生物体在完全腐烂前被沉积物迅速掩埋时，就会形成化石。
Hard parts such as shells, bones, and teeth are more likely to be preserved than soft tissues. Over time, minerals can replace the original material, turning it into stone. Fossils are often found in limestone and shale.
贝壳、骨骼和牙齿等坚硬部分比软组织更容易保存。经过一段时间，矿物质可以替换原始物质，使其变成石头。化石常见于石灰岩和页岩中。
The presence of a fossil can tell scientists the age of the rock and the type of environment that existed when the organism lived. This is why sedimentary rocks are so valuable for understanding the history of life.
化石的存在可以告诉科学家岩石的年龄以及生物生存时的环境类型。这就是沉积岩对了解生命历史如此重要的原因。
9. Using Sedimentary Rocks | 沉积岩的用途
Sedimentary rocks are very useful to humans. Limestone is quarried to make cement, concrete, and building blocks. Sandstone is often used as a building stone because it is easy to cut.
沉积岩对人类非常有用。石灰岩被开采用于制造水泥、混凝土和建筑砌块。砂岩因易于切割，常被用作建筑石材。
Shale can be crushed to make bricks and tiles. Coal is a sedimentary rock made from ancient plant material and is burned as a fuel. Some sedimentary rocks also hold groundwater, oil, and natural gas in their pore spaces.
页岩可以压碎用来制造砖和瓦。煤是由古代植物物质形成的沉积岩，可作为燃料燃烧。一些沉积岩的孔隙中还储存着地下水、石油和天然气。
Limestone is also used in agriculture to neutralise acidic soils and in industry to make glass and steel. Its many uses make sedimentary rocks economically important.
石灰岩还用于农业中中和酸性土壤，并在工业中用于制造玻璃和钢。它的广泛用途使沉积岩在经济上非常重要。
10. Chemical Tests and Sedimentary Rocks | 沉积岩的化学检验
Many sedimentary rocks contain carbonate minerals, especially limestone and chalk. A simple chemical test can be used to identify them. When a few drops of dilute hydrochloric acid are added to a carbonate rock, the rock fizzes and releases carbon dioxide gas.
许多沉积岩含有碳酸盐矿物，尤其是石灰岩和白垩。可以用简单的化学检验来识别它们。当向碳酸盐岩石上滴加几滴稀盐酸时，岩石会冒泡并释放出二氧化碳气体。
The gas can be tested by bubbling it through limewater. If the limewater turns cloudy or milky, carbon dioxide is present. This is evidence that the rock contains calcium carbonate.
可以将气体通入石灰水中进行检验。如果石灰水变浑浊或呈乳白色，就说明有二氧化碳存在。这证明岩石中含有碳酸钙。
CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂
This reaction also helps explain why acid rain can damage limestone buildings and statues. Acid rain reacts with calcium carbonate in the same way, slowly dissolving the stone.
这个反应也有助于解释为什么酸雨会损坏石灰岩建筑和雕像。酸雨以同样的方式与碳酸钙反应，缓慢地溶解石料。
11. Connection to the Rock Cycle | 与岩石循环的联系
Sedimentary rocks are part of the rock cycle. Weathering and erosion can turn any rock at the surface into sediment. That sediment can eventually become a new sedimentary rock.
沉积岩是岩石循环的一部分。风化和侵蚀可以把地表的任何岩石变成沉积物。这些沉积物最终可能形成新的沉积岩。
If a sedimentary rock is buried deep underground, heat and pressure can change it into a metamorphic rock. If it melts and then cools, it becomes an igneous rock. The rock cycle shows that rocks are constantly being recycled.
如果沉积岩被深埋地下，热和压力会把它变成变质岩。如果它熔化后再冷却，就变成岩浆岩。岩石循环表明岩石一直在不断地循环转化。
This means the sedimentary rocks we see today may one day be broken down again and form part of a completely different rock in the future.
这意味着我们今天看到的沉积岩将来可能再次被分解，并成为另一种完全不同岩石的一部分。
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