Sedimentary rocks (4500)

1. Learn the words and word combinations before reading:

common - ['kOmqn] - распространенный, общий, часто встречающийся

dolomite - ['dOlqmait] - доломит

conglomerate - [kqn'glOmqrqt] - конгломерат (сцементированная обломочная горная порода)

chemogenic - [kemq'dZenIk] - химогенный

clastic rock - ['klxstik] - обломочная горная порода

overburden - ["quvq'bWdn] - покрывающий сверху

pressure - ['preSq] - давление

squeeze - [skwJz] - сжимать, сдавливать, образовывать трещины

layer - ['leiq] - слой, пласт, прослойка

connate fluids - ['kOneit 'flHid] - реликтовые воды

expel - [iks'pel] - выбрасывать, выталкивать

diagenesis - ['daIqdZenisis]–диагенез, перестройка минералов (совокупность физических и химических превращений рыхлых осадков на дне водных бассейнов под воздействием температур и давлений верхней зоны земной коры)

chemical - ['kemikql] - химический

stratum / pl. strata - ['stra:tqm] - пласт, напластование, формация

superposition - ['sju:pqpq'ziSqn] - напластование

gradation - [grq'deiSqn] - постепенный переход от одной стадии к другой, из одного состояния в другое, сортировка

gap - [gxp] - брешь, промежуток, щель

unconformity - ['Ankqn'fLmiti] - несогласное напластование

lithification - ['litifi"keiSqn] - окаменение, литификация

equal - ['Jkwql] - одинаковый

size - размер

boulder - ['bquldq] - валун, глыба, большой камень

cobble - ['kObl] - булыжный камень, булыжник; крупная галька

successive - [sqksesIv] - следующий один за другим, последовательный

2. Read and translate the text:

Sedimentary rocks formed from sediments cover 75-80% of the Earth’s land area, and include common types such as chalk, limestone, dolomite, sandstone, conglomerate and shale. According to the agents involved in the deposition of sedimentary rocks we may have: 1) mechanically formed sediments (clastic rocks), 2) chemically formed sediments (chemogenic rocks), 3) organically formed sediments (organic rocks), 4) rocks of mixed origin.

Sedimentary rocks are formed because of the overburden pressure^* as particles of sediment are deposited out of air, ice, wind, gravity, or water flows carrying the particles in suspension. As sediment deposition builds up, the overburden (or ‘lithostatic’) pressure squeezes the sediment into layered solids in a process known as lithification (‘rock formation’) and the original connate fluids are expelled. The term diagenesis is used to describe all the chemical, physical, and biological changes, including cementation, undergone by a sediment after its initial deposition and during and after its lithification, exclusive of surface weathering.

Sedimentary rocks are laid down in layers called beds or strata. That new rock layers are above older rock layers is stated in the principle of superposition.There are usually some gaps in the sequence called unconformities. These represent periods in which no new sediments were being laid down, or when earlier sedimentary layers were raised above sea level and eroded away. The layers may vary as to kind of material, colour, texture and thickness.

The products of rock decay vary greatly in size, but when subjected to the action of running water they are sorted and graded into particles of approximately equal size in accordance with the strength of current. Grouped then according to the size beginning with the coarsest, the following names for this material may be employed: 1) boulders and cobbles (the coarsest), 2) gravel, 3) sand, 4) clay. Gradation of these into each other is very common. They are unconsolidated mechanical sediments.

Sedimentary rocks contain important information about the history of Earth. They contain fossils, the preserved remains of ancient plants and animals. Coal is considered a type of sedimentary rock. Differences between successive layers indicate changes to the environment which have occurred over time. Sedimentary rocks can contain fossils because, unlike most igneous and metamorphic rocks, they form at temperatures and pressures that do not destroy fossil remains.

The sedimentary rocks cover only 5% of the total of the Earth’s crust.

All rocks disintegrate when exposed to mechanical and chemical weathering at the Earth’s surface. Mechanical weathering is the breakdown of rock into particles without producing changes in the chemical composition of the minerals in the rock. (ice, water, heating and cooling). Chemical weathering is the breakdown of rock by chemical reaction. In this process the minerals within the rock are changed into particles that can be easily carried away.

Sedimentary rocks are economically important in that they can easily be used as construction material because they are soft and easy to cut. In addition, sedimentary rocks often form porous and permeable reservoirs in sedimentary basins in which petroleum and other hydrocarbons can be found.

Notes:

* overburden pressure – давление покрывающих пластов

* as to – относительно

3. Find in the text the equivalents:

вовлеченный в осаждение, механически сформированные осадки, называемые слоями, процесс известный как породообразование, смешанного происхождения, сохраненные останки, химическое выветривание, охлаждение, экономически важные, давление покрывающих пластов.

4. Make the resume of the text.

5. Answer the question: why are sedimentary rocks so important for petroleum geophysicists?

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