Text 5

detritus - детріт

silt – нанос, осад

interstitial – проміжний; щілистий

enclosing – що оточує; обмежувальний

permeability – проникність; прохідність

faulting – скид, скидоутворення

concave – увігнутий

impervious – непроникний, непрохідний

interstice – проміжок, щілина, розколина, шпара

The search for petroleum, life-blood of the twentieth-century machine age, occupies more geologists than any other branch of the profession. Surface studies in all parts of the world, enriched by information from hundreds of thousands of wells, have produced a general understanding of many aspects of the origin and accumulation of oil, but no method for accurately predicting where it will be found

Oil occurs almost exclusively in sedimentary rocks of marine origin. From this and its chemical composition it is clear that petroleum, a complex and somewhat variable mixture of hydrocarbons is formed by slow underground processes operating on organic material derived from animals or plants that accumulate with sediments, especially lighter than water and thus tend to rise through the interstitial waters of the enclosing sediments. If the pore spaces are sufficiently large and interconnected (i.e., if the permeability is high enough this slow upward movement of countless droplets will continue until they either escape at the surface in an oil seep, or are prevented from doing so by some underground obstructions. Such obstructions are known as oil traps and must consist, essentially, of an impervious layer or zone that, owing to folding, faulting, or to up-dip facies changes, is concave from below and accessible to the migrating oil. Trapped beneath this cap, the oil gradually displaces much of the pore water to from a reservoir, or “pool,” bounded below by water above by natural gas or the impervious rock. The oil, gas, and water occupy the interstices of the reservoir rock (usually sandstone, but sometimes porous limestone or fractured rocks of other kinds) and are kept from escaping upward by the shape of the overlying impervious roof.

The search for oil is a search for traps, but the only known way of learning whether or not a suspected trap actually contains oil is to drill into it.

Anticlines and domes are the most obvious oil traps and were the first to be recognized. They still are basically responsible for most of the world’s known reservoirs despite the later recognition of several other types of traps and almost endless subtle and complicated variations and combinations.

Text 6

contemporaneous – одночасний, сучасний

correlative – зв’язаний, кореляційний

upthrown – підкинений

downthrowing – скинений

subside – осідати

antithetic – прямо протилежний, антитетичний

throw – поштовх

steep – крутий

rifting – розтрісканий

downwards – низхідний

upwards – висхідний

daring – сміливий

burial –захоронення

flank – сторона

hiatus – пробіл, пропуск

Growth structures are folds and faults in which variations of rock-unit thickness are closely related to the structures itself. They result from deformation that took place during sediment accumulation, burial and compaction.

There is an element of interpretation in a short definition of growth structures. The structures that result solely from differential compaction are not strictly growth structures, but some degree of differential compaction exists in growth structures.

Growth faults (there are many synonyms, most common of which are contemporaneous and depositional) are faults in which the thickness of rock units in the downthrown block is greater than that of the correlative unit in the upthrown block.

Both blocks of a growth fault, in general, had a capacity to accumulate sediment, both were subsiding relative to baselevel; but the downthrowing block subsided faster than the “upthrowing” block, and so had a capacity to accumulate a greater thickness of sediment. The throw of a growth fault tends to increase with depth on account of the thickness contrast across it, but antithetic faults reduce the throw.

The fault plane in transgressive sequences is commonly steep to vertical. In regressive sequences, it is usually curved in plan and in section, concave to the direction of regression and concave.

Growth faults occur in two major assosiations : (a) in basins formed by rifting, where basement faulting continued and caused growth faults in the overlying (initially transgressive) sequence. These faults tend to die out upwards, commonly against an unconformity or disconformity; and (b) in regressive sequences, where growth faults occur in the upper, sandy part of the sequence. These die out downwards, and commonly also upwards.

Growth anticlines are anticlines in which rock units thicken from crest to flanks. They grew while the sediment was accumulating and compacting daring burial. The whole area of the anticline was subsiding, but the flanks subsided faster than the crest, and so accumulated a greater thickness of sediment. Growth synclines can be formed.

These process can and do lead to local stratigraphic hiatus, the recognition of which can be extremely difficult – but essential, of course, for the correct interpretation of such areas.

Sedimentary basins are growth structures on a large scale.