The phrase "are often preserved" is correct and usable in written English.
It can be used when discussing items, traditions, or practices that are maintained or kept intact over time.
Example: "Historical artifacts are often preserved in museums to educate future generations about our past."
Alternatives: "are frequently maintained" or "are commonly kept".
However, low levels of oxygen in the lake's waters and little disturbance of the sediments at the bottom of the lake resulted in the exceptional preservation of animals; animals are often preserved whole with soft tissue preservation, and even small details such as hairs, feathers and stomach contents can be observed.
When I see the actual volumes, they are often preserved in brown wrappers, with rubber bands holding their pages together.
Woods are often preserved on estates that have been passed down intact since the 18th or 19th centuries.
(Teeth are made of dentine and enamel and the latter is the body's hardest tissue. As a result, teeth are often preserved at prehistoric sites while other body parts decay and leave no trace).
For, although the soft tissue of the inner ear is long gone, the three bony semicircular canals in which that tissue resided are often preserved.Besides being involved in hearing, the semicircular canals are the location of the sense of balance.
The fish preserved in these sediments are often preserved complete, including the fins and scales (Fig. 2a), and would qualify as kosher.
In South America the heads were often preserved, as by the Jívaro, by removing the skull and packing the skin with hot sand, thus shrinking it to the size of the head of a small monkey but preserving the features intact.
A genuinely American fear of living and working in obscurity drives the young and upwardly mobile from these places where culture is often preserved rather than created, preventing change and permeating communities with self-deprecating humility.
The property of being an LCA group is often preserved under processes that are subject to natural technical restrictions.
Fossiliferous material within amber is often preserved to a higher degree of fidelity than perhaps any other medium.
Sulfur, which turns into sun-reflecting, planet-cooling sulfate particles once it hits the stratosphere, eventually settles around the globe, where it is often preserved in ice cores.
