In general, irregular periods are very common during the perimenopause. The most common early menstrual irregularity noticed in the perimenopause is a shortening of cycle length.
Abiogenic petroleum origin. Abiogenic petroleum origin is a term used to describe a number of different hypotheses which propose that petroleum and natural gas are formed by inorganic means rather than by the decomposition of organisms.
The process by which sediment undergoes chemical and physical changes during its lithification (conversion to rock). Compaction, leaching, cementation, and recrystallization are all forms of diagenesis. Erosion and metamorphism are not. Oil, gas, and coal form through the diagenesis of organic sedimentary matter.