WOOD FOSSILS have been discovered in Manchhar Formation exposed beside Ranikot Fort, district Jamshoro, Sindh, Pakistan. This petrified wood is about 23.03 to 5.3 million years old according geological time period of Miocene. As many as 24 specimens of trunks trees are displayed in museum, Pakistan Museum of Natural History (PMNH) Islamabad. Petrified wood (from the Greek root petro meaning “rock” or “stone”, literally “wood turned into stone”) is the name given to a special type of fossilized remains of terrestrial vegetation.
Plants that flourished on earth millions of years ago are perfectly preserved as fossils. This process could occur in less than one thousand years. In general, stem tissue takes less than 100 years to petrify. The organic matter needs to become petrified before it decomposes completely. Tree or tree-like plants were completely transitioned to stone by the process of per-mineralization. This petrification process generally results in a Quartz and Chalcedony mineralization. Petrified Wood is a fossil in which the organic remains have been replaced by minerals in the slow process of being replaced with stone.
The petrifaction process occurs underground, when wood becomes buried under sediment and is initially preserved due to an environment free or lack of oxygen which inhibits aerobic decomposition (anaerobic environment). A Mineral-laden water flowing through the sediment deposits minerals in the plant’s cells; as the plant’s lignin and cellulose decay, a stone mould forms in its place. Plant studies of the Miocene have focused primarily on spores and pollen. Such studies show that by the end of the Miocene 95 per cent of modern seed plant families existed, and that no such families have gone extinct since the middle of the Miocene. Petrified wood structures such as tree rings, various tissues and others features represent tree age and seasonal changing in plants. The geological field or laboratory information of plants fossils are used for pre-geological history and to determine the changing of global earth.
The forests, grasslands, Herbivores mammals, birds or small quick birds and rodents were appeared in Miocene Epoch of tertiary period. Many change in global circulation patterns due to slight position changes of the continents and globally warmer climates were seen in that time period. A mid-Miocene warming, followed by a cooling is considered responsible for the retreat of tropical ecosystems, the expansion of northern coniferous forests, and increased seasonality. With this change came the diversification of modern graminoids, especially grasses and sedges. Conditions on each continent changed somewhat because of these positional changes, however, it was an overall increase in aridity through mountain-building that favoured the expansion of grasslands. Because the positions of continents in the Miocene world were similar to where they lie today, it is easiest to describe the plate movements and resulting changes in the paleo-climate by discussing individual continents.
The writer is Research Associate in Pakistan Museum of National History (PMNH), Islamabad.