For the first time Inorganic chemistry has been used to study why and how sea water entered Jharkhand? Which fossils are responsible for coal reserves?
Won't be surprised If I say that there was a presence of sea water in the state of Jharkhand, because in the present scenario the sea is very far from Jharkhand. Senior scientist Dr Sankar Suresh Kumar Pillai and his team from Birbal Sahni Institute of Palaeosciences, Lucknow have found some proof that indicates the presence of sea water in some places of Jharkhand. This presence is not of today, it is of the time when India was not a part of Asia and a separate country. 180 million (18 crore) years ago, India was a part of a large group of islands including Australia, South Africa, South America and Antarctica. Presently it is known as Gondwana Land.
Studies have revealed during that period some incidents took place due to which sea water entered the present day Jharkhand region of India. Presence of fossils over there proves the existence of the sea. Studies have also revealed that the vegetation group and plant fossils found during this period are similar in all parts of the Gondwana region. Dr Pillai informed us that to get the information about sea remains in Jharkhand we took the help of geochemistry. The biggest success of this study is that for the first time in the country we used Geochemistry to obtain the information of vegetation and environment regarding millions of years back and confirmed that sea water entered that area.
Dr Pillai also told us that the study was conducted in Rajhara Damodar Basin. He told that different types of flora, mega and micro fossils of palaeo depositional environment of Early Permian (Artinskian age) period of Lower Permian Rajhara sequence located in Damodar Basin were used and studies has been done on the basis of geochemical proxy. Though this Gondwana sediment is considered as fluvio-lacustrine deposits, recent studies have indicated that sea floods might have entered here. An attempt has also been made in the study to know how shallow marine condition was formed here instead of fluviatile condition. This is also an important aspect of the study. Studies show that during the deposition of the Lower Barakar Formation thick ‘coal seams’ were formed. This layer is the source of coal production today. According to the information received from the study, based on geochemical proxy, Glossopteris vegetation was found in abundance in this region. Today, this vegetation has become a source of coal in the form of coal mines in all the continents related to Gondwana land.
Important information -Glossopteridales are responsible for the formation of coal in the Gondwana continents.
Fossils of macro plant assemblage indicate the presence of glossopteridales, cordaitales and equisetales, which specify the highest presence of bissacate also. Fossils found during the deposition of the Barakar sediments suggest that during that period there would have been swampy conditions as well as dense forests and a hot & humid climate. Dr. Pillai said that this study was divided into three phases.
First we will talk about two stages. (1) Climate information was obtained by studying megafossils, i.e. large fossils of vegetation groups or plants, (2) Age of sediments was ascertained from palynomorphs, i.e. pollen or pollen extracts. It is also called the biostratigraphic age. Geologists calculate two types of ages. This includes lithostratigraphic age and stratigraphic age. In both we can see the similarity.
In the third phase of study we tried to find out from where the sea water entered this area and under what circumstances? Dr. Pillai said that there are many theories related to this study. One theory indicates that sea water came from Khamgaon, today's Sikkim state and reached Manendragarh, while the second theory reveals that the water entered from Rajasthan state and reached Umria, the third route is considered to be from the Mahanadi side. If we talk about the circumstances, there used to be an ice age on Earth. As the temperature of the earth increased, the glaciers started melting, due to which the sea level started rising and this is the reason that sea water started coming to such places where sea water could not reach.
Doctor Pillai revealed the reason why they have used inorganic chemistry for investigations in his study is as follows. He said that just as lava comes out from a big volcano and all the plants and animals which comes in the path of lava get destroyed, similarly even at a very small level a lava like substance comes out from the ground, due to which all the biological organisms and substances around like pollen etc. get burnt. During that period a similar incident might have taken place, burning all the vegetation and no biological samples left for testing. So in this study, marine signatures were detected through inorganic chemistry.
For detailed study, Dr. Pillai and his team collected about 10 surface samples from the depth of the Earth to the upper surface. Samples which were collected from Rajhara Damodar Basin belonged to different periods. Out of the ten palynological samples analyzed by Sr/Cu and Rb/Sr, two samples (RDB-4 and 5) were rich in palynomorphs. Whereas in the remaining eight, plant debris and organic matter predominated in (RDB-1 to 3 and 6 to 10) .Examination of the collected samples of 7th surface revealed that there were no presence of trees and plants. This proves that sea water must have entered here during this phase. The presence of both marine and fresh water was recorded in the area till the 8th level. This suggests a relatively warm humid climate, except for the RDB-7 coal shale sample. All samples show that this area must have had a dry-hot climate. The Th/U reading for the uppermost surface or top section (RDB-1) indicates a freshwater environment. Th/U versus Sr/Ba cross-plot in the Rajhara Colliery sequence suggests the presence of a brackish/saline environment in RDB-7 and RDB-8.
by ,
P.D Saxena
Credit :
Environ Geochem Health
https://doi.org/10.1007/s10653-023-01517-8
Lower Permian Gondwana sequence of Rajhara (Daltonganj Coalfield), Damodar Basin, India: floristic and geochemical records and their implications on marine ingressions and depositional environment
Sankar Suresh Kumar Pillai · M. C. Manoj · Runcie Paul Mathews · Srikanta Murthy · Mrutyunjaya Sahoo · Anju Saxena · Anupam Sharma · Sanghamitra Pradhan · Suraj Kumar