Foraminifera as a Tool to Interpret the Depositional Environment
Microfossils such as foraminifera have been considered as useful tools in interpreting the dispositional environment. Despite this, their actual usage in applied micropaleontology is limited. In addition, there are few available literature and research that have successfully used the foraminifera fossils found in risks to study and interpret the dispositional environment. Based on this argument and the existing gaps in the available pieces of literature, this research study was designed to use foraminifera as a tool in studying and interpreting the characteristics of dispositional environments. The research considered various characteristics of dispositional environment such as grain surface texture, stratification sequence, sedimentary structures, grain shape, grain size, grain fabric, composition of the fossil, geometry of the sediment body, and the nature of the depositing fluid flow.
Key Words: Dispositional Environment, Foraminiferal, Fossils, Marine, Sedimentary, Sediments, Rocks
For many years, scientists have combined different techniques in the study and interpretation of dispositional environment, one of them which has proved very useful is the technique of foraminifera. Jones and Simmons (1999) asserted that foraminifera are ideal tools for measuring changes in the environment because they are found in great abundance in nearly all types of dispositional environments. Although traditionally applied in paleo environmental analysis and biostratigraphy, the application of foraminifera in solving some of the geoarchaeological and environmental problems such as interpreting the dispositional environment is growing in interest. This paper discusses how to interpret a depositional environment using foraminifera fossils found in rocks.
1.1 Foraminifera Fossils
Haq and Berggren (1998) defined foraminifera as fossils that originate single-celled protists having distinctive shells covered with some form of protoplasm in the exterior. The shell of foraminifera is divided into distinctive chambers often occurring in simple forms such as hollow spheres and tubes. In addition, the shell of foraminifera may be made of different elements such as sand grains, organic compounds, crystalline calcite, as well as other particles cemented together. Foraminifera are largely found in rocks and the length of a fully-grown one may range between 100 micrometers and 20 centimeters. Some foraminifera found in some rock have a symbiotic relationship with algae among other organisms.
There are more than 4,000 different species of foraminifera majority of which are found in ocean where more than 40 species are considered planktonic, a feature that makes them easily float in water. Other types of foraminifera are found living in rocks, sands, as well as mud and plants. They are the most abundant shelled organisms that are found in marine environment mostly on coral reefs, deepest ocean trenches, or intertidal salt marshes, and brackish estuaries among other areas. The dead foraminifera are deposited continuously down on the ocean floor in huge numbers where they are preserved as fossils in the accumulated sediments – because of their abundance, diversity, and complex morphology, foraminifera fossils can be used to provide an accurate interpretation of dispositional environment, which is the primary goal of this paper.
1.2 Dispositional Environment
Nations, Eaton, and Geological Society of America (1991) defined a dispositional environment also called sedimentary environment as a specific type of place where sediment are deposited and accumulated such as a lake, a stream channel, or the bottom of a deep ocean bed. Each type of a dispositional environment consists of a layer that has distinctive characteristics, which are useful in providing essential information for the study of geologic history of the environment or area. The characteristics of each type of a dispositional environment can be measured or observed in the sedimentary rock to deduce elements such as its lithology (the type of rock), sedimentary structure as well as other fossils that it may contain. Proper knowledge of dispositional environments serves many essential purposes such as reconstruction of the earth’s history, survival or humans on earth as well as understanding the earth processes. There are several different types of dispositional environments as illustrated in the table below: –
Table 1: Types of dispositional environments
|Marine||Deep water marineShallow water marineReef|
2. BACKGROUND TO THE STUDY
One of the basic and most essential tenets of geology and other earth sciences is that ‘the present is the key to the past’, meaning that the present can be used to understand the past. Based on this tenet, Flugel (2004) argued if humans document the distribution of organism today and some level of understanding of the combination of environmental variables that controlled their distribution then it is possible to use that information to not only understand but also reconstruct the past environments. The preset distribution of foraminifera, for example, can be used this way to study the interpretation of dispositional environments such as beach, lagoonal, Aeolian, fluvial, shallow water marine and deep-water marine environments among others. This may be successfully done using fossilized representatives of foraminifera found in rocks as the appropriate indicators – it is typically a classic use of microfossils alongside the concept and techniques of biostratigraphy.
In the recent years, there has been increased awareness of the structure of foraminifera fossils founds in rocks as well as the structure of dispositional environments. This new development has opened more avenues for further research in the understudying and interpretation of the dispositional environment, which has been greatly limited due to lack of appropriate tools. Many scientists and researchers have established that foraminifera fossils found in rocks can be used successfully to correctly interpret a wide range of deposition environments. In addition, some scholars have also argued that human beings can use foraminifera to interpret how, in the past, organisms responded to the environmental changes – this information will play crucial role in understanding how environmental changes might affect us in the future as well as how we need to respond.
As argued by Flemming and Bartholoma (2009), using foraminifera fossils found in rocks to interpret the dispositional environments is therefore, a topic that demonstrates relevance to all aspects of modern paleontology and the survival of human beings in the changing environments. It shows how knowledge that is obtained through the study of foraminifera can be used to make useful inference to the environmental conditions not only in the past but also in the future. This study will play crucial role in demonstrating the predictive side of science especially relations to what might happen to human beings due to the continuously changing environment induced by different argents such as pollutants and climate change among others.
The research was undertaken using interactive field methodology whereby surface samples from representatives of various modern dispositional environments such as tidal inlets, beach, dune, and high marsh as well low marsh were collected for analysis. After collection of the surface samples, they were subjected to foraminiferal analysis in the laboratory in order to provide an interpretation of the dispositional environment.
The collected samples were taken to a laboratory where they were sieved using 1 mm, 0.5 mm, and 0.074 mm screens and then analyzed using respective microfossil contents – the analysis was done while the samples were still wet. The laboratory methodology of analyzing foraminifera was done using digital photographs and Meiji EMZ5TR binocular microscopes. The down core assemblages of each modern biofacies were then matched to complete the analysis. During the analysis, the researcher looked for various characteristics of foraminifera in the sedimentary rocks that might be used in the interpretation of the dispositional environments – such characteristics include grain surface texture, stratification sequence, sedimentary structures, grain shape, grain size, and grain fabric. Other characteristics that were considered during the foraminiferal analysis include composition of the fossil, geometry of the sediment body, as well as body and traces of the fossils.
Perhaps, the most important and specific type of environmental interpretation that was considered in the analysis is the nature of the depositing fluid flow. The researcher collected only sediments that were deposited by the flow of fluids – this was done to make interpretation of the dispositional environment possible by sampling and examining the sequences of the ancient sediments. This interpretation served as a useful guide in farming and understanding the broader picture of the dispositional environments. During the analysis of the sediment sequences, focus was made on what can be done by examining the succession bed by bed in order to draw useful conclusion about the movement of fluid and transport modes.
The methodology essentially considered the whole concept of sedimentary arrangements of deposits and features of the foraminiferal fossils found in the collected rock samples with the primary goal of describing the overall dispositional environment. The main kind bed features that were studied in this methodology include texture, stratification, bed geometry, bed thickness, as well as nature of contacts. The features were chosen because they offered the most possible valuable information for the interpretation of the dispositional environments. This is because, fundamentally, they offered a direct reflection of the configuration that existed during the disposition time. In addition, the features vary greatly as a function of time and flow condition which makes them useful in interpreting the dispositional environments.
4. RESULTS OF THE STUDY
4.1 Evolutionary Significance of Foraminifera
Foraminifera have great evolutionary significance that makes it a useful tool in the study and interpretation of various types of dispositional environments. Previous independent research studies conducted by Bergman (1999), Martin, Parris, and Geological Society of America (2007) has showed that when planktonic foraminifera die, they continuously rain down on the ocean floor where they form great numbers of fossils which can be used to study the interpretation of dispositional environments. At the ocean beds, the dead foraminifera form mineralized tests, which are eventually stored as fossils in the accumulated sediments. The sediments keep on accumulating and increasing the number of stored mineral tests. This process is continuous and produces unlimited supply of these foraminifera on rocks dating back to the mid Jurassic period. These fossils present unparalleled records that can be used to study and interpret the dispositional environments.
Foraminifera fossils found in rocks are found to contain quality records that have the potential of providing detailed picture of the species interrelationships as well as the structure of the dispositional environments. Large sections of the foraminiferal fossils in rocks are found to react in a highly specific manner to the diverse range of dispositional environments depending on the overall complexity of their shell structure. As a result, the composition of assemblages as well as the distribution patterns directly reflects the simultaneous bottom types and nature of the disposition. The foraminifera are found to show high level of evolutionary process of adaptation associated with the dispositional environment thus can be used in the indexation of the fossils.
4.2 Uses of Foraminifera in Interpretation of Dispositional Environments
Because the foraminifera fossils found in rock have high level of diversity, complex morphology, abundance, and fossil assemblages, they can be used to interpret various types of dispositional environments. Foraminifera formed from calcareous fossils provide useful information which cane be used to interpret and reconstruct the present and past climate conditions in the dispositional environments. This is because the trace element content and stable isotope ratios found in the shells provide useful information, which can be used to reconstruct past climate in the dispositional environment. In addition, the isotopes of the oxygen when examined provide global temperature and ice volumes in the environment (Leone & Bennett, 2014).
The foraminifera contain varying concentration of trace elements such as lithium, magnesium as well as boron, all of which hold abundant information about the global temperature cycles, carbon cycles in the ocean, and continental weathering. In addition, it provides a wealth of information that relates to various features such as texture, stratification, bed geometry, bed thickness, as well as nature of contacts used to interpret the dispositional environment. These features offered a direct reflection of the configuration of the dispositional environment that existed during the disposition time. Certain types of foraminifera are found only in specific dispositional environment, which identified with the structure and nature of the disposition. Because of their uniqueness to the dispositional environment, such foraminifera can figure out and interpret the type of the environment in which the sediments were accumulating.
In interpreting the dispositional environment, foraminifera fossils found in rocks are also used as bio-indicators especially when studying the coastal and coral environments. In this way, they indicate the health of the coral real and other lives in the dispositional environment. However, it is essential to note that the changing climate directly affect the health of the foraminifera thus affecting the dispositional environment. In the interpretation of dispositional environment, foraminifera fossils found in rocks are used in estimating the thermal maturity especially in thermal generation. In addition, foraminifera fossils found in rocks are routinely used to interpret the ages of sedimentary strata in petroleum exploration.
4.3 Foraminifera as a Teaching Tool in Interpretation
Foraminifera have been identified as an ideal tool for interpreting and measuring the environment as well as the associated changes because they are found in great abundance in nearly all dispositional environments. Another advantage of the foraminifera as a tool for interpretation is that it has very short generation times, which is often less than one year. Weimer and Link (1991) asserted that foraminifera are essential tools in interpreting the dispositional environment because they have high degree of stratigraphic resolution. The research study indicated that foraminifera are effective tools in recording and illustrating present as well as previous changes in the environment. By identifying and recording changes in the environment, foraminifera fossils found in rocks act as a useful tool in the interpretation of dispositional environments.
According to Jones and North Carolina (2008), foraminifera have been widely used by other scholars to enhance previous interpretation of the archaeological findings. In a similar manner, the foraminifera found in the back barriers marshes along the coast have high potential of determining the position of lagoonal paleo environments: it provide information that corroborate with the archaeological data in interpreting various types of dispositional environments. The result of the study indicates that every dispositional environment is unique in terms of the sedimentary bed as well as the sediment rock that it contains. Characteristics that were used to interpret each type of dispositional environment include grain surface texture, grain size, grain shape, as well as grain fabric. The study also revealed that every type of dispositional environment shows different characteristics in terms of their sedimentary structures and composition such as the amount of carbonate, evaporite, siliciclastic coal, and chert among others.
The study also revealed that each type of dispositional environment is different in terms of its fossil body and fossil trace. The geometry structure of each dispositional environment is unique and can be used in interpreting its formation and the condition that existed during the period of disposition. In a similar manner, the stratification sequence of the sedimentary fossils is also unique in each dispositional environment and shows evolutionary process that took place from the time of disposition until present. The interpretation of dispositional environment was based on three different things namely the inference about the results, the study of modern environment, as well as the deductions about causes of the features seen in the fossil (Mueller et al, 2014).
4.4 Interpretation of marine dispositional environment
The study focused on using foraminifera in rocks to interpret marine dispositional environments. Foraminifera provide useful guidelines for interpreting the rocks in marine environment, which were categorized as marine fossils, carbonate rocks, red beds, and evaporite chemistry.
- Marine Fossils
Foraminifera play great roles in identifying and categorizing the marine fossils. In essence, it enables researchers to know and identify fossils that are considered marine and the organisms that lived in the ocean that they represent. Identifying the fossils help in the identification of the organism that lived in the ocean that it represents.
- Carbonate Rocks
Laboratory analysis of the foraminifera indicated that majority of rocks found in marine are carbonate. This is a suggestive piece of evidence provided by foraminiferal analysis, which can be sued in the interpretation of the dispositional environment by considering the availability and distribution of limestone in both marine and freshwater bodies.
- Red beds
Analysis of the foraminifera showed that red beds are typical rocks derived from either shale or sandstone successions. In addition, the laboratory analysis indicates that finer sediments of red beds contain a relatively small composition of hematite, which essentially produces its red color. The use of foraminifera fossils found in rocks can be used to trace the origin of the hematite pigment in the red rock.
- Evaporite minerals
The evaporite minerals present in the foraminifera fossils can make a good case for interpreting the composition and structure of dispositional environments such as the marine. In marine dispositional environment, the ionic composition of the oceanic water undergoes very little changes, which leads to regularity in the process of the formation of evaporite minerals in the fossils.
Foraminifera fossils found in rocks offer great deal of opportunity in interpreting various aspects of the dispositional environments – several features of the dispositional environments such as structure, grain surface texture, stratification sequence, sedimentary structures, grain shape, grain size, and grain fabric. Other characteristics that were considered during the foraminiferal analysis include composition of the fossil, geometry of the sediment body, as well as body and traces of the fossils. Perhaps, the most important and specific type of environmental interpretation that was considered in the analysis is the nature of the depositing fluid flow. The researcher collected only sediments that were deposited by the flow of the fluids (Zoeram et al, 2015).
The use of foraminifera fossils found in rocks has played great roles in augmenting the historical data in different fields of sciences such as archeology and geology. The research revealed some of the most important qualities of foraminifera in interpreting the dispositional environment to include the composition of the sediment by considering factors such carbonate, cola, evaporite, siliciclastic, as well as chert among others. In addition, both the trace fossil and the body fossils also play significant roles in the interpretation of the dispositional environments. The high significance of this research study is that it can be used to make useful inference to the conditions of the dispositional environment not only in the past but also in the future. The study also plays crucial role in demonstrating the predictive side of science especially relations to what might happen to human beings due to the continuously changing environment (Whittaker et al, 2010).
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