PALEONTOLOGY
Contents |
Introduction
The PPDM Biostratigraphic model addresses the myriad uses of paleontology, biostratigraphy and paleoecology by the petroleum industry over the last nine decades, in both the onshore and offshore settings. Paleontologic and related information is often voluminous and often varies from organization to organization. The module meets the business needs of the petroleum community by providing standardized templates for storing paleontologic reports, either from individual samples within a well, from a summary report, or from related biostratigraphic interpretations. Once stored, the biostratigraphic information can be retrieved in different formats, either queried for specific paleontologic information or for biostratigraphic summaries of a given borehole or outcrop.
Paleontology is the study of ancient life and its preservation. At the core of paleontology lies taxonomy, the morphologic description of individual species. Species names change with new knowledge or opinions of the important characteristics of a given species. With this in mind, a preferred (or current) species name may be set, and the historical synonomies (aliases) linked to that preferred name.
The biostratigraphic module is designed around micropaleontology, although it can be applied just as well to macropaleontology. The main micropaleontologic groups are foraminifera, coccoliths and other calcareous nannofossils, diatoms, radiolarians, conodonts, and pollen.
Biostratigraphy is the separation of rock units based on the description and analysis of the fossil species they contain (as opposed to distinguishing rock units based on other non-paleontologic information such as lithologic, magnetic or geochemical character). The key to biostratigraphy is the evolutionary nature of species. Origination, extinction and major species bioevents throughout the Phanerozoic can be discerned and used to map biohorizons. The basic unit in biostratigraphic classification is the biozone. The three major types are the interval zone, assemblage zone, and abundance zone. The group of fossils that occur at the same stratigraphic level is an assemblage. Once described, biostratigraphic correlation can be done utilizing the biozones from one locality (either borehole or outcrop) to another.
In addition to the taxonomic and biozonal information, paleoecologic data has increasingly been used as an aid in identifying and differentiating depositional environments. Here the ecozone concept is employed. The ecozone, or ecostratigraphic unit, is a zonation based on the mode of origin or environment of deposition of the rocks. The ecozone may represent the stratigraphic unit occasionally. Within the PPDM module, the ecozone refers to mainly the paleobathymetry (marine zonation). Ecozones can less frequently interpret the paleoaltitude (within a terrestrial context). The paleobathymetry, based on the paleoecologic assemblage of a given biozone, can be classified within the continental shelf or slope as needed.
Returning to biozones and assemblages, other characteristics of biozones have increased importance currently. Particular species abundance peaks and species acmes may be useful correlatives in basin analysis. Faunal and floral abundance and diversity changes downhole or across an outcrop may be correlated as well. Condensed sections, where fossil species bioevents appear within a narrow range within a stratigraphic section, indicate significant decrease in sedimentation rate, and is commonly found in the deepwater explorative trends within the slope environs. Identification of the condensed sections along with maximum flooding surfaces often is important clues to identifying sequence boundaries.
Besides the morphologic and paleoecologic character, post-depositional changes to fossils within the biozone can be described. The nature of the preservation of the fossils may indicate syndepositional or post-depositional changes. For conodonts, the conodont alteration index can be recorded indicating the thermal maturation of the rocks, and a thermal maturity map can be derived.
Business Process Overview
Paleontology is the study of ancient life and its preservation. At the core of paleontology lies taxonomy, the morphologic description of individual species. Species names change with new knowledge or opinions of the important characteristics of a given species. With this in mind, a preferred (or current) species name may be set, and the historical synonomies (aliases) linked to that preferred name.
The biostratigraphic module is designed around micropaleontology, although it can be applied just as well to macropaleontology. The main micropaleontologic groups are foraminifera, coccoliths and other calcareous nannofossils, diatoms, radiolarians, conodonts, and pollen.
Biostratigraphy is the separation of rock units based on the description and analysis of the fossil species they contain (rather than distinguishing rock units based on other non-paleontologic information such as lithologic, magnetic or geochemical character). The key to biostratigraphy is the evolutionary nature of species. Origination, extinction and major species bioevents throughout the Phanerozoic can be discerned and used to map biohorizons. The basic unit in biostratigraphic classification is the biozone. The three major types are the interval zone (a zone defined by two boundary events), the assemblage zone (a zone of overlapping biostratigraphic species ranges), and the abundance zone (a zone containing a high abundance of a particular species). The group of fossils that occur at the same stratigraphic level is an assemblage. Once described, biostratigraphic correlation can be done utilizing the biozones from one locality (either borehole or outcrop) to another.
In addition to the taxonomic and biozonal information, paleoecologic data has increasingly been used as an aid in identifying and differentiating depositional environments. Here the ecozone concept is employed. The ecozone, or ecostratigraphic unit, is a zonation based on the mode of origin or environment of deposition of the rocks. The ecozone may represent the stratigraphic unit occasionally. Within the PPDM module, the ecozone refers to mainly the paleobathymetry (marine zonation). Ecozones can less frequently interpret the paleoaltitude (within a terrestrial context). The paleobathymetry, based on the paleoecologic assemblage of a given biozone, can be classified within the continental shelf or slope as needed.
Returning to biozones and assemblages, other characteristics of biozones have increased importance currently. Particular species abundance peaks and species acmes may be useful correlatives in basin analysis. Faunal and floral abundance and diversity changes downhole or across an outcrop may be correlated as well. Condensed sections, where fossil species bioevents appear within a narrow range within a stratigraphic section, indicate a significant decrease in sedimentation rate. Condensed sections are commonly found in the deepwater explorative trends within the offshore continental slope environs. Identification of the condensed sections along with maximum flooding surfaces often is important clues to identifying sequence boundaries (depositional sequences bounded by unconformities).
Besides the morphologic and paleoecologic character, post-depositional changes to fossils within the biozone can be described. The nature of the fossil preservation may reveal syndepositional (deposits formed at the same time) or post-depositional changes. For conodonts, the conodont alteration index (CAI) can be recorded, indicating the thermal maturation of the rocks (the maximum temperature the rocks reached). A thermal maturity map can be derived, illustrating maximum temperatures reached in the subsurface rocks over an entire geologic basin. Hydrocarbons may have migrated away if temperatures reached beyond a certain point in the basin, so the CAI may be of high importance in some studies.
Purpose
The goal of the biostratigraphic module is to store and retrieve paleontologic data and information employed in the overall geologic assessment of the petroleum potential of a given well, prospect, local area or regional basin. The PPDM module meets the business needs of the petroleum community by providing standardized templates for storing paleontologic reports, either from individual samples within a well, from a summary report, or from related biostratigraphic interpretations. Once stored, the biostratigraphic information can be retrieved in different formats, either queried for specific paleontologic information or for biostratigraphic summaries of a given borehole or outcrop.
Description
The PPDM Biostratigraphic model addresses the myriad uses of paleontology, biostratigraphy and paleoecology by the petroleum industry over the last nine decades, in both the onshore and offshore settings. Paleontologic and related information is often voluminous and often varies from organization to organization. The module meets the business needs of the petroleum community by providing standardized templates for storing and retrieving the paleontologic data and information.
Key Business Processes
For biostratigraphic analysis, samples are collected in several ways. Onshore, samples are obtained by examining outcrops, either by recording surface observations, by physically hammering out specimens, or by drilling wells (boreholes). Macrofossils can be described at the regarding their type, abundance and preservation quality, as well as the lithology and stratigraphic context. Offshore, fossil samples are derived from drilling wells, either from drilled cores or from samples normally taken 30 feet apart. When individual samples are taken, the sample bags are identified by well depth and well location onsite. Since drilling bits are used in wells, most macrofossils are destroyed, with the remaining microfossils left whole for identification.
Samples can be split at a paleontologic laboratory for different further analyses, either chemical or physical. Various acids can be applied to remove surrounding matrix from the fossils. This is critical if the samples are from consolidated (already lithified or cemented together) rocks. Physically the samples go through a shaker to remove drilling muds and some of the shale matrix from unconsolidated (not cemented or lithified) samples.
The laboratory paleontologist proceeds to identify the species in each sample, either under a stereoscope or through a scanning electron microscope. The morphology (shape) of each specimen is the key to species identification. Given enough time, the sample descriptions may contain the morphologic descriptions as well. Often, however, just the species found in the sample are listed without further description. For abundance, she counts the number of individuals of a given species. For diversity, she notes the number of species within the sample. Other related sample information should be described such as overall sample preservation quality and remaining matrix description.
By observing the whole sample assemblage the paleobathymetry can be assessed. The ecozone in which the benthic assemblage (paleocommunity) lived is determined by identifying several species restricted in their environmental range. This is usually extrapolated from studies of the environmental ranges known from modern benthic foraminifera.
Occasionally the color is noted for individual fossil species, especially for conodonts. The color of the conodont species in a sample can be matched with a color alteration index (CAI). The CAI has proved to be indicative of the maximum temperature to which the fossil assemblage was subjected to after deposition, revealing the sample’s thermal (temperature) history (knowing this one can speculate on whether hydrocarbons migrated away or may be found in the area where the samples were taken).
After the identification and related information is known, the paleontologist or biostratigrapher often makes further paleontologic interpretations. The interpretations may be based on the number of species, the fossils associated in the sample, the sample’s preservation, the paleobathymetry, and the sample’s stratigraphic relationship with nearby samples either in the same well or adjacent wells. At this point, within the stratigraphic sequence any missing paleobioevents (i.e., extinction points expected but not observed) should be noticed. These interpretive events may indicate condensed sections (several marker fossils within a narrow stratigraphic range indicative of slow sedimentation rates in deepwater environs) or unconformities (gaps from erosional events or nondeposition).
From the fossil identification, paleobathymetry, abundance, diversity and interpretation the paleontologist makes a summary report. The report indicative the salient changes in stratigraphy and paleoecology. This can be stored separately within the PPDM biostratigraphic module or directly derived from the sample information.
