microfossils

Microfossils

from the Postgraduate Unit of Micropalaeontology
at University College London see their excellent site if you want more than just the thumbnails


SEM image of radiolaria, foraminifera and diatoms
The picture above is a scanning electron microscope (SEM)
image of a selection of microfossils.
The scale bars are 100 microns (one tenth of a millimetre)

Calcareous Nannofossils

Calcareous nannofossils include the coccoliths and coccospheres of haptophyte algae and the associated nannoliths which are of unknown provenance. The organism which creates the coccosphere is called a coccolithophore, they are phytoplankton (autotrophs that contain chloroplasts and photosynthesise). Their calcareous skeletons are found in marine deposits often in vast numbers, sometimes making up the major component of a particular rock, such as the chalk of England. One freshwater species has been reported. Formally coccolithophores are separated from other phytoplankton such as diatoms by the presence of a third flagella-like appendage called a haptonema, although the flagella bearing stage is often only one of a multi-stage life cycle.

A coccolith is a single disc-like plate which is secreted by the algal organism and held in combination with several other, sometimes varying shaped plates by an organic coating to form the coccosphere. On death the individual coccoliths invariably become separated and it is these that are most commonly preserved in the sedimentary record. Occasionally complete coccospheres are preserved and provide valuable information, particularly regarding coccospheres which possess two or more morphologicaly different coccoliths. There are two forms of coccoliths, the holococcoliths which are formed from calcite crystals which are essentially identical in shape and size and the heterococcoliths which are formed from larger calcite crystals which vary in size and shape. Most living forms are known to produce only heterococcoliths and then only during the non-motile stage of their life cycle. Those that do produce holococcoliths do so only during their motile stage.

The first recorded use of the term "coccoliths" is from Ehrenberg's 1836 study of the chalk from the island of Rugen in the Baltic Sea. Ehrenberg and other early workers beleived coccoliths to have an inorganic origin. It was not untill the second half of the nineteenth century when Wallich found coccoliths joined to form coccospheres that an organic origin was suggested. Even after the publication of Sorby's 1861 paper, following which the organic origin of coccoliths was generally accepted, Ehrenberg remained unconvinced. The 1872 HMS Challenger expedition recovered coccospheres from the upper water layers and correctly concluded that they were the skeletons of calcareous algae. The term nannoplankton was coined by Lohmann in 1902. The study of coccolithophores has flourished since the 1960's, with much ground breaking work done on their biology as well as on the systematics of fossil and living forms. The Deep Sea Drilling Project (DSDP), now the Ocean Drilling Program (ODP), brought the stratigraphic value of calcareous nannofossils to the attention of industry as well as the scientific community. Today, due to the speed of preparation, calcareous nannofossils have bec ome the preferred tool for quick accurate stratigraphic age determination in post-Palaeozoic calcareous sequences.

First recorded occurrences of calcareous nannofossils (nannoliths) are from the late Triassic (Carnian). The locations from which the earliest nannofossils are found include; the Northern and Southern Calcareous Alps, Timor, North-West Australia and Queen Charlotte Islands (Canada), all low latitude sites at the time. There are many claims for earlier occurrences but a lack of substantiated evidence means these must be excluded. One consequence of the first occurrence of calcareous nannofossils in the late Triassic lies in the fact that this was the first time open ocean planktonic organisms utilised calcareous skeletons and exported calcium carbonate into the deep oceans. This has important repercussions in terms of biogeochemical cycles. Today coccolithophores are one of the most important forms of phytoplankton found in the oceans, and may be described as the grass of the sea.

The classification of calcareous nannoplankton is carried out under the International Code of Botanical Nomenclature. They are formally classified in the Kingdom Protoctista, Phylum (or Division) Haptophyta, Class Prymnesiophyceae. Classification is complicated by the fact that some species are dimorphic, that is they possess more than one coccolith on a single coccosphere. This may lead to the belief that two species exist where in fact there is only one. Also, pleomorphism (where a holococcolith phase alternates with a heterococcolith phase) may also result in coccoliths being placed in different species or even genera when in fact they are simply different stages in the life cycle of the same species.

As the groups name suggests calcareous nannofossils are small, generally less than 30 microns across and usually between 5 and 10 microns (individual coccoliths). This has advantages and disadvantages. Advantages include:


Disadvantages include:

Culture techniques have resulted in great advances in the study of coccolithophore life cycles. The existence of a haploid and diploid phase has been proved by the extraction of DNA, with mitotic reproduction occurring in both stages. Syngamy (sexual reproduction) has not been observed but is assumed to occur, the recent discovery of combination coccospheres (where coccoliths of two distinct forms occur on the same coccosphere) has meant the traditional classification will have to be radically revised and updated.

The defining feature of the haptophytes is the flagella-like haptonema which is generally coiled. It differs from the flagella proper in its internal structure and its basal attachment. During the non-motile phase the flagella disappear but the haptonema often remains, the exact function of the haptonema is not fully understood. The algal cell contains a nucleus and two golden-brown chloroplasts which may be moved around the cell to optimise collection of available light. The cell also contains mitochondria which contain enzymes which produce the energy for cell function, vacuoles which deal with waste products and the Golgi body which is the site of coccolith secretion in many species. In many species overlapping oval organic scales coat the outer cell membrane. These have concentric ridges on their distal faces and radiating ridges on their proximal faces. It seems the organic scales act as bases for the precipitation of the calcite coccoliths. A variety of coccolith secretion strategies have been observed in different species, however it is probably true of all coccolithophores that the production of coccoliths is controlled by light. Emiliania huxleyi has been observed to start coccolith production within half an hour of being introduced to light, and produce an individual coccolith in one hour and a complete coccosphere in about thirty hours.

cross-section of coccosphere cell and cell wall coverings click to view larger version

Above diagram from Bown,P.(Ed.), 1998, Calcareous Nannofossil Biostratigraphy. Chapman and Hall.

The function of coccoliths is not known but may be one or more of four basic possibilities: Reproduction of coccolithophores is by single or double fission sometimes accompanied by a swarm-spore stage. The information we have on coccolithophore reproduction is based on only a few species so care must be taken when making generalisations, however, it is thought the coccolith-bearing phase is diploid and capable of asexual (mitotic) reproduction. This allows rapid population growth during periods of optimum conditions, producing what are known as "blooms". Motile naked haploid gametes may be produced by meiosis and non-motile benthic stages are also known to be produced. Sexual fusion has rarely been observed but is inferred by the variation of DNA found within coccolithophpores.

Please remember all preparation techniques require the use of hazardous materials and equipment and should only be carried out in properly equiped laboratories, wearing the correct safety clothing and under the supervision of qualified staff.

Smear slides are produced by first cleaning a hand specimen by paring the outer surfaces off. A fine "dust" of material is then scraped off onto a cover slip. This is then moistened with distilled water and spread across the cover slip with a suitable utensile such as a wooden tooth pick. This takes a certain amount of experience to get right but when the corrrect coverage is obtained the cover slip is placed on a hot plate to dry. Once dry the cover slip is inverted and glued to a slide using Norland optical adhesive which is cured under U.V. light. Centrifuge slides are produced by first cleaning the sample as in the smear slide technique and then scraping a dust of material into a centrifuge tube. This is topped up with distilled water and spun at 350 rpm in a centrifuge for about two minutes. The pellet is then put to one side and the supernatant kept. The supernatant is then re-suspended and centrifuged at 1000rpm for four minutes this time keeping the pellet. This re-suspending and centrifuging at 1000rpm may need to be repeated several times depending on the lithology of the sample. After centrifuging the sample is dilluted to a slightly milky consistency with distilled water and strewn on to a cover slip placed on a hot plate and left to dry. The cover slip can then be mounted as in the smear slide technique. One of the major advantages calcareous nannofossils have over other microfossil groups, particularly in terms of industrial application is the speed at which samples can be prepared. Simple smear slides can be made in minutes and even centrifuge preparations are ready in less than half an hour. Another advantage is that no harmful or dangerous chemicals are needed nor even a fume cupboard. This makes calcareous nannofossils an extremely useful and widely used biostratigraphic tool especially on offshore drilling platforms and ships.

Since individualcoccoliths preserve fine structural crystallographic detail in calcite observation techniques depend on the use of petrological microscopes. The calcite crystals forming hetero- and holococcoliths often have differently oriented optic axes which produce distinctive extinction patterns under crossed nicols of a polarising microscope. Transmitted, cross polarised light is regularly used but phase contrast and bright field settings may also be advantageous. Scanning Electron Microscopy has become more widely available and greatly enhanced the study of nannofossils. Much of the work on the fine structure and formation of coccoliths has been made possible by scanning electron microscopes.

The following images are of a representative selection of calcareous nannofossils aimed at giving a general overview of the different morphotypes. Each specimen is given a generic and if possible a species name followed by its age range, the site location from which the sample was obtained and the magnification at which the image was taken or its size in microns. PC (Phase Contrast), XPL (Crossed Polarised Light) SEM (Scanning Electron Microscope). Typical and selected marker species are illustrated from each main period of the geological column in which calcareous nannofossils occur.


Triassic and Jurassic
Anulasphaera helvetica Grun and Zweili, 1980
Callovian (Middle Jurassic)
Denver Borehole, UK
PC side view
Anulasphaera helvetica Grun and Zweili, 1980
Callovian (Middle Jurassic)
Denver Borehole, UK
XPL side view
Anulasphaera helvetica Grun and Zweili, 1980
Callovian (Middle Jurassic)
Denver Borehole, UK
(SEM) distal view
Anulasphaera helvetica Grun and Zweili, 1980
Callovian (Middle Jurassic)
Denver Borehole, UK
(SEM) proximal oblique view
Stephanolithion bigotii bigotii Deflandre, 1939
Lower Oxfordian (Upper Jurassic)
Cleveland Farm Pit, wiltshire, UK
XPL
Stephanolithion bigotii bigotii Deflandre, 1939
Upper Kimmeridgian (Upper Jurassic)
Gorodische, Russia
SEM
Stephanolithion speciosum octum Deflandre in Deflandre and Fert, 1954 ssp. Rood and Barnard, 1972
Lower Bathonian (Middle Jurassic)
Port en Bessin, N. France
XPL
Stephanolithion speciosum octum Deflandre in Deflandre and Fert, 1954 ssp. Rood and Barnard, 1972
Lower Bathonian (Middle Jurassic)
Port en Bessin, N. France
PC
Stephanolithion speciosum Deflandre in Deflandre and Fert, 1954 ssp. octum Rood and Barnard, 1972
Upper Bajocian-Lower Callovian (Middle Jurassic)
Escoville, France
distal view
Biscutum novum (Goy,1979) Bown, 1987
Aalenian/Bajocian
Brenha, Portugal
XPL
Biscutum novum (Goy,1979) Bown, 1987
Lower Toarcian
Trimeusel, Germany
distal view
Biscutum novum (Goy,1979) Bown, 1987
Upper Toarcian
Ballrechten, Germany
proximal view
Carinolithus superbus (Deflandre in Deflandre and Fert, 1954) Prins in Grun et al, 1974
Lower Toarcian-Lower Bajocian
Ilminster, UK
proximal oblique view SEM
Carinolithus superbus (Deflandre in Deflandre and Fert, 1954) Prins in Grun et al, 1974
Lower Toarcian-Lower Bajocian
Ilminster, UK
side view SEM
Crucirhabdus minutus Jafar, 1983
Norian-Rhaetian (Upper Triassic)
Fischerwiese, Austria
XPL distal view
Crucirhabdus minutus Jafar, 1983
Norian-Rhaetian (Upper Triassic)
Weissloferbach, S. Germany
distal view SEM
Lotharingius haufii Grun and Zweili in Grun et al, 1974
Lower Toarcian
Untersturmig, Germany
XPL
Lotharingius haufii Grun and Zweili in Grun et al, 1974
Upper Pliensbachian-Upper Bathonian
Untersturmig, Germany
PC
Lotharingius haufii Grun and Zweili in Grun et al, 1974
Upper Pliensbachian-Upper Bathonian
Untersturmig, Germany
SEM (collapsed coccosphere)
Parhabdolithus liasicus distinctus Deflandre in Grasse, 1952 ssp. Bown, 1987
Hettangian-Lower Toarcian
Timor
XPL plan view
Parhabdolithus liasicus distinctus Deflandre in Grasse, 1952 ssp. Bown, 1987
Hettangian-Lower Toarcian
Timor
XPL side view
Parhabdolithus liasicus distinctus Deflandre in Grasse, 1952 ssp. Bown, 1987
Hettangian-Lower Toarcian
Mochras Borehole, UK
side view (SEM)
Prinsiosphaera triassica Jafar, 1983
Norian-Rhaetian
Weissloferbach S. Germany
XPL
Prinsiosphaera triassica Jafar, 1983
Norian-Rhaetian
ODP Site 761, Wombat Plateau, NW Australian shelf
SEM
Lower Cretaceous
Axopodorhabdus albianus (Black, 1967) Wind and Wise in Wise and Wind, 1977
Middle Albian-Upper Cenomanian
Folkestone, UK
XPL
Axopodorhabdus albianus (Black, 1967) Wind and Wise in Wise and Wind, 1977
Middle Albian-Upper Cenomanian
English Channel Borehole R330, UK
distal view SEM
Calcicalathina oblongata (Worsley, 1971) Thierstein, 1971
Lower Valanginian-Lower Barremian
Bulgaria
XPL distal view
Calcicalathina oblongata (Worsley, 1971) Thierstein, 1971
Lower Valanginian-Lower Barremian
DSDP Site 547B, Atlantic Ocean
distal view SEM
Calcicalathina oblongata (Worsley, 1971) Thierstein, 1971
Lower Valanginian-Lower Barremian
DSDP Site 547B, Atlantic Ocean
side view SEM
Ceratolithina bicornuta Perch-Nielsen, 1988
Middle Albian-Upper Albian
Folkestone, UK
XPL
Corollithion kennedyi
Cenomanian
Lydden Spout, Folkestone, UK
XPL
Cruciellipsis cuvillieri (Manivit, 1966) Thierstein, 1971
Lower Berriasian-Upper Hauterivian
DSDP Site 397, E.Atlantic Ocean
XPL
Cruciellipsis cuvillieri (Manivit, 1966) Thierstein, 1971
Lower Berriasian-Upper Hauterivian
DSDP Site 547B, Atlantic Ocean
distal view SEM
Eiffellithus turriseiffelii (Deflandre in Deflandre and Fert, 1954) Reinhardt, 1965
Upper ALbian-Upper Maastrichtian
Folkestone, UK
XPL distal view
Eprolithus floralis (Stradner, 1962) Stover, 1966
Lower Aptian-?Lower Campanian
Folkestone, UK
XPL distal view
Gartnerago segmentatum
Cenomanian-Maastrichtian
Langdon Stairs, Dover, Kent, UK
XPL distal view
Micrantholithus obtusus Stradner, 1963
Berriasian-Upper Aptian
Speeton, UK
XPL
Micrantholithus obtusus Stradner, 1963
Berriasian-Upper Aptian
DSDP Site 398D, Atlantic Ocean
SEM
Nannoconus abundans Stradner and Grun, 1973
Barremian-?Lower Aptian
Speeton, UK
XPL
Nannoconus abundans Stradner and Grun, 1973
Barremian-?Lower Aptian
Speeton, UK
side view SEM
Prediscosphaera columnata (Stover, 1966) Perch-Nielsen, 1984
Lower Albian-Turonian
Folkestone, UK
XPL distal view
Prediscosphaera columnata (Stover, 1966) Perch-Nielsen, 1984
Lower Albian-Turonian
Folkestone, UK
XPL side view
Prediscosphaera columnata (Stover, 1966) Perch-Nielsen, 1984
Lower Albian-Turonian
Copt Point, UK
side view SEM
Watznaueria barnesae (Black in Black and Barnes, 1959) Perch-Nielsen, 1968
Lower Bajocian-Maastrichtian
Gorodische, Russia
XPL
Watznaueria barnesae (Black in Black and Barnes, 1959) Perch-Nielsen, 1968
Lower Bajocian-Maastrichtian
Speeton, UK
SEM (Coccosphere)
Watznaueria britannica (Stradner, 1963) Reinhardt, 1964
Lower Bajocian-Lower Cenomanian
Cleveland Farm Pit, Wiltshire, UK
XPL
Zeugrhabdotus erectus (Deflandre in Deflandre and Fert, 1954) Reinhardt, 1965
Lower Pliensbachian?-Upper Maastrichtian
Cleveland Farm Pit, Wiltshire, UK
XPL
Zeugrhabdotus erectus (Deflandre in Deflandre and Fert, 1954) Reinhardt, 1965
Lower Pliensbachian?-Upper Maastrichtian
Mochras Borehole, UK
distal view SEM
Zeugrhabdotus erectus (Deflandre in Deflandre and Fert, 1954) Reinhardt, 1965
Lower Pliensbachian?-Upper Maastrichtian
Dorset, UK
side view SEM
Upper Cretaceous
Arkhangelskiella cymbiformis Vekshina, 1959
Campanian-Maastrichtian
DSDP Site 249, Indian Ocean
XPL distal view
Arkhangelskiella cymbiformis Vekshina, 1959
Campanian-Maastrichtian
Keswick, Norfolk, UK
oblique distal view SEM
Eiffellithus eximius (Stover, 1966) Perch-Nielsen, 1968
Turonian-Campanian
Zoe C BH, South Africa
XPL
Eiffellithus eximius (Stover, 1966) Perch-Nielsen, 1968
Turonian-Campanian
Zoe C BH, South Africa
XPL rotated
Lithastrinus grillii Stradner, 1962
Coniacian-Campanian
near Plymouth Bluff, Lowndes County, Mississippi, USA
XPL
Lucianorhabdus cayeauxii Deflandre, 1959
Coniacian-Maastrichtian
near Portland, Dallas County, Alabama, USA
XPL
Marthasterites furcatus (Deflandre in Deflandre and Firt, 1954) Deflandre, 1959
Turonian-Campanian
DSDP Site 258, E.Indian Ocean
XPL
Marthasterites furcatus (Deflandre in Deflandre and Firt, 1954) Deflandre, 1959
Turonian-Campanian
DSDP Hole 550B, NE Atalntic Ocean
SEM
Microrhabdulus decoratus Deflandre, 1959
Cenomanian-Maastrichtian
DSDP Site 401, NE Atlantic Ocean
SEM
Microrhabdulus decoratus Deflandre, 1959
Cenomanian-Maastrichtian
DSDP Site 249, W. Indian Ocean
XPL
Micula staurophora (Gardet, 1955) Stradner, 1963
Coniacian-Maastrichtian
near Ripley, Tippah County, Mississippi, USA
XPL
Prediscosphaera arkhangelskyi (Reinhardt, 1965) Perch-Nielsen, 1984
Santonian-Maastrichtian
DSDP Site 249, W. Indian Ocean
XPL
Prediscosphaera cretacea (Arkhangelsky, 1912) Gartner, 1968
Cenomanian-Maastrichtian
DSDP Site 249, W. Indian Ocean
XPL
Prediscosphaera cretacea (Arkhangelsky, 1912) Gartner, 1968
Cenomanian-Maastrichtian
near Plymouth Bluff, Lowndes County, Alabama, USA
XPL
Quadrum gartneri Prins and Perch-Nielsen in Manivit et al, 1977
Turonian-?Maastrichtian
DSDP Site 217, N. Indian Ocean
XPL
Tranolithus orionatus (Reinhardt, 1966a) Reinhardt, 1966b
Albian-Maastrichtian
Folkestone, UK
XPL
Uniplanarius trifidus (Stradner in Stradner and Papp, 1961) Hattner and Wise, 1980
Campanian-Maastrichtian
DSDP Site 217 N. Indian Ocean
XPL
Uniplanarius trifidus (Stradner in Stradner and Papp, 1961) Hattner and Wise, 1980
Campanian-Maastrichtian
DSDP Site 241 W. Indian Ocean
XPL
Palaeogene
Chiasmolithus solitus (Bramlette and Sullivan, 1961) Locker, 1968
Lutetian-Bartonian (Middle Eocene)
Whitecliff Bay, UK
PC
Chiasmolithus solitus (Bramlette and Sullivan, 1961) Locker, 1968
Lutetian-Bartonian (Middle Eocene)
Fayum, Egypt
oblique distal view SEM
Discoaster tanii Bramlette and Riedel, 1954
Middle Eocene-Oligocene
Hampden Beach, New Zealand
distal view SEM
Discoaster saipanensis Bramlette and Riedel, 1954
Middle-Upper Eocene
Fayum, Egypt
distal view SEM
Discoaster saipanensis Bramlette and Riedel, 1954
Middle-Upper Eocene
Benidorm, Spain
distal view SEM
Discoaster saipanensis Bramlette and Riedel, 1954
Middle-Upper Eocene
Whitecliff Bay, UK
PC
Discoaster kuepperi Sradner, 1959
Lower-Middle Eocene
North Sea, UK
PC
Discoaster kuepperi Sradner, 1959
Lower-Middle Eocene
Benidorm, Spain
proximal view SEM
Discoaster kuepperi Sradner, 1959
Lower-Middle Eocene
Benidorm, Spain
distal view SEM
Discoaster kuepperi Sradner, 1959
Lower-Middle Eocene
Benidorm, Spain
side view SEM
Cruciplacolithus primus Perch-Nielsen, 1977
Upper Palaeocene
St. Paul Monastery, Egypt
oblique distal view SEM
Neococcolithus dubius (Deflandre in Deflandre and Fert, 1954) Black, 1967
Lower-Upper Eocene
Whitecliff Bay, UK
oblique distal view SEM
Neococcolithus dubius (Deflandre in Deflandre and Fert, 1954) Black, 1967
Lower-Upper Eocene
Whitecliff Bay, UK
distal view SEM
Fasciculithus tympaniformis Hay and Mohler in Hay et al, 1967
Upper Palaeocene-Lower Eocene
Pegwell Bay, Kent, UK
XPL
Fasciculithus tympaniformis Hay and Mohler in Hay et al, 1967
Upper Palaeocene-Lower Eocene
St. Paul Monastery, Egypt
oblique proximal view
Fasciculithus tympaniformis Hay and Mohler in Hay et al, 1967
Upper Palaeocene-Lower Eocene
St. Paul Monastery, Egypt
proximal view
Sphenolithus moriformis (Bronniman and Stradner, 1960) Brmlette and Wilcoxon, 1967
Palaeocene-Pliocene
DSDP Site 590B, S.W Pacific
SEM
Sphenolithus moriformis (Bronniman and Stradner, 1960) Brmlette and Wilcoxon, 1967
Palaeocene-Pliocene
DSDP Site 593, S.W Pacific
SEM
Discoaster lodoensis Bramlette and Riedel, 1954
Palaeocene-Pliocene
Benidorm, Spain
XPL
Discoaster lodoensis Bramlette and Riedel, 1954
Palaeocene-Pliocene
Benidorm, Spain
proximal view SEM
Discoaster lodoensis Bramlette and Riedel, 1954
Palaeocene-Pliocene
Benidorm, Spain
distal view SEM
Neogene
Amaurolithus amplificus (Bukry and Percival) Gartner and Bukry, 1975
Upper Miocene-Pliocene
Manavgat, S.Turkey
XPL
Amaurolithus amplificus (Bukry and Percival) Gartner and Bukry, 1975
Upper Miocene-Pliocene
Manavgat, S.Turkey
PC
Coccolithus pelagicus (Wallich, 1871) Schiller, 1930
Lower Palaeocene-Recent
N. Atlantic off S.W coast of Iceland
SEM entire coccosphere
Coccolithus pelagicus (Wallich, 1871) Schiller, 1930
Lower Palaeocene-Recent
ODP Site 1052b, Western N. Atlantic
SEM distal view 10 microns
Coccolithus pelagicus (Wallich, 1871) Schiller, 1930
Lower Palaeocene-Recent
ODP Site 1052b, Western N. Atlantic
SEM proximal view 10 microns
Discoaster challengeri Bramlette and Riedel, 1954
Miocene-Pliocene
Ghajn Tuffieha Bay, Malta
SEM proximal view
Discoaster challengeri Bramlette and Riedel, 1954
Miocene-Pliocene
G. Mihmandar Borehole, Malta
PC
Discoaster exilis Martini and Bramlette, 1963
Middle Miocene
Ghajn Tuffieha Bay, Malta
proximal view SEM
Discoaster exilis Martini and Bramlette, 1963
Middle Miocene
Ghajn Tuffieha Bay, Malta
PC
Discoaster variabilis Martini and Bramlette, 1963
Middle Miocene-Pliocene
Ghajn Tuffieha Bay, Malta
proximal view SEM
Discoaster variabilis Martini and Bramlette, 1963
Middle Miocene-Pliocene
Ghajn Tuffieha Bay, Malta
PC
Florisphaera profunda Okado and Honjo, 1973
Middle Miocene-Recent
Almerian Canyon, Western Mediterranian Sea
10 microns SEM
Gephyrocapsa oceanica Kamptner, 1943
Pleistocene-Recent
Almerian Canyon, Western Mediterranian Sea
10 microns SEM
Calcidiscus tropicus Kamptner, 1956
Lower Miocene-Recent
DSDP Site 593, S.W Pacific Ocean
SEM
Calcidiscus tropicus Kamptner, 1956
Lower Miocene-Recent
DSDP Site 593, S.W Pacific Ocean
SEM
Helicosphaera carteri (Wallich, 1877) Kamptner, 1954
Upper Oligocene-Recent
DSDP Site 590B, S.W Pacific Ocean
XPL
Helicosphaera carteri (Wallich, 1877) Kamptner, 1954
Upper Oligocene-Recent
DSDP Site 590B, S.W Pacific Ocean
proximal view SEM
Reticulofenestra pseudoumbilica (Gartner) Gartner, 1969
Miocene-Pliocene
Ghajn Tuffieha Bay, Malta
proximal view SEM
Reticulofenestra pseudoumbilica (Gartner) Gartner, 1969
Miocene-Pliocene
Ghajn Tuffieha Bay, Malta
coccosphere SEM
Sphenolithus heteromorphus Deflandre, 1953
Lower Miocene-Middle Miocene
DSDP Site 593, S.W Pacific Ocean
SEM
Sphenolithus heteromorphus Deflandre, 1953
Lower Miocene-Middle Miocene
DSDP Site 590B, S.W Pacific Ocean
SEM

conodonts


Conodont elements are phosphatic tooth-like structures whose affinity and function is now believed to be part of the feeding apparatus of an extinct early vertebrate. Early ideas concluded that the conodontophorid was a soft bodied, bilaterally symmetrical nektonic organism, although there is still much debate concerning possible benthic, nektonic or combined mode of life. Conodont elements are composed of calcium carbonate fluorapatite with additional organic matter. They are found in marine deposits, commonly in black shales associated with graptolites, radiolarians, fish remains, brachiopods, cephalopods, trilobites and palaeocopid ostracods.

con001.gif

The name "conodont" was coined by C.H. Pander (a Russian) in 1856, who worked on Silurian fish fossils of Eastern Europe. Ulrich and Bassler (1926) described many new species from North America and were the first to recognise their biostratigraphic usefulness. In 1934 Schmidt and Scott discovered groups of individual elements preserved together on the same bedding plain. This importantly led to the theory that the individual elements were in life held in pairs (termed an apparatus) often likened to mouth parts. From the 1960's onwards conodonts have developed into one of the most important biostratigraphic tools available in Palaeozoic and Triassic rocks.

The very earliest conodonts are known from rocks of probable Precambrian age in Siberia, they are found more commonly in Cambrian deposits, diversity increased in the Ordovician and again during the Devonian. The conodont-bearing organism clearly survived the Permo-Triassic boundary extinctions but became extinct during the late Triassic. It has been noted that the extinction of the conodonts coincides with the diversification of dinoflagellates and first appearance of calcareous nannofosils. The most primitive conodonts are single cones, which dominate early Ordovician assemblages and reach a peak in the Arenigian (late Early Ordovician). The first platform type conodonts occur around this time as well. Conodont diversity and abundance declined in the Silurian. During the early and mid Devonian diversity gradually increased, reaching an acme in the late Devonian. In the early Carboniferous conodonts remained abundant and widespread but diversity decreased during the late Carboniferous. In the Permian the conodonts almost became extinct, however, they made a recovery in the early to middle Triassic only to disappear in the late Triassic.

geologic time scale diagram click to view larger version


Conodonts have been assigned to their own Phylum, Conodonta, divided into two Orders based on chemical and ultrastructure differences. Eleven superfamilies have been recognised by reconstructing associations of individual elments into apparatuses; and morphological and element compositonal differences further divide these into forty seven families. One hundred and eighty genera have been recognised. It must be remembered that any classification of conodonts is an un-natural one, as it is based on morphology only. Morphologically, four main groups of conodonts can be distinguished.

conodont morphology terminology click to view larger version

The fact that conodonts are relatively common in rocks of Palaeozoic age, a period when other microfossil groups are either not present or scarce, has made them extremely useful stratigraphic tools. Together with acritarchs, chitinozoa and spores, conodonts are the primary microfossils available to palaeontologists working on Ordovician to Permo-Triassic strata.

Isolated conodonts are widespread and abundant. Untill the nineteen eighties their biological affinities were still not known. Two enlightening fossil finds provided a few clues to the affinity of conodonts. The first, a chordate animal with conodonts scattered within what is interpreted as its gut from the fish bearing Namurian (Carboniferous) Bear Gulch limestone of Montana. The second, from the famous Cambrian Burgess Shale of British Columbia, is a flattened worm-like animal 60mm long with a distinct head bearing a U-shaped structure interpreted as a lophophore (a circular or horseshoe shaped fleshy ridge surrounding the mouth, bearing tentacles found in Bryozoans and Brachiopods). At the base of each of the 20-25 tentacles is a compressed cone closely resembling some contemporaneous conodonts. However, the discovery of a Carboniferous fossil near Edinburgh (and subsequent finds in South Africa) has finaly solved the mystery of what the conodont elements are. It is now believed that they are the tooth-like feeding apparatus of a hagfish-like vertebrate. The co-occurrence of conodont elements in symmetrical pairs has allowed certain inferences to be made: The host animal probably exhibited bilateral symmetry. Several pairs of one sort can be associated with one or more pairs of another sort. The shape and arrangement of conodont elements in the apparatuses suggest that they were tooth-like feeding tools. The use of scanning electron microscopy has revealed signs of wear on conodont elements and it is thought that the host organism probably produced only one set in its life time.

Clearly very little can be stated about possible life cycles since the host organism of conodonts (conodontophorid) is extinct.

Since conodonts are resistant to mechanical and chemical attack preparation techniques can utilise acids such as acetic, formic, or monochloric to release the elements from their host rocks, which are commonly carbonates. Conodonts are commonly between 200 microns and 5 millimeters in size and can be sieved from finer materials and further concentrated by heavy liquid or ultrasonic techniques.

The cleaned specimens can then be viewed using a reflected light microscope and manipulated and mounted in slides in the same manner as foraminifera. Conodonts can also be observed in thin sections.

The following images are of a representative selection of conodonts aimed at giving a general overview of the different morphotypes. Each specimen is given a generic and if possible a species name followed by the formation and the site location from which the sample was obtained.  SEM images in all cases, courtesy of Leicester University




Aulacognathus kuehni Pa element
Hughley Shales, Telychian Stage, Llandovery Series, Silurian
Devils Dingle, nr. Buildwas, Shropshire

Apsidognathus tuberculatus Pa element
Wych Formation, Telychian Stage, Llandovery Series, Silurian
Gullet Quarry, Malvern Hills, UK

Distomodus staurognathoides Pa element
Hughley Shales, Telychian Stage, Llandovery Series, Silurian
Devils Dingle, nr. Buildwas, Shropshire

Eoplacognathus sp. Pa element
Middle Ordovician
Suhkrumagi Section, Tallinn, Estonia

Eoplacognathus sp. Pb element
Middle Ordovician
Suhkrumagi Section, Tallinn, Estonia

Gamachignathus macroexcavatus Pa element
Upper Member, Xiushan Formation, Llandovery Series, Silurian
Leijiatun Section nr. Shiqian, Guizhou Province, China

Gamachignathus macroexcavatus Pb element
Upper Member, Xiushan Formation, Llandovery Series, Silurian
Leijiatun Section nr. Shiqian, Guizhou Province, China

Gamachignathus macroexcavatus Sa element
Upper Member, Xiushan Formation, Llandovery Series, Silurian
Leijiatun Section nr. Shiqian, Guizhou Province, China

Gamachignathus macroexcavatus Sb element
Upper Member, Xiushan Formation, Llandovery Series, Silurian
Leijiatun Section nr. Shiqian, Guizhou Province, China

Gamachignathus macroexcavatus Sc element
Upper Member, Xiushan Formation, Llandovery Series, Silurian
Leijiatun Section nr. Shiqian, Guizhou Province, China

Icriodella inconstans Pa element
Wych Formation, Telychian Stage, Llandovery Series, Silurian
Storridge, Malvern Hills, UK

Ozarkodina gulletensis Pa element
Wych Formation, Telychian Stage, Llandovery Series, Silurian
Storridge, Malvern Hills, UK

Pseudooneotodus tricornis
Wych Formation, Telychian Stage, Llandovery Series, Silurian
Storridge, Malvern Hills, UK



<

diatoms

diatom Azpeitia nodulifera (A. Schmidt) G. Fryxell & P.A. SimsDiatoms are photosynthesising algae, they have a siliceous skeleton (frustule) and are found in almost every aquatic environment including fresh and marine waters, soils, in fact almost anywhere moist. They are non-motile, or capable of only limited movement along a substrate by secretion of mucilaginous material along a slit-like groove or channel called a raphe. Being autotrophic they are restricted to the photic zone (water depths down to about 200m depending on clarity). Both benthic and planktic forms exist. Diatoms are formally classified as belonging to the Division Chrysophyta, Class Bacillariophyceae. The Chrysophyta are algae which form endoplasmic cysts, store oils rather than starch, possess a bipartite cell wall and secrete silica at some stage of their life cycle. Diatoms are commonly between 20-200 microns in diameter or length, although sometimes they can be up to 2 millimeters long. The cell may be solitary or colonial (attached by mucous filaments or by bands into long chains). Diatoms may occur in such large numbers and be well preserved enough to form sediments composed almost entirely of diatom frustules (diatomites), these deposits are of economic benefit being used in filters, paints, toothpaste, and many other applications.


Diatoms have been studied since the late eighteenth century, however the first real advances in the field came in the early nineteenth century when diatoms were popular with microscopists utilising the emerging improvements in microscope resolution. Several European workers produced hand illustrated monographs on diatoms in the late nineteenth century. Notable amongst these are the works of Cleve, Ehrenberg, Grunow, Schmidt and Van Heurck. In the early twentieth century fossil diatoms were first studied and, most famously, Hustedt (1927-66) produced a taxonomic and ecological study of diatoms which remains a key reference today. Perhaps the most complete treatment of diatoms is that of Round et al. (1990).

First recorded occurrences of diatoms are from the Jurassic, however, these are uncertain and the earliest recorded well preserved diatoms are centric forms from the Aptian-Albian stages of the Cretaceous. Since these are quite diverse assemblages it is assumed diatoms have an earlier evolutionary history, perhaps lacking a relatively robust silica frustule. As with coccoliths, the earliest forms in the fossil record may reflect a biomineralisation event rather than an evolutionary appearance. The earliest araphid (lacking a raphe) pennate diatoms appear in the Late Cretaceous, and raphid pennates in the Middle Eocene. The earliest freshwater diatoms appear in the Palaeocene in Russia and the Late Eocene in North America. In a similar manner to Radiolaria, it has been noticed that there has been a gradual progression towards less heavily silicified frustules, probably as a result of increasing competition for a limited resource (silica).

Diatoms are divided into two Orders. The Centrales (now called the Biddulphiales) which have valve striae arranged basically in relation to a point, an annulus or a central areola and tend to appear radially symmetrical, and the Pennales (now called Bacillariales) which have valve striae arranged in relation to a line and tend to appear bilaterally symmetrical. The valve face of the diatom frustule is ornamented with pores (areolae), processes, spines, hyaline areas and other distinguishing features. It is these skeletal features which are used to classify and describe diatoms, which is an advantage in terms of palaeontology since the same features are used to define extant species as extinct ones. The classification system developed by Simonsen (1979) and further developed by Round et al. (1990) is currently the most commonly accepted. Diatoms commonly found in the marine plankton may be divided into the centric diatoms including three sub-orders based primarily on the shape of the cells, the polarity and the arrangement of the processes. These are the Coscinodiscineae, with a marginal ring of processes and no polarity to the symmetry, the Rhizosoleniineae with no marginal ring of processes and unipolar symmetry, and the Biddulphiineae with no marginal ring of processes and bipolar symmetry. The pennate diatoms are divided into two sub-orders, the Fragilariineae which do not posses a raphe (araphid) and the Bacillariineae which posses a raphe.

centric diatom suborders

The evolutionary history of diatoms has been punctuated by several floristic turnovers, these have been utilised to allow basin wide biostratigraphic correlations. Diatoms are also used extensively in palaeoenvironmental studies particularly in palaeoceanography. Dissolution of diatom frustules during descent through the water column, on the sediment surface and during diagenesis may seriously alter the preserved assemblage by preferentialy dissolving more lightly silicified forms. High alkalinity of pore waters and burial temperatures in excess of 50 degrees centigrade are also known to increase dissolution of silica. Incorporation into faecal pellets or muciligenous aggregations, rapid burial and the formation of heavily silicified resting spores tend to counteract these problems, however, in marine samples it is thought that only 1% to 5% of the living assemblage in surface plankton is represented in the death assemblage found on the sediment surface. Despite these problems diatoms are still a useful and to a certain extent under-utilised group in terms of biostratigraphy.

Living diatoms often have specific salinity, temperature and other environmental tolerences, this together with the fact that a high proportion of fossil genera and species are still extant, makes it possible to use transfer functions to produce accurate palaeonvironmental reconstructions. This type of work has been used extensively and very successfuly, particularly in palaeolimnology,and the ">Environmental Change Research Centre at University College London is at the forefront of such research. The Deep Sea Drilling Project (now the "> Ocean Drilling Program ) has recovered many kilometers of cores and allowed the construction of a diatom biostratigraphy for most of the Cenozoic. Diatoms are particularly advantageous for biostratigraphic studies of high latitude sediments where calcareous microfossils are often poorly preserved, sparse, or of low diversity.

Diatoms have been well studied both in their natural habitat and in cultures by biologists and there is therefore a wealth of knowledge on their biology and ecology. The protoplast of diatoms consists of a cytoplasmic layer that lines the interior of the frustule and surrounds a large central vacuole, within the cytoplasmic layer there is a diploid nucleus and two to several pigment-bearing plastids (the site of photosyntheseis). The diatom frustule is often likened to a pill-box or agar dish with an epitheca (larger upper valve), and a hypotheca (smaller lower valve). The vertical lip or rim of the epitheca is called the epicingulum, and the epicingulum fits over (slightly overlaps) the hypocingulum of the hypotheca. The epicingulum and hypocingulum with one or several connective bands make up the girdle. Many diatoms are heterovalvate, i.e., the two valves of the frustule are dissimilar. This is most obvious within the family Achnanthaceae where one valve has a raphe and the other does not, and the Cymatosiraceae where one valve has a tubular process and the other does not. Chain-forming species with cells linked together by siliceous structures may, in addition, have separation valves. These valves are morphologically different from the valves within the chain. Therefore, one species may have four morphologically distinct types of valves.

frustule terminology diagram

When a cell divides each new cell takes as its epitheca a valve of the parent frustule, and within ten to twenty minutes builds its own hypotheca; this process may occur between one and eight times per day. Availability of dissolved silica limits the rate of vegetative reproduction, but also because this method progressively reduces the average size of the diatom frustule in a given population there is a certain threshold at which restoration of frustule size is neccesary. Auxospores are then produced, which are cells that posses a different wall structure lacking the siliceous frustule and swell to the maximum frustule size. The auxospore then forms an initial cell which froms a new frustule of maximum size within itself. Many neritic planktonic diatoms alternate between a vegetative reproductive phase and a thicker walled resting cyst or statospore stage. The siliceous resting spore commonly forms after a period of active vegetative reproduction when nutrient levels have been depleted. Statospores may remain entirely within the the parent cell, partially within the parent cell or be isolated from it. An increase in nutreint levels and/or length of daylight cause the statospore to germinate and return to its normal vegatative state. Seasonal upwelling is therefore a vital part of many diatoms life cycle as a provider of nutrients and as a transport mechanism which brings statospores or their vegetative products up into the photic zone.

The resting spore morphology of some species is similar to that of the corresponding vegetative cell, whereas in other species the resting spores and the vegetative cells differ strongly. The two valves of a resting spore may be similar or distinctly different. Often the first valve formed is more similar to the valves of the vegetative cells than the second valve. This diversity of the valve types belonging to the same species calls for caution in identification work using cleaned diatom material.

simplified diatom lifecycle diagram click to view larger version

Diatoms are easily prepared for veiwing using a light microscope. Wet samples can be smeared onto a slide for immediate examination and determination of possible further treatments. Organic matter may obscure the detail of the frustule so this is commonly removed using hydrogen peroxide or some other oxidising agent. A small amount of hydrochloric acid may be added to remove any calcium carbonate and the sample then rinsed in distilled water until free of acids. The sample can then be dilluted and strewn onto coverslips, dried and mounted on slides. Because the refractive indices of water and silica are very similar, a mounting medium with a higher refractive index is used in order to increase the contrast. An excellent guide to preparing diatom slides is provided by the Geography Department at UCL.

Diatom preparations may be observed using brightfield as well as phase contrast settings on a light microscope, the later is better for veiwing lightly silicified genera. Times forty dry or times one hundred oil-immersion objectives are most commonly used. The use of the scanning electron microscope allows the differentiation of processes if the inside of the valve can be veiwed. This is of particular use when attempting to speciate some of the centric diatoms. A guide to microscopy in relation to diatom preparations is provided by the Geography Department at UCL.

The following images are of a representative selection of diatoms aimed at giving a general overview of the different morphotypes. Each specimen is given a generic and if possible a species name followed by its age range.


Diploneis suborbicularis (Gregory) Cleve

East Winch Borehole, Nar Valley, Norfolk, UK
30 microns x 20 microns
Auliscus sculptus (W. Smith) Ralfs ex. Pritchard

East Winch Borehole, Nar Valley, Norfolk, UK
50 microns
Lyrella lyra (Ehrenberg)

East Winch Borehole, Nar Valley, Norfolk, UK
80 x 30 microns
Dimeregramma sp.

East Winch Borehole, Nar Valley, Norfolk, UK
50 microns
Nitzschia punctata (W. Smith) Grun

East Winch Borehole, Nar Valley, Norfolk, UK
45 x 15 microns
Cocconeis molesta var. crucifera Grunow

East Winch Borehole, Nar Valley, Norfolk, UK
30 x 15 microns (SEM)
Actinoptychus senarius Ehrenberg
Cretaceous to Recent
East Winch Borehole, Nar Valley, Norfolk, UK
75 microns
Coscinodiscus radiatus Ehrenberg emend. Sancetta
Eocene to Recent
Chatham Deep, S.W. Pacific
75 microns
Actinocyclus ingens Rattray
Miocene to Pleistocene
Louisville Moat, S.W. Pacific
37 microns
Thalassiosira oestrupii (Ostenfeld) Hasle emend. Fryxell and Hasle
Miocene to Recent
Louisville Moat, S.W. Pacific
10 microns
Thalassiosira lentiginosa (Janisch) Fryxell
Mid to Upper Pliocene
Chatham Deep, S.W. Pacific
53 microns
Asteromphalus hookeri Ehrenberg
Pliocene to Recent
Bounty Fan, S.W. Pacific
76 microns
Nitzschia reinholdii Kanaya ex. Barron and Baldauf
Miocene to Pleistocene
Louisville Moat, S.W. Pacific
91 microns apical axis
Azpeitia tabularis (Grunow) Fryxell and Sims
Miocene to Recent
Chatham Deep, S.W. Pacific
19 microns
Fragilariopsis ritscheri Hustedt
Pliocene to Recent
Louisville Moat, S.W. Pacific
8 microns transapical axis (broken specimen)
Hemidiscus cuneiformis Wallich
Miocene to Recent
Chatham Deep, S.W. Pacific
31 microns
Chaetoceros Ehrenberg (Resting spore)

Chatham Deep, S.W. Pacific
18 microns
Chaetoceros Ehrenberg (Resting spore)

Louisville Moat, S.W. Pacific
13 microns
Thalassiosira eccentrica (Ehrenberg) Cleve
Recent
North Chatham Terrace, S.W. Pacific
25 microns
Cyclotella stelligera (Cleve et Grunow) Van Heurck
Freshwater form
North Chatham Terrace, S.W. Pacific
27 microns
Stellarima microtrias (Ehrenberg) Hasle and Sims (resting spore)
Recent
North Chatham Terrace, S.W. Pacific
50 microns
Thalassiosira ferelineata Jouse
Recent
Chatham Deep Terrace, S.W. Pacific
30 microns
Psammodictyon panduriforme (Gregory) Mann
Recent
Chatham Deep, S.W. Pacific
65 microns apical axis
Coscinodiscus radiatus Ehrenberg emend. Sancetta
Eocene to Recent
North Chatham Terrace, S.W. Pacific
36 microns
Thalassiosira lineata Jouse
Eocene to Recent
Chatham Deep, S.W. Pacific
30 microns
Thalassionema nitzschoides (Grunow) Grunow ex. Hustedt
Miocene? to Recent
Walvis Ridge, S.E. Atlantic
72 microns apical axis
Stephanopyxis turris (Greville and Arnott) Ralfs in Pritchard
Late Cretaceous to Recent
Walvis Ridge, S.E. Atlantic
23 microns (low focus)
Stephanopyxis turris (Greville and Arnott) Ralfs
Late Cretaceous to Recent
Walvis Ridge, S.E. Atlantic
23 microns (high focus)
Azpeitia nodulifer (Schmidt) Fryxell and Sims
Mid Miocene to Recent
Walvis Ridge, S.E. Atlantic
150 microns
Delphineis karstenii Fryxell in Fryxell and Miller

Walvis Ridge, S.E. Atlantic
32 microns
Eucampia antarctica (Castracane) Mangin 1915 (girdle veiw)
Mid Miocene to Recent
Walvis Ridge, S.E. Atlantic
26 microns (horn to horn)


foraminifera

foraminferaForaminifera have a geological range from the earliest Cambrian to the present day. The earliest forms which appear in the fossil record (the allogromiine) have organic test walls or are simple agglutinated tubes. The term "agglutinated" refers to the tests formed from foreign particles "glued" together with a variety of cements. Foraminifera with hard tests are scarce until the Devonian, during which period the fusulinids began to flourish culminating in the complex fusulinid tests of the late Carboniferous and Permian times; the fusulinids died out at the end of the Palaeozoic. The miliolids first appeared in the early Carboniferous, followed in the Mesozoic by the appearance and radiation of the rotalinids and in the Jurassic the textularinids. The earliest forms are all benthic, planktic forms do not appear in the fossil record until the Mid Jurassic in the strata of the northern margin of Tethys and epicontinental basins of Europe. They were probably meroplanktic (planktic only during late stages of their life cycle). The high sea levels and "greenhouse" conditions of the Cretaceous saw a diversification of the planktic foraminifera, and the major extinctions at the end of the Cretaceous included many planktic foraminifera forms. A rapid evolutionary burst occurred during the Palaeocene with the appearance of the planktic globigerinids and globorotalids and also in the Eocene with the large benthic foraminifera of the nummulites, soritids and orbitoids. The orbitoids died out in the Miocene, since which time the large foraminifera have dwindled. Diversity of planktic forms has also generally declined since the end of the Cretaceous with brief increases during the warm climatic periods of the Eocene and Miocene.

 History of Study

The study of foraminifera has a long history, their first recorded "mention" is in Herodotus (fifth century BC) who noted that the limestone of the Egyptian pyramids contained the large benthic foraminifer Nummulites. In 1835 Dujardin recognised foraminifera as protozoa and shortly afterwards d'Orbigny produced the first classification. The famous 1872 HMS Challenger cruise , the first scientific oceanographic research expedition to sample the ocean floor collected so many samples that several scientists, including foraminiferologists such as H.B. Brady were still working on the material well in to the 1880's. Work on foraminifera continued throughout the 20th century, workers such as Cushman in the U.S.A and Subbotina in the Soviet Union developed the use of foraminifera as biostratigraphic tools. Later in the 20th century Loeblich and Tappan and Bolli carried out much pioneering work.

 Range

Foraminifera have a geological range from the earliest Cambrian to the present day. The earliest forms which appear in the fossil record (the allogromiine) have organic test walls or are simple agglutinated tubes. The term "agglutinated" refers to the tests formed from foreign particles "glued" together with a variety of cements. Foraminifera with hard tests are scarce until the Devonian, during which period the fusulinids began to flourish culminating in the complex fusulinid tests of the late Carboniferous and Permian times; the fusulinids died out at the end of the Palaeozoic. The miliolids first appeared in the early Carboniferous, followed in the Mesozoic by the appearance and radiation of the rotalinids and in the Jurassic the textularinids. The earliest forms are all benthic, planktic forms do not appear in the fossil record until the Mid Jurassic in the strata of the northern margin of Tethys and epicontinental basins of Europe. They were probably meroplanktic (planktic only during late stages of their life cycle). The high sea levels and "greenhouse" conditions of the Cretaceous saw a diversification of the planktic foraminifera, and the major extinctions at the end of the Cretaceous included many planktic foraminifera forms. A rapid evolutionary burst occurred during the Palaeocene with the appearance of the planktic globigerinids and globorotalids and also in the Eocene with the large benthic foraminifera of the nummulites, soritids and orbitoids. The orbitoids died out in the Miocene, since which time the large foraminifera have dwindled. Diversity of planktic forms has also generally declined since the end of the Cretaceous with brief increases during the warm climatic periods of the Eocene and Miocene.

geologic time scale diagram click to view larger version

Classification

Foraminifera are classified primarily on the composition and morphology of the test. Three basic wall compositions are recognised, organic (protinaceous mucopolysaccharide i.e. the allogromina), agglutinated and secreted calcium carbonate (or more rarely silica). Agglutinated forms, i.e the Textulariina, may be composed of randomly accumulated grains or grains selected on the basis of specific gravity, shape or size; some forms arrange particular grains in specific parts of the test. Secreted test foraminifera are again subdivided into three major groups, microgranular (i.e. Fusulinina), porcelaneous (i.e. Miliolina) and hyaline (i.e. Globigerinina). Microgranular walled forms (commonly found in the late Palaeozoic) are composed of equidimensional subspherical grains of crystalline calcite. Porcelaneous forms have a wall composed of thin inner and outer veneers enclosing a thick middle layer of crystal laths, they are imperforate and made from high magnesium calcite. The hyaline foraminifera add a new lamella to the entire test each time a new chamber is formed; various types of lamellar wall structure have been recognised, the wall is penetrated by fine pores and hence termed perforate. A few "oddities" are also worth mentioning, the Suborder Spirillinina has a test constructed of an optically single crystal of calcite, the Suborder Silicoloculinina as the name suggests has a test composed of silica. Another group (the Suborder Involutina) have a two chambered test composed of aragonite. The Robertinina also have a test composed of aragonite and the Suborder Carterina is believed to secrete spicules of calcite which are then weakly cemented together to form the test.

 diagram showing foraminiferal suborders and their envisaged phylogeny

The morphology of foraminifera tests varies enormously, but in terms of classification two features are important. Chamber arrangement and aperture style, with many subtle variations around a few basic themes. These basic themes are illustrated in the following two diagrams but it should be remembered that these are only the more common forms and many variations are recognised.
  diagram showing principle chamber arrangements click to view larger version

 diagram showing principle aperture styles click to view larger version

Applications

As previously mentioned, foraminifera have been utilised for biostratigraphy for many years, and they have also proven invaluable in palaeoenvironmental reconstructions most recently for palaeoceanographical and palaeoclimatological purposes. For example palaeobathymetry, where assemblage composition is used and palaeotemperature where isotope analysis of foraminifera tests is a standard procedure. In terms of biostratigraphy, foraminifera have become extremely useful, different forms have shown evolutionary bursts at different periods and generally if one form is not available to be utilised for biostratigraphy another is. For example preservation of calcareous walled foraminifera is dependent on the depth of the water column and Carbonate Compensation Depth (the depth below which dissolution of calcium carbonate exceeds the rate of its deposition), if calcareous walled foraminifera are therefore not preserved agglutinated forms may be. The oldest rocks for which foraminifera have been biostratigraphically useful are Upper Carboniferous to Permian strata, which have been zoned using the larger benthic fusulinids. Planktic foraminifera have become increasingly important biostratigraphic tools, especially as petroleum exploration has extended to offshore environments of increasing depths. The first and last occurrence of distinctive "marker species" from the Cretaceous to Recent (particularly during the Upper Cretaceous) has allowed the development of a well established fine scale biozonation. Benthic foraminifera have been used for palaeobathymetry since the 1930's and modern studies utilise a variety of techniques to reconstruct palaeodepths. For studies of relatively recent deposits simple comparison to the known depth distribution of modern extant species is used. For older material changes in species diversity, planktic to benthic ratios, shell-type ratios and test morpholgy have all been utilised. Variations in the water temperature inferred from oxygen isotopes from the test calcite can be used to reconstruct palaeoceanographic conditions by careful comparison of changes in oxygen isotope levels as seen in benthic forms (for bottom waters) and planktic forms(for mid to upper waters). This type of study has allowed the reconstruction of oceanic conditions during the Eocene-Oligocene, the Miocene and the Quaternary. Benthic foraminifera have been divided into morphogroups based on the test shape and these groups used to infer palaeo-habitats and substrates; infaunal species tending to be elongate and streamlined in order to burrow into the substrate and epifaunal species tending to be more globular with one relatively flatter side in order to facilitate movement on top of the substrate. It should be remembered, however, that a large variety of morphologies and possible habitats have been recognised making such generalisations of only limited use. Studies of modern foraminifera have recognised correlations between test wall type (for instance porcelaneous, hyaline, agglutinated), palaeodepths and salinity by plotting them onto triangular diagrams.

 Biology

Studies of living foraminifera, in controlled laboratory environments, have provided limited information regarding trophic strategies but much has been inferred by relating test morphology to habitat. Foraminifera utilise a huge variety of feeding mechanisms, as evidenced by the great variety of test morphologies that they exhibit. From the variety of trophic habits and test morphologies a few generalisations may be made. Branching benthic foraminifera such as Notodendrodes antarctikos ,which resembles a microscopic tree, absorbs dissolved organic matter via a "root" system. Other sessile benthic foraminifera exhibit test morphologies dependent on the substrate on or in which they live, many are omnivorous opportunistic feeders and have been observed to consume autotrophic and heterotrophic protists (including other foraminifera), metazoans and detritus. Some suspension feeding foraminifera utilise their pseudopodia to capture food from the water column, or interstitial pore waters, Elphidium crispum forms a "spiders web" between the stipes of coralline algae. Infaunal forms are probably detritivores and commonly have elongate tests to facilitate movement through the substrate. Benthic and planktonic foraminifera which inhabit the photic zone often live symbiotically with photosynthesising algae such as dinoflagellates, diiatoms and chlorophytes. It is thought the large benthic, discoidal and fusiform foraminifera attain their large size in part because of such associations. Foraminifera are preyed upon by many different organisms including worms, crustacea, gastropods, echinoderms, and fish. It should be remembered that the biocoenosis (life assemblage) will be distorted by selectivedestruction by predators.

   diagram showing generalised foraminiferal life cycle click to view larger version

Life Cycle

Of the approximately 4000 living species of foraminifera the life cycles of only 20 or so are known. There are a great variety of reproductive, growth and feeding strategies, however the alternation of sexual and asexual generations is common throughout the group and this feature differentiates the foraminifera from other members of the Granuloreticulosea. An asexually produced haploid generation commonly form a large proloculus (initial chamber) and are therefore termed megalospheric. Sexually produced diploid generations tend to produce a smaller proloculus and are therefore termed microspheric. Importantly in terms of the fossil record, many foraminiferal tests are either partially dissolved or partially disintegrate during the reproductive process.The planktonic foraminifera Hastigerina pelagica reproduces by gametogenesis at depth, the spines, septa and apertural region are resorbed leaving a tell-tale test. Globigerinoides sacculifer produces a sac-like final chamber and additional calcification of later chambers before dissolution of spines occurs, this again produces a distinctive test, which once gametogenesis is complete sinks to the sea bed.

 Preparation Techniques

WARNING: Please remember all preparation techniques require the use of hazardous materials and equipment and should only be carried out in properly equiped laboratories, wearing the correct safety clothing and under the supervision of qualified staff. Foraminifera range in size from several millimeters to a few tens of microns and are preserved in a variety of rock types. The preparation techniques used depend on the rock type and the "predicted" type of foraminifera one expects to find. Very hard rocks such as many limestones are best thin sectioned as in normal petrological studies, except instead of grinding to a set thickness (commonly 30 microns) the sample is ground very carefully by hand until the optimum thickness is obtained for each individual sample. This is a skilled job and requires expensive equipment but provides excellent results and is particularly used in the study of larger benthic foraminifera from reef type settings. Planktic and smaller benthic foraminifera are prepared by crushing the sample into roughly five millimeter fragments. The crushed sample is then placed in a strong glass beaker or similar vessel and water and washing soda or 6% hydrogen peroxide added, left to stand and then heated and allowed to simmer. The length of time the sample is left to simmer depends on the rock type involved and if peroxide is used the sample should not be left immersed in the solution for more than about half an hour. Next, the material is washed through a 63 micron sieve untill the liquid coming through the sieve is clean (i.e. the clay fraction has been removed). The sample can then be dried and sieved into fractions (generally 63-125 microns, 125-250 microns, 250-500 microns and greater than 500 microns) using a "nest" of dry sieves. Care must be taken to clean all sieves and materials used between the preparation of each sample to prevent contamination.

 Observation Techniques

Thin sections are veiwed using transmitted-light petrological type microscopes. Washed, dried fossil samples can be picked from any remaining sediment using a fine brush and a reflected light, binocular microscope. The best method is to scatter a fine dusting of sieved sediment on to a black tray divided into squares, this can then be scanned under the microscope and any foraminifera preserved in the sediment can be picked out with a fine brush (preferably a 000 sable-haired brush). The picked specimens can then be mounted in card slides divided into numbered squares with sliding glass covers. Gum tragocanth was traditionally used to attach the specimens to the slides but modern office-type paper adhesives are now used.

Images

The following images are of a representative selection of foraminifera aimed at giving a general overview of the different morphotypes. Each specimen is given a generic and, if possible, a species name followed by its age range, the site location from which the sample was obtained and its size in microns. LM (Light Microscope) SEM (Scanning Electron Microscope) TS (Thin Section). Typical and selected marker species are illustrated from each main period of the geological column in which foraminifera occur. Because Foraminifera formsuch a diverse taxon they have been split into three groups: planktics, benthics and larger benthics. Planktic Foraminifera
  • Benthic Foraminifera
  • Larger Benthic Foraminifera
  • Planktic
    Globigerina bulloides d'Orbigny
    Pliocene-Recent
    South Africa
    380 microns spiral view SEM
    Globigerina bulloides d'Orbigny
    Pliocene-Recent
    South Africa
    416 microns umbilical view SEM
    Globigerinoides ruber d'Orbigny
    Miocene-Recent
    South Africa
    spiral view SEM
    Globigerinoides sacculifer (Brady)
    Miocene-Recent
    South Africa
    spiral view SEM
    Globigerinoides sacculifer (Brady)
    Miocene-Recent
    South Africa
    umbilical view SEM
    Globorotalia inflata d'Orbigny
    Pliocene-Recent
    South Africa
    spiral view SEM
    Globorotalia inflata d'Orbigny
    Pliocene-Recent
    South Africa
    umbilical view SEM
    Globorotalia menardii (Parker, Jones and Brady)
    Pliocene-Recent
    South Africa
    spiral view SEM
    Globorotalia menardii (Parker, Jones and Brady)
    Pliocene-Recent
    South Africa
    umbilical view SEM
    Neogloboquadrina pachyderma (Ehrenberg)
    Pliocene-Recent
    South Africa
    spiral view SEM
    Neogloboquadrina pachyderma (Ehrenberg)
    Pliocene-Recent
    South Africa
    umbilical view SEM
    Orbulina universa d'Orbigny
    Middle Miocene-Recent
    South Africa
    SEM
    Hantkenina alabamensis Cushman, 1927
    Eocene
    Montgomery Landing, Red River, Louisiana, USA
    side view (slightly broken specimen) SEM
    Pseudohastigerina micra (Cole, 1927)
    Eocene-Oligocene
    Montgomery Landing, Red River, Louisiana, USA
    side view SEM
    Globorotalia centralis Cushman and Bermudez, 1937
    Eocene
    Montgomery Landing, Red River, Louisiana, USA
    umbilical view SEM
    Globorotalia cerro-azulensis Cole, 1928
    Eocene
    Montgomery Landing, Red River, Louisiana, USA
    umbilical view SEM
    Parasubbotina varianta (Subbotina, 1953)
    Lower-Middle Palaeocene
    Zin Valley, Israel
    spiral view SEM
    Parasubbotina varianta (Subbotina, 1953)
    Lower-Middle Palaeocene
    Zin Valley, Israel
    umbilical view SEM
    Parasubbotina pseudobulloides (Plummer, 1926)
    Lower-Middle Palaeocene
    Zin Valley, Israel
    umbilical view SEM
    Subbotina triloculinoides (Plummer, 1926)
    lower-upper Palaeocene
    Zin Valley, Israel
    umbilical view SEM
    Subbotina triloculinoides (Plummer, 1926)
    Palaeocene
    Zin Valley, Israel
    spiral view SEM
    Abathomphalus mayaroensis (Bolli)
    Upper Maastrichtian (Upper Cretaceous)
    Kassbah, N.W. Syria
    umbilical view SEM
    Abathomphalus mayaroensis (Bolli)
    Upper Maastrichtian (Upper Cretaceous)
    Kassbah, N.W. Syria
    lateral view SEM
    Contusotruncana contusa (Cushman)
    Upper Maastrichtian (Upper Cretaceous)
    Kassbah, N.W. Syria
    dorsal view SEM
    Contusotruncana contusa (Cushman)
    Upper Maastrichtian (Upper Cretaceous)
    Kassbah, N.W. Syria
    ventral view SEM
    Globotruncana linneiana (d'Orbigny)
    Santonian-Maastrichtian (Upper Cretaceous)
    Kassbah, N.W. Syria
    dorsal view SEM
    Globotruncana linneiana (d'Orbigny)
    Santonian-Maastrichtian (Upper Cretaceous)
    Kassbah, N.W. Syria
    ventral view SEM
    Racemiguembelina fructicosa (Egger)
    Middle-Uppper Maastrichtian (Upper Cretaceous)
    Kassbah, N.W. Syria
    SEM
    Racemiguembelina fructicosa (Egger)
    Middle-Uppper Maastrichtian (Upper Cretaceous)
    Kassbah, N.W. Syria
    SEM
    Pseudotextularia elegans (Rzehak)
    Campanian-Maastrichtian (Upper Cretaceous)
    Kassbah, N.W. Syria
    SEM
    Pseudoguembelina excolata (Cushman)
    Campanian-Maastrichtian (Upper Cretaceous)
    Kassbah, N.W. Syria
    SEM
    Archaeoglobigerina cretacea (d'Orbigny)
    Coniacian-Maastrichtian (Upper Cretaceous)
    Sens, N. France
    scale bar 100 microns edge view SEM
    Archaeoglobigerina cretacea (d'Orbigny)
    Coniacian-Maastrichtian (Upper Cretaceous)
    Sens, N. France
    scale bar 100 microns dorsal view SEM
    Archaeoglobigerina cretacea (d'Orbigny)
    Coniacian-Maastrichtian (Upper Cretaceous)
    Sens, N. France
    scale bar 100 microns ventral view SEM
    Hedbergella delrioensis (Carsey)
    Coniacian-Santonian (Upper Cretaceous)
    Faircross, UK
    scale bar 100 microns ventral view SEM
    Whiteinella baltica Douglas and Rankin
    Coniacian-Santonian (Upper Cretaceous)
    Winterbourne, UK
    scale bar 100 microns ventral view SEM
    Heterohelix pulchra (Brotzen)
    Coniacian-Maastrichtian (Upper Cretaceous)
    N. Norfolk, UK
    scale bar 100 microns side view SEM
    Heterohelix globulosa (Ehrenberg)
    Coniacian-Maastrichtian (Upper Cretaceous)
    Sens, N. France
    scale bar 100 microns side view SEM
    Hedbergella planispira (Tappan)
    Aptian-Coniacian (Upper Cretaceous)
    Karai, S.E. India
    ventral view SEM
    Hedbergella sigali Moullade
    Barremian-Aptian (Lower Cretaceous)
    Karai, S.E. India
    ventral view SEM
    Ticinella primula Luterbacher
    Albian (Lower Cretaceous)
    Karai, S.E. India
    ventral view SEM
    Benthic
    Spiroloculina ornata (d'Orbigny)
    -Recent
    Sea of Marmara
    side view SEM
    Elphidium macellum (Fichtel and Moll)
    -Recent
    Sea of Marmara
    side view SEM
    Brizalina alata (Seguenza)
    -Recent
    Sea of Marmara
    side view SEM
    Cassidulina neocarinata (Thalmann)
    -Recent
    Sea of Marmara
    ventral view SEM
    Siphotextularia concava (Karrer)
    -Recent
    Sea of Marmara
    side view SEM
    Bigenerina nodosaria (d'Orbigny)
    ??-Recent
    Sea of Marmara
    side view SEM