CALCAREOUS MICROFOSSILS

by Dr. Paul F. Ciesielski University of Florida

FORAMINIFERA

INTRODUCTION TO FORAMINIFERA

I. What are Foraminifera?

belong to the Phylum Protozoa
unicellular, non-flagellate, possessing protoplasmic extensions called pseudopodia
assigned to the Class Sarcodina, differ from other Sarcodina by their possession of a mineralized test
benthic as well as planktic habit
dimorphism found among benthic forams but not planktic (caused by alternation of generations, sexual and asexual)

II. Morphology of Foraminiera

Foraminifera taxa are classified primarily on the basis of wall composition, test shape, and chamber shape and arrangement. Types of apertures, aperture position, and ornamentation are often diagnostic at the generic or specific level (see handouts).

initial chamber: proloculus
may have one or more subsequent chambers
see handout for other arrangements of chambers
see Haq and Boersma (on reserve) for other chamber shapes and arrangements

evolute: all chambers visible on both sides
involute: majority of previous coils hidden by outer whorl
trochospiral: spiral up the axis of coiling

side showing all whorls: dorsal
side showing outer whorl: ventral

streptospiral: trochospiral coiling in several planes

D. Positions of apertures (see handout)

E. Ornamentation (see handout)

FORAMINIFERAL EVOLUTION

I. Paleozoic

B. coiling:

attached- Tolypammina (Silurian)
planispiral- Ammodiscus (Silurian)
high spiral- Turittela (Silurian)

multichambered (Devonian)

calcareous microgranular (Devonian)

sugary appearance, microgranular

calcareous fibrous (Devonian)
porcelaneous (Late Carbon.-Permian) Miliolidae

e.g. Endothyra and Fusulinidae (Carboniferous)

G. Permian extinctions of 10 families

II. Mesozoic

B. first ornamented- Nodosariidae (Jurassic)

C. first bathyal- Nodosariidae (Jurassic)

D. first planktic- Nodosariidae (Jurassic)

E. major terminal extinction of terminal Cretaceous planktics

III. Cenozoic

B. large calcareous forams declined in the Paleogene, now only in the Indo-Pacific tropics

BENTHIC FORAMINIFERAL FUNCTIONAL MORPHOLOGY

Form, Structure, and Environment- "Form follows function", as within other organisms, foraminifera develop similar morphologies in similar environments (Convergent Evolution)

I. Buliminids and Uvigerinids

are well know examples exhibiting different forms in different depth habitats.

A. Uvigerinids

Ornamentation	Habitiat
finely striate to hispid (minute spines)	outer shelf to upper- mid bathyal
costate (ridges)	to upper bathyal-outer
costate spinose (spiny)	neritic (in warm climates)
spinose	lower bathyal-abyssal
papillate (nipple like structures)	abyssal

B. Bolivina

neritic species	small prolate shaped
bathyal species	large and compressed

species abundance correlates with dissolved oxygen
suggests form controlled by respiration or gas exchange of cell
compressed form: high surface area/ volume, better facilitating gas exchange

II. Compressed forms

Exhibited by many macroscopic foraminiera but form "follows a different function"

A. 3 forms: flattened

8% of lituolids (microgranular calcite with complicated interiors) discoidal
7% of miliolids (porcellaneous-imperforate)
8% rotalids

B. planispiral-fusiform

50% fusulinids
10% miliolids

In the above cases the large surface area/ volume appears adaptive to increasing the efficiency of symbionts. Many inhabited low-nutrient, tropical waters.

III. Other Form and Habitat Relationships

B. An erect test with aperature(s) oriented away from the substrate: suspension feeders

C. Mostly trochoid, lenticular or flattened: active herbivores

27% miliolids
21% fusulinids
19% lituolids
17% nodosarids
52% rotalids
20% of all foram genera

D. Chamberlets: test strengthing with thin walls for symbiont photosynthesis

FORAMINIFERA AND ANALYSES OF PALEOENVIRONMENT: SOME EXAMPLES

I. Planktic Foraminifera

Neogloboquadrina pachyderma

Orbulina universa

II. Benthic Foraminifera

STRATIGRAPHY

Standard zones have been established which are commonly refered to in Cenozoic stratigraphic studies. These zones have widespread application in low to mid-latitudes. The zonal scheme for the Neogne was established by Banner and Blow (Banner, F.T., Blow, W.H., 1965, Progress in the planktonic foraminiferal biostratigraphy of the Neogene. Nature, 208:1164-1166.) and subsequent papers established a zonal scheme for the Paleogene.

the Neogene has 20 zones; N4 (the oldest) to N23 (the youngest). Note: N stands for Neogene.
the Paleogene has 22 zones; P1 (earliest Paleocene) to P22 (latest Oligocene). Note: NP stands for nannofossils-Paleogene.
N1-N3 no longer exist having been shown to be equivalent to P20-P22.

CALCAREOUS NANNOFOSSILS

I. INTRODUCTION TO CALCAREOUS NANNOFOSSILS

Calcareous nannoplankton constitute a diverse group of calcareous microfossils which appear to be related to modern (extant) coccolithophores.
Coccolithophores are:

marine algae belonging to the Haptophyceae (algae)
most living species possess a flagellar apparatus called the haptonema
photoautotrophic
sometimes have a motile phase and a non-motile phase which normally secretes coccoliths

II. GEOLOGIC RANGE (includes related ancestors)

first appeared in the earliest Jurassic
first diversification in early part of the late Jurassic (Oxfordian)
very diverse by the end of the Cretaceous
massive extinctions during the terminal Cretaceous

III. STRATIGRAPHY

Since the advent of the Deep Sea Drilling Project the stratigraphic and biogeographic distribution of calcareous nannoplankton have been studied in great detail.
In most latitudes, stratigraphic ranges have been partially calibrated to paleomagnetic stratigraphy.
Diveristy is much reduced at high latitudes reducing their utility in these regions
Diachroneity exists with respect to datums across latitude
Standard zones have been established which are commonly refered to in Cenozoic stratigraphic studies:

Martini and Worsley (1970) established the standard zonal scheme for the Neogene and Quaternary and Martini (1970) for the Paleogene.
the Neogene has 21 zones; NN1 (the oldest) to NN21 (the youngest). Note: NN stands for nannofossils-Neogene.
the Paleogene has 25 zones; NP1 (earliest Paleocene) to NP25 (latest Oligocene). Note: NP stands for nannofossils-Paleogene.

IV. Key Cenozoic Genera Non-coccolithophore Nannoliths

1. Ceratoliths : Horse-shoe shapped (e.g. Ceratolithus and Amaurolithus)
2. Discoasters: Disc-shaped, rayed asteroliths, with or without stems or knobs. (e.g. Discoaster, Tribrachiatus).
3. Fasiculithids: Subcylindrical proximal column of wedge-shaped crystals whose thin edges meet along the center. Proximal end may have an apical spine. (One genus- Fasiculithus).
4. Sphenolithids: Rounded to polygonal base, mounted by an elongated rib-cone with one or more spines radiating from the center (Sphenolithus)
5. Heliolithids: Two abutting unequal shields lacking a connecting tube and one shield with subradial sutures (Heliolithus)

Genera Incertae sedis

1. Isthmolithus: Shaped like an elongate parallelogram with wide walls and transverse septa.
2. Triquetrorhabdulus: Rodlike nannoliths with three blades or edges 120^o apart and pointed or rounded ends.

Coccolithophores and related nannoliths

Coccolithids: Two-shielded coccoliths, each with one or more cycles of lelements connected at their inner margins.

Coccolithus- oval with central pore
Cruciplacolithus- +-shape dcentral structure
Chiasmolithus- x-shaped central structure Reticulofenestra- central area with fine reticulate grill

Rhabdosphaerids A central process that gives the coccolith a funnel or dome-shaped appearance. Rhabdosphaera