Page 86 - Carbonate Facies in Geologic History

Calcareous Algae 73

Figure III-2 illustrates the effect of water depth and wave energy on the mor-
phology of corals and hydrozoans in three parts of the geologic record. Several
assumptions are made: (1) Morphology has the same environmental significance
in hexacorals, rugose corals, and stromatoporoids. (2) Morphology is basically
controlled by water movement because this in turn controls such vital functions
as food gathering, mud cleaning, respiration, and lime secretion. (3) Water move-
ment is basically depth dependent. The diagram could be an oversimplification
because it does not emphasize various other interrelated controls on morphology,
e.g., currents, degree of light penetration, symbiosis, amount of fine sediment
influx. Even if the analysis is too simple the general sequence of morphologic
types seen in the geologic record permits a useful generalization.

Calcareous Algae

Another series of biological observations useful to environmental interpretation
can be made on calcareous algae. Although these forms constitute only 5--6% of

FORM AND
ENVIRON NT HOLOCE E LATE JURASSIC LATE DEVON I AN
L ITHOTHAMWI ow PTYCHOCHAETfTfS SOLEWOPORA. PARACHAETETES
CRUST RED ALGA CRUSTS RED ALGA CRUSTS, NODULES
REEF FLAT
~ -.;i ~ ~
WAVES CRASHING. LESS ACROPORA PALlIAu
THAN 1 METER; ~~
, ,
PALMATE OR I ENTED ~ AGAAA~:A"
BRANCHES, 1
BATTLEMENTS
MILLfPORA (DEEPER)
WAVE BASE TO ~/.:.:~
10 METER; .' ~~~~
MASSIVE AND ENCRUSTING
IRREGULAR, HYDROZOANS AND LARGE STROMATOPOROIDS AND
INTERSTITIAL LIME IUCROSOLEHA FINGER-LIKE FORMS
SAND AND SOME s
i~
MUD ~ !I ~~~r~ m!TABUlATE)
THAMWOPORA
T~TE FINGER ~)
MORE THAN 10 I£TERS; STVL1WA PHlLLI PSASTREA MASSIVE RI.-.osE
MUCH FORESLOPE AND FLANK
DEPTH APPLI ES ONLY .~ ":':: :-:.
~
• .t.
:
TO WINDWARD SIDE OF ~ ~ INTERSTITIAL DEBRIS
BARR I ER. MASSIVE 01 PLORIA,MOIITASTREA
KNOBBY AND DENDROID . CALAIlOPHYlLiA DISPHYLLIDS TABULAR
FINE SAND AND ~h IN MICRITE IN MICRITE STROMATOPOROIDS
I NTERNAL MUD ~-Y IN MICR ITE
': . ::' FORITES
FILLINGS BETWEEN THICKETS' OF t 5KET~
HEADS
ACRaFOl!.\. CEiVICOlII/lS HIGH LATOMEAWORA ~
BELOW 30 METERS; SHEETY THAUNASTERI A -'. .
DARK WATER; SHEETY MONTA.STRfA ~ ~
2 TO 3 I£TERl
FORKS. DEPTH ~ HIGH ~
APPLIES ONLY LS GONIOCORA~
WINDWARD CLAOOPHYlll A
Fig. III-2. Comparative morphology in genera of corals, red algae, and stromatoporoids
controlled by depth and water energy. This admittedly over-simplified sequence may be
modified by varying amounts of suspended fine clay and organic particles and by biological
evolution