Geology Reference
In-Depth Information
Warren, J. (1999): Evaporites. Their evolution and econom-
ics. - 448 pp., Oxford (Blackwell)
Further reading
: K065
Lucas, J., Prévost-Lucas, L. (2002): Phosphorite and lime-
stone, two independent end-member products of the range
of bio-productivity in shallow-marine environments. - In:
Glenn, C.R., Prévost-Lucas, L., Lucas, J. (eds.): Marine
authigenesis: from global to microbial. - SEPM, Special
Publications,
66
, 117-127
Nothold, A.J.G., Jarvis, I. (eds., 1990): Phosphorite research
and development. - Geological Society of America, Spe-
cial Publications,
52
, 326 pp.
Soudry, D. (2000): Microbial phosphate sediments. - In:
Riding, R., Awramik, S.E. (eds.): Microbial sediments. -
127-136, Berlin (Springer)
Trappe, J. (1998): Phanerozoic phosphorite depositional sys-
tems. A dynamic model for a sedimentary resource sys-
tem. - Lecture Notes in Earth Sciences,
76
, 316 pp.
Trappe, J. (2001): A nomenclature system for granular phos-
phate rocks according to depositional texture. - Sedimen-
tary Geology,
145
, 135-150
Further reading:
K066
Phosphates and phosphorites
Baturin, G.N. (1982): Stages of phosphorite formation. -
Developments in Sedimentology,
33
, 344 pp.
Bentor, Y.K. (ed., 1980): Marine phosphorites. - Society of
Economic Paleontologists and Mineralogists, Special Pub-
lications,
29
, 259 pp.
Föllmi, K.B. (1996): The phosphorus cycle, phosphogenesis
and marine phosphate-rich deposits. - Earth Science Re-
views,
40
, 55-124
Glenn, C.R., Föllmi, K.B., Riggs, S.R., Baturin, G.N., Grimm,
K.A., Trappe, J., Abed, A.M., Galli-Oliver, C., Garrison,
R.E., Ilyin, A.V., Jahl, C., Roehrlich, V., Sadaqah, R.M.Y.,
Schidlowski, M., Sheldon, R.E., Siegmund, H. (1994):
Phosphorus and phosphorites: sedimentology and envi-
ronments of formation. - Eclogae geologicae Helvetiae,
87
, 747-788
Plate 110 Phosphatization of Carbonate Rocks
Microfacies studies of phosphate rocks and phosphorites reveal striking textural similarities within carbonate
rocks. Phosphate fabrics are the result of biologic and authigenic processes as well as replacement of carbonate
particles and sediment. The term
phosphate rock
defines a rock composition with less than 50% phosphate
components, and
phosphorite
those of more than 50% phosphate components. Most ancient phosphate deposits
consist of granular phosphoritic rocks (Soudry and Nathan 1980). Paralleling the texture-based carbonate classi-
fication of Dunham (1962), orthochemical/microbial phosphorites, characterized by in situ phosphatic precipi-
tates, and granular fabrics with allochemical phosphate grains can be distinguished (Trappe 2001). The grains
are derived from: (a) the reworking of orthochemical/microbial phosphorites resulting in structureless phos-
phate grains, variously called pellets, peloids or ovoids. The spectrum of these grains also includes phosphatic
ooids, oncoids, pisoids, and fecal pellets. (b) Epigenetic replacement of carbonate grains, mostly bioclasts and
intraclasts; (c) phosphatic bioclasts, e.g. vertebrates and inarticulate brachiopods, some arthropods, and con-
odonts (see Fig. 4.9). Strong phosphatization of grains may be characteristic of lag deposits (-> 2, 3, 5); see the
Standard Microfacies Type 14.
Except for the difference in mineral composition, thin sections of phosphorites look very much like thin
sections of limestones. The plate displays texture types and grain types of granular phosphorites and phos-
phatized carbonates. Rock and grain names follow the suggestions of Trappe (2001).
1
Phosclast grainstone
. Silicified bone bed. Phosphatic skeletal grains ('phosbioclasts'; predominantly fish bones and
shark teeth, S), reworked and redeposited phosphate concretions (RPC) and black rounded lithoclasts ('phosclasts', PC)
derived from the reworking of phosphatized hard grounds. Cretaceous/Tertiary (Maastrichtian-Ypres): Imi-n-Tanoute,
Morocco.
2
Phosooid packstone
with layers of fish bones (FB) and phosphatized lithoclasts and phosooids within a carbonate matrix.
Note the open internal meshwork (arrow) and the solid exterior covering of the fish bones. Cretaceous/Tertiary (Maas-
trichtian-Ypres): Chichaoua, Morocco.
3
Phosclast rudstone.
Large phosphatized lithoclasts (L) and phosphatic skeletal grains. Early Tertiary (Thersirea Forma-
tion, Lutetian): Chichaoua, Morocco.
4
Phosphatized ooids
(OO) and small rounded skeletal grains. Same locality as -> 3.
5
Phosphatized lithoclasts.
Grains exhibit complete or only marginal phosphatization. Early Carboniferous (Delle Phos-
phatic Member, Oseagean-Meramecian): Eureka Mining District, Mammoth Mountain, U.S.A.
6
Hardground with microbial phosphate crusts
(arrows). The rock is a phoslitho/bioclastic packstone. Note the high com-
positional variability of grains comprising lithoclasts, ooids, quartz grains and skeletal grains including bryozoans (B),
echinoids (E) and serpulids (S). Early Tertiary (Amniter Formation, Thanet-Ypres): Iris-n-Sebt, Morocco.
-> 1-6: Courtesy of J. Trappe (Bonn)
