Geology Reference
In-Depth Information
is induced by desiccation, displacive crystallization of
calcite, root activity and/or extensive periods of disso-
lution.
sediments, and lacustrine carbonates and shallow-ma-
rine carbonates. Different host sediments cause differ-
ent associations of calcrete profiles, horizons and as-
sociations (Theriault and Desrochers 1994). Since pa-
leosols can form on limestones of marine origin only
when the relative sea level is lowered, paleosols are
key criteria for bounding surfaces in sequence stratig-
raphy. The combined use of paleocaliche and paleo-
karst criteria gives us a detailed picture of the emer-
gence evolution of platforms (Davies 1991; Webb 1994).
(6) Carbonate cement
•
Cement and microsparite.
Common cement types
in caliche are vadose micritic cement, blocky calcite
cement and meniscus cement. Microsparry fabrics are
common.
15.1.2 Significance of Paleocaliche and
Paleosols
Basics: Pedogenic carbonates and paleocaliche
Bain, R.J., Foos, A.M. (1993): Carbonate microfabrics re-
lated to subaerial exposure and paleosol formation. - In:
Rhezak, R., Lavoie, D.L. (eds.): Carbonate microfabrics.
- 19-27, New York (Springer)
Bullock, P., Fedoroff, N., Jongerius, A., Stoops, G., Tursina,
G., Babel, U. (1985): Handbook of soil thin section de-
scription. - 152 pp., Wolverhampton (Waine Research
Publications)
Davies, J.R. (1991): Karstification and pedogenesis on a late
Dinantian carbonate platform, Anglesey, North Wales. -
Proceedings of the Yorkshire Geological Society,
48
, 297-
321
Esteban, M., Klappa, C.F. (1983): Subaerial exposure envi-
ronment. - In: Scholle, P.A., Bebout, D.G., Moore, C.H.
(eds.): Carbonate depositional environments. - American
Paleosols have been known since the Precambrian.
Most case studies deal with examples from the Quater-
nary and Tertiary, but other papers deal with the Creta-
ceous, Jurassic, and Late Paleozoic.
The recognition of paleosols and paleocaliche is of
paramount importance in interpretating past climate
(Mack and James 1994; Theriault and Desrochers
1994), the evolution of the atmosphere (Cerling 1991;
Ekart et al. 1999), and weathering (Martini and Chesworth
1992). Most geological studies of paleosols focus on
caliche. Paleocaliche is hosted by sandstones, alluvial
Plate 128 Carbonate Paleocaliche and Paleosols: Microfacies Criteria
The plate displays a few diagnostic criteria including
Microcodium
(-> 4), laminar crusts (-> 1, 6), micritic
nodular structures (-> 2, 3, 6), spar-filled branching pedotubules (-> 5), circumgranular cracks (-> 3) and
pisoids (-> 6).
1
Laminar paleocaliche crust.
The foraminiferal grainstone, formed in a platform interior environment, is disconformably
overlain by a pedogenic crust consisting of light sparry and dark micritic, slightly undulated laminae. The caliche crust
represents a sequence boundary. Early Tertiary: Southern border of the Galala Basin, Egypt.
2
Nodular paleocaliche
formed on marginal carbonates of an episodically drying lake. The lacustrine carbonates were
pedogenically modified, resulting in the formation of palustrine limestones (see Sect. 2.4.1.2). Caliche criteria are
circumgranular cracks (white arrows) around nodules (N) consisting of dense micrite. The black arrow points to spar-
filled shrinkage cracks. Evidence of the lacustrine host rock are charophyte algae (CA). Early Tertiary (Claron Formation,
Paleocene): Brice Canyon National Park, Utah, U.S.A.
3
Circumgranular cracking
around a quartz-bearing nodule caused by alternating shrinkage and expansion processes in
soils. The circumgranular crack is filled with calcite. Same locality as -> 2.
4
Microcodium
Glück, characterized by elongate, radiating and petal-like calcitic elements grouped into ring-like struc-
tures. The structure is indicative of a meteorically influenced environment, e.g. a paleosol, and hence is a criterion for the
recognizing continental conditions, cessation of marine sedimentation, and subaerial exposure. Findings of isolated
Microcodium
within marine strata may be explained by the reworking of paleosols.
Microcodium
is abundant in many
Late Pennsylvanian to Permian, Late Cretaceous, Paleocene, Eocene, and Miocene paleosols. Pleistocene: Crete Island,
Greece.
5
Caliche nodule
containing irregularly bent and branching voids infilled with fine sparite (
pedotubules,
arrows) corre-
sponding to decayed root elements of higher plants. Early Cretaceous: Subsurface, Ostermünchen well, southern Bavaria,
Germany.
6
Paleocaliche.
The sample exhibits several criteria that are diagnostic for
alpha fabric caliche:
Clotted and inhomoge-
neous micrite, irregular nodular texture (N), fracturing and incipient brecciations (white arrows), undulating laminar
crusts (black arrow), and pisoid grains (P). Note the difference in the size, shape and internal lamination of these grains as
well as their irregular grading. Most of the pisoids consist of microspar and exhibit numerous fine pores. SMF 26. Quater-
nary: Agadir, Morocco.
