Geology Reference
In-Depth Information
Table 8.1 Facies description from the J-K Samba and Dekese cores. Facies codes are adapted from the schemes of Mutti ( 1992 ) for the turbidites,
Miall ( 2006 ) for the fluvial deposits, Kocurek ( 1996 ) for the aeolian dune deposits and Retallack ( 2001 ) for the paleosols
Lithofacies
Bedding and sedimentary structures
Process
A. Conglomerates
G-Stm
Mud pebble sandstones:
Fine- to coarse-grained sands, rip-up
mud clasts (1-7 cm)
Beds 0.1-3 m thick, with planar- and cross-stratifications.
The bases are erosional and the tops gradational
Deposition from
mainly bed-load
Gmc
Muddy carbonate conglomerates:
Clast- to matrix-supported small
rounded pebbles of carbonated mud
(0.5-3 cm)
Beds 0.1-1.5 m thick, with planar-stratifications.
The bases and tops are sharp
C-Gt
Calcretized conglomerates:
Clast-supported small pebbles (1-5 cm),
cemented by carbonate
Beds 5-25 cm thick, with cross-stratifications. The bases
are erosional and the tops gradational to sandstones
Gc
Carbonate breccias:
Clast- to matrix-supported fragments
of carbonate (0.5-5 cm)
Beds 10-50 cm, structureless. The bases are erosional
and the tops gradational
B. Sandstone facies
Sr
Ripple cross-laminated fine sandstones:
Fine-grained sands to silts and muds
with occasional calcretes and root traces
Beds 0.2-3 m thick with ripples and undulate (wavy)
laminations
Deposition from
high and low
regimes
Stf-b
Bioturbed cross-bedded fine sandstones:
Fine- to medium-grained sands and
muds with shallow conic burrows type
Monocraterion
Beds 0.5-1.5 m thick, with cross-stratifications and
mud drapes. The bases are erosional
Sm,
Sl,
and St
Massive, Planar- and Cross-bedded
sandstones:
Fine- to coarse-grained sands
Beds 0.5-5 m thick, structureless, or with planar- or
cross- stratifications. The bases are erosional
Deposition from
mainly bed-load
Slt and
Slt-b
Large-scale cross-bedded sandstones:
Fine to very coarse-grained and
well-sorted sands, ferruginous or
silicified, with diffuse bioturbations
Cross-beds sets 1-10 m thick, with inversely-graded
laminations. The bases are erosional
Smc
and
Smc-b
Massive and carbonated heterolithics:
Fine to very coarse-grained sands with
granules, diffuse bioturbations, burrows
and shells
Beds 0.2-5 m thick, with soft-sediment deformation
structures. The bases and tops are sharp
Debris-flows
C. Fine-grained facies and shales
Fb and
Fb-b
Black shales:
Organic-rich muds and fine-grained sands
Horizontal burrows type Planolites
Beds 0.2-2 m thick, with horizontal laminations.
The bases and tops are sharp
Deposition from
mainly
suspended-load
Fm
and
Fl
Massive or laminated mudstones:
Fine-grained sands to silts and muds
with bioturbations, calcretes and root traces
Beds 0.1-5 m thick, structureless, or with horizontal
laminations and ripples. The bases are gradational
Fmc
Carbonated mudstones to marlstones:
Fine-grained sands to silts and muds
with diffuse bioturbations, burrows
and shells
Beds 0.2-5 m thick, with soft-sediment deformation
structures. The bases and tops are sharp
D. Paleosols
Pr
Rooted paleosols:
Small pebbles, sands and muds with
calcretes, roots and rhizoliths
Beds 1-3 m thick, structureless. The bases are
gradational and the tops are truncated by conglomerates
Pedogenesis
Fig. 8.8 (continued) 2013 for details). ( b ) Sequence-stratigraphic
analysis of the J-K (and Cenozoic) Samba and Dekese core-sections,
with locations of sub-sections A to J (Figs. 8.9 , 8.10 , 8.11 , 8.12 and
8.13 ). In the Dekese section, 40 m thick red mudstones (Unit D6) are
sharply overlain by 10 m thick fluvial green coarse sandstones (Unit
D5), 310 m thick aeolian red sandstones (Unit D4) and 360 m thick
orange, purplish red delta front sandstones and flood plain mudstones
with abundant paleosols (Units D2 and D3). These sequences correlate
in the Samba section to 320 m thick fluvial-marine red-brown
sandstones and mudstones (Unit S5), 280 m thick lacustrine green
sandstones with black shale intercalations (Unit S4) and 370 m thick
fluvial-lacustrine red-brown, purple sandstones and carbonated
mudstones (Unit S3)
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