Migración desde el Cliente 3.2

2. The composition of material (clasts, matrix, exotic or intrabasinal).

3. Clast fabric – e.g. random or preferred ori- entation, jigsaw arrangement.

4. Clast interaction – e.g. fusing or partial melting, as in peperites.

5. Any signature of either glacial or tectonic influence. PRINCIP AL CHARACTERISTIC S OF SEDIMENT ARY ROCKS 3

element of tectonic control during emplace- ment (ie associated with large-scale mud vol- canoes, ophiolite emplacement, major thrust faulting, etc). They also possess a distinctive tectonic shear fabric.

The scale at which such features occur is very variable. Faults zones range from a few mm to tens and even hundreds of metres. Sediment injection can be as thin pseudo- beds to irregular zones over 1km2 _{in area.} Melanges can cover tens of square kilometers. At the smaller (bed) scale, complete laminae disruption can result in a thin chaotic horizon, whereas shale clast chaotic beds can be several metres thick.

Observe and measure:

1. The nature and geometry of the chaotic zone and its orientation.

3.66 Slump unit 2.5m thick between undisturbed beds (U) above and below. Basal slip plane (solid line with arrow), internal thrust (dashed line), and slump fold (S) indicate sense of downslope movement from left to right.

Cretaceous, Umbro-Marche, central Italy

Slides, slumps, and chaotica

NOTE

Chaotica are an intriguing and still poorly understood class of sedimentary rocks. They require much careful observation in the field before one is able to fully understand and correctly interpret them.

S

3.67 Small-scale slide–slump unit comprising mudstone– sandstone (partly carbonate cemented) over pro-delta silt- stones and sandstones. Slip plane dashed, sense of move- ment to right.

Notebook 15cm high. Cretaceous, central California, USA.

3.68 Part of relatively thin (4–5m) and laterally extensive (approximately 25km2_{) slide-}

slump unit in carbonate slope succession. Undisturbed beds (U) at top and base, basal slip plane (solid line), zone with internal thrust planes (dashed lines) passes laterally into more chaotic section (right). Height of section 10m. Miocene, southern Cyprus.

3.69 Detail of contorted strata in slide–slump unit.

Hammer 45cm. Miocene, southern Cyprus.

PRINCIP AL CHARACTERISTIC S OF SEDIMENT ARY ROCKS 3 U U

3.70 Chilean geologist (Manuel Suarez) standing in nose of slump fold within turbidite slope-apron succession. Triassic, Los Molles, west central Chile.

3.71 Overturned and dislocated limb of slump fold in turbidite slope-apron succession. Width of view 6m. Oligo–Miocene, N Sicily, Italy.

3.72 Slope-apron succession adjacent to carbonate shelf with large slump-disrupted and slide- stacked shelf edge limestone– marl units within chaotic debrite matrix. Height of cliff approxi- mately 100m.

Oligocene, El Charco, SE Spain

PRINCIP AL CHARACTERISTIC S OF SEDIMENT ARY ROCKS 3

3.73 Small-scale slump, showing contorted silt- laminated turbiditic mudstone unit. Normal bedding just in view at base of picture, and just out of view at top.

Width of view 12cm.

Paleogene, central California, USA.

3.74 Nose of slump-folded turbidite succession with inter- nal dislocation thrust (dashed line); note that this unit is inter- preted as forming a single large clast within a debrite megabed (Gordo Megabed).

Miocene, Tabernas Basin, SE Spain.

PRINCIP AL CHARACTERISTIC S OF SEDIMENT ARY ROCKS 3

PRINCIP AL CHARACTERISTIC S OF SEDIMENT ARY ROCKS 3

3.75 Fault breccia, sub-vertical, at margin of Jurassic-age limestone succession. Hammer 45cm. SE Cephallonia, Greece.

3.76 Ice-wedge fissure breccia fill through lacus- trine mudstone succession. Width of view 1m. Pleistocene, Rocky Mountains, Alberta, Canada.

3.78 Injectionite, comprising igneous conglomerate (breccia), formed by diapiric injec- tion of mixed igneous and sedimentary material (left of dashed line) into forearc slope-apron suc- cession (right). Width of view 2m.

Miocene, Miura Basin, south central Japan.

3.77 Solution collapse breccia of limestone blocks and over lying alluvial gravels into karstic cavity or solution hollow in underlying Miocene limestone succession. Karst surface marked with dashed line. Width of view 5m.

3.79 Sandstone injection, from deep-water massive sandstone unit, through slope mudstones. Width of view 15m.

Oligo–Miocene, Numidian Flysch, N Sicily, Italy.

3.80 Detail of injectionite unit (I) of dark volcaniclastic sand- stone mixed with disrupted pale hemipelagic mudstones, within vocaniclastic forearc basin suc- cession. Undisturbed beds left of centre. Width of view 50cm. Miocene, Miura Basin, S Central Japan.

3.81 Part of very large scale melange complex (tens of km2₎

associated with emplacement of the Troodos ophiolite. Blocks include: Triassic dolomitized limestone (part of reef talus breccia, R), Cretaceous seafloor pillow basalts (B), Paleogene deep-sea micrites (M). The matrix is a weakly sheared shale (S) with no visible bedding. Age uncertain, Aphrodites Bay, S Cyprus. PRINCIP AL CHARACTERISTIC S OF SEDIMENT ARY ROCKS 3 I S M B R

Deformed bedding and shale clasts

(Fig. 3.15–3.17; Plates3.82–3.89,5.17,6.6,

6.7,6.22)

At the small and medium scale there are a range of post-depositional processes that operate to disturb or deform the primary structures more or less in situ – i.e. without significant lateral displacement. These include the following:

•

induced shear and frictional drag on incipient ripples – asymmetric and over- turned in flow direction. This occurs as the T1division of the Stow sequence, and may occur in addition to or in place of ripple cross-lamination (C division) of the Bouma sequence of turbidites.

•

with no preferred orientation and can result from seismic shock, liquefaction, and sediment dewatering.

•

complete deformation/brecciation of laminae or beds – in some cases devel- oped from convolute or contorted lami- nation by very rapid dumping of sedi- ment load. This can sometimes be con- fused with extensive bioturbation.

•

steepened ripple/dune foresets collapse in a downflow direction, generally as a result of over-rapid deposition from high- energy, sediment charged flows.

•

more intensive bed disruption and partial or complete erosion of the underlying bed, through the passage of a strongly erosive current, and also from bank col- lapse into a passing flow. A wide range of types and sizes occur. Softer sediment may yield mud clasts, fine-grained lime- stones yield micrite clasts, and so on.

•

a result of differential sinking of one bed into another – typically sand into mud.

PRINCIP AL CHARACTERISTIC S OF SEDIMENT ARY ROCKS 3 topbed rip-down basebed raft basebed flame isolated floating clustered floating clustered amalgamation ordered stratified ordered scour-lag dispersed graded isolated sand-ripped shale-clast breccia shale-clast

conglomerate Erosion dominant Deposition dominant

Post-depositional injection clasts

A1 B1 A2 B2 A3 A3 A4 A5 B4 B5 C1 C2

Water-escape and desiccation structures

(Fig. 3.18, 3.19; Plates3.73–3.80)

A variety of deformational structures result from the lateral and upward passage of water through sediment. This can occur rapidly immediately after deposition (especially on sudden dumping from turbulent suspension) or more slowly through time. Structures include the following:

•

cm to dm scale.

•

extensive lateral movement of water.

•

caused by the upward flow of water.

•

where fluid and sand has escaped.

•

small-scale fluid breakthrough of laminat- ed sediment.

•

of water escape disrupting the lamination (see Deformed Bedding, above).

•

dewatering of seafloor or lake floor sedi- ment – trilete and spindle-shaped forms.

•

from seaweed and so on) as well as vol- canic bombs/ejecta may fall onto a soft sediment surface causing local depression of the laminae around the dropstone.

•

turbance to the bed surface, but leave a very distinctive pattern of minor depres- sions and rims.

Observe and measure:

1. The nature and scale of deformed bedding, where it occurs within the bed, and if it forms part of any structural sequence.

2. Any evidence of flow direction.

3. The type, nature, abundance, and orienta- tion of shale clasts.

4. Evidence of way-up of strata.

B4 B1 B2 B5 B3 A4 A5 B3 A4 A3 B2 A1 A2 deposition dominant erosion + deposition erosion dominant turbidity current processes debris flow processes

transport distance (time)

high conc. turbidity current PRINCIP AL CHARACTERISTIC S OF SEDIMENT ARY ROCKS 3

3.16 The principal types of shale clast that occur