Angular unconformity
Tilted beds truncated by an erosion surface hold still while the younger flat-lying beds above onlap upward and are stripped off again.
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Geology
15 animationsAnticline
A package of parallel beds buckles out of the flat into a paired anticline and syncline under inward shortening, the marker horizon carrying the fold.
CSSColumnar jointing
A polygonal cooling-joint net seen in plan contracts column by column, the joints opening in a front that runs inward from the chilled margin.
CSSCore run log
Recovered core sticks, their fracture ticks and the gamma trace beside them feed continuously past a fixed logging window against a depth scale.
CSSCross-bedding
Three sets of inclined foresets migrate inside their bounding surfaces, the middle set running the other way as a reversing current leaves herringbone.
CSSDike and sill
Magma climbs a discordant dike through the bedding and turns along two bedding planes in turn to spread as sills inside their chilled margins.
CSSFacies migration
Shoreface, shelf and basin belts step landward and back across the section as the shoreline marker rides the facies front under the sea-level datum.
CSSFault breccia
A fracture propagates down the damage zone between two hatched wall-rock blocks while the angular clasts of the breccia work against one another.
CSSGraded bed
A turbidite bed settles out of a waning current, the coarse clasts dropping onto the erosive base first and the fine tail arriving last.
CSSIsopach contours
Thickness contours are posted over a grid of well control points, closing in from the broadest line to the depocentre at the thick point.
CSSNormal fault
A dipping fault plane cuts a bedded section and the hanging wall slips down it in stick-slip increments, offsetting the marker horizon by a growing throw.
CSSRock cycle
Igneous, sedimentary and metamorphic reservoirs sit at the corners of a triangle and a parcel of material travels the full circuit, lighting each reservoir as it arrives.
CSSStratigraphic column
A measured column of beds with lithology ornament is logged downward as a read window and its depth cursor step from one unit to the next.
CSSThrust sheet
A barbed thrust plane carries the hanging-wall sheet up-dip over the footwall until the marker horizon sits twice in the same section.
CSSZoned pluton
A crystallisation front runs inward through the compositional zones of a pluton to the melt core, under country rock domed over the roof.
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