sedimentary basins

Foreland: Plate Tectonic setting

Adjacent to compressional mountain belts at convergent margins

Load = thrust sheet stack built by plate collision (e.g. Alps & Po Valley)

Strong lithosphere responds by regional flexture

Foreland: subsidence history

Concave-down tectonic subsidence curve — opposite to extensional basins

Subsidence slowest early on when load is far away, accelerating as mountain belt approaches

Location may first experience slight uplift as it rides the flexural forebulge before subsiding

Foreland: faulting

Not primarily fault-controlled like the adjacent thrust belt is

Subsidence is driven by flexure > brittle extension

Reverse, normal , and thrust faults may propagate as the load advances

Foreland: sedimentary infill

Directly from uplifting mountain belt into basin

Sorted: coarse conglomerates/alluvial fan deposits are near the thrust front, grading basinward into finer marine sediment

Subduction: plate tectonic setting

Forearc basin: downward flexure is produced in younger plate at point of contact, right behind the accretionary wedge

Backarc basin: behind volcanic island arc; formation is debated but lithosphere stretches due to secondary circulation current forming, or plate moving away from subduction zone

Trench basin: where the two plates meet; where accretionary wedge forms

Subduction: subsidence history

Trench basin: subsides rapidly similar to foreland basin due to mechanical load of overriding plate

Forearc basin: variable due to accretionary wedge growth, underplating, erosion

Backarc basin: similar to extensional; fast and then slow

Subduction: faulting

Forearc basin: thrust faults from accretionary wedge on one side, and normal faults where Forearc extends

Trench basin: décollement, prism thrusts, megasplay faults

Backarc basin: extensional aka normal faulting

Subduction: sedimentary infill

Trench: highly deformed through folding, mélanges common (chaotic mix of sediment), turbidities and mass flow deposits from overriding plate (younger is closer to subducting)

Forearc: less deformation = more layered/coherent; marine clastics, e.g. turbidites, siltstones, and coarser volcaniclastic material

Backarc: layered, undeformed strata; mix of volcanic material and marine sediments

Strike slip: tectonic setting

Along transform/strike-slip fault systems at releasing bends

I.e. Dead Sea along Dead Sea Transform

Strike slip: subsidence history

Greater rate of subsidence than rift/foreland type basin

Backstrip curve can show both rift/extensional (rapid early subsidence due to local extension) and foreland basin patterns (high sedimentation/compression rates cause late-stage acceleration)

Strike slip: faulting

Lateral/strike-slip faults dominate; negative flower structure (shallow synform with normal faults fanning out towards surface)

Strike slip: sediment infill

Quick subsidence and small/long structure

Fill with coarse, poorly sorted sediments derived from immediately adjacent uplifted fault blocks

Alluvial fans & coarse fluvial deposits near basin margins

Deeper lacustrine/marine facies in basin center

Sediment very thick relative to basin area

Extensional: tectonic setting

Divergent margins or backarc

Lithospheric stretching model shown by McKenzie

Extensional: subsidence history

Concave up subsidence curve

Fast subsidence during syn-rift, exponential slowing during post-rift thermal cooling

Extensional: faulting

Normal faulting: brittle faulting in upper crust, ductile at depth; domino-style rotating fault blocks

Syn-rift has localized faulting; post-rift sediments are largely unfaulted

Extensional: sediment infill

Syn-rift sediments are faulted and thicken towards the fault

Post rift sediments drape broadly and are unfaulted