can clastic rocks be used to reconstruct past provenance?

Can clastic rocks be used to reconstruct past

provenance?

Meg Stewart, AMNHNovember 7, 2014

Outline

• What is a provenance and what methods are used to look for provenance?

• Case studies in New York– Taconic orogeny sediments– Glacial history

Chile

Source Area

provenance or parent lithology

Chile

Source Area

weathering erosion abrasion sorting

Sedimentary Basin Chile

Source AreaSedimentary Basin

Sedimentary Basin

topography climate

Chile

• Stratigraphic sequences• Bulk chemistry• Cathodoluminescence• Isotope ages• Detrital zircons

Case study: Taconic Orogeny Sediments, New York

Modified from Ron Blakey at Northern Arizona University

Silurian Paleogeography~420 Ma

NEW YORKNEW JERSEY

PA CO

NN

EC

TIC

UT

Location of Shawangunk Conglomerate in New York

1 cm

Bernet, Kapoutsos & Bassett, 2007

Bernet, Kapoutsos & Bassett, 2007

McLennan, et al., 2001

Interpretation:The Silurian Shawangunk Conglomerate was deposited in an inland shallow sea. The topographic high was to the east of the sea. Clasts in the Shawangunk are not Taconic age but Grenvillian age. Provenance for the sediments was likely recycled, older sedimentary rocks exhumed in the orogeny.

Case study: Glacial history of New York

Long Island

Long Island

Pacholik, Gilbert, Hanson and Hemming 2001

Interpretation:Evidence of Wisconsinan glaciation on Long Island include two distinct moraine deposits and many glacial erratics (boulders). Provenance for the moraine is difficult to interpret because of obliteration of source rock and reworked sediments during the many glacial episodes. Provenance of the erratics show a range from the Long Inland Sound basement rock to Taconian age.

Conclusions

• Clastic rocks and sediments can help reconstruct provenance– Knowing the source rock tells the

direction the sediments came from• plate configurations• orogenesis• geomorphic changes