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1:20M Global Geologic Map Units Cratered terrain to 60°S, 100–300°E

1:20M Global Geologic Map Units Cratered terrain to 60°S, 100–300°E. Ross Irwin, 11/30/2007. Libya Montes Unit (Nl). 1:15M unit(s) : Nplh, Nm, Nh 1 Group : Cratered highland province Age : Early Noachian Type location : 1°N, 86°E

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1:20M Global Geologic Map Units Cratered terrain to 60°S, 100–300°E

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  1. 1:20M Global Geologic Map UnitsCratered terrain to 60°S, 100–300°E Ross Irwin, 11/30/2007

  2. Libya Montes Unit (Nl) • 1:15M unit(s): Nplh, Nm, Nh1 • Group: Cratered highland province • Age: Early Noachian • Type location: 1°N, 86°E • Description: Rugged, irregular, heavily cratered, often dissected mountains near impact basins. • Interpretation: Impact basin rim, ejecta, and basement rocks exposed by cratering and erosion. • Contacts: Certain to gradational. • Contact relationships: Oldest recognizable unit in group, underlies Nn and later units. 25 km

  3. Noachis Terra Unit (Nn) • 1:15M unit(s): Npl1, Npld, Nplr • Group: Cratered highland province • Age: Middle to Late Noachian • Type location: 9°S, 130°E • Description: Heavily cratered plateau, reworked and degraded surface, resistant intercrater plains, variably dissected, incorporates many small outcrops of other units. • Interpretation: Layered and reworked impact ejecta, sedimentary deposits, and volcanic rocks. • Contacts: Certain to gradational • Contact relationships: Overlies Nl and underlies all other map units. 25 km

  4. Nepenthes Mensae Unit (HNn) • 1:15M unit(s): Npl2 (part), HNu (Apk?) • Group: Cratered highland province • Age: Late N/Early H • Type location: 4°N, 125°E • Description: Mantle overlying cratered terrain along the crustal dichotomy boundary. Fractured and eroded to form mesas and knobs. • Interpretation: Deposits of unknown origin. • Contacts: Certain to gradational. • Contact relationships: Overlies Nn cratered terrain; underlies AAm and Elysium volcanic plains. 25 km

  5. Smooth basin fill (HNs) • 1:15M unit(s): Hr, s (some) • Group: Cratered highland province • Age: Late N/Early H • Type location: 20°S, 158°E • Description: Basin-filling plains; smooth at hectometer resolution; preservation of small craters gives rougher appearance at higher resolution; generally wind-resistant. • Interpretation: Lithified sedimentary fill and/or flood volcanics. • Contacts: Usually certain • Contact relationships: Overlies Nn. 5 km

  6. Rough basin fill (HNr) • 1:15M unit(s): Hr, s (some) • Group: Cratered highland province • Age: Late N/Early H • Type location: 24°S, 133°E • Description: Basin-filling plains; surface dominated by small, wind-eroded knobs or yardangs; few small craters preserved. Eroded terrain does not extend onto crater walls or adjacent highlands. • Interpretation: Eroded aeolian or aqueous fine-grained deposits • Contacts: Usually certain • Contact relationships: Overlies Nn. 7 km

  7. Layered deposits (HNl) • 1:15M unit(s): Hpl3 (some) • Group: Cratered highland province • Age: Late N/Early H • Type location: 5°S, 138°E • Description: Friable, thinly layered deposits, susceptible to aeolian erosion. Stepped outcrops common. • Interpretation: Airfall materials (possibly including tephra) and/or low-energy aqueous deposits. • Contacts: Usually certain, may use equant symbols. • Contact relationships: overlies Nn, may be confined within AHc units. 25 km

  8. Fan-shaped deposits (HNf) • 1:15M unit(s): none • Group: Cratered highland province • Age: ~N/H transition • Type location: 27°S, 34.4°W • Description: Fan-shaped, positive-relief deposits at the termini of valley networks or crater wall gullies. Distributary channels common in negative or positive relief. • Interpretation: Alluvial deposits. • Contacts: Equant symbols. • Contact relationships: Overlies Nn. 5 km

  9. Hesperia Planum Unit (Hh) • 1:15M unit(s): Hr (part) • Group: Cratered highland province • Age: Hesperian • Type location: 20°S, 113°E • Description: Plains overlying broad areas of cratered terrain, not confined to intracrater or local intercrater basins, some plana contain volcanic edifices or rilles, flow fronts rare. • Interpretation: Volcanic plains. • Contacts: Mostly certain. • Contact relationships: Overlies or embays Nn and Nl. 25 km

  10. Impact Crater Materials (AHc) • 1:15M unit(s): c • Group: Widespread • Age: Hesperian to Amazonian • Type location: 25°S, 113°E • Description: Morphologically fresh impact craters and their ejecta, mapped where a visible ejecta blanket is >~100 km in diameter. • Interpretation: Post-Noachian impact craters and ejecta. • Contacts: Certain to gradational. • Contact relationships: Overlies diverse geologic units. 25 km

  11. Pitted Mantle (Am) • 1:15M unit(s): None • Group: Cratered highland province • Age: Late Amazonian • Type location: 40°S • Description: Thin, pitted mantle covering mid-latitude Nn. • Interpretation: Airfall deposit of ice and dust. • Contacts: Gradational to inferred, stippled pattern over older units. • Contact relationships: Overlies all other units >~35°S. 25 km

  12. Other Possible Units and Distinctive Mid-Latitude Materials • Volcanic constructs? • Densely clustered aeolian dune fields? • Thick, light-toned, pitted material that comprises Gorgonum Chaos and nearby chaotic terrains. • Possible thick airfall mantles identified by Grant and Schultz (1990). Or do we want to suggest that mid-latitude mantling may have been episodic and accumulated more than thin layers over time? • Lineated valley fills or debris aprons.

  13. Linear Features • Major stem valleys with abundant tributaries. • Single-stem valleys (possible volcanic rilles) • Grabens (extensional faults). • Wrinkle ridges or lobate scarps (compressional faults) • Scarps

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