Low crater frequencies and low model ages in lunar maria: Recent endogenic activity or degradation effects?

TL;DR

This study analyzes small lunar structures using crater size frequency distributions, revealing recent resurfacing events and questioning the reliability of model ages based solely on crater counts.

Contribution

It provides new crater-based age estimates for lunar maria and wrinkle ridges, highlighting the effects of degradation and recent activity on crater populations.

Findings

Crater size frequency distributions show similar slopes in IMPs and nearby mare regions.

Control mare regions exhibit shallower slopes indicating equilibrium crater populations.

A wrinkle ridge shows very young age (~8.6 Ma) with recent crater formation.

Abstract

Recently a number of studies have identified small lunar geologic structures to be <100 Ma in age using standard remote sensing techniques. Here we present new crater size frequency distributions (CSFD) and model ages using craters D> 10 m for 5 small target units: 1 Irregular Mare Patch (IMP) in Mare Nubium and 4 regions located on lunar wrinkle ridges in Mare Humorum. For comparison we also date another IMP found in a recent study in Mare Tranquillitatis (Braden et al., 2014). Absolute model age derivation corresponds to 46$\pm$5 Ma and 22$\pm$1 Ma for Nubium and Sosigenes IMP. We show that for IMPs and in nearby control mare regions similar production-like cumulative log-log SFD slopes of -3 are observed. In contrast control mare regions in Mare Humorum exhibit shallower equilibrium slopes from -1.83 to -2. 3 out of 4 wrinkle ridges appear to be in equilibrium but with crater life times lower than on the corresponding maria. Low crater frequencies on one wrinkle ridge result in an age of 8.6$\pm$1 Ma. This study region contains 80% fresh craters which suggests that the crater population is still in production indicative of a recent resurfacing event.