Testing the Marine Hypothesis for The Opportunity Landing Site at Victoria Crater

Hypothesis Summary: 1. Meridiani Planum is a marine sulfate platform deposit, analogous to terrestrial carbonate platforms but with sulfate mineralogy, laid down during one or multiple marine transgressions over the landing site region. 2. Outcrop laminations, ripples, and larger, dune-scale bedforms are subaqueous in origin, produced by tidal currents. Aqueous deposits may be interbedded with crossbedded aeolian deposits of same composition derived from subjacent water-lain deposits during lowstands. At the scale of observations made by Opportunity, the marine hypothesis differs from the consensus, sabkha model, in two relatively minor ways (but with important differences in the inferred paleoenvironments). 3. Blueberry and cobble "lag" on top of outcrop is a lag, but indicates erosion of perhaps many meters, even tens of meters or more of outcrop material from the region by water. Wind erosion has been very limited over geologic time (perhaps less than a meter locally). 4. Remarkably-flat, horizontal geomorphic surface of outcrop was produced by shallow standing water locally, controlling both deposition and erosion of the sulfate outcrop material to within a few meters of sea level. 5. Craters in the landing site exhibit a continuum of degradation states, with Endurance and Victoria typifying the best preserved craters visited (or to be visited) by Opportunity, and Erebus and Terra Nova representing the most degraded craters visited that are larger than 100 meters across. Terra Nova is similar to numerous kilometer-scale "rock ring" craters in the Meridiani Planum landing site. 6. "Serrated" rim at Victoria is similar to, but fresher in expression, rim morphology at Erebus Crater, and may indicate water pouring over crater rim during tidal or storm surges in water level across the region. Predictions to be tested at Victoria Crater: 1. The crater's ejecta and raised rim have been destroyed by tidal currents in shallow standing water. There is no Endurance-like ejecta blanket at Victoria crater, and the rim is at most a few meters elevated in relation to the surrounding plains. 2. The annulus or sand sheet surrounding Victoria crater is similar to the plains surface between Eagle and Endurance craters, and was likely comminuted from Victoria's rim and ejecta, rather than overlying it. 3. Is the banding that is visible in MOC images indicative of layers exposed within Victoria? If there was standing water within the crater at the end of a marine setting in the region, they might not be layers at all, but strandlines. If so, they should exhibit overhangs, particularly at the promontories along the crater rim. They should maintain horizontality, even when cutting across dipping strata or bedform laminations.