The Mid Pleistocene Transition Impact
Hundreds of cosmic impacts have been identified in the Earth’s geological record, yet only four are known to have an accessible tektite strewn field. The Australasian strewn field is the largest of those in aerial distribution (China to Madagascar to Antarctica) [20] and estimated tektite mass (~60 billion tons). Although only 800,00 old (yesterday, geologically), it is the only one not paired with an astroblem.

The Australian tektites are composed of non-marine sedimentary strata lofted by the MPT Impact, suggesting the missing impact structure must be located on a continental surface [21] Perhaps these unique impact constraints demand that a truly rare cosmic impact event is at play, one that does not fit the impact model developed over the past 50 years. Urey observed that:

The residual crater may be very difficult to identify; but it might well be looked for while keeping some flexible ideas as to what its properties may be. [22]

The absence of an astrobleme has led to speculation that a “near miss” generated tektites by radiant melting, but that has been falsified [23]. We propose there is a continuum between a fly-by and a classic impact event; there is a statistical probability that a massive cosmic object could intersect the Earth’s limb, such that its momentum is not significantly interrupted and most of the impactor’s mass continues a heliocentric trajectory. Rather than a high pressure compressive event, the impact was grazing, with shear as the primary excavation agent. Shock metamorphic features would still be produced, but in far less quantities than expected for such a large impact event.

In our proposed scenario, the ground flow is driven laterally away from the trench in a butterfly pattern, creating the Carolina bays along an annulus with an 800-1200 km radius. Tektite precursor sediments near the surface were heated to a molten state by direct contact with the impactor, and expelled vertically out at near escape velocity. Ejecta velocity was enhanced by the outflow of vaporized ice sheet. Australasian tektites are accepted to have transited outside the atmosphere and re-entered at near Earth’s escape velocity, mandating a loft time measured in hours. Despite this, most workers are invoking astroblemes within the strewn field, and do not consider the effects of the Earth’s rotation during an extended near-escape velocity transit [2].

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