ALWAYS SOMETHING NEW IN THE MARYLAND MIOCENE

Old field areas are like old friends – you never forget them, just don’t see them as often, and when you do, both the deep and the fun conversations resume immediately. The Maryland Miocene is like that for both me and Tricia Kelley, as we are for each other, having first met by chance on the Calvert Cliffs as grad students. She was further along and so was the one giving the useful introductions to local landowners, and so I think of her whenever newcomers need help with this or other field areas. After her early, important dissertation analysis of stasis and punc eq using mollusks, she returned with students and colleagues for path-breaking studies of predator-prey interactions and valuable field trips.

This talk highlights new physical stratigraphic and taphonomic insights – the undercarriage of paleo analysis -- into this richly fossiliferous record, touching on 4 aspects. In retrospect, it was far more complex than either of us realized. First, just how non-layer-cake these famously layer-cake strata really are, although the evidence -- for lateral facies tracts, transgressive shoreface beveling, max-regressive shaving, condensation during both onlap and max-transgression, incised valleys and other lenticularity, and, yes, local faulting -- is subtle, requiring closely measured sections and scaled cross-sections. Second, the dinocyst biozone evidence that corroborates the largest of these changes to Shattuck’s (1904) original litho-zonation (in prep. with Lucy Edwards, building on deVerteuil & Norris 1996). Third, Sr-isotope evidence that the ~3 m-thick Zone 10 shell bed, one of several spectacularly dense and diverse shell gravels in the Cliffs, reflects ~600ky of accumulation, about an order-of-magnitude more time than my original upper estimate for this (and other) condensed 3^rd-order transgressive systems tracts here (with Josh Zimmt et al. 2022). Finally, petrographic analysis of bone fragments, whose authigenic infills, microbial tunneling, and microcracks reveal that, in fact, the shell-rich TSTs (Zones 10, 14, 17, 19) and even the 2^nd-order SMT (Zone 12 bone bed) experienced episodes of subaerial exposure, consistent with subtle physical evidence for erosional beveling, as opposed to uninterrupted submarine accumulation (with Rachel Laker, in prep. 2023). A toast to scientific friendships!