High-energy, microtidal nearshore deposits and their provenance (Lower Miocene, Burdigalian/Eggenburgian, Alpine-Carpathian Foredeep, Lower Austria)

Dur ing the Early Mio cene (Early Burdigalian/Eggenburgian) ma rine trans gres sion at the south east ern mar gin of the Bo he - mian Mas sif, grad ual flood ing oc curred along a rocky coast on gra nitic bed rock of the Thaya Batholith un der high-en ergy, wave-dom i nated, microtidal and mixed fair-weather and storm con di tions. De pos its of the Burgschleinitz For ma tion over lie a basal un con formity above a subaerial weath ered base ment sur face (transgressive ero sional sur face) and are in ter preted as a transgressive sys tems tract. The de pos its can be di vided into four fa cies as so ci a tions/depositional en vi ron ments, i.e., up -per-shoreface, fore shore, grav elly beach and backshore/la goon. Two stages of trans gres sion and suc ces sive over top ping of the base ment, with dif fer ent coastal physiographies, were doc u mented. Dur ing the ini tial stage of trans gres sion a bar rier is -land sys tem de vel oped with rel a tively fine-grained de pos its, re flect ing the flood ing of the dis tant parts of the Thaya Batholith with a rel a tive flat base ment mor phol ogy. The sub se quent con tin u a tion of the trans gres sion led to the flood ing of the more prox i mal parts of the Thaya Batholith with a steeper re lief and for ma tion of a rocky shore line with de po si tion of grav elly sed i - ments along palaeo-sea cliffs or wave-cut plat forms. While gravel clasts of the de pos its in ves ti gated orig i nate di rectly from the un der ly ing gran ites of the Thaya Batholith, prov e nance stud ies show that meta mor phic rocks of the Moravian Superunit in the hin ter land were the main source of sands. This dis tant source ma te rial was prob a bly de liv ered mainly by small creeks and al lu vial fans to the nearshore. Sig nif i cant dif fer ences in heavy min eral com po si tion of the same for ma tion in the wider vi -cin ity in di cate pri mar ily lo cal sources and rapid de po si tion with sub or di nate long shore trans port, which may re flect a com plex coastal palaeo ge ogra phy. The Lower Mio cene de pos its of the Burgschleinitz For ma tion in ves ti gated are a rare ex am ple of ancient rocky shore deposits, which generally have low preservation potential in the geological record.