The Oligocene paleoflora of Bulgaria is characterized by relatively low species diversity, with all known localities situated exclusively south of the Balkan Mountains. In this study, we report the first Oligocene paleobotanical assemblages from the Nikolaevo and Malinovo grabens (Western Srednogorie), where the fossil-bearing sediments belong to the recently defined Nikolaevo Formation. The specimens were collected from two localities: northeast of the village of Kosacha and northwest of the village of Kopanitsa (Radomir Disttrict). The paleofloral remains consist of leaf imprints assigned to the following taxa: Celastrus aeoli, Eotrigonobalanus furcinervis, Laurus pliocenica, Neolitsea palaeosericea, Persea princeps, Rhus blitum, and Typha latissima. Although all of these species have previously been documented within the Bulgarian Oligocene flora, this is the first time they have been recorded from these specific grabens.
Bozukov et al. (Sat,) studied this question.