MIOSPORE BIOSTRATIGRAPHY AND SEQUENCE STRATIGRAPHIC RELATIONS OF THE BORDEN DELTA COMPLEX (TOURNAISIAN-VISEAN) IN KENTUCKY AND INDIANA, U.S.A

The Borden Formation (Lower Carboniferous) in Kentucky and Indiana represents a prograding wedge of deltaic facies with their origins in the Acadian Highlands in the east. Outcrops of these rocks in Kentucky and Indiana represent the bottom-set beds containing prodeltaic muds and siliciclastic-rich fan deposits, fore-set beds of the delta slope, and the top-set beds of the shallow marine platform. Regional lithostratigraphic relations are not well known due to the time transgressive nature of the boundaries resulting from the progradation. The Borden Formation is subdivided into different members in different areas, and no good correlation exists for these units. The study area is subdivided into four Primary Depositional Centers (PDC-I through PDC-IV), which were sampled for miospores. In PDC-I (northeastern KY), the miospore assemblage is representative of the PC Biozone (Tn3a). The PC Biozone is defined by the first appearance of Spelaeotriletes pretiosus. In PDC-II (Tn3b; south-central KY), the miospores represent the upper part of the PC Biozone. In the westernmost localities in the study area, PDC-IV (Tn3c), the miospores are representative of the CM and Pu Biozones. In south-central Indiana, most of the sections are representative of the CM Biozone, which is defined by the first appearance of Schopfites claviger. In the upper part of the sections within PDC-IV, Lycospora pusilla makes its first appearance. The first appearance of L. pusilla marks the base of the Pu Biozone and also marks the base of the Visean (Vn1). Although the Primary Depositional Centers are part of the same sequence, they are represented by different progradational phases. Sequence stratigraphic concepts are applied to all the PDC’s and combined with the miospore biostratigraphic data to gain a better understanding of the spatial relationships of the time transgressive boundaries of the Borden Delta.