Abstract

Outcrops of the upper Simsboro to lower Calvert Bluff formations (Wilcox Group) are rare. Acme Brick Company quarry pits in Butler, Texas, contain temporary outcrop exposures of this stratigraphic interval. We provide an integrated sedimentologic-palynologic study, including drone photogrammetry and high-resolution photomosaics, that reveals complex facies relationships, stratal architectures, and deposystems across the Simsboro-Calvert Bluff contact.

Simsboro paleoenvironments include channel thalweg, channel bar, point bar, levee, and channel abandonment deposits of meandering channels, with no floodplain preserved. Diminutive Planolites and Teichichnus indicate marine-brackishwater influence. Abundant inclined heterolithic stratification, single/double mud-drapes, and mud clast lags suggest that channels experienced tidal effects. Simsboro channels are interpreted as distal fluvial-tidal channels.

Calvert Bluff paleoenvironments include channels/levees isolated within organic-rich floodplains, including lignite, paleosols, and lacustrine deposits. Mud-draped sedimentary structures are rare. Lateral accretion surfaces are prominent in sandbodies. Channel abandonment deposits are highly organic with abundant plant macrofossils and are interbedded with paleosols containing rhizoliths and mottles. Paleosols are gleyed and likely immature (entisols and inceptisols), with some containing in-situ tree stumps. Sand-bodies are interpreted as delta-coastal plain meandering channels, with high-angle abandonment (oxbow lakes) common.

Pollen assemblages for the Simsboro and Calvert Bluff and sparse in-situ dinoflagellates suggest a “middle“ Thanetian age. Assemblage composition is consistent with a coastal plain to delta plain paleoenvironment dominated by fluvial channels and riparian to floodplain-wetland deposition, with limited marine influence.

Although well data is sparse, outcrops can be correlated into the subsurface via wireline logs. Outcrops are equivalent to deposits of the Simsboro 6 and Calvert Bluff 1 sequences of Ambrose et al. (2020). Net sandstone maps reveal sand-rich fairways of fluvial systems similar to those found in outcrops at Acme Brick. Ancient analogs are proposed. We provide a framework to predict characteristics of similar deposits in frontier areas with poor well control.