Multiscale Erosion Surfaces of the Organic-Rich Barnett Shale, Fort Worth Basin, USA

Table 1

Summary of the erosional features associated with the erosion surfaces.

Relief	Ranges between 5 mm and 60 mm with an average 19 mm.
Lithology	Siliceous noncalcareous to calcareous mudstone groundmass, silty laminated, and phosphatic-rich mudstone. Pyrite is common and rarely dolomitized.
Surface nature
Lower	Sharp to irregular, scoured and down-cutting contact.
Upper	Sharp, gradational to irregular, rarely disturbed with burrowing.
Matrix components
Shelly laminae	Very thin (1–15 mm), singular to multiple, fragmented shelly laminae. Highly compacted (grain to grain contact), horizontally alignment. The most common types of shell fragments are bivalves, bryozoans, brachiopods, filling branch mollusks, and echinoderms with mainly calcite filling.
Shale rip-up clasts	Mainly flakey-like shapes with straight outlines. Others are rounded to subrounded, with the same lithology of the underlying facies. Occurs as suspended clasts in the overlying facies.
Reworked concretions	In situ sandy-size to transported gravely-size concretions. Rounded, subrounded to irregular clasts. Slightly to highly compacted and subhorizontally oriented. Shaley to silty and phosphatic internal lithology. Pyritic effect is very common.
Phosphatic pellets	Very common, rounded to subrounded with multiple internal cores, sometimes broken, irregular, rarely elongated with their long axis parallel to bedding planes. They range in size from less than 1 mm up to 1 cm. The nuclei of the phosphatic intraclasts may include shell fragments, detrital quartz, and glauconite grains.
Pyrite	Common as framboidal shape and rarely as fine euhedral crystal. Not in all samples.