The Dan River Group, a thick sequence of conglomerate, sandstone, and mud rock, is preserved in the northeast-trending Dan River-Danville basin of central North Carolina and Virginia. Thick lenses of organic-rich lacustrine strata (Cow Branch Formation) are surrounded by potential reservoir sandstones of fluvial, deltaic, and fan-delta origin.

Dan River sandstones consist of fine to very coarse-grained, moderately to poorly sorted, immature plagioclase arkose and lithic arkose. Source terrane was nearby and consisted of gneiss and schist with small amounts of granite and metavolcanic rock.

Diagenesis has significantly reduced initial porosity and permeability. Measured porosity of 125 representative sandstones averages 5.7% (ranging: 0.3-18.1%), and geometric mean permeability is 0.14 md (ranging: < 0.01-14.1 md). Variation in porosity and permeability results mainly from allogenic clay matrix, packing density, and cementation.

Porosity-reducing diagenetic processes include mechanical compaction (ductile grain deformation and pressure solution) and cementation. Calcite, siderite, quartz, albite, hematite, and authigenic clay (illite and chlorite) cements are widespread and are the main porosity occluding agents.

Rock-Eval pyrolysis T-max values, vitrinite reflectance data, and black coloration of spores and pollen from associated mud rocks indicate an advanced stage of burial diagenesis. These data and the low porosity and permeability values indicate that Dan River Group sandstones have poor reservoir potential.

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