New Mexico Geological Society Annual Spring Meeting — Abstracts

More than 28 m of the Upper Pennsylvanian (early Virgilian) Pine Shadow Member of the wild Cow Formation (Madera Group) are exposed at the Kinney Brick Company clay pit: in the SE1/4 sec. 18,T9N, R6E, Bernalillo County, New Mexico. The base of this section is 1 m or more of black to brownish black, laminar micrite that contains fossils of plants, insects, conchostracans, brachiopods, molluscs and disarticulated fish. Most of the fossils known from the clay pit come from the 0.75-m-thick brownish black to olive-black, calcareous shale above this limestone. Fossils from this interval represent a mixture of freshwater and marine organisms and include: plants (especially seed ferns and the conifer Walchia) , spirorbid worms, insects, ostracodes, conchostracans, eurypterids, shrimp, brachiopods, gastropods, bivalves (especially Dunbarella), fishes (actinopterygians, elasmobranchs, coelacanths and acanthodians) and trimerorhachid amphibians (including a newly discovered, complete skeleton). The overlying 1.8 m of olive-gray shale contain at least two thin (<10 cm) bentonite beds and a less diverse fossil assemblage dominated by plants, insects and small Dunbarella. Above these strata are 10.7 m of pale olive, laminar micaceous siltstone with a similar fossil content. The siltstone is overlain by 8.5 m of interbedded. grayish olive silty shale and light olive-brown, laminar-to-ripple-laminar, micaceous silty sandstone. More than 3 m of grayish yellow and yellowish brown, trough-crossbedded subarkosic and sublithic arenite and limestone-cobble conglomerate complete the section exposed at the clay pit. This section represents a prograding deltaic sequence beginning with prodelta and lagoonal micrite and shale overlain by delta-plain channel sandstones that complete the coarsening upward sequence.