Plant-Fossil Taphonomy, Late Pennsylvanian Kinney Quarry, New Mexico, USA

Abstract

Large numbers of plant fossils have been collected from the early Late Pennsylvanian (Missourian/Kasimovian) age Kinney Brick Company Quarry, southeast of Albuquerque, New Mexico. This location was the focus of a multi-disciplinary study, published in 1992 by the New Mexico Bureau of Mines and Mineral Resources as a collection of papers, and has been the source of animal and plant fossils published in numerous additional papers. In 2014, geologists from the Bergakademie in Freiberg, Germany and the New Mexico Museum of Natural History and Science (NMMNHS) in Albuquerque carried out a controlled excavation through the fossiliferous shales exposed in the quarry floor. The fossilbearing beds record a marine to brackish or nonmarine transition in a shallowing-upward sedimentary sequence, likely that of a sheltered embayment into which a delta prograded. Changes in the sedimentary environment were accompanied by changes in composition and relative taxonomic abundances of the vertebrate, invertebrate, and plant-fossil assemblages, as well as changes in the size of plant fragments from small to large upward in the fill sequence. In this study, we report a detailed investigation of the Kinney Quarry plant fossils held by the NMMNHS, many collected during the 2014 controlled excavation. The collections made in the excavation, and their distinctive and diagnostic lithological attributes, also served as a guide by which to sort stratigraphically the large plant collections from Kinney held by the National Museum of Natural History (NMNH). The latter collections were made at several different places, and from several different levels in the fossiliferous shales preserved in the quarry, primarily in May of 1967 and 1969. From the analyses of the NMNH and NMMNHS collections, the following generalities emerge: (1) Plant fossils occur in a 2.5 m-thick siltstone that changes in character upsection. All fossil-plant assemblages are allochthonous to varying degrees, diminishing upward in the fill sequence. (2) The flora, viewed as a whole, is a mixture of wetland and drought-tolerant taxa, which, based on the form of preservation, lived in close proximity to one another in the source area of the surrounding ancient coastline. (3) There are changes in the plant-fossil composition and preservation from the lower to the upper beds in the siliciclastic fill exposed in the quarry: (a) Wetland taxa dominate the farthest offshore deposits; xeromorphic, presumed more drought-tolerant taxa, increase in relative abundance in the upper beds. (b) Plant-fragment mean-size increases from the lowermost to the uppermost bed analyzed, which is congruent with increasing proximity to the paleo-shoreline. (4) The NMMNHS and NMNH collections, made in different areas of the quarry, are similar compositionally when sorted by stratigraphic collecting level. (5) The detailed, bed-scale excavations permitted the revitalization of museum collections made earlier and without reference to bed-scale stratigraphic position, thus permitting a more complete interpretation of fine-scale environmental and floral changes that otherwise could not be determined from the older collections alone.