LATE DESMOINESIAN SILICIFIED CONIFEROPSID TREES PRESERVED IN CHANNEL MARGIN SABKHA FACIES, WHISKEY CANYON, CENTRAL NEW MEXICO

A silicified coniferopsid tree was found on the margin of an incised channel within the Bartolo Formation in Whiskey Canyon near Truth or Consequences, NM. The lower portion was a 25cm diameter stump encased in enterolithic textured gypsum, anhydrite and carbonate crystals consistent with supertidal sabkha facies. The upper portion of the tree consists of four consecutively smaller diameter trunk segments. The channel incises approximately 8 m, and contains a 1 m thick basal conglomerate of thin platy limestone clasts, overlain by fine, silt sized anhydrite, carbonate and possibly gypsum. We interpret the channel to have incised during regression, leaving a basal lag of eroded limestone clasts. Coniferopsid trees grew on the channel margins during lowstand. Encroaching sea level and possible dryer climate during transgression brought the trees into the supertidal zone, rapidly changing the environment to saline and highly evaporative, silicifying the trunks and encasing the tree base in gypsum and anhydrite. The channel was backfilled by transported sediment derived from deflated sabkha and eroded limestones. Further transgression covered the region in carbonate mud.

Similar incised valleys of the same age, but without silicified trees, occur elsewhere in New Mexico. Outside of this time interval the Pennsylvanian is largely devoid of channel features in New Mexico. Intriguingly, fusulinid and conodont biostratigraphy correlates New Mexico incised valleys with major channels in the Appalachian Basin (‘Monster Channel’) and the Illinois Basin (Gimlet channel), both characterized by unusually deep incision. We interpret these features to represent a significant eustatic low.