3 Paleo-climate and -ecosystems of the Southwest and High Plains: From the Paleozoic to the Quaternary

Many Phanerozoic climates and ecosystems serve as potential analogues for the future; others highlight the Earth system response to tectonic and climatic forcings. We invite abstracts that probe the paleoclimate/ecosystems of the US Southwest

Monday, 18 May 2026
9:00 AM - 12:00 PM
Alvarado C

Contrast between Macroflora and Palynoflora from an Organic-shale Bed in the Tinajas Member, Atrasado Formation, Upper Pennsylvanian, Socorro County, NM

Paper number: 3-1
Program: Technical Sessions
Time: 9:20 AM – 9:40 AM

Authors

Abstract

Among the lithologies that comprise the Upper Pennsylvanian Tinajas Member, Atrasado Formation, central New Mexico is a widespread (60 km2 outcrop area) organic shale interpreted as deposits of a coastal lake, found in the midst of otherwise arid to semi-arid strata. Fusulinid and conodont biostratigraphy indicate a Late Pennsylvanian (Missourian) age.  The shale is thinly laminated with a fossil biota dominated by conchostracans and fishes (especially their coprolites) indicative of freshwater. The shale also contains a sparse, allochthonous macroflora dominated by plants characteristic of high soil moisture habitats (calamitaleans, pteridosperms), with an admixture of plants characteristic of seasonally dry habitats (conifers, taeniopterids, callipterids, noeggerathialeans). Surprisingly, it contains few remains of marattialean tree ferns, a widespread group that dominates peat-forming floras (coals) from Midcontinent and eastern US coal basins. Late Pennsylvanian palynoflora are almost always tree-fern rich, if not dominated; the Tinajas Member organic shale is no exception. Late Paleozoic marattialean tree ferns, like pteridosperms, are closely associated with "wet" habitats. Furthermore, the palynoflora contains few taxa of plants characteristic of seasonally moisture-stressed habitats. This raises the question of how such a nearly 180-degree difference may have arisen between the palynoflora and macroflora. The most likely underlying taphonomic variables include differential transportability of the macrofossil remains vs. the great dispersal potential of tree-fern spores, differences in proximity among plant groups to coastline and feeder streams, and selective decay susceptibility against lightly constructed remains, such as tree-fern foliage. It is generally considered that palynofloras represent a broader segment of the landscape surrounding a site of deposition than do macrofloras. In this case, however, the allochthonous macroflora was sampled at numerous sites and remained compositionally consistent. The palynoflora clearly was derived from a parent flora of “wet” habitus and transported, likely by wind. The macroflora was water transported. Thus, the climate signals from the two are strikingly different. They underline the need for caution, particularly when using palynofloras alone to interpret local paleoclimates and paleoenvironments. 

Geological Society of America Abstracts with Programs. Vol. 58, No. 4

doi: 10.1130/abs/2026RM-410595

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