Paleobotanical Estimates of Climate in Deep Time: Two Examples From the Late Cretaceous of Western North America

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1 Paleobotanical Estimates of Climate in Deep Time: Two Examples From the Late Cretaceous of Western North America Garland Upchurch 1, Ann Marie Prue 1, Joan Parrott 1, Emilio Estrada-Ruiz 2, and Dori Contreras 3 1 Texas State University, San Marcos, TX 2 National Polytechnic Institute of Mexico, Mexico City, Mexico 3 University of California, Berkeley, CA

2 Introduction Paleobotany provides important information on paleoclimate. Shallow geologic time Closest living relatives of fossil plant species Paleoclimate inferred from modern species distributions Deep geologic time Relationships with extant species and genera more distant. Adaptive characteristics of plants Physiognomy Paleoclimate inferred from relation between plant adaptive characteristics and modern climate

3 Physiognomy Physiognomy: Adaptive features of plant structure Environment: Evolved multiple times Life form (PFT) Organs Tissue structure Leaves of dicot flowering plants Margin, shape, size Woods Presence/absence of annual rings Dicot woods: Amount of soft tissue, water conduit diameter, other features Tropical leaf (left) vs. temperate zone leaf Tropical (balsa) wood

4 Physiognomic Methods Leaves Simple Linear Regression Leaf Margin Analysis (LMA) Mean Annual Temperature (MAT) Leaf Area Analysis (LAA) Left to right: Mean Annual Precipitation (MAP) Tropical, desert, and temperate leaves Multivariate ordination Climate Leaf Analysis Multivariate Program (CLAMP) Mean annual and seasonal temperatures, precipitation Multiple regression Digital Leaf Physiognomy (DiLP) Mean Annual Temperature, Precipitation Woods Multiple regression Mean annual and seasonal temperature, precipitation

5 Study Sites Campanian Stage Two Medicine Formation McRae Formation Two Medicine Formation Montana ~79.6 ma One horizon Jose Creek Member, McRae Formation New Mexico 76.1 to >72.5 ma Leaves One horizon Woods Formation thickness

6 Two Medicine Formation M.S. Thesis, Ann Marie Prue Texas State University, 2018 Assemblage of 31 dicot leaf species Palm leaf fossils MAT >13 C, CMMT >5 C Calcrete higher in formation Seasonal precipitation MAP <1 m (?)

7 Two Medicine Temperatures Leaf Margin Analysis: Too cold for palms MAT 7 12 C DiLP: Highest temperature, good for palms MAT = 19 C Much warmer than LMA Comparable to certain younger floras, WY and MT CLAMP: Mixed Different calibrations, highest values for Asia MAT = C WMMT = C CMMT = 2 7 C

8 Two Medicine Precipitation Leaf Area Analysis: Lowest MAP cm DiLP: Highest MAP 240 cm CLAMP: No MAP, just seasonal values 3 wet months: cm 3 dry months: 9 23 cm Wet/dry = ~4 Growing season: cm Reinforces evidence for monsoon inferred from model and isotopic data (Fricke et al., 2010, EPSL)

9 Jose Creek Member, McRae Formation Work published and in progress Joan Parrott, Emilio Estrada-Ruiz, Jacqueline Scherer, Dori Contreras Leaf macrofossils One volcanic ash bed Dicot woods Entire thickness of Jose Creek Member Palm and cycad leaves, palm stems MAT >13 C, CMMT >5 C Non-calcareous paleosols MAP = cm (Buck and Mack, 1995, Cretaceous Research) Cycad leaf

10 Jose Creek Temperatures Leaf Margin Analysis MAT C Sample sizes: 42 spp. and 150 spp. CLAMP (preliminary, no DiLP yet) MAT = 12 C Dicot wood anatomy MAT = 24 C (30 spp.) and 27 C (38 spp.) CMMT = 15 C (30 spp.) and 23 C (38 spp.) Diversity of species with high volume of soft tissue Dicot wood with wide rays (soft tissue)

11 Jose Creek Precipitation Leaf Area Analysis, various regressions MAP = cm Dicot wood anatomy MAP = 350 cm Upper limit Palms, gingers Year-round precipitation Well drained environments No groundwater No standing water In line with fossil soils Palm leaf

12 Summary and Conclusions No one method works all the time. LMA: MAT too cold for Two Medicine Formation CLAMP: MAT too cold for Jose Creek Member CLAMP potentially valuable method for detecting seasonality. Reinforces evidence for Late Cretaceous monsoon, Western North America DiLP gives high estimates of MAT. Assemblages north of 50 N Perhaps best method for MAT but: Extremely time-consuming: 1 month per assemblage Diverse calibrations and plant proxies need to be used. Congruence between proxies and calibrations Error Compare output of Earth System Models