Stable isotopic insights into paleoclimatic conditions and alluvial depositional processes in the Kaiparowits Formation (Campanian, south-central Utah, USA)

作者：Foreman Brady Z^*; Roberts Eric M; Tapanila Leif; Ratigan Deirdre; Sullivan Patrick

来源：Cretaceous Research, 2015, 56: 180-192.

DOI：10.1016/j.cretres.2015.05.001

• Paleoclimate
• Western Interior
• Stable isotopes
• Cretaceous
• Alluvial stratigraphy

The Kaiparowits Formation contains an exceptionally rich history of tectonic, climatic, and biologic conditions within the Western Interior of North America during the Campanian. Here we reconstruct aspects of the southern Cordilleran foreland basin's paleohydrology using delta O-18 and delta C-13 values determined from unionoid bivalve shells and pedogenic carbonate nodules derived from a suite of lithofacies associations. Unionoid shells derived from fluvial deposits display average water delta O-18 estimates of -13.7 parts per thousand +/- 2.1 (1 sigma) (VSMOW) and shell delta C-13 values of -4.0 parts per thousand +/- 1.5 (VPDB), whereas pedogenic carbonate nodules display average values of -6.0 parts per thousand +/- 0.5 and -8.7 parts per thousand +/- 0.8, respectively. Unionoid shells derived from pond deposits fall in between the two other environments with average values of -9.5 parts per thousand +/- 1.8 and -5.7 parts per thousand +/- 2.1, in delta O-18 and delta C-13 values respectively. Water delta O-18 estimates are interpreted to represent high altitude runoff within river systems, low elevation precipitation within the basin onto floodplain soils, and varying degrees of mixing between these two components within floodplain ponds. delta C-13 values track the isotopic composition of dissolved inorganic carbon within river, soil, and pond waters with high values likely reflecting greater contribution from chemically weathered marine carbonates exposed in the hinterland and lower values reflecting greater contributions from the in situ degradation of plant matter. Up-section there is a shift to lower delta O-18 values and higher delta C-13 values in fluvially-derived unionoid shells that post-dates an incursion of the Western Interior Seaway, but coincides with a shift in sediment provenance, an increase in basin sedimentation rates, and a change to a more anastomosed-style channel morphology within the basin foredeep depocentre. By combining the isotopic patterns with previously published sedimentologic, climate model, and paleofloral records we find: 1) additional evidence for humid, wet, and potentially monsoonal conditions within the region, 2) support for a tectonic uplift event, potentially related to Laramide deformation, and 3) greater aggradation and overbank flooding within the alluvial system in response to the uplift event.

• 出版日期2015-12