Paleoenvironmental Record and Applications of Calcretes and Palustrine Carbonates
Calcareous paleosols of the Upper Triassic Chinle Group, Four Corners region, southwestern United States: Climatic implications
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Published:January 01, 2006
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CiteCitation
Lawrence H. Tanner, Spencer G. Lucas, 2006. "Calcareous paleosols of the Upper Triassic Chinle Group, Four Corners region, southwestern United States: Climatic implications", Paleoenvironmental Record and Applications of Calcretes and Palustrine Carbonates, Ana María Alonso-Zarza, Lawrence H. Tanner
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Paleosols are prominent features of the Upper Triassic Chinle Group. The oldest (Carnian-age) formations of the Chinle Group (Zuni Mountains and Shinarump Formations) contain kaolinitic paleosols that display gley features but generally lack calcretes. Paleosols of the (Upper Carnian) Blue Mesa Member of the Petrified Forest Formation are mostly mature Alfisols that have distinctive horizonation and commonly host stage II to III calcretes. Mudstones of the Jim Camp Wash Bed of the overlying Sonsela Member host similarly mature paleosols with abundant stage II to stage IV calcretes. The (Lower Norian) Painted Desert Member of the Petrified Forest Formation is characterized by paleosols that lack well-developed A horizons but display thick, red B horizons in which pedogenic slickensides, rhizocretions, and stage II to III calcretes are locally abundant. Immature paleosols hosting stage II to stage III calcretes characterize the lower part of the (Middle Norian) Owl Rock Formation. The upper Owl Rock Formation contains stage III to IV calcretes and laterally persistent limestone ledges that formed as palustrine limestones and groundwater calcretes. The (Norian-Rhaetian) Rock Point Formation generally lacks pedogenic features in most of the study area, but the uppermost strata in some locations host multiple pedogenic horizons that display drab root traces, desiccation cracks, and stage II to III calcretes. Interformational variations in the types of paleosols and the maturity of calcretes in Chinle Group strata reflect gradual aridification across the Colorado Plateau during the Late Triassic. This climatic change overprinted variations in basin sedimentation rate that were potentially controlled by base level and tectonics.
La presencia de paleosuelos es uno de los rasgos más característicos del Grupo Chinle del Triásico Superior. Las formaciones más antiguas, Zuni Mountains y Shinarump, son de edad Carniense, no tienen calcretas y los paleosuelos son caoliníticos con rasgos de gley. Los paleosuelos del Miembro Blue Mesa de la Formación Petrified Forest son sobre todo Alfisoles maduros con horizontes bien diferenciados y con calcretas de estadios II a III. Las lutitas de las capas Jim Camp Wash del Miembro Sonsela suprayacente también tienen paleosuelos maduros con frecuentes calcretas de estadios II a IV. El miembro Painted Desert (Noriense inferior) de la Formación Petrified Forest se caracteriza por presentar paleosuelos que carecen de horizontes A bien desarrollados, pero que presentan horizontes B rojos y muy potentes con slickensides pedogénicos, rizocreciones, y calcretas de estadios II a III localmente abundantes. Los paleosuelos inmaduros que contienen calcretas de estadio II a III caracterizan la parte inferior de la Formación Owl Rock (Noriense medio). La parte superior de dicha formación contiene calcretas estadio III a IV y lateralmente incluyen lentejones de calizas, que se han interpretado como depósitos palustres y calcretas freáticas. La formación Rock Point (Noriense-Rhetiense) no presenta rasgos pedogénicos en la mayor parte del área estudiada, pero localmente en los estratos superiores hay horizontes pedogénicos múltiples que presentan trazas de raíces, grietas de desecación y calcretas estadios II–III. Las variaciones en el tipo de paleosuelos y en los estadios de madurez de las calcretas en las distintas formaciones del Grupo Chinle reflejan una aridificación gradual a lo largo de la Meseta del Colorado durante el Triásico Superior. Este cambio climático, controló las variaciones en la tasa de sedimentación en la cuenca que también estuvieron potencialmente controladas por cambios en el nivel de base y por la tectónica.
- Alfisols
- arid environment
- calcareous composition
- calcrete
- carbonate rocks
- Carnian
- Chinle Formation
- clastic rocks
- climate change
- fluvial environment
- Four Corners
- limestone
- lithostratigraphy
- maturity
- Mesozoic
- mudstone
- New Mexico
- Norian
- outcrops
- paleoclimatology
- paleoenvironment
- paleosols
- pedogenesis
- Petrified Forest Member
- Rhaetian
- sedimentary rocks
- sedimentation
- Shinarump Member
- soils
- Southwestern U.S.
- spatial distribution
- terrestrial environment
- Triassic
- unconformities
- United States
- Upper Triassic
- variations
- Zuni Mountains
- Owl Rock Member
- Sonsela Sandstone Bed
- Rock Point Member
- Little Painted Desert County Park