Multiproxy studies of Early Miocene pedogenic calcretes in the Santa Cruz Formation of southern Patagonia, Argentina indicate the existence of a warm temperate vegetation adapted to a fluctuating water table

M. SOL RAIGEMBORN; VERÓNICA KRAPOVICKAS; ELISA BEILINSON; LUCÍA E. GÓMEZ PERAL; ALEJANDRO F. ZUCOL; LUCIANO ZAPATA; M. RICHARD F. KAY; M. SUSANA BARGO; SERGIO F. VIZCAÍNO; ALCIDES N. SIAL

PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2018 vol. 500 p. 1 - 23

0031-0182

Theupper Lower Miocene Santa Cruz Formation in southern Patagonia(Austral Basin, Argentina) contains several horizons of pedogeniccalcretes, which we hypothese represent ~17.5 Ma coastal marinemarshmarginal marine with indicatiors of arboreal elements or at mid-to high paleolatitudes in the Southern Hemisphere. In order to testthis hypothesis, and to reconstruct the paleoenvironment,paleoclimate and paleoecosystem for the lower Santa Cruz Formation,we performed a multiproxy study of the pedogenic calcretesconsidering abiotic and biotic components. The studied pedogeniccalcretes exhibit a variety of morphologies (horizontal and verticalrhizoliths, laminar structure, nodules, massive crusts), microfabrics(Beta- predominant over Alpha-microfabrics), and δ18Oand δ13Cvalues that fluctuate within each morphotype and throughout theanalysed interval. Microfossils and phytoliths in the host materialof the calcretes indicate fluctuating terrestrial, freshwater, andmarine conditions, and represent an ecosystemsintegrated by herbaceous plants and arboreal elementsin association with a typical coastal ?Santacrucian? vertebratefauna. We propose that the calcretes developed in soils that werealternately waterlogged and well-drained in a coastal/fluvialfloodplain during periods of landscape stability that fluctuatedbetween 8,000?25,000 and 400,000 years, in an aggradational system.Different sedimentation rates at different positions in thefloodplain, the fine texture of the host sediment, and the influenceof a fluctuating water table also conditioned calcretization. A highwater table in low relief areas of the distal floodplain created theconditions necessary to form a horizontally extended rhizolithicsystem.that, jointly with the biotic proxy, can be correlated with amangrove-like environment. Abiotic and biotic proxies of the studiedinterval (~17.5 to older than 16.89 Ma)attest to environmental fluctuations recorded at different scalesthat took place under temperate?warm and subhumid?humidconditions with a marked rainfall seasonality where a subtropicalpaleofauna and a C3-dominatedecosystem developed. This climatic scenario probably marks the onsetof the Mid-Miocene Climatic Optimum, during which favourableconditions allowed worldwide-development of mangroves.p { margin-bottom: 0.25cm; direction: ltr; line-height: 120%; text-align: left; }a:link { color: rgb(5, 99, 193); }