Acritarchs of the Ediacaran Frecheirinha Formation, Ubajara Group, Northeastern Brazil

Abstract

We report for the first time the occurrence of organic-walled microfossils in Ediacaran limestones and marls of the Frecheirinha Formation, Ubajara Group, and the first Precambrian acritarchs so far reported for northeastern Brazil. The assemblage of the Frecheirinha Formation represents a low-diversity microflora comprising Leiosphaeridia, Lophosphaeridium and subordinated Bavlinella (=Sphaerocongregus). Sr values between 0.7075 and 0.7080 suggest an Ediacaran age. The acritarch assemblage is comparable to the Late Ediacaran Leiosphere Palynoflora (LELP) or Kotlin-Rovno assemblage, in broad agreement with chemostratigraphic data. Macrofossils belonging to the Ediacara fauna were reported from the overlying Jaibaras Group, which would constrain even further the depositional age of the Frecheirinha Formation to within ca. 575-555 Ma. A more comprehensive palynological study of the Frecheirinha Formation is necessary to confirm this age assignment.

Correlations of some Neoproterozoic carbonate-dominated successions in South America based on high-resolution chemostratigraphy

“…23), and the best exposures are observed at the quarry of the Companhia Cearense de Cimento Portland, north of the Aprazível village (Chiglino et al 2015 and references therein). The strata exhibit intense ductile deformation recorded by folds with axes with a NE-SW trend and, locally, low-grade metamorphism.…”

“…This metamorphism was probably caused by the intrusion of the nearby Mucambo granite and is not regional in nature. Chiglino et al (2015) selected the Araticum profile, located between the Frecheirinha and Ubajara villages, for palynological study because of the lower thermal overprint. There, limestone-marl rhythmites occur at the base, which pass into dark gray to black, finely laminated, organic-rich limestones, at the top.…”

“…Sial (2014, unpublished); (5) Misi et al (2007); (6) Alvarenga et al (2014); (7) Misi & Veizer (1998); (8) Torquato & Misi (1977); (9) Kaufman et al (2010); (10) Jacobsen & Kaufman (1999); (11) Warren et al (2011); (12) Mallmann et al (2007); (13) Oyhantçabal et al (2009); (14) Gaucher et al (2004, (15) Gaucher et al (2007); (16) Gómez Peral et al (2007); (17) Bagnoud- Velásquez et al (2013); (18) Gómez Peral et al (2014); (19) Boggiani et al (2010); (20) Santos et al, 2000, (21) Souza (2015), (22) Alvarenga et al (2010); (23) Chiglino et al (2015), (24) Fraga et al (2014) (25) Santana et al (2016), unpublished, (26) Babinski et al (2007), (27) carbonates in NW Canada, NW Namibia, and SW Brazil (Halverson et al 2007). Sr ratios of post-Sturtian and post-Marinoan carbonates led Babinski et al (2007) to question the use of Sr-isotope s...…”

Scientific Integrity, Precambrian Acritarchs from Brazil and Mangroves and Climate Change

“…Another interesting paper published in this issue of the AABC is on the occurrence of acritarchs from the Precambrian deposits of Northeastern Brazil (Chiglino et al 2015). These organic-walled microfossils are very important not only for dating purposes, but also for potentially providing information about the evolution of eukaryotes (Buick 2010), particularly before the Cambrian Explosion (e.g., Budd 2013).…”

“…These organic-walled microfossils are very important not only for dating purposes, but also for potentially providing information about the evolution of eukaryotes (Buick 2010), particularly before the Cambrian Explosion (e.g., Budd 2013). Leticia Chiglino and colleagues have found several acritarchs in the Frecheirinha Formation, which is a carbonate deposit of the Ubajara Group (Hackspacher et al 1988 suggested for these deposits which shows a microflora with low diversity, regarded by the authors as not being a taphonomic (preservational) artifact (Chiglino et al 2015). It should be noted that quite recently the first multicellular organisms of the Ediacaran fauna were also reported in Northeastern Brazil, coming from layers that are younger than the Frecheirinha Formation (Barroso et al 2014).…”