We are proud to share a new peer-reviewed paper by Jason Jeremiah (Technical Advisor, PetroStrat), co-authored with Spencer G. Lucas of New Mexico Museum of Natural History and Science. The study documents Early Cretaceous calcareous nannofossils from the Bisbee Group in southwestern New Mexico. We extend our gratitude to New Mexico Geology for publishing.

This new paper demonstrates how nannofossils can support more precise age dating and sea-level interpretation, by providing robust datasets to create high-resolution stratigraphic correlations. This presents an important case study how biostratigraphy is a key tool in understanding complex sedimentary sequences.

Paper Overview At A Glance

This paper documents the first recorded assemblage of Early Cretaceous calcareous nannofossils from the Bisbee Group in New Mexico, part of an east-west transgression that extended from the Gulf of Mexico, through New Mexico and Arizona, this seaway established prior to the Western Interior Seaway.
The fossils were recovered from the Old Hachita Member of the U-Bar Formation, providing new biostratigraphic data for a region where previous dating relied mostly on ammonite fossils.
These findings improve regional stratigraphic correlations and open new opportunities for detailed palaeoenvironmental reconstructions across the Bisbee basin and into adjacent regions.

Exclusive comments from co-author by Jason Jeremiah

“This paper highlights the potential of nannofossils in refining the age and paleoenvironemnts of the early Albian Bisbee Seaway. This fieldwork was a joint collaboration between Shell Oil geologists and research staff at the New Mexico Museum of Natural History and Science.”

Jason Jeremiah

Spotlight – Nannofossils of the Old Hachita Member, New Mexico

The section is dated to the earliest Albian, based on nannofossil evidence from Subzones NC8a/NC8b.
Braarudosphaera batilliformis was recovered at 25 m (sample 6B) together with Prediscosphaera columnata in earliest Albian sediments. Braarudosphaera batilliformis has previously been recorded from the North Sea, Brazil, Angola, and France, recovery from the Old Hachita Member confirms its narrow stratigraphic range across the Aptian/Albian boundary.
Crucibiscutum bosunensis is found throughout most of the section (24–83 m), a characteristic species of the late Aptian to earliest Albian and previously recorded from Texas, Morocco and the North Sea.
The nannoflora is a Tethyan (warm-water) assemblage, no cold-water species such as Seribiscutum primitivum or Repagulum parvidentatum were recorded.

First Record of Early Cretaceous Nannofossils from New Mexico co authored by Jason Jeremiah Fossils

Paper Abstract

The Bisbee Group is marine and nonmarine sedimentary rocks of Late Jurassic–Early Cretaceous age that were deposited in the extensional Bisbee basin, which covered parts of northwestern Mexico and adjacent areas of southwestern New Mexico and southern Arizona. The U-Bar Formation of the Bisbee Group records the peak of marine deposition in the New Mexico part of the basin and consists of about 1 km of shallow marine limestones, offshore shales, nodular limestones, and rudist reefs. Foraminiferans and ammonites have long been used to determine the geological ages of strata of the U-Bar Formation and indicate that it ranges in age from the late Aptian through the middle Albian (about 115–110 Ma). In the Little Hatchet Mountains of southwestern New Mexico, sampling of the Old Hachita Member of the U-Bar Formation, which is the offshore facies just below the rudist-reef interval, has yielded numerous fossils of calcareous nannoplankton of biostratigraphic significance. These nannofossils indicate an earliest Albian age for strata previously assigned (with somewhat less temporal precision) an early Albian age based on ammonite biostratigraphy. The nannofossils also indicate two rises in sea level during deposition of the sampled stratigraphic interval of the Old Hachita Member. Nannofossils thus can contribute to an understanding of paleobathymetric history during deposition and to determining the ages of Bisbee Group strata. They merit more collection and study.