GeoLab-UARK-GEOS

Monday, May 1, 2023

Note: Cylindrical core specimen collected from AR state capital site. Representative specimen of fossiliferous, buggy limestone from shortly after the Cretaceous-Tertiary boundary that famously is marked by a large asteroid impact with global iridium layer and resulting mass extinction (including the dinosaur group).

Photo
Lidar Scan:
ERA: Cenozoic
Period: Quaternary (wiki, alpha)
Epoch: Holocene
Age: 12,000 years ago (max)
Formation: [Travertine does not have a specific formation name. It is associated with hot springs emanating from the Hot Springs Sandstone.]
Lithology: Travertine (Tufa)
Original location: 34.5160136, -93.052589
Donor organization: On permanent loan from Arkansas Geological Survey
Donor contact: Scott Ausbrooks / Angela Chandler
Financial support:

Note: Sample chosen as an unusually large and pure example of limestone deposited around mineral springs.

Photo
Lidar Scan
ERA: Mesozoic
Period: Tertiary
Epoch: Wilcox-Eocene
Age: 60-34 million years ago
Formation: [Bauxite was a paleosol formed on the surface of the exposed nepheline syenite (GeoLab 4 & 5). It could be included in the 'basal Midway Formation']
Lithology: Bauxite (Aluminum-hydroxide Paleosol; weathered Nepheline Syenite)
Original location: 34.548284,-92.501283
Donor organization: McGeorge Contracting, Alabama Mine
Donor contact: Anthony Jones / Heather Thompson
Financial support:

MacNote: Classic bauxite texture reflecting mm to cm-scale aluminum hydroxide nodules. This is the weathering product of soil formation on an exposed surface of nepheline syenite. The nepheline syenite “parent rock” was emplaced during the Cretaceous. Its surface was exposed and altered to an aluminum rich paleosol under humid, tropical conditions during the Tertiary.
AGS note: Bauxite formed in the Tertiary (Eocene – Wilcox) and is a weathering product of Cretaceous age Syenite

MacNote: Moderate to poor economic quality light gray, coarser grained. Sampled selected to exhibit the composition and grain size.

MacNote: Next best economic quality mottled with lighter patches of coarser feldspar crystals. Sample was selected to illustrate internal variation of grain size and fracture fills. Note mottled appearance reflecting local changes in grain size and the sub parallel bands of coarser grained feldspars.
AGS note: Mottle color is late incipient alteration. Check your samples with a long-wave UV light at night – recent/ongoing studies indicate that a large percentage of syenite is composed of sodalite (it fluoresces a bright orange). Once the article is published, a large portion of syenite will most likely be referred to as Sodalite-Nepheline Syenite.

MacNote: Sample selected to illustrate the gray-green, mud-rich, fossiliferous limestone. Dominantly wackestone to packstone textures with cm-scale interbedded layers of grainstones indicating periods of higher energy. The dinosaurs walked across this surface during periods of low tide and subaerial exposure.

MacNote: Massive gypsum from “stray bed” quarried in the middle of the Interbedded green and gray calcareous claystone and gypsum. Interbedded gypsum beds periodic drying and evaporation events punctuated by flooding events and clay/silt deposition along a low relief coast line (e.g. present day Trucial Coast, Arabian Gulf).