Elemental mapping of white ammonite with SQX using small-spot analysis capability of ZSX Primus II

An ammonoid is an extinct cephalopod that first appeared in the Late Silurian to Early Devonian Periods (approx. 400 million years ago) and became extinct at the end of the Cretaceous Period (65 million years ago) as did the dinosaurs. (Drawing-1)

Analysis

A new ammonoid fossil (ammonite) specimen was acquired and seemed unique in some ways to warrant further examination as a previous ammonite. Four 1 mm diameter spots of the structural regions that make up the new, white ammonite were analyzed with the SQX semi-quantitative elemental analysis routine of the Rigaku ZSX Primus II spectrometer. In addition, there were four other unique features that drew our attention, for a total of eight features that were analyzed using the 1 mm diameter spots (see Image 1).

four 1 mm diameter spots of the structural regions of the ammonite were analyzed
Image 1



Analysis spots
  1. Outer (larger) camera wall or septum
  2. Dark interior of camera
  3. Dendritic region of camera
  4. Light interior of camera
  5. Red camera (could be intrusion of surrounding rock)
  6. Yellow area of interior
  7. Brown area of interior
  8. Inner (smaller) camera wall or septum

Results

Distinct elemental differences (see Image 2 and Table 1) were found to exist in the eight analyzed regions of the ammonite. As in the previous ammonite's case, the camera, or chambers, some having both gray and brown regions, the septa, or chamber walls, and the surrounding rock matrix appear to have distinct elemental compositions. This fossil also had dendritic crystallization running from the septa to the center of most camera.

elemental differences
Image 2


Ammonite-A spot
Green area
M001
mass%
White area
M002
mass%
Black area
M003
mass%
Red area
M004
mass%
Na2O
0.18
0.13
0.12
0.073
MgO
0.88
0.23
0.27
>0.93
AI2O3
2.32
1.51
1.28
0.83
SiO2
5.65
0.15
0.11
0.25
P2O5
0.048
nd
nd
0.095
SO3
0.078
nd
nd
0.075
CI
0.042
nd
nd
nd
K2O
0.22
nd
nd
0.013
CaO
82.98
96.68
87.72
75.11
MnO
0.73
0.89
0.69
0.061
Fe2O3
4.40
0.38
0.39
nd
NiO
0.0606
nd
nd
>nd
CuO
0.0058
nd
nd
nd
SrO
0.059
0.040
0.034
0.044
Ir203
??
nd
nd
nd
C02
(by balance)
2.35
0
9.38
22.51

Table 1: SQX results of ammonite spots

Benefit

The elemental differences, along with XRD analysis of these regions, could link the rock layer in which they are found to specific geological time periods and perhaps shed light on what environmental conditions existed at the time to form the fossil.

In this case, a high occurrence of strontium in specific regions of the ammonoid fossil structure raise the question of whether the animal metabolized Sr during its life or was Sr from its surroundings replacing Ca after its death at a very slow rate.


ZSX Primus II features an innovative optics-above configuration. Never again worry about a contaminated beam path or down time due to sample chamber maintenance. The optics-above geometry eliminates cleaning worries and increases up time. Read more...

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