BETA

Onondaga Limestone

Submitted by Intern on Tue, 2015-03-10 11:03
Stone Type (Commercial): 
Availability: 
Available
Geology
Stone Type (Lithologic): 
Grain Shape: 
Subangular
Grain Sorting: 
Moderately-Sorted
Grain Size: 
Very Coarse
Medium
Petrographic Description: 

Specimen: 2015-010-1
This is a fossiliferous limestone. The limestone is not grain supported with a predominantly micrite cement matrix. Allochems constitute about 50 percent of slide area. These criteria define the limestone as a wackestone. Allochem composition is near 100 percent bioclast. These estimates and the degree of sorting indicate this limestone is a packed biomicrite. Echinoderm (crinoids) are the most common fossil and have a maximum dimension of about 2.5 mm, brachiopods are also common and have a maximum dimension of 12 mm. Other identifiable bioclasts include bryzoans, bivalves, and a single trilobite. There is a gradient in bioclast size down to <.1 mm, making a mode in bioclast size difficult to identify. Small fragments of collophane are very rare but present. Voids are essentially absent. Non-carbonate minerals occur in only trace amounts and include what is likely authigenic quartz and iron oxide/hydroxides. There are a few very thin (7.5 µm) but long and irregular cracks filled with what is likely iron oxide/hydroxide. In the hand sample there are features that appear to be filled with secondary carbonate (sparite); these are not visible in this thin section.
MP 9/5/2015

Specimen: 2015-010-2
This is a fossiliferous limestone. The limestone is not grain supported with a predominantly micrite and fine grained sparite (.005 to .04 mm) cement matrix. Allochems constitute about 50 percent of slide area. These criteria define the limestone as a wackestone. Allochem composition is near 100 percent bioclast. These estimates and the degree of sorting indicate this limestone is a packed biomicrite. Echinoderm (crinoids) are the most common fossil and have a maximum dimension of about 2.8 mm, brachiopods are also common and have a maximum dimension of 6.8 mm (not measuring sinuosity). Other identifiable bioclasts include bryzoans, bivalves, and possible trilobite fragments. There is a gradient in bioclast size down to <.1 mm, making a mode in bioclast size difficult to identify. Voids are essentially absent. Non-carbonate minerals occur in only trace amounts and include what is likely authigenic quartz appearing in aggregates and as individual grains (~ .03 mm) and iron oxide/hydroxides. Larger sutured sparite is locally abundant with individual crystals up to .8 mm. In the hand sample there are both dark (likely ferromangnesium rich areas) and thin lines of light colored (calcite) running across the specimen. These do not clearly correlate to any feature noted in this thin section.
MP 9/5/2015

Specimen: 2015-010-3
This is a fossiliferous limestone. The limestone is mostly not grain supported, but this quality varies across the slide. The cement matrix is predominantly micrite and fine grained sparite (.005 to .04 mm). Allochems constitute about 60 to 70 percent of slide area. These criteria define the limestone as a wackestone. Allochem composition is near 100 percent bioclast. These estimates and the degree of sorting indicate this limestone is a packed biomicrite. Echinoderm (crinoids) are the most common fossil and have a maximum dimension of about 4 mm, brachiopods are also common and have a maximum dimension of almost 16 mm (not measuring sinuosity). Other identifiable bioclasts include bryzoans, bivalves, and trilobite fragments. There is a gradient in bioclast size down to <.1 mm, making a mode in bioclast size difficult to identify. Voids are essentially absent. Several areas of sparry calcite appear to have formed as replacement minerals after large, presumably, aragonite based shells. Silica is also present in some of these replacement fossils and rarely in mouldic voids. Small grains of authigenic quartz (~ .03 mm) are also present in the cementing matrix in trace amounts. There are a few very thin (7.5 µm) but long and irregular cracks filled with what is likely iron oxide/hydroxide.
MP 9/5/2015

Specimen: 2015-010-5
This is a fossiliferous limestone. The limestone is not grain supported. The cement matrix is predominantly micrite and fine grained sparite (.005 to .1 mm). Allochems constitute about 50 percent of slide area. These criteria define the limestone as a wackestone. Allochem composition is near 100 percent bioclast. These estimates and the degree of sorting indicate this limestone is a packed biomicrite. Echinoderm (crinoids) are the most common fossil and have a maximum dimension of about 2 mm. One example of a rarely preserved crinoid pinnule is present. Brachiopod/bivalve shell fragments are also common and have a maximum dimension of almost 9 mm (not measuring sinuosity). Bryzoans are also present. There is a gradient in bioclast size down to <.1 mm, making a mode in bioclast size difficult to identify. Voids are essentially absent. Larger grained sparry calcite is locally predominate with individual crystals reaching a maximum of 1.7 mm. Small grains of authigenic quartz up to .06 mm are also present in the cementing matrix in trace amounts. In the hand sample threads and clouds of light areas are likely relatable to areas of sparry calcite seen in thin section.
MP 9/5/2015

Specimen: 2015-010-6
This is a fossiliferous limestone. The limestone is mostly not grain supported, but this quality varies across the slide. The cement matrix is predominantly micrite and fine grained sparite (.005 to .05 mm). Allochems constitute about 60 to 70 percent of slide area. These criteria define the limestone as a wackestone. Allochem composition is near 100 percent bioclast. These estimates and the degree of sorting indicate this limestone is a packed biomicrite. Echinoderm (crinoids) are the most common fossil and have a maximum dimension of about 2.2 mm. Maximum observed dimensions of other bioclasts area as follows: trilobites 3.5 mm, brachiopods 1.2 mm, and bryzoans .6 mm. There is a gradient in bioclast size down to <.1 mm, making a mode in bioclast size difficult to identify. Voids are essentially absent. Sparry calcite is present as syntaxial overgrowth on some crinoid fragments. Small grains of authigenic quartz (~ .03 mm) are also present in the cementing matrix in trace amounts. There are a few thin (~.05 mm) but long and irregular cracks filled with what is likely iron oxide/hydroxide. There is no notable macrostructure present in the hand sample that can be tied to the thin section.
MP 9/5/2015

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