Early diagenesis, Atherton Formation (Quaternary), northern Indiana: a guide to understanding early cement distribution in nonmarine sandstones
In the area studied, the Atherton Formation accumulated primarily as outwash deposits dominated by trough and wedge cross-bedding. The distribution of these cements was controlled by at least three factors: (1) position within the deposit relative to the land surface, (2) average grain size, and (3) primary stratification. Over 90% of cement zones are within 7 m (23 ft) of the present land surface. Meteoric waters made more acidic by decaying organic material locally dissolved carbonate framework grains. As pore fluids continued to move downward and laterally, cementation occurred. On a second level, higher permeability zones associated with sediment of larger grain sizes was an important factor influencing the location of cementation. Cemented horizons are present in 48% of pebble and sandy pebble gravels (contact and pore lining types) and 17% of sands and pebbly sands (contact, pore lining, and occluded types). Moreover, within sand units primary stratification was a parameter that influenced the location of cementation sites. In wedge crossbed sets, cement zones parallel inclined laminations; in trough cross-beds, 79% of the cement is concentrated in the lower one-third of bed sets near trough axes or immediately below a trough's basal erosion surface. Carbonate cements in the Atherton range from a trace to 6 mole % MgCO/sub 3/ (X- = 3.6 mole %) with traces of Fe in 16% of the samples analyzed (205 total analyses). The source for Mg and Fe is believed related to the dissolution of dolomite and Fe-bearing silicate framework grains. The limonite/hematite cements are present as rare, pore-filling patches.
- Research Organization:
- Univ. of Texas, El Paso
- OSTI ID:
- 6436656
- Report Number(s):
- CONF-8304200-
- Journal Information:
- Am. Assoc. Pet. Geol., Bull.; (United States), Vol. 67:3; Conference: Annual AAPG/SEPM/EMD/DPA convention, Dallas, TX, USA, 17 Apr 1983
- Country of Publication:
- United States
- Language:
- English
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