About This Item
Share This Item
The Hammett Shale, Cow Creek Limestone, and overlying Hensel Sandstone represent a transgressive-regressive depositional cycle. Hammett shales and carbonates were deposited in low-energy marine lithotopes seaward of nearshore shoal, lagoonal, and beach environments represented in Cow Creek lithofacies. Fungalgal caliches and supratidal marshes developed in places in the beach backshore. Contemporaneously, smectitic red muds, caliches, and lenticular sands were deposited on the arid Hensel alluvial plain. Statistical analysis of matrix, cement, and allochems reveals that early diagenetic modifications in the marine carbonate sequence have distinctive vertical distributions. Fewer beds are dolomitized above the Hammett Shale. Lagoonal strata consist mainly of recrystallized pelleted nodules and pseudospar lime packstones; and beach grainstones are never dolomitized.
Aragonitic bioclasts underwent dissolution in the beach but stabilized by inversion in lower facies. Iron-free calcites predominate in the beach foreshore beds; ferroan calcites predominate in underlying units. Micritized and enveloped grains are most abundant in mud-free beach sediments.
The strandline meteoric-vadose zone and the mixed zone separating local and regional meteoric-phreatic waters from marine interstitial fluids were the loci of most diagenetic alteration. Caliche development, early cementation, and grain leaching were affected by equilibrating vadose waters. Cementation was inhibited and inversion allowed to proceed in the local mixed-phreatic zone, whereas dolomitization of Hammett carbonates took place in regional mixed-phreatic waters. Iron-free cements were precipitated in oxidized, phreatic, or vadose zones.
End_of_Article - Last_Page 630------------