Carbonate Ramp Facies
Carbonate Ramps Consistent shallow gradient from shoreline to basin (some may be distally steepened), somewhat analogous to siliciclastic shelf Highest Energy Lowest Energy
Carbonate Ramp Environments Deep ramp Mid ramp Inner ramp Peritidal Offshore Deep Subtidal Shallow Subtidal Offshore- Transition Offshore Shoreface Siliciclastic Equivalents
Thin packstone “tempestites” in lime mudstone (or siliciclastic mud) May be normally graded or contain HCS; gutter casts/sole marks on base Deep Subtidal, Offshore Offshore Deep Subtidal
Large subaqueous dunes, generating large-scale cross-bedding Shoals (ooids or skeletal) are much more common than in clastic settings Large subaqueous dunes, generating large-scale cross-bedding Shallow Subtidal
Other sedimentary structures and facies may be similar to siliciclastics (wave ripples, SCS, low-angle parallel beach laminations, etc.) Swaley cross-stratification (SCS) Beach deposits Low-angle beds with hardgrounds
Peritidal Carbonates
Typical facies: light gray or light brown limestone/dolostone with Crinkly or wavy lamination from microbial mats Fenestrae: mm-sized voids (sometimes filled by calcite spar) formed by trapped gas bubbles or beneath microbial mats
Polygonal desiccation cracks (wedge shaped in side view) formed by drying and thermal contraction during tidal cycle
Tepee Structures in high intertidal/supratidal zone
Continued cycles of desiccation disrupt tepees, forming flat pebble conglomerates
CAUTION: flat-pebble conglomerates occur in any place where thin layers of limestone are subject to seafloor lithification (e.g., also in wave-influenced beaches and in many subtidal environments before the Ordovician)
(or pseudomorphs after gypsum) Supratidal sabkha environments (arid supratidal flats) characterized by evaporite mineral (gypsum, anhydrite, rarely halite) formation Gypsum laths (or pseudomorphs after gypsum) Anhydrite nodules
Classic carbonate platform environments Next video: Classic carbonate platform environments Carbonate Ramp