ABSTRACT Rocks of the Upper Cretaceous Tuscaloosa Formation (Cenomanian) and Eutaw Formation (Santonian) in southwestern Georgia and southeastern Alabama record an interval of fluvial and nearshore marine deposition. In the vicinity of Columbus, Georgia, basal units of the Tuscaloosa Formation consist of a residual paleosol built on crystalline rocks of the Appalachian Piedmont covered by conglomeratic sandstones deposited in braided stream systems flowing across the mid-Cenomanian Coastal Plain unconformity. The unconformity, which separates Cretaceous detrital rocks from underlying metamorphic rocks and residual paleosols built on those metamorphic rocks, lies primarily within the Tuscaloosa Formation in this region and is marked at the modern surface by the geomorphic Fall Line. Mapping of the unconformity across the region reveals areas of significant paleorelief associated with a number of distinct paleovalleys incised into the mid-Cenomanian surface. The most distinct of these lie immediately east of the Alabama-Georgia state line, within 15 km of the modern Lower Chattahoochee River Valley. Spatially, these distinct paleovalleys lie immediately north of a Santonian estuarine environment recorded in the Eutaw Formation, disconformably above the Tuscaloosa Formation. Collectively, paleo-valleys in the mid-Cenomanian surface, the fluvial nature of the Tuscaloosa Formation in southwestern Georgia and southeastern Alabama, and the estuarine environment in the younger Eutaw Formation suggest a persistent (~10 m.y.) paleodrainage system that may be a forerunner to the modern Chattahoochee River.

Abstract Middle-late Miocene (ca. 13-10 Ma) Ponce Limestone exposures in southern Puerto Rico provide an opportunity to evaluate development of a tropical carbonate ramp system during a time of known regional upwelling in the Caribbean. Three sequences (DS1, DS2, and DS3) developed in response to relative sealevel fluctuations. Each sequence is characterized by basal heterozoan-larger benthic foraminifera (LBF) facies that grades upward to a photozoan facies composed of corals tolerant of cool and turbid water at the top. DS1 transgressive deposits include Kuphus (?incrassatus), Amphistegina-Archaias packstone interbedded with Amphistegina packstone, and Archaias angulatus and gastropod-rich packstone. Maximum flooding is indicated by a Globigerinid planktonic foraminiferal facies. Upper DS1 strata consist of Montastraea imperatoris, Goniopora imperatoris , and several species of Porites coral rud-floatstone and framestone, which were deposited during highstand and sea-level fall. DS1 is capped by a surface of subaerial exposure (SB1). DS2 transgressive deposits consist of Amphistegina -coralline red algae packstone-grainstone that grade upward to coralgal- Amphistegina packstone deposited during highstand and sea-level fall. DS2 is capped by a surface of subaerial exposure (SB2). A rapid sea-level rise for DS3 is interpreted due to the apparent lack of transgressive deposits. Preserved strata consist of prograding coralgal clinoforms developed during highstand. SB1 (~13-12 Ma) and SB2 (~11-10 Ma) may correlate with unconformities in other Caribbean areas, which could indicate regional tectonic or eustatic control on sequence development. The dominance of heterozoans and larger benthic foraminifera tolerant of mesotrophic and temperate water conditions and the presence only of those photozoan corals tolerant to turbidity and cooler water are consistent with a system affected by upwelling. The presence of photozoan corals only in the highstand and regressive portions of sequences suggests highest upwelling intensity and/or transport of upwelled water and nutrients to shallowest water ramp environments during transgressions. Our results have direct implications for other similar age-equivalent systems developed in the Caribbean, including those forming important reservoirs, and other tropical systems in the rock record affected by adverse photic zone conditions.