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USGS Participates in Everglades Geological Field Trip

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studying cores at Rock Reef Pass
Field trip participants studying maps and cores (in boxes) at Rock Reef Pass. At least eight northwest-southeast-trending rock reefs have been mapped and named on USGS topographic maps. Everglades cores were provided by the Florida Geological Survey, Tallahassee. Field trip leader Don McNeill, in white shirt and cap at right foreground, is from the Rosenstiel School of Marine and Atmospheric Science, University of Miami.
On January 22nd, the Miami Geological Society conducted a field trip on the geology of Everglades National Park, where the close interaction between geology, topography, hydrology, and biology of South Florida was best observed by an overflow crowd of 40 participants.

Although the area, being flat, lacks significant outcrops, the importance of the geology on the modern flora and fauna cannot be overstated. Lectures included South Florida climate (temperatures, rainfall, hurricanes, and tropical storms), geologic history, physiography (the Everglades, Atlantic Coastal Ridge, Big Cypress Swamp, and Coastal Marshes and Mangrove Swamp provinces), Pleistocene and Holocene sea-level history, stratigraphy of subsurface and surface formations, and surficial geology of the park.

Field trip stops included close examination of subaerially exposed karst features, freshwater marl, mangrove sedimentation, coastal storm levees, and an overlook to observe the River of Grass.

The most interesting stop was to examine so-called rock-reef ridges that are prominent features on aerial photographs and occur throughout the park. Although more than a dozen of the thin, elongate features exist averaging 10 m in width, 1 m in height, and extending 10 to 20 km in length, their origin is not known. Theories proposed include (1) Pleistocene faulting and preferential cementation around fractures, (2) relic depositional shoreline features, (3) diagenetic features, and (4) lithified mudbanks that developed in a paleo-lagoon. Regardless of how they formed, they retard southward flow of surface water and are responsible for a change in vegetation observed along the ridge axes.

In an effort to determine their origin, Don Hickey of the St. Petersburg Field Center used the USGS rotary core drill to core through and across one of these features for his Master's thesis. He hopes to determine the evolutionary processes responsible for the ridges by observing the subsurface structure in cores and using ground-penetrating radar surveys. Don made a presentation during the trip. Although the ridges look structural, and may impede subsurface flow of ground water as well as surface flow, their origin is still elusive.

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in this issue: Fieldwork Southern California

SF Bay Soil Liquifaction

Outreach Everglades Field Trip

Meetings cover story:
Interim Science Priorities Plan

Gulf of Mexico Integrated Science

CMG Webmasters

Carbonate Beaches 2000

Staff & Center News Colloquium to Honor Ernest Manheim

WHFC Arrivals

Robbins Keynote Address

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