Your plain-language glossary of Paleogene, Wilcox, and offshore energy terms, from geological time periods to modern deepwater development projects.
The Paleogene is one of the most significant offshore energy trends in the United States, yet its terminology can be a genuine stumbling block. Geological time periods, rock formation names, and industry shorthand are often used interchangeably across technical reports, regulatory filings, investor materials, and media coverage.
This guide cuts through the jargon. Whether you’re new to deepwater energy or just need a quick refresher, you’ll find clear definitions for every key term associated with the Paleogene play and modern Gulf of America development.
| Geological Term | Approximate Age | Relevance |
|---|---|---|
| Paleocene | 66–56 million years ago | Lower Wilcox deposited/Start of Upper Wilcox deposition |
| Eocene | 56–34 million years ago | Upper Wilcox deposited |
| Oligocene | 34–23 million years ago | Continued Gulf sediment development |
| Miocene | 23–5 million years ago | Many mature Gulf reservoirs |
| Present Day | Modern era | Current offshore development |
Geological Time Terms
When the Rocks Were Deposited
Understanding when Paleogene rocks were formed is the foundation for everything else. These terms refer to stretches of geological time, not specific rock units or fields.
Paleogene: Geological Period
GEOLOGICAL TIME PERIOD | ~66–23 MILLION YEARS AGO
The Paleogene encompasses roughly 43 million years of Earth’s history and is divided into three epochs: the Paleocene, Eocene, and Oligocene. In offshore energy discussions, ‘Paleogene’ has become industry shorthand for the broader deepwater oil and gas trend associated with rocks deposited during this time.
Think of it this way: when someone says ‘the Paleogene play,’ they’re talking about a commercial opportunity. When a geologist says ‘Paleogene-age rocks,’ they’re describing when those rocks were formed.
| Paleogene at a Glance |
|---|
| Covers approximately 66–23 million years ago |
| Includes Paleocene, Eocene, and Oligocene |
| Refers to a geologic time period |
| Usage: preferred modern industry term for the deepwater trend |
Paleocene: Geological Epoch
GEOLOGICAL EPOCH | ~66–56 MILLION YEARS AGO
The Paleocene is the oldest epoch within the Paleogene and spans approximately 66 to 56 million years ago. The Lower Wilcox interval, the primary target for many modern 20k offshore developments, was deposited during this period. The Upper Wilcox deposition starts toward the end of the Paleocene.
| Paleocene at a Glance |
| Time span: approximately 66–56 million years ago |
| Key deposit: Lower Wilcox Formation |
| Reservoir quality: generally high — sandstone-dominated |
| Development relevance: primary interval for 20k deepwater projects |
The Eocene Epoch
GEOLOGICAL EPOCH | ~56–34 MILLION YEARS AGO
The Eocene follows the Paleocene and is associated with deposition of the Upper Wilcox interval. Upper Wilcox reservoirs tend to be shallower and exhibit different characteristics than their Lower Wilcox counterparts.
| Eocene at a Glance |
| Time span: approximately 56–34 million years ago |
| Key deposit: Upper Wilcox Formation |
| Reservoir characteristics: higher clay content, variable permeability |
| Pressure regime: generally below 20k threshold |
Rock Formation Terms
What the Rock Units are Called
Geological time periods tell us when rocks formed. Formation names tell us what those rocks are called. Here’s the distinction — and why it matters for understanding industry discussions.
Wilcox Formation (Wilcox Group)
ROCK FORMATION | DEPOSITED DURING THE PALEOGENE
The Wilcox Formation — sometimes locally called the Wilcox Group — is a large package of sandstones and shales deposited during the Paleogene period. It exists both onshore across Texas and Louisiana, and offshore in the deepwater Gulf of America.
Quick distinction worth knowing: when someone refers to ‘the Wilcox,’ they’re naming the rock formation. When they refer to ‘the Paleogene play,’ they’re describing the commercial offshore opportunity associated with those rocks.
| Wilcox Formation at a Glance |
| Composition: sandstones and shales |
| Geographic range: onshore Texas and Louisiana; deepwater Gulf of America |
| Geological age: Paleogene |
| Significance: primary deepwater development target in the Gulf |
Lower Wilcox
PRIMARY 20K DEVELOPMENT INTERVAL | PALEOCENE AGE
The Lower Wilcox is the deeper, older portion of the Wilcox Formation — and the most commercially significant interval in the modern deepwater Gulf of America. Deposited during the Paleocene, these reservoirs are typically found 23,000 to 28,000 feet below the seafloor and often require 20,000 psi-rated equipment to develop safely.
| Characteristic | Description |
| Geological Age | Paleocene |
| Typical Depth | ~23,000–28,000 feet below seafloor |
| Pressure Regime | Often requires 20k-rated systems |
| Reservoir Style | Sandstone-dominated; generally high quality |
Upper Wilcox
SHALLOWER WILCOX INTERVAL | EOCENE AGE
The Upper Wilcox is the younger, shallower portion of the Wilcox Formation, generally linked to Eocene-age deposition. Compared to the Lower Wilcox, these intervals sit at lesser depths, have different pressure profiles, and often contain higher clay content that affects permeability and reservoir performance.
| Characteristic | Description |
| Geological Age | Mostly Eocene |
| Typical Depth | ~16,000–23,000 feet below seafloor |
| Pressure Regime | Generally below 20k threshold |
| Reservoir Style | More variable properties; higher clay content |
Industry and Development Terms
How Companies and Analysts Refer to the Play
Once you move from geology into commercial development, the vocabulary shifts. These are the terms you’ll encounter in investor presentations, earnings calls, regulatory filings, and news coverage.
Paleogene Play / Paleogene Trend
PREFERRED MODERN INDUSTRY TERM | ~66–23 MILLION YEARS AGO
‘Paleogene play’ is now the standard term for the commercial offshore energy opportunity associated with Paleogene-age rocks in the Gulf of America. In offshore energy parlance, a ‘play’ is a commercially prospective geological system, while a ‘trend’ refers to its geographic extent across the basin.
Lower Tertiary
LEGACY INDUSTRY TERMINOLOGY — STILL WIDELY USED
‘Lower Tertiary’ is the older name for what the industry now more commonly calls the Paleogene play. You’ll still encounter it frequently in historical reports, regulatory filings, market analysis, and some industry presentations. The two terms refer to the same offshore opportunity — just from different points in geological nomenclature history.
If you’re writing for a broad audience, ‘Paleogene play’ is the more accurate and current term. If you’re referencing older documents or filing with regulators, ‘Lower Tertiary’ may still be the operative language.
Inboard Trend
PRIMARY 20K DEVELOPMENT AREA
The inboard trend describes the deeper, higher-pressure portion of the Paleogene play that is closer to the coast— the zone where most 20,000 psi developments are concentrated. These areas are characterized by greater salt coverage over the production zones, which creates both imaging challenges and the subsurface conditions associated with high-pressure reservoirs.
| Inboard Trend — Key Characteristics |
| Location: deeper, higher-pressure portions of the Paleogene play |
| Salt coverage both thickness and areal extent : significant — drives subsalt imaging challenges |
| Pressure: associated with 20,000 psi (20k) development systems |
| Potential: large-scale resource base; long-term production horizon |
Outboard Trend
LEGACY INDUSTRY TERMINOLOGY — STILL WIDELY USED
The outboard trend refers to shallower, lower-pressure portions of the Paleogene play that are farther out from the coast. These areas generally have less salt overburden, which can make seismic imaging more straightforward — but they also carry different reservoir characteristics and development economics than inboard trend projects.
Deep Paleogene/Ultradeep Paleogene
TECHNICAL LITERATURE TERMINOLOGY
These terms appear primarily in technical and academic contexts to describe the deeper, high-pressure portions of the Paleogene trend — the same areas often called the inboard trend in commercial discussions. They’re more precise than ‘deep Gulf’ generically, but less commonly used in investor communications or public-facing content.
Why This Trend Matters?
The Paleogene is not a single field, a single rock layer, or a single project. It is a basin-wide offshore energy trend — one of the most important next-generation opportunities in U.S. energy development.
What makes it significant is the convergence of scale, infrastructure, technology, and expertise that has been building for decades:
| The Paleogene Opportunity: What Supports It |
| Decades of geological research and subsurface understanding |
| Long-term investment in deepwater infrastructure |
| Advanced offshore engineering — including 20k-rated systems |
| Modern subsea technology purpose-built for ultra-deep environments |
| Extensive operational experience in the Gulf of America |
| Continuous advancement in subsalt seismic imaging |
About NOIA
The National Ocean Industries Association – NOIA – serves the offshore oil, gas, wind and ocean minerals industries and provides tremendous value to its members by uniting and advancing the business and professional interests of its members and the industry.
Learn MoreMISSION
NOIA represents and advances a dynamic and growing offshore energy industry, providing solutions that support communities and protect our workers, the public and our environment.
VISION
NOIA is the sought-after and credible voice, advocate and forum for uniting and advancing the interests of the offshore energy industry, recognized for promoting solutions that provide the energy vital for lifting society in a safe and environmentally sustainable way.