Cajun Pioneers of the Vermilion Prairie and Marsh Land

THE GEOLOGY OF VERMILION PARISH

PREFACE

This narrative about the geology of Vermilion Parish is intended for the layman and is not meant to be all inclusive – it is only a select mixture of important items and concepts or a jambalaya of geology.  The major part of this story has been passed on from father to son by word of mouth, geologist to geologist, much as the various professions, experiences, principals, and stories of my family ancestors that lived and worked in Bayou Tigre and Prairie Gregg were sometimes passed on to those of the younger generations  – “the Cajun Way”.

This is the story of my recently deceased father, Rufus J. LeBlanc, Sr.’s original findings about his land – a story that was gleaned from his life work as a geologist researching and describing recent sedimentation processes, or, how the land surface of south Louisiana and his homeland Vermilion Parish was created.  He was first employed by the Mississippi River Commission, under the auspices of the U.S. Army Corps of Engineers, from 1939 to 1947 after attaining his MS degree in geology from LSU.  Later he was employed as a geologist in the departments of research, operations, and training for Shell Oil Company in Houston, Texas from 1947 to 1986.  He was a native son of Vermilion Parish born in 1917 on a sugar cane and cotton farm on the banks of Bayou Tigre.  As a boy of 10 years old, he was an eye-witness to the great Mississippi River flood of 1927 – perhaps spurning an early interest in geology and fluvial processes.  Like so many other Vermilion Parish Acadians of his generation, he spoke only French until starting school in Erath and was the youngest and only member of his family fortunate enough to attend college.  This is Rufe LeBlanc’s story about “his land”.

GENERAL GEOLOGY OF VERMILION PARISH

Surface Geologic Units and River Basins

The surface geological units in the State of Louisiana, and in Vermilion Parish, as mapped by the Louisiana Geological Survey are shown in Figure 1.  Generally, the oldest geologic units are in the north of the state and youngest units are located at the coast.  All geologic units dip to the south toward the Gulf of Mexico with older units underlying the successively younger units.  In Vermilion Parish, the oldest geologic unit, at higher elevations, in the north part of the parish is the Pleistocene age Prairie Terrace Formation (500,000 to 10,000 ybp [years before present]).  The Recent age geologic units (10,000 ybp to today) in the south of the Parish, at low or near-sea level elevations, are the fresh and saline coastal marshes and the coastal chenier plains.  Additionally, Recent age river deposits are also found along the courses of Bayou Queue de Tortue, which is the northern boundary of the Parish, the Vermilion River, and the Bayous Tigre-Carlin-Petite Anse complex - the three principal water courses of the Parish.  The Pleistocene and Recent age geologic units each cover about 50% of the surface of the Parish.

The extent of these two geologic units is very easily recognized from satellite photographs of Vermilion Parish.  The Pleistocene age Prairie Terrace Formation appears as a patchwork, or mosaic, of cultivated fields (in colors of green, brown, and tan), townsites, and forested areas.  The Recent age wetland marshes and chenier plain units appear as darker colored landforms dissected and riddled with circular and linear water bodies and also alternating bands of trees on the chenier “islands” along the coast.

The Pleistocene and Recent age geologic units of Vermilion Parish are located either totally within, or, within part of three different river basins.  In terms of decreasing areal extent, and from west to east across the Parish, they are the Mermentau River Basin (Bayou Queue de Tortue is a tributary), the Vermilion River Basin, and the Bayous Tigre-Carlin-Petite Anse basin.

Subsurface geologic units are discussed below.  Only those geologic units of cultural and economic importance are discussed.  These different age subsurface geologic units are discussed from youngest to oldest age as they are successively encountered in the subsurface of Vermilion Parish.

Subsurface Geologic Units
Pleistocene Age Units
Chicot Aquifer (surface to 100’s of feet)
The source of fresh groundwater in Vermilion Parish, and the whole of southwest Louisiana, is the Pleistocene age Chicot aquifer (2 million to 100,000 ybp).  The subsurface Chicot aquifer is composed of hundreds of feet of alternating layers of sand, small gravel, and clay.  Aquifer studies have indicated that the origin of the sands, gravels, and clays, as well as the outcropping Pleistocene Terrace units, are from river processes of an ancestral Mississippi River that was in the vicinity of Vermilion Parish building a delta farther out into the Gulf of Mexico during Pleistocene time.  Ample water for rural domestic use can usually be obtained from wells in the Chico aquifer with depths ranging in the tens of feet depending on the specific location.  Heaver usage such as agriculture irrigation or industrial use requires deeper wells to depths of 300 feet or deeper where sands are thicker and have greater volumes of stored fresh water.

Water levels in the Chicot aquifer are steadily falling, however, hydrologists predict that because the thickness and lateral extent of the Chicot is so massive that there will be an ample supply of fresh groundwater for decades to come.  The majority of the groundwater demands in the Parish are for rice farming in the northwestern two-thirds of the Parish.  The total volume of water used for rice irrigation is about equally divided between surface water and ground water.  Heavy pumpage of groundwater in drought years has caused some salt water encroachment in upper sand zones of the aquifer from the coastal bays.  Typical groundwater uses in Vermilion Parish are as follows: irrigation 68%, aquaculture 8%, public supply 11%, industry 9%, and other uses 4%.

Miocene Age Units
Miocene Sands and Shales of the Planulina Gas Trend (9000 to 15,000 feet)
The majority of the onshore producing oil, condensate, and gas fields in Vermilion Parish are from Miocene age Planulina sands (24 million to 5 million ybp).  The Planulina Sand Gas Trend extends over southwest Louisiana in a swath 160 miles long in an west to east direction and 20 miles in a north to south direction and incorporates the subsurface of the Parishes of Cameron, Vermilion, Iberia, St. Mary, and Assumption.  These hydrocarbon bearing sand reservoirs occur at depths between 9000 to 15,000 feet.  From west to east, the fields with the major petroleum reserves in Vermilion Parish are Florence, Abbeville, Live Oak, Erath, and Tigre Lagoon Fields.  Initial discovery in the Vermilion Parish portion of the Planulina Gas Trend was in 1939 at Erath Field.  Generally, oil was discovered first in shallow wells of most of the fields and the gas and condensate reservoirs were discovered later by deeper drilling.

The most prolific oil and gas field in the Parish is the giant Tigre Lagoon Field in the eastern part of the Parish which was discovered by Union Oil of California in 1946.  Ultimate production for the field was estimated by Union Oil engineers to be 471 billion cubic feet of gas and 20.8 million barrels of oil.  At today’s prices for oil and natural gas,  this would be a total revenue of $4.5 billion dollars.  The oil and gas are almost depleted now after over 64 years of production. Many residents of Vermilion Parish in the Erath, Prairie Gregg and Bayou Tigre areas have received royalty payments from production in  Erath and Tigre Lagoon fields.

Jurassic Age Units
Louann Salt
When the North American and South American continental plates started to separate and drift apart in Triassic and Jurassic geologic time, an ancestral Gulf of Mexico was formed between the two continents that started to receive super-saturated amounts of salt water as ancient rivers drained into this ancient gulf.  By the end of Jurassic time thousands of feet of Louann Salt had accumulated in the expanding basin.  This massive salt layer was later buried by thousands of feet of younger sediment that was carried into the ever-expanding ancestral Gulf of Mexico.  Where sediment deposits were thickest, the lighter density salt layer was squeezed upward into domes and penetrated the overlying geologic units and, in the process, sometimes provided hydrocarbon traps in sand layers that were upturned by the salt domes.  In areas where the salt domes reached the surface, or near-surface, they provide opportunities for salt and sulfur mining such as at Jefferson and Avery Island salt domes.  Jefferson Island and Avery Island salt domes in neighboring Iberia Parish are the closest salt domes to Vermilion Parish. 

IMPACT OF GEOLOGY AND GEOGRAPHY ON MANKIND

General
Since the initial formation of the surface of Vermilion Parish in Pleistocene time, there has always been a constant interaction of the water and the land and then, relative to geologic time, much later mankind.  Rivers and coastal currents carrying loads of sediment created the land through river, delta, and shallow coastal geologic processes in four different time periods - geologic, prehistoric, historic, and present day time.  Mankind has needed the water for travel, commerce, and the sustaining of life in addition to the land for habitation and food supply.  However, whatever land the sediment-laden water processes initially helped create, the water then later tries to reclaim along the coastal areas from the processes of natural subsidence, waves and current action, rising sea level, and over millions of years of geologic time, literally thousands of hurricanes.  There has always been, and always will be, a constant and never-ending battle of the land and the sea in the south Louisiana coastal areas.

Sadly we are now finding out that man, inadvertently, has also been responsible for some of the loss of coastal wetland areas due to the pursuit of economic opportunities.  There has been dredging of canals for agricultural and petroleum industry needs, artificial control of the water courses of some rivers in the parish and the state by the U. S. Army Corp of Engineers, and also by decades of production of hydrocarbons and groundwater from subsurface reservoirs and aquifers which have caused noticeable subsidence in some areas.

The river, deltaic, and shallow-coastal geologic processes that formed Vermilion Parish and environs are of the utmost cultural and economic importance because these factors are the primary reason why our land is as it is today and was for both our ancestors and the indigenous peoples of the area in historic times.  Additionally, there is also archeological evidence that this area was also settled in prehistoric times at Avery Island in neighboring Iberia Parish.  Therefore, Vermilion Parish and environs have been inhabited continually by man for at least the past 12,000 years.  The most attractive land areas were always consistently settled first for each age and generation of mankind from cave man to Cajun.

Surface
The surface geologic nature of the land is why the first Acadians in the Parish, and adjacent areas, settled where they did along the rivers, bayous, and coulees of Vermilion Parish and those of the adjacent Attakapas Territory.  These water courses were the highways where the first settlements would be located and then spread out into the inviting flat, fertile prairies and grassy, wet marshlands as the population of the Attakapas Territory, and specifically Vermilion Parish, gradually grew over the centuries.

The principal water courses that were initially important in the Parish are Bayou Queue de Tortue, the Vermilion River, the Bayou Tigre-Bayou Carlin-Bayou Petit Anse complex, and Vermilion Bay.  Initially settlements were always along water courses or water bodies, rather than the expansive prairies, because they were efficient highways for travel and commerce and provided flood protection on the high-elevation natural levees.

Equally as important, the waterways provided the following basic essentials to sustain life: (1) extra-fertile soils for cultivating crops or grazing livestock because of periodic flooding of rivers; (2) provided ample, very shallow, domestic groundwater from high water tables associated with the river; (3) provided ample surface water for irrigation canals; (4) rivers and bayous were usually always associated with a large supply of timber in the immediate vicinity for building and fuel; and (5) the association of the water and trees were a natural haven for numerous species of birds, wildlife, fish, and shellfish that could provide both food and an alternative means of support.  Connecting canals to, or from, these major water courses were sometimes later constructed by the early settlers as needed for transportation and/or irrigation purposes.

The rivers, bayous, coulees, and constructed canals were also the early highways of commerce, before the railroads came to the towns of the Parish at the turn of the century, and were paramount in sustaining, developing and escalating the young and growing economy of the Parish.  The rich soils of the riverine, deltaic, and coastal-interdeltaic geologic units, their associated vegetations, and natural wetlands are the reason that the corn, sugar cane, rice, and cotton crops thrived, and the cattle and dairy industries in addition to fur trapping, fishing, and timber industries prospered.  The water courses continue to be important today as there are now minor ports for commerce on the Vermilion River, Vermilion Bay, and on Bayou Carlin / Delcambre Canal south of Delcambre.

Subsurface
The subsurface geologic nature of the land is one of the reasons that the people and the farming and cattle industries thrived because there was always a shallow, adequate supply of fresh groundwater.  Of equal importance, it is why the stagnant economy of Vermilion Parish got a much needed boost during the Great Depression era of the 1930’s and early 1940’s from the production of vast underground oil, condensate, and natural gas resources of Vermilion Parish, and the also the important mining industries of salt, sulfur, and oyster shells which were discovered and developed.

Revenues from oil and gas production were a welcome supplement to the normal budget of countless families all over the Parish especially near the end of the Depression years.
Salt has always been one of mankind’s necessary staples.  It has been craved in the diet by prehistoric man, historic man, and present day man.  Other uses of salt were in livestock diets, curing and preserving meats, tanning animal skins, and later the chemical industry.  The Attakapas Indians were able to trade with other tribes in Louisiana and surrounding territories for needed items because they had an inexhaustible supply of salt at Avery Island where there is evidence that man has inhabited the site for at least 12,000 years.  There was even a minor skirmish fought during the Civil War over the salt works at Avery Island because the mine supplied virtually the entire Confederate Army with salt.

The initial gas-cycling plant constructed at Erath Field near Henry was later developed into a major natural gas distribution plant.  This facility, now known as Henry Hub, has been converted into a major petroleum gathering and distribution facility for the vast offshore reserves in the Gulf of Mexico and actually is responsible for determining natural gas prices in the US.

The exploration and production of these natural resources onshore, as well as in the State and Federal offshore waters of Louisiana, was also responsible for thousands of jobs, of multiple varieties, being created for Vermilion Parish residents from 1940 to the present day.  Job careers were no longer restricted to merchandising, farming, cattle ranching, the dairy industry, commercial fishing, or trapping.  These new jobs in the petroleum industry, however, mostly required relocation to other areas and the newer generations were not able to reside in the Parish as their ancestors had done for generations.  The Cajun culture, sadly, had lost some of its uniqueness by this opportunity and migration.

Conclusions
Because geologic processes created inviting areas for habitation - for Prehistoric man, the Attakapas Indians, early Acadian pioneers, and modern day Cajuns alike, the general quality of life in this land we call Vermilion Parish has always been, as my French speaking ancestors said countless times, “Ca c'est bon!”

Rufus J. LeBlanc, Jr.
March 2010

Figure 1 - Geologic Map of Louisiana