Collecting Fossils in Arkansas pdf - Arkansas Geological Survey

Collecting Fossils in ArkansasFossil collecting is a fun activitythat should be approached responsibly. Arkansas has manylocationsthat offer great opportunities tocollect fossils. The best places tosearch includeroadside outcrops, streams cutsand old quarries. Fossils are the property ofthe land owner.Always ask permission before entering private property. Vertebrate fossils are protected onmost public land butinvertebrate remains are usually available for collection. If you are unsureabout the regulations on public land, pleasee contact thee agency in charge of the land on whichyou wish to collect. State and National Parksare off limits.Remember to be safe when collecting fossils. Proper clothing, including footwear, glovesandsafety glasses are essential. Always be mindful of traffic, and in the summertime beware ofsnakes, spiders, ticks and chiggers. Most importantly, have fun, but be patient and carefulwhen you collect.What to write down: A good scientist takes good notes. .Geographic location: Take a GPS reading A legal description(State, county, topo quad, section, township, range, ..) Verbal description(“200 feetsouthwest of the bridge over Peyton Creek”) Keep a record of land ownerscontact informationGeological Information:The tools you will needA good rock hammer (not a nail hammer), chisel, safetyglasses, samplebags, labels, markers and mapss are essential tools forfossil collecting.It is very important to properly note your collectinglocation. Manycollectors loose vital information about their fossil finds by forgettingto take good notes. Here are some helpful hints: Rock type (For example, “cherty limestone, sandstone, shale, micrite, etc…”) Geological formation (This can be determined by finding your location on aGeological Map of Arkansas. For further details about Geological Formationconsult the “Stratigraphic Summary of Arkansas”) Keep a field journal with youwhen you collect. Record your observations,drawpictures of what you find, take pictures and measurements.

What toknow before you goArkansass is divided into 5 physiographic regions based on geology. Fossil collecting is possible inall regions, but is it important tohave a handle on Arkansas geology before you head into thefield. A little researchbefore yougo never hurts. Here iss a helpful overview of Arkansas geologyby region.The Ozark PlateausThe geology of the Ozark Plateaus Region is characterized bysedimentary rock deposited mostly by shallow marine seas(where a variety of animals could live) fromthe Ordovicianthrough the Pennsylvanian Period makingthis the mostfossiliferous region inn the state.The Salem Plateau contains theoldest rock present and ismade up of dolostone, limestone andsandstone ofOrdovician age. Algal structures called stromatolites,corals, brachiopods, bryozoa, crinoids,gastropods, and some cephalopods are the fossils mostt commonlyfound in the limestonee anddolostone. Trilobite fragments are less common but are present in these strata. The St. PeterSandstone contains the vertical trace fossil Skolithos. Silurian and Devonian strata are limited intheir outcrop area. Silurian limestones contain crinoids, trilobitefragments,and small algalmounds. Devonian strata are usually unfossiliferous.The Springfield Plateau is made up of limestone, sandstone,shale, and chert fromtheMississippian Period. Corals, bryozoa, brachiopodss, crinoids, bivalves, cephalopod, andgastropods are common in these rock types. Trilobite fragments are less common but arepresent in these rock types as well.Echinoid fragments are present in the Boone Formation.Starfish and bivalve resting traces called Asteriacites and Lockeia respectively,and worm trailsare common at certain localities in the Batesville Sandstone.Mississippian age shales offer the easiest collecting of fossils in the Ozark Plateau Region. Shaleweathersrapidly to mud, which washes away leaving the fossils behind. Theree are three majorMississippian age fossiliferous shale units innorth Arkansas. From oldest to youngest they arethe Moorefield Shale; the Fayetteville Shale;and the Imo member of the Pitkin Formation.Fayetteville and Moorefield Shales – Ammonoids and nautiloids are the mostcommon fossilspresent. Fossil fauna in the Fayetteville Shale are oftenn replaced by iron sulfide (pyrite). Plantfossils are less common in the Fayetteville Shale but aree present locally.

Imo member of Pitkin Limestonee – This unitoutcrops inn limited areas of Searcy and Van BurenCounties. It contains an abundant, diverse, and well preserved fauna including ammonoids,nautiloids, bivalves, brachiopods, bryozoan, plant material, blastoids, crinoids, gastropods,shark teeth, and trilobites. Plantfossils are also presentt in this unit. .The Boston Mts. Plateau is made up of Pennsylvanian age rocks. Itt contains mostly sandstone,siltstone,and shale, however limestone is present at various localities. Trace fossils such asConostichus, Zoophycus, and Asterosoma are most commonly found in sandstone and siltstoneof this region. Plantfossils are not abundant but are present in the sandstone, siltstone, andshale. Limestone in this region is usually fossiliferous and containss crinoids, blastoids, bryozoa,brachiopods, corals, and ammonoids.Arkansas River ValleyThe Arkansas River Valley is characterizedby sedimentaryrocks deposited by river systems flowing from the northandeast during the Pennsylvanian Period. This area representsthe northern extent of the Ouachita orogenic (mountainbuilding) system innArkansas. Once flat‐lying,thesePennsylvanian sedimentary rocks have been compressedintowell‐developed east‐west trending open folds (anticlinesandsynclines) and faults, which gradually diminish northwardintothe Ozark Plateau Region. Pennsylvanian sandstones, shalesand siltstones often contain abundant plant fossils. Lepidodendron, Calamities, Stigmaria, andfossil ferns may be discovered. Trace fossilss such as Conostichus arepresent locally in siltstonesin the area.Sandstones at various localities contain ammonoids, crinoids, gastropods,brachiopods, and bivalves.Ouachita MountainsThe Ouachita Mountains Region contains thick sequences ofsedimentaryrocks deposited in a deep ocean basin that havebeen uplifted and compressednorthward into east‐westand thrustfaultsdueto majororogenic(mountainbuilding)processes. The most intensely deformed area is in the centralportion of the fold belt. The rocks in the Ouachita Mountainstrending complex foldss (anticliness and synclines)

are sparsely fossiliferous but some units, notably the Ordovician age Womble Shale, containgraptolites. At one locality, trilobites are present and date the oldest rocks inArkansas in thecentral Ouachitas. Worm trails are present in shale at various localities.West Gulf Coastal PlainThe West Gulf Coastal Plain is characterized by gentlysouthward‐dipping sedimentaryrocks deposited mostly inshallow marine water of the Gulf of Mexico that onceextended into Arkansas. The area in orange consists ofTertiary clays, sands and silts with lignite deposits andQuaternarygravels, sands and clays. Thearea in greenconsists of Cretaceous age formations.Some of theCretaceousunits are very rich in fossils. Oyster, echinoid,gastropod and cephalopod fossils are most commonly found. The Cretaceous rocks are theonlyrocks outcropping inArkansas that were deposited during the Age of Dinosaurs. It is only fromthese rocks that dinosaur fossils have ever been found in the state. In addition to thefewdinosaurbones (Arkansaurus fridayi) a largenumber off dinosaur tracks are know from a LowerCretaceous limestone that outcrops in a limited area. Other vertebrate fossils discovered in thearea include shark teeth, mosasaur, reptile teeth and plates, and miscellaneouss fish parts. Mostof these rocks are not as hard asthe Paleozoic rocks, soo collecting is fairly easy. Petrified woodhas beendiscovered in Quaternary terrace deposits andd amber is present locally in Tertiary agedeposits.Mississippi Alluvial PlainThe geology of thee Mississippi River Alluvial Plain ischaracterized by unconsolidated, flat‐lying alluvium frompresent dayand older streams, overlying poorly consolidatedTertiary formations.Petrified wood is occasionally foundassociated with gravel deposits of Quaternary age intheMississippi River Alluvial Plain. Iceage mammal fossils such asmammoth, mastodon, dire wolf, saber‐tooth cat, bear, groundsloth, peccary, and more have alsobeen discovered in gravelsof the Mississippi River. Oysters, gastropods, bivalves, shark and ray teeth, andplant fossils arepresent in Eocene age formations along Crowley’s Ridge.