Maryland Fossil Guide - Geologic Time

Geologic Time Scale

Maryland has changed a lot in since the earth was born 4.5 billion years ago. The State used be south of the equator and bordered Africa. Where the Appalachian Mountains are now there used to be a sea, and sharks used to swim across what is now Calvert County. If you want to learn the story of how Maryland came to look like it does, start digging. The rocks and fossils beneath your feet are the pages in the State's biography.

Era	Period/System		Epoch	Years Ago MY= Million Years	Events FA= First Appearence LA=Last Appearence	Maryland's Fossil Record	Maryland's Rock Record † Fossiliferous Formation
	Quartenary		Holocene	8,000 to present
	Quartenary		Pleistocene	1.8 MY to 8,000	Glaciation in Northern Hemisphere		Lowland Deposits, Eastern Lowland Deposits, Western Upland Deposits - Eastern Shore
		Neogene	Pliocene	5.3 MY to 1.8 MY			Upland Deposits - Western Shore
		Neogene	Miocene	23.8 MY to 5.3 MY	FA of horses FA of hominids		Calvert Formation† Choptank Formation† St Mary Formation† Yorktown Formation
		Paleogene	Oligocene	33.7 MY to 23.8 MY	Red Sea opens
			Eocene	55.5 MY to 33.7 MY	Australia & Antarica seperate FA of rodents		Nanjemoy Formation† Piney Point Formation †
			Paleocene	65 MY to 55.5 MY	FA of grasses FA of primates		Aquia Formation† Brightseat Formation
	Cretaceous			145 MY to 65 MY	FA of marsupials FA of angiosperms Labrador Sea opens South Atlantic opens		Magothy Formation Matawan Formation Monmouth Formation Potomac Group
	Jurassic			213 MY to 145 MY	India, Madagascar & Antactica seperate Gondwana & Laurasia seperate Central Atlantic opens		Undifferentiated Mesozoic Rocks
	Triassic			248 MY to 213 MY	FA of dinosaurs		Diabase Sills & Dikes Gettysburg Shale New Oxford Formation
	Permian			286 MY to 248 MY	Appalachian Mountains Pushed up Atlantic Ocean closed LA of trilobites		Dunkard
		Pennsylvanian		325 MY to 286 MY	FA of cotylosaurs LA of graptolites		Alleheny & Pottsville Formations† Conemaugh Formation † Monongahela Formation †
		Mississippian		360 MY to 325 MY	Sharks Winged Insects Fern Trees		Greenbrier Formation Mauch Chunk Formation Pocono Group† Martinsburg Formation
	Devonian			410 MY to 360 MY	FA amphibians (labyrinthodonts) Wingless Insects Early Ferns		Chemung Formation Hampshire Formation † Hamilton Group, Tioga Metabentonite Bed & Needmore Shale† Oriskany Group † Helderburg Formation & Keyser Limestone†
	Silurian			440 MY to 410 MY	FA of land plants		Clinton Group Mckenzie Formation Tuscarora Sandstone Tonoloway Formation † W ills Creek Shale & Bloomsburg Formation
	Ordovician			505 MY to 440 MY	Sponges Crynoids Bryozoans EarlyMollusks		Chambersburg Limestone † Juniata Formation Pinesburg Station Dolomite Rockdale Run Formation Stonehenge Limestone Cardiff Metaconglomerate Peach Bottom Slate Cambro-Ordivician Grove Limestone
	Cambrian			544 MY to 505 MY	Trilobites FA jawless fish FA of invertebrates		Antietam Formation† Elbrook Limestone Frederick Limestone Tomstown Dolomite Waynesboro Formation Harpers Formation Conococheague Limestone Early Paleozoic - Late Precambrian Baltimore Gabro Complex Georgetown Mafic Complex Relay Quartz Diorite Ultramafic Rocks Undifferentiated Crystalline Rock
				544 MY - The Origin of Earth	FA bacteria, algae & Eukaryotes Oldest Sedimentary Rocks Earth's Crust Formed		Late Precambrian ? Cockeysville Marble Ijamsville Formation/Marburg Schist James Run Formation Libertytown Metahyolite Catoctin Metabasalt Metarhyolite & Associated Pyroclastic Sediments Swift Run Formation Sams Creek Metabasalt Setters Formation Sugarloaf Mountain Quartzite Silver Run Limestone Urbana Formation Volcanic Complex of Cecil County Weverton Formation Wissahickon Formation Undifferentiated Upper Pelitic Schist Metagraywacke Metaconglomerate Boulder Gneiss Lower Pelitic Schist Wakefield Marble Precambrian Baltimore Gneiss Granodiorite & Biotite Granite Gneiss

Fossils in and around Maryland

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Geologic Time Scale

MY= Million Years

FA= First Appearence
LA=Last Appearence

† Fossiliferous Formation

Cambro-Ordivician

Early Paleozoic -
Late Precambrian

Late Precambrian ?

Precambrian

Fossils in and around Maryland

Menu:

Geologic Time Scale

MY= Million Years

FA= First Appearence LA=Last Appearence

† Fossiliferous Formation

Cambro-Ordivician

Early Paleozoic - Late Precambrian

Late Precambrian ?

Precambrian

FA= First Appearence
LA=Last Appearence

Early Paleozoic -
Late Precambrian