382 



J. BARRELL RECOGNITION OF ANCIENT DELTA DEPOSITS 



blanket of sediments which extends across the shore may pass outward 

 into deposits of the open sea and must be classified into zones according 

 to the changing- conditions of deposition. All those zones which con- 

 tribute to the building of a delta are parts of it as a complex physio- 

 graphic structure. Those which do not aid in the outward or upward 

 growth of the delta should be ruled out of its membership. For greater 

 clearness of view a table is given showing a classification of sedimentary 

 deposits and those divisions which may contribute to delta growth. 



Classification of Sedimentary Deposits 



SUBDIVISIONS 



Continental 

 (Above tidal 

 reach) 



Littoral 



(Between ti- 

 dal limits "1 



Terrestrial 



Paludal 



Lacustrine 



(fresh and salt) 



Tidal marsh 



Lagoon 



Beach 



Marine 



(Below tidal 

 limits) 



Terriyrenous 



Pelajj:ic 



Glacial 

 Eolian 

 Pluvial 

 Fluvial 



Intermittent 

 Perennial 



Shore 

 Bottom 



r Offshore 



(Breaking waves, 

 undertow) 



Estuarine or bay 

 (Brackish water) 



Shallow sea 



( Epicontinental 

 sea) 



Oceanic 



(Also Mediterra- 

 nean ) 



Epici)ntinental 



limestones 

 Oozes 

 Abvssal red clav 



DEPOSITS OFjMIXED 

 CONTINENTAL AND 

 MAHINE FORMATIONS 

 ( DELTAS FACING* ^ 



SEAS) jg^. , - 



L Subaeriol topset beds 

 (mostly fluvial) 



(The littoral and 

 fluvial zones are not 

 sharply separated 

 in deltas.) 

 The shore face 

 ( Steeper slope pro- 

 duced by wave 

 action ) 



Suhaqueoustopsel beds 



(Gently sloping 



surface prothice<l 



by wave action) 



Forei<et beds 



(Steeper slopes 



below wave base) 



Boftoittset beds 



i Flat distal slopes 



below wave base) 



The dominance of river action over the opposing sea is expressed by a 

 broad but irregular convexity of shoreline, though confluent deltas may 

 give rise to an extended coastal plain of fluviatile origin and conform to 

 the regional trend of the shore, either concave or convex toward the sea. 

 A delta is typically built in front of a river valley, not within its walls. 

 A drowned valley, however, is reclaimed by the river readvancing into it 



