Sequence stratigraphy of the lower part of the Muscatatuck Group (Middle Devonian) in southeastern Indiana

Abstract

Sequence stratigraphic concepts are applied to the Muscatatuck Group (Middle Devonian) in order to establish a temporal and spatial framework for these carbonates in southeastern Indiana. Eight major lithofacies (facies mosaics) are recognized and include: (1) a lower-energy, biostromal and shallow-marine facies; (2) a higher-energy, biostromal and skeletal shoaling facies; (3) a restricted marine or lagoonal facies; (4) a restricted (lagoonal) peloidal facies; (5) a skeletal and peloidal shoaling facies; (6) an upper intertidal-supratidal facies; (7) a shallow, open-marine facies; and (8) a deepermarine facies. At least three distinct genetic units, allo-units, are delineated in the lower part of the Muscatatuck Group (Jeffersonville Limestone and basal North Vernon Limestone) based on the vertical and lateral distribution of facies and parasequences. Each of the three allostratigraphic units, or allo-units, contains one or more parasequences, and are probably parasequence sets. The lowermost allo-unit is bound basally by a well-documented regional unconformity (sequence boundary) between the Middle Devonian Muscatatuck Group and Silurian rocks. The upper boundary is the marine flooding surface (and lower boundary) of the next allo-unit. This surface is represented by a brachiopod-dominated, restricted marine or lagoonal facies directly overlying a stromatoporoid-and coral-bearing higher-energy biostromal and shoaling facies in the southern part of the study area, and a skeletal and peloidal shoaling facies overlying a dolomitized lower-energy biostromal or shallow-marine facies in the north. The upper boundary of the second allo-unit is another marine flooding surface and the lower boundary of the uppermost allo-unit. The lower bounding surface of the uppermost allo-unit is represented by a shallow-marine facies abruptly overlying a restricted marine or lagoonal facies in the southern part of the study area, and overlying an intertidal-supratidal facies in the north. The basal surface of the uppermost allo-unit marks a change in the stacking patterns of facies and parasequences from progradational and shoaling upwards in the lower two allo-units, to aggradational or retrogradational in the upper allo-unit. This surface may be the boundary between two distinct depositional systems. The upper bounding surface for this allo-unit is problematic. Paleontologic evidence suggests that this surface, marking the boundary between the Jeffersonville and North Vernon Limestones, is an unconformity, although it is not regional in extent. This discordant surface does mark the boundary between two carbonate intervals with very different depositional styles; hence, this surface may be more significant in the sequence-stratigraphic hierarchy than a flooding surface or major flooding surface, and may represent a sequence boundary. The three allo-units

Taxonomic revision and paleoecology of Middle Devonian (Eifelian) fishes of the Onondaga, Columbus and Delaware limestones of the eastern United States

“…The bone beds are transgressional lag deposits indicating an inundation during the time of the upper Seneca. This event is similar to what occurred in earlier units of the Delaware and North Vernon Limestones (Leonard, 1996), both correlable with the Seneca (Patchen et al, 1985;Shaver, 1985), and discussed later.…”

“…The unit above is very similar, only a bit coarser indicating a slight increase in energy. This unit is similar to Leonard's (1996) allo-unit 1, though the water depth of the Columbus unit may have been a bit deeper, i.e., the carbonate platform of the Columbus Sea may have been deeper in southern Ohio than the Wabash platform was in southern Indiana ( Figure 1B). The basal unit of the Columbus is interpreted as being slightly deeper based on the near absence of fossils and the lack of evidence for an overlying lagoonal deposit.…”

“…They contradicted Newberry's (1889, in Westgate andFischer, 1933) claim that organic material indicated a deep-water deposition and the rounding was due to mastication. However, Leonard (1996) found bone beds that were transgressional lag deposits, rather than the result of normal current reworking at the base of the North Vernon Limestone in Indiana, a unit correlable with the Delaware (Shaver, 1985). It is now clear that the bone beds of the Delaware also represent flooding surfaces rather than normal current hash or fecal consolidation.…”

“…In Sandusky, the classic members, sans the Bellepoint (Figure 6), are obvious, but further south, the lower unit, including the coral layer, should be considered the "lower Columbus", or the Bellepoint, and the fossiliferous, coarse units above, the "upper Columbus". Leonard (1996) examined the sequence stratigraphy of the Jeffersonville Limestone in Indiana, a unit correlative with the Columbus (Shaver, 1985; Figure 16). The base consisted of a shallow-open or low-energy marine unit with biostromal tabulate, colonial rugose and solitary rugose corals, and stromatoporoids.…”

“…The basal unit of the Columbus is interpreted as being slightly deeper based on the near absence of fossils and the lack of evidence for an overlying lagoonal deposit. Leonard's (1996) next unit, allo-unit 2, is lagoonal with rugose corals and gastropods. The next unit in the Columbus, however, is not very muddy and is very coarse, but does contain the only gastropods found in the section.…”