Validation of Sediment Accumulation Regions in Kansas, USA
353
Muncie Creek GS. This would reflect infilling of the lower shelf and possibly represent a relative fall in sea level. Again, the sites of significant stratigraphic
changes closely correspond to SAR boundaries.
The Muncie Creek GS represents another period of transgressive (backstepping) and regression (lateral accretion). The first part of the interval is dominated by carbonate deposition that led to development of a prominent carbonate
bank margin. The succeeding clastics stepped over the carbonates and also filled
in the basin in front of the carbonate shelf margin, suggesting flooding and
backstepping followed by low-stand infilling of the basin. The geometries of the
Douglas and Toronto Limestones suggest offlapping and lateral accretion of the
clastic-dominated interval, suggesting probable low-stand conditions late in this
genetic set prior to the next prominent marine flooding.
The Muncie Creek genetic set is brought to a close by another prominent condensed section, the Heebner Shale. The Heebner GS is initiated by a backstepping event and apparent drowning of the lower shelf. The Oread Limestone in
the Heebner GSU downlaps in the midportion of the cross section immediately
southeast of boundary C. The carbonate lithofacies overlying the Queen Hill
GSU step slightly basinward to boundary F before it, too, downlaps. Clastics are
abundant in the lower shelf, suggesting that the lower shelf remained drowned
for extended times during accumulation of the Heebner GS.
It is evident from the above discussion that the SARs and SAR boundaries are
important features associated with significant changes in the corresponding
stratigraphy of the GSUs and GSs used to obtain the thickness data. Lithofacies
change abruptly at SAR boundaries including downlapping of carbonate bank
margins into later clastic filled basin areas, mixed clastic-carbonate lithofacies
to clean carbonate, and onlapping of limestone. Relative changes in sea level
were used to explain many of the relationships. However, sites of stratal changes
closely follow structural elements, SARs, that probably reflect changes in elevation of the depositional surface and changes in subsidence rate. SARs apparently
also affect the distribution of sediment by influencing the pathways for clastic
sediment transport and patterns of lateral accretion of carbonate lithofacies.
Eustacy is probably an important process in the formation of these deposits, but
local changes in shelf configuration apparently exert important controls themselves on the relative sea-level history and strongly control the nature of observed sedimentation.
5
Gravity and Magnetic Maps
Although regional Precambrian lithology and structure have been interpreted
from the gravity and magnetic data of Kansas (Yarger 1983) the studies did not
address the issue of Phanerozoic basement reactivation and the development of
sediment accumulation regions. The presence of the SARs and their impact on
lithofacies distribution reveals a complex three-dimensional view of apparent
basement reactivation. Previous work (Watney et al. 1997) has established that
353
Muncie Creek GS. This would reflect infilling of the lower shelf and possibly represent a relative fall in sea level. Again, the sites of significant stratigraphic
changes closely correspond to SAR boundaries.
The Muncie Creek GS represents another period of transgressive (backstepping) and regression (lateral accretion). The first part of the interval is dominated by carbonate deposition that led to development of a prominent carbonate
bank margin. The succeeding clastics stepped over the carbonates and also filled
in the basin in front of the carbonate shelf margin, suggesting flooding and
backstepping followed by low-stand infilling of the basin. The geometries of the
Douglas and Toronto Limestones suggest offlapping and lateral accretion of the
clastic-dominated interval, suggesting probable low-stand conditions late in this
genetic set prior to the next prominent marine flooding.
The Muncie Creek genetic set is brought to a close by another prominent condensed section, the Heebner Shale. The Heebner GS is initiated by a backstepping event and apparent drowning of the lower shelf. The Oread Limestone in
the Heebner GSU downlaps in the midportion of the cross section immediately
southeast of boundary C. The carbonate lithofacies overlying the Queen Hill
GSU step slightly basinward to boundary F before it, too, downlaps. Clastics are
abundant in the lower shelf, suggesting that the lower shelf remained drowned
for extended times during accumulation of the Heebner GS.
It is evident from the above discussion that the SARs and SAR boundaries are
important features associated with significant changes in the corresponding
stratigraphy of the GSUs and GSs used to obtain the thickness data. Lithofacies
change abruptly at SAR boundaries including downlapping of carbonate bank
margins into later clastic filled basin areas, mixed clastic-carbonate lithofacies
to clean carbonate, and onlapping of limestone. Relative changes in sea level
were used to explain many of the relationships. However, sites of stratal changes
closely follow structural elements, SARs, that probably reflect changes in elevation of the depositional surface and changes in subsidence rate. SARs apparently
also affect the distribution of sediment by influencing the pathways for clastic
sediment transport and patterns of lateral accretion of carbonate lithofacies.
Eustacy is probably an important process in the formation of these deposits, but
local changes in shelf configuration apparently exert important controls themselves on the relative sea-level history and strongly control the nature of observed sedimentation.
5
Gravity and Magnetic Maps
Although regional Precambrian lithology and structure have been interpreted
from the gravity and magnetic data of Kansas (Yarger 1983) the studies did not
address the issue of Phanerozoic basement reactivation and the development of
sediment accumulation regions. The presence of the SARs and their impact on
lithofacies distribution reveals a complex three-dimensional view of apparent
basement reactivation. Previous work (Watney et al. 1997) has established that