Print this pageABSTRACT: Redesignation
of the Upper 
Lithofacies
in the Hensel Formation on the Southwestern Flank
of the Llano Uplift, Kimble County, Texas: A New Interpretation of the
Depositional Environments
JONES, JAMES O. and AARON JOHN KULLMAN
The Hensel Formation
is the terrigenous component of the last limestone-clastic couplet in the
upper Trinity Group (Cretaceous). Most previous studies involving the Hensel
have been in depocenters to the southeast of the Llano Uplift. Analysis
of the Hensel to the southwest of the uplift has been cursory.
Exposures of the Hensel Formation
along the upper Llano River drainage basin around Junction, Texas exhibit
three distinct lithofacies. A basal conglomerate consisting of clast supported,
high energy fluvial channel lag lenses exhibiting poor sorting and crude
lateral accretionary crossbedding. The middle facies is extensively calcretized
alluvial sandstones and mudstones with paleosol horizons and well developed
rhizoconcretion zones. An upper marine facies is composed of fossiliferous
calcareous siltstone intercalated with thin limestone beds. Clasts in the
lower and middle facies, and the siltstone of the upper facies are derived
from Pre-Mesozoic limestone and crystalline rocks from the Llano Uplift.
The Hensel was deposited as a series of coalescing fan deltas that prograded
from the positive Llano Uplift.
Fossil ostracodes and foraminifers
in the upper facies indicate that it is Cretaceous in age and marine in
origin and lithofacies analysis
supports recognizing it a thin westward
extension of the down dip laterally equivalent Glen Rose Limestone.
AAPG Search and Discovery Article #90941©1997 GCAGS 47th Annual Meeting, New Orleans, Louisiana