Evidence for Milankovitch orbital forcing in the Cretaceous upper Glen Rose Formation of the East Texas Basin and the Fort Terrett Formation of the Central Texas platform

The Lower Cretaceous (Lower Albian) upper Glen Rose Formation within the East Texas Basin and the Fort Terrett Formation of the Central Texas platform consist of upward-shoaling, cyclic carbonates deposited under “greenhouse” conditions. To delineate meter-scale cycles, wireline logs were used for the upper Glen Rose Formation, and outcrop data were used for the Fort Terrett Formation. Along dip, cycles within the Fort Terrett Formation were continuous for over 23 km and cycles within the upper Glen Rose Formation were continuous for over 170 km.; Thin-section and field data for the Fort Terrett Formation indicated that the lowermost 46 m could be subdivided into 15 meter-scale cycles and four high-frequency sequences. Cluster and correlation coefficient analysis of environmental indicators within these high-resolution data sets revealed normal-to near normal-marine conditions throughout each cycle. This suggested that the meter-scale cycles within the study area were not caused by radical, environment-induced changes in sedimentation.; Cycle stacking patterns indicated that the Fort Terrett Formation could possibly be subdivided into two composite sequences based on one- and two-dimensional cycle stacking patterns. An oxidized bed that was correlative throughout the study area defined the boundary between these two long-term (∼1.5–2.5 Ma) transgressive-regressive cycles. The meter-scale cycle immediately above this possible subaerial exposure surface onlapped it in the updip direction; giving further indication of a possible sequence boundary.; In both formations, cycles were caused by an allocyclic mechanism that exhibited a strong Milankovitch orbital signature. The spectral analysis of the gamma-uncorrected facies data for the upper Glen Rose Formation revealed the two precession periods (18.5 ka, 22.3 ka) and the short-term (100 ka) and long-term (413 ka) eccentricity periods. For the Fort Terrett Formation, spectral analysis of the gamma-corrected cycle facies data also displayed a strong match to a Malinkovitch orbital signature. The short-term obliquity period (38.8 ka) and two of the short-term eccentricity periods (95 ka, 100 ka) were indicated.