Depositional environments and controls on the stratigraphic architecture of the Cenomanian Buda Limestone in west Texas, U.S.A.

Abstract

The Cenomanian Buda Limestone is a widespread coccolith-rich carbonate unit deposited on the Comanche Shelf of the Texas Gulf Coast Basin. This formation is a key stratigraphic marker, and its hydrocarbon resources have been exploited since the 1920s. Despite its stratigraphic and economic importance, the depositional environments, and controls on the stratigraphic architecture of the Buda Limestone remain poorly understood. Here, based on the integration of high-resolution sedimentology, mineralogy and stratigraphy, the west Texas Buda Limestone is interpreted to be deposited in inner-neritic waters (likely < 40 m deep), of a lagoonal shelf (above SWB), with variable restriction (nearly open to slightly-restricted). Important thickness variations and oceanic-circulation were highly influenced by a wide, low-gradient paleo-shelf, in conjunction with local and regional paleo-structures (e.g., Terrel Arch, drowned Stuart City/Sligo reefal complex). Vertical facies variability, on the other hand, may be a function of orbitally-controlled, climate-driven sea-level fluctuations. The Buda Limestone is stratigraphically composed of two 4th-order (high-frequency) sequences (S1 and S2). The Lechuguilla and Red Light members belong to S1, whereas the Love Station Member corresponds to S2. The carbonate-richer Lechuguilla Member and Love Station Member (excluding its uppermost section) were deposited during transgressive periods possibly linked to higher temperatures and increased Earth's eccentricity. The clay-/quartz-richer Red Light Member, in contrast, was deposited during a regressive phase likely coupled with decreased Earth's eccentricity and a cooler climate. The carbonate-rich upper Love Station Member (uppermost 2.6 m), though deposited under similar conditions than the Red Light Member, was sedimented during an early HST phase with waters still warm and clear (low-turbidity) enough to promote the carbonate factory, as well sufficiently deep and energetic to prevent clay ponding. This study also provides solid evidence of subaerial exposure at the Buda Limestone bounding surfaces.