Palinspastic reconstructions of southeastern Marlborough, New Zealand, for mid‐Cretaceous‐Eocene times

Abstract

Southeastern Marlborough, New Zealand, preserves many complete sections through the Cretaceous/ Tertiary (K/T) boundary. Attempts to understand the paleogeography of these sections are hampered by the pervasive, Neogene deformation of the area associated with the propagation of the modern Pacific/Australian plate boundary through New Zealand. In this paper, we produce palinspastic maps of southeastern Marlborough for five intervals of Cretaceous and Paleogene time, based on a retro‐deformed, pre‐Neogene geographic model. Retro‐deformation takes account of: displacements on five major faults; distributed, between‐fault shortening; and a uniform, vertical axis, clockwise rotation of 100°. The mapped intervals are: (1) part of the Urutawan‐Motuan (middle‐late Albian, c. 105–102 Ma); (2) the Piripauan (latest Coniacian to late Santonian, 86.5–84.5 Ma); (3) the Early to early Late Haumurian (late Santonian‐Campanian, 84.5–72 Ma); (4) the late Late Haumurian to late Teurian (late Maastrichtian to late Paleocene, 68–58 Ma); and (5) the Waipawan‐Mangaorapan (early Eocene, 55–51 Ma).

During the Cretaceous and Paleogene, southeastern Marlborough lay on the generally north‐facing, Pacific margin of proto‐New Zealand. The palinspastic maps record the progressive drowning of what we infer to be a faulted platform, the “Marlborough paleo‐platform”, that formed the eastern boundary of a large embayment, the “Marlborough paleo‐embayment”. In the late Early and early Late Cretaceous, terrigenous clastic sediments were deposited on the platform at mostly shelf to upper bathyal depths. Ngaterian (late Albian‐Cenomanian) and Piripauan (latest Coniacian to late Santonian) paleoshorelines lay within the study area and were oriented northeast‐southwest. Subsequently, regional, passive subsidence of the continental margin resulted in transgression towards the south and southeast and a switch from terrigenous clastic to biogenic sedimentation. By the end of the Cretaceous, much of the Marlborough paleo‐platform was at outer shelf to bathyal depths; by the early Eocene, it lay entirely at bathyal depths. During the latest Cretaceous and Paleogene, the position of the Marlborough paleo‐embayment coincided approximately with a significant boundary in sedimentary regime, separating dominantly biogenic sediments in the east from mixed biogenic‐siliciclastic sediments to the west.

The palinspastic maps show internal consistencies that give us some confidence in the new analysis. Differences from previous maps are attributed both to the retro‐deformation and also to variations in the locations, values, and number of data points used to construct isopachs. Locally restoring paleogeography by retro‐deforming structures is likely to be of most use where the amount of deformation is high (e.g., >20% shortening and/or some tens of kilometres of fault displacements), where the isopachs are well constrained by robust data points, and where regional or global controls on sedimentary and biological patterns are significant and of interest.

Keywords:

• Amuri Limestone
• Cretaceous
• Eocene
• Herring Formation
• Marlborough
• Mead Hill Formation
• New Zealand
• Paleocene
• paleogeography
• palinspastic maps
• Paton Formation
• Split Rock Formation